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Functional Aromatic Amino Ketones as UV/Vis probes for

various liquid and solid environments

von der Fakultät für Naturwissenschaften der Technischen Universität Chemnitz

genehmigte Dissertation zur Erlangung des akademischen Grades

doctor rerum naturalium

(Dr. rer. nat.)

vorgelegt von Master in Chemie Mohamed El-Sayed

geboren am 16.11.1966 in Port-Said, Ägypten

eingereicht am 20 Dezember 2002

Gutachter:

Prof. Dr. Stefan Spange, Technische Universität Chemnitz

Prof. Dr. Heinrich Lang, Technische Universität Chemnitz

Prof. Dr. Rainer Beckert, Friedrich-Schiller-Universität Jena

Tag der Verteidigung: 1 April 2003

Bibliographische Beschreibung und Referat 2

Bibliographische Beschreibung und Referat

El-Sayed, M.

Functional Aromatic Amino Ketones as UV/Vis probes for various liquid and solid

environments

Technische Universität Chemnitz-Zwickau, Fakultät für Naturwissenschaften, Dissertation,

2003, 140 Seiten, 141 Literaturzitate, 35 Abbildungen, 24 Tabellen, 14 Diagramme.

Zum gegenwärtigen Kenntnisstand bezüglich Solvatochromie, Sol-Gel Prozesse, und

der Synthese von Polyketonen wird eine kurze Einführung gegeben. Die Synthese-

konzeptionen funktionalisierter aromatischer Aminoketone werden vorgestellt. Die neuen

Verbindungen wurden mittels Elementaranalyse, Röntgenstrukturanalyse, und

spektroskopischen (NMR, UV/Vis, MS) Methoden aufgeklärt. Im Mittelpunkt der

Untersuchungen steht die Untersuchung des Einflusses von unterschiedlichen Medien

(Lösungmittel, Oberflächen, Sol-Gel Materialien und Nachbarnmoleküle im Kristall) auf die

Lage der UV/Vis-Absorptionsmaxima verschiedener aromatischer Aminoketone. Die

Ergebnisse der Untersuchungen liefern Informationen in Bezug auf der spezifische

Solvotationsvermögen, die Polarität von Feststoffoberflächen, der Einfluss funktionaler

Gruppen in aromatischen Aminoketonen auf die intermolekulare Wasserstoff-

brückenbindungen in Kristallen, und über die Natur der Gast-Host- Wechselwirkungen.

Auf der Basis von nucleophilen Substitutionsreaktionen wurden zwei verschiedene

Prozesse für die Synthese von Poly(benzophenone-co-piperazin) und der Kompositform

entwickelt. Molekulare Strukturen und Eigenschaften konnten durch Elementaranalyse,

mehrere spektroskopische (IR, Festkörper-NMR, UV/Vis, MALDI-TOF) Methoden,

Zetapotentialmessungen in wässriger Phase und thermogravimetrischen Bestimmungen

charakterisiert werden.

Aromatische Aminoketonen, Aerosil 300, Sol-Gel-Prozess, Ormosile, Hybridmaterialien,

Solvatochromie, Acidität, Basizität, Dipolarität/Polarisierbarkeit, intermolekulare

Wasserstoffbrückenbindungen, Poly(benzophenone-co-piperazine).

Contents 3

Table of contents 3

List of publications 5

Acknowledgement 6

Symbols and abbreviations 7

I General part 10

1.1 Introduction 10

1.2 Solvatochromism 11

1.2.1 Aromatic amino ketones 12

1.2.2 Related compound 16

1.3 Sol-gel process 18

1.4 Aromatic amino ketone polymers 21

II Aim of this work 23

III Results and discussion 25

3.1 Aromatic amino ketones 25

3.1.1 UV/Vis absorption spectroscopy and linear solvation energy (LSE)

relationships 25

3.1.1.1 Solvent effects on the UV/Vis absorption spectra 25

3.1.1.2 Mathematical calculations based on LSE relationships 36

3.1.2 X-ray crystal structure analysis and powder reflectance UV/Vis

spectroscopy 52

3.1.2.1 Solid-state X-ray crystal structure analysis 52

3.1.2.2 UV/Vis diffuse reflectance spectra of the solid powders 63

3.1.3 Adsorption of aromatic amino ketones on Aerosil 300 68

3.1.4 Sol-gel materials containing aromatic amino ketones 73

3.1.4.1 Physical entrapment in a microporous silica network 73

3.1.4.2 Chemical linking to the silica network 83

3.2 N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitroaniline [HDBN] 90

3.2.1 UV/Vis absorption spectroscopy of HDBN 90


spectroscopy of HDBN 96

3.2.3 Adsorption of HDBN on Aerosil 300 99

3.3 Poly(benzophenone co-piperazine) and its silica-composite 102

3.3.1 Syntheses and structure analysis 102

3.3.2 Characterization 110

Contents 4

3.3.2.1 Electrokinetic data 110

3.3.2.2 Thermal stability 112

3.3.2.3 N2 adsorption/desorption data 114

3.3.3 Solvatochromic analysis 115

IV Summary 119

V Experimental section 123

5.1 General considerations 123

5.1.1 Instruments 123

5.1.2 Working procedures 125

5.1.3 Correlation analysis 125

5.1.4 Starting materials 125

5.2. Synthetic part 126

5.2.1 Aromatic amino ketones by Friedel Craft acylation reaction 126

5.2.2 Aromatic amino ketones by nucleophilic aromatic substitution reaction 129

5.2.3 3-(4-Di(2-hydroxyethyl)amino)phenyl-1-(2-furyl)-2-propene-1-one 132

5.2.4 N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitroaniline 132

5.3 Preparation of sol-gel hybrid materials 133

5.3.1 Physical entrapment in a microporous silica network 133

5.3.2 Chemical linking to the silica network 134

5.4 Poly(benzophenone co-piperazine) and its composite form 137

5.4.1. Solution polymerization 137

5.4.2. Solid-state polymerization 137

5.5 Crystal structure analyses 137

VI References 142

List of publications 5

List of publications

Original contributions:

1. El-Sayed, M.; Müller, H.; Rheinwald, G.; Lang, H.; Spange, S.: Linear solvation

energy (LSE) correlations of the solvatochromic response and x-ray structure

analysis of hydrophilically N-substituted Michler’s Ketone Derivatives. J. Phys.

Org. Chem. 2001, 14, 247-255.

2. Zimmermann, Y.; El-Sayed, M.; Prause, S.; Spange, S.: The Solvent-Like Nature

of Silica Particles in Organic Solvents. Monatsh. Chem. 2001, 132, 1347-1361.

3. Spange, S.; El-Sayed, M.; Müller, H.; Rheinwald, G.; Lang, H.; Poppitz, W.:

Solid-state Structures of N-substituted Michler’s Ketones and their relation to

Solvatochromism. Eur. J. Org. Chem. 2002, 24, 4159-4168.

4. El-Sayed, M.; Müller, H.; Rheinwald, G.; Lang, H.; Spange, S.: UV/Vis

spectroscopic properties of N-(2’-hydroxy-4’-N,N-dimethyl-aminobenzylidene)-

4-nitroaniline in various solvents and solid environments. Monatsh. Chem. 2003,

134, 361-370.

5. El-Sayed, M.; Müller, H.; Rheinwald, G.; Lang, H.; Spange, S.:

Solvatochromism, Crystallochromism, and Solid State Structures of

Hydrophilically Functionalized Aromatic Amino Ketones containing Furan and

Thiophene Rings. Chem. Mat. 2003, 15, 746-754.

Poster:

1. El-Sayed, M.; Schmidt, C.; Spange, S.; Kricheldorf, H.: Hydrophilically

Functionalized Michler’s Ketone Derivatives as Polarity Probes for Different

solid Materials. Berliner Polymerntage 2000, Poster (P 64, page 127), Berlin, 9. -

11. October 2000.

Acknowledgement 6

Acknowledgement

The experimental part of this work was carried out in the laboratories of Prof. Dr.

Stefan Spange, Chemnitz University of Technology from July 1998 until April 2002.

First of all, I wish to express my deep thanks and gratitude to Prof. Dr. Stefan Spange,

who welcomed me in his research group, who introduced me into German life and who

suggested the point and successfully guided me through my studies.

I would like to thank Prof. Dr. Heinrich Lang very much for his scientific support in crystal

structure analyses, and his evaluation of this thesis.

I would also like to thank Dr. Gerd Rheinwald for X-ray intensity data collection.

My deepest thanks are also to Dr. Hardy Müller for his interest and continuous

encouragement.

I would like to thank staff members in our research group for their co-operation, friendship

by means which the daily work has always been a pleasure.

I want to express my deepest gratitude to my parents Kauther El-Gamel and Mohamed El-

Sayed, and to my sister Frial and to my brothers Ashraf and Ibrahim for their constant

support and understanding.

I extend my thanks to my wife Dr. Eng. Hanan Koutta and my daughters Mirna and Manar

for understanding my demanding work and long working hours.

Finally, I would like to thank the Germany Ministry of Education, the Fonds der Chemischen

Industrie, Frankfurt am Main and Chemnitz University of Technology for their financial

support.


Symbols and abbreviations

δ chemical shift

β hydrogen-bond accepting capacity

α hydrogen-bond donating capacity

δ polarizability correction term

π* dipolarity/polarizability

δ2H solvent cohesive energy density

δH hildebrand solubility parameter

λmax maximum wave length

νmax maximum wave number

[M+] molecule-ion

a solvent-independent correlation coefficient of α

a.u. arbitrary units

b Solvent-independent correlation coefficient of β

b.p. boiling point

BBP 1,4-bis(4-benzoylphenyl)piperazine

BET brunauer-Emmett-Teller

BuOH 1-butanol

CH c-hexane

CP cross-polarization

d doublet

D two oxygen atoms and two alkyl group attached to silicon atom

DAFP 3-(4-di(2-hydroxyethyl)amino)phenyl-1-(2-furyl)-2-propene-1-one

DCE 1,2-dichloroethane

DCM dichloromethane

dd doublet of doublets

DEE diethyl ether

DEI desorption electron ionization

DeOH 1-decanol

DH Dollimore-Heal

DMAc N,N-dimethylacetamide

DMF N,N-dimethylformamide

DMSO dimethylsulfoxide

DPAB 4-dimethylamino-4’-[di(2-propyltriethoxysilylcarbamatoethyl)amino]-

benzophenone


DPAF [4-di(2-propyltriethoxysilylcarbamatoethyl)amino]-2-furylmethanone

DPAT [4-di(2-propyltriethoxysilylcarbamatoethyl)amino]-2-thienylmethanone

DSC differential scanning calorimetry

EG ethane-1,2-diol

ESI electron spray ionization

EtOH ethanol

Exp. Sect. experimental section

F significance

Fig. figure

FT-IR Fourier transform-Infrared

Fur(OAc)2 [4-di(2-acetoxyethyl)aminophenyl]-2-furylmethanone

Fur(OH)2 [4-di(2-hydroxyethyl)aminophenyl]-2-furylmethanone

g gram

h hour

HBA hydrogen-bond accepting

HBD hydrogen-bond donating

HDBN N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitroaniline

HeOH 1-hexanol

HFP 1,1,1,3,3,3-hexafluoro-2-propanol

J coupling constant

LSE linear solvation energy

m.p. melting point

m/z mass/charge

MALDI-TOF matrix assisted laser desorption ionization time-of-flight

MAS magic angle spinning

MeOH methanol

MHz megahertz

MK 4,4’-bis-(dimethylamino)benzophenone, Michler’s Ketone

MK(mor)2 4,4’-bis(morpholino)benzophenone

MK(NEt2)2 4,4’-bis(diethylamino)benzophenone

MK(OAc)2 4-dimethylamino-4’-[di(2-acetoxyethyl)amino]benzophenone

MK(OH)2 4-dimethylamino-4’-[di(2-hydroxyethyl)amino]benzophenone

MK(pip)2 4,4’-bis(piperidino)benzophenone

MK(pipaz)2 4,4’-bis(piperazino)benzophenone

MK(pipazOH)2 4,4’-bis[4-(2-hydroxyethyl)piperazino]benzophenone

MK(pipOEt)2 4,4’-bis(4-ethoxycarbonylpiperazino)benzophenone

mmol millimole


MS mass spectra

MTMOS methyltrimethoxysilane

N normal

n number of solvents

nm nano-meter

NMR nuclear magnetic resonance

OcOH 1-octanol

Ormosil organically modified silica

pm pico-meter

PrOH 1-propanol

PSD pore-size distribution

Q four oxygen atoms attached to silicon atom

r correlation coefficient

s solvent-independent correlation coefficient of π*

SD standard deviation

T three oxygen atoms and one alkyl group attached to silicon atom

t triplet

Tab. table

TCE 1,1,2,2-tetrachloroethane

TEOS tetraethylorthosilicate

TFE 2,2,2-trifluoroethanol

Tg glass transition temperature

TGA thermogravimetric analysis

Thi(OAc)2 [4-di(2-acetoxyethyl)aminophenyl]-2-thienylmethanone

Thi(OH)2 [4-di(2-hydroxyethyl)aminophenyl]-2-thienylmethanone

TMOS tetramethoxysilane

tol. toluene

UV/Vis ultraviolet/visible

General part 10

I. General part

1.1 Introduction

The color change of a compound induced by external influences, e. g. by solvents

(solvatochromism), applied stress (mechanochromism), salts (halochromisms) and/or

temperature (thermochromism) has been studied intensively over the last decades.1-9 In this

context, solvatochromic dyes have been established as empirical polarity indicators for

solvents, solvent mixtures and solution of several solutes in various liquids.1,10-13 This

empirically derived concept for volume effects has been also widespread applied to evaluate

the internal and external polarities of surfaces of macro-molecular and related materials.14-24

In this sense, the term surface polarity is an argument often used in interpreting experimental

results obtained from Chromatography22 and heterogeneous catalysis.25 The effect of solid

matrix is important, because many compounds (such as dyes, stabilizers and others) are

applied as components of a more complex system in the solid phase. Therefore it is important

to evaluate the medium effect for these systems as well.

The solvatochromic effects of rigid matrices are complex and as yet less understood as

compared with solvents. It is important to take into account not only the matrix itself but its

mode of preparation and the way in which the solute has been incorporated into the matrix.

To date, no generally agreed upon definition of the term surface polarity has emerged. In the

broadest and most general sense the surface polarity can be viewed as the sum of all

interactive forces between an adsorbed molecule and the occupied surface site or sites. This

definition is based on the related interpretation of the term solvent polarity.1,26 Most solvent

polarity scales are empirical and are based on kinetic, thermodynamic, or spectroscopic data

relating to certain reference reactions.1 Significantly, different empirical solvent polarity

scales have been shown to correlate well with each other, pointing to the existence of an

underlying common feature.1

Since, a chromophor is covalently functionalized by a polar group or another suitable

moiety for molecular recognition in its periphery, manifold influences on the UV/Vis spectra

can result from the intermolecular interaction in the solid-state (crystal) or in molecular

aggregates of the dye.27-31 Thus, quantum size effects have been observed for organic nano-

crystals29 and carotenoid dye nano-particles.28 However, two different influences, the supra-

molecular structure and quantity of accumulated dye molecules in the nanocrystal seem of

importance for the resulting UV/Vis spectroscopic property. Because both influences are

General part 11

associated properties, a reasonable interpretation of the UV/Vis spectrum of those nanosized

dye aggregates is still complicated and requires further experimental results and theoretical

studies.

Examination of chromophoric aggregates and supramolecular structures by UV/Vis

spectroscopy is an experimental challenge and of importance both for academic research and

for practical applications in nano-science.28-31 For this objective, the exact knowledge of

solid-state structures (X-ray structure analysis) is necessary and the corresponding UV/Vis

spectra have to be significantly different as function of structure variation. This requires the

choice of suitable model systems which show color changes as function of nature of

accumulation processes.

1.2 Solvatochromism

Solvatochromism is defined as the pronounced change in position and sometimes

intensity of an electronic absorption or emission band accompanying a change in the polarity

of the medium.1 This medium may include solids, micelles, organized molecular films and

even a vacuum, apart from liquid solvents.1c Solvatochromic shifts result from the difference

of solvation energies between the two electronic states involved in the observable absorption

or emission transition. These shifts are important for the description of the relative energies of

electronic states, the dipole moment and polarizability of molecules. In addition they often

provide information about specific interactions such as hydrogen bonding.

Quantification of general properties of solvents and micelle environments has been

studied by physical organic chemists for many years.1 Using solvatochromic probe dyes has

several advantages: the measurements require very low concentrations of the probe

molecules, are easy to do, and reproduce well. The requirement is that the employed probe

dye must adequately reflect the relevant properties of the environment under study. The

responses of solvatochromic indicators on changing solvent environments have been used as

the phenomenological basis for several empirical „solvent polarity“ scales.1b Among such

quantitative scales, the Kamlet-Taft system1,32 is the most inclusive with respect to all solvent

types and it is well supported by theoretical reaction field models for the solvent influences

upon the solvatochromic probes.32,33

The general equation for the influence of solvent effects on a single solute is shown as

eq 1,1,10,32 where XYZ is the property to be correlated

XYZ = (XYZ)0 + hδ2H + s(π* + dδ) + aα + bβ (1)

General part 12

(XYZ)0 is a property relating to a standard process, δ2H is the solvent cohesive energy density

(δH is the Hildebrand solubility parameter), π* is the dipolarity/polarizability, δ represents a

polarizability correction term, α is the hydrogen-bond donating (HBD) capacity, and β is the

hydrogen-bond accepting (HBA) capacity.32 This linear solvation energy (LSE) relationship is

suitable for experimental proving of solvent effects, because it simply allows the separation of

“dipolarity/polarizability” from other solvent-solute interactions such as hydrogen bonding by

a multiple square correlation analysis. However, the parameters used in multi-parameter LSE

relationships are seldom interrelated, featuring just different blends of fundamental

intermolecular forces. This makes the interpretation of individual polarity parameters relating

to non-specific or specific interaction mechanism in special cases ambiguous.

1.2.1 Aromatic amino ketones

Aromatic aminoketones of the Michlers Ketone type and related compounds have

already been widely investigated thanks to their outstanding solvatochromic and

photophysical properties.2,34-39 They are also of importance as precursors for producing a

photo-initiator for cationic polymerization38 and di- and triphenylmethylium cations.41-43

Mayr et al. have recently shown that the electrophilicity of bis-[4-N,N-substituted]

diphenylmethylcarbenium ions significantly depends on the substitution at the nitrogen

atoms.41

Solvatochromic properties of Michler’s Ketone 4,4’-bis(dimethylamino)benzophenone

MK 4g and related compounds have been established as a suitable tool for investigating the

polarity of various liquids2,37,39,44 and solid environments, such as functionalized silica

particles, amino acid crystals, polyamino acids, and synthetic and native macromolecular

materials. 14a,15-18,45-47 In this context, we were able to show that the polarity observed by MK

and two related probes does not only depend on its chromophoric π-electron system, but also

on the quantity of hydrophilic substituents located at the periphery of the probe.47 The

introduction of polar groups at the nitrogen atom(s) of MK, for example –CH2-CH2-OH

moieties, gives rise to specific interactions with the carbonyl group in the solid-state (crystals)

or in aggregated forms of them, when adsorbed externally on solid surfaces, because the –

CH2-CH2-OH substituent has an effect like an internal polar solvent.2,47 These specific

intermolecular interactions cause significant changes in the UV/Vis spectrum

(bathochromicity) of the material which corresponds to structural features.2

General part 13

Since ground-state aromaticity of thiophene or furan is lower than that of the benzene ring and

the solubility of thiophene or furan derivative is usually higher than that of the parent benzene

compounds, much attention has recently been paid to solvatochromic compounds that contain

thiopene.48-52 Similar compounds found a wide range of application in the field of nonlinear

optics and nano-technology devices.48-50

In this work, we report on the solvatochromic behavior and the solid-state structures of

a novel aromatic amino ketones, which are functionalized with furan and thiophene

heterocyclic rings (Chart 1).

C

O

NN

OCCH3

OCCH3

CH3

H3C

O

OC

O

NN

OH

OH

CH3

H3C

1a 2a

C

O

N

OCCH3

OCCH3

O

OX C

O

N

OH

OH

X

1(b-c) 2(b-c)

Chart 1. Di-ester and diol of aromatic aminophenyl ketones used in this work.

No Name Substituent Abbreviation

1a 4-Dimethylamino-4’-[di(2-acetoxyethyl)amino]benzophenone ---------- MK(OAc)2

1b [4-Di(2-acetoxyethyl)aminophenyl]-2-furylmethanone X = O Fur(OAc)2

1c [4-Di(2-acetoxyethyl)aminophenyl]-2-thienylmethanone X = S Thi(OAc)2

2a 4-Dimethylamino-4’-[di(2-hydroxyethyl)amino]benzophenone ---------- MK(OH)2

2b [4-Di(2-hydroxyethyl)amino-phenyl]-2-furylmethanone X = O Fur(OH)2

2c [4-Di(2-hydroxyethyl)aminophenyl]-2-thienylmethanone X = S Thi(OH)2

General part 14

Also, because of the usefulness of MK derivatives for solvatochromic studies, due to

the large extent of the bathochromic solvatochromic shift observed in increasing the

environments polarity,2,37,52 we intended to study the influence of substituents at the nitrogen

atom of MK on the UV/Vis spectroscopic properties in the solid-state and in various solvents

of different polarity. It is expected that acid-base interactions (hydrogen bonds) and dipolarity

/polarizability effects cause significant shifts in the UV/Vis spectra of those compounds

which are associated with the structure of the crystal as well as solvation behavior in well

behaved regular solvents. For this work, in extension to earlier study on MK, we have chosen

the following N-substituted Michler’s Ketones including 4,4’-bis[di(2-hydroxyethyl)-

amino]benzophenone MK(OH)4 3, 4,4’-bis(4-ethoxycarbonylpiperazino)benzophenone

MK(pipOEt)2 4a, 4,4’-bis(piperidino)benzophenone MK(pip)2 4b, 4,4’-bis(morpholino)-

benzophenone MK(mor)2 4c, 4,4’-bis(piperazino)benzophenone MK(pipaz)2 4d, 4,4’-bis[4-

(2-hydroxyethyl)piperazino]benzophenone MK(pipazOH)2 4e, and 4,4’-bis(diethyl-

amino)benzophenone MK(NEt2)2 4f as shown in Chart 2.

General part 15

C

O

R2R1

Chart 2. Michler’s ketones used in this work.

The linking of two identical solvatochromic chromophors by a rigid spacer

(piperazine) was also used as a model to study the influence of molecular polarity of the

chromophore itself on each other. Both chromophors are oppositely arranged concerning their

own dipolar direction (Chart 3)

No R1 R2 Abbreviation

3 NCH2CH2OH

CH2CH2OH

NCH2CH2OH

CH2CH2OH

MK(OH)4

4a NN C

O

OC2H5 NN C

O

OC2H5

MK(pipOEt)2

4b N

N

MK(pip)2

4c N O

N O

MK(mor)2

4d NN H

NN H

MK(pipaz)2

4e NN CH2CH2OH NN CH2CH2OH

MK(pipazOH)2

4f NCH2CH3

CH2CH3

NCH2CH3

CH2CH3

MK(NEt2)2

4g NCH3

CH3

NCH3

CH3

MK

General part 16

C

O

N N C

O

Chart 3. 1,4-bis(4-benzoylphenyl)piperazine BBP 5.

The specific question to be answered is: do both solvatochromic moieties compensate

their dipolarity or not and how is this effect detectable by means of UV/Vis spectroscopy?

To evaluate the respective contribution of vinylene spacer on the solvatochromic

properties, 3-(4-di(2-hydroxyethyl)amino)phenyl-1-(2-furyl)-2-propene-1-one [DAFP] 6

(Chart 4) was synthesized. The difference between Fur(OH)2 2b and DAFP 6 is evidently, in

the insertion of a single vinylene group between the carbonyl and the N,N-di-

hydroxyethylaminophenyl group to the backbone of 2b.

H

HC

N

HO

OH

O O Chart 4. 3-(4-Di(2-hydroxyethyl)amino)phenyl-1-(2-furyl)-2-propene-1-one [DAFP] 6.

This novel compound belongs to the α,β-unsaturated ketones of heterocyclic series.

The presence of a single vinylene group between the dimethylaminophenyl and carbonyl

group in this type of compounds is sufficient for the appearance of luminescence under

ordinary conditions.53

1.2.2 Related compound

The concepts for the molecular design of the dyes include the introduction of multiple

(both positive and negative) charges on both ends of the large conjugated π-electron system of

the dye molecule, so that the dye interacts with many chemical species or environments, the

General part 17

introduction of different substitution (electron-donating or electron-accepting) groups in the

conjugated π-electron system of the dye molecule, so that the dye has a different pKa and

solvatochromic property, and the introduction of an immobilization site in the dye molecule,

so that the dye can be easily prepared as a sensing probe.54

Based on these concepts, push-pull substituted aromatic azomethine compounds like

salicylidene-anilines can manifold interact with acids and bases as well as polar solvent

molecules, because both several basic and acidic sites as well as a dipolar delocalized π -

electron system is present.55-61 This makes the interpretation of the change of UV/Vis

spectrum as function of external influences sometimes difficult.

Therefore, it is of interest to know whether acid-base interaction and different

solvation of highly polar molecules can be treated with the same concept derived from

“indicator” chemistry or solvatochromism. Furthermore, the knowledge of the structure of the

molecules in the solid-state (crystal) and its relation to the color is of importance to

understand effects of crystallochromism with respect to dipolar and acid-base interactions for

NLO and photochromic applications in thin films and optical devices. For this study, we have

chosen N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitroaniline (HDBN) dye 7 (chart 5)

due to various inter- and intramolecular interactions with dipolar solvents, acids, and bases,

respectively are possible.

It will be shown that, this type of compound serves to all chromophoric effects

expected in a good combination in order to study by UV/Vis spectroscopy, because each

specific interaction is associated with a characteristic change in the UV/Vis spectrum.

N

O HNH3C

N

O

O

CH3

Chart 5. N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitro-aniline (HDBN) 7.

Furthermore, azomethines with –OH groups in the ortho position of the methine site

linked ring undergo reversible absorption changes upon light irradiation due to reversible

proton transfer reaction, which makes this class of compounds of interest to study

General part 18

photocrystallochromic effects as function of acid-base interaction e.g. in mixed crystals. The

general agreement56-60 about the photocoloration processes of hydrazones such as

salicylidene-aniline derivatives was also suggested as the mechanism of intramolecular proton

transfer from the O-hydroxyl group to the lone electron pair of the imine (-CH=N-) nitrogen

atom.

Intramolecularly hydrogen-bonded Schiff bases have attracted considerable attention,

because they exhibit also thermochromism. Thus the study of their structure related

properties, like environmentally influenced tautomerism equilibria, is of special importance.

Extensive studies have revealed that the thermochromism of N-salicylidene aniline

derivatives originates from the tautomerism between the OH and NH forms.60 However, due

to the high proton exchange rate, it is not possible to isolate the individual tautomeric forms.

Consequently, quantitative analysis of these processes, as well as relationships

between structural properties and tautomers, are difficult to obtain.

Therefore, it was of interest to study of the environmental effects (solvent, sol-gel

glasses, neighboring groups and molecules in the crystal) of the salicylidene aniline 7 bearing

both strong electron-donating and-withdrawing moieties in the same molecule.

1.3 Sol-gel process

Sol-gel-derived organic-inorganic nanocomposites have received a great importance in

scientific and technological interests during the past two decades.62-66 Sol-gel processing

involves hydrolysis and polycondensation of molecular precursors, mostly metal and

semimetal alkoxides, under ambient conditions and leads to the formation of ceramic

materials.67-69

The sol-gel process is amenable to the incorporation of organic moieties in inorganic

matrixes, in both hybrid and composite forms (Chart 6). There are two different types of sol-

gel materials that have been extensively used in the past. In these, organic chromophores can

be either physically blended with the silica network or chemically bound to tri(alkoxy)silanes

before hydrolytic condensation.70 Probing the microenvironment of the entrapped molecules

in the nanocomposites is another area of interest.71-78 Of utmost importance in many

applications of sol-gel derived materials is the nature of reagent entrapment.79

Device performance is strongly influenced by the translational and rotational mobility

of entrapped species, the degree and chemical nature of molecular interactions with the wall

of the matrix, and molecular scale properties (polarity, rigidity) of the individual cages/pores

General part 19

in the host framework. As a result, numerous bulk spectroscopic, electrochemical, and

chemical studies have been performed.70,71,77,79-91 These previous studies have established that

the incorporated organic moieties remain accessible to species which are in contact with the

organic-inorganic hybrid or composite, due to the porosity of the matrix.70,79 Furthermore, the

properties of the hybrid or composite can be tuned to achieve specific requirements by

varying reaction conditions. Additionally, by choosing an appropriate organic moiety and

maintaining optical transparency, the silica-based material would be suitable for spectroscopic

and spectroelectrochemical applications.

In this work the solvatochromic aromatic amino ketones 2(a-c) (Chart 6), 3, and/or 4g

are employed in order to follow the variations in the cage interfacial polarities of Ormosils

prepared by the sol-gel process from various proportions of methyltrimethoxysilane

(MTMOS) and tetramethoxysilane (TMOS).75

Sol-gel derived chromophore-bound materials are prepared according to the standard

synthetic procedures70,92,93 by linking MK(OH)2, Fur(OH)2 and/or Thi(OH)2 to 3-isocyanato-

propyltriethoxysilane (IP-TriEOS) followed by hydrolysis and condensation with

tetraethoxysilane (TEOS) in presence of hydrochloric acid as a catalyst to enhance the

formation of an amorphous silica network (see Chart 6). The resulting cross-linked matrixes

were spectroscopically characterized.

General part 20

Chart 6. Schematic illustration of the synthetic concepts and characterization of the spectral

properties of the two different classes of xerogels.

The solvatochromic probes 2(a-c) are used in two different sol-gel approaches to

compare, by UV/Vis spectroscopy, between the structure of the environment in the two hybrid

and composite sol-gel materials.

C

N

Si(OEt)3

O

2+

Si(OCH3)4

CH3Si(OCH3)3

CH3OH

Physical entrapment Chemical linking

+ Si(OC2H5)4 Sol-gel process

Class II xerogel Class I xerogel

UV/Vis measurements

Solvent influence

Solvent influence

N

HO

HO

OC

Ar

O SH3CN

H3C; ;Ar =

2a 2b 2c

General part 21

1.4 Aromatic amino ketone polymers

Polyketones are high-performance materials and have several attractive properties

including high glass transition temperature (Tg) and thermal stability because of the

incorporation of carbonyl and/or aromatic groups in the polymer backbones, as well as the

ease of modification to other functionalized polymers.94 Moreover, aliphatic polyketones have

been used as photodegradable polymers.95 Aromatic polyketones are typically synthesized by

Friedel-Crafts or nucleophilic aromatic substitution reactions.96 These materials are usually

insoluble and intractable. Aliphatic polyketones have been prepared through the

copolymerization of CO with ethylene or α-olefines.97

Donor-acceptor polymers have received increased attention recently due to their low

band gaps, luminescence, and potential third-order nonlinear optical properties.98

Piperazines form the backbone of many biologically interesting molecules.99 Their

incorporation into biologically active molecules has even been associated with an increase in

potency.100 Very recently, several new methods have been proposed for the synthesis of such

compounds using solid support101 or palladium-catalyzed aromatic amination reaction.102

Supported reagents on mineral oxide surfaces have been widely employed in organic

synthesis.103 Reagents immobilized on porous solid materials have several advantages over

the conventional solution phase reactions because of the good dispersion of active sites

leading to improved reactivity and milder reaction conditions. The recyclability of the

inorganic solid support is often possible thus rendering the procedure relatively

environmentally acceptable. In addition, polymer nanocomposites, especially polymer-layered

silicate nanocomposites, represent a rational alternative to conventionally filled polymers.

Because of their nanometer scale dispersion, nanocomposites exhibit markedly

improved properties when compared with the pure polymers or conventional composites.104

Polymer-layered silicate nanocomposites possess several advantages such as: (a)

mechanical properties that are potentially superior to fiber-reinforced polymers; (b) a lighter

weight compared to conventionally filled polymers, because high degrees of stiffness and

strength can be realized with far less high-density inorganic materials; and (c) their

outstanding diffusional barrier properties without requiring multipolymer layered design.105

Aromatic aliphatic polyketones containing piperazine moiety (donor) in the polymer

backbone have, however, not been reported. We described herein two different processes

based on nucleophilic substitution reactions for preparation of poly(benzophenone co-

piperazine).

General part 22

We first investigated the polymerization reaction in solution using dimethylsulfoxide

(DMSO) as solvent and potassium carbonate as a base. Secondly, we developed a facile

solvent-free method for synthesis of poly(benzophenone co-piperazine).

