Res. Chem. Intermed.
, Vol. 27, No. 1,2, pp. 73–88 (2001)
Pico- and nano-second laser ash photolysis study on
photoinduced charge separation in oligothiophene-C
, KEISUKE MATSUMOTO
, OSAMU ITO
, YOSHIO ASO
and TETSUO OTSUBO
Institute for Chemical Reaction Science, Tohoku University, Katahira, Aoba-ku,
Sendai 980-8577, Japan
Department of Applied Chemistry, Faculty of Engineering, Hiroshima University,
Higashi-Hiroshima 739-8527, Japan
Received 24 March 2000; accepted 25 May 2000
Abstract—Photoinduced charge separation (CS) and charge recombination (CR) processes of octa-
dyad molecules (8T-C
, respectively) have
been investigated by time-resolved absorption spectroscopy in the visible and near-IR regions. In
showed energy transfer to
-moiety predominantly, while
contribution of CS was small. In various polar solvents, on the other hand, CS states were
predominantly formed from both singlet-excited oligothiophene and
-moiety because of lower
CS level in polar environments. The CR process generating both the triplet state of oligothiophene
and the ground state was con rmed in anisole and anisole/toluene mixture within a few nanoseconds.
In more polar solvents (dielectric constant ."
/ > 7/, CS states showed two components decay: Slow
decay component showed lifetime in the hundred nanosecond-region, while fast component decayed
within a few nanoseconds. For the mechanism of the long-living CS state in polar solvents ("
equilibrium between the CS state and the triplet state was proposed. Furthermore, effects of length of
oligothiophene on the CS and CR processes were discussed on the basis of the free energy changes.
Conjugated polymers are attractive materials. Their properties have been found to t
many demands of material engineering. For understanding the properties, oligomers
have been investigated experimentally and theoretically, since structural ambiguity
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