Scandium ion-promoted photoinduced electron-transfer oxidation of fullerenes and derivatives by p-chloranil and p-benzoquinone

Article abstract of DOI:10.1021/ja016335d

In the presence of scandium triflate, an efficient photoinduced electron transfer from the triplet excited state of C₆₀ to p-chloranil occurs to produce C₆₀ radical cation which has a diagnostic NIR (near-infrared) absorption band at 980 nm, whereas no photoinduced electron transfer occurs from the triplet excited state of C₆₀ (³C₆₀*) to p-chloranil in the absence of scandium ion in benzonitrile. The electron-transfer rate obeys pseudo-first-order kinetics and the pseudo-first-order rate constant increases linearly with increasing p-chloranil concentration. The observed second-order rate constant of electron transfer (k_et) increases linearly with increasing scandium ion concentration. In contrast to the case of the C₆₀/p-chloranil/Sc³⁺ system, the k_et value for electron transfer from ³C₆₀* to p-benzoquinone increases with an increase in Sc³⁺ concentration ([Sc³⁺]) to exhibit a first-order dependence on [Sc³⁺], changing to a second-order dependence at the high concentrations. Such a mixture of first-order and second-order dependence on [Sc³⁺] is also observed for a Sc³⁺-promoted electron transfer from CoTPP (TPP^2- = tetraphenylporphyrin dianion) to p-benzoquinone. This is ascribed to formation of 1:1 and 1:2 complexes between the generated semiquinone radical anion and Sc³⁺ at the low and high concentrations of Sc³⁺, respectively. The transient absorption spectra of the radical cations of various fullerene derivatives were detected by laser flash photolysis of the fullerene/p-chloranil/ Sc³⁺ systems. The ESR spectra of the fullerene radical cations were also detected in frozen PhCN at 193 K under photoirradiation of the fullerene/p-chloranil/Sc³⁺ systems. The Sc³⁺-promoted electron-transfer rate constants were determined for photoinduced electron transfer from the triplet excited states of C₆₀, C₇₀, and their derivatives to p-chloranil and the values are compared with the HOMO (highest occupied molecular orbital) levels of the fullerenes and their derivatives.

Full text of DOI:10.1021/ja016335d

12458
J. Am. Chem. Soc. 2001, 123, 12458-12465
Scandium Ion-Promoted Photoinduced Electron-Transfer Oxidation of
Fullerenes and Derivatives by p-Chloranil and p-Benzoquinone
Shunichi Fukuzumi,*,† Hisahiro Mori,† Hiroshi Imahori,*,† Tomoyoshi Suenobu,†
Yasuyuki Araki,‡ Osamu Ito,*,‡ and Karl M. Kadish*,§
Contribution from the Department of Material and Life Science, Graduate School of Engineering, Osaka
UniVersity, CREST, Japan Science and Technology Corporation (JST), 2-1, Yamada-oka, Suita,
Osaka 565-0871, Japan, Institute of Multidisciplinary Research for AdVanced Materials, Tohoku
UniVersity, CREST, Japan Science and Technology Corporation (JST), Sendai, Miyagi 980-8577, Japan,
and Department of Chemistry, UniVersity of Houston, Houston, Texas 77204-5003
ReceiVed June 2, 2001
Abstract: In the presence of scandium triflate, an efficient photoinduced electron transfer from the triplet
excited state of C60 to p-chloranil occurs to produce C60 radical cation which has a diagnostic NIR (near-
infrared) absorption band at 980 nm, whereas no photoinduced electron transfer occurs from the triplet excited
state of C60 (3C60*) to p-chloranil in the absence of scandium ion in benzonitrile. The electron-transfer rate
obeys pseudo-first-order kinetics and the pseudo-first-order rate constant increases linearly with increasing
p-chloranil concentration. The observed second-order rate constant of electron transfer (ket) increases linearly
with increasing scandium ion concentration. In contrast to the case of the C60/p-chloranil/Sc3+ system, the ket
3
value for electron transfer from C60* to p-benzoquinone increases with an increase in Sc3+ concentration
([Sc3+]) to exhibit a first-order dependence on [Sc3+], changing to a second-order dependence at the high
concentrations. Such a mixture of first-order and second-order dependence on [Sc3+] is also observed for a
Sc3+-promoted electron transfer from CoTPP (TPP2- ) tetraphenylporphyrin dianion) to p-benzoquinone.
This is ascribed to formation of 1:1 and 1:2 complexes between the generated semiquinone radical anion and
Sc3+ at the low and high concentrations of Sc3+, respectively. The transient absorption spectra of the radical
cations of various fullerene derivatives were detected by laser flash photolysis of the fullerene/p-chloranil/
Sc3+ systems. The ESR spectra of the fullerene radical cations were also detected in frozen PhCN at 193 K
under photoirradiation of the fullerene/p-chloranil/Sc3+ systems. The Sc3+-promoted electron-transfer rate
constants were determined for photoinduced electron transfer from the triplet excited states of C60, C70, and
their derivatives to p-chloranil and the values are compared with the HOMO (highest occupied molecular
orbital) levels of the fullerenes and their derivatives.
Introduction
electron-transfer systems in both the ground and excited
states.5-7 In comparison to the facile reduction of C60, however,
the oxidation of C60 is rendered more difficult with a reported
one-electron oxidation potential of 1.26 V versus ferrocene/
ferricenium.8,9 Reed et al. have recently succeeded in oxidizing
C60 by a strong one-electron oxidant (hexabrominated phenyl-
carbazole radical cation with inert CB11H6X6- carborane anion)
The spherical shape of buckminsterfullerenes makes these
carbon allotropes ideal probes for the investigation of electron-
transfer reactions, especially in light of aspects regarding the
electron-transfer theory of Marcus.1,2 In the reduction of C60,
the first electron is added to a triply degenerate t1u unoccupied
molecular orbital to which up to six electrons are accommodated,
resulting in a maximum degree of delocalization.3,4 The small
reorganization energy of fullerenes, especially in electron-
transfer reactions, and the long triplet excited-state lifetimes have
rendered fullerenes as useful components in the design of novel
to produce stable C60 in solution.10 The electron-transfer
•+
oxidation of C60 has also been achieved by using the singlet
excited state of 10-methylacridinium ion, which has a strong
electron acceptor property, or by using the biphenyl radical
(5) (a) Guldi, D. M.; Kamat, P. V. In Fullerenes, Chemistry, Physics,
and Technology; Kadish, K. M., Ruoff, R. S., Eds.; Wiley-Interscience:
New York, 2000; pp 225-281. (b) Guldi, D. M.; Prato, M. Acc. Chem.
