ESR study of light-generated polarons in poly(p-phenylene vinylene) derivatives

Light-induced ESR (LESR) has been employed to study light-generated polaron s in two dialkoxy derivatives of poly(p-phenylene vinylene) (PPV), MEH-PPV and CN-PPV, where cyano groups are attached at the vinylic carbon sites in the latter. LESR action spectra of both polymers show a clear threshold ene rgy around 3eV, which compares well with the photocurrent action spectra re ported for PPV derivatives. A clear reduction of LESR linewidth is observed in CN-PPV compared with MEH-PPV, providing direct evidence that the spin d ensity of polaron predominantly resides on the vinylic carbons. This featur e can be reproduced by the linewidth analysis based on the theoretical spin distribution of a polaron with the extension of approximately 4 phenyl rin gs.