J. Phys. Chem. C 2007, 111, 1517-1523
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Zinc 5,10,15,20-meso-Tetraferrocenylporphyrin as an Efficient Donor in a Supramolecular Fullerene C60 System Pierluca Galloni,*,† Barbara Floris,† Luisa De Cola,*,‡,§ Elio Cecchetto,‡ and Rene´ M. Williams§ Dipartimento di Scienze e Tecnologie Chimiche, UniVersita` di Roma “Tor Vergata”, Via della Ricerca Scientifica, 00133 Roma, Italy, Physikalisches Institut, Westfa¨lische Wilhelms-UniVersita¨t Mu¨nster, Mendelstrasse 7, D-48149 Mu¨nster, Germany, and Molecular Photonic Materials, Van’t Hoff Institute for Molecular Science, UniVersiteit Van Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands ReceiVed: July 9, 2006; In Final Form: October 16, 2006
The supramolecular assembly containing an electron donor, zinc 5,10,15,20-meso-tetraferrocenylporphyrin, and a pyridine-substituted fulleropyrrolidine as an electron acceptor, has been investigated. A comparison of the photophysical properties of the separate components and of the assembled system revealed a photoinduced electron-transfer process from the porphyrin to the fullerene unit. Time-resolved spectroscopy, on the subpicosecond time scale, was performed to determine the rate of the forward and back electron-transfer reactions.
Introduction Electron-transfer processes are among the most studied reactions because the understanding of the factors affecting their rates and efficiencies is crucial for the comprehension of natural phenomena as well as for the development of artificial photosynthetic systems.1-3 Moreover, the control and prediction of photoinduced processes may lead to applications in molecular photonic devices.4-7 A large number of covalently and noncovalently linked molecular donor-acceptor systems have been studied.8 Among the systems investigated, particular attention has been devoted to those containing fullerene C60 as the electron acceptor moiety due to its interesting redox properties and its stable and easily detectable radical anion.9,10 Different donors have been coupled with fullerene derivatives such as tetrathiafulvalene and tetracene,11 anilines,12 chlorines,13 metallophthalocyanines,14 porphyrins,15 and ferrocenes.16 In particular, promising results were obtained with the latter two donors, thus prompting researchers to investigate complex systems containing porphyrins and ferrocenes in combination with a functionalized fullerene. At the same time, other triads (donor-donor-acceptor or donoracceptor-donor)17 showed good results in energy- and electrontransfer studies obtained with ferrocene-porphyrin-fullerene systems.18 Many of the systems mentioned above have donor and acceptor units covalently bound. Supramolecular systems, in particular with zinc porphyrins,19 were also investigated because they offer a wider choice of chromophores and their assembly recalls the natural photosystems. Recently, supramolecular complexes between heterocyclic derivatives of a fulleropyrrolidine (acceptor) and a zinc tetraphenylporphyrin (donor), which was ferrocene-substituted in the para position of the phenyl rings, were obtained.20 In these systems, however, the * To whom correspondence should be addressed. E-mail: decola@ uni-muenster.de (L.D.C.);
[email protected] (P.G.). † Universita ` di Roma “Tor Vergata”. ‡ Westfa ¨ lische Wilhelms-Universita¨t Mu¨nster. § Universiteit van Amsterdam.
