Molecular Structure and Helical Twisting Power

Abstract

The helical structure of the chiral nematic phases induced by chiral dopants in nematic solvents provides macroscopic information about the molecular chirality of the dopant. The surface model, which combines the order parameters of the dopant in nematic host phase and chirality parameters of the dopant, is a simple method to characterise the molecular properties and the induced chiral nematic phases. In this model, the representation of the molecular surface accesible from the nematic solvent plays an important role. The rolling sphere method, in common use for calculation of the molecular surface, rolls over a set of the van der Waals spheres representing constituent atoms of the molecule. In this paper we will present the effect of changing the radius of the rolling sphere on the values of the surface chirality indices. Here chiral binaphthyl molecules have been choosen since their twisting ability has a relatively strong dependence on the molecular structure. We also discuss a range of chirality indices and their dependence on the ordering strength of the solvent.