jp048364r_si_001.pdf (44.79 kB)

Photoinduced Charge Separation and Charge Recombination of Oligothiophene−Viologen Dyads in Polar Solvent

Download (44.79 kB)
journal contribution
posted on 02.12.2004 by Yasuyuki Araki, Hongxia Luo, Takumi Nakamura, Mamoru Fujitsuka, Osamu Ito, Hiroki Kanato, Yoshio Aso, Tetsuo Otsubo
Photoinduced intramolecular charge separation and charge recombination of oligothiophene−methyl viologen dyads (Tn−MV2+·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−MV2+·2X-, the radical cation pair (T8•+−MV•+·2X-) was produced via the excited singlet state of T8 (1T8*), because the fluorescence lifetime of the 1T8* moiety in T8−MV2+·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−MV2+·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-.