phenyl group between the ferrocene and porphyrin moieties reduces the electronic coupling between the two chromophores. We have therefore chosen to study the properties of a multichromophoric system in which two electron donors, one porphyrin and four ferrocene units, that are strongly interacting are fused into one extensive electron-donating molecule, 5,10,15,20-meso-tetraferrocenylporphyrin (TFcP). Furthermore, a zinc ion coordinated to the ferrocenylporphyrin, ZnTFcP, can lead to a donor-acceptor system obtained by a coordinative bond formed between the metal ion and a pyridine derivative of fullerene C60 (pyC60). It is interesting to notice that the component ZnTFcP is a conjugated system in which the porphyrin and the ferrocene constitute a single unit and no evidence for electron transfer between ferrocene and porphyrin was obtained. We report the synthesis, characterization, and photophysical behavior of the components as well as the assembly. Furthermore, we describe the photoinduced processes occurring upon excitation of one of the components and in particular the electron-transfer processes from ZnTFcP to pyC60. The rates of the forward and back electron transfer have been obtained by time-resolved emission and transient absorption spectroscopy. Experimental Section General Procedures. All the solvents used were spectroscopic grade commercial products (Acros and Merck Uvasol) and were distilled when necessary. NMR spectra were recorded with a Bruker AMX 400 spectrometer, with CDCl3 as the solvent and using the residual signal solvent as a reference (7.23 ppm). The electrochemical experiments were performed with an EG&G potentiostat/galvanostat, model 263A, controlled by model 270/250 Research Electrochemistry software (version 4.23). A three-electrode system was used, consisting of a platinum (Pt) working electrode, a platinum (Pt) auxiliary electrode, and a Ag/AgCl reference electrode separated from the test solution by a glass frit. The experiments were carried out in 1,2-dichlorobenzene at room temperature in a nitrogen
10.1021/jp064307h CCC: $37.00 © 2007 American Chemical Society Published on Web 01/03/2007
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CHART 1
atmosphere with tetrabutylammonium hexafluorophosphate (TBAH) as the electrolyte (0.1 M). Electronic absorption spectra were recorded on a HewlettPackard UV-vis diode array 8453 spectrophotometer or on a Varian Cary 100 scan UV-vis spectrophtometer. Steady-state emission spectra were obtained with a SPEX 1681 Fluorolog spectrofluorometer equipped with two double monochromators (excitation and emission) and were corrected for the photomultiplier response. Femtosecond pump and probe transient absorption measurements were performed using a Spectra-Physics Hurricane titanium/sapphire regenerative amplified laser system. The full spectrum pumping tunability was based on an optical parametric amplifier (Spectra-Physics OPA 800). A residual fundamental light was used for generation of a white light continuum from a sapphire window (450-1500 nm) as the probe, which was detected with two separated diode array based spectrometers (OceanOptics and Control Development). The laser output (800 nm) was typically 0.8 µJ pulse-1 (130 fs fwhm) with a repetition rate of 1 kHz. The OPA was used to generate excitation pulses at 430 nm (1.5 µJ pulse-1). To avoid local heating by the laser beam, the sample cuvette (1 mm) was placed on a moving kinematics stage. The solution’s optical stability was verified by checking the absorbance before and after the measurements. All photophysical properties reported have error bars of 5-10%. Measurements were mainly performed on aerated solutions. Deaeration was applied but with no substantial effect. Substrates. 5,10,15,20-meso-Tetraferrocenylporphyrin21 and 2-pyridyl-3,4-fulleropyrrolidine22 were synthesized following the literature procedure. All the reagents and solvents used for the reactions were commercially available ACS reagent grade. For 2-pyridyl-3,4-fulleropyrrolidine, at variance with the reported method, we found that anhydrous toluene and an inert atmosphere are important. In fact, the yield improved from 44% to 70%.
Zinc 5,10,15,20-meso-tetraferrocenylporphyrin was prepared in quantitative yield by adding a 10-fold excess of a saturated Zn(OAc)2 methanol solution to 200 mg (0.18 mmol) of 5,10,15,20-meso-tetraferrocenylporphyrin dissolved in 4 mL of dichloromethane. The reaction procedure was followed by UVvis spectra, and after 2 h of reaction, 20 mL of CH2Cl2 was added. After washing with water (3 × 20 mL), drying with Na2SO4, and evaporating the solvent, a crude solid remained, which was crystallized from dichloromethane-hexane. MS (FAB, 3-nitrobenzyl alcohol): m/z 1108 (M+ + H, cluster, Fe isotopes, isotopic pattern identical to that calculated for ZnTFcP). 1H NMR (CDCl3): δ (ppm) 4.00 (s, 5H, Cp), 4.76 (br s, 2H, β protons of the substituted cyclopentadienyl ring), 5.36 (br s, 2H, R protons of the substituted cyclopentadienyl ring), 9.83 (s, 2H, pyrrole ring).
Figure 1. Comparison of molar extinction coefficients of ZnTPP (solid line) and ZnTFcP (dashed line). Inset: complete spectra.
Figure 2. Comparison of the absorption spectra of 3.4 × 10-5 M ZnTFcP (dashed line) and 4.1 × 10-5 M pyC60 (solid line).
