Relaxation processes in the excited state of C60-o-quinodimethane adducts

DOI: 10.1039/FT9969200377

Source and publish data:

Journal of the Chemical Society - Faraday Transactions p. 377 - 382 (1996)

Update date:2022-09-26

Topics:

Authors:

Nakamura, Yosuke

Minowa, Toshiyuki

Hayashida, Yoshitou

Tobita, Seiji

Shizuka, Haruo

Nishimura, Jan

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Article abstract of DOI:10.1039/FT9969200377

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 T_n ← T₁ bands, in good agreement with those of C₆₀-OQD without a dimethylamino group. In benzonitrile, however, the T_n ← 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.