Journal of Porphyrins and Phthalocyanines

ECS 2005 article

J. Porphyrins Phthalocyanines 2005; 9: 698-705

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A supramolecular Star Wars Tie Fighter Ship: electron transfer in a self-assembled triad composed of two zinc naphthalocyanines and a fullerene Francis D’Souza*a∏, Suresh Gaddea, Mohamed E. El-Khoulyb, Melvin E. Zandlera, Yasuyaki Arakib and Osamu Ito*b Department of Chemistry, Wichita State University, 1845 Fairmount, Wichita, KS 67260-0051, USA Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira, Sendai 980-8577, Japan a

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Received 29 September 2005 Accepted 2 November 2005 ABSTRACT: Photoactive supramolecules composed of electron donor and electron acceptor entities are important for light energy harvesting applications. In the present study, a Star Wars Tie Fighter Ship shaped supramolecular triad was constructed by self-assembling two zinc naphthalocyanines to a fulleropyrrolidine bearing two pyridine entities using an axial coordination approach. Optical absorption and emission studies revealed stable complex formation, and the experimentally determined freeenergy change revealed the possibility of electron transfer from singlet excited zinc naphthalocyanine to the fulleropyrrolidine. The picosecond time-resolved emission technique was utilized to evaluate the kinetics of charge separation while nanosecond transient absorption spectral studies provided evidence for electron transfer quenching. The measured charge-separation rate, kCS and quantum yield, ΦCS were found to be 5.7 × 109 s-1 and 0.93 in toluene, respectively, indicating an efficient process within the supramolecular triad. The charge recombination rate (kkCR) of the supramolecular ion-pair calculated from the nanosecond transient absorption technique was found to be 3.5 × 107 s-1 yielding a lifetime for the radical ion-pair (τRIP) of about 30 ns. Changing the solvent from the noncoordinating toluene to the coordinating benzonitrile or THF destroyed the supramolecular structure, and under these experimental conditions, only intermolecular electron transfer from the triplet excited zinc naphthalocyanine to fulleropyrrolidine could be observed. Under these conditions, the measured electron transfer rates, ket,Tinter, were found to be 2.6 × 107 M-1.s-1 in benzonitrile and 1.2 × 107 M-1.s-1 in THF, respectively. Copyright © 2005 Society of Porphyrins & Phthalocyanines. KEYWORDS: supramolecular triad, zinc naphthalocyanine, fullerene, electron transfer, charge stabilization.

INTRODUCTION Photoinduced electron transfer in donor-acceptor systems is a topic of current interest aimed primarily to mimic the primary events of photosynthetic ∏SPP full

member in good standing

*Correspondence to: Francis D’Souza, email: Francis. [email protected], fax: +1 316-978-3431 and Osamu Ito, email: [email protected], fax: +81 22-217-5610 Copyright © 2005 Society of Porphyrins & Phthalocyanines

reaction center and also as materials to develop molecular electronic devices [1, 2]. Among the different electron donors, phthalocyanines (Pc), the well known synthetic porphyrin analogues, are highly versatile and stable chromophores with unique physicochemical properties [3]. Additional improvements on the physicochemical properties of phthalocyanines were achieved by introducing fused benzene rings at the periphery of the phthalocyanine macrocycle resulting in the naphthalocyanine (Nc) Published on web 01/05/2006

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macrocycle [4]. Because of larger size and extended conjugation, naphthalocyanines exhibit (i) improved solubility, (ii) absorption and emission bands well into the near-IR region, and (iii) facile oxidation potentials [4]. As a consequence, several studies have examined the utilization of naphthalocyanines as nonlinear optical materials, optical limiting agents, organic light emitting diodes, electrode materials for photoelectrochemical cells, and photodynamic therapy agents, to name a few [4]. However, photoinduced electron transfer studies using naphthalocyanine are scarce [5], especially in the field of supramolecular chemistry although the above listed properties of naphthalocyanine make them ideal candidates to build donor-acceptor dyads, triads, etc. In the present study we have explored the building of supramolecular donor-acceptor systems using zinc 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (ZnNc) as the electron donor. Fullerene, C60 is the choice for electron acceptor because of its three dimensional structure, low reduction potentials, and absorption spectra extending over most of the visible region [6]. We have employed the well-established metal-ligand axial coordination approach [7] for the self-assembly of the molecule using a functionalized fullerene bearing two pyridine entities, C60(py)2 (Scheme 1). These pyridine entities, transposed almost in the opposite direction to each other are expected to bind two naphthalocyanine entities to result in the formation of a supramolecular triad. Because of the large, rectangular shape of the naphthalocyanine, spherical shape of the fullerene bearing two pyridine entities disposed in the opposite direction (acting also as spacers), and the adopted axial binding methodology, supramolecules of unusual shape and size

