8/12/2019 ZnPc-Quinone

1/5

Oxidative uorescence quenching of Mg-phthalocyanine by quinones

M. Asha Jhonsi a,, A. Kathiravan b

a Department of Chemistry, B.S. Abdur Rahman University, Chennai, Tamil Nadu 600 048, Indiab National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai, Tamil Nadu 600 113, India

a b s t r a c ta r t i c l e i n f o

Article history:

Received 24 August 2013

Received in revised form 17 February 2014

Accepted 25 February 2014Available online 14 March 2014

Keywords:

Phthalocyanine

Quinone

Fluorescence quenching

TCSPC

PET

The quenching of the excited singletstateof magnesium phthalocyanine (MgPc)by quinoneswas investigatedin

DMSO, acetonitrile and methanol. The quinones used were benzoquinone (BQ), duroquinone (DQ) and

naphthaquinone (NQ). Fluorescence intensity/lifetime decreases with increasing concentration of the quinonefollowing a linear SternVolmer behavior. Bimolecular quenching rate constants (kq) obtained from both thesteady-state and time-resolved measurements for the singlet state quenching process were agreed well. Singlet

quenching rate constants are diffusion controlled in all solvents. The quenching rate constants were decreasedwhen the polarity of solvent is decreased. The thermodynamic parameter (Get) estimated by using the

RehmWeller equation were used to propose a suitable mechanism for electron transfer occurring betweenMgPc and quinones. The obtained Getis more negative which clearly indicates that electron transfer type ofmechanism is operative in these systems.

2014 Elsevier B.V. All rights reserved.

1. Introduction

Electron transfer (ET) reaction involves the transfer of an electronfrom a donor to an acceptorwhich can occur both thermally and photo-chemically. The latter reaction is referred to as photoinduced electrontransfer (PET)[1].The development of bioinspired electron donoracceptor complexes that can undergo efcient PET is attracting more

in the current scenario. These systems mimic the function of photosyn-thetic reaction center and are useful for solar energy conversion, storageand in many optoelectronic devices [2,3]. Moreover, the investigation of

PET is essential to understandingthe physical processes involvingin dyesensitized solar cells (DSSC). In a DSSC[4], dyes are used to absorb inci-dentlight, which leads to electron injection fromthe excited state dye tothe conduction band of semiconductor electrode, normally titanium di-

oxide (TiO2). Insuch a system, the dye serves asan electrondonorandasemiconductor is used as electron acceptor. A number of dyes[5]havebeen studied in an attempt to nd correlation between the molecularstructure of the dye and its ability to generate a photocurrent in a

DSSC. In this context, ruthenium complexes represent an extremelypopular for investigations of photoinduced electron transfer[6,7]be-cause the ruthenium complex sensitizers (N3, N719 and black dye)have shown high photoelectric conversion efciencies of over 12%

under AM 1.5 conditions[811]. On the other hand, porphyrins arealso one of the choices for DSSC due to their close resemblance to thephotosynthetic pigment and chlorophyll and their extremely high

molar extinction coefcient (i.e., intense Soret band at 400 nm andmoderate Q bands at 500600 nm) and synthetic versatility. Recently,

Yella et al. have raised the power conversion ef

ciency of a porphyrin-based DSSC beyond 12% by using a cobalt-based electrolyte[12]. Todate, various organic dyes including coumarin, indoline, squaraine,polyene, cyanine, hemicyanine, oligothiophene, perylene, carbazole,benzothidizole and truexene have been developed and have attained

high efciencies up to 10.3%[5,13].Among the red-light-absorbing dyes, metallophthalocyanine (MPc)

is one of the most promising because of its high hardiness and intense

absorption band (called the Q-band) at 650700 nm [14,15]. While var-iousMPcs have beensynthesized andevaluated as light-harvestingdyesfor DSSCs, the conversion efciencies of MPc-based DSSCs have beenlower than those of other macrocyclic dyes with similar absorption

spectra, such as porphyrins [1618]. The highestpower conversion ef-ciency of DSSC sensitized by an MPc is 4.6% [19].Recently, Kimura et al.[20]reported an improved power conversion efciency of MPc is 5.3%by enhancing the pushing ability of the peripheral bulky substituents

