A NEW CLASS OF HIGH-BIREFRINGENCE SMECTIC-C LIQUID-CRYSTALS - 3,3'-DIFLUORODIPHENYLDIACETYLENES

Ferroelectric smectic C liquid crystals have been shown to exhibit hi gh speed, multistate electro-optic switching, particularly when incorp orated into the surface stabilized ferroelectric liquid crystal (SSFLC ) light valve. Certain applications utilizing IR modulation, waveguide , and fibre-optic devices can benefit from a birefringence higher than the value of DELTAn=0.15 seen in typical FLC materials. By incorporat ing the highly conjugated diacetylene moiety into an FLC core, an incr ease in birefringence to greater than DELTAn=0.3 is achieved. Fluorina tion of the core induces a strong preference for the tilted smectic C phase as compared to the unfluorinated materials which typically show the nematic phase. The effect of different tail substitutions is exami ned in the 3,3'-difluorodiphenyldiacetylene system.