could be envisioned. As discussed in the manuscript, this is found to be indeed a reality, i.e. the DFT optimized structure of the supramolecular triad yielded a shape resembling the Star Wars Tie Fighter Ship. Photochemical studies performed in toluene revealed efficient charge separation within this Tie Fighter Ship supramolecular triad from the singlet excited zinc naphthalocyanine to the axially bound fulleropyrrolidine.

EXPERIMENTAL Fullerene, C60 was from SES Research, Houston, TX. Zinc 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine was from Aldrich Chemicals (Milwaukee, WI). The syntheses and characterization of the bispyridine appended fulleropyrrolidine (two geometric isomers) are given elsewhere [8]. All chromatographic materials and solvents were procured from Fisher Scientific and were used as received. Tetran-butylammonium perchlorate, (n-C4H9)4NClO4 was from Fluka Chemicals. The UV-visible spectral measurements were carried out with a Shimadzu Model 1600 UV-visible spectrophotometer. The fluorescence emission was monitored by using a Spex Fluorolog-tau spectrometer. Right angle method was utilized. Cyclic voltammograms were recorded on an EG&G Model 263A potentiostat using a three electrode system. A glassy carbon electrode was used as the working electrode. A platinum wire served as the counter electrode and a Ag/AgCl was used as the reference electrode. The ferrocene/ferrocenium redox couple was used as an internal standard. All solutions were purged prior to electrochemical and spectral

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R Scheme 1. Structure of the investigated bis zinc naphthalocyanine-fulleropyrrolidine supramolecular triad constructed by axial coordination binding approach Copyright © 2005 Society of Porphyrins & Phthalocyanines

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measurements using argon gas. The computational calculations were performed by ab initio B3LYP/321G(*) methods with GAUSSIAN 03 software package [9] on high speed computers. Time-resolved fluorescence spectra were measured by a single-photon counting method using a second harmonic generation (SHG, 410 nm) of a Ti:sapphire laser (Spectra-Physics, Tsunami 3950-L2S, 1.5 ps full width at half-maximum (fwhm)) and a streak scope (Hamamatsu Photonics, C4334-01) equipped with a polychromator (Action Research, SpectraPro 150) as an excitation source and a detector, respectively [10]. Nanosecond transient absorption measurements were carried out using SHG (532 nm) of Nd:YAG laser (Spectra-Physics, Quanta-Ray GCR-130, fwhm 6 ns) as an excitation source. For transient absorption spectra in the near-IR region (600-1600 nm), monitoring light from a pulsed Xe lamp was detected with a Ge-avalanche photodiode (Hamamatsu Photonics, B2834) [10]. All the samples in a quartz cell (1 × 1 cm) were deaerated by bubbling argon through the solution for 20 min.

RESULTS AND DISCUSSION Spectral and electrochemical characterization of the supramolecular triad The formation of the supramolecular triad was monitored by using optical absorption and fluorescence studies in nonpolar toluene. The zinc naphthalocyanine bands revealed diminished intensity of the near-IR band located at 681 nm upon titrating with bispyridine functionalized fullerene as shown in Fig. 1. One or two sets of isosbestic points were also observed. A Jobs plot of continuous variation revealed the expected 2:1 composition of the zinc naphthalocyanine:fulleropyrrolidine complex. The binding constant, K was obtained from fluorescence data, as discussed in the next paragraph. No new absorption bands in the near IR region were observed suggesting the absence of π−π type interactions between them. Steady-state fluorescence of zinc naphthalocyanine revealed two near-IR emission bands at 784 and 812 nm, consistent with extended conjugation of the macrocycle (Fig. 2). Addition of the fullerene acceptor quenched the emission of ZnNc with a slight blue shift of ~5 nm in the emission bands. The overall binding constant calculated from a Benesi-Hildebrand plot [11] using the quenching data was found to be 1.1 × 105 M-2 suggesting stable complex formation. The Stern-Volmer plot of I/Io vs. [C60] revealed a KSV value of 1.3 × 105 M-1 which resulted in a bimolecular quenching constant, kq of 5.2 × 1013 M-1.s-1. This kq is 4 orders of magnitude higher than that calculated Copyright © 2005 Society of Porphyrins & Phthalocyanines