Aim of the work 23

II Aim of this work

The design and development of novel optical chemical sensors (optodes) are subject of

active research in recent years for both chemists and physicists.106 In relation to these optodes,

functional dyes such as solvatochromic dyes,1 pH indicator dyes,107 fluorescent dyes,108 and

their derivatives109 play an important role in the signal transduction process of detecting

analytes using optodes. As pointed out in Section 1.2.1 a significant interest has been

generated during the past decade in the field of preparing aromatic aminoketones of the

Michlers Ketone type and related compounds for various applications. Therefore it should be

of interest to investigate the incorporation of these chromophores into macromolecular

architectures.

This approach generally requires the introduction of appropriate reactive

functionalities, such as hydroxy groups, at the electron donating site of the chromophore. The

bis-(hydroxyethyl)-amino substituent was chosen to mimic the dimethylamino group’s steric

and electronic (inductive) effects and to provide a reactive site for further attachment.

The nature of the local microenvironment(s) within a sol-gel-derived nanocomposite is

an important factor in designing materials for sensing or photonic application. For example,

factors such as microscopic phase separation can dramatically alter the behavior of dopants

within a nanocomposite. Furthermore, the environment experienced by the dopant (i.e.,

polarity, local microviscosity, interactions with pore walls, and preferential partitioning into a

given phase) will have an impact on the dynamics, stability, and accessibility of the dopant

and as such may lead to unwanted material properties.

The need to understand the nature of the local microenvironments within

nanocomposites requires a method that is sensitive to phenomena occurring at the molecular

scale. In these instances UV/Vis absorption spectroscopy is the method of choice as it reports

on the local microenvironment surrounding a probe molecule.75

One aim of this thesis was the synthesis of novel functionalized aromatic amino

ketones containing bis-(hydroxyethyl)amino substituent and study of the environmental

effects (solvent, solid surfaces, sol-gel glasses and neighboring molecules in the crystal) on

their UV/Vis spectra. From these studies, a large amount of information concerning the

polarity of the solid surfaces, the substituent-effect in aromatic amino ketones on the solvent

polarity parameters, the intermolecular hydrogen bonding in solid crystals and in their

solutions, and the nature of the guest-host interactions was obtained.

Aim of the work 24

The evaluation of the solvatochromic response of related compound (HDBN)

containing more extended double bonds was another aim of this work.

Furthermore, in the following sections, the generation of a novel polymer containing

4,4’-bis-(piperazino)benzophenone moiety is introduced. The structure of this polymer had to

be elucidated by spectroscopic methods (solid-state-NMR, UV/Vis spectroscopy, and

MALDI-TOF spectroscopy.

Results and discussions 25

III Results and discussion

3.1 Aromatic amino ketones

3.1.1 UV/Vis absorption spectroscopy and linear solvation energy (LSE) relationships

3.1.1.1 Solvent effects on the UV/Vis absorption spectra

The UV/Vis absorption spectra of the solvatochromic UV/Vis band (the longest

wavelength band of the π- π* transition) of 1(a-c), 2(a-c), 3, 4(a-f), 5 and 6 have been

measured in 32 most common solvents at 293 K as shown in Tables (1-3). Solvents are used

with wide-ranging properties for which α, β, and π* are known.10

Altogether, in increasing the solvent polarity from cyclohexane (CH) to 1,1,1,3,3,3-

hexafluoro-2-propanol (HFP) (Tables 1-3), the UV/Vis absorption spectra of MK(OAc)2 1a

Fur(OAc)2 1b, Thi(OAc)2 1c, MK(OH)2 2a, Fur(OH)2 2b, Thi(OH)2 2c, MK(OH)4 3,

MK(pipOEt)2 4a, MK(pip)2 4b, MK(mor)2 4c, MK(NEt2)2 4f, BBP 5 and DAFB 6 show a

significant bathochromic shift of the long-wavelength UV/Vis band. A representative series of

UV/Vis spectra is shown in Fig. 1[A-E] for compounds 1(a-c), 2a, 3, 4(b-c), 4f, 5 and 6.


350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

3

6

5

4

2

1

1: 1a in CH 2: 1b in CH 3: 1c in CH 4: 1a in DMSO 5: 1b in DMSO 6: 1c in DMSO

Abs

orba

nce

(a.u

.)

λ (nm)

[A]

350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.05

6

3

4

2

1

1: 2a in DEE 2: 2a in water 3: 2a in TFE 4: 3 in DEE 5: 3 in water 6: 3 in TFE

Abs

orba

nce

(a.u

.)

λ (nm)

[B]


350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

1.2

4

2

1

3

6

5

1: 4b in DEE 2: 4b in EG 3: 4c in DEE 4: 4c in EG 5: 4f in DEE 6: 4f in EG

Abs

orba

nce

(a.u

.)

λ (nm)

[C]

350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

5

43

2

1

1: 5 in CH 2: 5 in DMAc 3: 5 in TFE 4: 5 in HFP 5: 5 in p-xylene

Abs

orba

nce

(a.u

.)

λ (nm)

[D]


350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

1.2

6 in TCM 6 in DMAc 6 in BuOH 6 in HFP

Abs

orba

nce

(a.u

.)

λ (nm)

[E]

Figure 1[A-E]. UV/Vis absorption spectra of [A] MK(OAc)2 1a, Fur(OAc)2 1b, and

Thi(OAc)2 1c in cyclohexane (CH) and dimethylsulfoxide (DMSO), [B] MK(OH)2 2a and

MK(OH)4 3 in diethyl ether (DEE), water, and 2,2,2-trifluoroethanol (TFE), [C] MK(pip)2 4b,

MK(mor)2 4c, and MK(NEt2)2 4f in diethyl ether (DEE) and ethane-1,2-diol (EG), [D] BBP 5

in CH, p-xylene, DMAc, TFE, and 1,1,1,3,3,3-hexafluoro-2-propanol (HFP) and [E] DAFP 6

in tetrachloromethane (TCM), N,N-dimethylacetamide (DMAc), 1-butanol (BuOH), and

HFP.

The bathochromicity of the solvatochromic UV/Vis absorption band of Michler’s

Ketones 1a, 2a, 3, and 4(a-c), and 4f, are theoretically expected and in agreement with

established results.34-37 This result as a whole indicates that these compounds are more dipolar

in the excited singlet state than in the ground state. However, for 4d and 4e the extent of the

positive solvatochromic shift is lower and shows also unprecedented UV/Vis absorption band

shifts as function of solvent polarity. Therefore, the solvatochromism of these two compounds

will be discussed separately (see below).


Table 1. UV/Vis absorption maxima of MK(OAc)2 1a, Fur(OAc)2 1b, Thi(OAc)2 1c,

MK(OH)2 2a, Fur(OH)2 2b, and Thi(OH)2 2c measured in diverse solvents1.

solvent ν max 1a

/103cm-1

ν max 2a

/103cm-1

ν max 1b

/103cm-1

ν max 2b

/103cm-1

ν max 1c

/103cm-1

ν max 2c

/103cm-1

Cyclohexane 30.03 2 29.41 28.82 29.76 29.24

Triethylamine 29.94 29.33 29.24 28.01 29.50 28.25

Tetrachloromethane 29.41 29.24 28.82 28.41 29.07 28.82

Diethyl ether 29.67 29.15 29.07 28.25 29.33 28.41

p-Xylene 29.15 28.99 28.74 28.09 28.99 28.41

Toluene 29.07 28.90 28.65 28.09 28.99 28.33

Ethyl acetate 28.90 28.82 28.65 27.93 28.82 28.09

1,4-Dioxane 28.90 28.74 28.57 27.78 28.82 28.01

Benzene 28.90 28.74 28.57 27.93 28.74 28.25

Tetrahydrofuran 28.99 28.74 28.49 27.70 28.57 27.93

1,2-Dimethoxyethane 28.99 28.65 28.49 27.70 28.74 27.86

Acetone 28.82 28.41 28.33 27.55 28.49 27.62

Chloroform 28.41 28.09 28.17 27.70 28.49 28.01

Dichloromethane 28.49 28.25 28.17 27.70 28.41 27.93

1,2-Dichloroethane 28.49 28.33 28.17 27.70 28.41 27.86

1,1,2,2-Tetrachloroethane 28.25 27.78 27.78 27.47 28.09 27.62

Acetonitrile 28.41 28.17 28.17 27.47 28.33 27.47

Benzonitrile 28.01 27.78 27.78 27.10 27.93 27.17

N,N-Dimethylformamide 28.25 27.78 27.93 27.03 28.01 27.03

N,N-Dimethylacetamide 28.33 27.78 27.86 26.95 27.93 27.03

Pyridine 28.25 27.7 27.86 26.95 28.01 26.88

Ethanol 27.62 27.25 27.55 26.81 27.86 27.03

Methanol 27.40 27.03 27.40 26.81 27.70 26.95

1-Butanol 27.70 27.32 27.47 26.67 27.78 26.88

Dimethylsulfoxide 27.86 27.47 27.47 26.74 27.62 26.67

Acetic acid 27.62 26.67 27.17 26.60 27.55 26.88

Formamide 26.95 26.60 27.03 26.25 27.10 26.39

Ethane-1,2-diol 26.74 26.46 26.88 26.25 27.03 26.39

2,2,2-Trifluoroethanol 26.04 25.91 26.81 26.53 27.10 26.81

Water 26.39 26.11 26.53 25.97 26.67 26.11

1,1,1,3,3,3-Hexafluoro-2-propanol 25.19 25.00 26.18 26.04 26.46 26.39


Table 2. UV/Vis absorption maxima for MK(OH)4 3, MK(pipOEt)2 4a, MK(pip)2 4b,

MK(mor)2 4c, MK(pipaz)2 4d, and MK(pipazOH)2 4e in 32 solvents of different polarity and

hydrogen bond ability.

solvent ν max 3

/103cm-1

ν max 4a

/103 cm-1

ν max 4b

/103 cm-1

ν max 4c

/103 cm-1

ν max 4d

/103 cm-1

ν max 4e

/103 cm-1

Cyclohexane 2 30.67 29.94 30.67 2 30.86

Triethylamine 28.82 30.58 29.85 30.58 29.94 30.21

Diethyl ether 29.07 30.30 29.41 30.30 29.76 29.94

Tetrachloromethane 2 30.12 29.15 30.03 29.33 30.40

p-Xylene 29.07 29.76 28.99 29.85 29.50 30.00

Toluene 28.74 29.67 28.90 29.76 29.33 29.94

Tetrahydrofuran 28.49 29.59 28.90 29.67 29.15 29.67

1,2-Dimethoxyethane 28.57 29.50 28.90 29.76 29.15 29.50

Ethyl acetate 28.65 29.24 28.99 29.85 29.33 29.76

1,4-Dioxane 28.49 29.50 28.82 29.33 29.15 29.85

Benzene 28.65 29.41 28.74 29.50 29.24 29.85

Acetone 28.17 29.33 28.33 28.82 28.65 29.50

Dichloromethane 28.57 29.15 28.17 29.24 28.90 29.33

1,2-Dichloroethane 28.33 29.15 28.25 28.90 28.90 29.33

Chloroform 28.41 29.15 28.09 28.99 28.82 29.33

Acetonitrile 28.01 28.99 28.25 29.15 28.82 29.41

N,N-Dimethylacetamide 27.78 28.82 28.17 28.74 28.41 29.07

1,1,2,2-Tetrachloroethane 27.86 28.74 27.62 28.90 29.50 28.90

N,N-Dimethylformamide 27.70 28.82 28.09 28.99 28.41 28.99

Pyridine 27.62 28.82 27.93 28.90 28.33 28.90

Benzonitrile 27.78 28.74 27.93 28.65 28.33 27.25

1-Octanol 27.40 28.90 27.78 28.90 28.49 29.07

Dimethylsulfoxide 27.25 28.41 27.70 28.57 28.01 28.64

1-Butanol 27.17 28.65 27.55 28.82 28.33 28.82

Ethanol 27.17 28.65 27.62 28.82 28.65 28.74

Acetic acid 26.67 28.17 27.03 28.49 29.41 30.21

Methanol 27.03 28.57 27.32 28.74 28.41 28.82

Formamide 26.53 27.86 26.81 28.09 28.90 29.41

Ethane-1,2-diol 26.46 27.78 26.67 28.09 28.74 29.85

Water 25.97 2 2 2 28.49 29.33

2,2,2-Trifluoroethanol 26.32 27.25 25.97 27.62 28.33 28.49

1,1,1,3,3,3-Hexafluoro-2-propanol 25.51 26.04 25.06 26.60 29.24 29.94


Table 3. UV/Vis absorption maxima for MK(NEt2)2 4f, MK 4g, BBP 5 and DAFP 6 in 32 solvents.

solvent ν max 4f

/103 cm-1

ν max 4g3

/103 cm-1

ν max 5

/103 cm-1

ν max 6

/103 cm-1

α β π*

Cyclohexane 29.33 29.88 30.86 24.94 0.00 0.00 0.00

Triethylamine 29.15 29.68 30.30 24.21 0.00 0.71 0.14

Diethyl ether 28.99 29.414 30.30 24.69 0.00 0.47 0.27

Tetrachloromethane 28.74 29.24 30.21 24.94 0.00 0.10 0.28

p-Xylene 28.49 29.00 29.85 24.51 0.00 0.12 0.43

Toluene 28.49 28.92 29.67 24.39 0.00 0.11 0.54

Tetrahydrofuran 28.41 28.84 29.41 23.92 0.00 0.55 0.58

1,2-Dimethoxyethane 28.41 28.904 29.15 23.98 0.00 0.41 0.53

Ethyl acetate 28.52 29.04 29.67 24.15 0.00 0.45 0.55

1,4-Dioxane 28.41 28.92 29.59 24.10 0.00 0.37 0.55

Benzene 28.33 28.76 29.59 24.33 0.00 0.10 0.59

Acetone 28.01 28.64 29.15 23.92 0.08 0.43 0.71

Dichloromethane 27.62 28.08 28.99 24.07 0.13 0.10 0.82

1,2-Dichloroethane 27.78 28.20 29.07 23.98 0.00 0.10 0.81

Chloroform 27.40 28.04 28.99 24.04 0.20 0.10 0.58

Acetonitrile 27.72 28.32 28.90 23.87 0.19 0.40 0.75

N,N-Dimethylacetamide 27.62 28.16 28.65 23.31 0.00 0.76 0.88

1,1,2,2-Tetrachloroethane 27.25 27.88 28.65 23.81 0.00 0.00 0.95

N,N-Dimethylformamide 27.55 28.04 28.65 23.31 0.00 0.69 0.88

Pyridine 27.40 27.88 28.65 23.15 0.00 0.64 0.87

Benzonitrile 27.32 27.88 28.25 23.47 0.00 0.37 0.90

1-Octanol 26.88 27.624 28.99 23.36 0.77 0.81 0.40

Dimethylsulfoxide 27.10 27.64 28.17 22.99 0.00 0.76 1.00

1-Butanol 26.74 27.36 28.65 23.04 0.84 0.84 0.47

Ethanol 26.74 27.32 28.41 23.26 0.86 0.75 0.54

Acetic acid 26.25 26.68 28.00 23.09 1.12 0.45 0.64

Methanol 26.46 27.08 28.17 23.26 0.98 0.66 0.60

Formamide 26.04 26.64 28.99 22.68 0.71 0.48 0.97

Ethane-1,2-diol 25.97 26.40 28.57 22.62 0.90 0.52 0.92

Water 2 2 2 22.62 1.17 0.47 1.09

2,2,2-Trifluoroethanol 24.88 25.76 27.17 23.04 1.51 0.00 0.73

1,1,1,3,3,3-Hexafluoro-2-propanol 24.96 24.96 26.11 22.78 1.96 0.00 0.65

1 Solvatochromic parameters α, β, and π* for all solvents were taken from reference 10. 2 Probe is insoluble in this solvent. 3 Results from reference 37. 4 Data were measured also in this work.


Also, the bathochromic displacement of the long-wavelength UV/Vis absorption band

for 1(b-c) and 2(b-c) towards the more polar solvent is in agreement with an increased

delocalization due to the conjugation of the lone pair of electrons of the [-N(CH2CH2OH)2] or

[-N(CH2CH2OCOCH3)2] donor substituent with the aromatic π-electron system and the

carbonyl group. This result indicates that the heterocyclic substituted aromatic aminoketones

are more polar in the singlet excited state than in the ground state.

Taking into account all solvents studied, for any solvent, compounds 1(a-c) absorb

hypsochromically in comparison with their diols 2(a-c). This is a clear result of the electron

withdrawing influence of the acetyl group, which lowers the electron density at the nitrogen

atom. Thus, the delocalization ability of the lone pair of electrons at the nitrogen atom is

slightly decreased. The extent of the hypsochromic shift, for example, from Fur(OH)2 to

Fur(OAc)2, occurs stronger in HBA (hydrogen-bond accepting) solvents such as triethyl

amine (TEA) (∆ν = 1203 cm-1) than in HBD (hydrogen-bond donating) solvents like water

(∆ν = 533 cm-1) or HFP (∆ν = 140 cm-1) indicating an additional electron pushing influence

of HBA solvents upon the –N(CH2CH2OH)2 substituent.

The solvatochromic effect of MK(OAc)2 shows that the long-wavelength UV/Vis

absorption maximum ranges from λ = 333 nm in CH to λ = 397 nm in HFP, corresponding to

∆λ = 64 nm (∆ν = 4840 cm-1) stabilization energy between these two solvents of extremely

different polarity. However, the extent of the solvatochromic UV/Vis band shift is smaller for

MK(OH)2. It ranges from λ = 341 nm in TEA to λ = 400 nm in HFP, corresponding to ∆λ =

59 nm (∆ν = 4330 cm-1), while in the case of the furan [Fur(OAc)2, Fur(OH)2] and thiophene

[Thi(OAc)2, Thi(OH)2] analogues (Table 1), The UV/Vis shifts range from λ = 340 nm in CH

to λ = 382 nm in HFP, corresponding to ∆λ = 42 nm (∆ν = 3230 cm-1), from λ = 347 nm in

CH to λ = 385 nm in water, corresponding to ∆λ = 38 nm (∆ν = 2850 cm-1), from λ = 336 nm

in CH to λ = 378 nm in HFP, corresponding to ∆λ = 42 nm (∆ν = 3300 cm-1), and from λ =

342 nm in CH to λ = 383 nm in water, corresponding to ∆λ = 41 nm (∆ν = 3130 cm-1),

respectively. Thus, the extent of the solvatochromic shift as function of solvent polarity of the

hydroxyl functionalized homomorph is lower than that of the acetoxy functionalized

homomorph, which is likely caused by a competing influence of the polar substituent with the

solvent molecules.

A hypsochromic band shift from MK to MK(OH)4 is observed when strong HBD

solvents (TFE, water or HFP) are considered. This result indicates a specific solvation of the

oxygen atoms of the (HOCH2CH2)N- substituent by the active hydrogen atoms of the HBD


solvents. Consequently, the positive mesomeric effect of the (HOCH2CH2)N- substituent is

lowered.

C

O

N

CH3

H3CN

OH

OH

H OCH2CF3C

O

N

CH3

H3CN

O

OH

H N(C2H5)3

(a) (b)

Scheme 1. Suggested solvation mechanism of MK(OH)2 in (a) Strong HBD solvents such as

trifluoroethanol, which lower the (+M) effect and increase the (-I) effect of the

(HOCH2CH2)N- substituent, which causes a hypsochromic and band shift compared to MK

and (b) HBA solvents such as triethylamine enhance the (+M) effect or/and lower the (-I)

effect of the (HOCH2CH2)N- substituent, which causes a bathochromic band shift compared

to MK.

A solvation of the lone pair of electrons of the nitrogen atom is unlikely, since in that

case a significant hypsochromic shift is expected. We assume that the specific interaction

between the HAB solvent and the (HOCH2CH2)N- substituent plays the major role (Scheme

1), because the bathochromic band shift obtained in going from MK to MK(OH)4 is negligible

for common alcohols (methanol, ethanol, n-butanol). These solvents show both HBD and

HBA properties of similar strength. In aromatic and halogenated solvents also no significant

difference of νmax between MK(OH)4, MK(OH)2 and MK is observed.

UV/Vis measurements of Thi(OH)2 as function of its concentration show no

significant indication of probe aggregation in the concentration interval studied for the

solvatochromic measurement. The long-wavelength UV/Vis absorption maximum ranges

from λ = 353 ± 1 nm to λ = 355 ± 1 nm with increasing the concentration of Thi(OH)2 from c

= 1.59*10-5 to c = 42.86*10-5 M in toluene as solvent. Since, the concentration exceed

1.20*10-3 M, then a bathochromically shifted new UV/Vis absorption as a shoulder at λ = 392

nm appears. Thus, dye dimerisation as the simplest case of aggregation in solutions (eq. 1) is

only observed at large dye concentration.


(1)

λ = 353 nm (toluene) λ = 392 nm (toluene)

Low concentration (c <10-3 M) high concentration (c >10-3 M)

It is worth to note from figure 1B that, in the case of HBA and weak polar solvents

such as diethyl ether, MK(OH)4 and MK(OH)2 show a symmetrical UV/Vis band because the

n-π* and π-π* transition interfere,4 whereas in strong HBD solvents such as 2,2,2-

trifluoroethanol (TFE) and water, an additional shoulder at about 350 nm is observed which is

probably caused by a separate n-π* transition. For the regression analysis (see below), only

the intense absorption (π-π* transition) at the longer wavelength was used.

The long-wavelength UV/Vis absorption maximum of BBP 5 (Table 3, Figure 1D)

ranges from λ = 324 nm in CH to λ = 383 nm in HFP, corresponding to ∆λ = 59 nm (∆ν =

4750 cm-1). Thus, this compound shows quite the same solvatochromic effect than does MK.

The largest solvatochromic bathochromic UV/Vis band shift is observed in HFP for

MK(OAc)2, MK(NEt2)2, MK(pipOEt)2, MK(pip)2, MK(mor)2, and BBP including MK and

two hydrophilically substituted derivatives MK(OH)2, and MK(OH)4. The extent of the

positive solvatochromic shift, from TEA to HFP, decreases in the following order: MK(pip)2

(∆ν = 4790 cm-1) > MK(OAc)2 (∆ν = 4750 cm-1) > MK (∆ν = 4720 cm-1) > MK(pipOEt)2 (∆ν

= 4540 cm-1) > MK(OH)2 (∆ν = 4330 cm-1) > MK(NEt2)2 (∆ν = 4190 cm-1) > MK(mor)2 (∆ν

= 3980 cm-1) MK(OH)4 (∆ν = 3310 cm-1).

The solvatochromic effect of DAFP 6 (Table 3, Figure 1E) shows that the long-

wavelength UV/Vis absorption maximum ranges from λ = 401 nm in CH and TCM to λ =

442 nm in 1,2-ethandiol and water, corresponding to ∆λ = 41 nm (∆ν = 2320 cm-1)

stabilization energy between these solvents of extremely different polarity. This bathochromic

displacement for 6 is in agreement with an increased delocalization, due to a more extended

conjugated π-system. This result indicates that compound 6 is more polar in the excited

singlet state than in the ground state. Going from non polar solvent CH to polar solvent water,

the extent of solvatochromic bathochromic shift for 6 is similar to that of 2b (vide supra).

However, the difference between the long-wavelength UV/Vis absorption maximum of 6 and

2b in the same solvent is more significant (∆λ = 54, and 57 nm in case of CH and water,

respectively).

2 Thi(OH)2 [Thi(OH)2]2


Ambiguous solvatochromic UV/Vis band shifts as function of solvent polarity show

MK(pipaz)2 and MK(pipazOH)2. The long-wavelength UV/Vis absorption maxima of

MK(pipaz)2 and MK(pipazOH)2 are less pronounced and range from λ = 334 nm in TEA to λ

= 353 nm in pyridine, benzonitrile, 1-butanol and TFE, corresponding to ∆λ = 19 nm (∆ν =

1610 cm-1) and from λ = 324 nm in CH to λ = 367 nm in benzonitrile, corresponding to ∆λ =

43 nm (∆ν = 3610 cm-1), respectively.

In strong HBD solvents, such as water, acetic acid and HFP a strong hypsochromic

shift of the UV/Vis band is observed, which shows that the positive mesomeric effect of the

nitrogen atom at the aromate is suppressed. However, the basicity of the secondary nitrogen

atom of the piperazine ring is larger than that of the tertiary nitrogen directly bonded at the

aromate. Therefore, it is expected that a HBD solvent interacts preferably with the secondary

nitrogen atom of the piperazine ring due to its larger basicity. This raises the question which

role play acid-base interactions at the piperazino ring and how do they contribute to the shift

of the solvatochromic UV/Vis band?

350 400 450 500 550 600 650 700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

4d in EtOH pH = 7.3 λmax= 349 nm 4d in EtOH pH = 10.5 λmax= 354 nm 4d in EtOH pH = 1.2 λmax= 335 nm

Abs

orba

nce

(a.u

.)

λmax (nm)

Figure 2. UV/Vis absorption spectra of MK(pipaz)2 4d in ethanol (EtOH) at different pH

values using aqueous solution of HCl (36 %) and/or ethanolic solution of NaOH for adjusting

pH strength.


UV/Vis absorption spectra of MK(pipaz)2 in ethanolic solutions with different pH’s

are shown in Fig. 2. At low pH, protonation takes place at the secondary nitrogen atoms and

the UV/Vis absorption maxima is hypsochromically shifted. This shows that acid-base

interactions at the secondary nitrogen atom have an influence on the tertiary nitrogen atom,

likely via the through-space interaction from the nitrogen atom bonded at the aromate to the

nitrogen atom in the 4-position of piperazine, because solely piperazine substituents with

strong basic nitrogen atoms show this effect.

In increasing the pH, the solvatochromic UV/Vis band shifts bathochromically, even

at pH > 7. This effect can be explained in terms of enhancing the through space interaction

from the secondary nitrogen atom to the nitrogen atom at the aromate which causes an

increase of the positive mesomeric effect of the latter (Scheme 2).

NN C

O

NH

H

(a) In acid medium, electrostatic repulsion between the two nitrogen atoms of the piperazine moiety take place.

HB NN C

O

N

(b) In basic medium, electrostatic attraction between the two nitrogen atoms of the piperazine moiety may occur.

Scheme 2. Proposed modification of the positive mesomeric effect by through-space

interaction of piperazino-functionalized aromatic ketones.

3.1.1.2 Mathematical calculations based on linear solvation energy (LSE) relationships

In order to evaluate the respective contributions of the dipolarity/polarizability of the

solvent and its hydrogen-bonding ability in the ground and excited singlet state solute-solvent

interactions of the aromatic amino ketones, the simplified form of the Kamlet-Taft LSE


relationship was used. This equation which applied to single solvatochromic shifts, XYZ =

νmax (probe)1, 10 is given in eq. (2).

XYZ = (XYZ)0 + aα + bβ + s(π*+dδ) (2)

The challenge is to relate the values of the Kamlet-Taft parameters to microscopic

interactions such as specific hydrogen bonds. To achieve this goal, we set out to compare

MK(OH)2, Fur(OH)2, and Thi(OH)2 with their ester analogue, MK(OAc)2, Fur(OAc)2 and

Thi(OAc)2. The difference between them is, evidently, in the replacement of the hydroxyl

hydrogen atom by acetyl group. If only the OH group contributes to b, we expect to be b = 0

for MK(OAc)2, Fur(OAc)2, and Thi(OAc)2, respectively.

XYZ = (XYZ)0 + s(π* + dδ) + aα (3)

Thus, in non protic or other solvents with α = 0, the UV/Vis shifts of the acetoxy

derivatives are governed exclusively by polarity effects.

If the substitution at the hydroxyl oxygen does not affect drastically the electron density of the

residual molecular structure of MK(OH)2, Fur(OH)2, and Thi(OH)2, the dipole moments of

the esters MK(OAc)2, Fur(OAc)2, and Thi(OAc)2 compared to their alcohols should be

similar. If, in addition, their a coefficients are similar, the excess UV/Vis shift, ∆ν max = νmax

[X(OAc)2] - νmax [X(OH)2] (X = MK, Fur or Thi), is to be expected solely a function of β:

∆ν = ∆ν 0 - bβ (4)

The above presumptions will be tested by the expected solvatochromic UV/Vis shifts

of the six compounds studied. Similar strategies with other homomorph solvatochromic dyes

have been employed for the creation of related empirical solvent HBA, HBD, and dipolarity/

polarizability scales.13

The solvatochromic parameters α, β, and π* for the square multiple correlation

analysis were taken from ref.10 The wave numbers of the absorption maxima (νmax) as energy

adequate measure have been used in the regression analysis.

The correlations statistically provide a solid base for understanding solvent effects on

the solvatochromic long-wavelength UV/Vis absorption band of these molecules. The LSE

relationships show a high quality in particular as indicated by correlation coefficients larger


than 0.90 for special mathematical functions of νmax with α, β, and π*, respectively (Fig. 3[A-

E]).

νmax *10-3 MK(OAc)2 = 30.12 - 1.64 α - 2.06 π* n = 28 r = 0.99 SD = 0.13

25.5

26

26.5

27

27.5

28

28.5

29

29.5

30

30.5

25.5 26 26.5 27 27.5 28 28.5 29 29.5 30 30.5

measured νmax *10-3 cm-1

calc

ulat

ed ν

max

*10

-3 c

m-1

[A]

νmax *10-3 Thi(OH)2 = 29.36 - 0.83 α - 1.05 β - 1.79 π* n = 31 SD = 0.13 r = 0.99

25.5

26

26.5

27

27.5

28

28.5

29

29.5

30

25.5 26 26.5 27 27.5 28 28.5 29 29.5


calc

ulat

ed ν

max

*10

-3 c

m-1

[B]


νmax *10-3 MK(pipOEt)2 = 30.73 - 1.18 α - 2.13 π* n = 29 SD = 0.14 r = 0.99

27

27.5

28

28.5

29

29.5

30

30.5

31

27 27.5 28 28.5 29 29.5 30 30.5 31


calc

ulat

ed ν

max

*10

-3 c

m-1

[C]

νmax *10-3 MK(pip)2 = 30.01 - 1.62 α - 2.19 π* n = 31 SD = 0.17 r = 0.99

24.5

25.5

26.5

27.5

28.5

29.5

30.5

24.5 25.5 26.5 27.5 28.5 29.5 30.5


calc

ulat

ed ν

max

*10

-3 c

m-1

[D]


22

23

24

25

26

27

28

29

22 23 24 25 26 27 28 29


calc

ulat

ed ν

max

*10

-3 c

m-1

2b6c-hexane

water

[E]

Figure 3. Relationships between calculated and measured νmax values for [A] MK(OAc)2, [B]

Thi(OH)2, [C] MK(pipOEt)2, [D] MK(pip)2 and [E] Fur(OH)2 2b and DAFP 6.

The results of the multiple square correlation analysis are summarized in Tables (4-5).


Table 4. Values of the solvent-independent correlation coefficients (a, b, and s of the Kamlet-

Taft parameters α, β, and π*), solute property of a reference system (XYZ)0, standard

deviation (SD), and number of solvents (n) for the solvatochromism of aromatic amino

ketones 1(a-c)and 2(a-c), respectively.

Compound (XYZ)0 a b s r SD n Probe > F

30.05 -1.61 0.10 -2.00 0.98 0.21 315 < 0.0001

30.08 -1.62 ------ -1.98 0.98 0.21 315 < 0.0001

30.12 -1.64 ------ 2.06 0.99 0.13 286 < 0.0001

30.13 ------ 0.01 -2.14 0.99 0.11 187 < 0.0001

MK(OAc)2 1a

30.13 ------ ------ -2.14 0.99 0.10 187 < 0.0001

29.50 -1.07 -0.19 -1.65 0.99 0.13 315 < 0.0001

29.45 -1.06 ------ -1.69 0.99 0.14 315 < 0.0001

29.54 ------ -0.10 -1.81 0.98 0.11 187 < 0.0001

Fur(OAc)2 1b

29.52 ------ ------ -1.84 0.98 0.11 187 < 0.0001

29.87 -1.01 -0.29 -1.85 0.99 0.13 315 < 0.0001

29.79 -1.00 ------ -1.90 0.98 0.15 315 < 0.0001

29.88 ------ -0.28 -1.92 0.98 0.11 187 < 0.0001

Thi(OAc)2 1c

29.82 ------ ------ -2.00 0.98 0.13 187 < 0.0001

29.86 -1.64 -0.25 -1.99 0.99 0.19 308 < 0.0001

29.77 -1.63 ------ -2.00 0.98 0.20 308 < 0.0001

30.04 ------ -0.43 -2.22 0.98 0.12 179 < 0.0001

MK(OH)2 2a

29.91 ------ ------ 2.29 0.97 0.17 179 < 0.0001

28.91 -0.90 -0.82 -1.48 0.99 0.12 315 < 0.0001

28.69 -0.88 ------ -1.63 0.94 0.26 315 < 0.0001

28.82 ------ -0.72 -1.86 0.74 0.51 315 < 0.0001

28.92 -0.84 ------ -1.52 0.98 0.10 187 < 0.0001

Fur(OH)2 2b

28.75 ------ ------ -1.75 0.91 0.25 187 < 0.0001

29.36 -0.83 -1.05 -1.79 0.99 0.13 315 < 0.0001

29.07 -0.80 ------ 1.98 0.92 0.32 315 < 0.0001

29.27 ------ -0.96 -2.14 0.82 0.47 315 < 0.0001

29.38 ------ -1.10 -1.82 0.99 0.12 187 < 0.0001

29.15 ------ ------ -2.13 0.90 0.32 187 < 0.0001

Thi(OH)2 2c

28.51 ------ -1.69 ------ 0.66 0.54 187 0.00282


Table 5. Values of the solvent-independent correlation coefficients (a, b, and s of the Kamlet-Taft parameters α, β, and π*), solute property of a reference system (XYZ)0, standard deviation (SD), and number of solvents (n) for the solvatochromism of aromatic amino ketones 3, 4(a-g) and 5 respectively.

