micelar effect, j y h dimers

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doi:10.1016/j.jlu

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safaaehe@gega.

Journal of Luminescence 121 (2006) 431–440

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Micellar effects on the molecular aggregation and fluorescenceproperties of benzazole-derived push–pull butadienes

Tarek A. Fayed�, Safaa El-Din H. Etaiw�, Naglaa Z. Saleh

Chemistry Department, Faculty of Science, Tanta University, 31527-Tanta, Egypt

Received 8 August 2005; accepted 18 November 2005

Available online 4 January 2006

Abstract

The absorption and fluorescence spectral behaviour of 1-(2-benzoxazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene

and its benzothiazolyl analogue (abbreviated as BODB and BTDB, respectively) have been investigated in

dioxane–water mixtures and micellar environments using steady-state techniques. In water, water-rich mixtures or

premicellar solutions, BODB and BTDB tend to form molecular aggregates labelled as H-aggregates. These aggregates

dissociate on adding surfactants forming micellized monomers. In all micellar media the fluorescence quantum yield is

greatly enhanced along with a large hypsochromic shift. Also, in TX-100, CTAB and SDS both dienes show dual

emission from the locally excited (LE) and intramolecular charge transfer (ICT) states. For BTDB in TX-100 and

DODB in all solutions, the LE fluorescence predominates, while for BTDB in CTAB and SDS, the ICT fluorescence is

the predominant. The fluorescence shifts suggest that the fluorescing molecules penetrate the core of the micellar unit in

TX-100, whereas in CTAB and SDS they occupy the interfacial region. The binding constants and the micelle properties

(such as polarity and CMC) have been determined using both dienes as probes.

r 2005 Elsevier B.V. All rights reserved.

Keywords: Diarylbutadienes; Benzazole; Dual fluorescence; Micelles; Probes; H-aggregates

1. Introduction

A variety of organic molecules containingdonor–acceptor moieties exhibit fluorescence pro-perties that depend on the physical and chemicalnature of the medium. This is due to population of

e front matter r 2005 Elsevier B.V. All rights reserve

min.2005.11.006

ng authors. Tel.: +20403120708;

804.

esses: [email protected] (T.A. Fayed),

net (S.H. Etaiw).

conformationally relaxed intramolecular chargetransfer (ICT) or twisted ICT (TICT) excitedstates as emissive states [1–3]. The high sensitivityof these states to solvation, polarity and molecularmobility changes render such molecules to be effi-cient reporters (provide a wealth of information)of their microenvironments. Push–pull stilbenes,i.e. stilbenes substituted with an electron donorand an acceptor group in conjugated positions,have attracted great interest in view of their fluore-scence sensing properties [2,4–7]. Donor–acceptor

d.

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T.A. Fayed et al. / Journal of Luminescence 121 (2006) 431–440432

styryl derivatives have been fruitfully employed incellular calcium sensing [8] and in the visualizationof membrane nerve potential [9]. Also, they areutilized in structural investigations of systemsincluding micelles [10,11], vesicles [12] and poly-mers [13,14].Diphenylbutadienes are interesting models of

the retinyl polyenes that are involved in biologicalsensory and energy transduction [15]. Recentstudies with donor–acceptor-substituted diphenyl-butadienes [14,16–18] have shown that thesecompounds are also capable of exhibiting fluores-cence from conformationally relaxed ICT excitedstates. Therefore, these compounds have been usedto characterize the microenvironment of micelles[16,19,20] as well as probes for saccharides [21] andmetal ions [22]. However, nature and dynamics ofexcited state of diphenylpolyenes are not clearlyknown and the sensing applications are verylimited.In this respect, very recently we have synthesized

and investigated the photophysical properties oftwo new diphenylbutadiene derivatives [23], viz, 1-(2-benzoxazolyl)-4-(p-dimethylaminophenyl)buta-1,3-diene and its benzothiazolyl analogue, abbrevi-ated as BODB and BTDB, respectively, Scheme 1.The absorption and fluorescence characteristics ofthese derivatives exhibit large solvent polarity andviscosity as well as acidity-dependent changes.Hence, they could be utilized as sensors for themicroenvironment of organized assemblies.Surfactant molecules aggregate in water with

their polar head-groups pointing toward water toform micelles. These aggregates are interestingmodels of biological systems. Thus, in the presentwork, the absorption and fluorescence properties