Results and Discussion All the compounds investigated and their abbreviations are shown in Chart 1. TFcP was prepared following the literature method.21 The zinc complex is a new compound that was obtained by adding Zn(OAc)2 to the free base and was fully characterized by 1H NMR, mass spectrometry, UV-vis absorption, and cyclic voltammetry (see the Experimental Section for details). N-Methyl-2-(4-pyridyl)-3,4-fulleropyrrolidine (pyC60) was prepared by a slight modification of the literature procedure.22 The use of anhydrous toluene as the solvent and an inert atmosphere significantly improved the yield. Electrochemistry. The electrochemical measurements were performed in freshly distilled o-dichlorobenzene, and the results were compared with the data for the donor and acceptor units present in the literature. The pyC60 compound exhibits an electrochemical behavior that is in agreement with literature data (-1.10 V vs Fc/Fc+ in o-dichlorobenzene).20,22 ZnTFcP showed
ZnTFcP as a Donor in a Fullerene C60 System
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SCHEME 1: Components and Their Assembly ZnTFcP⊂pyC60 via the Coordinative Bond
an irreversible oxidation peak at -0.03 V (vs Fc/Fc+), probably due to a difficult re-reduction of the stable cationic species easily formed by oxidation of the highly conjugated ferrocenyl derivative. The electrochemical data of the separate components can be employed to calculate the exoergonicity of the electron-transfer process in the assembly, which might occur upon excitation of the porphyrin unit. The reduction potential for pyC6020 is Ered ) -1.10 V in o-dichlorobenzene, while the oxidation potential of the substituted porphyrin is Eox ) -0.03 V. E00 was estimated by the absorption spectrum of ZnTFcP (see Figure 1) since in such a compound the lowest absorption band is strongly shifted to lower energy compared with that of the reported zinc tetraphenylporphyrin (ZnTPP). Due to the lack of emission at room and low temperature, we have estimated E00 (∼1.8 eV) from the lowest absorption band assuming the same Stokes shift reported for porphyrin. Using the approximated equation ∆Gcs ) e(Eox(D) - Ered(A)) - E00, neglecting the Coulombic contribution, we can estimate a ∆G ≈ -0.7 eV in polar media for the electron transfer from ZnTFcP to pyC60. This value could be slightly more exoergonic if one considers that the complexation with Zn usually lowers the oxidation potential of the porphyrin (for ZnTTP the oxidation potential is 0.2 V lower than for the free porphyrin). Photophysical Characterization and Complexation Constants. The absorption spectra of the ZnTFcP complex and of the reference compound ZnTPP are shown in Figure 1. The spectra are dominated by the strong absorption in the 380-450 nm region attributed to the Soret band of the porphyrins, and at lower energy the Q-band can be observed. Due to the envisaged strong electronic coupling between the ferrocene units and the porphyrin, the absorption spectrum of
ZnTFcP shows very different features compared to that of ZnTPP (Figure 1). The Soret band of ZnTFcP has a much lower molar extinction coefficient than that of ZnTTP (440 nm ) 2.8 × 104 and 420 nm ) 4.5 × 105 M-1 cm-1, respectively). Furthermore, a very strong red shift of the Q-band, a shoulder around 480 nm (due to the ferrocenes), and a reduced difference in relative intensities of the Soret band and Q-band can be observed. In Figure 2 are reported the absorption spectra of the separate components, which will then be assembled through coordination of the zinc porphyrin to the pyridine, to lead to the dyad. The main absorption of pyC60 is in the UV region, and only weaker bands of the fullerene moiety are visible in the 400-700 nm region. Upon complexation of the Zn ion with the pyridine unit, the assembly ZnTFcP⊂pyC60 containing donor (ZnTFcP) and acceptor (pyC60) groups (Scheme 1) is formed. For spectroscopic studies the association constants are extremely important, since we must determine at which concentration it is possible to have the assembly. Such association should be as high as possible to avoid bimolecular quenching, which will be a predominant mechanism if high concentrations must be employed to have the assembly. From literature data23 for similar systems, the association constants are on the order of 7.7 × 103 M-1 in o-dichlorobenzene. From the analysis of the absorption spectra of the separate components (Figure 2), it is possible to identify a spectral region where the association constant can be calculated through a photometric titration with high accuracy. We have therefore analyzed the data in the Q-band instead of the more intense Soret band since only negligible absorption of pyC60 is present in this region even at a relatively high concentration. To a solution containing the ZnTFcP component, microliters of a concentrated solution of pyridine or pyC60 has been added.
Figure 3. Spectral UV-vis absorption changes observed upon titration of ZnTFcP with pyridine in toluene. Inset: Scatchard plot at 668 nm.
