INVERSION OF CHIRALITY-DEPENDENT PROPERTIES IN HELICAL LIQUID-CRYSTALS - EFFECTS OF STRUCTURAL MODIFICATION

The effects of structural modification on the inversion of chirality-d ependent properties in the helical mesophases of a number of terphenyl s have been investigated. The occurrence of inversion phenomena are ve ry sensitive to small changes in the molecular structure and subtle ch anges can often produce profound effects. Structural modification of t he non-chiral or chiral terminal chains has been shown to destabilize the inversion of chirality-dependent properties; however, a stable roo m temperature ferroelectric smectic C phase has been prepared. The in clusion of lateral fluoro-substituents in the aromatic core causes a l arge reduction in the melting points of the terphenyl materials and th e stabilization of inversion phenomena in the cholesteric phase. Chang es in the fluor-substitution pattern results in a change in the direct ion of the molecular dipole and hence a change in the sign of the spon taneous polarization. Helical mesophases and therefore also inversion phenomena are suppressed in the non-fluorinated material.