N

X

NMe2

X = O, (BODB)

X = S, (BTDB)

Scheme 1.

of BODB and BTDB have been investigated in 1,4-dioxane–water binary mixtures and in micro-hetero-geneous media of sodium dodecyl sulphate (SDS),cetyltrimethyl ammonium bromide (CTAB) andTriton X-100 (TX-100) as examples of anionic,cationic and neutral surfactants, respectively. This isto examine the effect of micelles on the diene H-aggregates formed in aqueous media. The study aimsalso to explore the usefulness of these dienes asfluorescence probes for characterization of themicelle properties.

2. Experimental

The investigated diarylbutadienes (BODB andBTDB) were prepared and characterized asreported in a previous study [23]. SDS and CTABwere from BDH while TX-100 from Aldrich wereused without purification. Double distilled waterwas used for preparation of micelle solutionswhereas highly spectroscopic-grade ethanol anddioxane (Merck) were used for preparation ofbinary mixtures.

The absorption spectra were measured on aShimadzu UV-3101PC scanning spectrophot-ometer. The steady-state fluorescence measure-ments were preformed using a Perkin-Elmer LS50B spectrofluorimeter fitted with a temperaturecontrolled unit (Fischer Scientific Isotherm Refri-gerated Circular Model 9000). The fluorescencequantum yield (ff) was measured relative toquinine sulphate (ff ¼ 0:54 in 0.1M H2SO4) [24].For all measurements, 2.0� 10�5M diene solu-tions were used and handled under dim light toavoid the trans/cis photoreaction. Since the dienesare sparingly soluble in water, their stock solutionswere made in ethanol and added to the appro-priate amounts of surfactant to make differentconcentrations (the ethanol content is less than2%). The surfactant concentration was variedwithin the range 0.1–12.5mM depending on thenature of the used surfactant. For recordingfluorescence spectra of BODB and BTDB inmixed solvents or micellar solutions, the sampleswere excited at the maximum of the long-wavelength absorption band to ensure excitationof monomers.

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T.A. Fayed et al. / Journal of Luminescence 121 (2006) 431–440 433

3. Results and discussion

3.1. Molecular aggregation of the investigated

dienes in aqueous solutions

The structure and spectroscopy of molecularaggregates in which the molecular arrangement ishighly ordered (namely; J- and H-aggregates) areof much interest because of their special propertiesand possible technological applications [25–27].Briefly, J-aggregates are one-dimensional side-by-side while the H-aggregates are face-to-face

300 400 500 600 7000.0

0.4

0.8

1.2

Flu

ores

cenc

e in

tens

ity (

a. u

.)

Abs

orba

nce

Wavelength (nm)

Fig. 1. Absorption and fluorescence emission spectra of BODB

in: dioxane (- - -), ethanol (y.)and water (—). Excitation

wavelength is 415 nm.

Table 1

Polarity parameters of dioxane–water mixtures as well as the absorpt

mixtures

Dioxane % (v/v) e (D) ET(30)

(kcalmol�1)

BODB

la

0 78.48 63.6 354 (41

10 70.33 — 357

20 61.86 — 360

30 53.28 — 415

40 44.54 55.8 416

50 35.85 — 418

60 27.21 52.1 419

70 19.07 — 418

80 11.86 49.2 416

90 6.07 46.3 414

95 3.89 43.8 411

100 2.21 36.6 408

Values in parenthesis are the maxima in ethanol.

