Supramolecular Formation of Li+@PCBM Fullerene with Sulfonated Porphyrins and Long‐Lived Charge Separation |
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| Authors: | Yuki Kawashima Dr. Kei Ohkubo Dr. Hiroshi Okada Prof. Dr. Yutaka Matsuo Prof. Dr. Shunichi Fukuzumi |
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| Affiliation: | 1. Department of Material and Life Science, Graduate School of Engineering, Osaka University, Suita, Osaka 565‐0871 (Japan), Fax: (+81)?6‐6879‐7370;2. Department of Chemistry, School of Science, The University of Tokyo, Bunkyo‐ku, Tokyo 113‐0033 (Japan) |
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| Abstract: | Lithium‐ion‐encapsulated [6,6]‐phenyl‐C61‐butyric acid methyl ester fullerene (Li+@PCBM) was utilized to construct supramolecules with sulfonated meso‐tetraphenylporphyrins (MTPPS4?; M=Zn, H2) in polar benzonitrile. The association constants were determined to be 1.8×105 M ?1 for ZnTPPS4?/Li+@PCBM and 6.2×104 M ?1 for H2TPPS4?/Li+@PCBM. From the electrochemical analyses, the energies of the charge‐separated (CS) states were estimated to be 0.69 eV for ZnTPPS4?/Li+@PCBM and 1.00 eV for H2TPPS4?/Li+@PCBM. Upon photoexcitation of the porphyrin moieties of MTPPS4?/Li+@PCBM, photoinduced electron transfer occurred to produce the CS states. The lifetimes of the CS states were 560 μs for ZnTPPS4?/Li+@PCBM and 450 μs for H2TPPS4?/Li+@PCBM. The spin states of the CS states were determined to be triplet by electron paramagnetic resonance spectroscopy measurements at 4 K. The reorganization energies (λ) and electronic coupling term (V) for back electron transfer (BET) were determined from the temperature dependence of kBET to be λ=0.36 eV and V=8.5×10?3 cm?1 for ZnTPPS4?/Li+@PCBM and λ=0.62 eV and V=7.9×10?3 cm?1 for H2TPPS4?/Li+@PCBM based on the Marcus theory of nonadiabatic electron transfer. Such small V values are the result of a small orbital interaction between the MTPPS4? and Li+@PCBM moieties. These small V values and spin‐forbidden charge recombination afford a long‐lived CS state. |
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| Keywords: | charge separation endohedral fullerenes electron transfer porphyrinoids supramolecular chemistry |
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