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New electroluminescent, PPV-like, conjugated polymers containing bipyridylene−vinylene subunits were prepared and characterized with respect to their electrooptical properties. The polymers were found to exhibit reversible and tunable optical properties depending on protonation−deprotonation processes. pH sensitivity and reversible tunability of the polymers were observed by photo- and electroluminescence, optical absorption, photoinduced-absorption, and electroabsorption experiments. A luminescence red-shift of as much as 0.2 eV (∼60 nm) was observed upon full protonation of a free-base film. Films of the free-base form of the new polymers showed, in general, sharper spectra than the corresponding protonated films, probably due to increased disorder and stronger interchain interactions in the latter.

Linear and nonlinear recombination kinetics with various lifetime distributions were identified for long-lived photoexcitations in a series of pi-conjugated polymer films using modulation frequency and excitation intensity dependencies of the photoinduced absorption. This includes monomolecular, bimolecular, and defect-limited recombination processes that lead to saturation. Using generalized kinetics parameters, we found characteristic plots for all recombination processes. Specifically, the bimolecular recombination process shows superlinear intensity dependence away from the steady state; on the contrary, dispersive bimolecular recombination leads to sublinear dependence.

The application of conjugated polymers having electroactive pendant groups, such as poly(N-methyl-N‘-(3-pyrrol-1-ylpropyl)-4,4‘-bipyridinium), p-Pyr-V2+-Me, and poly(N-hydrogen-N‘-(3-pyrrol-1-ylpropyl)-4,4‘-bipyridinium), p-Pyr-V2+-H, as active photovoltaic and photoconducting media is investigated. Photoinduced charged species are characterized using photomodulated differential transmission spectroscopy and photoconductivity. The ability of using such media as active layers in photovoltaic cells is demonstrated.

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