Ultrafast energy and electron transfer in donor-acceptor molecules for photovoltaics

The rapid advancement in fullerene chemistry allows the covalent functionalization of C60 with electron donors. Various C60-based donor-acceptor dyads have been synthesized and studied to gain insight in the intramolecular photophysical processes, like energy and electron transfer. Although these dyads can serve as a model compounds for the conjugated photovoltaic cells, only a few examples have been reported with these C60-based dyads. Apart from being well-defined model systems for photophysical characterization, the covalent linkage between donor, and acceptor in these molecular arrays provides a simple method to achieve control over the phase segregation in donor-acceptor networks. We investigate an oligo(phenylene vinylene)fullerene dyad with 4 phenyl groups (C60-OPV4) in solvents of different polarity using femtosecond pump-probe spectroscopy. We find that photoexcitation of the oligomer leads first to an intramolecular energy transfer to the fullerene, while an electron transfer is a secondary process, only allowed in polar solvents.