Fig. 1. Optical absorption spectra of ZnNc (4.9 μM) with increasing addition of C60(py)2 (0.9 μM each addition) in toluene

for a diffusion controlled bimolecular rate constant which suggests the occurrence of an intramolecular quenching process in the triad. Density functional calculations (DFT) at the B3LYP/3-21G(*) level were performed to arrive at the structure of the triad. As shown in Fig. 3 in the optimized structure, the two naphthalocyanine rings were almost coplanar with a small tilt angle. The two macrocycles were separated by 15.5 Å (Zn-toZn distance). The fullerene spheroid, sandwiched between the two rings was at the top of the center of the two rings. The center-to-center distances between the two ZnNc-C60 entities of the triad were found to be 9.2 and 9.8 Å, respectively. The edgeto-edge distances between ZnNc and C60 were greater than 3.6 Å indicating little if any π−π type interactions, in support of the optical absorption results. Interestingly, on a general note, the overall structure of the supramolecular triad resembled that of a Star Wars Tie Fighter Ship as shown in Fig. 3 inset. The large planar-rectangular shape of the zinc naphthalocyanine (as opposed to the smaller zinc porphyrin or zinc phthalocyanine analogs) acted as the two wings leaving the central fullerene spheroid as the cockpit (body) of the vehicle! This serves as a nice example of utilizing a self-assembly approach to build exotic supramolecular structures capable of undergoing light induced processes. J. Porphyrins Phthalocyanines 2005; 9: 698-705

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Fig. 2. (a) Fluorescence spectra of ZnNc (6.9 μM) on increasing addition of C60(py)2 (1.8 μM each addition) in toluene. (b) Benesi-Hildebrand plot constructed for binding constant determination. (c) Stern-Volmer plot of quenching data analysis

Fig. 3. Space filling model of the B3LYP/3-21G(*) optimized structure of zinc naphthalocyanines interacting with bispyridine functionalized fulleropyrrolidine, shown in two orientations. Inset: model of Star Wars Tie Fighter Ship

The driving forces for charge recombination (-ΔGCR) and charge separation (-ΔGCS) were calculated according to Equations 1 and 2 using the Copyright © 2005 Society of Porphyrins & Phthalocyanines

electrochemical redox and emission data [12]: -ΔGCR = Eox - Ered - ΔGs

(1)

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-ΔGCS = E0,0 - (-ΔGCR)

(2)

where Eox is the first oxidation potential of the zinc naphthalocyanine (ZnNc0/•+), Ered is the first reduction potential of the fullerene (C600/•−), E0,0 is the energy of the 0-0 transition between the lowest excited state and the ground state of the ZnNc evaluated from the fluorescence peaks. In toluene, however, since the redox potentials could not be measured, we employed the redox potentials in o-dichlorobenzene after incorporating corrections for the difference of Coulomb interactions between the dielectric constants of toluene and o-dichlorobenzene. ΔGS refers to the static energy, calculated by using the ‘Dielectric Continuum Model’ [12] according to Equation 3. ΔGS = e2 / (4 π ε0 εS RCt-Ct)

(3)

The symbols ε0 and εS represent vacuum permittivity and dielectric constant of the solvent benzonitrile, respectively. Values of center-to-center distance, RCt-Ct were based on the computed structures shown in Fig. 3. The free-energy changes for charge separation, ΔGCS and charge recombination, ΔGCR estimated in toluene were found to be exothermic with values of -0.18 eV and -1.40 eV, respectively. Intramolecular photoinduced electron transfer: time-resolved emission and transient absorption spectral studies The time-resolved fluorescence results were consistent with those of the steady-state fluorescence observations. Figure 4 shows the fluorescence decaytime profiles of the supramolecular system along with pristine zinc naphthalocyanine in toluene monitored in the 750-850 nm spectral range. The fluorescence time profile of ZnNc exhibited a single exponential decay with a lifetime (τf0) of 2.5 ns, which agrees well with the earlier reported value in o-dichlorobenzene [5b]. For the supramolecular triad C60(Py)2:(ZnNc)2 in toluene, shortening of the fluorescence lifetime of ZnNc was observed and the decay could be fitted satis-