Res. 2000, 33, 695.
(6) (a) Imahori, H.; Sakata, Y. AdV. Mater. 1997, 9, 537. (b) Fukuzumi,
S.; Imahori, H. In Electron Transfer in Chemistry; Balzani, V. Ed.; Wiley-
VCH: Weinheim, 2001; Vol. 2, pp 927-975.
* To whom correspondence should be addressed. E-mail: fukuzumi@
ap.chem.eng.osaka-u.ac.jp; imahori@ap.chem.eng.osaka-u.ac.jp; ito@
tagen.tohoku.ac.jp; KKadish@uh.edu.
† Osaka University.
‡ Tohoku University.
§ University of Houston.
(1) (a) Marcus, R. A. Annu. ReV. Phys. Chem. 1964, 15, 155. (b) Marcus,
R. A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1111.
(2) Fukuzumi, S.; Guldi, D. M. In Electron Transfer in Chemistry;
Balzani, V., Ed.; Wiley-VCH: Weinheim, 2001; Vol. 2, pp 270-337.
(3) (a) Xie, Q.; Pe´rez-Cordero, E.; Echegoyen, L. J. Am. Chem. Soc.
1992, 114, 3978. (b) Echegoyen, L.; Echegoyen, L. E. Acc. Chem. Res.
1998, 31, 593.
(4) Echegoyen, L.; Diederich, F.; Echegoyen, L. E. In Fullerenes,
Chemistry, Physics, and Technology; Kadish, K. M., Ruoff, R. S., Eds.;
Wiley-Interscience: New York, 2000; pp 1-51.
(7) (a) Gust, D.; Moore, T. A. In The Porphyrin Handbook; Kadish, K.
M., Smith, K. M., Guilard, R., Eds.; Academic Press: San Diego, CA, 2000;
Vol. 8, pp 153-190. (b) Gust, D.; Moore, T. A.; Moore, A. L. Acc. Chem.
Res. 2001, 34, 40. (c) Mart´ın, N.; Sa´nchez, L.; Illescas, B.; Pe´rez, I. Chem.
ReV. 1998, 98, 2527. (d) Diederich, F.; Go´mez-Lo´pez, M. Chem. Soc. ReV.
1999, 28, 263.
(8) Xie, Q.; Arias, F.; Echegoyen, L. J. Am. Chem. Soc. 1993, 115, 9818.
(9) Reed, C. A.; Bolskar, R. D. Chem. ReV. 2000, 100, 1075.
(10) Reed, C. A.; Kim, K.-C.; Bolskar, R. D.; Mueller, L. J. Science
2000, 289, 101.
10.1021/ja016335d CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/22/2001

Scandium Ion-Promoted Oxidation of Fullerenes
J. Am. Chem. Soc., Vol. 123, No. 50, 2001 12459
cation produced by photoinduced electron transfer from biphenyl
to photosensitizers.11-13 In this process, the primary acceptor
is excited and abstracts an electron from the biphenyl donor.
The longer lifetime of the generated biphenyl radical cation
enables the occurrence of an electron transfer from C60 to
the electron-transfer oxidation reactivities of fullerenes, higher
fullerenes, or their functionalized derivatives.
The use of an appropriate metal ion which can accelerate
electron-transfer reactions may remove the need of very strong
oxidants to accomplish the electron-transfer oxidation of
fullerenes. In the presence of such a metal ion, photoinduced
electron-transfer reactions, which would otherwise be unlikely
to occur, are reported to proceed efficiently.23,24 We have
recently reported that scandium triflate [Sc(OTf)3] acts as the
strongest Lewis acid which can effectively accelerate the
electron-transfer reactions of oxygen and p-benzoquinone.25
produce C60 .
•+ 11 Various polycyclic arene π-radical cations can
also be produced by pulse radiolysis, and the electron-transfer
oxidation of fullerenes by these radical cations has been
reported.14 The oxidation of the triplet excited state of C60
(3C60*) has also been studied by using strong electron acceptors
such as tetracyano-p-quinodimethane (TCNQ),15 tetracyanoet-
hylene (TCNE),16 and p-chloranil17 in photolysis experiments
of the oxidative quenching of triplet excited fullerenes. In
general, very fast quenching reactions of the triplet states of
fullerenes are reported in the presence of these electron
acceptors, but these processes are not accompanied by a
separation of the free radical pairs. A triplet “exciplex” formation
has been proposed as a possible mechanism in most cases. Only
in the case of a strong oxidant (TCNE) is the exciplex considered
as an ion-radical pair.18 Such a limitation of oxidants has
precluded a detailed study of electron-transfer oxidation of the
triplet excited states of fullerenes and derivatives. Although the
oxidation of fullerenes typically becomes easier upon deriva-
tization,19 the radical cations of derivatized fullerenes have yet
to be characterized. The ionization energies of higher fullerenes
are also theoretically suggested to decrease with the cage
size.20,21 This has been shown experimentally by measurements
of these compounds using photoionization, photoelectron spec-
troscopy, and the ion-molecular equilibria-Knudsen cell mass
spectrometry.21,22 However, there has so far been no report on
We report herein that an efficient photoinduced electron
transfer from the triplet excited state of C60 to p-chloranil and
p-benzoquinone occurs in the presence of Sc(OTf)3 in benzoni-
trile (PhCN) to produce C60 radical cation which has a diagnostic
NIR (near-infrared) absorption band at 980 nm. The promoting
effect of Sc(OTf)3 is compared with the results for an electron
transfer from CoTPP (TPP2- ) tetraphenylporphyrin dianion)
to p-benzoquinone in PhCN. With regard to the derivatized
fullerenes, a series of dibenzyl derivatives of C60 were synthe-
sized by the reactions of C602- with alkyl halides.26,27 We then
systematically generated the radical cations of C60, C70, and their
derivatives produced by the Sc3+-promoted electron transfer
from the fullerene triplet excited states to p-chloranil. The
electron-transfer oxidation reactivities of a series of fullerenes
were determined for the first time and they are compared with
the HOMO (highest occupied molecular orbital) levels of the
fullerenes.
Experimental Section
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Sci. 1994, 106, 1671. (b) Michaeli, S.; Meiklyar, V.; Schulz, M.; Mo¨bius,
K.; Levanon, H. J. Phys. Chem. 1994, 98, 7444. (c) Steren, C. A.; Levstein,
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204, 23.
