Keizo Nakajima

Polystyrene Derivative Films for Liquid Crystal Alignment

Abstract We studied the alignment of liquid crystal molecules on rubbed, thin polymer films of polystrene and its derivatives. Liquid crystal molecules were aligned perpendicular to the rubbing direction, although the polymer main chains of rubbed films were oriented along the rubbing direction. The alignment of the liquid crystal depended on the choice of side phenyl groups of polystyrene derivatives, and the pretilt angle varied with the type and the position of the substituents that were introduced into the side phenyl groups. Homogeneous alignment for ferroelectric liquid crystal was obtained by using poly(NO2 styrene), poly(p-OH styrene) and poly(4-vinylpyridine) films, which have relatively high β-dispersion and glass transition temperatures.

Theoretical study of the ground and excited states of silicon clusters: Si8Hx

The electronic structures of small silicon clusters in the ground and excited states have been studied based on ab initio configuration interaction by the single-substitutions approximation method. We consider Si8Hx clusters of chain, branch, ladder, and cubic types as model compounds, due to their variety of molecular structures. Calculated Stokes shifts and oscillator strengths successfully reproduce the experimental electronic spectrum. These phenomena are well explained by the detailed analysis of the orbital patterns and energy level changes related to the excitation. The optical properties of the cubic Si cluster are considerably different from those of the other Si8 clusters. It shows zero oscillator strength, i.e., “forbidden transition,” from the first to 20th excited states because of its high symmetry.