arrangement of molecules [25]. The theory predictsthat the strong coupling of the several similarmonomers in the J- and H-aggregates results in ared and blue shift of their absorption bands,respectively, relative to the monomer [25]. Inaddition, the spectrum gets narrower due to theabsence of vibrational coupling to the molecularmode [25].The absorption and fluorescence spectra of

BODB in water, ethanol and dioxane are shownin Fig. 1, while the spectral peak positions of bothdienes in the mentioned solvents as well as indioxane–water mixtures are collected in Table 1.There are significant variations in the shape andspectral peak position on going from organicsolvents to water. The broad absorption band ofDODB that appears at 417 or 411 nm in ethanoland dioxane, respectively, is replaced by a narrowband at 354 nm in water, with a broad tailextending to over 500 nm. The spectral behaviourof BTDB is similar except for red shifts in theabsorption maximum. Thus, based on the shape ofthe absorption band, the large hypsochromic shiftand narrowing of the band in water, is due toformation of H-aggregates [25,26] while the broadtail was attributed to absorption of monomers.The very low solubility of the investigated dienesin water makes it difficult to study the effect of

ion and emission maxima (nm) of the dienes measured in these

BTDB

lf la lf

7) 580 (531) 363 (422) 600 (560)

578 368 588

573 368 586

567 419 585

563 423 582

553 427 579

547 427 573

537 426 569

531 424 562

519 421 550

514 420 537

503 416 516

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concentration on the absorption spectra. To getinformation about the effect of solvents on theaggregation of the used dienes, their absorptionspectra have been studied in aqueous binarymixtures containing dioxane or ethanol. Theabsorption spectra of BODB in various dioxane–-water mixtures are depicted in Fig. 2a as arepresentative example. Similar behaviour wasobserved in the case of BTDB. As the watercontent increases, the long-wavelength absorptionband suffers a pronounced red shift (ca. 10 nm)relative to that in dioxane due to increase in thepolarity of the medium. This shift is accompaniedby a decrease in the absorbance and build-up ofthe H-aggregates narrow band at the shorterwavelength side with appearance of a well-definedisosbestic point. The appearance of an isosbesticpoint indicates the monomer-H-aggregate equi-librium. Using a protic solvent such as ethanol as acosolvent instead of dioxane results in similarspectral changes, see Fig. 2b. So, attribution of theblue-shifted absorption band to hydrogen-bondedcomplex formation (due to interaction between–NMe2 group and water molecules) was ruled out.Also, it indicates that the self-association of thepresent dienes takes place only in pure or water-rich solvent mixtures.The fluorescence emission of both dienes was

also studied in the mentioned solvents anddioxane–water mixtures. As shown in Fig. 1, thefluorescence spectrum of BODB is red shifted ongoing from dioxane to water. However, the

300 350 400 450 5000.0

0.4

0.8

1.2Dioxane%(v/v)

70.050.040.030.020.010.0

0.0

95.0

100.0

Wavelength (nm)

Abs

orba

nce

0.

0.

0.

1.

Abs

orba

nce

(a) (b)

Fig. 2. UV–visible absorption spectra of BODB in: (a) dioxane–w

mixtures is mentioned in the figure.

fluorescence spectra of both dienes, recorded inwater, are independent of the excitation wave-length and the intensity decreases strongly uponexcitation at lexco370 nm (not shown here). Thus,it was concluded that the formed aggregates arenon-fluorescent and the emission in water is due tomonomers. Consequently, the strong red shift isdue to stabilization of the charge transfer excitedstate of BODB and BTDB in the polar media [23].

