## Abstract

Photoinduced intramolecular charge separation and charge recombination of oligothiophene-methyl viologen dyads (T_{n}-MV ^{2+}·2X^{-}, n = 4 or 8, X^{-} = I^{-} or PF6^{-}), which were designed to generate positively charged radical ion pairs (T_{n}^{·+}-MV ^{·+}·2X^{-}), have been investigated by the time-resolved fluorescence and transient absorption spectra in CH_{3}CN. Upon excitation of the T_{8} moiety in T_{8}-MV ^{2+}·2X^{-}, the radical cation pair (T_{8} ^{·+}-MV^{·+}·2X^{-}) was produced via the excited singlet state of T_{8} (^{1}T_{8} ^{*}), because the fluorescence lifetime of the ^{1}T _{8}^{*} moiety in T_{8}-MV ^{2+}·2X^{-} becomes short compared with pristine ^{1}T_{8}^{*}. The lifetimes of T_{8} ^{·+}-MV^{·+}·2X^{-} were evaluated to be 720-980 ns depending on the counteranion, I^{-} or PF_{6}^{-}. On the other hand, T_{4}-MV ^{2+}·2X^{-} leads to lifetimes of T_{4} ^{·+}-MV^{·+}·2X^{-} of 210-240 ns, although the charge separation seems to occur via the excited triplet state of T_{4} (^{3}T_{4}^{*}), because the fluorescence quenching of the ^{1}T_{4}^{*} moiety in T_{4}-MV^{2+}·2X^{-} was not observed. As factors to achieve these relatively long lifetimes of T_{n} ^{·+}-MV^{·+}·2X^{-}, the charge recombination between of the positive charges (holes) on the T_{n} and MV moieties and the center-to-center distance between the positive charges (holes) on the T_{n} and MV moieties may be considered, in addition to the triplet spin character of T_{n}^{·+}-MV ^{·+}·2X^{-}.

Original language | English |
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Pages (from-to) | 10649-10655 |

Number of pages | 7 |

Journal | Journal of Physical Chemistry A |

Volume | 108 |

Issue number | 48 |

DOIs | |

Publication status | Published - 2004 Dec 2 |