Electroclinic effect in nematic liquid crystals: The role of molecular and environmental chirality

The electroclinic (EC) effect is the tilt of the optical axis of a liquid crystal in the plane perpendicular to an applied electric field. Chirality plays a key role for its emergence. Based on the molecular and phase symmetry we derive a molecular expression for the EC coefficient, the material property that quantifies the linear coupling between tilt and electric field, in nematic liquid crystals. Modeling the relevant molecular properties (shape, elec- tricdipolemoment,andpolarizability)withatomicresolution,wecalculatetheECcoefficientforprototypemolec- ular structures. We demonstrate that molecular chirality, needed for the occurrence of the EC effect in nematics withauniformdirector,isnotanecessaryrequirementinthepresenceofatwisteddirector.Ourresultsshowthatin the latter case conformational deracemization, invoked to explain recent experiments, is not the only mechanism.