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.

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We have studied acceptor-substituted poly(3-butylthiophene) in an attempt to examine the role of acceptor molecules as intrinsic charge traps under light excitations by measuring the transient photoconductivity response following pulse excitation. The specially synthesized acceptor molecule is a chemically prepared high electron affinity (HEA) monomer, 1-(4-nitrophenyl)-2-(3-thienyl)ethene. In the copolymers prepared with this acceptor monomer we have observed simultaneous decrease of the sub-nanosecond photoconductivity and increase of the slow component (t > 10 ns) photoconductivity, with increasing HEA group concentration in the substituted poly-(butylthiophene)s. The slow component is attributed to a bimolecular recombination process.

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