The fluorescence spectra of both dienes (lexc ¼410 nm) are strongly influenced by changing thewater content in dioxane. The fluorescence max-ima are highly red shifted (ca. 73 and 64 nm forBODB and BTDB, respectively) when the solventis changed from dioxane to 80% water in thedioxane mixture, Table 1. In addition, the spectraexhibit dual emission where two overlappingbands appear in dioxane–water binary mixturescontaining 20–80% water. Fig. 3 shows suchspectral changes for BTDB in dioxane–watermixtures. One possible explanation for the ob-served dual emission is the participation of a polarICT excited state and/or formation of a hydrogen-bonded complex in addition to the local excitedstate (LE). However, contribution of emissionfrom a hydrogen-bonded complex was ruled outsince both dienes exhibit dual emission also inaprotic solvents, e.g. DMF [23]. The fluorescencemaximum has been correlated with the dielectricconstant and the empirical polarity parameterET(30) of the used dioxane–water mixtures [28,29].The ET(30) correlation plots are linear (r40:97)

300 400 500 6000

4

8

2 % of H2O (v/v)

0.05070758090

100

Wavelength (nm)

ater and (b) ethanol–water mixtures. The composition of the

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0 10 20 30 40 50 60 70 80500

520

540

560

580

600

620

Flu

ores

cenc

e m

axim

um (

nm)

Dielectric constant or ET(30)

Fig. 4. Plots of the fluorescence maximum of BODB (closed

symbols) and BTDB (open symbols) versus dielectric constant

(squares) and ET(30), (circles) of the dioxane–water mixtures.

Fig. 5. Effect of CTAB concentration on the absorption

spectrum of BODB. Inset is the surfactant concentrations.

Table 2

Spectral maxima (nm) and fluorescence quantum yields of the

dienes in SDS, CTAB and TX-100 (12.5, 2.5 and 1.25mM,

respectively)

Medium BODB BTDB

la lf ff la lf ff

SDS 418 532, 565 0.0085 422 533, 583 0.0093

CTAB 424 532, 562 0.0101 435 534, 582 0.0115

TX-100 421 532, 543 0.019 431 531, 567 0.013

Water 354 580 o10�3 363 600 o10�3

450 500 550 600 650 7000

200

400Dioxane (v%)1009080705030200

BTDB

Wavelength (nm)

Flu

ores

cenc

e in

tens

ity (

a. u

.)

Fig. 3. Fluorescence spectra of BTDB in dioxane–water

mixtures. The composition of the mixtures is shown in the

figure.


whereas those of the dielectric constant are non-linear, Fig. 4. Both correlations show that thefluorescence maximum is red shifted by increasingthe polarity of the medium. Therefore, the largered-shifted fluorescence band is attributed to apolar ICT excited state, which is stabilized inwater-rich mixtures.

3.2. Disaggregation and fluorescence spectra of the

investigated dienes in micellar solutions

The absorption spectra of BODB and BTDB(ca. 2� 10�5M) have been recorded in aqueous

solutions having different concentrations of thethree surfactants. Representative spectra are pre-sented in Fig. 5, and the spectral data aresummarized in Table 2. On adding CTAB, as anexample, the absorbance of the H-aggregatesnarrow band (at 354 and 363 nm for BODBand BTDB, respectively) diminishes and a broadabsorption band appears at longer wavelengths(around 424 and 435 nm, respectively) with distinctisosbestic point. Similar changes were also ob-served in SDS and TX-100. These results indicatethat the addition of surfactants promotes disag-gregation of BODB and BTDB, and the resultingdiene monomers are solubilized by the surfactantmolecules to give stable structures (micellizedmonomers). At relatively higher surfactant con-centrations (beyond critical micelle concentration,CMC) almost all diene molecules are present asmicellized monomers as evident from the absence

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450 500 550 600 650 7000

200

400

BODB

H2O

H2O

SDS

CTAB

Flu

ores

cenc

e in

tnsi

ty (

a. u

.)

Wavelength (nm)

450 500 550 600 650 7000

200

400BTDB

TX-100

TX-100

SDS

CTAB

Flu

ores

cenc

e in

tens

ity (

a. u

.)

Wavelength (nm)

Fig. 6. Fluorescence spectra of BODB (upper panel) and

BTDB (lower panel) recorded in micellar solutions with

concentrations of 12.5, 2.5 and 1.25mM for SDS, CTAB and

TX-100, respectively.

