Photo-induced charge-transfer precesses in fullerene-containing dyad and triad molecules

We report on pulsed electron-spin-resonance (ESR) investigations of novel model systems for photo-induced electron-transfer processes. The schematic structures of the molecules are T-5-C-60 and A-T-5-C-60, i.e., the fullerene C-60 is used as the acceptor, and quinquethiophene (T-5) or anthracene (A) act as a donor. In frozen solutions of both the dyad and triad, Ne find rather long-lived radical signals (lifetime approximate to 2 mu s) after laser-pulse excitation. The observed signals can be assigned by the g factor and the linewidth to the anion C-60(-) and the cation T-5(+). We have examined the influence of the solvent polarity (toluene or benzonitrile) and of the excitation wavelength (355 nm or 532 nm) on the efficiency of the charge transfer.