Materials. C60 (1) (>99.95% pure) and C70 (7) (>99.95% pure)
were purchased from Science Laboratories Co., Ltd., Japan, and used
as received. Benzonitrile (PhCN) was purchased from Wako Pure
Chemical Ind. Ltd., Japan, and distilled over P2O5 prior to use.28
p-Benzoquinone and p-chloranil were obtained commercially and
purified by the standard method.28 Dimeric 1-benzyl-1,4-dihydronico-
tinamide [(BNA)2] was prepared according to literature procedures.29
Scandium trifluoromethanesulfonate, Sc(OTf)3 (99%, FW ) 492.16)
was obtained from Pacific Metals Co., Ltd. (Taiheiyo Kinzoku). Cobalt-
(II) tetraphenylporphyrin, CoTPP, was prepared as described in the
literature.30 The examined 1,4-R2C60 derivatives (2-6) [R ) 4-BrC6H4-
CH2 (2), 3-BrC6H4CH2 (3), 2-BrC6H4CH2 (5), and C6H5CH2 (6)] and
1,4-(But)(C6H5CH2)C60 (4) were prepared by a reaction of electrogen-
erated C60 with RBr as described previously.26,27 The C60-N-
2-
methylpyrrolidine derivative (8)31 was synthesized according to literature
procedures. To eliminate the problem of multiple isomers in function-
alized C70, [1,9]methaofullerene[70] carboxylic acid was prepared
selectively according to literature procedures.32 Condensation of [1,9]-
(17) (a) Steren, C. A.; van Willigen, H.; Biczo´k, L.; Gupta, N.; Linschitz,
H. J. Phys. Chem. 1996, 100, 8920. (b) Michaeli, S.; Meiklyar, V.;
Endeward, B.; Mo¨bius, K.; Levanon, H. Res. Chem. Intermed. 1997, 23,
505.
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C., Volman, D. H., von Bu¨nau, G., Eds.; Wiley: New York, 1998; Vol.
25, pp 107-172.
(24) Fukuzumi, S. In Electron Transfer in Chemistry; Balzani, V., Ed.;
Wiley-VCH: Weinheim, 2001; Vol. 4, pp 3-67.
(19) (a) Boudon, C.; Gisselbrecht, J.-P.; Gross, M.; Herrmann, A.;
Ru¨ttimann, M.; Crassous, J.; Cardullo, F.; Echegoyen, L.; Diederich, F. J.
Am. Chem. Soc. 1998, 120, 7860. (b) Suzuki, T.; Maruyama, Y.; Akasaka,
T.; Ando, W.; Kobayashi, K.; Nagase, S. J. Am. Chem. Soc. 1994, 116,
1359. (c) Zhou, J.; Rieker, A.; Grosser, T.; Skiebe, A.; Hirsch, A. J. Chem.
Soc., Perkin Trans. 2 1997, 1. (d) Cardullo, F.; Seiler, P.; Isaacs, L.;
Nierengarten, J.-F.; Haldimann, R. F.; Diederich, F.; Mordasini-Denti, T.;
Thiel, W.; Boudon, C.; Gisselbrecht, J.-P.; Gross, M. HelV. Chim. Acta
1997, 80, 343.
(20) (a) Cioslowski, J.; Raghavachari, K. J. Chem. Phys. 1993, 98, 8734.
(b) Nagase, S.; Kobayashi, K. J. Chem. Soc., Chem. Commun. 1994, 1837.
(c) Seifert, G.; Vietze, K.; Schmidt, R. J. Phys. B 1996, 29, 5183.
(21) Boltalina, O. V.; Ioffe, I. N.; Sidorov, L. N.; Seifert, G.; Vietze, K.
J. Am. Chem. Soc. 2000, 122, 9745.
(25) Fukuzumi, S.; Ohkubo, K. Chem. Eur. J. 2000, 6, 4532.
(26) (a) Subramanian, R.; Kadish, K. M.; Vijayashree, M. N.; Gao, X.;
Jones, M. T.; Miller, M. D.; Krause, K. L.; Suenobu, T.; Fukuzumi, S. J.
Phys. Chem. 1996, 100, 16327. (b) Fukuzumi, S.; Suenobu, T.; Gao, X.;
Kadish, K. M. J. Phys. Chem. A 2000, 104, 2908. (c) Kadish, K. M.; Gao,
X.; Van Caemelbecke, E.; Hirasaka, T.; Suenobu, T.; Fukuzumi, S. J. Phys.
Chem. 1998, 102, 3898.
(27) Fukuzumi, S.; Suenobu, T.; Hirasaka, T.; Arakawa, R.; Kadish, K.
M. J. Am. Chem. Soc. 1998, 120, 9220.
(28) Perrin, D. D.; Armarego, W. L. F. Purifiction of Laboratory
Chemicals; Butterworth-Heinemann: Oxford, 1988.
(29) Wallenfels, K.; Gellerich, M. Chem. Ber. 1959, 92, 1406.
(30) Adler, A. D.; Longo, F. R.; Va´radi, V. Inorg. Synth. 1976, 16, 213.
(31) Imahori, H.; Ozawa, S.; Ushida, K.; Takahashi, M.; Azuma, T.;
Ajavakom, A.; Akiyama, T.; Hasegawa, M.; Taniguchi S.; Okada, T.;
Sakata, Y. Bull. Chem. Soc. Jpn. 1999, 72, 485.
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Relat. Phenom. 1996, 78, 461.

12460 J. Am. Chem. Soc., Vol. 123, No. 50, 2001
Fukuzumi et al.
methaofullerene[70] carboxylic acid with 4-alkoxyaniline gave [1,9]-
methaofullerene[70] (9).
time scale measurements (>5 µs), a continuous xenon lamp (150 W)
was used for the probe beam, which was detected with an InGaAs
photodiode module (Hamamatsu, G5125-10) after passing through the
photochemical quartz vessel (10 × 10 mm) and a monochromator. The
outputs from Ge-APD and InGaAs module were recorded with a
digitizing oscilloscope (HP 54510B, 300 MHz). The transient spectra
were recorded with fresh solutions in each laser excitation. All
experiments were performed at 298 K.
Kinetic Measurements. Kinetic measurements of electron-transfer
reactions from CoTPP to p-benzoquinone in the presence of Sc(OTf)3
were performed on a Unisoku RSP-601 stopped-flow rapid scan
spectrophotometer with a Unisoku thermostated cell holder. Typically,
a deaerated MeCN solution of CoTPP (2.0 × 10-5 M) and Sc(OTf)3
(5.0 × 10-2 to 2.0 × 10-1 M) was added to a deaerated MeCN solution
of p-benzoquinone (2.0 × 10-4 to 8.0 × 10-4 M) under Ar with stirring.