300 350 400 450 500 550 6000

100

200

Inte

nsity

(a.

u.)

Wavelength (nm)

Fig. 7. Fluorescence excitaion spectra of BTDB measured in

CTAB (- - -) and SDS (—) solutions as in Fig. 6, monitored at

lem ¼ 530 and 580 nm, lower and higher intensities, respec-

tively.


of the narrow absorption band characteristic forthe H-aggregates.The fluorescence spectra of BODB and BTDB in

the three surfactants (above CMC) are shown inFig. 6. The emission profile shows two overlappingbands whose intensities and maxima change ongoing from water to anionic, cationic and neutralmicelles. The fluorescence maxima and quantumyields are given in Table 2. In addition, theexcitation spectra monitored at both the emissionmaxima in CTAB and SDS for BTDB asexamples, Fig. 7, are independent on the emissionwavelength. This indicates that only one species isresponsible for the observed dual emission. Thefluorescence decay profiles of BTDB in ethanoland DMF follow biexponential fits suggest emis-sion from two states. The lifetime values in ethanolare 0.028 and 0.102 ns while those in DMF are

0.088 and 0.169 ns [30]. Unfortunately, the fluor-escence decay could not be measured in dioxane–water mixtures or micellar solutions due totechnical reasons. Based on the insensitivity ofthe excitation spectra to the monitoring wave-length and the biexponential decay of fluorescencein ethanol and DMF, it was suggested that thedual emission is due to participation of an ICTexcited state in addition to LE one [23]. Inaddition, the maximum of the short-wavelengthemission is independent of the polarity of the usedmicelle (Table 2) while that of the long wavelengthone is strongly red shifted on going from TX-100to CTAB or SDS, which justifies our conclusion.In SDS and CTAB aqueous solutions, the ICTfluorescence of BTDB (around 580 nm) predomi-nates with the fluorescence from the LE state as ashoulder around 530 nm. In case of TX-100, theLE fluorescence with maximum at 530 nm ispredominant while the ICT fluorescence appearsas a shoulder around 565 nm. In contrast, the LEfluorescence of BODB predominates in all micellarmedia, and the ICT fluorescence appears as ashoulder at longer wavelengths.

Fig. 8 illustrates the fluorescence spectra ofBTDB in aqueous TX-100 micellar solutions as afunction of the surfactant concentration. Gener-ally, gradual addition of CTAB or TX-100 isassociated with a hypsochromic shift of theemission maximum along with a great enhance-ment of fluorescence intensity. Both observations

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500 600 7000

110

220 BTDB [TX-100]x10-5 ,M

125856050403020100

wavelength (n.m)

Flu

ores

cenc

e in

tens

ity (

a.u.

)

Fig. 8. Fluorescence spectra of BTDB measured in TX-100

micellar solutions, lexc ¼ 431nm. The surfactant concentra-

tions are shown in the figure.

500 600 7000

250

500[SDS]x10-3, M

4.03.05.02.07.5

12.51.00.50.0

Wavelength (nm)

Flu

ores

cenc

e in

tens

ity (

a.u.

)

Fig. 9. Fluorescence spectra of BODB measured in SDS

micellar solutions, lexc ¼ 418nm. The concentrations of SDS

are shown in the figure.


reflect that the microenvironment around thedienes in micellar solutions is quite different fromthat in pure aqueous phase. The blue shift in thefluorescence spectra as well as the great enhance-ment of the fluorescence intensity within themicellar solutions indicates that the polarity sensedby BODB and BTDB is less than the polarity ofbulk water. It was reported that the fluorescenceyield of the present dienes decreases with increas-ing the solvent polarity [23]. In addition, theenhancement of fluorescence quantum yield inmicelles, Table 2, can be attributed to restrictionsimposed on the radiationless free rotationalmotions (mainly twisting around the CQCbonds) and/or disaggregation of the non-fluores-cent H-aggregates.

