Correlation between molecular structure and helicity of induced chiral nematics in terms of short-range and electrostatic-induction interactions. Thecase of chiral biphenyls

The helical structure of the chiral nematic phases induced by chiral dopant s in nematic solvents provides a macroscopic image of the molecular chirali ty of the dopant promoted by the orientational order. Chiral biphenyls are challenging systems because their twisting ability shows a strong dependenc e on the molecular structure. which does not conform to empirical correlati on rules. This points out the need for adequate interpretative tools, able to establish a link between molecular properties and macroscopic response. In this paper the twisting ability of chiral biphenyls is reviewed, by repo rting examples taken from the literature together with some new experimenta l results. The microscopic origin of the observed behavior is explained in terms of chirality and anisotropy of short-range and electrostatic-inductio n interactions. These are described, respectively, by a shape model and a r eaction field method, having the common characteristics of a realistic repr esentation of the structure and properties of the chiral dopants in terms o f molecular surface, atom charges, and distributed polarizabilities.