Figure 4. Spectral UV-vis absorption changes observed upon titration of ZnTFcP with pyC60 in toluene. Inset: detail of the Q-band region.
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TABLE 1: Complexation Constants of ZnTFcP-N-Heterocyclic Complexes and Related Species complex
solvent
λ,a nm
K, M-1
ZnTFcP-pyridine ZnTFcP-pyC60 ZnTPP-pyridine23 ZnTPP-pyC6023
toluene toluene o-dichlorobenzene o-dichlorobenzene
668 668 421 421
6.50 × 103 1.60 × 103 7.75 × 103 7.65 × 103
a
Wavelength used for the determination of the binding constant.
The absorption spectra and spectral changes observed upon Zn complexation with pyridine, and with the fullerene derivative, are shown in Figures 3 and 4, respectively. An isosbestic point in the Q-band region (around 670 nm) can be seen clearly in the latter case. For the titration with pyridine, the overall spectral variation between free ZnTFcP and the complex ZnTFcP⊂pyridine in solution is shown in Figure 3, where the decrease of the Soret band (around 450 nm) and the increase of the Q band, together with a red shift of both bands, are evident. In both systems a very clean reaction following a 1:1 stoichiometry is observed. The data obtained by the UV-vis absorption spectra at different ratios were analyzed by using a Scatchard plot20 (see Figure 3, inset), and all the results are summarized in Table 1. As can be seen in Table 1, the association constants of complexes between ZnTFcP and pyridine or pyC60 are of the same order of magnitude and are similar to those previously reported for ZnTPP.23 Modeling. By using the X-ray crystal structure of TFcP,24 an optimized configuration of the complex was obtained with semiempirical PM3 (see the Experimental Section) calculations (Figure 5). In accordance with the X-ray structure, two ferrocenyl groups are above the plane of the porphyrin ring and two are below it. This orientation of the ferrocenyl groups relative to the porphyrin plane enforces a close contact between the two ferrocene moieties and the fullerene unit. In the more flexible system investigated by D’Souza and co-workers,20 a different configuration was reported in which the ferrocene unit is mobile and is held close to C60 by edge-to-edge interaction. In our system one of the ferrocenyl groups is forced to be close to the fullerene, due to the structure of the complex and its rather high rigidity (see Table 2). Steady-State Emission. The emission spectra of the ZnTFcP compound, of N-methyl-2-pyridyl-3,4-fulleropyrrolidine, and of their assembly were recorded in toluene (Figure 6). For ZnTFcP no emission could be observed. Since ZnTPP is a strong emitter,6 the lack of fluorescence for ZnTFcP must be attributed to the quenching of the porphyrin-based emission by the ferrocenyl groups. It is not possible to establish the mechanism for the observed quenching. We believe however that, due to the efficiency of the process, and to the endergonicity of the photoinduced electron transfer (∆G ) +0.1 eV, calculated taking as a reference the oxidation potential of the ferrocene moiety, 0 V, and the reduction potential of the porphyrin, -1.91 V, and E00 ) 1.8 eV in a polar solvent), energy transfer is the most likely quenching mechanism. Also the transient absorption
Figure 5. PM3-optimized structure of the ZnTFcP⊂pyC60 complex.