Fig. 4. Fluorescence decay profiles of (a) ZnNc (0.01 mM) in toluene and (b) decay profile in the presence of C60(Py)2 (0.1 mM) in toluene. λex = 400 nm and λmonitor = 775 nm Copyright © 2005 Society of Porphyrins & Phthalocyanines

factory to a biexponential decay. The fast-decaying component had a lifetime (τf) of 170 ps (30%), while the slow decaying component had a lifetime of 2.1 ns (70%). The lifetime of the slow-decaying component was close to that of the free ZnNc. The short τf value of ZnNc in the supramolecular triad was shorter than the τf0 value, suggesting that the fluorescence quenching occurs from the 1ZnNc* moiety. The rateconstant (kkCS) and quantum-yield (ΦCS) of the chargeseparation process were calculated using the shorter lifetimes of zinc naphthalocyanine according to the usual procedure adopted for intramolecular charge separation, according to Equations 4 and 5 below [13]: kSCS = (1/ (1/τf)complex - (1/ (1/τf)ZnNc

(4)

ΦSCS = [(1/ [(1/τf)complex - (1/ (1/τf)ZnNc] / (1/ (1/τf)complex

(5)

The kCS and ΦCS were evaluated as 5.7 × 109 s-1 and 0.93 in toluene, respectively. These values agree reasonably well with the previously reported C60Im: ZnNc (where C60Im is an imidazole functionalized fullerene) supramolecular dyad in toluene and dichlorobenzene [5b]; covalently linked porphyrinC60 dyads [13]; self-assembled C60Im:ZnP dyad (where ZnP = zinc tetraphenylporphyrin) in odichlorobenzene [14]; and a supramolecular triad comprised of covalently linked zinc porphyrin dimer coordinated to a bispyridine functionalized fullerene [15]; thus suggesting efficient charge separation within the studied supramolecular tie fighter ship triad. A nanosecond transient absorption study at an excitation wavelength of 532 nm was performed to characterize the electron transfer products. On addition of C60(Py)2 to ZnNc (1:2 eq.) in toluene, the transient spectra (Fig. 5) exhibited an intense absorption peak at 600 nm at 50 ns after the laser

Fig. 5. Nanosecond transient absorption spectra obtained by 532 nm laser light at 50 ns of ZnNc (0.2 mM) in the presence of C60(Py)2 (0.1 mM) in Ar-saturated toluene J. Porphyrins Phthalocyanines 2005; 9: 698-705

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pulse corresponding to the population of the triplet state of ZnNc (3ZnNc*) [5b]. The triplet state of C60(Py)2 at 700 nm was overlapped with the peak of 3 ZnNc* [5b]. These absorption bands, attributable to the triplet state, did not show the decay until 1 μs in deaerated solution. The depletion of peak intensity at 750-850 nm was attributed either to the fluorescence or to the strong absorption of ZnNc in this wavelength region. At 50 ns, additional bands were observed in the 980-1020 nm region corresponding to the formation of the ZnNc cation radical (ZnNc•+) and the fulleropyrrolidine anion radical, (C60•−) [5b], indicating the formation of the a supramolecular radical ion-pair. The characteristic band at 1000 nm was employed to determine the rate constants of the charge recombination process (kkCR) of the supramolecular triad, since the decay could be fitted by a single-exponential function. The time profile for the 1000 nm band showed a quick rise-decay behavior (Fig. 5, inset). From the rapid decay time-profile, the charge recombination rate (kkCR) of the supramolecular ion-pair was estimated to be 3.5 × 107 s-1. The slow decay in the time profile of Fig. 5 has been attributed to the tails of the absorption bands of 3ZnNc* and 3 C60(Py)2*. In the presence of oxygen, both the triplet states and the long-lived component of the 1000 nm time profile decayed much faster indicating the occurrence of triplet energy transfer to O2. However, the presence of oxygen had no effect on the quick risedecay behavior of the 980 nm band, which suggests that the charge separation occurs via 1ZnNc* and kCR >> kO2[O2]. From the kCR value, the lifetime of the radical ion-pairs (τRIP) was evaluated to be 30 ns. This lifetime of the radical ion-pair of the C60(Py)2:(ZnNc)2 is slightly longer compared to the previously reported supramolecular triad C60(Py)2:(ZnP)2 [8]. Intermolecular electron transfer in coordinating solvents The transient absorption spectra showed quite different features in the coordinating solvent benzonitrile as shown in Fig. 6. In the presence of one equivalent C60(Py)2 and ZnNc, the transient absorption spectra exhibited slow growth of the absorption bands of ZnNc•+ at 980 nm accompanied by an concurrent decay of the absorption band of 3ZnNc* at 600 nm. Furthermore, the rise rate of ZnNc•+ was almost similar to that of C60(Py)2•−, although the absorption band of C60(Py)2•− at 1020 nm overlapped with the strong absorption band of the ZnNc•+. Furthermore, the contribution of 3ZnNc* to the electron transfer process (Equation 6) was confirmed by the oxygen effect on the yields of ZnNc•+. The decay of 3ZnNc* was accelerated on addition of O2, indicating that the 3ZnNc* was quenched owing to energy transfer from 3ZnNc* to O2. Consequently, the generations of Copyright © 2005 Society of Porphyrins & Phthalocyanines