Compound (XYZ)0 a b s r SD n Probe > F

29.86 -1.47 -0.72 -1.85 0.99 0.17 3010 < 0.0001

29.50 -1.46 ------ -1.77 0.97 0.26 3010 < 0.0001

MK(OH)4 3

29.90 ------ -0.76 -1.95 0.97 0.14 1611 < 0.0001

30.70 -1.36 0.16 -2.13 0.98 0.21 3112 < 0.0001

30.76 -1.36 ------ -2.11 0.98 0.21 3112 < 0.0001

30.75 -1.18 -0.04 -2.12 0.99 0.14 2913 < 0.0001

30.73 -1.18 ------ -2.13 0.99 0.14 2913 < 0.0001

MK(pipOEt)2 4a

30.77 ------ -0.04 -2.21 0.98 0.12 1814 < 0.0001

29.94 -1.62 0.22 -2.22 0.99 0.16 3112 < 0.0001

30.01 -1.62 ------ -2.19 0.99 0.17 3112 < 0.0001

MK(pip)2 4b

30.00 ------ -0.24 -2.37 0.99 0.12 1814 < 0.0001

30.69 -1.13 0.16 -2.06 0.97 0.23 3112 < 0.0001

30.74 -1.13 ------ -2.04 0.96 0.23 3112 < 0.0001

MK(mor)2 4c

30.79 ------ 0.07 -2.21 0.98 0.15 1814 < 0.0001

30.07 -0.14 -0.76 -1.20 0.74 0.34 3115 < 0.0001

30.04 ------ -0.76 -1.24 0.72 0.35 3115 < 0.0001

30.01 -0.07 -0.92 -1.14 0.86 0.25 2616 < 0.0001

30.00 ------ -0.93 -1.15 0.85 0.24 2616 < 0.0001

MK(pipaz)2 4d

30.36 ------ -0.70 -1.64 0.88 0.28 1717 < 0.0001

30.63 -0.01 -0.63 -1.49 0.64 0.55 32 0.00183

30.63 ------ -0.63 -1.49 0.64 0.54 32 0.00049

30.83 -0.11 -0.74 -1.64 0.91 0.24 2418 < 0.0001

30.80 ------ -0.73 -1.65 0.91 0.24 2418 < 0.0001

MK(pipazOH)2 4e

30.95 ------ -0.30 -2.23 0.85 0.46 1814 < 0.0001

29.48 -1.77 -0.07 -2.14 0.98 0.21 3112 < 0.0001

29.46 -1.77 ------ -2.15 0.98 0.20 3112 < 0.0001

MK(NEt2)2 4f

29.53 ------ 0.04 -2.29 0.98 0.15 1814 < 0.0001

29.97 -1.80 0.03 -2.14 0.99 0.15 3112 < 0.0001

29.98 -1.80 ------ -2.14 0.99 0.15 3112 < 0.0001

MK 4g

30.01 ------ -0.03 -2.25 0.98 0.13 1814 < 0.0001

30.66 -1.25 0.02 -2.05 0.92 0.39 3112 < 0.0001

30.67 -1.25 ------ -2.05 0.92 0.38 3112 < 0.0001

30.94 -1.24 -0.02 -2.39 0.99 0.12 2619 < 0.0001

30.87 -1.26 ------ -2.41 0.99 0.13 2619 < 0.0001

BBP 5

30.96 ------ -0.33 -2.45 0.98 0.17 1814 < 0.0001


5 All measured ν max data for all solvents in table (1) are used in correlation analysis. 6 Measured νmax data for acetic acid, water, and HFP are excluded. 7 Measured νmax data for all solvents with α = 0 in table (1) are only used in correlation analysis. 8 MK(OH)2 is insoluble in cyclohexane, therefore, the measured νmax data used in correlation analysis were 30. 9 Measured νmax data for all solvent with α = 0 in table (1) are only used in correlation analysis with the exception of cyclohexane. 10 Probe was measured in 30 solvents because it is insoluble in CH and TCM. 11 Excluding solvents with α > 0 with the exception of CH and TCM. 12 Probe was measured in 31 solvents because it is insoluble in water. 13 Excluding νmax values of methanol and HFP. 14 Excluding solvents with α > 0. 15 Probe was measured in 31 solvents because it is insoluble in CH. 16 Excluding νmax values of TEA, TCE, formamide, acetic acid and TFE. 17 Excluding solvents with α > 0 with the exception of CH. 18 Excluding νmax values of ethanol, 1-butanol, ethane-1,2-diol, benzonitrile, water, formamide, acetic acid and TFE. 19 Excluding νmax values of 1,2-dimethoxyethane, 1,2-ethandiol, benzonitrile, water, formamide, and HFP.


As shown from Tables 4 and 5, the improvement of the correlation coefficient r does

not seem to change significantly on going from a two-parameter equation to a three parameter

equation.

The best regression fits νmax = f (α, β, π*) which are obtained for the aromatic amino

ketones are expressed by Eqns. (5-20), respectively.

νmax *10-3 [MK(OAc)2] = 30.12 - 1.64 α – 2.06 π* (5)

n = 28 r = 0.99 SD = 0.13 F < 0.0001

νmax *10-3 [Fur(OAc)2] = 29.45 - 1.06 α – 1.69 π* (6)

n = 31 r = 0.99 SD = 0.14 F < 0.0001

νmax *10-3 [Thi(OAc)2] = 29.79 - 1.00 α – 1.90 π* (7)

n = 31 r = 0.98 SD = 0.15 F < 0.0001

νmax *10-3 [MK(OH)2] = 29.86 - 1.64 α – 0.25 β - 1.99 π* (8)

n = 30 r = 0.99 SD = 0.19 F < 0.0001

νmax *10-3 [Fur(OH)2] = 28.91 - 0.90 α – 0.82 β - 1.48 π* (9)

n = 31 r = 0.99 SD = 0.12 F < 0.0001

νmax *10-3 [Thi(OH)2] = 29.36 – 0.83 α – 1.05 β - 1.79 π* (10)

n = 31 r = 0.99 SD = 0.13 F < 0.0001

νmax *10-3 [MK(OH)4] = 29.86 - 1.47 α – 0.72 β - 1.85 π* (11)

n = 30 r = 0.99 SD = 0.17 F < 0.0001

νmax *10-3 [MK(pipOEt)2] = 30.73 - 1.18 α – 2.13 π* (12)

n = 29 r = 0.99 SD = 0.14 F < 0.0001

νmax *10-3 [MK(pip)2] = 30.01 - 1.62 α – 2.19 π* (13)

n = 31 r = 0.99 SD = 0.17 F < 0.0001

νmax *10-3 [MK(mor)2] = 30.73 - 0.96 α – 2.08 π* (14)

n = 28 r = 0.98 SD = 0.17 F < 0.0001

νmax *10-3 [MK(pipaz)2] = 30.00 - 0.93 β – 1.15 π* (15)

n = 26 r = 0.85 SD = 0.24 F < 0.0001

νmax *10-3 [MK(pipazOH)2] = 30.80 - 0.73 β – 1.65 π* (16)

n = 24 r = 0.91 SD = 0.24 F < 0.0001

νmax *10-3 [MK(NEt2)2] = 29.46 - 1.77 α – 2.15 π* (17)

n = 31 r = 0.98 SD = 0.20 F < 0.0001

νmax *10-3 [MK] = 29.98 - 1.80 α – 2.14 π* (18)


n = 31 r = 0.99 SD = 0.15 F < 0.0001

νmax *10-3 [BBP] = 30.87 - 1.26 α – 2.41 π* (19)

n = 26 r = 0.99 SD = 0.13 F < 0.0001

νmax *10-3 [DAFP] = 25.23 - 0.72 α - 0.89 β – 1.44 π* (20)

n = 35 r = 0.97 SD = 0.15 F < 0.0001

Here and in the following, νmax is expressed in cm-1, r: correlation coefficient, SD:

standard deviation, n: number of solvents, F: significance.

By applying eq. (2), and eq. (3) to the long-wavelength UV/Vis absorption bands of

1(a-c), 4(a-c, f, g), and 5 (Tables 4 and 5), it can be concluded that the influence of the β term

of the solvent upon νmax can be ignored, because of the smaller value of the coefficient b in

addition to the high error in this value. For 4d and 4e (eqs. 15 and 16) the effect of β is more

pronounced and significantly evident. The smaller influence of the β term for 4e on the extent

of the bathochromic shift, because the distance of the interacting groups -N–CH2CH2OH with

the HBA solvent, to the nitrogen atom at the aromatic ring is larger than that for 4d.

Due to versatile specific interactions of the HBD capacity (α term) of the solvent with

4d and 4e cause opposite influences on the UV/Vis shift, no significant influence of the α

term on νmax for these compounds has been found by multiple square analysis when utilizing

eq. 2 and the Kamlet-Taft solvents parameter set.

Also, the result indicates that the HBA property of the solvent affects the -

N(CH2CH2OH)2 substituent of Thi(OH)2 in a greater extent than does the HBA property the

carbonyl oxygen, because the value of coefficient b = 1.05 is larger than that of a = 0.83 (eq.

10). The influence of the β (b = 0.82) and α (a = 0.90) term, respectively, makes a small

difference on νmax for Fur(OH)2 as shown from eq. 9, whereas the more pronounced influence

on νmax of MK(OH)2 in going from HBA to HBD solvent which arises from the large

difference between the two coefficients a and b (1.39, eq. 8).

The results of the correlation analysis for 2(a-c), and 3 show that the influence of the

HBA property arises exclusively from the formation of hydrogen bonds donated from the

hydroxyl group of the probe to the lone pair of electrons of the solvent molecule. Also, the

significant increasing in b value in going from 2a to 2c indicates that the electron density and

size of the aromatic ring (e.g. furyl, thienyl or 4-dimethylaminophenyl) controls the HBD

strength of the -N(CH2CH2OH)2 group and accordingly the strength of interactions between


the HBD groups and the HBA substituents (either the lone pair of electrons on nitrogen and

oxygen atom and/ or of the heterocyclic moieties) of the molecules.

The negative signs of the s coefficients indicate that in increasing the solvent

dipolarity/ polarizability (π*), a bathochromic shift of νmax for all these compounds is

observed. This result demonstrates that the singlet excited state of these molecules becomes

more stabilized when the solvents dipolarity increases.

The influence of the π* on the bathochromic shift of νmax [DAFP] is more pronounced

than the α term (s /a ≈ 2, eq. 20). This demonstrates that the ability of the solvent to donate

hydrogen bonds is weaker than do solute-solvent dipole-dipole interactions occurring

preferably in the excited singlet state of the above compounds. Thus, a satisfactory linear

correlation with high significance is also observed between νmax [DAFP] and solely the

Kamlet-Taft’s solvation parameter π* (eq. 21).

νmax *10-3 [DAFP] = 24.66 – 1.60 π* (21)

n = 35 r = 0.62 SD = 0.52 F < 0.0001

On going from a three-parameter equation with π*, α and β, to a two-parameter

equation considering only π* and α, a significant change in the correlation coefficient r for

DAFP produced (eq. 22).

νmax *10-3 [DAFP] = 24.85 – 1.43 π* - 0.78 α (22)

n = 35 r = 0.89 SD = 0.31 F < 0.0001

The negative sign of the a coefficients of the LSE relationships in Tables 4 and 5

demonstrates that increasing solvent HBD ability also induces a red shift of νmax. This

indicates the formation of solute-solvent hydrogen bonds between the carbonyl oxygen and

the HBD site of the solvent. Moreover, the a coefficients significantly vary as a function of

the structure of these compounds. According to SOEDs12 systematic study on the influence of

the basicity of the solvatochromic probe upon a in LSErs, it is expected the larger the basicity

of the carbonyl oxygen the stronger interact a HBD solvent with the probe at this site which

should be reflected by an increase of the coefficient a. This interpretation is reasonable for

compounds 1a, 2a, 4b, 4f, and 4g where the LSErs show large a values. Substituents with

electronegative atoms (morpholino and acetoxypiperazino) bring low influence on a. Thus,


the LSEr of 4c and 4a show lower values of the a coefficient than 4f and 4b. In increasing the

HAMMETT σp+-substituent constant,41 an increase of a is expected.12 In general it seems that

the specific acid-base interactions are difficult to quantify, because basicity parameters for the

compounds used are still not available and difficulty to determine.

Also, the value of the coefficient a (Tables 4 and 5) decreases in the following order:

MK [a = 1.80] > MK(NEt2)2 [a = 1.77] > MK(pip)2 [a = 1.62] > MK(OH)2 [a = 1.64] >

MK(OAc)2 [a = 1.61] > MK(OH)4 [a = 1.47] > MK(pipOEt)2 [a = 1.36] > BBP [a = 1.25] >

MK(mor)2 [a = 1.13] > Fur(OAc)2 [a = 1.07] > Thi(OAc)2 [a = 1.01] > Fur(OH)2 [a = 0.90] >

Thi(OH)2 [a = 0.83] > MK(pipaz)2 [a = 0.14] > MK(pipazOH)2 [a = 0.01]. It is likely that the

electron-donor strength (+M effect) of the p-substituent decreases in the same order.

However, the basicity of the carbonyl oxygen can be reflected in particular by the 13C-

NMR chemical shift of the corresponding carbonyl carbon atom. The expected trend is

detectable. However, a linear fit is not obtained between δ of 13C(CO) (in ppm) (Experimental

Section) and a, because s is also affected by the respective substituent. Furthermore, cyclic

substituents cause additional steric peculiarities. Thus, in saturated six membered ring

systems, like the piperidino substituent, which adopts a rigid chair conformation, the

equatorial protons of the α methylene groups are directed towards the H-atoms in the ortho

position of the aromatic ring. The –CH2- groups of the linked rigid six membered rings are

restricted in their thermally induced rotation compared to a single methyl or ethyl substituent.

The later arrangement induces an average mesomeric effect taking into account all

conformation states of rotation. For rigid six memebered rings, as a result of enhanced

twisting of the aromatic ring and the +M substituent, due to conformational restriction, a

hypsochromic shift upon νmax is the result, because the overall extend of π conjugation is

lowered.

The decrease of the +M effect from diethylamino > dimethylamino > piperidino>

morpholino is supported by 1H NMR spectroscopic studies using data from the ortho H-

position of –NR2 substituted benzenes.110 Dipole moments (µ in debye) of related N-phenyl

amines also show a decrease of the +M effect in the order –N(C2H5)2 (µ = 1.80) > piperidino

(µ = 1.41±0.02) > morpholino (µ = 0.58±0.01). The dipole moments are taken from ref.111

Also, Effenberger et al. have shown that a –N(CH3)2 substituent possess a stronger +M

effect (quantitative parameter for the mesomeric potential k = 0.84) than does a piperidino

ring (k = 0.775), which agrees with the results from solvatochromic measurements.

The s coefficient significantly increases from Fur(OAc)2 (s = 1.69) to MK(OAc)2 (s =

1.98) and from Fur(OH)2 (s = 1.48) to MK(OH)2 (s = 1.99), which indicates that the


dipolarity/ polarizability influence of the solvent becomes of greater importance in the case of

the dimethylaminophenyl substituents 1a and 2a. May be, a highly polar solvation shell is

induced by interacting solvent molecules at the dimethylaminophenyl substituent responsible

for this effect.

It is also worth to notice that a coefficients are significantly smaller than the s

coefficients for the calculated LSE relationships. This demonstrates that the ability of the

solvent to donate hydrogen bonds is much weaker than do solute-solvent dipole-dipole

interactions.

The measured νmax data for MK(OH)2, Fur(OH)2, and Thi(OH)2 with their di-ester

analogs, MK(OAc)2, Fur(OAc)2 and Thi(OAc)2 were fitted by multiple regression in order to

verify eq. (4) (vide supra).

Table 6. Values of the solvent-independent correlation coefficients (b and s of the Kamlet-

Taft parameters β and π*), the difference in wave number of the two reference systems (∆ν0)

i.e. the diol and its di-ester, number of solvents with α = 0 (n), correlation coefficient (r) and

standard deviation (SD).

As shown in Table 6, the dependence of the difference in wave number in the case of

Thi(OAc)2 and Thi(OH)2 (∆ν c) on the solvatochromic parameter β for 18 solvents with α = 0

is strong in comparison with the difference in wave number in the case of Fur(OAc)2 and

Fur(OH)2 (∆ν b), indicating the strong influence of the thienyl group on the HBD capacity of

the p-(HOCH2CH2)2N substituent, which makes this group important as “internal

immobilized HBD solvent molecule”.

When ∆ν is correlated with the two solvatochromic parameters β and π*, although the

correlation coefficient (r) is more pronounced compared to the previous case, the error in s

value is also high, so we concluded that the effect of π* can be ignored.

∆ν ∆ν 0 b s n r SD Probe > F

ν1a - ν2a 0.14 0.41 0.02 17 0.62 0.15 < 0.0001

ν1a - ν2a 0.16 0.41 -------- 17 0.62 0.14 < 0.0001

ν1b - ν2b 0.62 0.74 -0.29 18 0.91 0.09 < 0.0001

ν1b - ν2b 0.48 0.64 -------- 18 0.83 0.12 < 0.0001

ν1c - ν2c 0.50 0.82 -0.10 18 0.85 0.14 < 0.0001

ν1c - ν2c 0.46 0.79 -------- 18 0.85 0.14 < 0.0001


We have shown that UV/Vis shifts of the compounds are significantly influenced by

external interactions as demonstrated by solvent molecules as model. For each compound

used depending on the structure of the aromatic moiety, the respective contributions of acid

and basic sites of an externally interacting partner is significantly different as shown by the

coefficients ratios of the LSE relationship a/ s, a/ b, and b/ s.

Also, the solvatochromic parameters (α, β and π*) as function of νmax have been

determined by means of multiple regression analysis as shown from Tables 7 and 8.


Table 7. Values of the independent correlation coefficients c, d, e, f, g and h of the measured wave numbers (νmax *10-3 cm-1) of the solvatochromic compounds MK(OAc)2 1a, MK(OH)2 2a, Fur(OAc)2 1b, Fur(OH)2 2b, Thi(OAc)2 1c, and Thi(OH)2 2c respectively, which can be used to calculate the Kamlet-Taft parameters α, β, and π*.

20 For different values of number of solvent (n), see footnote of table (4).

Param-

eter

Y-

Intercept

c d e f g h n20 r SD Probe > F

α 12.41 -0.43 ------ ------ ------ ------ ------ 31 0.88 0.27 < 0.0001

α 12.89 ------ -0.45 ------ ------ ------ ------ 30 0.89 0.26 < 0.0001

α 16.17 ------ ------ -0.57 ------ ------ ------ 31 0.83 0.31 < 0.0001

α 15.66 ------ ------ ------ -0.56 ------ ------ 31 0.76 0.36 < 0.0001

α 15.20 ------ ------ ------ ------ -0.53 ------ 31 0.79 0.34 < 0.0001

α 13.09 ------ ------ ------ ------ ------ -0.46 31 0.67 0.41 < 0.0001

α 9.68 -0.67 ------ -1.51 ------ -1.83 ------ 31 0.94 0.20 < 0.0001

α 13.22 ------ -0.44 ------ -1.63 ------ 1.61 30 0.95 0.18 < 0.0001

α 9.83 -0.36 -0.48 -0.18 -1.79 1.18 1.26 30 0.97 0.14 < 0.0001

β 4.62 ------ ------ 1.04 -1.22 ------ ------ 31 0.90 0.12 < 0.0001

β 3.41 ------ ------ ------ ------ 0.82 -0.95 31 0.89 0.13 < 0.0001

β 11.24 ------ 0.61 ------ -0.99 ------ 0.03 30 0.85 0.15 < 0.0001

β 7.41 0.03 0.23 0.12 -1.06 0.60 -0.20 30 0.92 0.12 < 0.0001

β 5.73 ------ ------ 0.90 -1.12 ------ ------ 18 0.93 0.10 < 0.0001

β 3.01 ------ ------ ------ ------ 0.74 -0.85 18 0.88 0.14 < 0.0001

π* 6.82 ------ ------ -0.22 ------ ------ ------ 31 0.68 0.19 < 0.0001

π* 7.27 ------ ------ ------ -0.24 ------ ------ 31 0.69 0.19 < 0.0001

π* 7.18 ------ ------ ------ ------ -0.23 ------ 31 0.73 0.18 < 0.0001

π* 7.36 ------ ------ ------ ------ ------ -0.24 31 0.75 0.17 < 0.0001

π* 9.46 0.28 ------ 0.67 ------ -1.25 ------ 31 0.86 0.14 < 0.0001

π* 3.41 ------ -0.14 ------ 1.20 ------ -1.15 30 0.79 0.15 < 0.0001

π* 8.20 0.15 0.18 -0.11 1.35 -0.95 -0.87 30 0.94 0.09 < 0.0001

π* 13.74 -0.46 ------ ------ ------ ------ ------ 18 0.99 0.05 < 0.0001

π* 12.23 ------ -0.41 ------ ------ ------ ------ 17 0.97 0.07 < 0.0001

π* 15.51 ------ ------ -0.52 ------ ------ ------ 18 0.98 0.06 < 0.0001

π* 13.61 ------ ------ ------ -0.47 ------ ------ 18 0.91 0.13 < 0.0001

π* 14.23 ------ ------ ------ ------ -0.48 ------ 18 0.98 0.07 < 0.0001

π* 11.12 ------ ------ ------ ------ ------ -0.38 18 0.90 0.13 < 0.0001


Table 8. Values of the independent correlation coefficients i, j, k, l, m, n, o, p and q of the measured

wave numbers (νmax *10-3 cm-1) of the solvatochromic compounds MK(OH)4 3, MK(pipOEt)2 4a,

MK(pip)2 4b, MK(mor)2 4c, MK(pipaz)2 4d, MK(pipazOH)2 4e, MK(NEt2)2 4f, MK 4g and BBP 5

respectively, which can be used to calculate the Kamlet-Taft parameters α, β, and π*.21

The results from Tables 7 and 8 show that, by using one solvatochromic compound, α

and π* parameters can be well determined. However, β parameters can be determined by

measuring the long-wavelength UV/Vis absorption maxima of two solvatochromic probes

Fur(OAc)2 and Fur(OAc)2 or their thiophene analogous Thi(OAc)2 and Thi(OAc)2.

21 Probe > F is less than 0.0001 for all correlation tests.

Para-

meter

Y-

Intercept

i j k l m n o p q n r SD

α 14.25 -0.50 ----- ----- ----- ----- ----- ----- ----- ----- 30 0.87 0.27

α 13.38 ----- -0.45 ----- ----- ----- ----- ----- ----- ----- 31 0.80 0.32

α 12.14 ----- ----- -0.42 ----- ----- ----- ----- ----- ----- 31 0.85 0.29

α 14.10 ----- ----- ----- -0.47 ----- ----- ----- ----- ----- 31 0.76 0.35

α 11.44 ----- ----- ----- ----- ----- ----- -0.40 ----- ----- 31 0.87 0.27

α 11.76 ----- ----- ----- ----- ----- ----- ----- -0.41 ----- 31 0.88 0.26

α 12.50 ----- ----- ----- ----- ----- ----- ----- ----- -0.42 31 0.75 0.36

β 13.28 ----- ----- ----- ----- -0.45 ----- ----- ----- ----- 20 0.79 0.16

β 4.53 -0.48 ----- ----- 0.66 -0.35 ----- ----- ----- ----- 29 0.86 0.15

β 3.92 -0.57 0.65 ----- ----- -0.31 0.09 ----- ----- ----- 29 0.85 0.15

π* 6.24 ----- ----- ----- -0.19 ----- ----- ----- ----- ----- 31 0.66 0.19

π* 13.43 ----- ----- ----- -0.44 ----- ----- ----- ----- ----- 18 0.98 0.07

π* 12.27 -0.41 ----- ----- ----- ----- ----- ----- ----- ----- 16 0.91 0.11

π* 13.42 ----- -0.44 ----- ----- ----- ----- ----- ----- ----- 18 0.98 0.05

π* 12.62 ----- ----- -0.42 ----- ----- ----- ----- ----- ----- 18 0.98 0.06

π* 11.83 ----- ----- ----- ----- -0.39 ----- ----- ----- ----- 17 0.82 0.15

π* 9.64 ----- ----- ----- ----- ----- -0.31 ----- ----- ----- 18 0.84 0.16

π* 12.43 ----- ----- ----- ----- ----- ----- -0.42 ----- ----- 18 0.98 0.06

π* 12.99 ----- ----- ----- ----- ----- ----- ----- -0.43 ----- 18 0.98 0.05

π* 11.50 ----- ----- ----- ----- ----- ----- ----- ----- -0.37 18 0.97 0.07


The best regression fits obtained for the α, β, or π* parameters as a function of νmax

(measured in all solvents or solvents with α = 0) of one or two of the solvatochromic aromatic

aminophenyl ketones are expressed by the following equations:

α = 12.89 – 0.45 [νmax *10-3 MK(OH)2] (23)

n = 30 r = 0.89 SD = 0.26 F < 0.0001

β = 4.62 + 1.04 [νmax *10-3 Fur(OAc)2] – 1.22 [νmax *10-3 Fur(OH)2] (24)

n = 31 r = 0.90 SD = 0.12 F < 0.0001

β = 5.73 + 0.90 [νmax *10-3 Fur(OAc)2] – 1.12 [νmax *10-3 Fur(OH)2] (25)

n = 18 r = 0.93 SD = 0.10 F < 0.0001

π* = 7.36 - 0.24 [νmax *10-3 Thi(OH)2] (26)

n = 31 r = 0.75 SD = 0.17 F < 0.0001

π* = 13.74 – 0.46 [νmax *10-3 MK(OAc)2] (27)

n = 18 r = 0.99 SD = 0.05 F < 0.0001


spectroscopy

3.1.2.1 Solid-state X- ray crystal structure analysis

Crystallographic data for Fur(OAc)2, MK(OH)2, Fur(OH)2, Thi(OH)2, MK(pip)2,

MK(mor)2 and BBP are listed in Tables (3-5, Experimental Section). The solid-state

structures of 1b, 2(a-c), 4(b-c), and 5 are shown in Figures 4 – 10, respectively.

[4-Di(2-acetoxyethyl)aminophenyl]-2-furylmethanone Fur(OAc)2

Fur(OAc)2 crystallizes from ethyl acetate at 25 °C as yellow plates in the

orthorhombic space group Pbca with a = 1445.46(2), b = 1264.26(2), c = 1932.44(4) pm, α =

β = γ = 90°, V = 3531.41(10)*106 pm3 and Z = 8.

Figure 4 shows a representation of this molecule. Relevant bond distances and angles

are given in the Figure caption. In the molecular structure, the planar furan and phenyl rings

are twisted differently around the planar ketone subunit C6-C1(O1)-C2 by torsional angles

ω(C1-C2-C3) = 128.92(13)° for furan ring and ω(O1-C1-C6-C11) = -173.34(16)°.


C19

O5

C18

O6

C17

C16

C12

O3

N1C13

C15

C14

C9C10

O4

C11

C8

C7C6

O2 C5

C1C2

C4

O1

C3

Figure 4. ZORTEP drawing (50 % probability level) of Fur(OAc)2, 1b. Selected bond lengths

[pm]: C(1)-O(1) 123.44(18), C(1)-C(2) 146.7(2), C(1)-C(6) 148.03(19); selected bond angels

[°]: O(1)-C(1)-C(2) 115.62(13), O(1)-C(1)-C(6) 120.70(14), C(2)-C(1)-C(6) 123.66(12);

selected torsion angles [°]:O(1)-C(1)-C(2)-C(3) -7.3(3), O(1)-C(1)-C(2)-O(2) 171.52(16),

C(2)-C(1)- C(6)-C(7) -171.48(15), C(2)-C(1)-C(6)-C(11) 8.3(2).

The planes of furan ring and carbonyl groups are twisted relative to each other by

171.52(16)° and their oxygen centers approach an anti configuration, which avoids repulsive

interaction between the lone pair of electron on O2 atom and the in-plane electron density

around the center O1. Inside the bulky diacetoxy ethyl amino group, the acetoxy ethyl groups

extend themselves asymmetrically a way from the nitrogen atom. The sp2 and sp3 hybridized

states for C9 and C12 or C16, respectively cause the difference in the N-C bond lengths in

Fur(OAc)2 molecule. The distances in pm around N1, 137.75(17) to C9, 146.03(18) to C12,

145.77(17) to C16 are consistent with significant localization of electron density.

4-Dimethylamino-4’-[di(2-hydroxyethyl)amino]benzophenone MK(OH)2

Compound MK(OH)2 crystallizes from ethanol at 25 °C as yellow rods in the

monoclinic space group P2(1)/n with a = 475.17(2), b = 1481.78(5), c = 2378.810(10) pm, α

= γ = 90, β = 93.588(2)°, V = 1671.63(9)*106 pm3 and Z = 4.


X-ray structure analysis of acid-base adducts of MK with pentachlorophenol and

trifluoromethansulfonic acid, respectively, were investigated by Gramstad,112 who reported

that depending on the co-ordination of either the carbonyl group or the nitrogen atom,

different colors of the adducts have been observed.

The result of the X-ray structure determination for MK(OH)2 is shown in Figure 5[A-

B]. Relevant bond distances and angles are given in the Figure 5A caption. The positions of

the hydrogen atoms in the hydrogen bonds are experimentally determined. In the crystal

lattice, the molecules are bridged by two kinds of hydrogen bonds, firstly between the

hydroxyl group O2-H2O and the keto group C1=O1 and secondly between the two hydroxyl

groups of neighboring molecules (the oxygen O2 and the hydrogen H3O). The tow hydrogen-

bonding motifs build up a two-dimensional structure.

C9

C6

N1

C7

C5

C8

O1

C2

C4

C1

C3

C10C11

C15

C12

C14

C13

N2C16

C17

O2

C18

C19 O3

Figure 5A. ZORTEP drawing (50 % probability level) of MK(OH)2 2a; Selected bond

lengths [pm]: C(1)-O(1) 124.00(2), C(1)-C(2) 148.40(3), C(1)-C(10) 146.00(3); selected bond

angels [°]: O(1)-C(1)-C(2) 118.97(18), O(1)-C(1)-C(10) 119.37(17), C(2)-C(1)-C(10)

121.65(16); selected torsion angles [°]:O(1)-C(1)-C(2)-C(3) -151.5(2), O(1)-C(1)-C(2)-C(7)

24.30(3), C(2)-C(1)-C(10)-C(11) -158.81(18), C(2)-C(1)-C(10)-C(15) 26.40(3).


Figure 5B. Packing in unit cell of MK(OH)2 2a with intermolecular hydrogen bonds

(dashed lines).

The strong hydrogen bridge to the carbonyl oxygen is responsible for the intense color

of the crystals, because the hydroxyethyl substituents force the chromophore into acentric

environments through hydrogen-bonding network, and this enhances the extent of the overlap

between the nitrogen lone-pair orbital and the aromatic π-electron cloud, resulting in an

increased bathochromic shift of the π-π* transition.

The result of the structure analysis of MK(OH)2 is in agreement with the results of the

solvatochromic measurements.

