Photoinduced energy and electron transfer in oligo(p-phenylene vinylene)-fullerene dyads

The intramol. photoinduced charge sepn. within an oligo(p-phenylene vinylene)-fulleropyrrolidine dyad with four Ph rings (OPV4-C60) has been investigated with femtosecond pump-probe spectroscopy in solvents of different polarity and in the solid state. In soln., photoexcitation of the OPV4 moiety of OPV4-C60 results in an ultrafast (<190 fs) singlet energy transfer reaction, creating the fullerene singlet excited state. In polar solvents, the ultrafast energy transfer is followed in the picosecond time domain by an intramol. electron transfer. In accordance with Marcus theory, the rates for forward and backward intramol. electron transfer in OPV4-C60 are influenced by the polarity of the solvent. In the solid state the photophysics of OPV4-C60 is dramatically different. In thin films, the forward electron transfer proceeds within 500 fs, irresp. of which chromophore is photoexcited. The increased rate for charge sepn. in the solid state is attributed to a more favorable orientation of the donor and acceptor that results in an intermol. electron transfer. In the films, energy and electron transfer processes compete at the earliest moments after photoexcitation. In the solid state, the photogenerated electrons and holes have long lifetimes as a result of migration of these charges to thermodynamically more favorable sites in the film