Orientational ordering and polarizability of molecules in the columnar phase of discotic liquid crystal

The structural and molecular-optical properties of the columnar discotic liquid crystal 2,3,6,7,10,11-hexaheptyloxytriphenylene were studied by using of refractometric and infrared (IR) measurements. Temperature dependence of the orientational order parameter S with allowance for the anisotropy of the local field of a light wave and mixing of molecular excitations was evaluated for C-C aromatic stretching band. The local field parameters have been. evaluated within approximation of the effective spheroidal Lorentz cavity model. The anisotropy gamma(alpha) and the mean value (gamma) over bar of the molecular polarizability of triphenylene were investigated for several wavelengths. The experimentally observed changes of molecular-optical properties in columnar phase seem, to be affected by the induction mechanism of the variety of the molecular polarizability with increasing of S, proposed previously for calamitic liquid crystals. Furthermore, these properties are not related to the effects of aliphatic tails disordering.