Photoinduced charge separation in poly(1,4-phenylenevinylene) derivatives studied by electron paramagnetic resonance

We report a study of photoinduced charge separation in poly(1,4-phenylenevinylene) (PPV) derivatives with enhanced exciton dissociation using light-induced electron paramagnetic resonance (EPR). Four polymers were studied; all contained alkoxy and fluorenyl side chain units, and two of them also contained a nitro group on the 7-positon of the fluorenyl moieties. Pulsed EPR detected a light induced polaron for all the polymers with the intensity significantly higher for those with nitro groups. A second center was observed for these materials and spectra could be fitted assuming a radical anion was localized on the nitro groups. The fraction of radical anion and polaron centers was comparable, consistent with intramolecular exciton dissociation for the PPV derivatives containing the nitro groups.