Enhancement of photorefractivity in the isotropic phase of polymer liquid crystals

The photorefractivity of a series of polymer liquid crystals that possess a 4-nitrobenzylideneaniline moiety or a cyanobiphenyl moiety as a mesogen an d simultaneously as a nonlinear optical chromophore was investigated using two-beam coupling experiments. A large diffraction efficiency (eta) of 65% under application of a 37 V/mu m external electric field was obtained in th e isotropic phase of a polymer liquid crystal mixed with charge transportin g compounds. The photorefractivity was compared between the liquid crystall ine polymers and amorphous polymers. The photorefractivity was found to be significantly enhanced in the isotropic phase of the liquid crystalline pol ymers compared to that of the amorphous polymers with almost the same molec ular structure.