Competition between Intramolecular Electron-Transfer and Energy-Transfer Processes in Photoexcited Azulene-C60 Dyad

Takashi Makinoshima, Mamoru Fujitsuka, Mikio Sasaki, Yasuyuki Araki, Osamu Ito, Shunji Ito, Noboru Morita

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21 Citations (Scopus)

Abstract

Photoinduced intramolecular processes in a dyad of azulene and C 60 (Az-C60) were compared with those of a dyad of naphthalene and C60 (Naph-C60) on the basis of laser flash photolysis experiments. Upon photoexcitation of C60 in the presence of azulene, intermolecular electron transfer proceeded from azulene to the triplet state of C60 (C60(T1), although the rate constant was small (107 M-1 s-1), because of the small free-energy change for electron transfer via C 60(T1). In Az-C60, it was revealed that the S2 state of the Az moiety (Az(S2)-C60(S 0)) donates the excited energy to the C60 moiety, effectively generating Az(S0)-C60(S1). In polar solvents, a charge-separated state (Az.+-C60 .-) was generated from Az(S0)-C60(S 1), from which the Si state of the Az moiety (Az(S 1)-C60(S0)) was also generated by competitive energy transfer. The lifetimes of the charge-separated states were on the order of nanoseconds. Successive energy-transfer processes {Az(S2)-C 60(S0) → Az(S0)-C60(S n), Az(S1)-C60(S0) → Az(S 1)-C60(S0), where n ≥ 2} demonstrate that the multiple energy transfer is achieved in a simple dyad molecule. On the other hand, Naph-C60 dyad did not show charge separation upon excitation of the C60 moiety, but deactivated via intersystem crossing, generating almost quantitatively the C60(T1) moiety. These findings indicate the favorable donor ability of azulene compared to that of naphthalene, even though both azulene and naphthalene have the same 10-π-electron system.

Original languageEnglish
Pages (from-to)368-375
Number of pages8
JournalJournal of Physical Chemistry A
Volume108
Issue number3
DOIs
Publication statusPublished - 2004 Jan 22

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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