Away from CTAB and TX-100, the fluorescencespectra of both dienes show anomalous behaviouron changing the concentration of SDS, Fig. 9. Insolutions containing lower SDS concentrations(o4.0mM), the fluorescence spectra suffer astrong blue shift (ca. 58 nm) along with a greatenhancement in intensity of the LE emission. Onadding more SDS, the fluorescence intensitydecreases with developing of the ICT emissionand a red shift in the emission maximum (ca. 18and 50 nm for BODB and BTDB, respectively).The great enhancement in the fluorescence inten-sity (more than 10 fold) as well as the blue shift, atlower SDS concentrations, is attributed to associa-tion of dienes with free SDS molecules and/or

small premicellar aggregates, in such a way thattheir exposure to water is minimized [10] hencesense a less polar environment. On the other hand,the fluorescence quenching and the observed redshift near and above CMC are due to changesin the shape and size of the micelle. This isalso consistent with the fact that the micellarenvironment of SDS is richer in water contentthan that in CTAB and TX-100 [31] and thedye molecules occupy the interfacial region, videinfra. So, the red shift of the fluorescence is dueto increased polarity of the SDS micelle–waterinterface.

3.3. Probing of the micelle properties

The micropolarity [expressed as the dielectricconstant (e) and ET(30)] as well as CMC of theused micelles has been determined by using BODBand BTDB. The obtained values are listed inTable 3. The dielectric constant and ET(30) of themicelle–water interface in SDS, CTAB and TX-100 micelles were estimated by using Fig. 4 and themeasured ICT fluorescence maximum (Table 2).Table 3 gives also the polarity parameters of thesemicelles as determined by some other probes forcomparison [32,33]. The values indicate that thedienes occupy interfacial region, which may be dueto presence of the dimethylamino group. Also, thedata show that the polarity of the interface isdependent on the nature of the surfactant where it

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0 2 64 8 10 12 14 160

4

8

12SDS

CTAB

[Surfactant], (mM)

I f /I

fo

Fig. 10. Variation of fluorescence intensity ratios for BODB as

a function of SDS and CTAB concentrations, calculated at 522

and 552 nm, respectively. The [CTAB] scale is multiplied by 10.

Table 3

Polarity (e, D, and ET(30), kcal/mol) and critical micelle concentrations (CMC, mM) of SDS, CTAB and TX-100 estimated using

BODB and BTDB as fluorescence probes

Probe parameter BODB BTDB

SDS CTAB TX-100 SDS CTAB TX-100

e 47.6 (40) 43.6 (36) 22.8. (28) 44.7 40.5 19.0

ET(30) 58.0 (57.9) 57.0 (56.3) 51.8 (55.6) 56.2 55.1 52.3

CMC 6.5, 3.95 (8.0) 0.89 (0.9) 0.28 (0.3) 5.7, 4.0 0.86 0.25

Values in parenthesis were determined by using 4-aminophthalimide as a probe [32].


increases from neutral to cationic and anionicmicelles. Furthermore, the values obtained by bothprobes are in fair agreement.The fluorescent dienes studied herein have been

also employed to determine the CMC for SDS,CTAB and TX-100. This was achieved by plottingthe ratios of fluorescence intensities (in the absenceand presence of surfactants) against the concen-tration of surfactants, Fig. 10. The CMC values ofCTAB and TX-100 were calculated from the breakat the abrupt increase of the fluorescence intensity,and the calculated values are given in Table 3. Theobtained values are in good agreement with thosereported in the literature [32].On the other hand, the plots of fluorescence

intensity against the concentration of SDS giverise to two break points. The first point is at4.0mM and the second one is around 6.0mM.Multiple CMCs for SDS are already reportedin a number of current scientific reports [34,35].The lower CMC is often assigned to a phasewith premicellar aggregates while the higherone is referred to some changes in the shape andsize of the micelle. These results clearly suggestthat the present probes perform a better role assensors for monitoring the aggregation of surfac-tant molecules than do other probes. For example,nile red gave only one CMC value of 8.0mM forSDS [36].The previous results indicate that the ICT

fluorescence of BODB and BTDB can serve as agood probe for the properties of the differentmicelles. Furthermore, it can sense the type ofcharge on the polar head group, thus differen-tiating between anionic, cationic and neutralsurfactants.