[4-Di(2-hydroxyethyl)amino-phenyl]-2-furylmethanone Fur(OH)2

Fur(OH)2 crystallizes from ethyl acetate at 25 °C as yellow plates in the monoclinic

space group P21/c with a = 1179.84(16), b = 1140.66(16), c = 1011.52(14) pm, α = γ = 90, β

= 94.766(3)°, V = 1356.60(3)*106 pm3 and Z = 4 (Figure 6)


C3C4

O1C2

C5

C1

O2

C6C11C7

C10 C8C9

N1

C12

C13

O3

C14

C15

O4

Figure 6A. ZORTEP drawing (50 % probability level) of Fur(OH)2 2b. Selected bond lengths


[°]: O(1)-C(1)-C(2) 115.72(13), O(1)-C(1)-C(6) 121.09(13), C(2)-C(1)-C(6) 123.19(12);

selected torsion angles [°]:O(1)-C(1)-C(2)-C(3) 3.8(2), O(1)-C(1)-C(2)-O(2) -175.39(12),

C(2)-C(1)-C(6)-C(7) 14.4(2), C(2)-C(1)-C(6)-C(11) -167.38(12).

Figure 6B. Packing in unit cell of Fur(OH)2 showing intermolecular hydrogen bonds as

dotted lines.


C3

C4

O1

C2

C5

C1

O2

C6

C11

C7

C10

C8

C9

N1

C12

C13

O3

C14

C15O4

H1O3

H1O4

Figure 6C. Molecular structure of Fur(OH)2 with intermolecular hydrogen bonds O3-

H1O3…O4 and O4-H1O4…O3.

The dashed lines in Figure 6B represent distances of 277.84(16) and 278.26(16) pm

for the O3....O4 and O4....O3 interactions, respectively (see below). With respect to these

separations, compound Fur(OH)2 interacts with four nearest neighbors, which results in the

zigzag motif, as depicted in Figure 4B. The O3....O4 and O4....O3 distances are less than 280

pm and thus, corresponds to a strong hydrogen bond according to Emsley et al.113a C13-O3-

H(1O4) and C15-O4-H(1O3) angles of 106.4(12)°, and 107.7(14)°, respectively, in Fur(OH)2

indicate that the direction of the -OH....O4 and -OH....O3 bonds are towards the sp3-

hybridized lone pairs of electrons of O4 and O3. The N1-C9 bond length in Fur(OH)2 is

smaller (136.65(18) pm) than the N1-C9 interatomic distance in Fur(OAc)2 (137.75(17) pm),

indicating a stronger conjugation of the lone pair of electrons at the nitrogen atom and the

benzene ring in Fur(OH)2.

[4-Di(2-hydroxyethyl)aminophenyl]-2-thienylmethanone Thi(OH)2

Thi(OH)2 crystallizes from ethyl acetate at 25 °C as yellow plates in the monoclinic

space group P21/c with a = 792.80(12), b = 1270.14(19), c = 1415.10(2) pm, α = γ = 90, β =

103.083(3)°, V = 1388.00(4)*106 pm3 and Z = 4 (Fig. 7)


C15

O3

C14

O2

N1

C12

C10

C13

C9

C11

C8

C3

C4

C6

C7

C2

C5

C1S1

O1

Figure 7A. ZORTEP drawing (50 % probability level) of Thi(OH)2 2c, selected bond lengths

[pm]: C(1)-O(1) 124.76(14), C(1)-C(2) 147.48(15), C(1)-C(6) 145.53(15); selected bond


120.63(10); selected torsion angles [°]:O(1)-C(1)-C(2)-C(3) 149.92(12), O(1)-C(1)-C(2)-S(1)

-21.71(13), C(2)-C(1)-C(6)-C(7) 162.03(10), C(2)-C(1)-C(6)-C(11) -17.87(16).

Figure 7B. Packing in unit cell of Thi(OH)2 showing the hydrogen bonds as dotted lines.


C5aC4a

S1a

C3a

C2a

C13

C11a

C1a

H1O2

C12

C10a

O2

C6a

O1aH1O3

O3

C8

C15a

N1

C14aC9a

C7

C7a

C9

C14

N1a

C15

C8a

O3aH1O3a

O1

C6

O2a

C10

C12a

H1O2a

C1

C11

C13a

C2

C3

S1

C4C5

Figure 7C. Dimeric structure of Thi(OH)2 with intermolecular hydrogen bonds O2-

H1O2…O1a, O2a-H1O2a…O1, O3-H1O3…O1a and O3a-H1O3a…O1.

The dashed lines in Figure 7B represent distances of 277.43(13) and 285.52(13) pm

between the O2....O1 and O3....O1 separations, respectively. With respect to these

interactions, compound Thi(OH)2 interacts with three nearest neighboring molecules. The two

O-H groups deriving from one molecule form two hydrogen bonds with the carbonyl oxygen

atom of two other molecules. While each carbonyl oxygen atom is involved in two hydrogen

bonds with the O-H bonds of which one is significantly shorter.

The strong participation of the C = O group in two hydrogen bonds results in an

elongation of the C = O bond length in the Thi(OH)2 crystal (dC = O = 124.76(14) pm) in

comparison to the C = O length in Fur(OH)2 (dC = O = 123.44(16) pm), where no hydrogen

bond to the oxygen atom of the carbonyl group occurs. In Thi(OH)2, the C6-C1-C2 angle (γ =

120.63(10)°) is less than that in Fur(OH)2 (γ = 123.19(12)°). This difference is due to a

conformation changes induced by hydrogen bonds to the carbonyl oxygen’s as shown in

Figure 7B. Also, the difference between the two distinct structures of Fur(OH)2 and Thi(OH)2

reflects the hydrogen-bond-acceptor directed properties of the sp3- (the oxygen atom of the

hydroxyl group in Fur(OH)2) versus the sp2- (the carbonyl oxygen atom in Thi(OH)2)

hybridized oxygen atoms.


4,4’-Bis(piperidino)benzophenone MK(pip)2

MK(pip)2 4b crystallizes from ethyl acetate at 50 oC as yellow plates (Experimental

Section) in the trigonal space group P3121, with a = 948.11(11), b = 948.11 (11), c =

1818.0(3) pm, α = β = 90, γ = 120°, V = 1415.30(3)*106 pm3 and Z = 3 (Figure 8). Molecule

4b consist a two fold rotation axis of symmetry (symmetry code y, x, -z). The symmetry

generated atoms are indicated with the suffix a.

The structure of MK(pip)2 is depicted in Figure 8. Relevant bond distances and angles

are given in the figure caption.

C10C11

C12

C9 C8N1

C5

C4

C6

C3

C7

C2

C7aC6a

C1

C11a

C2a

C12a

C5a

O1

N1a

C3a

C10a

C4a

C9a

C8a

Figure 8. ZORTEP drawing (50 % probability level) of MK(pip)2 4b, selected bond lengths

[pm]: C(1)-O(1) 123.07(18), C(1)-C(2) 149.06(11), C(1)-C(2a) 149.07(11); selected bond

angels [°]: O(1)-C(1)-C(2) 118.93(6), O(1)-C(1)-C(2a) 118.93(6), C(2)-C(1)-C(2a)

122.13(12); selected torsion angles [°]:O(1)-C(1)-C(2)-C(3) 19.79(9), O(1)-C(1)-C(2)-C(7) -

155.69(8), C(2a)-C(1)-C(2)-C(3) -160.21(9), C(2a)-C(1)-C(2)-C(7) 24.31(8).

The N1-C5 and N1a-C5a bond distances are quit typical and equal to 140.05(12) pm.

This can be compared with values of 146.69(12) and 147.15(13) pm for N1-C8 and N1-C12,

respectively. The N1-C5 bond distance is shorter than N1-C8 and N1-C12. The lone pair of

electrons of N1 and N1a are involved in conjugation with the π-system of the aromatic rings

attached to N1 and N1a and this leads to shortening of the N1-C5 and N1a-C5a distances,

respectively. The C = O double bond length in MK(pip)2 is 123.07(18) pm as compared to

123.24(18) pm in MK(mor)2 4c (wide infra) in which there is no hydrogen bond to the oxygen


atom, and to ca. 1.23 pm which is normal for ketones.113b The carbonyl group angle C2-C1-

C2a of 122.13(12)° is widened from 120° in MK(pip)2.

4,4’-Bis(morpholino)benzophenone MK(mor)2

MK(mor)2 4c crystallizes from saturated ethyl acetate solution at 50 °C as pale yellow

rods in the orthorhombic space group Pna21, with a = 1259.90(2), b = 910.16(17), c =

1586.20(3) pm, α = β = γ = 90°, V = 1819.00(6)*106 pm3 and Z = 4.

The structure of MK(mor)2 is depicted in Figure 9. Relevant bond distances and angles

are given in the figure caption.

O1

C13

C1 C14C3

C12C2 C18C4

C15

C7C19C17

N2C5

C8C16C6N1 O3C21

C9

C11 C20O2

C10

Figure 9. ZORTEP drawing (50 % probability level) of MK(mor)2 4c, selected bond lengths


[°]: O(1)-C(1)-C(2) 120.66(15), O(1)-C(1)-C(12) 119.68(14), C(2)-C(1)-C(12) 119.65(12);

selected torsion angles [°]:O(1)-C(1)-C(2)-C(3) -22.6(2), O(1)-C(1)-C(2)-C(7) 152.94(15),

O(1)-C(1)-C(12)-C(13) -37.0(2), O(1)-C(1)-C(12)-C(17) 140.88(16).

The torsion angles for MK(pip)2 resemble to -1.49(14)° (C8-N1-C5-C4), 174.82(9)°

(C8-N1-C5-C6), whereas in MK(mor)2, the values are 25.1(2)° (C8-N1-C5-C4), -158.60(15)°

(C8-N1-C5-C6), 22.7(2)° (C18-N2-C15-C14) and -159.30(16)° (C18-N2-C15-C16). These

data demonstrate that the terminal morpholino groups in 4c are tilted more than the terminal

piperidino groups in 4b with respect to the central benzophenone moiety. This result also


explains why the electron donating density is greater for 4b than for 4c. In the solid-state, the

piperidino phenyl and the morpholino phenyl groups in 4b and 4c are twisted in a different

way around the planar ketones substituent C2-C1-O1-C2a and C2-C1-O1-C12, respectively,

indicated by torsional angles O1-C1-C2-C3 = 19.79(9)° and O1-C1-C2-C7 = -155.69(8)° (in

4b), and O1-C1-C2-C3 = -22.6(2)° and O1-C1-C12-C17 = 140.88(16)° (in 4c). This shows

that the piperidino phenyl and the morpholino phenyl entities are bent with respect to the

carbonyl plane. Thus, the conformational differences of 4b and 4c in the solid-state seem

responsible for the differences in the UV/Vis absorption spectra of the two molecules.

1,4-Bis(4-benzoylphenyl)piperazine BBP

BBP 5 crystallizes from a chloroform/ethyl acetate (1:2) mixture at 25 °C as yellow

blocks in the triclinic space group P-1, with a = 1034.0(2), b = 1079.9(2), c = 1127.2(2) pm, α

= 72.062(4), β = 73.361(4), γ = 74.549(4)°, V = 1125.2(4)*106 pm3 and Z = 2.

C29b

C28b

C30b

C27b

C25b

C26b

C16b

C18b

O2b

C17b

C19b

C22b

C20b

C21b

C23bN2b

C24b

C24

N2

C23

C21

C20C22

C19C17

O2

C18

C16

C26

C25

C27

C30

C28

C29

Figure 10A. ZORTEP drawing (50 % probability level) of BBP 5, selected bond lengths

[pm]:C(16)-O(2) 122.08(3), C(16)-C(17) 147.8(3), C(16)-C(25) 150.07(3); selected bond


120.9(2); selected torsion angles [°]:O(2)-C(16)-C(17)-C(18) 155.1(3), O(2)-C(16)-C(17)-

C(22) -22.6(4), O(2)-C(16)-C(25)-C(26) 148.0(3), O(2)-C(16)-C(25)-C(30) -27.1(4).

The molecular structure of BBP, as resolved by X-ray diffractometry, is shown in

Figure 10A, together with the atomic numbering scheme used. Relevant bond distances and


angles are given in the Figure caption. As we can observe in this Figure, the molecule

contains two benzophenone units bridged by a piperazine molecule.

The planar phenyl rings attached to N2 and N2b are twisted differently around

piperazine moiety by tortional angles of 28.8(4) and 165.6(3)° for C19-C20-N2-C23 and

C19b-C20b-N2b-C24, respectively.

C23b

C12

N2b

C11

C24b

C13

C24

C10

N2

O1C23

C21

C14

C1

C20

C15

C22

C3C2

C4

C19

C17

C7

O2

C18

C16

C5

C6C26

C9a

C25

N1

C27

C8

C30

C28

N1a

C29

C9

C8b

Figure 10B. Crystal structure (unit cell) of BBP 5; for further details see Exp. Sect.

The crystal packing diagram for BBP 5 is shown in Figure 10B. The unit cell contains

two geometrically similar, but crystallographically independent molecules, each with a

crystallographically imposed centre of symmetry. Interatomic bond distances and angles are

identical within the experimental limits for both molecules. The two carbonyl groups of 5 are

trans-arranged to each others. It is interesting to note that the intermolecular aryl groups are

not directly stacked over each other, but are closer to the carbonyl groups of the adjacent

molecules.

3.1.2.2 UV/Vis diffuse reflectance spectra of the solid powders

The UV/Vis absorption spectra of the powders of aromatic aminophenyl ketones 1b,

2(a-c), 4(a-g), 5 and 6 have been measured by means of diffuse reflectance spectroscopy.

Representative UV/Vis spectra of MK(OH)2, Fur(OH)2, Thi(OH)2, MK(pip)2, MK(mor)2,

MK(NEt2)2, BBP and DAFP measured as powders are shown in Figure 11[A-B].


350 400 450 500 550 600 650 700-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

MK(OH)2 Fur(OH)2 Thi(OH)2 DAFP

Abs

orba

nce

(a.u

.)

λ (nm)

[A]

350 400 450 500 550 600 650 700-0.2

0.0

0.2

0.4

0.6

0.8

1.0

MK(pip)2 MK(mor)2 MK(NEt2)2

BBP

Abs

orba

nce

(a.u

.)

λ (nm)

[B]

Figure 11[A-B]. UV/Vis reflectance spectra of [A] MK(OH)2, Fur(OH)2, Thi(OH)2, and

DAFP and [B] MK(pip)2, MK(mor)2, MK(NEt2)2, and BBP measured as powders in the solid-

state.


As shown from Figure 11A, the diffuse reflectance spectrum of a MK(OH)2 powder

revealed two absorption band systems, a less intense band at λmax = 329 nm (ν = 30395 cm-1)

and a more intense band at λmax = 423 nm(ν = 23641 cm-1). The Fur(OH)2 powder shows a

broad UV/Vis absorption section in the diffuse reflectance spectrum with three small poorly

resolved peaks at λmax = 333, 400, and 427 nm. However, the spectrum of DAFP powder

shows three peaks, the more intense band at λmax = 353 nm and the other two peaks are weak

and show at λmax = 436, and 486 nm. The bathochromic band systems shift of DAFP

compared with that of Fur(OH)2 is related to the more extent double bond conjugation in

DAFP. In the UV/Vis absorption diffuse reflectance spectrum of Thi(OH)2, two long-

wavelength UV/Vis absorption bands at 357 and 447 nm are clearly detectable. Since, two or

three OH-functionalized probes interact simultaneously in the solid-state, the UV/Vis

spectrum is modified depending on the structure formed. The following conclusion can be

drawn. Three different mechanism of hydrogen bond formation in the solid-state can be

clearly recognized as visualized in Chart 7.

Table 9. Intermolecular hydrogen bond distances [pm] and angles [°] of the participating

moieties of MK(OH)2 2a, Fur(OH)2 2b and Thi(OH)2, 2c according to Chart 7.

The corresponding bond distances and angles of the participating functional groups are

summarized in Table 9. The small D-A (donor-acceptor) distances of 267.1(2) and 269.9(2)

pm for MK(OH)2 indicates the presence of a strong intermolecular hydrogen bond between

these molecules. The directed specific interaction between the carbonyl oxygen of the probe

and one HO-CH2CH2- moiety [specifically observed for MK(OH)2] causes a significant

bathochromic UV/Vis shift, which is associated with a sharp UV/Vis absorption peak in the

UV/Vis spectrum of the crystal. This effect is related to the interaction of the probe with

strong HBD solvents like HFP.

Compound D-H H....A D....A < (DHA) D-H...A

94.0 (3) 174.0 (3) 267.1 (2) 168.0 (3) O2-H2O2...O1 MK(OH)2

90.0 (3) 180.0 (3) 269.9 (2) 176.0 (3) O3-H3O3...O2

89.0 (2) 190.0 (2) 277.84 (16) 168.5 (18) O3-H1O3...O4 Fur(OH)2

85.0 (2) 193.0 (2) 278.26 (16) 176 (2) O4-H1O4...O3

74.0 (2) 204.0 (2) 277.43 (13) 173 (2) O2-H1O2...O1 Thi(OH)2

85.0 (2) 202.0 (2) 285.52 (13) 166.7 (19) O3-H1O3...O1


Chart 7. Classification of the intermolecular hydrogen bonds in the solid state of MK(OH)2

2a, Fur(OH)2 2b, and Thi(OH)2 2c.

No Abbreviation structure unit nature of the hydrogen bond

2a

MK(OH)2

C O HO

HO

N

N

D-H

D-HH-A

H-A

In the crystal lattice, the

molecules are bridged by two

kinds of hydrogen bonds, one

of them between the hydroxyl

hydrogen atom and the

carbonyl oxygen atom and the

other between the two hydroxyl

groups of neighboring

molecules.

2b

Fur(OH)2

H

N

O

O

N

H

H

H

O

N

N

O

D-HH-A

D-H

D-H

H-A

In the crystal lattice, each

hydroxyl group form two types

of hydrogen bonds with another

two hydroxyl groups of two

Fur(OH)2 molecules.

2c

Thi(OH)2

C O

H

H

O

N

O

N

D-H

D-H

H-A

H-A

In the crystal lattice, there are

two qualitatively different types

of hydrogen bonds between the

two –CH2CH2OH substituents

of two different Thi(OH)2

molecules with one carbonyl

oxygen of the third.


In the case that specific interactions between the carbonyl oxygen and the HO-

CH2CH2- group do not occur in the solid-state like for Fur(OH)2, therefore no sharp UV/Vis

absorption peak is observed. However, the broad and poorly resolved UV/Vis absorption

bands in the visible spectrum of Fur(OH)2 indicate non-specific π – π interactions and long

ranging dipolar interactions. However, a detailed interpretation of this UV/Vis spectrum

requires a deeper theoretical treatment.

The UV/Vis diffuse reflectance spectrum of the Thi(OH)2 powder shows a long

wavelength absorption at λ = 447 nm due to the strong interaction of two -CH2CH2OH

substituents of two different Thi(OH)2 molecules with one carbonyl oxygen of a third species.

The unprecedented bathochromic UV/Vis shift of the solid observed, would be in agreement

with the strong influence of the β term (of the solvent) on νmax in solution and that especially

the -CH2CH2OH substituents of Thi(OH)2 bear the highest HBD capacity of the compounds

studied. The other UV/Vis band at λ = 357 nm probably relate to the single chromophoric

system.

The complete explanations of all UV/Vis spectroscopic effects observed in the solid-

state relating to the crystal structure is still a challenge for further theoretical work and

promising experimental studies on related supra-molecular solid-state dye systems.

As shown from Figure 11B, three Michler’s Ketone derivatives 4(b-c) and 4f exhibit red-

shifted UV/Vis absorption band maxima (λmax ≈ 400 nm, νmax ≈ 25000 cm-1) in the solid-state

which is comparable to the UV/Vis spectrum in solution of a strong polar solvent like HFP.

The results are summarized in Tab. 10. However, the UV/Vis absorption bands are not

symmetric. They show that different electronic transitions occur in the solid-state. This result

is probably due to the formation of aggregates indicating strong dipolar interactions in the

solid-state. Among the other compounds, 4c and 5 show evidently an additional UV/Vis

maximum bathochromically shifted in its reflectance spectrum.


Table 10. UV/Vis reflectance absorption maxima (uncorrected) of the crystal powders of

seven aromatic aminoketones.

Compound λmax (1)

/nm

λmax (2)

/nm

I1/I222 Comment

MK(pipOEt)2 4a 365

MK(pip)2 4b 375 394 1.00

MK(mor)2 4c 384 449 2.61 λmax (2) appears as shoulder

MK(pipaz)2 4d 366

MK(pipazOH)2 4e 355

MK(NEt2)2 4f 377 397 0.97 λmax (2) a small shoulder

BBP 5 375 469 2.11 λmax (2) is poorly resolved

We think that the position of the first absorption band at λmax ≈ 400 nm in the solid-

state resembles to the position of the UV/Vis absorption spectra in polar solvents suggesting

an average interaction with neighboring molecules. The second UV/Vis band at λmax ≈ 450 -

500 nm is significantly red-shifted with respect to the first band. This UV/Vis absorption band

is likely attributed to the presence of strong intermolecular π-π stacking interactions in the

solid-state between the aromatic moieties as suggested by the crystal structure analysis. Also,

charge transfer transitions may contribute to this new UV/Vis absorption band.

3.1.3 Adsorption of aromatic amino ketones on Aerosil 300

Aromatic amino ketones 1(a-c), 2(a-c), 3, and 4g adsorb readily on silica particles

from non hydrogen bond accepting (HBA) solvents such as 1,2-dichloroethane, 1,1,2,2-

tetrachloroethane, toluene or benzene. The adsorption is accompanied by a strong

bathochromic shift of the solvatochromic UV/Vis absorption band (Table 11 and Figure 12).

22 Intensity ratio of the two UV/Vis absorption band λmax (1)/λmax (2).


350 400 450 500 550 600 650 700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1b Aerosil/DCM 1b Aerosil/TCE 1b in DCM 1b in TCE

Abs

orba

nce

(a.u

.)

λ (nm)

[A]

350 400 450 500 550 600 650 700-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

2c in benzene 2c in toluene 2c Aerosil/benzene 2c Aerosil/toluene

Abs

orba

nce

(a.u

.)

λ (nm)

[B]

Figure 12[A-B]. UV/Vis spectra of [A] Fur(OAc)2 1b in DCM and TCE and [B] Thi(OH)2

2c in benzene and toluene and after their adsorption on Aerosil 300 from the same solvents.


In diols 2(a-c), the shift amounts to ∆ν = 3130, 2500, and 2710 cm-1 in TCM

(strongest), and ∆ν = 1460, 1360, 1090 cm-1 in TCE (weakest), respectively. The change of

polarity at the solid/liquid interface is therefore the highest for TCM. In the moderately strong

HBA solvents such as DMF, DMSO, acetonitrile and THF the observed shift is negligible

indicating that the probes are not adsorbed on silica from these solvents. HBA solvents DMF,

THF or acetonitrile strongly interact with the surface silanol groups. Thus, the probe cannot

surmount the solvent barrier on the surface (see table 11).

Table 11. UV/Vis absorption maxima (νmax, cm-1) of the probes MK(OAc)2 1a, Fur(OAc)2

1b, Thi(OAc)2 1c, MK(OH)2 2a,Fur(OH)2 2b, Thi(OH)2 2c, MK(OH)4 3, and MK 4g when

adsorbed on Aerosil 300 in various solvents.

By a comparison of diesters 1(a-c) with diols 2(a-c) we have found that the difference

in value of the strongest shift ∆ν = 2960, 2330, and 2390 cm-1 (toluene) whereas, the

difference in value of the weakest shift ∆ν = 2370 cm-1 (chloroform) for 1a and ∆ν = 1180

and 1210 cm-1 (TCE) for 1b and 1c respectively.

Since the carbonyl oxygen of aromatic amino ketones interact with the HBD sites on

the silica surface, a strong bathochromic shift of the solvatochromic UV/Vis band takes place.

23 Probe is insoluble in the pure solvent.

Solvent/Aerosil

(suspension system)

ν max *

10-3 1a

ν max *

10-3 1b

ν max *

10-3 1c

ν max *

10-3 2a

ν max *

10-3 2b

ν max *

10-3 2c

ν max *

10-3 3

ν max *

10-3 4g

Diethyl ether 29.50 29.15 29.33 29.15 28.09 28.49 29.15 29.33

Triethylamine 29.59 29.15 29.41 28.99 27.86 28.09 28.25 28.65

Tetrahydrofuran 28.99 28.49 28.65 28.65 27.70 27.93 28.57 28.90

Acetonitrile 28.33 27.93 28.25 28.01 27.70 27.93 28.17 28.33

N,N-Dimethylformamide 28.33 27.86 27.78 27.70 26.95 26.95 27.62 28.09

Dimethylsulfoxide 28.01 27.55 27.55 27.40 26.74 26.67 27.40 27.70

1,1,2,2-Tetrachloroethane 25.71 26.60 26.88 26.32 26.11 26.53 26.60 26.95

Benzene 26.11 26.60 26.88 26.18 26.11 26.60 26.18 25.58

Tetrachloromethane 26.74 26.81 26.81 26.11 25.91 26.11 -------23 26.53

Toluene 26.11 26.32 26.60 25.91 25.84 26.11 26.46 25.64

p-Xylene 26.46 27.03 26.81 25.91 26.04 26.25 26.25 25.58

Chloroform 26.04 26.39 26.53 25.84 25.97 26.11 26.04 25.64

1,2-Dichloroethane 25.84 26.32 26.81 25.77 25.97 26.32 26.74 25.51

Dichloromethane 25.91 26.25 26.39 25.77 25.91 26.11 26.32 25.38


This bathochromic shift can be well interpreted in terms of the result derived from the

solvent influence on νmax for these compounds.

For Michler’s ketone MK and its hydrophilically substituted derivative MK(OH)2 as

polarity indicators, when completely adsorbed on Aerosil 300 in a suitable solvent, a

significant influence of the β term of the solvent upon the UV/Vis absorption maximum has

been found (eq. 28 - 31).

νmax *10-3 [MK] = 28.75 – 18.94 β – 1.88 π* (28)

n = 8 r = 0.97 SD = 0.16 F = 0.0008

νmax *10-3 [MK] = 26.93 – 11.87 β (29)

n = 8 r = 0.79 SD = 0.38 F = 0.0201

νmax *10-3 [MK(OH)2] = 26.94 – 6.11 β – 0.64 π* (30)

n = 8 r = 0.87 SD = 0.12 F = 0.0296

νmax *10-3 [MK(OH)2] = 26.31 – 3.68 β (31)

n = 8 r = 0.68 SD = 0.16 F = 0.0640

However, for MK(OAc)2 adsorbed on Aerosil 300, the influence of the π* term of the

solvent upon the bathochromic band shift is more pronounced (eq. 32 and 33).

νmax *10-3 [MK(OAc)2] = 27.20 – 1.15 β – 1.58 π* (32)

n = 8 r = 0.96 SD = 0.11 F = 0.0017

νmax *10-3 [MK(OAc)2] = 27.02 – 1.45 π* (33)

n = 8 r = 0.96 SD = 0.11 F = 0.0002

α, β, and π* parameters of the solid/liquid (Aerosil 300/solvent) surface interface can

be determined by applying eqs. 23, 25, and 26 respectively. The α value ranged from 1.05 in

Aerosil 300/TCE to 1.29 in Aerosil 300/DCM or Aerosil 300/DCE system. The β value

ranged from 0.33 in Aerosil 300/DCE to 0.89 in Aerosil 300/p-xylene system. However, the

π* value ranged from 0.98 in Aerosil 300/benzene to 1.09 in Aerosil 300/toluene, Aerosil

300/TCM, or Aerosil 300/chloroform system. These α and π* values well agree with values

reported in ref.114

The influence of the silanol groups on the UV/Vis shift is similar to the interaction in

the diol crystals 2(a-c) as shown by comparison the UV/Vis spectra of the pure diol crystal 2a


(Fig. 11A) with the reflectance spectrum of 2a /Aerosil adsorbate (Fig. 13). Because the band

shift in the crystal is quite strong as observed for the 2a /Aerosil adsorbate, the distance

between the silanol and carbonyl group should be only slightly greater than for the N–(CH2)2-

OH….OC distance in the crystal. But it must be considered that the HBD strength of ethanol

moiety is lower than that of a silanol group.

350 400 450 500 550 600 650 700-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8346

417

419376

3*10-6 mol/cm3 of 2a in tol.

3*10-6 mol/g of 2a on Aerosil (solid powder)

0.15*10-3 mol/g of 2a on Aerosil (solid powder)

0.30*10-3 mol/g of 2a on Aerosil (solid powder)

Abs

orba

nce

(a.u

.)

λ (nm)

Figure 13. UV/Vis electronic absorption spectra of neat MK(OH)2 2a in toluene (3*10-6

mol/cm3), and 3*10-6, 0.15*10-3, and 0.30*10-3 mol/g of 2a adsorbed on Aerosil 300

measured as a solid powder.

The concentration dependence of the specific interactions of 2a adsorbed on Aerosil

300 has been investigated in the concentration range 3*10-6-0.30*10-3 mol/g. The result for

the 2a-Aerosil 300 intermolecular interactions and 2a-2a self-association interactions are

shown in Figure 13. A significant indication of MK(OH)2 self-association on Aerosil 300

surface at high concentrations (0.15*10-3, and 0.30*10-3 mol/g) is evident. This effect is the

same as observed in the pure diol crystal 2a (Fig. 11A). It is also evident that the 3*10-6

mol/cm3 of 2a-toluene and 3*10-6 mol/g of 2a-Aerosil 300 spectra show only singular peaks


at λmax = 346, 376 nm, respectively, suggesting that only 2a-toluene and 2a-Aerosil

interactions are observed. The absence of 2a-2a interactions results from the probe

concentration being low in the solvent and on Aerosil (3*10-6 mol/g).

However, the results have clearly shown that adsorption of aromatic amino ketones on

HBD surfaces can be measured readily by the UV/Vis shift of 1(a-c), 2(a-c), 3, or 4g and that

the shift also is influenced by the dipolarity/polarizability of the environment.

3.1.4 Sol-gel materials containing aromatic amino ketones

As mentioned in section 1.3 and Chart 6 (General part), two different types of sol-gel

composites have been produced. MK(OH)2, Fur(OH)2, and/or Thi(OH)2 have been either

simply embedded in organically modified silica (Ormosil) xerogels or chemically linked to 3-

Isocyanatopropyltriethoxysilane before hydrolytic condensation with tetraethylorthosilicate

(TEOS) takes place. MK and MK(OH)4 have been used as control compounds when

physically entrapped to show the influence of the polarity in the periphery on the

solvatochromic shift.

3.1.4.1 Physical entrapment in a microporous silica network

MK(OH)2, Fur(OH)2, Thi(OH)2, MK(OH)4, and MK were entrapped in various

Ormosils (Chart 8). They were prepared using different proportions of methyltrimethoxy-

silane (MTMOS) to tetramethoxysilane (TMOS) according to an established sol-gel

procedure75 which is described in the Experimental section.

Marked differences in the νmax values of MK(OH)2, Fur(OH)2, or Thi(OH)2 as a function of

the MTMOS/TMOS ratio used for the Ormosil system were observed in the presence of

alkanols at the interface (Table 12).

Representative UV/Vis spectra of 2(a-c), 3, and 4g doped Ormosil 5 and 2b doped

Ormosils (1-5) measured as a suspension in 1-hexanol and 1-decanol, respectively, are shown

in Figure 14[A-B]. The shapes of the UV/Vis absorption bands are broad, probably due to the

wide polarity distribution inside the cage of Ormosils.


Ar C

O

NR

R+ H3CO Si

OCH3

OCH3

OCH3

H3C Si

OCH3

OCH3

OCH3

+

Ar

C O

NR R

Ar

C O

NR R

Ar

C O

NR R

HClCH3OH

OSi

OSi

OHSi

O

OSi

OSi

O

OSi

OH

OSi

OOSi

OSi

O O O

OHHO

OSi

SiO

SiO

Si

O

Si

O

OH

O

O

O O

SiO

SiO

Si

O

O

HO

O OHSi

O

SiHO

SiO

SiO

OHO

SiO

SiO

OO SiSi

O

O SiO

SiO

OSi

OHOSi

O

O O

SiO

SiO

Si

OOH

O

SiO

SiO

HO

OSi

O

SiSi

O

HO

O

SiO

SiO

Si

O

OSi

OSi Si

OSi

OSi

O

OO

Si

OH

OOOO

Si

SiHO

OH

O

Si

O

Si

O

O

SiO O

HO

Si

OSiHO

Si

O

OHSiO

Ar R Ormosil

NH3C

H3C

CH2CH2OH

(1-5)A

O

CH2CH2OH

(1-5)B

S

CH2CH2OH

(1-5)C

N

HO

HO

CH2CH2OH

5D

NH3C

H3C

CH3

5E

Chart 8. Proposed structures of aromatic amino ketones 2(a-c), 3, and 4g in xerogel hosts.