spectra (see the next section) do not reveal any features typical of the formation of a radical anion or cation. It is interesting to notice however that in this system contrary to those already reported20 the porphyrin and the ferrocenyl groups are directly linked, enhancing the electronic coupling between the two components. This could enhance the normal nonradiative processes. pyC60 shows a very weak emission around 700 nm, Figure 6, which is typical for fulleropyrollidine units.12 In the assembled system ZnTFcP⊂pyC60, obtained by mixing solutions of the separated componentsswith only a slight excess of pyC60sand exciting at both 430 and 365 nm, no fluorescence was detected. The lack of emission can be ascribed to an efficient electron transfer from the excited porphyrin to the electron acceptor C60 as demonstrated in the next section. Ultrafast Transient Absorption Spectroscopy. To fully understand and quantify all the processes occurring in the shortlived excited states of the components and of the assembly, we have performed subpicosecond transient absorption spectroscopy. All the spectra have been measured in aerated toluene solution. ZnTFcP shows the spectra depicted in Figure 7. Upon excitation at 430 nm a strong positive transient band at around 465 nm due to the singlet excited state of the porphyrin, with a lifetime of 20 ps (Figure 7, inset), is observed. Accordingly, in the visible region, the spectrum shows the bleaching of the ground state (Q-band; see Figure 3) around 620-670 nm, due to the formation of the singlet excited state (band at 465 nm). The bleaching was also fitted with a monoexponential decay (τ ) 20 ps). The broad absorption at low energy is attributed to the large electronic delocalization involving the ferrocene units and extends into the near-infrared region. Also the NIR region has been investigated but did not show any spectral features which would suggest the formation of any new transient species. The decay of the broad absorption, extending from the visible, follows the same decay kinetics of the 700-800 nm band (Figure 7). As already mentioned we do not have any clear evidence of a photoinduced electron transfer. Indeed, the radical cation of the ferrocene expected at about 800 nm is not observed due also to the low molar absorption extinction coefficient27 and the absorption of the triplet state of the ZnFc4Porf compound. Furthermore, the radical anion of the porphyrin, which is known to be at about 600 nm, is not present.20 Looking at the spectra and at the kinetics, it is possible to observe the formation of a weak band between 500 and 600 nm. We believe however that this band is due to the formation of the triplet state of the porphyrin20 since it does not decay on our time scale (1 ns) and it forms rather slowly. We have also analyzed the transient absorption spectrum of pyC60 (excited at 365 nm measured under identical experimental conditions), which showed the already known spectral features reported in the literature, i.e., the characteristic broad singletstate absorption which extends over the whole visible range with a stronger band around 900 nm with a lifetime of ca. 1.2 ns.26,12. The transient absorption spectrum of the supramolecular complex gave us insight into the ZnTFcP luminescence quenching process upon complexation. A solution containing ZnTFcP (7.0 × 10-5 M) and an excess of pyC60 (4.4 × 10-4 M) in toluene, with ca. 50% of the porphyrin complexed, was excited at 430 nm and probed in the visible and NIR regions. As can be seen after excitation in the porphyrin band an energy transfer populates the singlet excited state of the fullerene as probed by the formation of the absorption band at about 900 nm. In the NIR spectra (Figure 8), at early times (1, 10 ps) the spectral feature is assigned to the absorption of the singlet state
ZnTFcP as a Donor in a Fullerene C60 System
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TABLE 2: Significant Distances for the Investigated Systems center-to-center distance, Å
edge-to-edge distance, Å
complex
Fc-C60
Zn-Fc
Zn-C60
Fc-C60
ZnTFcP-pyC60 ZnTPP-pyC6020 Zn(p-FcPh)TriPP-pyC6020
15.5
6.9
10.6 10.4 9.9
4.15
direct bond
2.8
4.3
10.7
of the fullerene ligand. At a longer time scale (3, 600 ps) a clear maximum at 1020 nm develops which we attribute to the pyC60 radical anion.9,10,26 The 1020 nm band kinetics (Figure 9) shows indeed a fast decay (τ ) 170 ps compared with that of the reference singlet excited state of pyC60, τ ) 1.2 ns) of the tail of the singlet-state band of the fullerene and the formation (τ ) 290 ps) of its radical anion which recombines at longer times (τ ) 600 ps). The constant absorption in the singlet region is due to the presence of uncomplexed pyC60 because of the higher concentration of this component used to ensure the formation of the assembly. A similar behavior was reported with oligo(p-phenylenevinylene)-fullerene dyads,24 although it should be noted that in our study such data were obtained in a nonpolar solvent such as toluene where we would not expect a fast electron-transfer process due to the endergonicity of the process (∆Gtoluene > 0).
TFcP core
The charge-transfer process should be more easily detected using a higher concentration of the components and thus a higher complex concentration. We analyzed a [ZnTFcP] ) 1.6 × 10-4 M solution with an excess of pyC60 (1.0 × 10-3 M). Using a high pyC60 excess, direct excitation of the pyC60 ligand is clearly visible. Indeed, the band around 900 nm (pyC60 singlet) is now more intense. Nevertheless, in the concentrated solution, the 1020 nm band shows the same kinetic pattern as observed for the diluted solution. Transient absorption spectra in the visible region show a band around 550 nm assigned to the porphyrin radical cation as suggested also by the kinetic decay which corresponds to the decay of the IR band attributed to the C60 radical anion. The structured feature forming rather slowly (see the inset in Figure 10) around 700 nm is due probably to the superposition of the decay of the bleach of the Q-band at 680 nm and the absorption band of 3C60.9,10,12,26 Such triplet absorption does not decay on our time scale as expected for the long-lived lifetime of the 3C excited state. 60 All the processes occurring after excitation of the supramolecular complex ZnTFcP⊂pyC60 are summarized in Scheme 2. Conclusions The supramolecular assembly obtained in nonpolar solvent between zinc 5,10,15,20-meso-tetraferrocenylporphyrin and pyridine-substituted fulleropyrrolidine has been investigated. Ex-
Figure 6. Emission spectra of ZnTFcP (solid line) and pyC60 (dotted line). Diluted toluene solutions (10-5 M) were excited at 430 nm.
