Electrical and Optical Properties of a Poly(p-Phenylenevinylene) Derivative with a Mesogenic Substituent

Electrical and optical properties of a poly( p -phenylenevinylene) derivative substituted with a long side chain containing alkoxybiphenyl mesogenic unit have been studied. A liquid-crystalline molecular alignment and layer structure have been confirmed by optical microscopic observation and X-ray diffraction measurement, respectively. The dielectric constant changes in a stepwise manner at phase transition temperatures. The band gap of the new polymer in the liquid-crystalline phase has been evaluated to be 2.3 eV, which monotonously decreases with decreasing temperature. A photoluminescence peak was observed at around 560 nm, which corresponds to the emission originating from the poly( p -phenylenevinylene) main chain. An electroluminescnce device has been fabricated using this liquid-crystalline polymer and it has been found that the emission spectra depend on the polarity of the applied electric field.