Photoinduced charge separation and charge recombination of oligothiophene-viologen dyads in polar solvent

Yasuyuki Araki, Hongxia Luo, Takumi Nakamura, Mamoru Fujitsuka, Osamu Ito, Hiroki Kanato, Yoshio Aso, Tetsuo Otsubo

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)

Abstract

Photoinduced intramolecular charge separation and charge recombination of oligothiophene-methyl viologen dyads (Tn-MV 2+·2X-, n = 4 or 8, X- = I- or PF6-), which were designed to generate positively charged radical ion pairs (Tn·+-MV ·+·2X-), have been investigated by the time-resolved fluorescence and transient absorption spectra in CH3CN. Upon excitation of the T8 moiety in T8-MV 2+·2X-, the radical cation pair (T8 ·+-MV·+·2X-) was produced via the excited singlet state of T8 (1T8 *), because the fluorescence lifetime of the 1T 8* moiety in T8-MV 2+·2X- becomes short compared with pristine 1T8*. The lifetimes of T8 ·+-MV·+·2X- were evaluated to be 720-980 ns depending on the counteranion, I- or PF6-. On the other hand, T4-MV 2+·2X- leads to lifetimes of T4 ·+-MV·+·2X- of 210-240 ns, although the charge separation seems to occur via the excited triplet state of T4 (3T4*), because the fluorescence quenching of the 1T4* moiety in T4-MV2+·2X- was not observed. As factors to achieve these relatively long lifetimes of Tn ·+-MV·+·2X-, the charge recombination between of the positive charges (holes) on the Tn and MV moieties and the center-to-center distance between the positive charges (holes) on the Tn and MV moieties may be considered, in addition to the triplet spin character of Tn·+-MV ·+·2X-.

Original languageEnglish
Pages (from-to)10649-10655
Number of pages7
JournalJournal of Physical Chemistry A
Volume108
Issue number48
DOIs
Publication statusPublished - 2004 Dec 2

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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