The ability of the different types of silanol (isolated, geminal, and vicinal) groups in

Ormosils to interact relatively strongly with polar molecules (gust molecules) bearing apolar

moieties should be taken into account to correlate the nature and amount of polar

(hydrophilic) and apolar (hydrophobic) functionalities at the surface of Ormosils with their

possible interaction with silanol groups.

Table 12. Wave number (νmax *10-3 cm-1) values of aromatic amino ketones 2(a-c), 3, and 4g

and their corresponding various Ormosils in presence of diverse alcohols such as methanol

(MeOH), ethanol (EtOH), 1-propanol (PrOH), 1-butanol (BuOH), 1-hexanol (HeOH), 1-

octanol (OcOH), and 1-decanol (DeOH).

ν max *10-3 cm-1 alkanols at the interface Ketone

doped

MTMOS:TMOS

Molar ratio

Name of

probe MeOH EtOH PrOH BuOH HeOH OcOH DeOH

neat ketone MK(OH)2 2a 27.03 27.25 27.25 27.32 27.32 27.32 27.32

1:9 Ormosil 1A 26.60 26.25 26.11 25.91 26.32 26.81 26.95

2:8 Ormosil 2A 26.74 26.32 26.18 26.04 26.60 26.95 27.03

3:7 Ormosil 3A 26.88 26.53 26.32 26.11 26.67 27.03 27.17

4:6 Ormosil 4A 27.03 26.67 26.46 26.18 26.81 27.17 27.32 MK

(OH

) 2 2

a

5:5 Ormosil 5A 27.17 26.81 26.53 26.25 26.88 27.25 27.55

neat ketone Fur(OH)2 2b 26.81 26.81 26.67 26.67 26.67 26.74 26.74

1:9 Ormosil 1B 25.91 25.64 25.58 25.19 25.71 26.04 26.11

2:8 Ormosil 2B 26.04 25.77 25.71 25.64 25.97 26.18 26.39

3:7 Ormosil 3B 26.32 25.91 25.84 25.77 26.18 26.32 26.60

4:6 Ormosil 4B 26.67 26.39 26.04 25.91 26.32 26.53 26.74 Fur(

OH

) 2 2

b

5:5 Ormosil 5B 26.74 26.53 26.18 25.97 26.39 26.67 26.88

neat ketone Thi(OH)2 2c 26.95 27.03 26.88 26.88 26.88 26.95 26.95

1:9 Ormosil 1C 25.77 25.91 25.71 25.25 26.04 26.46 26.53

2:8 Ormosil 2C 26.25 26.11 25.97 25.38 26.25 26.53 26.67

3:7 Ormosil 3C 26.46 26.32 26.04 25.77 26.32 26.74 26.88

4:6 Ormosil 4C 26.67 26.46 26.18 25.91 26.60 26.81 27.03 Thi(O

H) 2

2c

5:5 Ormosil 5C 26.95 26.60 26.32 26.04 26.67 26.95 27.25

neat ketone MK(OH)4 3 27.03 27.25 27.32 27.40 27.40 27.32 27.32 MK(OH)4

3 5:5 Ormosil 5D 27.25 27.03 26.67 26.46 27.03 27.32 27.62

neat ketone MK 4g 27.08 27.32 27.44 27.36 27.52 27.62 27.70 MK

4g 5:5 Ormosil 5E 27.40 27.10 26.74 26.53 27.17 27.47 27.78


350 400 450 500 550 600 650 7000.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.405

4

3

2

1 1: Ormosil 5A in HeOH 2: Ormosil 5B in HeOH 3: Ormosil 5C in HeOH 4: Ormosil 5D in HeOH 5: Ormosil 5E in HeOH

Abs

orba

nce

(a.u

.)

λ (nm)

[A]

350 400 450 500 550 600 650 7000.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.205

4

3

2

1 1: Ormosil 1B in DeOH 2: Ormosil 2B in DeOH 3: Ormosil 3B in DeOH 4: Ormosil 4B in DeOH 5: Ormosil 5B in DeOH

Abs

orba

nce

(a.u

.)

λ (nm)

[B]

Figure 14. UV/Vis absorption spectra of [A] Ormosils 5(A-E) measured as suspensions in 1-

hexanol (HeOH) and [B] Ormosils (1-5)B measured as suspensions in 1-decanol (DeOH).


As shown in Table 12 and Figure 14B, the polarity of the environment surrounding the

solvatochromic probes 2(a-c) slightly decreases with increasing the content of MTMOS from

10 to 50 % (Ormosils 5[A-C]) as indicated by a hypsochromic shift. This result is attributed to

the decreased polarity provided by increasing the ratio of the nonhydrolysable Si-CH3

functional group which enhances the surface hydrophobicity.

The solvation of the entrapped solvatochromic probes 2(a-c), 3 and 4g is readily

possible, because there is enough space available in the cage for external solvent molecules to

enter the probe.

Also, Table 12 and Figure 15 show that the polarity observed by the entrapped

solvatochromic probes 2(a-c), 3 and 4g is more sensitive to alcohols in their cavity cage than

the polarity of solvatochromic probes themselves in alkanols. These express that, the

solvatochromic probe caging increases with greater degree of condensation of the precursors

(MTMOS, TMOS).

The probability of caging increases on going from Ormosil 5 to Ormosil 1. Since the

MTMOS precursors contains three hydrolysable methoxy groups, the Si-CH3 bond remains

intact under typical Sol-gel synthesis conditions. After gel formation, the non-bridging Si-

CH3 groups are part of the three dimensional silicatic backbone and structurally act as

network modifiers that terminate the silicate network. Therefore, Cage flexibility is highest

for the highest ratio of MTMOS/TMOS. This means that Ormosils 5[A-C] are more sensitive

to solvent polarity, both because of the more flexible cage and decreased leveling effect of the

silanols.

The surface areas and pore-size distributions were investigated for a variety of

Ormosils. The surface analysis results for MK(OH)2 doped Ormosils A(1-5) are shown in

table 13.

It is known that a number of factors can affect the surface area, pore volume, porosity,

and pore sizes of silica xerogels.70 Such factors include the synthetic conditions (e.g.,

monomer concentration, r value (water: alkoxide molar ratio), temperature, and the pH value

of the catalyst) and the addition and nature of encapsulated probe.70

Table 13 shows a high ratio of MTMOS/TMOS resulted in low surface area material

with low porosity. The highest carbon content (12.32 %) of Ormosil 5A is mostly due to

nonhydrolysable methyl groups (Si-CH3). The higher carbon concentration in Ormosil 5A

thus hints at an increase in the surface hydrophobicity compared to the Ormosil 1A.


Table 13. Physical properties and carbon content of MK(OH)2 doped Ormosils A(1-5) series

synthesized from different compositions of MTMOS/TMOS

Figure 15 depicts the measured wave number (νmax *10-3, cm-1) of Ormosils 5[A-E] as

function of the number of methylene groups (n) in CH3(CH2)nOH. There is a specific

tendency observed for νmax. It decreases on going from methanol to 1-butanol, then νmax

increases in the same direction with increasing n. This result suggests that, the solvation of

Ormosils with alcohol containing short alkyl chain is more likely due to the ease of diffusion

to the silica network. However, the long alkyl chain covers the Ormosil surface and prevents

the polar alcoholic hydroxyl groups to interact with the entrapped solvatochromic probe.

24 Porosity, ф = Vp/Vp + 0.455) (100 %); Vp is the pore specific volume. 25 Average pore diameter, D = 0.9(4Vp/A); A is the BET specific surface area.

Ormosil

1A

Ormosil

2A

Ormosil

3A

Ormosil

4A

Ormosil

5A

Monolayer volume (cm3/g) 118.217 115.042 73.213 32.189 2.708

Specific surface area (m2/g) 514.620 500.802 318.712 140.126 11.787

Pore specific volume (cm3/g) 0.315 0.307 0.179 0.183 0.038

Total adsorbed volume (cm3/g) 204.289 260.446 117.310 120.186 43.222

Pore volume max. (cm3/g) 0.254 0.193 0.073 0.043 0.023

Porosity (ф)24 (%) 41 40 28 29 8

Average pore diameter (D)25 (∆) 22.036 22.069 20.219 47.015 116.060

Carbon content (%) 4.51 6.89 8.24 10.84 12.32


25.8

26

26.2

26.4

26.6

26.8

27

27.2

27.4

27.6

27.8

0 1 2 3 4 5 6 7 8 9 10

Number of n

ν max

*10

-3 c

m-1

Ormosil 5AOrmosil 5BOrmosil 5CMK(OH)2Fur(OH)2Thi(OH)2

[A]

26.2

26.4

26.6

26.8

27

27.2

27.4

27.6

27.8

28

0 1 2 3 4 5 6 7 8 9 10

Number of n

ν max

*10

-3 c

m-1

Ormosil 5DOrmosil 5EMK(OH)4MK

[B]

Figure 15. UV/Vis absorption maxima of aromatic amino ketones and their doped Ormosils

as function of the number of methylene groups (n) in CH3(CH2)nOH. [A] MK(OH)2,

Fur(OH)2, Thi(OH)2 and their doped Ormosils 5(A-C), [B] MK, MK(OH)4, and their doped

Ormosil 5(D-E).


In addition, the effect of the long alkyl chain on the hydroxyl group in alcohol is

similar to the effect of alkane such as n-hexane on the more polar alcohols such as methanol.

UV/Vis spectroscopic (νmax *10-3, cm-1) results obtained for Ormosils 5[A-D] in

presence of diverse non HBD solvents with different polarity and HBA ability are listed in

Table 14. These results demonstrate the synergetic effect between the cavity and the enclosed

solvent.

Table 14. Wave number values (νmax*10-3, cm-1) of Ormosils 5[A-D] in the presence of

diverse solvents with different polarity and hydrogen-bonding ability.

Figure 16 shows UV/Vis absorption spectra of Ormosil 5B particles measured as a

suspension in different solvents (ethanol (EtOH), tetrahydrofuran (THF), and N,N-

dimethylacetamide (DMAc)). The absorption maximum of Ormosil 5B shows a blue shift

with increasing solvent polarity, from THF (λmax = 378 nm) to DMAc (λmax = 369 nm). This

result indicates that, these types of Ormosils are solvatochromic; i.e. it shows a solvent-

dependent shift in the absorption spectra. In contrast, the absorption maximum of the neat

Fur(OH)2 2b measured in the same solvents (Table 1, vide supra) is shifted bathochromically

with increasing solvent polarity. These results support the hydrophobic character of Ormosil

5B which has the highest ratio of MTMOS/TMOS.

Solvent Ormosil

5A

Ormosil

5B

Ormosil

5C

Ormosil

5D

Ormosil

5E

1,1,2,2-Tetrachloroethane 29.07 27.47 27.62 28.41 28.99

Dimethylsulfoxide 28.65 27.62 27.70 28.33 28.25

N,N-dimethylacetamide 27.78 27.10 27.32 27.55 28.01

1,2-Dichloroethane 27.70 26.81 27.17 27.10 27.17

Tetrachloromethane 26.95 26.46 26.74 26.81 26.60

Tetrahydrofuran 26.95 26.46 26.74 27.32 27.10

Acetonitrile 26.88 26.11 26.67 26.67 27.10


350 400 450 500 550 600 650 7000.0

0.1

0.2

0.3

0.4

0.5

0.6

Ormosil 5B in EtOH Ormosil 5B in THF Ormosil 5B in DMAc

Abs

orba

nce

(a.u

.)

λ (nm)

Figure 16. UV/Vis absorption spectra of Ormosil 5B measured as a suspension in ethanol

(EtOH), tetrahydrofuran (THF), and N,N-dimethylacetamide (DMAc).

CP MAS solid-state 29Si nuclear magnetic resonance (NMR) is a powerful technique

for examining the structure of silicates.115-119

Figure 17 illustrates possible silicate structures that can be formed by the sol-gel

process.118 Q represents a quaternary oxygen tetrahedron; T represents a three oxygen, one

alkyl group tetrahedron; and D represents a two oxygen, two alkyl group tetrahedron. The

superscripts denote the number of alkoxide groups that have reached to form Si-O-Si

linkages. Therefore, Q0, T0, and D0 represent unreacted precursors, while Q4, T3, and D2

represent completely reacted species.


O Si O

O

O

RR

R

R

O Si O

O

O

XR

R

R

O Si O

O

O

XR

X

R

O Si O

O

O

XR

X

X

O Si O

O

O

XX

X

X

Q0 Q1 Q2 Q3 Q4

O Si O

CH3

O

RR

R

O Si O

CH3

O

XR

R

O Si O

CH3

O

XX

R

O Si O

CH3

O

XX

X

T0 T1 T2 T3

O Si O

CH3

CH3

RR O Si O

CH3

CH3

XR O Si O

CH3

CH3

XX

D0 D1 D2

R = H or C2H5 X = Q, T, or D

Figure 17. Possible silicate structures formed in the sol-gel process and classification of the

Si-atom relating to the signal observed in the 29Si spectra.

Figure 18 shows the 29Si NMR spectra of Ormosil 5A. There are five peaks at -56.40, -

64.56, -92.67, -102.04, and -110.89 ppm, which correspond to T2, T3, Q2, Q3, and Q4,

respectively. The T peaks originate from MTMOS and Q peaks from TMOS.


-190-190-180-180-170-170-160-160-150-150-140-140-130-130-120-120-110-110-100-100-90-90-80-80-70-70-60-60-50-50-40-40-30-30-20-20-10-1000

Figure 18. Solid-state CP-MAS 29Si-NMR spectrum of the sol-gel hybrid material

synthesized from equimolar composition of MTMOS and TMOS of Ormosil 5A.

3.1.4.2 Chemical linking to the silica network

The triethoxysilyl functional chromophore was prepared by the reaction of MK(OH)2,

Fur(OH)2, and Thi(OH)2 respectively with 3-isocyanatopropyltriethoxysilane (IP-TriEOS) to

form the carbamate linked reactive chromophores 4-(Dimethylamino)-4’-[di(2-propyltri-

ethoxysilylcarbamatoethyl)amino]benzophenone DPAB 8a, [4-Di(2-propyltriethoxysilyl-

carbamatoethyl)amino]-2-furylmethanone DPAF 8b, and [4-Di(2-propyltriethoxysilyl-

carbamatoethyl)amino]-2-thienylmethanone DPAT 8c. Hybrid materials I(A-C), II(A-C),

III(A-C), and IV(A-C) were prepared by reacting of the sol-gel precursor 8a, 8b, or 8c with

varying molar ratios of TEOS in presence of acidic water (pH = 3) (see Chart 9 and

Experimental section).

Q4 Q3

Q2

T2

T3


Ar C

O

N

OH

OH

+ 2 O C N Si(OEt)3

DMAcurethane reaction110 °C /6 h

Ar C

O

N

O

O

C N

C N

O H

O H

Si(OEt)3

Si(OEt)3

DMAcaddition ofSi(OC2H5)4H2O / H

8(a-c)

Ar

C O

N

O OC

NC

N

O

HO

H

SiO Si OSi O

SiOSiO

O

OO

SiO

O

SiO

SiO

O

SiO

Si

OO

O

O

SiO

SiO

O

O

O

SiO

SiO

Si

OO

O

Si

OSi

O

O

O

SiO

SiO

O

SiO

SiO

SiO

O

O

SiO

Si

OSi

O

O

OSi

O

O

SiO

Si

O

O

OSi

O

Si

O

O

SiO

Si

OSi

O

O O

Si

O

O

SiO

Si

O

OO

O

Si

O

SiO Si

O

O Si

OSi

OSiO

Ar

C O

N

O OC

NC

N

O

HO

H

Si Si O

OO O Si

O

O

O

SiO

SiO

O

SiO

SiO

O

Si O

O

O

Si

OSi

O

SiOO

OSi

O

O

SiO

Si

OO

SiO

O O

Si

OSi

O

SiO

SiOSi

O

O

O

SiO

Si

O

O OO

O

SiSi SiO

O

SiO

SiO

SiO

SiO

Si

O

O

O

O

SiO

SiO

Si

O

O O

O

SiO

SiO

Si

OSi

O

O OO

O

Si

O

O

SiSi

O

O

NH3C

H3C O SAr = Ar = Ar =

8a, Hybrid A 8b, Hybrid B 8c, Hybrid C

Chart 9. Synthesis of organic/silica hybrid materials by the sol-gel process.


The extent of cross-linkages in the hybrid materials was controlled by varying the

molar amounts of TEOS in the reaction mixture. The addition of TEOS could give a greater

chance of cross-linking between Si-OH and Si-OEt, due to the congestion of TEOS between

silanol and ethoxysilane groups attached to the bulky chromophore. Therefore, there are more

active sites for the condensation reaction for the copolymer system consisting of large

amounts of TEOS, given that the homopolymer has lower degree of polycondensation than

the copolymer does contain.

29Si NMR spectra for hybrid materials I(A-C), II(A-C), III(A-C), and IV(A-C) xerogel

will have T peaks from 8a, 8b, or 8c and Q peaks from TEOS. There was no identifiable

evidence of any unreacted 8a, 8b, or 8c (T0), indicating that all the triethoxysilyl functional

chromophore 8a, 8b, or 8c has been bonded to the matrix.

-190-190-180-180-170-170-160-160-150-150-140-140-130-130-120-120-110-110-100-100-90-90-80-80-70-70-60-60-50-50-40-40-30-30-20-20-10-1000

Figure 19. Solid-state CP-MAS 29Si-NMR spectrum of the sol-gel hybrid material

synthesized from 4-(Dimethylamino)-4’-[di(2-propyltriethoxysilylcarbamatoethyl)amino]-

benzophenone and TEOS (1:2) (hybrid IIA).

Q4

Q3

Q2

T3


Hybrid materials I(A-C), II(A-C), III(A-C), and IV(A-C) showed four peaks in their

cross-polarized solid-state 29Si NMR spectra that can be assigned to tri-and tetrafunctional Si-

O units of T3 (-65.85 ppm), Q4 (-110.84 ppm), Q3 (-101.39 ppm), and Q2 (-92.33 ppm) type,

respectively as shown in Figure 19 for hybrid IIA. Also, this Figure showed the more intense

peak for Q3-type Si-O units as compared with the other two peaks for Q2- and Q4-types Si-O

units. This result indicates that the sol-gel precursor 8a, 8b, or 8c is completely homo-and co-

polymerized with TEOS.

The 13C-1H CP-NMR spectrum of hybrid IB with MAS at 10 KHz is depicted in

Figure 20. The spectrum is in full agreement with the proposed structure. The two carbonyl

carbons, between furyl and phenylene groups and carbamic ones (179.94 and 171.93 ppm),

are well separated, which is consistent with the fact that no hydrolysis of urethane linked

precursor 8b occurs during the hydrolysis and polycondensation reactions.

O C

O

N

O

O

C

C

O

N

N

H

Si

O

H

Si

O

O O

OO

O

1

2

3

56

78

9

10

4

1112

1314

15

-25-2500252550507575100100125125150150175175200200225225250250

Figure 20. Solid-state 13C-1H CP-NMR spectrum of hybrid IB with MAS at 10 KHz.

1 23

5

6

4

11

813,14

9

12,15

7,10


The internal polarity of the respective silicate hybrid materials, as observed by the

UV/Vis absorption shift of the covalently bonded aromatic amino ketone moieties 2(a-c),

significantly depends on the proportion of TEOS used for the sol-gel process. By comparing

the UV/Vis absorption spectra of the hybrids containing similar chromphores, it was observed

that the long-wavelength UV/Vis absorption band shifted hypsochromically with an increase

of the molar ratio of TEOS (Fig. 21A and Tab. 15). This is due to the greater degree of

condensation of the TEOS, which creates a more complete cage. Also, similar effect for the

same type of hybrid was observed on going from methanol to 1-octanol (Fig. 21B).

Table 15. Wave number values (νmax *10-3, cm-1) of hybrids I(A-C), II(A-C), III(A-C), and

IV(A-C) in presence of diverse alcohols.

The variation of absorption maximum of hybrids I(A-C) with the number of methylene

group (n) in CH3(CH2)nOH and as function of the concentration of tetraethylorthosilicate

(TEOS) are shown in Fig. 22A and 22B, respectively. There is a systematic regular

hypsochromic shift of the UV/Vis absorption maxima of hybrids I(A-C) on going from

methanol to 1-octanol (Fig. 22A) in compared with that of Ormosil 5(A-C) (Fig. 15A, vide

supra). This result may be attributed to a homogeneous incorporation of the aromatic amino

ketones 2(a-c) to the silica network which was achieved by the method of modifying 2(a-c)

with alkoxysilanes.

26 Water used is acidic water pH = 3 and the ratio of water to silanes is constant (4:1).

ν max*10-3 cm-1 hybrid Alkoxy-

silane

Molar ratio of alkoxy-

silane:TEOS:H2O26 MeOH EtOH 1-PrOH 1-BuOH 1-HeOH 1-OcOH

IA 8a 1:1:8 25.13 25.32 25.51 25.77 25.97 26.18

IB 8b 1:1:8 23.58 23.81 24.04 24.27 24.63 25.06

IC 8c 1:1:8 24.21 24.69 25.06 25.32 25.51 25.64

IIA 8a 1:2:12 25.71 25.84 25.97 26.11 26.53 26.67

IIB 8b 1:2:12 24.33 24.63 24.81 25.00 25.19 25.32

IIC 8c 1:2:12 24.81 24.94 25.32 25.45 25.58 25.71

IIIA 8a 1:3:16 26.11 26.32 26.60 26.74 26.88 27.03

IIIB 8b 1:3:16 25.19 25.32 25.45 25.64 25.77 25.97

IIIC 8c 1:3:16 25.00 25.13 25.32 25.64 25.77 25.97

IVA 8a 1:4:20 26.81 27.03 27.17 27.32 27.62 27.78

IVB 8b 1:4:20 25.45 25.64 25.77 25.84 25.97 26.11

IVC 8c 1:4:20 25.51 25.71 25.84 25.97 26.11 26.67


350 400 450 500 550 600 650 700

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70 hybrid IB in BuOH hybrid IIB in BuOH hybrid IIIB in BuOH hybrid IVB in BuOH

Abs

orba

nce

(a.u

.)

λ (nm)

[A]

350 400 450 500 550 600 650 7000.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

3

45

6 2

1

1: hybrid IVC in MeOH 2: hybrid IVC in EtOH 3: hybrid IVC in PrOH 4: hybrid IVC in BuOH 5: hybrid IVC in HeOH 6: hybrid IVC in OcOH

Abs

orba

nce

(a.u

.)

λ (nm)

[B]

Figure 21. UV/Vis absorption spectra of [A] hybrid (I-IV)B and [B] hybrid IVC measured as

a suspension in methanol (MeOH), ethanol (EtOH), 1-propanol (PrOH), 1-butanol (BuOH),

1-hexanol (HeOH), and 1-octanol (OcOH).


23

23.5

24

24.5

25

25.5

26

26.5

0 1 2 3 4 5 6 7 8

Number of n

ν max

*10

-3 c

m-1

hybrid IAhybrid IBhybrid IC

[A]

23

23.5

24

24.5

25

25.5

26

26.5

27

1 1.5 2 2.5 3 3.5 4 4.5 5 5.5

Concentration of TEOS (mmol)

ν max

*10

-3 c

m-1

hybrid Ahybrid Bhybrid C

[B]

Figure 22. UV/Vis absorption maxima of [A] hybrids I(A-C) as function of the number of

methylene groups (n) in CH3(CH2)nOH and [B] hybrids A-C measured in methanol as

function of the concentration of tetraethylorthosilicate (TEOS).


Functionalization of 2(a-c) with IP-TriEOS enhance the miscibility of these ketones

with TEOS and prevent the phase separation or the probe aggregation during the sol-gel

process.

3.2 N-(2’-hydroxy-4’-dimethylamino-benzylidene)-4-nitroaniline [HDBN]

3.2.1 UV/Vis absorption spectroscopy of [HDBN]

The electronic absorption spectra of HDBN 7 were investigated in several solvents of

different polarity and hydrogen bonding ability. The UV/Vis absorption maxima of 7

measured in diverse solvents and the corresponding empirical Kamlet-Taft parameters used

are collected in Table (16). HDBN is insoluble in the strong polar solvents water and ethane-

1,2-diol. In increasing the solvent polarity from cyclohexane (CH) to formamide (Fig. 23 and

Tab. 16), the UV/Vis absorption spectra of 7 exhibit a bathochromic shift of the long-

wavelength band.

350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

7 in CH 7 in EtOH 7 in formamide 7 in TCM 7 in HFP

Abs

orba

nce

(a.u

.)

λ (nm)

Figure 23. UV/Vis absorption spectra of HDBN 7 in different solvents with different polarity

and hydrogen bonding ability such as cyclohexane (CH), ethanol (EtOH), formamide, TCM,

and HFP.


Table 16. UV/Vis absorption maxima for HDBN 7 in diverse solvents of different polarity

and hydrogen bonding ability.

Solvent ν max 7 /103 cm-1 α β π*

c-Hexane 24.57 0.00 0.00 0.00

Triethylamine 24.57 0.00 0.71 0.14

Diethylether 24.27 0.00 0.47 0.27

Tetrachloromethane 24.21 0.00 0.10 0.28

1,4-Dioxane 23.98 0.00 0.37 0.55

Ethyl acetate 23.92 0.00 0.45 0.55

p-Xylene 23.75 0.00 0.12 0.43

1,2-Dimethoxyethane 23.75 0.00 0.41 0.53

Benzene 23.70 0.00 0.10 0.59

Toluene 23.70 0.00 0.11 0.54

Acetone 23.70 0.08 0.43 0.71

Tetrahydrofuran 23.64 0.00 0.55 0.58

Acetonitrile 23.58 0.19 0.40 0.75

Ethanol 23.58 0.86 0.75 0.54

1-Hexanol 23.58 0.80 0.84 0.40

1-Decanol 23.58 0.70 0.82 0.45

1-Octanol 23.53 0.77 0.81 0.40

1-Propanol 23.42 0.84 0.90 0.52

Methanol 23.42 0.98 0.66 0.60

Chloroform 23.36 0.20 0.10 0.58

Dichloromethane 23.36 0.13 0.10 0.82

Pyridine 23.31 0.00 0.64 0.87

1-Butanol 23.31 0.84 0.84 0.47

Dimethylsulfoxide 23.26 0.00 0.76 1.00

N,N-Dimethylacetamide 23.15 0.00 0.76 0.88

N,N-Dimethylformamide 23.09 0.00 0.69 0.88

1,2-Dichloroethane 22.99 0.00 0.10 0.81

Benzonitrile 22.99 0.00 0.37 0.90

1,1,2,2-Tetrachloroethane 22.68 0.00 0.00 0.95

2,2,2-Trifluoroethanol 22.37 1.51 0.00 0.73

Acetic acid 22.32 1.12 0.45 0.64

1,1,1,3,3,3-Hexafluoro-2-propanol 22.12 1.96 0.00 0.65

Formamide 22.03 0.71 0.48 0.97


The solvatochromic effect of HDBN 7 shows that the long-wavelength UV/Vis

absorption maximum ranges from λ = 407 nm in CH and triethylamine (TEA) to λ = 454 nm

in formamide, corresponding to ∆λ = 47 nm (∆ν = 2540 cm-1) stabilization energy over the

wide range of different solvent polarity. This bathochromic displacement for 7 is in agreement

with an increased delocalization, due to a more extended conjugated π-system. This result

indicates that compound 7 is more polar in the excited singlet state than in the ground state.

N

NO2

ONH3C

CH3

H NH3C

CH3

N

O

N

O

H

O

N

NO2

NH3C

CH3

OH

hν

enol form I enol form II

cis-keto form III trans-keto form IV

ONH3C

CH3

NH

NO2

Scheme 3. Suggested mechanism of intramolecular proton transfer in HDBN 7.

For HDBN system, which is characterized by a strong intramolecular hydrogen bond

(Scheme 3), a different intermolecular interaction is expected with each of the solvents used.

For instance, the dominating tautomer-H…..OH-solvent interaction in 7 when competing with

an alcohol would require breaking of the intramolecular hydrogen bond in this compound.

Thus, for these molecules a tautomer-O…..H-solvent interaction with alcohols as well as

halogenated aliphatic hydrocarbon solvents such as CHCl3 should be energetically more

favorable. Specific interactions of the tautomer-H…..O=solvent interaction (DMSO, acetone)

should hardly be possible, because of unfavorable steric repulsion.


The measured νmax data for 7 were fitted by multiple regression in order to evaluate

the respective contributions of the nonspecific and specific, intermolecular forces to the

overall interaction between 7 and solvent molecules.

νmax *10-3 [HDBN] = 24.66 – 1.88 π* - 0.72 α + 0.34 β (34)

n = 33 r = 0.94 SD = 0.22 F < 0.0001

The best regression fit for the solvatochromism of 7 is obtained by excluding the νmax

values of ethanol, methanol, dichloromethane, acetic acid, and formamide. It is given by eq.

(35) and shown in Figure (24).

νmax *10-3 [HDBN] = 24.61 – 1.79 π* - 0.68 α + 0.32 β (35)

n = 28 r = 0.97 SD = 0.15 F < 0.0001

22

22.5

23

23.5

24

24.5

25

22 22.5 23 23.5 24 24.5 25

measured νmax*10-3 cm-1

calc

ulat

ed ν

max

*10-3

cm

-1

Figure 24. Relationship between calculated and measured values of HDBN 7 in 28 solvents

of different polarity and hydrogen bonding ability.

The negative sign of the s coefficient indicates that in increasing the solvents polarity

/polarizability (π*) a bathochromic shift in νmax for HDBN takes place. This result


demonstrates that the excited singlet state of this molecule becomes more stabilized when the

solvent polarity increases. The negative sign of the a coefficient found for the solvatochromic

UV/Vis absorption shift of HDBN indicates that in increasing the solvent HBD ability a HBD

solvation at the N,N-dimethylamino group is unlikely. The red shift in νmax is in agreement

with an increase in the formation of solute-solvent hydrogen bonding at the nitro group or

azomethine moiety. However, the contribution of the α term on the shift of νmax [HDBN] is

not so important, because the coefficient a (≈ 0.7) is significantly smaller than the coefficient

s (≈ 1.7) from eqs. 34 and 35. This demonstrates that the ability of the solvent to donate

hydrogen bonds is weaker than do solute-solvent dipole-dipole interactions occurring

preferably in the excited singlet state of the above compound. Thus, a satisfactory linear

correlation with high significance is also observed between νmax [HDBN] and solely the

Kamlet-Taft’s solvation parameter π* (36).

νmax *10-3 [HDBN] = 24.51 – 1.72 π* (36)

n = 28 r = 0.74 SD = 0.40 F < 0.0001

On going from a three-parameter equation with π*, α and β, to a two-parameter

equation considering only π* and α, the improvement in r of HDBN does not seem to change

significantly. (eq. 37).

νmax *10-3 [HDBN] = 24.74 – 1.78 π* - 0.67 α (37)

n = 28 r = 0.95 SD = 0.18 F < 0.0001

Therefore, we concluded that the effect of the β term (basicity) of the solvent on the

solvatochromic shift of νmax [HDBN] can be ignored. This indicates that the effect of β, which

should arise from the formation of a hydrogen bond donated from the o-hydroxyl group to the

solvent, is competed by the presence of the intramolecular hydrogen bond in HDBN. The

positive sign from eqs. 34 and 35 for β, however, shows that the breaking of the

intramolecular hydrogen bond brings a weaker effect upon ∆νmax than the expected formation

of the negatively charged phenolate.

Now the question is which role play acid-base interactions at the active centers of

HDBN and how do they contribute to the shift of the solvatochromic UV/Vis band?


UV/Vis absorption spectra of HDBN in ethanolic solutions with different pH’s are

shown in Fig. 25. The pH has been adjusted with either aqueous HCl or NaOH solution. Thus

mobile H+ and OH-, respectively, serve as acid and base. In strong alkaline ethanolic solution

(pH = 11.75), then the UV/Vis absorption band maximum of HDBN is observed at λ = 444

nm (bathochromic effect), whereas the UV/Vis absorption maximum of HDBN in acidic

ethanol solution (pH = 2.5) appears at λ = 344 nm (hypsochromic effect). These results are

opposite to those obtained in the various solvent, where acidic environments caused

bathochromic UV/Vis shifts. It seems likely that the large blue-shift for HDBN in going from

strong basic to acid solutions is due to protonation at the N,N-dimethylamino nitrogen atom

which strongly decreases the extend of the π conjugated system. Protonation at the imino

nitrogen is difficult to interpret, because two opposite effects on shift of νmax [HDBN] are

expected caused either by intramolecular H-bond breaking or intermolecular H-bond

formation. A protonation at the nitro group would cause a bathochromic UV/Vis shift.

