Dielectric and Fluorescence Study on Phase Transitions in Liquid Crystal 5CB and 8CB

Successive phase transitions, isotropic(I)-nematic(N)-crystal(C) of 5CB (pentyl cyanobiphenyl) and I-N-smectic(Sm)-C of 8CB (octyl cyanobiphenyl) were studied by dielectric measurement and time-resolved uorescence spectroscopy. Dielectric constants in 5CB and 8CB are very similar and show a considerable change at the I-N transition and an abrupt decrease at the crystallization point. In uorescence spectra, a broad and intense band from excimers (dimers in the excited state) and a weak band from monomers are observed at around at 405 nm and 350 nm, respectively. The temperature dependence of uorescence spectra and lifetime show a gradual change before the melting point as a precursor of the rst-order transition, while only little change was observed at the N-I transition KCI Citation Count: 15