Orientational Effect on the Photophysical Properties of Quaterthiophene-C_(60) Dyads

摘要

Two quaterthiophene[60]fullerene dyads in which C_(60) is singly (4TsC) or doubly (4TdC) connected to the inner #beta#-position of the terminal thiophene rings have been synthesized. The electronic properties of these donor-acceptor compounds were analyzed by UV/Vis spectroscopy and cyclic voltametry, and their photophysical properties in solution and in the solid state by (time-resolved) photoluminescence (PL) and photoinduced absorption (PIA) spectroscopy. Both the flexible and geometrically constrained 4TsC and 4TdC dyads exhibit photoinduced charge transfer from the quaterthiophene to the fullerene in toluene and o-dichlorobenzene (ODCB). In toluene charge transfer occurs in both dyads by an indirect mechanism, the first step of which is a singlet-energy transfer from the 4T(S_1) state to the C_(60)(S_1) state. In the more polar ODCB, direct electron transfer from 4T(S_1) competes with energy transfer, and both direct and indirect chargetransfers are observed. The geometrical fixation of the donor and acceptor chromophores in 4TdC results in rate constants for energy and electron transfer that are more than an order of magnitude larger than those of the flexible 4TsC system. for both dyads, charge recombination is extremely fast, as inferred from picosecond-resolved temporal evolution of the excited state absorption of the 4T~(centre dot+) radical cation both in toluene and ODCB.