3.4. Estimation of the probe-micelle binding

constant

In order to know how strongly BODB andBTDB bind with the surfactants, the bindingconstant between each and the different micelleshas been determined using the following equation[35]:

ðIm � IoÞ=ðI t � IoÞ ¼ 1þ ðK ½M�Þ�1, (1)

where Io, It and Im are the fluorescence intensitiesof the probe in the absence of surfactant, at anintermediate concentration [M] and under com-plete micellization, respectively. K is the bindingconstant. The micellar concentration [M] is deter-mined by

½M� ¼ ðS � CMCÞ=N, (2)

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0 2 4 6 8 10 120

1

2

3

4

TX-100

CTAB

(Im

- I o

)/(I

t - I o

)

[M]-1 x10-5

Fig. 11. Plot of (Im–Io)/(It–Io) against [M]�1 for DODB in

CTAB and TX-100.

Table 4

Binding constants (K, � 10�5 lmol�1) and the free energy

change (DG, kJmol�1) for dienes–micelle interaction at 300K

Surfactant BODB BTDB

K �DG K �DG

CTAB 2.770.15 31.18 5.270.33 32.81

TX-100 2.170.076 30.55 1.670.078 29.87


where S represents the surfactant concentrationunder experimental conditions and N is theaggregation number of the micelles. The N valueswere taken as 60 and 143 for CTAB and TX-100,respectively [37]. The plots of (Im–Io)/(It–Io) vs.[M]�1 are linear (r40:96) in correspondence withEq. (1). Representative plots are presented inFig. 11. The K values have been determined fromthe slopes of the plots, and collected in Table 4with the free energy changes associated with thediene–micelle binding calculated at 300K. Thecorresponding values for SDS could not becalculated due to the complicated behaviour inthis surfactant. The relatively stronger bindingbetween both dienes and CTAB can be attributedto the polar nature of BODB and BTDB (ground-state dipole moment amount to 3.6) [23], whichenhances their association with the chargedsurfactant molecules.

References

[1] P. Plaza, D. Laage, M.M. Martin, V. Alain, M. Blanchard-

Dsce, W.H. Thompson, J.T. Hynes, J. Phys. Chem. A 104

(2000) 2396.

[2] W. Rettig, Top. Curr. Chem. 169 (1994) 253.

[3] M. Blanchard-Dsce, V. Alain, L. Midrier, R. Wortmann,

S. Lebus, C. Glania, P. Kramer, A. Fort, J. Muller, M.

Barzoukas, J. Photochem. Photobiol. A 105 (1997) 115.

[4] D. Pines, E. Pines, W. Rettig, J. Phys. Chem. A 107 (2003)

236.

[5] A.K. Singh, S. Kanvah, J. Chem. Soc. Perkin Trans. 2

(2001) 395.

[6] H. Gruen, H. Gorner, Z. Naturforsch. 38a (1983) 928.

[7] N. Dicesare, J.R. Lakowicz, J. Phys. Chem. A 105 (2001)

6834.

[8] W. Rettig, K. Rurack, M. Sczepan, New trends in

fluorescence spectroscopy, in: B. Valur, J. Brochon

(Eds.), Applications to Chemical and Life Sciences,

Springer, Berlin, 2001, p. 125.

[9] P. Fromberz, K.H. Dambacher, H. Ephardt, A. Lamba-

cher, C.O. Muller, R. Neigl, H. Schaden, O. Schenk, Ber.

