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Dielectric and Fluorescence Study on Phase Transitions in Liquid Crystal 5CB and 8CB
Kohji Abe,Atsushi Usami,Kenji Ishida,Takeshi Shigenalri,Yoshiharu Fukushima 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.1
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