The rates of electron-transfer reaction from CoTPP (1.0 × 10-5 M) to
the p-benzoquinone derivatives [(1.0-4.0) × 10-4 M] in the presence
of Sc(OTf)3 [(2.5-1.0) × 10-2 M] were monitored in MeCN at 298 K
by the rise of the absorption band at 434 nm and the decay of the band
at 412 nm due to CoTPP+ and CoTPP, respectively. Kinetic measure-
ments were carried out under pseudo-first-order conditions where the
concentrations of electron acceptors were maintained at greater than
10-fold excess of the concentrations of electron donors at 298 K.
Pseudo-first-order rate constants were determined by least-squares curve
fits of the data using a microcomputer.
ESR Measurements. ESR measurements were carried out to detect
the radical ion pair produced in the photoinduced electron transfer from
3C60* to p-chloranil in the presence of Sc(OTf)3. These experiments
were performed in frozen PhCN at 193 K under irradiation of light
with a high-pressure mercury lamp (USH-1005D) focusing at the sample
cell in the ESR cavity. The ESR spectra were measured with a JEOL
X-band spectrometer (JES-RE1XE). The ESR spectra were recorded
under nonsaturating microwave power conditions. The magnitude of
modulation was chosen to optimize the resolution and the signal-to-
noise (S/N) ratio of the observed spectra. The g values were calibrated
with an Mn2+ marker.
Theoretical Calculations. Semiempirical MO calculations were
performed at the MNDO level with Gaussian 98.33 Final geometries
and energetics were obtained by optimizing the total molecular energy
with respect to all structural variables. The heats of formation (∆Hf)
were calculated with the restricted Hartree-Fock (RHF) formalism
using a key word “PRECISE”.
Synthesis of [1,9]Methanofullerene[70] (9). To a stirred suspension
of sodium hydride (745 mg, 18.6 mmol) in THF (70 mL), 4-cyanophe-
nol (2.13 g, 17.5 mmol) was added in one portion at 0 °C and stirring
was continued at 0 °C for 2 h. The solvent was removed under reduced
pressure and the residue was resuspended in DMF (70 mL). To the
suspension, 1-bromodocosane (7.61 g, 19.5 mmol) was added and the
solution was maintained at 70 °C for 2 h. The reaction mixture was
allowed to cool to room temperature and then evaporated to dryness at
a reduced pressure. The residue was dissolved in CHCl3, washed with
brine, dried over anhydrous Na2SO4, and evaporated. Reprecipitation
from hexane-benzene gave 4-cyano-1-docosanoxybenzene as a pale
1
yellow solid (7.28 g, 17.0 mmol, 97%). H NMR (270 MHz, CDCl3)
δ 7.57 (d, J ) 8 Hz, 2 H), 6.93 (d, J ) 8 Hz, 2 H), 3.99 (t, J ) 7 Hz,
2 H), 1.80 (quintet, J ) 7 Hz, 2 H), 1.50-1.20 (m, 38 H), 0.88 (t, J )
7 Hz, 3 H); MS(FAB) 428 (M + H+). To a stirred solution of LiAlH4
(3.17 g, 83.5 mmol) in dry THF (100 mL), a solution of 4-cyano-1-
docosanoxybenzene (7.25 g, 16.9 mmol) in dry THF (50 mL) was added
dropwise at 0 °C and stirring was continued at 0 °C for 4 h. The reaction
mixture was quenched by addition of 5 mL of ethyl acetate followed
by addition of 300 mL of 3 M HCl aqueous solution. The organic layer
was extracted with benzene, washed with saturated Na2CO3, and dried
over anhydrous Na2SO4 and then the solvent was evaporated. Flash
column chromatography on silica gel with ethyl acetate-ethanol (2:1)
as an eluent (Rf ) 0.05) and subsequent reprecipitation from hexane-
benzene gave 4-aminomethyl-1-docosanoxybenzene as a white solid
1
(72% yield, 5.27 g, 12.2 mmol). H NMR (270 MHz, CDCl3) δ 7.20
(d, J ) 8 Hz, 2 H), 6.86 (d, J ) 8 Hz, 2 H), 3.94 (t, J ) 7 Hz, 2 H),
3.79 (s, 2 H), 1.79 (quintet, J ) 7 Hz, 2 H), 1.50-1.20 (m, 38 H),
0.88 (t, J ) 7 Hz, 3 H); MS (FAB) 432 (M + H+). To a stirred solution
of [1,9]methanofullerene[70] carboxylic acid32b (23.5 mg, 0.0261 mmol)
and 1-hydroxybenzotriazole hydrate (HOBT) (6.3 mg, 0.0410 mmol)
in 5 mL of bromobenzene-DMSO (5:1), was added under nitrogen
atmosphere 1,3-dicyclohexylcarbodiimide (DCC) (28.5 mg, 0.138
mmol) followed by 4-aminomethyl-1-docosanoxybenzene (12.2 mg,
0.0282 mmol). The reaction was stirred at room temperature for 20 h,
after which the solvent was evaporated to yield a black solid. Flash
column chromatography on silica gel with benzene as an eluent (Rf )
0.15) and subsequent reprecipitation from benzene-acetonitrile gave
9 as a dark grayish brown solid (25.0 mg, 0.0190 mmol, 73% yield).
Mp >300 °C; 1H NMR (270 MHz, CDCl3) δ 7.36 (d, J ) 8 Hz, 2 H),
6.92 (d, J ) 8 Hz, 2 H), 6.56 (t, J ) 5 Hz, 1 H), 4.63 (d, J ) 5 Hz,
2 H), 3.96 (t, J ) 7 Hz, 2 H), 3.50 (s, 1 H), 1.78 (quintet, J ) 7 Hz,
2 H), 1.60-1.20 (m, 38 H), 0.88 (t, J ) 7 Hz, 3 H); MS (FAB) 1313
(M + H+); 13C NMR (101 MHz, CDCl3) δ 164.41, 159.04, 155.88,
155.18, 151.45, 151.17, 150.68, 150.61, 150.56, 149.39, 149.27, 149.18,
148.95, 148.60, 148.55, 148.46, 148.35, 148.27, 148.24, 147.71, 147.64,
147.53, 147.38, 147.33, 146.98, 146.87, 145.98, 145.87, 145.53, 145.21,
143.86, 143.43, 143.30, 143.16, 142.84, 142.67, 142.02, 141.95, 141.53,
140.32, 139.15, 138.89, 137.05, 133.82, 133.70, 132.74, 130.86, 130.76,
130.66, 129.64 (C6H4), 129.12, 114.97 (C6H4), 68.18 (OCH2), 65.33
(C70-sp3), 64.13 (C70-sp3), 44.14 (CH2C6H4), 31.92, 30.91, 29.70, 29.62,
29.42, 29.36, 29.26, 26.15, 26.07 (CH), 22.69, 14.12.