Bunsenges. Phys. Chem. 95 (1991) 1333.

[10] T.A. Fayed, Coll. Surf. A 236 (2004) 171.

[11] P. Martin, M.A. Martin, D. Castillo, I. Cayre, Anal. Chim.

Acta 205 (1988) 129.

[12] Y. Singh, A. Gulyani, S. Bhattacharya, FEBS Lett. 541

(2003) 132.

[13] E. Miller, B. Wandlet, S. Wysoki, D. Jozwik, A.

Mielniczak, Biosens. Bioelectron. 20 (2004) 1196.

[14] C. Peinado, E.F. Salvador, F. Catalina, A.E. Lozano,

Polymer 42 (2001) 2815.

[15] I.M. Pepe, J. Photochem. Photobiol. B 48 (1999) 1.

[16] A.K. Singh, G.R. Mahalaxmi, Photochem. Photobiol. 71

(2000) 387.

[17] H. El-Gezawy, W. Rettig, R. Lapouyade, Chem. Phys.

Lett. 401 (2005) 140.

[18] A.K. Singh, M. Darshi, S. Kanvah, J. Phys. Chem. A 104

(2000) 464.

[19] A.K. Singh, S. Kanvah, New J. Chem. 24 (2000) 639.

[20] A.K. Singh, M. Darshi, Biochim. Biophys. Acta 1563

(2002) 35.

[21] N.D. Cesare, J. Lakowicz, J. Photochem. Photobiol. A 143

(2001) 39.

[22] S.P. Gromov, A.I. Vendernikov, E.N. Ushakov, L.G.

Kuzmina, A.V. Feofanov, V.G. Avakyan, A.V. Churakov,

Y.S. Alaverdyan, E.V. Malysheva, M.V. Alfnov, J.A.K.

Howard, B. Eliasson, U.G. Edlund, Helv. Chim. Acta 85

(2002) 60.

[23] S.H. Etaiw, T.A. Fayed, N.Z. Saleh, J. Photochem.

Photobiol. A (2005), in press.

[24] J.N. Demas, G.A. Crosby, J. Phys. Chem. 75 (1971) 991.

[25] N.C. Maiti, S. Mazumdar, N. Periasamy, J. Phys. Chem. B

102 (1998) 1528.

[26] M. Mishra, G.B. Behra, M.M.G. Krishna, N. Periasamy,

J. Lumin. 92 (2001) 175.

ARTICLE IN PRESS


[27] A.S. Tatikolov, G. Ponterini, Zh.A. Krasnaya, Int. J.

Photoenergy 2 (2000) 17.

[28] S.K. Saha, S. Santra, S.K. Dogra, J. Mol. Struct. 478

(1999) 199.

[29] D. Mandal, S.K. Pal, D. Sukul, K. Bhattacharya, J. Phys.

Chem. A 103 (1999) 8156.

[30] Unpublished results, the measurement technique was

described previously, see; S. Landgraf, Spectrochim. Acta

A 57 (2001) 2029.

[31] S.M. Dennison, J. Guharay, P.K. Sengupta, Spectrochim.

Acta 55A (1999) 903.

[32] G. Saroja, A. Samanta, Chem. Phys. Lett. 246 (1995) 506.

[33] K. Kalyanasundaram, J.K. Thomas, J. Phys. Chem. 81

(1977) 2176.

[34] A. Mallick, B. Haldar, S. Maiti, N. Chattopadhyay,

J. Colloid Interf. Sci. 278 (2004) 215.

[35] M. Almgren, F. Grieser, J.K. Thomas, J. Am. Chem. Soc.

101 (1979) 279.

[36] K. Goodling, K. Johnson, L. Lefkowitz, B.W. Williams,

J. Chem. Educ. 71 (1994) A8.

[37] G. Saroja, B. Ramachandan, S. Saha, A. Samanta, J. Phys.

Chem. B 103 (1999) 2906.

micelar effect, j y h dimers

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