through the introduction of electron-donating methoxy groups.Measuring the ET kinetics between the sensitizer and inorganic

semiconductor has been a subject of intense research becauseunderstanding the interfacial injection process is essential for designing

the interfaces that are favorable for charge injection and high solar cellefciency. Hence, understanding photophysical processes in MPc istherefore becoming an interesting topic[21]. In order to imitate the ETprocess operating between excited dyes and a semiconducting

electrode in a DSSC, one can monitor the correlation between the dye

uorescence quenching behaviors together with electron acceptor

Journal of Molecular Liquids 194 (2014) 188192

Corresponding author.

E-mail address:asha@bsauniv.ac.in(M. Asha Jhonsi).

http://dx.doi.org/10.1016/j.molliq.2014.02.033

0167-7322/ 2014 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Journal of Molecular Liquids

j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / m o l l i q

http://dx.doi.org/10.1016/j.molliq.2014.02.033http://dx.doi.org/10.1016/j.molliq.2014.02.033http://dx.doi.org/10.1016/j.molliq.2014.02.033mailto:asha@bsauniv.ac.inhttp://dx.doi.org/10.1016/j.molliq.2014.02.033http://www.sciencedirect.com/science/journal/01677322http://www.sciencedirect.com/science/journal/01677322http://dx.doi.org/10.1016/j.molliq.2014.02.033mailto:asha@bsauniv.ac.inhttp://dx.doi.org/10.1016/j.molliq.2014.02.033http://crossmark.crossref.org/dialog/?doi=10.1016/j.molliq.2014.02.033&domain=pdf

8/12/2019 ZnPc-Quinone

2/5

using uorescence spectroscopy. In other words, the photophysicalcharacterization of the electron donor and electron acceptor in a ho-mogenous system is a requirement for the better understanding of theeffects occurring in DSSC. Recently, Yenilmez et al. [22]reported the

uorescence quenching of zinc phthalocyanine (ZnPc) with benzoqui-none (BQ). They observed that there is a progressive decrease in uo-rescence intensity of ZnPc as the concentration of BQ increases. The

observed quenching is due to electron transfer with rate constant of

9.7 10

9

M

1

s

1

, which was one magnitude lower than when com-pared to unsubstituted ZnPc (5.59 1010 M1 s1) due to presence ofthiazole groups. However, the BQ quenching of simple ethoxy group

substituted ZnPc shows almost identical quenching rate constant com-paring with standard ZnPc [23]. On the other hand, improved BQquenching rate constant (1011 M1 s1) was observed with a Schiffbase-connected ZnPc[24].

The general idea of this paper is to follow the optical properties ofthe MPc in the presence of acceptor in a homogeneous medium, inorder to elucidate the electron-transfer reaction operating betweenphthalocyanine anda strong electron acceptor.For that we have cho-

sen quinone derivatives as an accepting material due to their essen-tial role in electron transport in natural systems [25,26]. In thiscontext, the uorescence quenching and electron transfer processin a solution of MgPc in the presence of quinone were studied. We

have used both the steady-state (SS) andtime-resolved (TR) uores-cence techniques to monitor the electron transfer processes occurbetween excited MgPc and quinones. Chemical structures of MgPcand quinones are shown inScheme 1.

2. Experimental

2.1. Materials

Magnesium phthalocyanine (MgPc) was purchased from Aldrichand used as such without further purication. All the quinones were

obtained from Fluka.

2.2. Instrumentation

2.2.1. Spectroscopic measurements

Absorption spectra were recorded using Cary 300 UV-visible

spectrophotometer. The steady-state uorescence quenching mea-surements were carried out with JASCO FP-6500 spectrouorometer.For uorescence studies, much diluted solutions were used to avoidspectral distortions due to the inner-lter effect and emission reab-

sorption. Time-resolved uorescence decays were obtained by thetime correlated single-photon counting (TCSPC) technique exciting thesample at 400 nm. The typical full width at half-maximum (FWHM) ofthe system response using a scatterer is about 50 ps. Data analysis was

carried out by the software provided by IBH (DAS-6), which is based on

deconvolution techniques using nonlinear least-squares method andthe quality of the t is ascertained with the value of2 b1.2.

