Photophysics of a poly„phenylenevinylene... with alternating meta-phenylene and para-phenylene rings

We have investigated the photophysics of the luminescent polymer poly~1,3-phenylenevinylene-alt-2,5dioctyloxy-1,4-phenylenevinylene! by a variety of optical spectroscopies. The incorporation of alternating meta-phenylene and para-phenylene rings restricts conjugation with respect to poly~para-phenylenevinylene! derivatives. As a consequence, excited states are blueshifted and the nonlinear susceptibility is reduced. Absorption by aggregates, which can be obscured by scattering and interference, is clearly revealed by electroabsorption spectroscopy. The reduced symmetry of 1,3-PPV modifies optical selection rules, resulting in strong overlap of the fluorescence spectrum with excited state absorption by charged polarons.