Temperature dependence of the molecular reorientational dynamics in nematic and isotropic EBBA and 5CB by fluorescent probe depolarization spectroscopy

Information on molecular reorientational dynamics in nematic and isotropic phases has been obtained by a simple combination of time resolved and steady state fluorescence measurements on the dyes DMANS and DPH dissolved in homeotropically aligned samples of EBBA (4-ethoxybenzylidene-4′-n-butylaniline) and 5CB (4-n-pentyl-4′-cyanobiphenyl) respectively. In particular, two reorientational correlation times τr 0 and τr 2 have been identified. Their evolution with temperature, both in the nematic and well within the isotropic phase, has been studied and evaluated using stochastic models for the molecular reorientational dynamics.