Alternating oligo(p-phenylene vinylene)-perylene bisimide copolymers : synthesis, photophysics, and photovoltaic properties of a new class of donor-acceptor materials

A Suzuki polycondensation reaction has been used to synthesize two copolymers consisting of alternating oligo(p-phenylene vinylene) (OPV) donor and perylene bisimide (PERY) acceptor chromophores. The copolymers differ by the length of the satd. spacer that connects the OPV and PERY units. Photoinduced singlet energy transfer and photoinduced charge sepn. in these polychromophores have been studied in soln. and in the solid state via photoluminescence and femtosecond pump-probe spectroscopy. In both polymers a photoinduced electron transfer occurs within a few picoseconds after excitation of the OPV or the PERY chromophore. The electron transfer from OPV excited state competes with a singlet energy transfer state to the PERY chromophore. The differences in rate consts. for the electron- and energy-transfer processes are discussed on the basis of correlated quantum-chem. calcns. and in terms of conformational preferences and folding of the two polymers. In soln., the lifetime of the charge-sepd. state is longer than in the films where geminate recombination is much faster. However, in the films some charges are able to escape from geminate recombination and diffuse away and can be collected at the electrodes when the polymers are incorporated in a photovoltaic device.