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et,T ZnNc* + C60 (Py)2 coordinatin  → ZnNcc•+ + C60 (Py) (Py)2•- (6) coor dinating 

polar solvents lvents

From the pseudo-first-order rate kinetics at 600 nm, the second-order rate constant (kkq,Tinter) for quenching of 3ZnNc* by C60(Py)2 was calculated to be 6.6 × 108 M-1.s-1, which is smaller than the kq,Tinter value (2.2 × 109 M-1.s-1) for the intermolecular electron quenching of 3 ZnNc* with pristine C60. By assuming the molar absorptivity of 3ZnNc* to be 1.4 × 104 M-1.cm-1 at 600 nm and that of ZnNc•+ to be 3 × 104 M-1.cm-1 at 980 nm [16], the calculated quantum-yield for the electron transfer via 3ZnNc* (Φet,Tinter) was found to be 0.04. The small Φet,Tinter value suggests the existence of other competitive deactivation routes apart from the electron-transfer process. From both kq,Tinter and Φet,Tintert, the rate-constant of the intermolecular electron transfer process, ket,Tinter, was evaluated to be 2.6 × 107 M-1.s-1, which was two-order of magnitude smaller than the diffusion-controlled limit of kdiff = 5.6 × 109 M-1.s-1 in benzonitrile.

Fig. 6. Nanosecond transient absorption spectra obtained by 532 nm laser light of ZnNc (0.1 mM) in the presence of C60(Py)2 (0.1 mM) in Ar-saturated benzonitrile

Fig. 7. Decay of ZnNc•+ peak generated in Fig. 6 at long time scale in benzonitrile J. Porphyrins Phthalocyanines 2005; 9: 698-705

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In coordinating THF, similar transient spectra to those in benzonitrile were observed. The kq,Tinter value was evaluated as 6.0 × 108 M-1.s-1. The Φet,Tinter value was evaluated as 0.02, which is smaller than that of benzonitrile due to the decreased solvent polarity of THF compared with benzonitrile. The ket,Tinter in THF evaluated to be 1.2 × 107 M-1.s-1. Figure 7 shows the time profile of ZnNc•+ in the long time-scale after the laser pulse in Ar-saturated benzonitrile solution. At longer time-scale, the ZnNc•+ begins to decay slowly after reaching the maximal absorbance. The decay time profile was fitted with second-order kinetics, suggesting that the bimolecular back electron-transfer between C60(Py)2•- and ZnNc•+ takes place (Equation 7). kb ZnNc•+ + C60 (Py ((Py) Py))2•- coordinatin  → ZnNc + C60 ((Py)2 (7) coor dinating  2nd-orde or r orde

polar lar solvents la lvents

From the slopes of the second-order plot of 1/ΔAbs vs time (inset Fig. 7), the ratio of the back electron transfer (kkbet) to molar absorptivity of radical ions (ε) was estimated. By employing the reported εA of ZnNc•+ [5b], the kbet values were estimated to be 1.8 × 1010 M-1.s-1 in benzonitrile and 8.0 × 1010 M-1.s-1 in THF, respectively. The smaller kbet value in benzonitrile compared to that in THF suggests that the higher polar solvents stabilize the radical ions by stronger solvation before the occurrence of back electron transfer. Since the concentrations of the cation and anion radicals are sufficiently lower than the reactants, the observed decay rates of the backward process are far slower than those of the forward process, even though kbet >> ket.

