Journal of the Chemical Society - Faraday Transactions p. 377 - 382 (1996)
Update date:2022-09-26
Topics:
Nakamura, Yosuke
Minowa, Toshiyuki
Hayashida, Yoshitou
Tobita, Seiji
Shizuka, Haruo
Nishimura, Jan
Intramolecular electron transfer and exciplex formation in a C60 adduct possessing an N,N-dimethylaniline (DMA) moiety, C60-DMA, in cyclohexane and benzonitrile have been investigated in comparison with the intermolecular reactions between C60-o-quinodimethane (OQD) and DMA. The fluorescence of C60-DMA in cyclohexane was little quenched by the DMA moiety and was almost the same as that of C60-OQD, in contrast with the decrease and red shift in the fluorescence of C60-OQD in the presence of excess DMA in cyclohexane, mainly resulting from exciplex formation. The difficulties in the intramolecular exciplex formation of C60-DMA in cyclohexane are considered to result from its unfavourable molecular structure, which also affects charge-transfer complex formation. On the other hand, in benzonitrile the fluorescence of C60-DMA was significantly quenched and red shifted. The quenching is due to the intramolecular electron transfer from the DMA moiety to the S1 state of the C60 moiety, where the rate constant was estimated as 1.5 × 1010 s-1. The red shift is brought about by the charge-transfer character in the S1 state, resulting from the through-bond interaction between the two chromophores. The transient absorption spectra of C60-DMA in cyclohexane exhibited the Tn ← T1 bands, in good agreement with those of C60-OQD without a dimethylamino group. In benzonitrile, however, the Tn ← T1 bands were considerably weakened by the decrease in the triplet population, and the lifetime (7 μs) of T1 was reduced relative to that in cyclohexane (28 μs). The decrease in the lifetime in benzonitrile can be ascribed to the weak charge-transfer interaction between the T1 of the C60 moiety and the S0 of the DMA moiety.
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