Laser Flash Photolysis. The measurements of radical cation
absorption spectra in the photochemical reaction of C60, C70, and their
derivatives with p-benzoquinone and p-chloranil in the presence of
Sc(OTf)3 (0.11 M) were performed according to the following
procedures: The solution was deoxygenated by argon purging for 10
min prior to the measurement. The deaerated PhCN solution containing
C60, C70, and their derivatives (1.2 × 10-4 M) and p-benzoquinone
(0.10 M) or p-chloranil (0.04 M) was excited by a Nd:YAG laser
(Quanta-Ray, GCR-130, 6 ns fwhm) at 532 nm with the power of 10
mJ per pulse. For shorter time-scale measurements (<5 µs), a pulsed
xenon flash lamp (Tokyo Instruments, XF80-60, 15 J, 60 ms fwhm)
was used for the probe beam, which was detected with a Ge-APD
module (Hamamatsu, C5331-SPL) after passing through the photo-
chemical quartz vessel (10 × 10 mm) and a monochromator. For longer
Results and Discussion
3
Sc3+-Promoted Electron Transfer from C60* to p-Ben-
zoquinones. Photoexcitation of C60 with 532-nm laser light at
which C60 has its absorption maximum results in formation of
3C60* via the fast intersystem crossing from the singlet excited
state and is characterized by the triplet-triplet absorption band
at 740 nm.34Although 3C60* is quenched by p-chloranil (Cl4Q)
•+
with a rate constant of 2.0 × 107 M-1 s-1, no C60 is formed
as reported previously17a (see Supporting Information S1). This
result is reasonable, judging from the positive free energy change
(∆G0et) obtained from the one-electron oxidation potential of
3C60* (E0ox ) 0.20 V vs SCE)35,36 and the one-electron reduction
potential of p-chloranil (E0 ) 0.01 V vs SCE).37
red
Photoexcitation of p-benzoquinone generates its triplet
excited state with unit efficiency owing to the ultrafast rate of
intersystem crossing.38 The high energy of the triplet quinone
with ET ) 2.17 eV39 is energetically sufficient to accomplish
(33) (a) Dewar, M. J. S.; Thiel, W. J. Am. Chem. Soc. 1977, 99, 4899.
(b) Dewar, M. J. S.; Thiel, W. J. Am. Chem. Soc. 1977, 99, 4907.
(34) Foote, C. S. Top. Curr. Chem. 1994, 169, 347.
(35) The E0ox value of C60 (1.26 V vs ferrocene/ferricenium) is converted
3
to the value vs SCE (1.76 V).8 Subtraction of the triplet energy of C60*
3
(1.56 eV)36 from the E0 value of C60 gives the E0 value of C60* (0.20
ox
ox
V vs SCE).
(32) (a) Wang, Y.-H.; Cao, J.-R.; Schuster, D. I.; Wilson, S. R.
Tetrahedron Lett. 1995, 36, 6843. (b) Wang, Y.-H.; Schuster, D. I.; Wilson,
S. R.; Welch, C. J. J. Org. Chem. 1996, 61, 5198.
(36) Hung, R. R.; Grabowski, J. J. J. Phys. Chem. 1991, 95, 6073.
(37) Fukuzumi, S.; Koumitsu, S.; Hironaka, K.; Tanaka, T. J. Am. Chem.
Soc. 1987, 109, 305.

Scandium Ion-Promoted Oxidation of Fullerenes
J. Am. Chem. Soc., Vol. 123, No. 50, 2001 12461
Figure 1. Transient absorption spectra observed in photoinduced
electron transfer from C60 (1.1 × 10-4 M) to Cl4Q (4.0 × 10-2 M) in
the presence of Sc3+ (0.11 M) after laser irradiation at λ ) 532 nm in
deaerated PhCN at 298 K (black circles ) 5 µs, black square ) 25 µs,
and black triangle ) 100 µs). Inset: Time profile of the absorption
3
•+
band at 740 and 980 nm due to C60* and C60
.
the oxidation of aromatic donors including fullerenes. However,
selective photoexcitation with a 440-nm laser light of p-
benzoquinone in PhCN containing C60 results in formation of
3C60*, which has a diagnostic band at 740 nm (see Supporting
Information S2). This suggests that an efficient energy transfer
from the triplet excited state of p-benzoquinone to C60 (ET )
1.56 eV)34 occurs rather than an electron transfer from C60.
In the presence of scandium triflate [Sc(OTf)3], photoexci-
tation with 532-nm laser light of C60 in PhCN containing Cl4Q
results in the appearance of a new absorption band at 980 nm,
Figure 2. ESR spectra of (a) C60•+/Cl4Q•--Sc3+ and (b) 1,4-(C6H5-
CH2)2C60•+/Cl4Q•--Sc3+ generated in photoinduced electron transfer
from C60 (2.8 × 10-4 M) and 1,4-(C6H5CH2)2C60 (2.8 × 10-4 M) to
Cl4Q (1.0 × 10-2 M) in the presence of Sc3+ (5.6 × 10-3 M) in
deaerated PhCN at 193 K and (c) Cl4Q•--Sc3+ generated in photoin-
duced electron transfer from (BNA)2 (4.0 × 10-2 M) to Cl4Q (4.0 ×
10-2 M) in the presence of Sc3+ (5.6 × 10-3 M) in deaerated PhCN at
193 K.
which is readily assigned to C60 ,
•+ 9,10,40 as shown in Figure 1.41
The absorption band due to the p-chloranil radical anion
(Cl4Q•-)-Sc3+ complex, which should be formed together with
•+
C60 seems to be overlapped at 500 nm with the residual
3
3
absorption due to C60*. The decay of C60* at 740 nm is
•+
accompanied by the appearance of C60 at 980 nm, but this
Scheme 1
species decays at prolonged reaction time (see inset of Figure
1). This indicates that photoinduced electron transfer from 3C60*
•+
to Cl4Q (ket) occurs in the presence of Sc3+ to produce C60
and the Cl4Q•--Sc3+ complex, both of which decay via a back
electron-transfer (kbet) process (Scheme 1). The strong binding
between Cl4Q•- and Sc3+ makes the electron transfer energeti-
cally feasible as reported for the Sc3+-catalyzed electron-transfer
reduction of p-benzoquinone.25
The formation of the radical intermediate complex [C60
•+
-
Cl4Q•--Sc3+] in Scheme 1 is confirmed by the ESR spectrum
observed in the Sc3+-promoted photoinduced electron transfer
3
from C60* to Cl4Q in frozen PhCN at 193 K under photoirra-
CH2)2C60, the ESR signal at g ) 2.0024 (Figure 2b) becomes
more prominent as compared to the case of C60.
