An assessment of carborane-containing liquid crystals for potential device application

Two 4-alkoxyphenyl 12-pentylcarborane-1-carboxylate nematic liquid crystals have been synthesized. The materials are found to exhibit ideal mixing of nematic phases in their binary mixtures with analogous bicyclo[2.2.2]octane derivatives and with the polar nematogen 4-(4-isothiocyanatophenyl)-1-(trans-hexyl)cyclohexane. The smectic phases for the bicyclo[2.2.2]octanes are destabilized by addition of the carborane derivative. For carborane compound 5BC5 the extrapolated dielectric anisotropy and measured optical anisotropy are 1.3 and 0.057 respectively at 20°C. The refractive indices have been correlated with the calculated electronic polarizabilities and the low birefringence measured for 5BC5 can, at least in part, be attributed to the carborane cylindrical symmetry.