3. Results and discussion

3.1. Ground state absorption characteristics

Fig. 1shows the ground state absorption spectra of MgPc in the ab-sence and presence of duroquinone in acetonitrile. In the absence of

duroquinone, MgPc exhibits sharp and intense absorption in its Qband region. However, we observed that there is no change in the ab-sorption spectrum of MgPc in the presence of highest concentration ofduroquinone (5 mM), and also, there is no peak shift and nor new

peak was formed. This inference indicates the absence of interactionbe-tween MgPc and duroquinone in the ground state. The other twoquinones such as nathaquinone and benzoquinone were also shownthe similar type of interaction; their spectra were not shown here.

3.2. Steady-stateuorescence characteristics

Fig. 2shows the uorescence emission spectrum of MgPc in the

absence and presence of various concentrations of naphthaquinonein acetonitrile. Result from theFig. 2indicates that there is a regulardecrease in the emission intensity of MgPc with the addition of

naphthaquinone. This shows the quenching has been occurred be-tween MgPc and quinone. At the same time, there is no signicantpeak shift and no peak broadening was observed. The other two qui-nones (benzoquinone and duroquinone) were also gave the similar

type of quenching behavior (spectra were not shown here).In order to predict the possible quenching mechanism, the uores-

cence quenching data were subjected to SternVolmer analysis[27]using SternVolmer Eq.(1)as follows:

I0=I 1 KSVss

Q 1

N

N

N

N

N

N

N

NMg

Magnesium Phthalocyanine

O

O O

O

Duroquinone Benzoquinone

O

O

1,4 Naphthaquinone

Scheme 1.Structure of MgPc and quinines.

500 550 600 650 700 750 8000.0

0.2

0.4

0.6

0.8

A

bsorbance

Wavelength (nm)

No DQ

5mM DQ

Fig. 1.UV-visible absorption spectrum of MgPc in the absence (solid line) and presence

(dashed line) of duroquinone (5 103 M) in acetonitrile. (For interpretation of the

references to colour in this gure, thereader is referredto theweb version of this article.)

189M. Asha Jhonsi, A. Kathiravan / Journal of Molecular Liquids 194 (2014) 188192

8/12/2019 ZnPc-Quinone

3/5

where I0 and Iarethe uorescence intensities of theuorophore (MgPc)in the absence and the presence of quencher (quinones), respectively,Ksv is theSternVolmer quenching constant and [Q] is the concentration

of quencher (quinones). The bimolecular quenching rate constant (kq)is calculated using Eq.(2)as follows:

Ksv 0kq 2

where 0 is the excited state lifetime of MgPc in theabsence of quinone,obtained from the uorescence lifetime measurement (6.6 ns). Plots of

I0/I vs [Q] were linear for all three quinone with MgPc systems, indicat-ing that dynamic nature of quenching process has been occurred. Thecomparison of SternVolmer plot for the quenching of MgPc by the

three quinones in acetonitrile was shown inFig. 3.Such observations

on dynamic quenching based on steady-state method are quite com-mon. From the slope of linear S-V plot, we determined theKSV, andusing Eq.(2), we obtained thekqvalues, which are shown inTables 1

and 2. It was proposed that the decreased uorescence of ZnPc withbenzoquinone was due to an electron-transfer reaction[24]. Moreover,the obtained quenching rate constants were in excellent agreement

with the reported values [28]. Meaning that this commercial MgPc

shows similar kind of donating property in theexcitedstate by compar-ing reported ZnPc derivatives.

3.3. Time-resolveduorescence characteristics

Thesteady-state measurement aloneis notenough to conrm thetype ofuorescence quenching whether it is dynamic or static in na-ture. In general, lifetime measurement is the most denitive method

to distinguish the static and dynamic quenching process. Fig. 4shows the uorescence decay of MgPc in the absence and presenceof different concentrations of benzoquinone in acetonitrile solvent.The emission of MgPc exhibits single exponential decay not only in

the dilute solution but also in the presence of benzoquinone. Whileincreasing the concentration of benzoquinone, a gradual decreasein the uorescence lifetime of MgPc has been observed. The resultfrom the lifetime measurement conrms that the quenching of

MgPc by quinone is belongs to dynamic type.The other two quinonessuch as nathaquinone and duroquinone also show the similar type ofdecrease in uorescence lifetime of MgPc, their spectra were notshown here.

