Persistence of ordering in 4-n-pentyl-4′-cyanobiphenyl above the nematic-isotropic transition as detected by picosecond time-resolved fluorescence spectroscopy

Abstract

The orientational ordering of 4-n-pentyl-4′-cyanobiphenyl (5CB) was explored with the aid of picosecond, time-resolved fluorescence spectroscopy by monitoring the time dependence of excimer formation of the mesogen at various temperatures. It was found that in the nematic phase the excimer is formed with high efficiency, while in the isotropic phase the excimer formation was less effective. Immediately after pulse excitation the time-resolved fluorescence spectra revealed that short range ordering persists just above the N-I transition, although the macroscopic order had disappeared.