Novel mesophases in fluorine substituted banana-shaped mesogens

A new homologous series of achiral banana-shaped mesogens (`Dn') has been s ynthesized and studied by the classical techniques (optical microscopy, dif ferential scanning calorimetry, X-ray diffraction, miscibility studies and electro-optic investigations). The short homologues (D6-D8) exhibit a two-d imensional phase `B1(x)' different from a B1 phase with a rectangular latti ce. The longer homologues (D9-D14) present a mesophase which displays the d efects of the B7 phase of the PIMB-NO2 compounds. Nevertheless the D9-D14 m esophase is not miscible with the B7 phase, and contrary to B7, exhibits a bistable behaviour (`ferroelectric' type) suggesting at least a B7 variant.