SUMMARY In summary, the spectroscopic, redox, computational, and photochemical behavior of a self-assembled via axial coordination zinc naphthalocyanine-fulleropyrrolidine triad, is reported. For this supramolecular donor-acceptor construction, fulleropyrrolidine functionalized with two pyridine moieties, C60(Py)2 was utilized. Optical absorption and emission studies revealed stable supramolecular 2:1 triad formation between ZnNc and C60(Py)2 with an overall formation constant, K of 1.1 × 105 M-2 in toluene. Density functional calculations at the B3LYP/3-21G(*) level revealed a structure that resembled a Star Wars Tie Fighter Ship with two zinc naphthalocyanine macrocycles holding the fullerene in the center via axial coordination. No appreciable π−π type interactions between the different entities were observed either experimentally or computationally. In toluene, upon coordination of the pyridine entities of C60(Py)2 to two ZnNc entities, the main quenching pathway involved charge-separation from the singlet Copyright © 2005 Society of Porphyrins & Phthalocyanines

excited zinc naphthalocyanine to the fullerene moiety. The measured charge-separation rate, kCS and quantum yield, ΦCS were evaluated as 5.7 × 109 s-1 and 0.93 in toluene, respectively, indicating an efficient charge separation process within the supramolecular triad. The charge recombination rate (kkCR) of the supramolecular ion-pair was found to be 3.5 × 107 s-1 resulting in a lifetime for the radical ion-pair (τRIP) of about 30 ns. In polar coordinating solvents, intermolecular electron transfer from the triplet excited zinc naphthalocyanine to the fullerene occurred with rate constant, ket,Tinter of 2.6 × 107 M-1.s-1 in benzonitrile and 1.2 × 107 M-1.s-1 in THF, respectively. Acknowledgements The authors are thankful to the National Science Foundation (Grant 0453464 to FD), Petroleum Research Funds administered by the American Chemical Society, and Japan Ministry of Education, Science, Technology, Culture and Sports for support of this work (priority area 417). MEK thanks JSPS for a fellowship.

REFERENCES 1. a) Connolly JS and Bolton JR. in Photoinduced electron transfer Fox MA, Channon M, Part D. (Eds.) Elsevier, 1988. b) Gust D, Moore TA and Moore AL. Acc. Chem. Res. 1993; 26: 198. c) Wasielewski MR. Chem. Rev. 1992; 92: 435. d) Sessler JS, Wang B, Springs SL and Brown CT. in Comprehensive Supramolecular Chemistry Atwood JL, Davies JED, MacNicol DD, Vögtle F. (Eds.) Chapter 9, Pergamon, 1996. e) Ward MD. Chem. Soc. Rev. 1997; 26: 365. 2. a) Introduction of Molecular Electronics Petty MC, Bryce MR and Bloor D. (Eds.) Oxford University Press: New York, 1995. b) Molecular Switches Feringa BL. (Ed.) Wiley-VCH GmbH, Weinheim, 2001. c) Molecular Electronics: Science and Technology Aviram A, Ratner M. (Eds.) Annals NY Acad. Sci. 1998; 852. d) Balzani V and Scandola F. Supramolecular Chemistry Ellis Horwood: New York, 1991. 3. a) Phthalocyanines: Properties and Applications, Leznoff CC and Lever ABP. (Eds.) VCH: Weinheim, 1989, 1993, 1996; Vols. 14. b) Hanack M, Heckmann H and Polley P. In Methods in Organic Chemistry Schaumann E. (Eds.) Houben-Weyl: Thieme, Stuttgart, 1998; E 9d: 717. c) de la Torre G, Nicolau M and Torres T. In Phthalocyanines: Synthesis, Supramolecular Organization and Physical Properties (Supramolecular Photosensitive and Electroactive Materials) Nalwa HS. (Eds.) J. Porphyrins Phthalocyanines 2005; 9: 698-705