The bimolecular quenching rate constant has also been calculatedfrom the time-resolved uorescence quenching measurements usingthe following Eq.(3):

0= 1 KSVTR

Q 1 kqTR0 Q 3

The symbols0andare the lifetime ofuorophore, in the absenceand presence of quencher. The typical comparison of SternVolmer

plots for the time-resolved uorescence quenching of MgPc by qui-nones in acetonitrile medium is shown inFig. 5. The plots were linearwith the correlation coefcient (R2) of greater than 0.9969, indicating

630 660 690 720 7500

100

200

300

400

Intensity

Wavelength (nm)

No NQ

1 mM NQ

2 mM NQ

3 mM NQ

4 mM NQ

5 mM NQ

Fig. 2. Steady-state uorescencequenching of MgPc (1 105 M)in the presenceof var-

ious concentrationsof naphthaquinone(05 103 M) in acetonitrile. (Forinterpretation

of the references to colour in this gure, the reader is referred to the web version of this

article.)

0 1 2 3 4 5

1.0

1.1

1.2

1.3

1.4

1.5

1.6

NQ

BQ

DQ

I0/I

[Q] x 10-3 M

Fig. 3.Comparison of SternVolmer plot for the steady-state uorescence quenching ofMgPc(1 105 M) by quinonesin various concentrations (05 1 03 M) in acetonitrile.

(For interpretation of the references to colour in this gure, the reader is referred to the

web version of this article.)

Table 1

Bimolecular quenching rate constant (kq) for MgPc in various solvents from steady-state

measurements.

S. No Quinones kq/ (1010 M1 s1)

DMSO CH3CN CH3OH

1 Naphthaquinone 4.43 1.66 1.24

2 Benzoquinone 4.11 1.43 1.16

3 Duroquinone 3.75 1.10 1.06

10 20 30 40 50100

101

102

103

104 IRFNo BQ

1 mM BQ

2 mM BQ

3 mM BQ

4 mM BQ

5 mM BQ

Log

Counts

Time (ns)

Fig. 4. Time-resolveduorescence quenchingof MgPc (1 105 M)inthepresenceofvar-ious concentrationsof benzoquinone (05 1 03 M) in acetonitrile. (Forinterpretationof

the references to colour in this gure, the reader is referred to the web version of this

article.)

190 M. Asha Jhonsi, A. Kathiravan / Journal of Molecular Liquids 194 (2014) 188192

8/12/2019 ZnPc-Quinone

4/5

the dynamic nature of quenching occurred. The quenching rate con-stants (kq) were calculated from the initial slopes of SternVolmer

plots, and the values are complied in Table 2. Larger value ofkq(1010

M1 s1, diffusion controlled limit) indicates efcient quenching ofMgPc by quinones and the observed quenching is due to a diffusiveprocess.

The quenching rate constant follows the same order as shown belowin both steady-state and time-resolved measurements:

NaphthaquinoneNbenzoquinoneNduroquinone

Usually, quinones are good electron acceptors, but due to thepresence of four methyl groups in its structure, duroquinone showslesser quenching rate constant among the three. Benzoquinone shows

the next higher quenching rate constant because it does not contain

any substituent groups for decreasing the electron accepting naturelike duroquinone. Comparing the three quinones, naphthaquinoneshows the higher rate constant due to it having phenyl group with

resonance (electron delocalization).Moreover, the effect of solvent on the quenching rate constant has

also been studied. Time-resolved measurements show the most accu-rate results for the solvent effect. The decreasing order of quenching

rate constant for the solvent effect is shown as follows:

DMSONCH3CNNCH3OH

From the above trend, we observed that while the solvent polaritydecreases, quenching rate constant also decreases.