Figure 8. Subpicosecond NIR transient absorption spectra of the 7.0 × 10-5 M ZnTFcP and 4.4 × 10-4 M pyC60 solution excited at 430 nm at different probe time delays (1, 10 ps; 2, 200 ps; 3, 600 ps; 4, 900 ps).
Figure 7. Subpicosecond transient absorption spectra of ZnTFcP, excited at 430 nm, at different probe delays. The inset shows the dynamics with the probe at (O) 465 nm and (0) 650 nm.
Figure 9. Kinetic trace at 1020 nm of the solution containing 7.0 × 10-5 M ZnTFcP and 4.4 × 10-4 M pyC60, λexc ) 430 nm.
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Figure 10. Subpicosecond NIR transient absorption spectra of the 1.6 × 10-4 M ZnTFcP and 1.0 × 10-3 M pyC60 solution excited at 430 nm at different probe time delays. The inset shows the dynamics with the probe at 700 nm.
SCHEME 2: Schematic Energy Diagram of the Processes Occurring in the Excited State of the Supramolecular System Made of ZnTFcP and pyC60a
a
Decay times are also indicated.
citation at 430 nm was followed by a decay during which different excited species could be detected and their lifetimes measured. The overall result is an efficient and fast electron transfer from the strong electron donor (zinc 5,10,15,20-meso-tetraferrocenylporphyrin) to the electron acceptor (2-pyridyl-3,4fulleropyrrolidine) occurring in 290 ps with formation of the charge-separated species which decays with a kinetics of 600 ps. Interestingly, a comparison with previously reported systems in which the ferrocene unit is separated from the porphyrin by a phenyl spacer20 shows that in our system the photoinduced electron transfer is 1 order of magnitude faster. This could be due to the stronger electronic coupling between the ferrocene and the porphyrin, which leads to the formation of a stronger electron donor system, due to increased electron density on the porphyrin unit. References and Notes (1) Raymo, F. M.; Tomasulo, M. Chem. Soc. ReV. 2005, 34, 327-336 and references therein. (2) Zinth, W.; Wachtveitl, J. ChemPhysChem 2005, 6, 871-880 and references therein. (3) (a) Lubitz, W. Pure Appl. Chem., 2003, 75, 1021-1030. (b) Mi, D.; Chen, M.; Lince, M.; Larkum, A. W. D.; Blankenship, R. E. M. J. Phys. Chem. B 2003, 107, 1452-1457.
