Orientational order of some liquid crystals as studied by optical spectroscopy methods

The orientational behavior of some liquid crystals with various molecular structure was studied by means of classical methods of optical spectroscopy: absorption of the polarized light in the visible region, fluorescence depolarization and Raman scattering depolarization. The dichroic dye dimethylamino-nitrostilbene was added to liquid crystals and acted as guest probe reflecting the host orientation in absorption and fluorescence measurements. The absorption, emission and Raman scattering spectra of the linearly polarized light were recorded as a function of temperature in the nematic phase. On the basis of these spectra the order parameters and as well as the molecular distribution function were determined. It was found that the molecular structure of liquid crystals affects the orientational order of molecules. Moreover, the effect of the dye presence on the orienting properties of liquid crystalline hosts was discussed.