diation with a high-pressure mercury lamp. The resulting
spectrum is shown in Figure 2a and consists of two overlapping
isotropic ESR signals which have different g values (g ) 2.0068
and 2.0024). However, when C60 is replaced by 1,4-(C6H5-
To assign these ESR signals, the Cl4Q•--Sc3+ complex was
independently produced by photoinduced electron transfer from
dimeric 1-benzyl-1,4-dihydronicotinamide [(BNA)2]42 to p-
chloranil in frozen PhCN at 77 K. (BNA)2 is known to act as
a unique two-electron donor to produce radical anions of electron
acceptors.43 The ESR spectrum of Cl4Q•--Sc3+ thus produced
(eq 1) is shown in Figure 2c. This signal in the spectrum at
(38) (a) Rathore, R.; Hubig, S. M.; Kochi, J. K. J. Am. Chem. Soc. 1997,
119, 11468. (b) Sun, D.; Hubig, S. M.; Kochi, J. K. J. Org. Chem. 1999,
64, 2250.
(39) Calvert, J. G.; Pitts, J. N., Jr. Photochemistry; Wiley: New York,
1996; p 786.
(40) Kato, T.; Kodama, T.; Shida, T.; Nakagawa, T.; Matsui, Y.; Suzuki,
S.; Shinoharu, H.; Yamaguchi, K.; Achiba, Y. Chem. Phys. Lett. 1991, 180,
446.
(41) Since the transient absorption spectra were measured at 20-nm
interval, the determined absorption maximum has an uncertainty of 10-20
nm.
(42) (a) Patz, M.; Kuwahara, Y.; Suenobu, T.; Fukuzumi, S. Chem. Lett.
1997, 567. (b) Fukuzumi, S.; Suenobu, T.; Patz, M.; Hirasaka, T.; Itoh, S.;
Fujitsuka, M.; Ito, O. J. Am. Chem. Soc. 1998, 120, 8060.
(43) Fukuzumi, S.; Suenobu, T.; Urano, T.; Tanaka, K. Chem. Lett. 1997,
875.

12462 J. Am. Chem. Soc., Vol. 123, No. 50, 2001
Fukuzumi et al.
3
Figure 4. (a) Plot of decay rate constant (kd) of C60* vs [Q] in the
presence of Sc3+ (0.10 M) in deaerated PhCN at 298 K. (b) Plot of ket
vs [Sc3+] for electron transfer from 3C60* to Q (white circles) and from
CoTPP (1.0 × 10-5 M) to Q (1.0 × 10-2 M) (black circles) in the
presence of Sc3+ in deaerated PhCN at 298 K.
3
Figure 3. (a) Plot of decay rate constants (kd) of C60* vs [Cl4Q] in
the presence of Sc3+ (0.11 M) in deaerated PhCN at 298 K. (b) Plot of
ket vs [Sc3+] for electron transfer from 3C60* to Cl4Q in deaerated PhCN
at 298 K.
concentrations, changing to a second-order dependence at high
concentrations as shown in Figure 4b (open circles).
g ) 2.0068 agrees with the ESR signal with the g value of
2.0068 in Figure 2a. The other ESR signal at g ) 2.0024 in
•+ 10,44
Such a mixture of first-order and second-order dependence
on [Sc3+] is also observed in electron transfer from CoTPP
(TPP2- ) tetraphenylporphyrin dianion) to Q. No electron
transfer from CoTPP to Q occurs in PhCN at 298 K. In the
presence of Sc(OTf)3, however, efficient electron transfer from
CoTPP to Q occurs to yield CoTPP+ (see Supporting Informa-
tion S3). The electron-transfer rates obey second-order kinetics,
Figure 2a agrees with that reported for C60
.
3
The decay rate of the absorbance due to C60* at 740 nm
(inset of Figure 1) obeys pseudo-first-order kinetics and the
pseudo-first-order rate constant (kd) increases linearly with
increasing the p-chloranil concentration [Cl4Q] as shown in
Figure 3a. From the slope of the linear correlation in Figure 3a
is obtained the second-order rate constant of electron transfer
(ket) in Scheme 1. The ket value increases linearly with increasing
the Sc3+ concentration as shown in Figure 3b.
showing a first-order dependence on each reactant concentration.
The dependence of the observed electron-transfer rate constant
(ket) on [Sc3+] was examined for electron transfer from CoTPP
to Q at various concentrations of Sc3+. The results are shown
in Figure 4b (black circles), where the ket value increases linearly
with [Sc3+] to show a first-order dependence on [Sc3+] at low
concentrations, changing to a second-order dependence at high
concentrations as is the case of the Sc3+-promoted electron
When p-chloranil is replaced by p-benzoquinone (Q), the ket
value for electron transfer from 3C60* to Q, which was evaluated
from the slope of the line in Figure 4a, increases with an increase
in [Sc3+] to exhibit a first-order dependence on [Sc3+] at low
3
transfer from C60* to Q in Figure 4b (open circles).
A mixture of first-order and second-order dependence on
[Sc3+] is ascribed to formation of 1:1 and 1:2 complexes
between the semiquinone radical anion and Sc3+ at the low and
high concentrations of Sc3+ (eqs 3 and 4, respectively), which
results in acceleration of the rate of electron transfer. The
complex formation of Q•- and Sc3+
(44) Siedschlag, C.; Torres-Garcia, G.; Wolff, C.; Mattay, J.; Fujitsuka,
M.; Watanabe, A.; Ito, O.; Dunsch, L.; Ziegs, F.; Luftmann, H. J. Inform.
Res. 1998, 24, 265.