3.4. Analysis of quenching

Theuorescence quenching of MgPc by quinones may occur alongfour pathways: (i) the formation of (excited) charge transfer complex,(ii) energy transfer, (iii) proton transfer or (iv) electron transfer. To

test the formation of exciplex, we have measured the kqvalues byvarying solvent polarity. Thekqvalues decreased from more polarsolvent to less polar solvent. The inverted solvent effect has notbeen observed in this case. From this observation, the formation of

an exciplex can be ruled out. The mechanism of energy transferfrom the excited MgPc to quinones is also ruled out due to absenceof overlap between the emission and absorption spectra of MgPc

and duroquinone (Fig. 6). A mechanism involving hydrogen atom

transfer can be excluded because of exergonic thermodynamics cal-culated from the RehmWeller equation (discussed in the followingsection). Hence, the probable mechanism should be electron trans-

fer. It can therefore be concluded that theuorescence quenchingshown in Figs. 2 and 4 is purely caused by electron transfer.Scheme 2represents a general idea showing the many stages in-volved in electron transfer from excited MgPc to quinone in solution.

3.5. Calculation of free energy changes (Get) for the electron transfer

reactions

The thermodynamics driving force (Get) of electron transferreactions can also be veried according to the well-known RehmWeller expression (Eq. (4))[29]. The energy balance of a photoinduced

electron transfer reaction is givenby theRehmWeller equation, whichcombines the oxidation potential (Eox) of the electron donor, thereduc-tion potential (Ered) of the electron acceptor, an electrostatic correctionterm C and the excited state energy of the sensitizer. Therefore, RehmWeller equation remains valid for measurements of uorescence

quenching through electron transfer.

Get Eox E

red EsC

where E(ox) is the oxidation potential of the donor, E

(red) is the reduction

potential of the acceptor (Table 3), Esis the excited state energy of theMgPc (1.82 eV) and C is the coulombic term. Since one of the species

is neutral and the solvent used is polar in nature, the coulombic termin theabove expression is neglected [30]. The Get values thus calculat-

ed for the ET processes in the systems studied in acetonitrile are allnegative (Table 3). Hence, the ET process studied is thermodynamicallyfavorable [31]. Thus, it is suggested that the observed quenchingreaction involves an oxidative mechanism (i.e., electron transfer from

excited MgPc to quinones).

0 1 2 3 4 5

1.0

1.1

1.2

1.3

1.4

1.5

[Q] x 10-3M

0/

Fig. 5.Comparison of SternVolmer plot for the time-resolveduorescence quenching of

MgPc(1 105 M) byquinonesin various concentrations (05 1 03 M) in acetonitrile.

(For interpretation of the references to colour in this gure, the reader is referred to the

web version of this article.)

Table 2

Bimolecular quenching rate constant (kq) for MgPc in various from lifetime measurements.

S. No Quinones kq/ (1010 M1 s1)

DMSO CH3CN CH3OH

1 Naphthaquinone 4.97 2.25 1.41

2 Benzoquinone 4.51 2.22 1.24

3 Duroquinone 3.78 1.91 1.08

280 350 420 490 560 630 700 7700.0

0.2

0.4

0.6

0.8

1.0

DQ absorption

MgPc emission

Wavelength (nm)

Absorbance

0

50

100

150

200

250

300

350

Intensity

Fig. 6. Emission spectra of MgPc (1 105 M) and absorption spectrum of

duroquinone (5 103 M) in acetonitrile. (For interpretation of the references to colour

in thisgure, the reader is referred to the web version of this article.)

191M. Asha Jhonsi, A. Kathiravan / Journal of Molecular Liquids 194 (2014) 188192

8/12/2019 ZnPc-Quinone

5/5

4. Conclusion

The interaction between MgPc and quinone derivatives has beenstudied by UV-visible, steady-state and time-resolved uorescence

spectroscopy. The results presented clearly indicated that, quinonequenches theuorescence of MgPc through dynamic process, since noground-state complex is formed between MgPc and quinones. Thequenching rate constants were calculated according to the relevant

uorescence quenching data. The obtained quenching rate constants

were in the order of 1010 M1 s1, which is in diffusion controlledlimit indicates that occurrence of quenching process is efcient. More-over, by decreasing solvent polarity quenching rate constant have also

been decreases. The quenching mechanism was analyzed on the basisof exciplex formation, proton transfer, energy transfer and electrontransfer. The data suggest that the quenching mechanism has been at-tributed to electron transfer from the excited state MgPc to the ground

state quinones. Moreover, the negativeGet value indicates the electrontransfer processes studied are thermodynamically favorable. This fun-damental work may be giving some hint in various emerging elds.

