Structural ordering and molecular-optical properties of a discotic liquid crystal (Col_ho)

Abstract

The infrared absorbance and the dispersion of the refractive indices in the region 0.49–0.63 μm of the discotic mesogen 2,3,6,7,10,11-hexaheptyloxytriphenylene were studied for the columnar and isotropic phases. The temperature dependence of the orientational order parameter S and the local field parameters of a light wave acting on the sample have been evaluated. It is shown that the mixing of molecular excitations modifies the behaviour of S as a function of temperature. Molecular-optical properties of the triphenylene derivative, such as the anisotropy of the polarizability, Δγ and the mean polarizability, γ were investigated on the basis of the generalized Lorenz-Lorentz relation for uniaxial liquid crystals. The experimentally observed changes of these properties in the columnar phase seem to be affected by the induction mechanism of the change in the molecular polarizability with increasing S.