Scandium Ion-Promoted Oxidation of Fullerenes
J. Am. Chem. Soc., Vol. 123, No. 50, 2001 12463
K1
{\
Q
•- + Sc3+
} Q•--Sc3+
(3)
(4)
K2
Q
•- + Sc3+ + Sc3+{ } Q•--2Sc3+
\
should result in the positive shift of the one-electron reduction
potential of Q (Ered) and the Nernst equation is given by eq 5,
where E0 is the one-electron reduction potential
red
Ered ) E0red + (2.3RT/F) log K1[Sc3+](1 + K2[Sc3+]) (5)
of Q to Q•- in the absence of Sc3+ and K1 and K2 are the
formation constants for the 1:1 and 1:2 complexes between Q•-
and Sc3+, respectively. Since Sc3+ has no effect on the oxidation
potential of CoTPP and 3C60*, the free energy change of electron
transfer in the presence of Sc3+ (∆Get) can be expressed by eq
6, where ∆G0et is the free energy change in the absence of Sc3+
Thus, electron transfer from CoTPP and C60* to Q and
.
Figure 5. (a) Plot of ket/[Sc3+] vs [Sc3+] for electron transfer from C60
to Q in the presence of Sc3+ in deaerated PhCN at 298 K (white circles).
(b) Plot of ket/[Sc3+] vs [Sc3+] for electron transfer from CoTPP to Q
in the presence of Sc3+ in deaerated PhCN at 298 K (black circles).
3
∆Get ) ∆G0et - (2.3RT) log(K1[Sc3+] + K1K2[Sc3+]2) (6)
Cl4Q becomes more favorable energetically with an increase
in the concentration of Sc3+. If such a change in the energetics
is directly reflected in the transition state of electron transfer,
the dependence of the observed rate constant of electron transfer
(ket) on [Sc3+] can be derived from eq 6 as given by eq 7, where
k0 is the rate constant in the absence of Sc3+
.
ket/[Sc3+] ) k0K1(1 + K2[Sc3+])
(7)
The validity of eq 7 is confirmed by the linear plot of ket/
[Sc3+] vs [Sc3+] for the Sc3+-promoted electron transfer from
3C60* and CoTPP to Q as shown in Figure 5 (part a and b,
respectively). From the slopes and intercepts in Figures 5a and
5b are obtained the K2 values as 1.7 and 2.0, respectively. The
agreement of these two K2 values supports the validity of the
analysis.
Since there is no interaction between Q and Sc3+ as indicated
by the lack of spectral change of Q in the presence of Sc3+, the
acceleration of electron transfer from CoTPP to Q is ascribed
to the complexation of Sc3+ with Q•-. The formation of the
1:2 complex between Q•- and Sc3+ (eq 4) is confirmed by the
ESR spectrum of Q•--2Sc3+, which shows superhyperfine
structure due to the interaction of Q•- with two Sc nuclei. Since
Q•--2Sc3+ is unstable because of the facile disproportionation
reaction, the Q•--Sc3+ complex was generated in photoinduced
electron transfer from [(BNA)2]38 to Q at low temperatures. The
photochemical reaction was carried out in an ESR cavity where
an ESR tube containing a propionitrile (EtCN) solution of
(BNA)2, Q, and Sc3+ was irradiated with a mercury lamp at
203 K. Propionitrile was used instead of PhCN to avoid freezing
the solvent at 203 K. The observed ESR spectrum of the
semiquinone radical anion (Q•-) in the presence of Sc3+ (4.4
× 10-2 M) is shown in Figure 6a. The well-resolved 19 lines
of the spectrum clearly indicate the hyperfine splitting (a(4H))
due to four protons of semiquinone radical anions and super-
hyperfine splitting (a(2Sc)) of two equivalent Sc3+ nuclei (I )
7/2). The hyperfine splitting constants are almost the same
between a(4H) and a(2Sc), resulting in the overall nuclear spin
) 9, which causes 19 lines. The computer simulation spectrum
with a(4H) ) 1.15 G, a(2Sc) ) 1.15 G with the line width
(∆Hmsl) ) 0.50 G is shown in Figure 6b for comparison. The
Figure 6. (a) ESR spectrum of propionitrile solution containing (BNA)2
(1.6 × 10-2 M), p-benzoquinone (4.9 × 10-2 M), and Sc(OTf)3 (4.4
× 10-2 M) with irradiation of a high-pressure mercury lamp at 203 K.
(b) Computer simulation spectrum with g ) 2.0034, a(4H) ) a(2Sc)
) 1.15 G, ∆Hmsl ) 0.50 G.
agreement between the observed and simulation spectra confirms
the formation of the 1:2 complex between Q•- and Sc3+ 45
.
Formation of Radical Cations of Fullerene Derivatives.
The formation of C60•+ by Sc3+-promoted photoinduced electron-
3
transfer oxidation of C60* by p-chloranil (vide supra) enables
us to examine the oxidation reactivities of a series of fullerene
derivatives quantitatively, because oxidation of fullerenes is
expected to be easier upon derivatization.19 The examined
fullerene derivatives are shown in Chart 1.
As is the case for C60 (Figure 1), the transient absorption
maxima of other fullerene radical cations were determined by
(45) The 1:2 complex between Q•- and Sc3+ is exclusively formed at
203 K probably because of the large K2 value at the low temperature as
compared to the value at 298 K.

12464 J. Am. Chem. Soc., Vol. 123, No. 50, 2001
Fukuzumi et al.
Chart 1
Table 1. Absorption Maxima (λmax) and g Values of Fullerene
Radical Cations, Rate Constants of Electron Transfer (ket) from
Fullerene Triplets to p-Chloranil in the Presence of Sc(OTf)3 (0.11
M), and Relative HOMO Level of Fullerenes (∆EHOMO
)
a
λmax ket,
,
∆EHOMO,
compound
nm g value
M-1 s-1
eV
1
2
3
4
5
6
7
8
9
C60
980 2.0024 1.1 × 106
920 2.0024 2.3 × 106
920 2.0024 2.5 × 106
900 2.0024 2.6 × 106
900 2.0024 2.7 × 106
920 2.0024 3.0 × 106
1400 2.0017 4.0 × 106
0
1,4-(4-BrC6H4CH2)2C60
1,4-(3-BrC6H4CH2)2C60
1,4-(But)(C6H5CH2)C60
1,4-(2-BrC6H4CH2)2C60
1,4-(C6H5CH2)2C60
C70
0.22
0.24
0.31
0.32
0.32
0.46
0.51
0.60
Figure 7. Time profiles observed in the photoinduced electron transfer
from C70 (1.1 × 10-4 M) to Cl4Q (4.0 × 10-2 M) in the presence of
Sc3+ (0.11 M) at (a) 900, (b) 770, and (c) 1400 nm. Time profile at
3
•+
N-methylpyrrolidine-C60 960 2.0026 5.9 × 106
900 nm is mainly due to C70*. The time profile of C70 is obtained
3
1400 2.0012 8.4 × 106
by subtracting the time profile of C70* (the dotted line) from the
[1,9]methano-C70
observed time profile at 770 and 1400 nm (part b and c, respectively).
a Calculated by the MNDO semiempirical method in reference to
C60.
laser flash photolysis experiments for the Sc3+-promoted pho-
toinduced electron-transfer reactions from the triplet excited
states of the fullerene derivatives to p-chloranil (e.g., see
Supporting Information S4). The λmax values of the fullerene
radical cations are listed in Table 1 (vide infra).