Acknowledgments

A.K. thanks the Department of Science and Technology, India, for

DST-INSPIRE Faculty Award [IFA12-CH-78], Dt.: 01.02.2013.

References

[1] B. Wardle, Principles and Applications of Photochemistry, John Wiley & Sons, Ltd, U.K., 2009

[2] C.D. Clark, M.Z. Hoffmann, Coord. Chem. Rev. 159 (1997) 359373.[3] A.A. Alkaitis, G. Beck, M. Gratzel, J. Am. Chem. Soc. 97 (1975) 57235729.[4] J. Gong, J. Liang, K. Sumathy, Renew. Sust. Energ. Rev. 16 (2012) 58485860.[5] A. Mishra, M.K.R. Fischer, P. Buerle, Angew. Chem. Int. Ed. 48 (2009) 24742499

(48).[6] S. Ardo, G.J. Meyer, Chem. Soc. Rev. 38 (2009) 115164.[7] A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo, H. Pettersson, Chem. Rev. 110 (2010)

65956663.[8] M. Grtzel, Acc. Chem. Res. 42 (2009) 17881798.[9] F. Gao, Y. Wang, D. Shi, J. Zhang, M. Wang, X. Jing, R. Humphry-Baker, P. Wang, S.M.

Zakeeruddin, M. Grtzel, J. Am. Chem. Soc. 130 (2008) 1072010728.[10] C.Y. Chen, M. Wang, J.Y. Li, N. Pootrakulchote, L. Alibabaei, C. Ngoc-le, J.D. Decoppet,

J.H. Tsai, C. Grtzel, C.G. Wu, S.M. Zakeeruddin, M. Grtzel, ACS Nano 3 (2009)31033109.

[11] L. Han, A. Islam, H. Chen, C. Malapaka, B. Chiranjeevi, S. Zhang,X. Yang, M. Yanagida,Energy Environ. Sci. 5 (2012) 60576060.

[12] A. Yella, H.-W. Lee, H.N. Tsao, C. Yi, A.K. Chandiran, M.K. Nazeeruddin, E.W.-G. Diau,C.-Y. Yeh, S.M. Zakeeruddin, M. Grtzel, Science 334 (2011) 629634.

[13] W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan, P. Wang, Chem.Mater. 22 (2010) 19151925.

[14] G. de La Torre, C.G. Claessens, T. Torres, Chem. Commun. (2007) 20002015.[15] J. Mack, N. Kobayashi, Chem. Rev. 111 (2011) 281321.[16] M.G. Walter, A.B. Rudine, C.C. Wamser, J. Porphyrins Phthalocyanines 14 (2010)

759792.[17] M.K. Nazeeruddin, E. Hummphry-Baker, M. Grtzel, D. Whrle, G. Schnurpfeil, G.

Schneider, A. Hirth, N. Trombach, J. Porphyrins Phthalocyanines 3 (1999) 230237.[18] S. Eu, T. Kato, T. Ueyama, Y. Matano, H. Imahori, Dalton Trans. (2008) 54765483.

[19] S. Mori, M. Nagata, Y. Nakahata, K. Yasuta, R. Goto, M. Kimura, M. Taya, J. Am. Chem.Soc. 132 (2010) 40544055.[20] M. Kimura, H. Nomoto, N. Masaki, S. Mori, Angew. Chem. Int. Ed. 51 (2012)

43714374.[21] D. Sharma, G. Steen, J.P. Korterik, M. Garca-Iglesias, P. Vzquez, T. Torres, J.L. Herek,