Galloni et al. (4) Holten, D.; Bocian, D. F.; Lindsey, J. S. Acc. Chem. Res. 2002, 35, 57-69. (5) Coppo, P.; Duati, M.; Kozhevniov, V. N.; Hofstraat, J. W.; De, Cola, L. Angew. Chem., Int. Ed. 2005, 44, 1806 - 1810. (6) Milanesio, M. E.; Gervaldo, M. G.; Otero, L. A.; Sereno, L.; Silber, J. J.; Durantini, E. N. J. Phys. Org. Chem. 2002, 15, 844-851. (7) (a) Boyd, P. D.; Reed, C. A. Acc. Chem. Res. 2005, 38, 235-242. (b) Segura, J. L.; Martin, N.; Guldi, D. M. Chem. Soc. ReV. 2005, 34, 3147. (8) Balzani, V., et al., Eds. Electron Transfer in Chemistry; WileyVCH: Weinheim, Germany, 2001; Vol. 2; Topics in Current Chemistry; Springer: Berlin, 2005; Vol. 257 and references therein. (9) Hirsch, H.; Brettreich, M. Fullerenes. Chemistry and Reactions, Wiley-VCH: Weinheim, Germany, 2005. (10) Kadish, K. M., Ruoff, R. S., Eds. Fullerenes. Chemistry, Physics and Technology, Wiley-Interscience: New York, 2000. (11) See, for example: (a) Guldi, D. M.; Maggini, M.; Martin, N.; Prato, M. Carbon 2000, 38, 1615-1623. (b) Diaz, M. C.; Herranz, M. A.; Illescas, B. M.; Martin, N.; Godbert, N.; Byrce, M. R.; Luo, C.; Swartz, A.; Anderson, G.; Guldi, D. M. J. Org. Chem. 2003, 68, 7711-7721. (c) Taillemite, S.; Fichou, D. Eur. J. Org. Chem. 2004, 4981-4984. (12) See, for example: (a) Williams, R. M.; Zwier, J. M.; Verhoeven, J. W. J. Am Chem Soc. 1995, 117, 4093-4099. (b) Williams, R. M.; Koeberg, M.; Lawson, J. M.; An, Y.; Rubin, Y.; Paddon-Row: M. N.; Verhoeven, J. W. J. Org. Chem. 1996, 61, 5055-5062. (13) See, for example: Ohkubo, K.; Kotani, H.; Shao, J.; Ou, Z.; Kadish, K. M.; Li, G.; Pandey, R. K.; Fujitsuka, M.; Ito, O.; Imahori, H.; Fukuzumi, S. Angew. Chem., Int. Ed. 2004, 43, 853-856. (14) See, for example: Guldi, D. M.; Zilbermann, I.; Gouloumis, A.; Vazquez, P.; Torres, T. J. Phys. Chem. B 2004, 108, 18485-18494. (15) Selected references: (a) Imahori, H. Org. Biomol. Chem. 2004, 2, 1425-1433. (b) Guldi, D. M. Chem. Soc. ReV. 2002, 31, 22-36. (c) Guldi, D. M.; Nuber, B.; Bracher, P. J.; Alabi, C. A.; MacMahon, S.; Kukol, J. W.; Wilson, S. R.; Schuster, D. I. J. Phys. Chem. A 2003, 107, 32153221. (d) Guldi, D. M. Pure Appl. Chem. 2003, 75, 1069-1075. (e) Kashiwagi, Y.; Ohkubo, K.; McDonald, J. A.; Blake, I. M.; Crossley, M. J.; Araki, Y.; Ito, O.; Imahori, H.; Fukuzumi, S. Org. Lett. 2003, 5, 27192721. (f) Schuster, D. I.; Cheng, P.; Jarowsi, P. D.; Guldi, D. M.; Luo, C.; Echegoyen, L.; Pyo, S.; Holzwarth, A. R.; Braslavsky, S. E.; Williams, R. M.; Klihm, G. J. Am. Chem. Soc. 2004, 126, 7257-7270. (g) Schuster, D. I.; Cheng, P.; Wilson, S. R.; Prokhorenko, V.; Katterle, M.; Holzwarth, A. R.; Braslavsky, S. E.; Klihm, G.; Williams, R. M.; Luo, C. J. Am. Chem. Soc. 1999, 121, 11599-11600. (16) (a) Arrais, A.; Diana, E.; Gobetto, R.; Milanesio, M.; Viterbo, D.; Stanghellini, P. L. Eur. J. Inorg. Chem. 2003, 1186-1192. (b) Nakamura, E. Pure Appl. Chem. 2003, 75, 427-434. (c) Carano, M.; Chuard, T.; Deschenaux, R.; Even, M.; Marcaccio, M.; Paolucci, F.; Prato, M.; Roffia, S. J. Mater. Chem. 2002, 12, 