Time dependent fluorescence polarization studies using isotropic and liquid crystal media

Abstract

The fluorescence decay of all-trans-1,6-diphenylhexa-1,3,5-triene (DPH) has been observed in methylcyclohexane, paraffin oil, and a nematic liquid crystal medium (cholesteryl laurate/cholesteryl chloride). By means of fluorescence polarization measurements the effects of rotational diffusion have been observed. In methylcyclohexane rotation is rapid, occurring within about 1 ns. In the liquid crystal solvent system no rotation is observed over the time scale of the measurements. Paraffin oil solutions are intermediate between these two extremes. The DPH molecule in its excited state fits a model in which it is assumed to be a prolate ellipsoid. The results show that liquid crystals provide suitable media for studying the spectroscopy of oriented molecules.