A. Huijser, J. Phys. Chem. C 117 (2013) 2539725404.[22] H.Y. Yenilmez, A.M. Sevim, Z.A. Bayr, Synth. Met. 176 (2013) 1117.[23] M.Gksel, M. Durmus, D. Atilla, J. Photochem. Photobiol.A Chem. 266(2013)3746.[24] G. Gmrk, G.K. Karaolan, A. Erdomus, A. Gl, U. Avcata, Dyes Pigments 95

(2012) 280289.[25] D. Dolphin (Ed.), The Porphyrins, Academic Press, New York, 1978.[26] M.R. Gunner, P.L. Dutton, J. Am. Chem. Soc. 111 (1989) 34003412.[27] J.R. Lakowicz, Principles of Fluorescence Spectroscopy, 3rd ed. Springer Publications,

NewYork, USA, 2006. 278.[28] A. Erdomus, M. Durmus, A.L. Uur, O. Avciata, U. Avciata, T. Nyokong, Synth. Met.

160 (2010) 18681876.[29] D. Rehm, A. Weller, Isr. J. Chem. 8 (1970) 259271.[30] S. Parret, F.M. Savary, J.P. Fouassier, P. Ramamurthy, J. Photochem. Photobiol. A

Chem. 83 (1994) 205209.

[31] S. Nath, H. Pal, D.K. Palit, A.V. Sapre, J.P. Mittal, J. Phys. Chem. A 102 (1998)58225830.

[32] N. Barboy, J. Feitelson, J. Phys. Chem. 88 (1984) 10651068.[33] E. Ough, Z. Gasyna, M.J. Stillman, Inorg. Chem. 30 (1991) 23012310

D* + A (D*.....A) (D-.....A+) D- + A+

D.....A Products

h

k -d

kd

k -et

ket kesc

kRkb

D = MgPc; A = Quinone

D + A

Scheme 2. A general scheme for electron transfer reactions of donor to acceptor, wherekdandkdare the rate constants of diffusion and dissociation of the encounter complex, respec-

tively. ket and ket is the activation controlled rate constants of electron transfer, and kesc israte constant for the separation of radicals.kbis rate constant forthe recombination of radical

pair.kRis the rate constant for the decay of D radical.

Table 3

Electrochemical data and driving forces for electron transfer processes.

S. No. Quinones E1/2 (V)a G(eV)b

1 Naphthaquinone 0.82 0.30

2 Benzoquinone 0.48 0.64

3 Duroquinone 0.84 0.28

a

Reduction potential of quinones[32].b G is determined from RehmWeller equation. Oxidation potential of Mg-

phthalocyanine is +0.70 V vs SCE[33].

192 M. Asha Jhonsi, A. Kathiravan / Journal of Molecular Liquids 194 (2014) 188192

http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0145http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0145http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0010http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0010http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0010http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0015http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0015http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0015http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0020http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0020http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0020http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0150http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0150http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0150http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0150http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0155http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0155http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0155http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0025http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0025http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0025http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0025http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0030http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0030http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0030http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0035http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0035http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0035http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0035http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0045http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0045http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0045http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0045http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0050http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0050http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0050http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0050http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0055http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0055http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0055http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0055http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0160http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0160http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0160http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0060http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0060http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0060http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0065http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0065http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0065http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0065http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0070http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0070http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0070http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0070http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0165http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0165http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0165http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0080http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0080http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0080http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0080http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0085http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0085http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0085http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0085http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0090http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0090http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0090http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0090http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0095http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0095http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0095http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0095http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0095http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0170http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0170http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0170http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0110http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf1115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf1115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0120http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0120http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0120http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0125http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0125http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0125http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0125http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0130http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0130http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0130http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0130http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0135http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0135http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0135http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0140http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0140http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0140http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0140http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0135http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0130http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0130http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0125http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0125http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0120http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0180http://refhub.elsevier.com/S0167-7322(14)00091-9/rf1115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf1115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0115http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0110http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0105http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0170http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0095http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0090http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0090http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0085http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0085http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0080http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0080http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0165http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0070http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0070http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0065http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0065http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0060http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0160http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0055http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0055http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0050http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0050http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0045http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0045http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0040http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0035http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0035http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0030http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0025http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0025http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0155http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0150http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0150http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0020http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0015http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0010http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0145http://refhub.elsevier.com/S0167-7322(14)00091-9/rf0145