350 400 450 500 550 600 650 700

0.0

0.2

0.4

0.6

0.8

1.0

1.2

876

5

4

3

2

1 1 pH = 7.8 λmax= 426 nm 2 pH = 5.8 λmax= 426 nm 3 pH = 5.2 λmax= 344, 424 nm 4 pH = 2.5 λmax= 344 nm 5 pH = 11.5λmax= 432 nm 6 pH = 11.6λmax= 436 nm 7 pH = 11.7λmax= 442 nm 8 pH = 11.8λmax= 444 nm

Abs

orba

nce

(a.u

.)

λ (nm)

Figure 25. UV/Vis absorption spectra for HDBN in ethanol at different pH.

As shown in Fig. 25, the UV/Vis absorption spectra of HDBN in ethanolic solution at pH =

5.2 revealed two long-wavelength UV/Vis absorption bands, one with higher intensity and


higher energy (λmax = 344 nm) and the other one with a lower intensity and lower energy

(λmax = 424 nm). The position of the first UV/Vis absorption band is attributed to the

protonated form of HDBN. The second band is significantly red-shifted with respect to the

first band by approximately ∆λ = 80 nm. This UV/Vis absorption is likely attributed to the

presence of the quinoid structure of HDBN (Scheme 3), which seems of importance in

ethanolic solutions with pH ≥ 5.8.

3.2.2 X-ray crystal structure analysis in relation to powder reflectance UV/Vis

spectroscopy of HDBN

For these investigations, we have chosen the pure crystal powder of HDBN and

HDBN when entrapped in a sol-gel glass which is comparable to the polarity of methanol. In

both environments, directed dipolar and/or acid base interactions are expected to occur due to

the rigidity of the environment. The X- ray crystal structure analysis of HDBN has been

carried out in order to judge the intense red color of the crystals in relation to structural

features. HDBN crystallizes from benzene at 25 °C as red blocks in the monoclinic space

group P21/c, with a = 1683.380(10), b = 723.06(2), c = 1159.95(2) pm, α = γ = 90, β =

109.568(2)°, V = 1330.33(4)*106 pm3 and Z = 4. Relevant bond distances and angles are

given in the Figure 26A caption.

The observed bond lengths of O3-C9, C7-C8, C8-C9, and N1-C7 were 135.27(19),

143.18(17), 142.2(2) and 129.9(2) pm, respectively. The length of O3-C9 bond that of C7-C8

bond are considerably longer than the standard length of the C=O bond (122.2 pm) and that of

C=C bond (134.0 pm) in conjugated enones,120 respectively, and the length of C8-C9 and that

of N1-C7 bond are considerably shorter than the standard length of the C-C bond (146.4 pm)

in conjugated enones and that of C(sp2)-N bond (135.5 pm) in enamines, respectively. The

results suggest that the molecule HDBN exists in an enol form and also reveals the presence

of strong intramolecular hydrogen bond between the hydroxyl hydrogen atom and the imine

nitrogen atom in the molecule. The intramolecular hydrogen bonding in HDBN has a

profound effect since it holds that molecule in a planar conformation thereby maximizing the

molecular orbital overlap.


O3C3C2

O1

C14C10 C9 N1

C4

N2C1

N3 C11 C8 C7O2

C5C6C15 C12C13

H3O

Figure 26A. ZORTEP drawing (50 % probability level) of HDBN 7, selected bond lengths

[pm]: C(9)-O(3) 135.27(19), O(3)-H(3O) 88.0(2), C(7)-C(8) 143.18(17), C(8)-C(9) 142.2(2),

N(1)-C(1) 140.87(15), N(1)-C(7) 129.9(2); selected bond angels [°]: C(6)-C(1)-N(1)

124.86(14), C(7)-N(1)-C(1) 121.49(13), N(1)-C(7)-C(8) 121.69(14), C(9)-C(8)-C(7)

122.59(14), C(9)-O(3)-H(3O) 106.2(17); selected torsion angles [°]:C(7)-N(1)-C(1)-C(2)

176.54(15), N(1)-C(7)-C(8)-C(9) 1.4(2), C(7)-C(8)-C(9)-O(3) -0.4(2), C(1)-N(1)-C(7)-C(8) -

179.57(13).

Figure 26B Crystal packing of HDBN 7.


Representative crystal packing diagram is displayed in Figure 26B. In the unit cell, the

molecules are arranged oppositely to each other.

The UV/Vis absorption spectra of the solid crystal powder (see below) of HDBN and

its corresponding sol-gel Ormosil (organic modified silicate) glasses have been measured by

means of diffuse reflectance spectroscopy. Representative UV/Vis spectra of HDBN

measured as solid powder and encapsulated in sol-gel glasses are shown in Figure 27.

350 400 450 500 550 600 650 700 750 800-0.05

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

HDBN in ormosil HDBN solid powder

Abs

orba

nce

(a.u

.)

λ (nm)

Figure 27. UV/Vis reflectance spectra of HDBN 7 as solid powders and encapsulated in

Ormosil.

As seen from Fig. 27, the diffuse reflectance spectrum from fine-powder of HDBN

shows a broad UV/Vis absorption section with three small poorly resolved peaks at λmax =

337, 380, and 492 nm. The first two UV/Vis bands relate to contributions of NH and keto

tautomeric structures, respectively, whereas the third one likely reflects an electronic

transition derived from the strong dipolar oppositely arranged aggregation of the dye

molecules.

Fig. 27 revealed an UV/Vis absorption band at λmax = 355 nm for HDBN when entrapped

within the solid Ormosil hosts. The large hypsochromic UV/Vis spectral shift for entrapped

HDBN may be preferably due to protonation of the N,N-dimethylamino group of HDBN.


Also, since the formation of Schiff base is reversible, the change in the UV/Vis

absorbance may be due to breakage of the Schiff base bond (-CH=N-) in entrapped molecule

at higher pH.

3.2.3 Adsorption of HDBN on Aerosil 300

HDBN adsorbs readily on silica particles from non HBA solvents such as 1,2-

dichloroethane (DCE), TCE, toluene or benzene. The adsorption of HDBN on silica particles

from those solvents is associated with a significant bathochromic shift of the solvatochromic

UV/Vis absorption band (Tab. 17 and Fig. 28). This bathochromic shift can be well

interpreted in terms of the result derived from the solvent influence on νmax [HDBN]. The

increased stabilization of the polar ionic structure (Scheme 3) on silica, which is more

dominant in the excited singlet state than electronic ground state, is well in accord to the result

obtained in the strong dipolar solvents TFE, HFP or formamide. Compared to these solvents,

Aerosil-silica nano-particles in a liquid slurry have α value between 0.9 and 1.4 and π*

between 0.6 and 1.1 as function of HBA capacity and dipolarity/polarizability of solvents

used.114 β of silica particles can be neglected.

For instance, the calculated value of νmax [7/Aerosil] in CH2Cl2 (with α = 0.98 and π* =

1.14 from ref.114 = 22.046 cm-1 (from eq. 37) well agrees with the measured value of νmax

[7/Aerosil in CH2Cl2] = 22.270 cm-1 (from Tab. 17). Accordingly, hydrogen bond formation

which may occur solely at the oxygen atoms of the nitro group when HDBN is adsorbed on

silica enhances the electron push-pull conjugation effect. However, it seems that hydrogen

bonds at the dimethylamino and hydroxyl groups of HDBN on silica are of minor importance.

According to results from the literature, interaction of silanol groups at the nitro group

of push-pull aromates are preferred rather than at N,N-dimethylamino or OH groups.45,121

Additionally, the presence of intramolecular hydrogen bonds in HDBN would require

energy to break and formation a new intermolecular hydrogen bond between the dye indicator

HDBN and silanol group. It seems that HDBN when adsorbed is in a rigid conformation state

fixed and not in a twisted one.


Table 17. UV/Vis absorption maxima of N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitroaniline

HDBN 7 when adsorbed onto dried Aerosil 300 in various solvents (suspension) and the difference of

the wave number (∆νmax) to νmax [HDBN] in the pure solvent as well as the comparison with expected

νmax values from the LSEr eq. 37.

Solvent νmax *10-3 cm-1 ∆ν max *10-3 cm-1

Toluene (α = 1.14; π* = 0.97)27 21.65 (22.24)28 2.05

Tetrachloromethane (α = 1.52; π* = 0.56)27 22.32 (22.7)28 1.89

Benzene 21.83 1.87

p-Xylene 22.08 1.67

1,2-Dichloroethane (α = 1.15; π* = 1.01)27 21.74 (21.17)28 1.25

Dichloromethane (α = 0.98; π* = 1.14)27 22.27 (22.07)28 1.09

1,1,2,2-Tetrachloroethane 21.60 1.08

Chloroform (α = 0.95; π* = 1.1)27 22.37 (22.14)28 0.99

Dimethylsulfoxide 22.62 0.64

Acetonitrile29 23.70 -0.12

Diethyl ether29 24.15 0.12

N,N-Dimethylformamide29 23.15 -0.06

Tetrahydrofuran29 23.58 0.06

Triethylamine29 24.57 0.00

The UV/Vis shift of HDBN after adsorption amounts to ∆ν = 2050 cm-1 in toluene

(strongest) and ∆ν = 990 cm-1 in chloroform (weakest). The change of polarity observed at the

solid /liquid interface is therefore the highest for the aromatic solvent toluene and 1,1,2,2-

tetrachloroethane. Both solvents also posses the highest polarizability in this series.

Moderately strong HBA solvents (β > 0.3), such as triethylamine, diethylether,

tetrahydrofuran, dimethylformamide, and acetonitrile, themselves interact strongly with the

silanol groups of silica particles.122

27 The parameters in parenthesis are those fort he Aerosil /solvent interface independently determined with Fe(phen)2(CN)2 and Michlers Ketones as a surface polarity indicator from ref. 114. 28 The value in parenthesis is the calculated νmax value for adsorbed HDBN from eq. 37 using the independently determined α and π* from ref. 114. 29 HDBN, 7 is not completely adsorbed.


350 400 450 500 550 600 650 700

0.0

0.1

0.2

0.3

0.4

0.5

7 in tol. 7 in DCM 7 Aerosil/DCM 7 Aerosil/tol.

Abs

orba

nce

(a.u

.)

λ (nm)

Figure 28. UV/Vis absorption spectra for N-(2‘-hydroxy-4‘-dimethylaminobenzylidene)-4-

nitroaniline 7 in toluene (tol.), dichloromethane (DCM) and its adsorption on Aerosil 300

from the same solvents.

Altogether, the solvents used for the adsorption of HDBN possess no HBD capacity. It

seems that the polarity difference of the silica/solvent interface to the pure solvent is the

largest for solvents with high polarizability, π* value, of the solvent. In a previous paper,47 we

reported on the influence of the solvent upon the polarity of the silica/solvent interface using

suitable solvatochromic indicators.

Consequently, the probe HDBN does not completely adsorb onto silica from those

solvents and sometimes no UV/Vis band in the slurry which is different from the pure solvent

can be measured (Table 17).


3.3 Poly(benzophenone co-piperazine) and its silica composite

3.3.1 Syntheses and structure analysis

Matrix polymerization can be viewed as an intriguing procedure for the preparation of

homogeneous blends that are otherwise difficulty or practically impossible to prepare.

Poly(benzophenone co-piperazine) 9a has been synthesized by direct polycondensation of

piperazine with 4,4’-difluorobenzophenone in DMSO (solution polymerization).

Poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b was prepared by the same

way. However, in this case the reaction was carried out in the presence of LiChroprep Si 60 as

a template and without solvent as a melt (solid-state polymerization) (Chart 10).

C

O

F F + NNH H

1

23

4

n n

-nHF -nHF

SiO2 + K2CO3

140 °CDMF + K2CO3

140 °C

5 6

1'2' 3'

4'

5'6'

N N C

O

N N HC

O

F

n-1

Chart 10. Synthesis of poly(benzophenone co-piperazine) using two different synthetic

procedures, solution and solid-state polymerization.

Special focus has been made in this work to ascertain whether the solution

polymerization is different from that solid-state polymerization. The structure of these

polymers was elucidated by elemental analysis (C, H, N) and spectroscopic methods (IR,

solid-state-NMR, UV/Vis spectroscopy, and MALDI-TOF MS spectroscopy).

3.3.1.1 Elemental analysis

The theoretical composition for (C17H16ON2)n was calculated at (C, 77.18; H, 6.05; N,

10.59). This is comparable to the experimentally found values for 9a (C, 76.05; H, 5.73; N,


9.85). The slightly differences in these values is due to the presence of three different end

groups in the polymer chains as seen below from MALDI-TOF analysis. The experimentally

found values for the hybrid material 9b amount (C, 19.42; H, 2.34; N, 2.21).

3.3.1.2 IR-spectroscopy

The FT-IR absorption spectra of LiChroprep Si 60, poly(benzophenone co-piperazine)

9a, and poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b in KBr matrix have

been studied by transmission (Tab. 18).

Table 18. Assignments of the Infrared absorption bands in the 4000-400 cm-1 range for

LiChroprep Si 60, Poly(benzophenone co-piperazine) 9a, and Poly(benzophenone co-

piperazine) modified LiChroprep Si 60 9b.

Assignments LiChroprep Si 60 9a 9b

ν(Si-OH) 3424 3424

H-bonded ν(N+H) 3402 3402

aromatic 3118 3114

ν(NH) 2950

νs(CH2) 2827 2826

δ(H2O) 1638 1647 1642

ν(C=O) 1586 1598

δ(NH)-ν(C-N) 1548 1541

δ(CH2) 1421 1413

νas(Si-O-Si) 1098 1095

νas(NC2) 1229 1225

νs(NC2) 944 944

νs(Si-O-Si) 801 812

δ(Si-O-Si) 456 452

The spectra of LiChroprep Si 60 and 9b show broad band at 3424 cm-1 corresponding to the

stretching vibrations of the surface silanols SiOH perturbed by hydrogen bonding either

intramolecularly or with physically adsorbed water. Because a band in this region is generally


associated with a band near 1640 cm-1 (presumably caused by H2O deformation), assignment

to H2O is usually favored. The broad band at 3402 cm-1 in 9a and 9b is attributed to the H-

bonded ν(NH) stretching vibrations. The presence of an intense band at 2827 cm-1 in 9a may

be explained by a strong νs (CH2) stretching vibrations. However, a weak band appears at

2826 cm-1 in case of 9b. The band at 2950 cm-1, which attributed to ν(NH) stretching

vibration, appearing only on 9a. The absence of this band in 9b indicates that the terminal NH

groups in poly(benzophenone co-piperazine) are interacted with the silanol groups to form

SiO-…H-NH+. The C = O stretching mode of carbonyl appears at 1586 and 1598 cm-1 in 9a

and 9b, respectively. The shape of the ν(C = O) band in case of 9b is sharp and blue shifted

(12 cm-1) from that of 9a. This is an indication that in the hybrid 9b the carbonyl group is not

involved in the same kind of interactions (intermolecular hydrogen bonding between the

carbonyl and the NH groups) as in the neat polymer 9a. The peaks at 944 and 1229 or 1225

cm-1 in 9a and 9b are assigned to the symmetric and anti-symmetric stretching bands of the

amine group, respectively, i.e. νs(NC2) and νas(NC2). The peaks observed at 1548 and 1541

cm-1 in 9a and 9b is associated with the NH bending coupled with C-N stretching vibrations.

The low frequency bands at 456 and 452 cm-1 in LiChroprep Si 60 and 9b are attributed to

rocking motions of the oxygen atoms perpendicular to the Si-O-Si plane. On both LiChroprep

Si 60 and 9b spectra, the broad bands at 1098 and 1095 cm-1, characteristic of the

antisymmetric stretching vibration of the Si-O-Si, and the more intense bands at 801 and 812

cm-1 (Si-O-Si symmetric stretching vibrations) are observed.

3.3.1.3 Solid-state NMR

29Si NMR. Solid-state {1H}-29Si CP MAS NMR spectra of LiChroprep Si 60 and

poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b are depicted in Figure 29.

The spectrum of LiChroprep Si 60 reveals three signals at -111.32, -102.05, and -92.69 ppm

(Figure 29 [A]). However, in the case of poly(benzophenone co-piperazine) modified

LiChroprep Si 60 9b, the spectrum represents three peaks at -112.29, -102.67, and -91.95 ppm

(Figure 29 [B]). These signals are usually assigned to the 4Q, 3Q, and 2Q species, respectively.

The raw data from the CP technique reveal that the 4Q:3Q:2Q ratios are 1.0:7.7:0.4 for

LiChroprep Si 60 and 0.7:2.2:0.5 for 9b. There is, however, low cross-polarization efficiency

with the 4Q species because there are fewer H atoms nearby to facilitate the transfer of

polarization. It is reasonable to assume that only 3Q- and 2Q-type silicones provide sites for

adsorption.


-190-190-180-180-170-170-160-160-150-150-140-140-130-130-120-120-110-110-100-100-90-90-80-80-70-70-60-60-50-50-40-40-30-30-20-20-10-1000 [A]

-190-190-180-180-170-170-160-160-150-150-140-140-130-130-120-120-110-110-100-100-90-90-80-80-70-70-60-60-50-50-40-40-30-30-20-20-10-1000 [B]

Figure 29. 29Si CP/MAS NMR spectra of [A] LiChroprep Si 60 and [B] poly(benzophenone-

co-piperazine) modified LiChroprep Si 60 9b.

Q4

Q2

Q3

Q2

Q4

Q3


The 1H-29Si CP MAS provides more information on the interaction between polymer

chains and the silica surface. The three sites, 4Q, 3Q, and 2Q, are distinguished not only by

their different chemical shifts, but also by the strength of the dipolar interactions with the

protons of the organic species (the heteronuclear dipolar interaction is inversely proportional

to the cube of the internuclear distances).123

13C NMR. The 13C-{1H} CP MAS NMR spectra of poly(benzophenone co-piperazine)

9a and poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b are shown in Figure

30. Complete resolution of the signals from all nonequivalent carbon sites was obtained for 9a

and 9b. The assignment of the signals was made on the basis of comparison of these spectra

with the spectrum obtained from the model compound MK(pipaz)2 4d in CD3OD (see

experimental section). The signals of the neat polymer 9a have been compared to the

spectrum of the composite polymer 9b. Significant differences are not observed. The

resonance of the carbonyl carbon of the silica composite shows a downfield chemical shift of

about half ppm. Furthermore, a clear increase in the line width at half height (LWH) is present

(C=O9a: 191.86 ppm, LWH = 166.45 Hz; C=O9b: 192.28, LWH = 127.42 Hz) (Figure 30).

-25-2500252550507575100100125125150150175175200200225225250250

[A]

NCH2 ArC-4,4’

C = O

ArC-1,1’

ArC-2,6,2’,6’ ArC-3,5,3’,5’


-25-2500252550507575100100125125150150175175200200225225250250 [B]

Figure 30. 13C-{1H} CP/MAS NMR spectra of [A] poly(benzophenone co-piperazine) 9a and

[B] poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b.

Therefore, at a level of a few angstroms the polymer chains and LiChroprep Si 60 in

the synthetic composite 9b do not interact strongly, nor do the polymer chains change their

conformational arrangement, even though the carbonyl feels a different environment. The

small variation in the chemical shifts and the broadening of the resonance of this carbon can

be explained considering that a fraction of polymer chain carbonyls in close contact with the

surface Si-OH groups of LiChroprep Si 60. The formation of hydrogen bonds between these

carbonyls and Si-OH groups determine a slight decrease in electron density on the carbonyl

and a low field shift of the carbon resonance.124

3.3.1.4 Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) analysis

Successful MALDI-TOF analysis is highly dependent upon matrix selection and

sample preparation.125 1,8,9-Trihydroxyanthracene (dithranol) is the most applicable and

reproducible matrix. Therefore, it was used for the analysis of the samples examined in this

study.

NCH2

ArC-3,5,3’,5’

ArC-1,1’

ArC-2,6,2’,6’

C = O

ArC-4,4’


0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

0 200 400 600 800 1000 1200 1400

m/z

a. i.

38.9

227.2

549.3

615.3747.2

813.3

[A]

0

25

50

75

100

125

150

175

200

225

990 1090 1190 1290 1390 1490

m/z

a. i. 1011.2

1009.2

1077.3

1143.3 1275.3

1407.3

1341.4

[B]

Figure 31. MALDI-MS spectrum of the soluble fraction of poly(benzophenone co-

piperazine) 9a in HFP.


Figure 31 represents the positive-ion MALDI spectrum of poly(benzophenone co-

piperazine) 9a. This spectrum shows a series of peaks corresponding to a distribution of

oligomers with increasing degree of polymerization. The presence of three ion series as

shown in Figure 31 indicates that 9a contains alternating copolymer chains with three

different end group arrangements (piperazine, 4,4-difluorobenzophenone, and the mixture of

piperazine/4,4-difluorobenzophen-one) as shown in Chart 11.

N N C

O

N NH H

F C

O

N N C

O

F

F C

O

N N C

O

N N H

n

n

1

2

3

n = 1, 2, 3, 4, 5 M = 351.2, 615.3, 879.4, 1143.4, 1407.3

n = 1, 2, 3, 4 M = 483.2, 747.2, 1011.2, 1275.3

n = 1, 2, 3, 4 M = 549.3, 813.3, 1077.3, 1341.4

n

Chart 11. Possible alternating copolymer chains present in poly(benzophenone co-peprazine)

9a.

The spectrum shows two peaks at 38.9 and 227.2 for potassium ion and the matrix

respectively. However, the peaks at 351.2, 615.3, 879.4, 1143.4, and 1407.3 are related to the

copolymer chain with piperazine end group, whereas, the peaks at 483.2, 747.2, 1011.2, and

1275.3 are belong to the chain with 4,4-difluorobenzophenone end group. The last chain

series, which contains piperazine/4,4-difluorobenzophenone end group, shows peaks at 549.3,

813.3, 1077.3, and 1341.4. Poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b

shows the same spectrum pattern of 9a. It is worth to note that, the presence of an isotopic

distribution at the left from every main peak.


3.3.2 Characterization

3.3.2.1 Electrokinetic data

The zeta (ζ) potential, formally defined as the electrical potential at the electrokinetic

plane of shear, is a very important property of charged solid-liquid interfaces because the

actual surface electric potential cannot be determined experimentally.126 The studies of the

influence of pH, ion concentration, surface active agent, etc. on the ζ potential provide

valuable information regarding the nature of solid surfaces.127 The acidity or basicity of solid

surfaces can be determined qualitatively by the pH that corresponds to a zero ζ potential

(isoelectric point, IEP). At this pH, the number of negative charges equals the number of

positive ones. If specifically adsorbed ions are lacking from the Stern layer,128 these charges

may be attributed to the dissociation of acidic or basic groups. In the case of low IEP values,

the number of acidic groups dominates. When the IEP lies in the alkaline pH range, basic

group dominate.

The results of electrokinetic measurements on LiChroprep Si 60 (reference sample),

poly(benzophenone co-piperazine) 9a, and poly(benzophenone co-piperazine) modified

LiChroprep Si 60 9b are shown in Figure 32. For all surfaces tested the ζ potential becomes

more negative with increasing pH. As expected, the ζ potential calculated for a reference

sample (solid circles) is negative across the pH range tested (3 < pH < 10). The trend

observed suggests the IEP to be around pH 2.5-3.

The other two samples tested resulted in curves characteristic of amphoteric surfaces,

with acidic and basic functional groups. The ζ potential of the poly(benzophenone co-

piperazine) 9a (inverse triangles) varies almost linearly with solution pH over the range from

6.5 to 10, and the IEP occurs at pH of ca 8.5. Below pH 6, the ζ potential appears to saturate

at a value of ca. +50 mV. The ζ potential of poly(benzophenone co-piperazine) modified

LiChroprep Si 60 9b (triangles) is neutrally charged at pH value of ca. 7.5.


2 3 4 5 6 7 8 9 10-50

-40

-30

-20

-10

0

10

20

30

40

50

60

LiChroprep Si 60 (EKA) 9b (Zetasizer 3) 9a (Zetasizer 3)

ζ po

tent

ial (

mV

)

pH (0.001 mol/l KCl)

Figure 32. Zeta (ζ) potential data of LiChroprep Si 60 (reference sample),

poly(benzophenone co-piperazine) 9a powder, and poly(benzophenone co-piperazine)

modified LiChroprep Si 60 9b particles as function of pH measured in the presence of 0.001

M KCl.

The model used in the calculation was the Helmholtz Smoluchowski limit (k a >> 1)

for which the general relationship related to ζ potential given by:127a

,0 ζη

εευ=

E (38)

where k is the inverse double-layer thickness (Debye Hückel length), a is the particle radius, υ

is the particle velocity, E is the field strength, ε and ε0 are the relative and absolute dielectric

constant respectively, η is the viscosity of the liquid, and ζ is the zeta potential.


3.3.2.2 Thermal stability

The thermal stability of the poly(benzophenone co-piperazine) 9a and

poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b was investigated in the

temperature range from 30 °C to 700 °C in a helium atmosphere and over 700 to 850 °C in air

(flow rate 20 ml/min) by thermogravimetric analysis (TGA).

100 200 300 400 500 600 700 8000

10

20

30

40

50

60

70

80

90

100 9b 9a

Wei

ght L

oss (

%)

Temperature (°C)

Figure 33. Thermograms of poly(benzophenone co-piperazine) 9a and poly(benzophenone

co-piperazine) modified LiChroprep Si 60 9b measured from 30 to 700 °C in a helium

atmosphere and over 700 to 850 in air (flow rate 20 ml/min).

The neat polymer 9a showed the main weight loss (79.762 %) at 460 °C, indicating a

good thermal stability. However, below 200 °C, the weight loss of 3.607 % is attributed to the

evaporation of water and the thermal decomposition of the residual organic solvents. Over

700 °C, the weight loss obtained from the oxidation of the residual polymeric material is

15.649 %.


Figure 33 shows also the TGA curve of the powder 9b. The weight loss occurs at four

stages, namely, below 200 °C, between 200 and 455 °C, from 455 °C to 700 °C, and between

700 and 750°C (switch to air). Below 200 °C, therefore, the weight loss (3.081 %) is

considered to be due to the evaporation of water and the volatilization and the thermal

decomposition of the remnant of organic solvents. Between 200 and 455 °C, the weight loss

(12.283 %) is attributed to the carbonization or the decomposition of the organic polymer, that

is to say, this weight reduction is due to the loss of carbon, hydrogen, nitrogen, and oxygen.

Between 455 and 700 °C, the weight losses (5.709 %) are probably ascribed to the

further decomposition of the organic polymer. From 700 to 750°C, the weight loss (9.749 %)

is attributed to combustion (air oxidation) of the residual organic polymer, which entrapped or

covalently bonded to the surface of LiChroprep Si 60. As there is no major weight loss

afterwards, it can be considered that, for the powdered sample, the organic polymer has been

completely burnt off. Calculation of the weight loss for every stage with respect to the total

weight loss (30.759 %) for the composite polymer give a weight losses of 9.81, 39.93, 18.56,

and 31.69 % for the previous four stages. Thermal analysis results therefore indicated that this

composite polymer has good thermal stability and the LiChroprep Si 60 enhances this

stability.

Thermally induced phase transition behavior of poly(benzophenone co-piperazine) 9a

was investigated with differential scanning calorimetry (DSC) in a nitrogen atmosphere. DSC

thermogram of 9a obtained with a higher sensitivity is reproduced in Figure 34.


100 120 140 160 180 200 220 240-2

0

2

4

6

8

10

12

183 °C

202 °C

164.5 °C

152 °C

129 °C

122 °C

First run Second run

Nor

mal

ized

hea

t flo

w r

ate

Wg-1

end

o up

Temperature (°C)

Figure 34. DSC thermogram of poly(benzophenone co-piperazine) 9a obtained under a

nitrogen atmosphere at the heating rate of 10 °C/min.

As seen from Figure 34, 9a displays two distinctive endothermic peaks at 152 and 202

°C in the first heating scan, meaning that it has crystalline nature.

3.3.2.3 N2 adsorption/desorption data

Adsorption/desorption isotherms of nitrogen for the LiChroprep Si 60 R1,

poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b, and their calcined (800 °C)

analogue R2 and 9c were obtained at 77 K using a Sorptomatic 1900 automatic gas

adsorption instrument. Several pore characteristics calculated from them are listed in Table

19. The specific surface areas were calculated by using the Brunauer-Emmett-Teller (BET)

equation from the adsorption isotherm at P/P0 ranged from 0.05 to 0.3.


Table 19. Specific surface calculations for LiChroprep Si 60 R1, poly(benzophenone co-

piperazine) modified LiChroprep Si 60 9b, and their calcined analogue R2 and 9c,

respectively.

In hybrid 9b, in which poly(benzophenone co-piperazine) was present, the surface

area and specific pore volume of the material were reduced compared to neat LiChroprep Si

60 R1. This might be expected since the oligomer will have occupied some of the pore

volume within the R1. As evident from Table 19, the surface area of the calcined LiChroprep

Si 60 R2 (346.431 m2/g) is larger than that of non calcined probe R1 (346.072 m2/g). On the

other hand, the surface area of the calcined poly(benzophenone co-piperazine) modified

LiChroprep Si 60 9c (84.105 m2/g) is smaller than that of non calcined probe 9b (116.697

m2/g). This result shows the occurrence of pore size modification during the formation of the

poly(benzophenone co-piperazine) on the surface of LiChroprep Si 60. Also, the result may

be ascribed to the presence of a specific interaction such as a strong intermolecular hydrogen

bond between the NH end groups of the polymer and the silanol groups of LiChroprep Si 60

or the condensation of piperazine and 4,4’-difluorobenzophenone monomers within the

mesopores to form oligomers.

The pore specific volume of R1 (0.686 cm3/g) is the largest among the other three

samples, indicating that the average pore size of that sample is the largest.

3.3.3 Solvatochromic analysis

The UV/Vis spectroscopic properties of the oligomer 9a and the composite polymer

9b were measured in diverse solvents with different polarity and hydrogen bonding ability.

30 Brunauer-Emmett-Teller method. 31 Dollimore-Heal method.

R1 9b R2 9c

Monolayer volume (cm3/g) 79.498 26.807 79.581 19.320

Specific surface area (m2/g) 346.072 116.679 346.431 84.105

C value of BET equation30 107.901 131.379 85.174 117.267

Correlation factor 0.999 0.999 0.999 0.999

Pore specific volume (cm3/g) 0.686 0.337 0.634 0.341

Total Adsorbed volume (cm3/g) (Dol./Heal)31 535.886 332.818 429.997 242.509

Cumulative area max. (m2/g) 547.818 160.425 527.427 114.892

Pore volume max. (cm3/g) 0.802 0.358 0.746 0.374


The UV/Vis absorption maxima of 9a have been compared to the data of 9b, and as shown

from Table 20 no changes are evident. However, a strong bathochromic UV/Vis shift,

especially in a strong HBD solvents like HFP (∆ν max = 3790 cm-1), by a comparison of these

UV/Vis absorption maxima with the data of the model compound 4d (Table 3, vide supra), is

observed. The UV/Vis spectra of 9b were measured as suspension in different solvents.

However, no absorption band for the supernatant solution was recorded.

Table 20. UV/Vis absorption maxima of poly(benzophenone co-piperazine) 9a, and

poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b measured in diverse

solvents

solvent νmax 9a /103

cm-1

νmax 9b /103

cm-1

p-Xylene 29.33 29.67

1,2-Dichloroethane 28.74 28.82

Formic acid 28.33 28.65

Dimethylsulfoxide 28.09 28.09

Methanol 27.93 28.01

Acetic acid 27.78 27.86

2,2,2-Trifluoroethanol 27.10 27.10

1,1,1,3,3,3-Hexafluoro-2-propanol 25.45 25.58

A representative collection of solvent dependent UV/Vis spectra of 9a is shown in Figure 35.


350 400 450 500 550 600 650 700

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

23

45

1

1: 9a in p-xylene 2: 9a in TFE 3: 9a in HFP 4: 9a in DMSO 5: 9a in 1,2-DCE

Abs

orba

nce

(a.u

.)

λ (nm)

[A]

350 400 450 500 550 600 650 700

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

9a 9b

Abs

orba

nce

(a.u

.)

λ (nm)

[B]

Figure 35. UV/Vis absorption spectra of [A] poly(benzophenone co-piperazine) 9a in p-

xylene, 2,2,2-trifluoroethanol (TFE), 1,1,1,3,3,3-hexafluoro-2-propanol (HFP), dimethyl-

sulfoxide (DMSO), and 1,2-dichloroethane (DCE) and [B] UV/Vis reflectance spectra of 9a

and its composite form 9b.


With increasing solvent polarity from p-xylene to HFP, the UV/Vis spectrum of 9a

shows a bathochromic shift of the solvatochromic long-wavelength UV/Vis band (Table 20

and Fig. 35A). The solvatochromic effect of 9a shows that the long-wavelength UV/Vis

absorption maximum ranges from λ = 341 nm in p-xylene to 393 nm in HFP, corresponding

to ∆λ = 52 nm (∆ν =4080 cm-1) stabilization energy between these two solvents of extremely

different polarity.