829-833. (d) Campidelli, S.; Va´zquez, E.; Milic, D.; Prato, M.; Barbera´, J.; Guldi, D. M.; Marcaccio, M.; Paolucci, D.; Paolucci, F.; Deschenaux, R. J. Mater. Chem. 2004, 14, 12661272. (17) (a) Nakamura, T.; Fujitsuka, M.; Araki, Y.; Ito, O.; Ikemoto, J.; Takimiya, K.; Aso, Y.; Otsubo, T. J. Phys. Chem. B 2004, 108, 1070010710. (b) Herranz, M. A.; Illescas, B.; Martin, N.; Luo, C.; Guldi, D. M. J. Org. Chem. 2000, 65, 5728-5738. (c) D’Souza, F.; Smith, P. M.; Zandler, M. E.; McCarty, A. L.; Itou, M.; Araki, Y.; Ito, O. J. Am. Chem. Soc. 2004, 126, 7898-7907. (d) D’Souza, F.; Zandler, M. E.; Smith, P. M.; Deviprasad, G. R.; Arkady, K.; Fujitsuka, M.; Ito, O. J. Phys. Chem. A 2002, 106, 649656. (e) Zandler, M. E.; Smith, P. M.; Fujitsuka, M.; Ito, O.; D’Souza, F. J. Org. Chem. 2002, 67, 9122-9129. (f) D’Souza, F.; Deviprasad, G. R.; Zandler, M. E.; El-Khouly, M. E.; Kujitsuka, M.; Ito, O. J. Phys. Chem. B 2002, 106, 4952-4962. (18) (a) Guldi, D. M.; Imahori, H.; Tamaki, K.; Kashiwagi, Y.; Yamada, H.; Sakata, Y.; Fuzukumi, S. J. Phys. Chem. A 2004, 108, 541-548. (b) Kujitsuka, M.; Ito, O.; Imahori, H.; Yamada, K.; Yamada, H.; Sakata, Y. Chem. Lett. 1999, 721-722. (19) (a) El-Khouly, M. E.; Ito, O.; Smith, P. M.; D’Souza, F. J. Photochem. Photobiol., C 2004, 5, 79-104. (b) Armaroli, N. Photochem. Photobiol. Sci. 2003, 2, 73-87. (c) Imahori, H.; Guldi, D. M.; Tamaki, K.; Yoshida, Y.; Luo, C.; Sakata, Y.; Fuzukumi S. J. Am. Chem. Soc. 2001, 123, 6617-6628. (d) Gust, D.; Moore, T. A.; Moore A. L. J. Photochem. Photobiol., B 2000, 58, 63-71. (e) Armaroli, N.; Diederich, F.; Echegoyen, L.; Habicher, T.; Flamigni, L.; Marconi, G.; Nierengarten, J.-L. New J. Chem. 1999, 23, 77-83. (f) Da Ros, T.; Prato, M.; Guldi, D. M.; Ruzzi, M.; Pasimeni, L. Chem.sEur. J. 2001, 7, 816-827. (20) D’Souza, F.; Smith, P. M.; Gadde, S.; McCarty, A. L.; Kullman, M. J.; Zandler, M. E.; Itou, M.; Araki, Y.; Ito, O. J. Phys. Chem. B 2004, 108, 11333-11343. (21) Naranayan, S. J.; Venkatraman, S.; Dey, S. R.; Sridevi, B.; Anand, V. R. G.; Chandrashekar, T. K. Synlett 2000, 1834-1836. (22) Prato, M.; Maggini, M.; Giacometti, C., Scorrano, G.; Sandona`, G.; Farnia, G. Tetrahedron 1996, 52, 5221-5234.
ZnTFcP as a Donor in a Fullerene C60 System (23) D’Souza, F.; Deviprasad, G. R.; Zandler, M. E.; Hoang, V. T.; Klykov, A.; VanStipdonk, M.; Perera, A.; El-Khouly, M. E.; Fujitsuka, M.; Ito, O. J. Phys. Chem. A 2002, 106, 3243-3252. (24) Venkatraman, S.; Prabhuraja, V.; Mishra, R.; Kumar, R.; Chandrashekar, T. K.; Teng, W.; Senge, R. R. Indian J. Chem., A 2003, 42A, 2191-2197. (25) Van, Hal, P. A.; Meskers, S. C. J., Janssen, R. A. J. Appl. Phys. A
J. Phys. Chem. C, Vol. 111, No. 3, 2007 1523 2004, 79, 41-46. (26) (a) Guldi, D. M., Prato, M. Acc. Chem. Res. 2000, 33, 695-703. (b) Guldi, D. M., Maggini, M. Gazz. Chim. Ital. 1997, 127, 779-785. (c) Tanigaki, K.; Ebbesen, T.W.; Kuroshima, S. Chem. Phys. Lett. 1991, 185, 189. (27) Imahori, H.; Tamaki, K.; Guldi, D. M.; Luo, C.; Fujitsuka, M.; Ito, O; Sakata, Y.; Fuzukumi S. J. Am. Chem. Soc. 2001, 123, 2607-2617.