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Academic Press, New York, 2001. 4. a) Chen Y, Hanack M, Araki Y and Ito O. Chem. Soc. Rev. 2005; 34: 517. b) Ali H, Van L and Johan E. Chem. Rev. (Washington, D. C.) 1999; 99: 2379. c) Kudrevich SV and van Lier JE. Coord. Chem. Rev. 1996; 156: 163. d) Seto J, Tamura S, Asai N, Kishii N, Kijima Y and Matsuzawa N. Pure Appl. Chem. 1996; 68: 1429. e) Coe BJ. Comprehensive Coord. Chem. II 2004; 9: 621. f) Pandey RK and Zheng G. Porphyrin Handbook 2000; 6: 157-230. 5. a) Tai S, Hayashida S, and Hayashi N. J. Chem. Soc., Perkin Trans. 2 1991; 10: 1637. b) ElKhouly ME, Rogers LM, Zandler ME, Suresh G, Fujitsuka M, Ito O and D’Souza F. Chem. Phys. Chem. 2003; 4: 474. 6. a) Fullerene and Related Structures Hirsch A. (Ed.) Springer, Berlin, 1999. b) Guldi DM. Chem. Commun. 2000; 321. c) Imahori H and Fukuzumi S. Adv. Func. Mater. 2004; 14: 525. d) Martín N, Sánchez L, Illescas B and Pérez I. Chem. Rev. 1998; 98: 2527. e) Guldi DM and Kamat PV. In Fullerenes Kadish KM and Ruoff RS. (Eds.) John Wiley & Sons: New York, 2000; Chapter 5, pp 225-281. 7. a) Guldi DM. Chem. Commun. 2000; 321. b) Meijer MD, van Klink GPM and van Koten G. Coord. Chem. Rev. 2002; 230: 141. c) ElKhouly ME, Ito O, Smith PM and D’Souza F. J. Photochem. Photobiol. C 2004; 5: 79. 8. El-Khouly ME, Gadde S, Deviprasad GR, Fujitsuka M, Ito O and D’Souza F. J. Porphyrins Phthalocyanines 2003; 7: 1. 9. Frisch MJ, Trucks GW, Schlegel HB, Scuseria GE, Robb MA, Cheeseman JR, Montgomery Jr JA, Vreven T, Kudin KN, Burant JC, Millam JM, Iyengar SS, Tomasi J, Barone V, Mennucci B, Cossi M, Scalmani G, Rega N, Petersson GA, Nakatsuji H, Hada M, Ehara M, Toyota K, Fukuda R, Hasegawa J, Ishida M, Nakajima

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15. 16.

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T, Honda Y, Kitao O, Nakai H, Klene M, Li X, Knox JE, Hratchian HP, Cross JB, Adamo C, Jaramillo J, Gomperts R, Stratmann RE, Yazyev O, Austin AJ, Cammi R, Pomelli C, Ochterski JW, Ayala PY, Morokuma K, Voth GA, Salvador P, Dannenberg JJ, Zakrzewski VG, Dapprich S, Daniels AD, Strain MC, Farkas O, Malick DK, Rabuck AD, Raghavachari K, Foresman JB, Ortiz JV, Cui Q, Baboul AG, Clifford S, Cioslowski J, Stefanov BB, Liu G, Liashenko A, Piskorz P, Komaromi I, Martin RL, Fox DJ, Keith T, Al-Laham MA, Peng CY, Nanayakkara A, Challacombe M, Gill PMW, Johnson B, Chen W, Wong MW, Gonzalez C and Pople JA. Gaussian 03, Revision A.2, Gaussian, Inc., Pittsburgh, PA, 2003. a) Nojiri T, Watanabe A and Ito O. J. Phys. Chem. A 1998; 102: 5215. b) Fujitsuka M, Ito O, Yamashiro T, Aso Y and Otsubo T. J. Phys. Chem. A 2000; 104: 4876. Benesi HA and Hildebrand JH. J. Am. Chem. Soc. 1949; 71: 2703. a) Rehm D and Weller A. Isr. J. Chem. 1970; 7: 259. b) Mataga N and Miyasaka H. In Electron Transfer J. Jortner, M. Bixon. (Eds.) John Wiley & Sons: New York, 1999; Part 2: 431-496. a) D’Souza F, Gadde S, Zandler ME, Klyov A, El-Khouly ME, Fujitsuka M and Ito O. J. Phys. Chem. A 2002; 106: 12393. b) D’Souza F, Deviprasad GR, El-Khouly ME, Fujitsuka M and Ito O. J. Am. Chem. Soc. 2001; 123: 5277. D’Souza F, Deviprasad GR, Zandler ME, Hoang VT, Klykov A, Van Stipdonk M, Perera A, ElKhouly ME, Fujitsuka M and Ito O. J. Phys. Chem. A, 2002; 106: 3243. D’Souza F, Gadde S, Zandler ME, Itou M, Araki Y and Ito O. Chem. Commun. 2004; 2276. Lawerence DS and Whitten DG. Photochem. Photobiol. 1996; 64: 923.

J. Porphyrins Phthalocyanines 2005; 9: 698-705