As shown from Figure 35B, the diffuse reflectance spectra of 9a and 9b powders

revealed two absorption maxima at λmax = 349 and 346 nm respectively. The 9a powder

shows a broad UV/Vis absorption section in the diffuse reflectance spectrum.

The measured νmax data for 9a and 9b were fitted by multiple regression in order to evaluate

the respective contributions of the nonspecific and specific, intermolecular forces to the

overall interaction between 9a or 9b and solvent molecules.

νmax *10-3 [9a] = 30.60 – 2.58 π* - 1.34 α + 0.54 β (39)

n = 8 r = 0.90 SD = 0.68 F = 0.0641

νmax *10-3 [9b] = 31.18 – 3.17 π* - 1.39 α + 0.53 β (40)

n = 8 r = 0.90 SD = 0.72 F = 0.0684

νmax *10-3 [9a] = 30.61 – 2.29 π* - 1.39 α (41)

n = 8 r = 0.89 SD = 0.63 F = 0.0195

νmax *10-3 [9b] = 31.18 – 2.89 π* - 1.44 α (42)

n = 8 r = 0.89 SD = 0.67 F = 0.0206

It is also worth to notice that coefficient a is significantly larger than the coefficient b

in the calculated equations 39 and 40. The significance is improved by ignoring parameter α

in the correlation analysis (eq. 41 and 42). This demonstrates that the ability of the solvent to

donate hydrogen bond is much stronger than the ability to accept hydrogen bond. However, in

the case of MK(pipaz)2 4d, the value of a is smaller than the b value and it can be ignored

from the correlation analysis (Table 5 and eq. 15). This result can be explained in terms of the

presence of the more basic secondary nitrogen atom in 4d which enhances the through space

interaction as discussed in Scheme 2 (vide supra).

Summary 119

IV Summary

This work is divided into three parts. The first part deals with the synthesis of novel

functionalized aromatic amino ketones containing bis-(hydroxyethyl)amino substituent using

three types of reactions including Friedel Craft acylation, aromatic nucleophilic substitution,

and aldol-crotonic condensation reactions. The environmental effects (solvent, solid surfaces,

sol-gel glasses and neighboring molecules in the crystal) on their UV/Vis spectra were

investigated in the second part. From these studies, a large amount of information concerning

the polarity of the solid surfaces, the substituent-effect in aromatic amino ketones on the

solvent polarity parameters, the intermolecular hydrogen bonding in solid crystals and in their

solutions, and the nature of the guest-host interactions have been obtained.

Two different processes based on nucleophilic substitution reactions for synthesis of

poly(benzophenone co-piperazine) were reported in the third part of this thesis. The structure

of this polymer had to be elucidated by spectroscopic methods (FT-IR, solid-state-NMR,

UV/Vis spectroscopy, and MALDI-mass spectroscopy).

Hydrophilically substituted derivatives of Michler’s ketone, MK(OH)2 and MK(OH)4, were

obtained through successive replacement of the dimethylamino groups by (HOCH2CH2)2N

groups. The solvatochromism of these new MK derivatives is slightly modified compared

with MK.

The influence of hydrophilic functionalities as substituents at the periphery of

heterocyclic aromatic aminoketones like Fur(OH)2 or Thi(OH)2 has been successfully studied

to achieve information on aggregation versus solvatochromic properties of polar compounds.

In organic solvents and Ormosil glasses single molecule solvation is observed. This can be

well explained in terms of empirically derived LSE relationship using the Kamlet-Taft

solvents parameter set. Depending on the nature of the aromatic moiety, 4-

(dimethylamino)phenyl, furan, or thiophene, significantly differences in the solid-state

structures and solvatochromic properties are observed which are attributed to the modified

HBD capacity of the –N(CH2CH2OH)2 group and their ability to interact with other species.

In increasing the HBD capacity of the –N(CH2CH2OH)2 substituent, indicated by an increase

of the b coefficient of the Kamlet-Taft LSErs from 4-(dimethylamino)phenyl < 2-furyl < 2-

thienyl, a bathochromic shift of the solvatochromic and crystallochromic long wave UV/Vis

π-π* transition is monitored.

Also, the influence of polar, HBD, and HBA functionalities (e.g. morpholino,

piperidino, piperazino, and N-substituted piperazines) as para-substituents at the peripheries

Summary 120

of aromatic amino ketones of Michler’s ketone type, and also of a piperazino-bridged diketo

derivative, have been studied and have provided detailed information on the solvatochromic

properties of polar compounds in relation to structural features. The influence of the solvent

on the position of the solvatochromic UV/Vis depends on the nature (polarity, basicity, and

steric requirements) of the (+ M) substituent. The stronger the (+ M) effect of the substituent,

the larger the extent of the solvatochromic effect induced by the HBD capacity of the solvent.

The introduction of basic moieties such as piperazine causes a worsening of the LSE

relationships, due to competing acid-base interactions. This sometimes makes interpretation

of the solvatochromism ambiguous.

The interaction of a solvatochromic probe with a surface environment in a solvent can

be well measured by the UV/Vis shift of the adsorbed polarity indicator when adsorbed on

silica in transparent slurries. The quantitative adsorption of the probe dye requires specific

conditions because the solvent competes with the probe. Therefore, unambiguously

measurable UV/Vis absorption maxima of the adsorbed probe cannot be measured for each

solvent used. It seems that a basic requirement is that the probe should be less basic than the

solvent used for the silica slurry. Also, care must be taken to avoid overloading the surface

with the indicator used, as multi-layer adsorption is expected in solution at higher

concentrations as well as interfering absorption from the non-adsorbed probe from the

solution. Acid-base interactions between the probe and the silica surface predominate as

shown by the correlation analyses of νmax (probe) measured at the solvent/Aerosil 300

interface with the Kamlet-Taft solvents parameter set.

Aromatic amino ketones MK(OH)2, Fur(OH)2, Thi(OH)2, MK(OH)4, and MK are a

suitable probes to study the polarity inside Ormosil cages. The results demonstrate that the

polarity varies inside Ormosils as a function of the ratio of MTMOS to TMOS. Furthermore,

the polarity observed by these entrapped ketones is more sensitive to alcohols in their

surrounding than the polarity of solvatochromic probes themselves in alkanols. Therefore,

these specific analyte results in an optical modulation of the probes by encapsulating probe

molecules in a sol-gel host presents itself as viable method for optical chemical sensors.

The synthesis and characterization of novel silica hybrids based on functionalized bis-

(hydroxyethyl)amino aromatic ketones have been reported. The solvatochromic aromatic

amino ketone –attached sol-gel monomers 8(a-c) were homo- and copolymerized with TEOS

Summary 121

by hydrolysis and polycondensation in the presence of acidified water (pH = 3). There was no

identifiable evidence of any unreacted 8a, 8b, or 8c (T0), indicating that all the triethoxysilyl

functional chromophore 8a, 8b, or 8c has been bonded to the matrix.

Salicylidene-anile HDBN, which consider also as a related compound to aromatic

amino ketones has been used as a model for investigating intra- and intermolecular D-A

(donor-acceptor) interactions in various environments by means of UV/Vis spectroscopy. The

introduction of hydrophobic and hydrophilic functionalities at the periphery of salicylidene-

aniles are expected to change solid-state structures in relation to UV/Vis absorption

properties, which makes this kind of compound promising for investigating chromophores in

terms of environmental effects relating to optical properties for application.

HDBN reflects environment influences by manifold shifts of its absorption band in the

UV/Vis spectrum. The LSE analyses show that dipolar interactions preferably contribute to

the environmentally induced color changes. Genuine solvatochromism is suppressed if mobile

protons co-interact with the dimethylamino group. This is observed in acidic aqueous media

and in sol-gel glasses. Hydroxide ions attack the 2’-hydroxy group which causes a

bathochromic shift. The intense red color of the HBDN crystal is attributed to intermolecular

interactions of the oppositely arranged dipolar molecules in the solid-state. The X-ray crystal

structures of aromatic amino ketones 2(a-c) have been determined, to learn how the influence

and control lattice hydroxy group hydrogen bonding using crystal engineering ideas. Hydroxy

group hydrogen bonding results in formation of a network helical arrays of Fur(OH)2

molecules 2b.

The crystallographic structure analysis of MK(OH)2, Fur(OH)2, Thi(OH)2, BBP, and

HDBN and their solid powder UV/Vis reflectance spectra are in accord with the proposed

solvation mechanism. If the crystals of the compounds studied are densely packed, then a new

UV/Vis band at about λ = 450 nm is observed. These effects are perhaps attributable to charge

transfer transitions due to π stacking and induced dipole-dipole interactions. These results

merit deeper theoretical and extended optical studies.

Poly(benzophenone co-piperazine) oligomer contains alternating copolymer chains

with three different end groups (piperazine, 4,4’-difluorobenzophenone, and the mixture of

piperazine/4,4’-difluorobenzophenone). LiChroprep Si 60 in the synthetic composite 9b does

not interact strongly, nor do the polymer chains change their conformational arrangement,

even though the carbonyl feels a different environment. Thermal analysis results of 9a and 9b

Summary 122

indicated that 9b has good thermal stability and the LiChroprep Si 60 enhances this stability.

The UV/Vis spectroscopic properties of the oligomer 9a and the composite polymer 9b were

measured in diverse solvents with different polarity and hydrogen bonding ability. The

UV/Vis absorption maxima of 9a have been compared to the data of 9b, and no changes are

evident.

Experimental section 123

V Experimental section

5.1 General considerations

5.1.1 Instruments

UV/Vis-spectroscopy

UV/Vis spectrometer MCS 400 diode-array spectrometer from Carl Zeiss Jena,

connected with an immersion cell (TSM 5) via glass-fiber optics. A diffuse reflectance

accessory was attached to the spectrometer for diffuse reflectance measurements, which were

carried out with properly characterized crystalline powdered samples using BaSO4 powder as

a reference.

IR-spectroscopy

The FT-IR spectra were recorded at room temperature in the wave number range from

400 to 4000 cm-1 with a resolution of 1 cm-1 using a Perkin-Elmer Fourier transform 1000

spectrometer. The samples LiChroprep Si 60, 9a and 9b were analyzed by the transmission

technique. A sample concentration of 5 % in desiccated KBr was used.

Nuclear magnetic resonance (NMR)-spectroscopy

Varian Gemini 300 FT NMR spectrometer, operating at 300 MHz for 1H and 75 MHz

for 13C. The signals of solvents (CDCl3, CD3OD, or DMSO-d6) were used as internal

standards. All measurements were made at 20 °C. All data are given as: chemical shift δ

[ppm] (multiplicity, coupling constant J, integration, correlated protons) for 1H-NMR and

chemical shift δ [ppm] (correlated carbons) for 13C-NMR.

Solid-state NMR-spectroscopy

Cross-polarization (CP) magic angle spinning (MAS) solid-state 13C and 29Si NMR

spectra were performed on the solid SiO2 xerogels using a Bruker Model Avance-400 Digital

NMR spectrometer, whose 1H, 13C, and 29Si resonance frequencies were 400.13, 100.62, and


79.49 MHz, respectively. For the CP spectra, a 5 ms contact time was applied. A MAS Bruker

probe was used with 7 mm ZrO2 rotors, and the spinning speed was set to 6 kHz for 29Si and

10 kHz for 13C. Experiments were run collecting 1000-10000 scans. Chemical shifts are given

as δ from the external polydimethylsilane (PDMS) standard.

Mass spectrometry

ESI-MS spectra were obtained with a Mariner system 5229 spectrometer (Applied

Biosystems) and the EI-MS spectrum with a MAT 95XL.

MALDI-MS analysis

All MALDI-MS were acquired using a Bruker “Biflex III”, MALDI-TOF mass

spectrometer. The instrument is equipped with a N2 laser emitting at 337 nm. All spectra were

recorded in the reflection mode with an acceleration potential of 20 kV and a reflection

potential of 26 kV. Each spectrum is a sum of 100 shots, unless otherwise noted. Polymer

samples were dissolved in HFP at 10 mg/ml. The 1,8,9-trihydroxyanthracene (dithranol)

matrix solution was prepared by dissolving 30 mg in 1 ml of HFP. Matrix and polymer

solutions were mixed in a 10:1 ratio. One to two microliters of matrix/polymer solution was

deposited onto the sample target and air-dried.

Elemental analysis

C, H, N, S quantitative analyses were performed with a Vario-EL from the company

Elementaranalysen GmbH, Hanau.

Thermogravimetric analysis (TGA)

TGA of poly(benzophenone co-piperazine) modified LiChroprep Si 60 9b was

performed using a Perkin-Elmer PE PC Series TGA-7 thermogravimetric analyzer at a

heating rate of 20 °C/min.

Differential scanning calorimetry (DSC) measurements


DSC measurements were recorded using a Perkin-Elmer DSC-7 thermal analyzer, in

dry nitrogen atmosphere, with a temperature scanning rate of 10 °C/min. The DSC analyzer is

modified by equipment for program control and data acquisition (ifa GmbH Ulm, Germany).

Electrokinetic measurements

Electrophoresis measurements were performed with a Zetasizer 3 (Malvern, UK). The

velocity of the particles in an electric field of 150 V was measured by Laser Doppler

Anemometric using a He/Ne laser beam. The measuring fluid was a 0.001 M KCl solution

with different pH values between 3 and 10. A commercial Electrokinetic Analyser (EKA)

streaming potential measurement apparatus (Anton Paar KG, Graz, Austria) was used for

LiChroprep Si 60 (reference probe).

N2 adsorption/desorption measurement

N2 adsorption isotherms were measured at 77 K using a Sorptomatic 1900 automatic

gas adsorption apparatus. The pore-size distribution (PSD) was performed by the Dollimore-

Heal (DH) method from which the pore volume was calculated. The surface area was

obtained from the BET (Brunauer-Emmett-Teller) plot.

5.1.2 Working procedures

All experiments were carried out under an atmosphere of argon. Solvents for the

solvatochromic measurements were used as commercially available in the highest available

quality (analytical or spectroscopic grade) and were additionally dried and purified according

to the usual standard methods.1a, 129, 130

5.1.3 Correlation analysis

Multiple regression analysis was performed with the Origin 5.0 statistic programs.

5.1.4 Starting Materials


The reagents were of analytical grade and purchased from Lancaster, Aldrich and

Acros. Michler’s ketone was purchased from Merck (Darmstadt), recrystallized twice from

EtOH, and carefully dried before use. The Solvents were dried and distilled as usual. Merck

silica gel 60 (70-230 mesh ASTM) was used for column chromatography. As adsorbents,

Aerosil 300 (BET-surface area 240 m2g-1) was heated at 400 °C for 12 h. After cooling to

room temperature under dried argon, a solution of the probe dye in the corresponding solvent

(about 10-5 mol/dm3) was added to Aerosil 300. Care must be taken to avoid overloading the

surface with the dye used, as multilayer adsorption is expected in solution at higher

concentrations as well as interfering absorptions from the non-adsorbed dye from the solution.

Merck LiChroprep Si 60(40-63 µm) was used as a carrier in synthesis of poly(benzophenone

co-piperazine).

5.2 Synthetic part

5.2.1 Aromatic amino ketones by Friedel Craft acylation reaction

5.2.1.1 General procedure for preparation of 4-Dimethylamino-4’-[di(2-acetoxyethyl)amino]-

benzophenone MK(OAc)2 1a, [4-Di(2-acetoxyethyl)aminophenyl]-2-furylmethanone

Fur(OAc)2 1b, and [4-Di(2-acetoxyethyl)aminophenyl]-2-thienylmethanone Thi(OAc)2 1c

The synthesis of [di(2-acetoxyethyl)amino]benzene was previously described.131

A solution of 52.50 mmol of acid chloride [4-(dimethylamino)benzoyl chloride, 9.64 g, furyl-

2-carbonyl chloride, 6.85 g, 5.19 mL, or thienyl-2-carbonyl chloride, 7.33 g, 5.34 mL] in 30

mL of 1,2-dichloroethane was gradually added to a suspension of anhydrous AlCl3 (8.00 g, 60

mmol) in 20 mL 1,2-dichloroethane at 23 °C. The reaction mixture was Further stirred for 1 h

and then treated with a solution of [di(2-acetoxyethyl)amino]benzene (9.64 g, 50 mmol) in 20

mL 1,2-dichloroethane for 1 h at 23 °C and kept stirring for 4 h at the same temperature. Then

the reaction mixture was poured into water, acidified with 1 N HCl, and extracted with ethyl

acetate. The ethyl acetate extract was washed with water, dried over Na2SO4, and evaporated

under reduced pressure. The residue was purified by column chromatography on silica gel 60

with a mixture from ethyl acetate and n-hexane (2:1) as eluant, affording MK(OAc)2 1a,

Fur(OAc)2 1b, or Thi(OAc)2 1c.

5.2.1.2 4-Dimethylamino-4’-[di(2-acetoxyethyl)amino]benzophenone MK(OAc)2 1a


Yield ((10.91 g, 26.45 mmol, 53%), pale yellow viscous oil, C23H28N2O5 [412.20], MS

(EI) m/z (RA, %) 413 (M++1, 1.5), 412 (M+, 4), 339 (15), 148 (30), 106 (26), 87 (100), 45

(15), 43 (81); MS (ESI) 413.2 (M++1); 1H-NMR (CDCl3): δ 7.66 (dd, J = 9.06, 3.02 Hz, 4H,

ArH-2,6,2’,6’), 6.68 (d, J = 9.06 Hz, 2H, ArH-3,5), 6.56 (d, J = 9.06 Hz, 2H, ArH-3’,5’), 4.16

(t, J = 5.91 Hz, 4H, CH2-O), 3.59 (t, J = 5.91 Hz, 4H, CH2-N), 2.91 (s, 6H, N-CH3), 1.94 (s,

6H, C-CH3), 13C-NMR (CDCl3): δ 192.9 (C=O), 170.2 (C=O ester), 152.2 (ArC-4), 149.5

(ArC-4’), 131.7 (ArC-2,6), 131.6 (ArC-2’,6’), 126.2 (ArC-1), 125.2 (ArC-1’), 110.1 (ArC-

3,5), 109.9 (ArC-3’,5’), 60.7 (CH2-O), 49.1 (CH2-N), 39.6 (N-CH3), 20.4 (C-CH3).

5.2.1.3 [4-Di(2-acetoxyethyl)aminophenyl]-2-furylmethanone Fur(OAc)2 1b

Yield (8.62 g, 23.99 mmol, 48%), m.p. 72°C (ethyl acetate), pale-yellow crystals

(Found: C, 63.52; H, 5.75; N, 3.89. C19H21NO6 [359.14], calc. C, 63.51; H, 5.85; N, 3.90%); 1H-NMR (CDCl3): δ 8.04 (d, J = 9.16 Hz, 2H, ArH-2,6), 7.67 (s, 1H, FurH-5’), 7.22 (d, J =

3.48 Hz, 1H, FurH-3’), 6.82 (d, J = 9.16 Hz, 2H, ArH-3,5), 6.58 (dd, J = 3.48, 1.74 Hz, 1H,

FurH-4’), 4.30 (t, J = 6.16 Hz 4H, CH2-O), 3.73 (t, J = 6.16 Hz, 4H, CH2-N), 2.07 (s, 6H, C-

CH3); 13C-NMR (CDCl3): δ 180.8 (C=O), 171.2 (C=O ester), 153.5 (FurC-2’), 151.3 (ArC-4),

146.4 (FurC-5’), 132.5 (ArC-2,6), 126.0 (ArC-1), 119.1 (FurC-3’), 112.3 (FurC-4’), 111.3

(ArC-3,5), 61.4 (CH2-O), 49.9 (CH2-N), 21.2 (C-CH3).

5.2.1.4 [4-Di(2-acetoxyethyl)aminophenyl]-2-thienylmethanone Thi(OAc)2 1c

Yield (9.75 g, 25.97 mmol, 52%), green oil, (Found: C, 59.31; H, 5.64; N, 3.53; S,

8.66. C19H21NO5S [375.11], calc. C, 60.80; H, 5.60; N, 3.73; S, 8.53%); 1H-NMR (CDCl3): δ

7.90 (d, J = 9.16 Hz, 2H, ArH-2,6), 7.65 (d, J = 4.58 Hz, 2H, ThiH-3’,4’), 7.15 (t, J = 4,35 Hz,

1H, ThiH-5’), 6.82 (d, J = 9.16 Hz, 2H, ArH-3,5), 4.30 (t, J = 6.16 Hz 4H, CH2-O), 3.73 (t, J

= 6.16 Hz 4H, CH2-N), 2.07 (s, 6H, C-CH3); 13C-NMR (CDCl3): δ 186.5 (C=O), 171.3 (C=O

ester), 151.2 (ThiC-2’), 144.5 (ArC-4), 133.6 (ThiC-4’), 133.0 (ThC-5’), 132.4 (ArC-2,6),

128.0 (ThiC-3’), 126.8 (ArC-1), 111.3 (ArC-3,5), 61.5 (CH2-O), 50.0 (CH2-N), 21.2 (C-CH3).

5.2.1.5 General procedure for preparation of 4-Dimethylamino-4’-[di(2-hydroxyethyl)amino]-

benzophenone MK(OH)2 2a, [4-Di(2-hydroxyethyl)amino-phenyl]-2-furylmethanone

Fur(OH)2 2b, and [4-Di(2-hydroxyethyl)aminophenyl]-2-thienylmethanone Thi(OH)2 2c


4-(Dimethylamino)-4’-[di(acetoxyethyl)amino]benzophenone MK(OAc)2 (0.41 g, 1

mmol), [4-di(2-acetoxyethyl)aminophenyl]-2-furylmethanone Fur(OAc)2 (0.36 g, 1 mmol) or

[4-di(2-acetoxyethyl)aminophenyl]-2-thienylmethanone Thi(OAc)2 (0.38 g, 1 mmol) was

added to a solution of potassium carbonate (0.28 g, 2 mmol) dissolved in methanol and water

20 mL (1:1). The mixture was refluxed for 2 h at 80°C in a water bath. After cooling to room

temperature, the mixture was poured into ice water and neutralized with conc. HCl. The

precipitate was filtered off, washed with water, and crystallized from ethanol to give pure

compound 2a, 2b, or 2c.

5.2.1.6 4-Dimethylamino-4‘-[di(2-hydroxyethyl)amino]benzophenone MK(OH)2 2a

Yield (0.29 g, 0.88 mmol, 88%), m.p. 161-162°C as yellow needles. (Found: C, 69.40;

H, 7.42; N, 8.41; C19H24N2O3 [328.18], requires C, 69.49; H, 7.37; N, 8.53%); 1H-NMR

(CD3OD): δ 7.66 (dd, J = 9.06, 4.39 Hz, 4H, ArH-2,6,2’,6’), 6.81 (d, J = 9.06 Hz, 2H, ArH-

3,5), 6.76 (d, J = 9.06 Hz, 2H, ArH-3’,5’), 3.77 (t, J = 5.91 Hz, 4H, CH2-O), 3.65 (t, J = 5.91

Hz, 4H, CH2-N), 3.06 (s, 6H, N-CH3); 13C-NMR (CD3OD): δ 197.1 (C=O), 155.1 (ArC-4),

153.2 (ArC-4’), 134.0 (ArC-2,6), 133.8 (ArC-2’,6’), 127.2 (ArC-1), 122.3 (ArC-1’), 112.22

(ArC-3,5), 112.16 (ArC-3’,5’), 60.6 (CH2-O), 55.2 (CH2-N), 40.6 (N-CH3); MS (EI) m/z (RA,

%) 329 (M++1, 3), 328 (M+, 12.5), 298 (19), 297 (100), 148 (64), 132 (23), 45 (15), 43 (100),

31 (21); MS (ESI) 329.2 (M++1).

5.2.1.7 [4-Di(2-hydroxyethyl)aminophenyl]-2-furylmethanone Fur(OH)2 2b

Yield (0.23 g, 0.85 mmol, 85%), m.p. 94°C, yellow crystals (Found: C, 65.21; H, 6.16;

N, 5.07. C15H17NO4 [275.12], calculated: C, 65.45; H, 6.18; N, 5.09%); 1H-NMR (CD3OD): δ

7.97 (d, J = 9.32 Hz, 2H, ArH-2,6), 7.85 (dd, 1H, J = 1.74, 0.79 Hz FurH-5’), 7.29 (dd, J =

3.63, 0.79 Hz, 1H, FurH-3’), 6.86 (d, J = 9.32 Hz, 2H, ArH-3,5), 6.69 (dd, 3.63, 1.74 Hz, 1H,

FurH-4’), 3.80 (t, J = 6.16 Hz, 4H, CH2-O), 3.68 (t, J = 6.16 Hz, 4H, CH2-N); 13C-NMR

(CD3OD): δ 181.3 (C=O), 153.2 (FurC-2’), 152.7 (ArC-4), 147.0 (FurC-5’), 132.2 (ArC-2,6),

124.1 (ArC-1), 119.4 (FurC-3’), 112.1 (FurC-4’), 111.2 (ArC-3,5), 59.2 (CH2-O), 53.7 (CH2-

N).

5.2.1.8 [4-Di(2-hydroxyethyl)aminophenyl]-2-thienylmethanone Thi(OH)2 2c


Yield (0.26 g, 88%) , m.p. 101°C, canary-yellow crystals (Found: C, 61.69; H, 5.84;

N, 4.73; S, 11.32. C15H17NO3S [291.09], calculated: C, 61.86; H, 5.84; N, 4.81; S, 11.00%); 1H-NMR (CD3OD): δ 7.85 (d, J = 9.32 Hz, 2H, ArH-2,6), 7.71 (dd, J = 3.79, 1.1 Hz, 2H,

ThiH-3’,4’), 7.23 (dd, 3.79, 4.90 Hz, 1H, ThiH-5’), 6.87 (d, J = 9.32 Hz, 2H, ArH-3,5), 3.80

(t, J = 6.16 Hz, 4H, CH2-O), 3.68 (t, J = 6.16 Hz, 4H, CH2-N); 13C-NMR (CD3OD): δ 187.2

(C=O), 152.5 (ThiC-2’), 144.1 (ArC-4), 133.9 (ThiC-4’), 133.1 (ThiC-5’), 132.2 (ArC-2,6),

127.9 (ThiC-3’), 124.9 (ArC-1), 111.2 (ArC-3,5), 59.2 (CH2-O), 53.8 (CH2-N).

5.2.2 Aromatic amino ketones by nucleophilic aromatic substitution reaction

5.2.2.1 4,4’-Bis[di(2-hydroxyethyl)amino]benzophenone MK(OH)4 3

A mixture of 7.64 g (35 mmol) of 4,4’-difluorobenzophenone and 70.00 g (666 mmol)

of diethanolamine was stirred at 150-160 °C for 48 h. The resulting reaction mixture was

distilled under reduced pressure to remove the excess of diethanolamine. The residue was

purified by column chromatography on silica gel using a mixture of ethanol and ethyl acetate

(1:1), affording (3) (8.15 g, 21 mmol, 60%) as a pure yellow viscous oil; C21H28N2O5

[388.20], MS (DEI) m/z (RA, %) 388 (M+, 2), 357 (3.5), 208 (2.5), 180 (3), 132 (10.5), 61

(14.5), 45 (84), 43 (100), 31 (30); MS (ESI) 389.2 (M++1); 1H-NMR (CD3OD): δ 7.63 (d, J =

8.79 Hz, 4H, ArH-2,6,2’,6’), 6.78 (d, J = 8.79 Hz, 4H, ArH-3,5,3’,5’), 3.75 (t, J = 5.50 Hz,

8H, CH2-O), 3.62 (t, J = 5.50 Hz, 8H, CH2-N); 13C-NMR (CD3OD): δ 196.5 (C=O), 152.8

(ArC-4,4’), 133.6 (ArC-1,1’), 126.7 (ArC-2,6,2’,6’), 111.8 (ArC-3,5,3’,5’), 60.2 (CH2-O),

54.8 (CH2-N).

5.2.2.2 4,4’-Bis(4-ethoxycarbonylpiperazino)benzophenone MK(pipOEt)2 4a

4.36 g (20 mmol) of 4,4’-difluorobenzophenone and 12.66 g (80 mmol) of ethyl-N-

piperazine carboxylate was stirred at 140°C under argon for 40 h in 25 mL dimethylsulfoxide.

The resulted reaction mixture was poured into ice water. The crude material was filtered and

washed with water then crystallized from ethyl acetate to give 4a (5.93 g, 12 mmol, 60 %), m.

p. 158 as a slightly yellowish powder.

Found: C, 65.65; H, 6.84; N, 11.14; C27H34N4O5 [494.25], requires C, 65.57; H, 6.93; N,

11.33; 1H-NMR (CDCl3): δ 7.72 (d, J = 8.69 Hz, 4H, ArH-2,6,2’,6’), 6.88 (d, J = 8.69 Hz, 4H,

ArH-3,5,3’,5’), 4.16 (q, J = 7.11 Hz, 4H, COOCH2), 3.62 (t, J = 4.90 Hz, 8H, CH2NCOO),


3.30 (t, J = 4.90 Hz, 8H, CH2NPh), 1.27 (t, J = 7.11 Hz, 6H, CH3); 13C-NMR (CDCl3): δ

194.15 (C=O), 155.79 (C=O ester), 153.69 (ArC-4,4’), 132.36 (ArC-2,6,2’,6’), 129.27(ArC-

1,1’), 114.32 (ArC-3,5,3’,5’), 61.94 (OCH2), 48.00 (CH2NCOO), 43.63 (CH2NPh), 15.08

(CH3).

5.2.2.3 4,4’-Bis(piperidino)benzophenone MK(pip)2 4b

21.82 g (100 mmol) of 4,4’-difluorobenzophenone and 34.06 g (400 mmol) of

piperidine were refluxed at 140 °C under argon for 30 h in 100 mL tetramethylene sulphone.

After cooling to room temperature, the solution was poured onto cold water (2 dm3). The

resulting solid was filtered, washed thoroughly with 50 mL water, and dried under vacuum.

After crystallization from ethyl acetate, (22.62 g, 65 mmol, 65 %), m. p. 152 °C (lit.132 140-

142 °C from acetone) of a pale yellow solid crystals of MK(pip)2 4b was obtained.

Found: C, 79.19; H, 7.96; N, 7.96; C23H28N2O [348.22], requires C, 79.27; H, 8.10; N, 8.04; 1H-NMR (CDCl3): δ 7.76 (d, J = 8.69 Hz, 4H, ArH-2,6,2’,6’), 6.92 (d, J = 8.69 Hz, 4H, ArH-

3,5,3’,5’), 3.36 (t, J = 5.37 Hz, 8H, NCH2), 1.72 (m, 12H, NCH2CH2CH2), 1.27 (t, J = 7.11

Hz, 6H, CH3); 13C-NMR (CDCl3): δ 194.23 (C=O), 154.26 (ArC-4,4’), 132.46 (ArC-

2,6,2’,6’), 128.18(ArC-1,1’), 113.87 (ArC-3,5,3’,5’), 49.33 (NCH2), 25.84 (NCH2CH2), 24.77

(NCH2CH2CH2).

5.2.2.4 4,4’-Bis(morpholino)benzophenone MK(mor)2 4c

MK(mor)2 4c was prepared in a similar manner from 21.82 g (100 mmol) of 4,4’-

difluorobenzophenone and 34.85 g (400 mmol) of morpholine. After crystallization from

ethyl acetate at 50 °C, (28.16 g, 80 mmol, 80 %) , m. p. 171 °C (lit.132 162-164 °C from

ethanol) of cream needles from MK(mor)2 4c were obtained.

Found: C, 71.08; H, 6.68; N, 7.94; C21H24N2O3 [352.18], requires C, 71.57; H, 6.86; N, 7.95; 1H-NMR (CDCl3): δ 7.69 (d, J = 8.85 Hz, 4H, ArH-2,6,2’,6’), 6.82 (d, J = 8.85 Hz, 4H, ArH-

3,5,3’,5’), 3.79 (t, J = 4.90 Hz, 8H, OCH2), 3.23 (t, J = 4.90 Hz, 8H, NCH2); 13C-NMR

(CDCl3): δ 194.38 (C=O), 154.01 (ArC-4,4’), 132.39 (ArC-2,6,2’,6’), 129.38 (ArC-1,1’),

113.76 (ArC-3,5,3’,5’), 67.04 (OCH2), 48.24 (NCH2).

