Some geometrical aspects of packing of bent-core molecules in the triclinic smectic-C_{g} liquid crystals and simple models of the modulated SmC_{gmod} phase.

Abstract

Organic compounds with bent-core (BC) molecules usually form the layered smectic liquid crystals with tilted molecules and polarization (P) which lies in the plane of the layer. A few such compounds have been found in which P itself tilts out of the plane of the layer, and the medium with general tilt (SmC_{g}) of the molecules has the low chiral triclinic symmetry. We discuss the geometric constraints of molecular packing in this structure to show that projecting groups attached to one of the arms of the BC molecules favors the formation of the SmC_{g} phase. We also extend our model for the modulated phases exhibited by BC molecules to show that the stripe structure made of bilayers shown by a few BC compounds, which is a signature of SmC_{g} layers, is preferentially formed by rotation of the BC molecules about their long axes, rather than about the layer normal. The theoretical results based on the unified model which describes all the modulated phases exhibited by the BC molecules broadly reflect experimental trends.