Inversion of chirality-dependent properties in helical liquid crystals: effects of structural modification

Abstract

The effects of structural modification on the inversion of chirality-dependent properties in the helical mesophases of a number of terphenyls have been investigated. The occurrence of inversion phenomena are very sensitive to small changes in the molecular structure and subtle changes can often produce profound effects. Structural modification of the non-chiral or chiral terminal chains has been shown to destabilize the inversion of chirality-dependent properties; however, a stable room temperature ferroelectric smectic C* phase has been prepared. The inclusion of lateral fluoro-substituents in the aromatic core causes a large reduction in the melting points of the terphenyl materials and the stabilization of inversion phenomena in the cholesteric phase. Changes in the fluoro-substitution pattern results in a change in the direction of the molecular dipole and hence a change in the sign of the spontaneous polarization. Helical mesophases and therefore also inversion phenomena are suppressed in the non-fluorinated material.