5.2.2.5 4,4’-Bis(piperazino)benzophenone MK(pipaz)2 4d


8.73 g (40 mmol) of 4,4’-difluorobenzophenone and 34.46 g (400 mol) of piperazine

in 50 mL dimethyl sulfoxide were stirred under argon at 140 °C for 40 h. After cooling to

room temperature, the mixture was poured into ice-water. The precipitate was filtered off ,

washed with water and crystallized at 70 °C from ethanol to give (7.35 g, 21 mmol, 52.5 %),

m. p. 170-172 °C of a pale yellow powder of MK(pipaz)2 4d; C21H26N4O [350.21], MS (EI),

m/z (relative abundance, %) 351 (M++1, 4), 350 (M+, 12), 308 (16), 256 (22), 129 (20), 97

(16), 83 (16), 73 (26), 57 (26), 45 (28), 31 (36); 1H-NMR (CD3OD): δ 7.74 (d, J = 9.00 Hz,

4H, ArH-2,6,2’,6’), 7.10 (d, J = 9.00 Hz, 4H, ArH-3,5,3’,5’), 3.62 (t, J = 5.21 Hz, 8H, NCH2),

3.31 (t, J = 5.21 Hz, 8H, CH2NH); 13C-NMR (CDCl3): δ 196.77 (C=O), 154.97 (ArC-4,4’),

133.54 (ArC-2,6,2’,6’), 130.76 (ArC-1,1’), 115.95 (ArC-3,5,3’,5’), 46.77 (NCH2), 44.80

(CH2NH).

5.2.2.6 4,4’-Bis[4-(2-hydroxyethyl)piperazino]benzophenone MK(pipazOH)2 4e

Piperazine-2-ethanol (6.51 g, 50 mmol) was added at 25 °C. to a mixture of

difluorobenzophenone (5.46 g, 25 mmol) and potassium carbonate (6.9 g, 50 mmol) in dry

dimethylsulfoxide (50 mL). After heating to 140 °C for 48 h, the solution was cooled to room

temperature, and poured into water(1 L). The precipitate was filtered off, and washed several

times with water, dried and recrystallized from ethanol to afford 4e; yield: 7.80 g (18 mmol,

71.2 %) as fine, pale yellow powder with m. p. 115-117 °C; C25H34N4O3 [438.26], MS (ESI),

m/z = 439 (M++1); 1H-NMR (DMSO-d6): δ 7.62 (d, J = 8.37 Hz, 4H, ArH-2,6,2’,6’), 7.00 (d,

J = 8.37 Hz, 4H, ArH-3,5,3’,5’), 3.60 (t, J = 5.5 Hz, 4H, CH2O), 3.28 (t, J = 5.5 Hz, 4H,

NCH2CH2O), 2.44-2.60 (m, 16H, NCH2CH2N); 13C-NMR (DMSO-d6): δ 192.67 (C=O),

153.59 (ArC-4,4’), 131.78 (ArC-2,6,2’,6’), 127.48 (ArC-1,1’), 115.51 (ArC-3,5,3’,5’), 60.56

(CH2O), 58.92 (CH2CH2O), 53.27 (NCH2), 46.87 (NCH2CH2NH).

5.2.2.7 1,4-Bis(4-benzoylphenyl)piperazine BBP 5

4-fluorobenzophenone (2.00 g, 10 mmol), potassium carbonate (1.38 g, 10 mmol), and

anhydrous piperazine (0.43 g, 5 mmol) in dimethylsulfoxide (20 mL) were heated at 140 °C

for 48 h. After cooling to room temperature, the crude reaction mixture is taken up in water

(400 mL) and the precipitate formed was filtered off, and washed several times with water,

dried and purified by column chromatography (silica gel, chloroform/ethyl acetate 2:1)

affording 5; yield: 1.78 g (4 mmol, 80.0 %) as yellow crystals with m.p. 213°C;


C30H26N2O2 [446.20], MS (ESI), m/z = 447 (M++1); 1H-NMR (CDCl3): δ 7.86 (d, J = 8.69

Hz, 4H, ArH-2,6,2’,6’), 7.78 (d, J = 8.69 Hz, 4H, ArH-8,12,8’,12’), 7.46-7.58 (m, 6H, ArH-

9,10,11,9’,10’,11’), 6.96 (d, J = 8.85 Hz, 4H, ArH-3,5,3’,5’), 3.60 (s, 8H, NCH2); 13C-NMR

(CDCl3): δ 195.57 (C=O), 153.74 (ArC-4,4’), 139.12 (ArC-1,1’), 132.96 (ArC-2,6,2’,6’),

131.98 (ArC-7,7’), 129.99 (ArC 8,12,8’,12’), 128.54 (ArC-9,11,9’,11’), 128.14 (ArC-10,10’),

113.74 (ArC-3,5,3’,5’), 47.38 (NCH2).

5.2.3 3-[4-Di(2-hydroxyethyl)amino]phenyl-1-(2-furyl)-2-propene-1-one [DAFP]

The synthesis of 4-formyl-4’-[di(2-acetoxyethyl)amino]benzene was previously

described.133

A mixture of 2-acetylfuran (1.10 g, 10 mmol), 4-formyl-4’-[di(2-acetoxyethyl)amino]-

benzene (2.93 g, 10 mmol) and 20 % aqueous sodium hydroxide (5 mL) in methanol (20 mL)

was stirred at room temperature for about 2 h. The resulting solid was washed with water (20

mL), dried and crystallized from ethanol affording DAFP 6; yield: 2.41 g (8 mmol, 80 %) as

orange crystals with m.p. 133-134 °C.

Found: C, 67.55; H, 6.29; N, 4.55; C17H19NO4 [301.13], requires C, 67.76; H, 6.36; N, 4.65; 1H-NMR (CD3OD): δ 7.83 (d, J = 8.85 Hz, 2H, ArH-2,6), 7.75 (dd, 1H, J = 1.74, 0.79 Hz

FurH-5’), 7.48 (dd, J = 3.63, 0.79 Hz, 1H, FurH-3’), 7.40 (d, J = 15.40 Hz, 1H, COCH=CH),

6.80 (d, J = 8.85 Hz, 2H, ArH-3,5), 6.71 (dd, 3.63, 1.74 Hz, 1H, FurH-4’), 6.60 (d, J = 15.90

Hz, 1H, COCH=CH), 3.77 (t, J = 5.79 Hz, 4H, CH2-O), 3.63 (t, J = 5.79 Hz, 4H, CH2-N); 13C-

NMR (CD3OD): δ 180.5 (C=O), 155.6 (FurC-2’), 152.5 (ArC-4), 148.9 (COCH=CH), 147.2

(FurC-5’), 132.5 (ArC-2,6), 124.0 (ArC-1), 119.2 (FurC-3’), 116.7 (COCH=CH), 114.1

(FurC-4’), 113.5 (ArC-3,5), 60.4 (CH2-O), 55.2 (CH2-N).

5.2.4 N-(2’-hydroxy-4’-dimethylaminobenzylidene)-4-nitroaniline [HDBN]

m-N,N-Dimethylaminophenol (13.70 g, 100 mmol) and 4-nitroaniline (15.18 g, 110

mmol) were added to a stirred solution of triethylorthoformate (16 mL, 97 mmol). The

mixture was heated under reflux for 5 min. After the reaction mixture had cooled to room

temp., methanol (30 mL) was added and the mixture was stirred for 5 min, during which time

a red precipitate formed. The red precipitate was filtered off, washed several times with water.

The resulting solid contains N,N’-bis(p-nitrophenyl)-formamidine as a yellow by-product


crystals. Crystallization from acetonitrile then benzene affording 1 yield: 24.25 g (85 %) as

red crystals with m.p.238 °C (lit.134 236 °C from acetonitrile).

Found: C, 62.89; H, 5.32; N, 14.84; C15H15N3O3 [285.11], requires C, 63.15; H, 5.30; N,

14.73; 1H-NMR (CDCl3): δ 8.45 (s, 1H, azomethine), 8.25 (d, J = 8.69 Hz, 2H, ArH-3,5),

7.26 (m, 3H, salicyl 6’, phenyl 2,6), 6.25 (d, J = 8.69 Hz, 1H, salicyl 5’), 6.12 (s, 1H, salicyl

3’), 3.10 (s, 6H, CH3); 13C-NMR (CDCl3): δ 159.51 (salicyl 4’), 157.40 (azomethine),

150.26 (C-4), 140.49 (C-2’), 130.18 (C-1), 120.76 (C-3’), 116.63 (C-2,6), 108.85 (C-3,5),

104.61 (C-1’), 100.56 (C-5’), 93.64 (C-6’), 35.67 (CH3).

5.3 Preparation of sol-gel composite and hybrid materials

5.3.1 Physical entrapment in microporous silica network

The standard molar ratio of component for all materials has been solvatochromic

probe: water: methanol: silanes = 9.5*10-4: 4.0: 5.0: 1.0, where “silanes” are composed of

various monomers ratios of tetramethoxysilane (TMOS) and methyl trimethoxysilane

(MTMOS) according to an established sol-gel procedure.75 With this synthetic procedure, five

kinds of composite materials, which had a different molar ratio of TMOS and MTMOS were

prepared (Table 20).

Table 20. Data on the preparation of the solvatochromic probes doped Ormosils: Composition of the starting solutions

Name of ormosil

MTMOS [ml]

TMOS [ml]

Solvatochromic probe [mg]

MTMOS:TMOS molar ratio

Ormosil 1A 0.24 2.23 MK(OH)2, 5.25 1:9 Ormosil 2A 0.48 1.99 MK(OH)2, 5.25 2:8 Ormosil 3A 0.72 1.74 MK(OH)2, 5.25 3:7 Ormosil 4A 0.96 1.49 MK(OH)2, 5.25 4:6 Ormosil 5A 1.20 1.24 MK(OH)2, 5.25 5:5 Ormosil 1B 0.24 2.23 Fur(OH)2, 4.40 1:9 Ormosil 2B 0.48 1.99 Fur(OH)2, 4.40 2:8 Ormosil 3B 0.72 1.74 Fur(OH)2, 4.40 3:7 Ormosil 4B 0.96 1.49 Fur(OH)2, 4.40 4:6 Ormosil 5B 1.20 1.24 Fur(OH)2, 4.40 5:5 Ormosil 1C 0.24 2.23 Thi(OH)2, 4.66 1:9 Ormosil 2C 0.48 1.99 Thi(OH)2, 4.66 2:8 Ormosil 3C 0.72 1.74 Thi(OH)2, 4.66 3:7 Ormosil 4C 0.96 1.49 Thi(OH)2, 4.66 4:6 Ormosil 5C 1.20 1.24 Thi(OH)2, 4.66 5:5 Ormosil 5D 1.20 1.24 MK(OH)4, 6.21 5:5 Ormosil 5E 1.20 1.24 MK, 4.29 5:5 Ormosil 5F 1.20 1.24 HDBN, 4.56 5:5


Taking into consideration, the molar ratio of silane mixtures (TMOS and MTMOS)

relative to the molar ratio of the other three components (solvatochromic probe, water, and

methanol) was constant in every composite. A typical example for synthesis one kind of

composites (ormosil 5[A-F]) as follow: A mixture of 1.24 mL (8.40 mmol) of tetramethoxy

silane (TMOS), 1.20 mL (8.40 mmol) of methyltrimethoxysilane (MTMOS) (molar ratio of

0.5:0.5), and 2.20 mL of methanol was sonicated for 10 min. and then 0.016 mmol of the

appropriate solvatochromic compound (5.25 mg MK(OH)2, 4.40 mg Fur(OH)2, 4.66 mg

Thi(OH)2, 4.29 mg MK, 6.21 mg MK(OH)4, or 4,56 mg HDBN) dissolved in 0.8 mL

methanol and 1.20 mL of acidic deionized water (pH = 3) to reach r = 4 (molar ratio of

H2O:Silanes) were added, followed by sonication for an additional 10 min. The mixture was

left in air at room temperature for 5 days and then at 60 °C for 2 days. The obtained solid was

ground in a mortar, and the resulting powder was heated at 120 °C for 24 h to complete the

sol-gel reaction. Matrix polarities were determined by UV/Vis absorption spectroscopy of

these materials. For solvent effects, the porous, transparent glasses were equilibrated with the

desired solvent for 30 min prior to measurements.

5.3.2 Chemical linking to the silica network

5.3.2.1 General procedure for preparation of 4-Dimethylamino-4’-[di(2-propyltriethoxysilyl-

carbamatoethyl)amino]benzophenone DPAB 8a, [4-Di(2-propyltriethoxysilylcarbamato-

ethyl)amino]-2-furylmethanone DPAF 8b, [4-Di(2-propyltriethoxysilylcarbamatoethyl)-

amino]-2-thienylmethanone DPAT 8c

3-Isocyanatopropyltriethoxysilane (0.82 g, 2.5 mmol) was added to a solution of 4-

(dimethylamino)-4’-[di(2-hydroxyethyl)amino]benzophenone MK(OH)2 (0.82 g, 2.5 mmol),

[4-di(2-hydroxyethyl)aminophenyl]-2-furylmethanone Fur(OH)2 (0.69 g, 2.5 mmol) or [4-

di(2-hydroxyethyl)aminophenyl]-2-thienylmethanone Thi(OH)2 (0.73 g, 2.5 mmol) in dry

dimethylacetamide (20 mL). The reaction mixture was stirred for 6 h at 110 °C under argon

atmosphere. This solution was used for the in situ sol-gel process. The sample for NMR

analysis was obtained by distillation under reduced pressure.

5.3.2.2 4-(Dimethylamino)-4’-[di(2-propyltriethoxysilylcarbamatoethyl)amino]benzophen-

one DPAB 8a


Yield: 1.48 g (90 %) as a yellow viscous liquid. 1H-NMR (CDCl3): δ 7.72 (d, J = 8.79 Hz, 4H, ArH-2,6,2’,6’), 6.76 (d, J = 8.79 Hz, 2H, ArH-

3,5), 6.66 (d, J = 8.79 Hz, 2H, ArH-3’,5’), 4.24 (t, J = 7.14 Hz, 4H, NCH2CH2O), 3.80 (q, J =

6.20 Hz, 12H, OCH2CH3), 3.68 (t, J = 7.14 Hz, 4H, NCH2CH2O), 3.16 (t, J = 7.30 Hz, 4H,

CH2CH2CH2Si), 3.04 (s, 6H, NCH3), 1.60 (m, 4H, CH2CH2CH2Si), 1.20 (t, J = 6.2 Hz, 18H,

OCH2CH3), 0.60 (t, J = 7.30 Hz, 4H, CH2CH2Si); 13C-NMR (CDCl3): δ 193.0 (C=O), 157.3

(CO2N), 153.0 (ArC-4), 151.5 (ArC-4’), 133.6 (ArC-2,6), 133.2 (ArC-2’,6’), 126.5 (ArC-1’),

126.0 (ArC-1’), 112.2 (ArC-3,5), 112.0 (ArC-3’,5’), 61.2 (NCH2CH2O), 58.4 (CH3CH2OSi),

50.9 (NCH2CH2O), 43.4 (CH2CH2CH2Si), 40.0 (NCH3), 24.0 (CH2CH2CH2Si), 18.3

(CH3CH2OSi), 7.5 (CH2CH2Si).

5.3.2.3 [4-Di(2-propyltriethoxysilylcarbamatoethyl)amino]-2-furylmethanone DPAF 8b

Yield: 1.37 g (91 %) as a pale yellow viscous liquid. 1H-NMR (CDCl3): δ 7.92 (d, J = 9.00 Hz, 2H, ArH-2,6), 7.55 (s, 1H, FurH-5’), 7.12 (d, J =

2.69 Hz, 1H, FurH-3’), 6.72 (d, J = 9.00 Hz, 2H, ArH-3,5), 6.48 (s, 1H, FurH-4’), 4.18 (t, J =

6.32 Hz, 4H, NCH2CH2O), 3.72 (q, J = 6.20 Hz, 12H, OCH2CH3), 3.62 (t, J = 6.32 Hz, 4H,

NCH2CH2O), 3.10 (t, J = 7.74 Hz, 4H, CH2CH2CH2Si), 1.55 (m, 4H, CH2CH2CH2Si), 1.14 (t,

J = 6.95 Hz, 18H, OCH2CH3), 0.55 (t, J = 7.74 Hz, 4H, CH2Si); 13C-NMR (CDCl3): δ 180.8

(C=O), 156.7 (CO2N), 153.5 (FurC-2’), 152.1 (ArC-4), 146.3 (FurC-5’), 132.4 (ArC-2,6),

125.6 (ArC-1), 119.2 (FurC-3’), 112.2 (FurC-4’), 111.4 (ArC-3,5), 61.6 (NCH2CH2O), 58.8

(CH3CH2OSi), 50.7 (NCH2CH2O), 43.8 (CH2CH2CH2Si), 23.6 (CH2CH2CH2Si), 18.7


5.3.2.4 [4-Di(2-propyltriethoxysilylcarbamatoethyl)amino]-2-thienylmethanone DPAT 8c

Yield: 1.38 g (89 %) as a canary yellow viscous liquid. 1H-NMR (CDCl3): δ 7.80 (d, J = 8.85 Hz, 2H, ArH-2,6), 7.57 (d, J = 4.74 Hz, 2H, ThiH-

3’,4’), 7.07 (t, J = 4.11 Hz, 1H, ThiH-5’), 6.72 (d, J = 8.85 Hz, 2H, ArH-3,5), 4.16 (t, J = 6.16

Hz 4H, NCH2CH2O), 3.80 (t, J = 6.16 Hz 4H, NCH2CH2O), 3.60 (q, J = 6.20 Hz, 12H,

OCH2CH3), 3.10 (t, J = 7.58 Hz, 4H, CH2CH2CH2Si), 1.52 (m, 4H, CH2CH2CH2Si), 1.16 (t, J

= 6.85 Hz, 18H, OCH2CH3), 0.56 (t, J = 7.58 Hz, 4H, CH2Si); 13C-NMR (CDCl3): δ 186.5

(C=O), 155.8 (CO2N), 151.2 (ThiC-2’), 145.5 (ArC-4), 133.4 (ThiC-4’), 132.9 (ThiC-5’),

132.2 (ArC-2,6), 127.6 (ThiC-3’), 126.9 (ArC-1), 111.3 (ArC-3,5), 61.4 (NCH2CH2O), 58.9


(CH3CH2OSi), 50.6 (NCH2CH2O), 43.6 (CH2CH2CH2Si), 23.7 (CH2CH2CH2Si), 18.8


5.3.2.5 General procedure for preparation of organic/SiO2 hybrid materials

The alkoxysilane containing the aromatic aminoketones (DPAB, DPAF, or DPAT)

was synthesized as mentioned above. With this synthetic procedure, four kinds of hybrid

materials, which had a different molar ratio of tetraethylorthosilicate (TEOS) and DPAB,

DPAF, or DPAT, were prepared. Table 21 summarizes the compositions obtained for

different starting mixtures of DPAB, DPAF, or DPAT and TEOS.

Table 21. Data on the preparation of the Hybrid materials: Composition of the starting solutions

A typical example for synthesis hybrid II (A-C) as follow: Tetraethylorthosilicate

(0.56 mL, 2.50 mmol) was added to a mixture of acidic water (pH = 3, 0.27 mL, 15.0 mmol)

and 10 mL of the resulting solution of dimethylacetamide containing DPAB (1.03 g, 1.25

mmol), DPAF (0.96 g, 1.25 mmol), or DPAT (0.98 g, 1.25 mmol). Various monomers were

homopolymerized and copolymerized with TEOS. The reaction mixture was stirred for 3 days

at room temperature, providing a homogeneous solution (sol). The viscosity of the reaction

mixture increased after the hydrolysis and poly condensation reaction. The sol solution was

converted into gel by drying under vacuum oven for 6 h at room temperature to remove the

residual solvent and then dried at 60 °C for 24 h. The obtained solid was ground in a mortar,

and the resulting powder was heated at 120 °C for 24 h to complete the sol-gel reaction.

Name of hybrid

Alkoxysilane 8(a-c) [g]

Tetraethylorth-osilicate [ml]

Acidic water pH = 3 [ml]

Molar ratio

Hybrid IA 1.03, 8a 0.28 0.18 1:1:8 Hybrid IB 0.96, 8b 0.28 0.18 1:1:8 Hybrid IC 0.98, 8c 0.28 0.18 1:1:8 Hybrid IIA 1.03, 8a 0.56 0.27 1:2:12 Hybrid IIB 0.96, 8b 0.56 0.27 1:2:12 Hybrid IIC 0.98, 8c 0.56 0.27 1:2:12 Hybrid IIIA 1.03, 8a 0.84 0.36 1:3:16 Hybrid IIIB 0.96, 8b 0.84 0.36 1:3:16 Hybrid IIIC 0.98, 8c 0.84 0.36 1:3:16 Hybrid IVA 1.03, 8a 1.12 0.45 1:4:20 Hybrid IVB 0.96, 8b 1.12 0.45 1:4:20 Hybrid IVC 0.98, 8c 1.12 0.45 1:4:20


5.4. Poly(benzophenone co-piperazine) 9a and its composite form 9b

5.4.1 Solution polymerization

A mixture of 4,4’-difluorobenzophenone (5.46 g, 25 mmol), piperazine (2.16 g, 25

mmol), dry dimethylsulfoxide (25 mL), and potassium carbonate (3.46 g, 25 mmol) was

stirred under argon at 140 °C for 48 h. After cooling to room temperature, the reaction

mixture was poured into water (800 mL). The produced fine precipitate was collected by

centrifugation, and washed with water, methanol, and acetone. Finally, the product was dried

in a vacuum oven at 40 °C over night affording poly(benzophenone co-piperazine) 9a, (5.28

g, 80 %), as a yellow solid.

5.4.2 Solid-state polymerization

A mixture of 4,4’-difluorobenzophenone (4.36 g, 20 mmol), piperazine (1.72 g, 20

mmol), potassium carbonate (2.76 g, 20 mmol), and LiChroprep Si 60 (10 g) as solid support

was magnetically stirred under argon at 140 °C (fusion temperature of the mixed organic

reactants) for 48 h. After cooling to room temperature, the purification of the crude solid

hybrid was achieved by thoroughly washing this solid hybrid with water (48 h), ethanol (24

h), and acetone (24 h) using Soxhlet technique. Finally, the solid hybrid product was dried in

a vacuum oven at 40 °C over night affording hybrid poly(benzophenone co-piperazine) 9b.

5.5 Crystal structure analyses

Crystal structures of MK(OH)2, Fur(OAc)2, Fur(OH)2, Thi(OH)2, MK(OH)2,

MK(pip)2, MK(mor)2, BBP, and HDBN were determined using single-crystal X-ray

diffraction methods. Data collection for these compounds were performed at -100 °C using

graphite monochromatized MoKα (λ = 71.073 pm) radiation on a Bruker AXS SMART

1KCCD area detector. The complete data collection parameters and details of the structure

solution and refinement are given in Tables (22-24).


Table 22. Crystal data, details of the data collection, and structure analysis of MK(OH)2 2a,

Fur(OH)2 2b and Thi(OH)2 2c.

MK(OH)2 Fur(OH)2 Thi(OH)2 Crystal color, shape Yellow, rod Yellow, plate Yellow, block Crystal size [mm] 0.35*0.20*0.20 0.95*0.55*0.10 1.10*0.50*0.30 Empirical formula C19H24N2O3 C15H17NO4 C15H17NO3S Chemical formula C19H24N2O3 C15H17NO4 C15H17NO3S Formula weight 328.40 275.30 291.36 Crystal system Monoclinic Monoclinic Monoclinic Space group P21/n P21/c P21/c Unit cell dimensions [pm], angles [°] a = 475.17(2)

b = 1481.78(5) c = 2378.81(10) α = 90 β = 93.588(2) γ = 90

a = 1179.84(16) b = 1140.66(16) c = 1011.52(14) α = 90 β = 94.766(3) γ = 90

a = 792.80(12) b = 1270.14(19) c = 1415.1(2) α = 90 β = 103.083(3) γ = 90

Volume [106 pm3] 1671.63(9) 1356.6(3) 1388(4) Z 4 4 4 Density (calculated) g cm-3 1.305 1.348 1.394 Linear absorption coefficient [mm-1] 0.089 0.098 0.240 Scan method ω scans Absorption correction Empirical Max. /min. transmission 0.9625 /0.7630 0.9903 /0.9126 0.9315 /0.7783 Measured reflections 7023 5835 11249 Independent reflections 3687 3105 4022 Observed reflections [I >2 σ (I)] 2359 2255 3350 R(int) 0.0435 0.0214 0.0263 θ range for data collection [°] 1.62 - 30.37 2.49 - 29.31 2.18 - 30.91 Completeness to maximum θ [%] 73.1 83.8 91.4 Index ranges -6 ≤ h ≤ 5,

-21 ≤ k ≤ 3, -30 ≤ l ≤ 28

-14 ≤ h ≤ 15, -15 ≤ k ≤ 8, -13 ≤ l ≤ 5

-11 ≤ h ≤ 10, -15 ≤ k ≤ 18, -20 ≤ l ≤ 19

Final R indices [I >2 σ (I)] R1 /wR2 0.0526 /0.1026 0.0381 /0.0966 0.0350 /0.0995 R indices (all data) R1 /wR2 0.0979 /0.1221 0.0603 /0.1061 0.0435 /0.1047 Maximum δ / σ 0.004 0.014 0.010 Max. /Min. e-density [106 e. * pm-3] 0.191 /-0.210 0.269 /-0.175 0.378 /-0.455


Table 23. Crystal data, details of the data collection, and structure analysis of MK(pip)2 4b, MK(mor)2 4c, and BBP 5.

MK(pip)2 4b MK(mor)2 4c BBP 5 Crystal color, shape Yellow, plate Light yellow, rod Yellow, block Crystal size [mm] 1.20*1.00*0.30 1.00*0.40*0.30 0.40*0.20*0.10 Empirical formula C23H28N2O C21H24N2O3 C30H26N2O2 Chemical formula C23H28N2O C21H24N2O3 C30H26N2O2 Formula weight 348.47 352.42 446.53 Crystal system Trigonal Orthorhombic Triclinic Space group P3121 Pna21 P-1 Unit cell dimensions [pm], angles [°] a = 948.11(11)

b = 948.11(11) c = 1818.0(3) α = 90 β = 90 γ = 120

a = 1259.9(2) b = 910.16(17) c = 1586.2(3) α = 90 β = 90 γ = 90

a = 1034.0(2) b = 1079.9(2) c = 1127.2(2) α = 72.062(4) β = 73.361(4) γ = 74.549(4)

Volume [106 pm3] 1415.3(3) 1819.0(6) 1125.2(4) Z 3 4 2 Density (calculated) [g cm-3] 1.227 1.287 1.318 Linear absorption coefficient [mm-1] 0.075 0.086 mm-1 0.083 mm-1 Scan method ω scans Absorption correction Empirical Max./ min. transmission 0.9779/ 0.9154 0.9745/ 0.9185 0.9918/ 0.9677 Measured reflections 11667 13320 9293 Independent reflections 2776 3716 6229 Observed reflections [I ≥2 σ (I)] 2464 3206 2329 R(int) 0.0247 0.0318 0.0521 θ range for data collection [°] 2.48 - 30.85 2.58 - 30.85 1.95 - 30.92 Completeness to maximum θ [%] 95.2 94.5 87.4 Index ranges -10 ≤ h ≤13,

-13 ≤ k ≤ 9, -25 ≤ l ≤ 22

-18 ≤ h ≤ 17, -13 ≤ k ≤ 12, -9 ≤ l ≤ 22

-14 ≤ h ≤ 12, -14 ≤ k ≤ 13, -12 ≤ l ≤ 15

Final R indices R1/ wR2 [I ≥2 σ (I)] 0.0345/ 0.0884 0.0352/ 0.0890 0.0634/ 0.1046 R indices R1/ wR2 (all data) 0.0401/ 0.0908 0.0444/ 0.0933 0.2015/ 0.1430 Maximum δ / σ 0.010 0.010 0.028

Max./ min. e-density [10-6 e. * pm-3] 0.165/ -0.205 0.190/ -0.191 0.209/ -0.255


Table 24. Crystal data, details of the data collection, and structure analysis of Fur(OAc)2 1b and HDBN 7

Further details of the crystal structure investigation (without structural factors) are

available from the Cambridge Crystallographic Data Centre and can be obtained by citing the

depositing number CCDC-147477 MK(OH)2, CCDC-197620 Fur(OAc)2, CCDC-197621

Fur(OH)2, CCDC-197622 Thi(OH)2, CCDC-193643 MK(pip)2, CCDC-193644 MK(mor)2,

CCDC-193645 BBP, and CCDC 188074 HDBA. The unit cell was determined with the

program SMART.135 For data integration and refinement of the unit cell program SAINT135

was used. The space group was determined using the programs XPREP135 for MK(OH)2,

Fur(OAc)2, MK(pip)2, MK(mor)2, and HDBA and ABSEN136 for Fur(OH)2, Thi(OH)2, and

BBP. The empirical absorption correction was done with SADABS.137 The structures were

solved using direct methods with the programs SHELXL-97138 for Fur(OAc)2 and SIR97139

Fur(OAc)2 1b HDBN 7 Crystal color, shape Yellow, plate red, block Crystal size [mm] 1.42*1.24*0.22 0.60*0.40*0.38 Empirical formula C19H21NO6 C15H15N3O3

Chemical formula C19H21NO6 C15H15N3O3 Formula weight 359.37 285.30 Crystal system Orthorhombic Monoclinic Space group Pbca P21/c Unit cell dimensions [pm], angels [°] a = 1445.46(2)

b = 1264.26(2) c = 1932.44(4) α = 90 β = 90 γ = 90

a = 1683.38(10) b = 723.06(2) c = 1159.95(2) α = 90 β = 109.568(2) γ = 90

Volume [106 pm3] 3531.41(10) 1330.33(4) Z 8 4 Density (calculated) [g cm-3] 1.352 1.424 Linear absorption coefficient [mm-1] 0.101 0.075 Scan method ω scans ω scans Absorption correction Empirical Empirical Max./ min. transmission 0.9781 /0.8698 0.9661/ 0.5862 Measured reflections 23957 5950 Independent reflections 5110 3012 Observed reflections [I ≥2 σ (I)] 3770 2153 R(int) 0.0306 0.0238 θ range for data collection [°] 2.11 - 30.62 1.28 - 30.65 Completeness to maximum θ [%] 93.9 73.0 Index ranges -12 ≤ h ≤ 20,

-17 ≤ k ≤ 17, -27 ≤ l ≤ 26

-23 ≤ h ≤6, -9 ≤ k ≤ 8, -13 ≤ l ≤ 15

Final R indices R1/ wR2 [I ≥2 σ (I)] 0.0498 /0.1250 0.0489/ 0.1331 R indices R1/ wR2 (all data) 0.0743 /0.1405 0.0718/ 0.1510 Maximum δ / σ 0.022 0.003

Max./ min. e-density [10-6 e. * pm-3] 0.398 /-0.190 0.319/ -0.249


for Fur(OH)2 and Thi(OH)2. The structure refinement by least-square methods based on F2

was done with SHELXL-97.138

All non-hydrogen atoms were fully refined in the calculated positions, the hydrogen

atoms were taken from the electron density difference map and in both their position and their

thermal parameters refined freely.

The plots of the molecular structures were visualized using the programs ZORTEP140

and PLATON.141

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Curriculum Vitae 150

Curriculum Vitae

Personal data

Name Mohamed Mohamed Ibrahim El-Sayed

Date of birth 16.11.1966

Place of birth Port-said, Egypt

Parents Kauther El-Gamel and Mohamed El-Sayed

Nationality Egyptian

Civil status Married since 05.10.1995, 2 Children

Name and occupation of wife Hanan Koutta, Dr. Eng., Faculty of Engineering

and Technology, Suez Canal University, Port-said, Egypt

Name of children Mirna El-Sayed and Manar El-Sayed

School Education

1972-1978 Children Education Nationalized Primary School

1978-1981 El Canal Prep School for Boys

1981-1984 El Canal Secondary School for Boys

University Education

1984-1988 Bachelor of Science in Chemistry, Faculty of Science,

Suez Canal University, Ismailia, Egypt

1991-1995 Master Science in Chemistry, Faculty of Science, Suez

Canal University, Ismailia, Egypt

Experience and Skills

1988-1997 Research Assistant, Faculty of Engineering and

Technology and Faculty of Education, Suez Canal

University, Port-said, Egypt. Also, in the same time,

I have occupied the following jobs:

1990-1995 Chemist in El-Naser Salines Co., Port-said, Egypt

1996-1997 Chemist in General Authority for Quality Controlling on

Import and Export., Port-said, Egypt

Since July 1998 Working as Research Fellow under the supervision of

Prof. Dr. S. Spange, Chemnitz University of Technology,

Chemnitz, Germany.

Selbständigkeiterklärung 151

Selbständigkeitserklärung

Hiermit erkläre ich, dass ich die vorliegende Arbeit selbständig und nur unter Verwendung

der angegebenen Literatur und Hilfsmittel angefertigt habe.

Chemnitz, den 20.12.2002

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