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

Ferroelectric smectic C* liquid crystals have been shown to exhibit high speed, multistate electro-optic switching, particularly when incorporated 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 incorporating the highly conjugated diacetylene moiety into an FLC core, an increase in birefringence to greater than DELTAn=0.3 is achieved. Fluorination 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 examined in the 3,3'-difluorodiphenyldiacetylene system.