Effect of Protonation−Deprotonation Processes on the Electrooptical Properties of Bipyridine-Containing Poly(p-phenylene−vinylene) Derivatives

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.