In the case of C70 (7), the triplet-triplet absorption band of
C70, which appears at λmax ) 900 nm, decays to reach a residual
•+
absorbance due to C70 as shown in Figure 7a. At other
wavelengths the rise in absorbance due to C70•+ is significantly
3
mixed with the decay in absorbance due to C70* as shown in
a time profile at 770 nm (Figure 7b) and at 1400 nm (Figure
3
7c). The decay of C70* obeys first-order kinetics and the
pseudo-first-order rate constant increases linearly with increasing
Cl4Q concentration [Cl4Q] as in the case of 3C60*. The second-
order rate constant of electron transfer (ket) is determined from
the slope of the linear correlation and is listed in Table 1. To
Figure 8. Transient absorption spectra after subtraction of the
absorption due to 3C70* in the photoinduced electron transfer from C70
(1.1 × 10-4 M) to Cl4Q (4.0 × 10-2 M) in the presence of Sc3+ (0.11
M) at 250 ns and 10 µs after laser excitation at λ ) 532 nm in deaerated
PhCN at 298 K.
•+
extract the time profile of C70 at 770 and 1400 nm, the time
3
profile of C70* (dotted line) is subtracted from the observed
time profile as shown in parts b and c of Figure 7, respectively.
This procedure is repeated at each wavelength to obtain the time-
resolved absorption spectrum due to C70•+. The maximum
absorbance due to C70•+ is obtained at 10 µs (Figure 7b,c). The
transient absorption spectra thus obtained at 250 ns and 10 µs
are shown in Figure 8, where a broad absorption band is
observed in the NIR region (1400 nm) together with the bands
at 770 and 500 nm in the spectrum at 10 µs.46 Reed et al.10
have recently reported that C70•+ has an absorption band at 770
nm which corresponds to the band observed at 770 nm in Figure
8. Since the time profile at 1400 nm (Figure 7c) is the same as
the profile at 770 nm after subtraction of the absorbance due to
3C70* (Figure 7b), the long-wavelength absorption band in the
NIR region (λmax ) 1400 nm) is clearly attributed to C70•+. A
similar broad NIR band is observed for [1,9]methanofullerene-
[70] (9) (Table 1, see also Supporting Information, S5).
The formation of the radical ion pair [C70•+Cl4Q•--Sc3+] is
confirmed by the ESR spectrum observed in Sc3+-promoted
(46) The absorption bands at shorter wavelengths than 700 nm may be
overlapped with the bands due to Cl4Q•--Sc3+, since these absorption bands
are commonly observed for other fullerene derivatives (e.g., see Figure 1).

Scandium Ion-Promoted Oxidation of Fullerenes
J. Am. Chem. Soc., Vol. 123, No. 50, 2001 12465
Cl4Q•- and the latter is assigned to C70•+. In contrast to the
•+
•+
case of C60 (g ) 2.0024 in Figure 2), the g value of C70 is
smaller than the free spin value (2.0023). When C70 is replaced
by a functionalized C70 (9), the g value of 9•+ (2.0012) becomes
even smaller as compared to C70•+. These g values are listed in
Table 1 together with those of other fullerenes obtained in a
similar manner.
Relationship between Rates of Electron-Transfer Oxida-
tion of Fullerene Triplet Excited States and the HOMO
Energies. The ket values of Sc3+-promoted photoinduced
electron transfer from the triplet excited states of a series of
fullerenes to p-chloranil were determined as for the case of C60
and C70 (vide supra) and these values are listed in Table 1. The
ket value also increases with increasing the cage size of the
fullerenes (Table 1). Such an increase in the ket value may be
primarily ascribed to the higher HOMO energies upon the
derivatization of C60 and C70 since the ionization energies of
fullerenes are reported to decrease for derivatized C60 and higher
fullerenes.19-22 Since the HOMO levels of fullerenes calculated
by the semiempirical MNDO method are shown to be well-
correlated with the one-electron oxidation potentials of fullerenes,5
an increase in the HOMO energy relative to C60 (∆EHOMO) has
been calculated for each fullerene in Table 1 (see Experimental
Section). A plot between log ket and ∆EHOMO is shown in Figure
10, where there is a good linear correlation between them. Such
a linear correlation suggests that the electron-transfer oxidation
reactivities of the triplet excited states of fullerenes to p-chloranil
are largely determined by the HOMO energies of fullerenes
when the triplet energies remain virtually the same among the
fullerenes.
Figure 9. ESR spectra of (a) C70•+/Cl4Q•--Sc3+ and (b) 9•+/Cl4Q•-
-
Sc3+ generated in photoinduced electron transfer from C70 (2.8 × 10-4
M) and 9 (2.8 × 10-4 M) to Cl4Q (1.0 × 10-4 M) in the presence of
Sc3+ (5.6 × 10-3 M) in deaerated PhCN at 193 K.
Acknowledgment. This work was partially supported by a
Grant-in-Aid for Scientific Research Priority Area (No. 11228205)
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan. The support of the Robert A. Welch
Foundation (K.M.K) is also gratefully acknowledged.
Supporting Information Available: Transient absorption
spectra of 3C60* (S1, S2), UV-vis spectral changes in electron
transfer from CoTPP to Q in the presence of Sc3+ (S3), transient
absorption spectra of 5•+ (S4), and time-profile and transient
absorption spectra observed in the photoinduced electron transfer
Figure 10. Plot between log ket and ∆EHOMO based on the data in
Table 1.
3
from 9* to Cl4Q in the presence of Sc3+ (S5) (PDF). This
3
photoinduced electron transfer from C70* to Cl4Q in frozen
material is available free of charge via the Internet at
http://pubs.acs.org.
PhCN at 193 K under photoirradiation with a high-pressure
mercury lamp as shown in Figure 9a. As is the case for C60
(Figure 2a), two isotropic ESR signals (g ) 2.0068 and g )
2.0017) are observed in Figure 9a. The former is attributed to
JA016335D