Effects of carborane-containing liquid crystals on the stability of smectic phases

The mesogenic properties of three structurally similar compounds containing 1,10-dicarbadecaborane, 1,12-dicarbadodecaborane (carboranes), or bicyclo[2.2.2]octane are investigated in pure states and binary mixtures. The carborane-containing compounds (BC10 and BC12) exhibit nematic and monotropic smectic C transitions at lower temperatures than the analogous bicyclo[2.2.2]octane compound(BO1). The thermal stabilities of the smectic phases for BO1 are generally reduced by addition of the carborane analogues except for the smectic C phase, the stability of which is enhanced for equimolar concentrations. The effects exerted by the carborane mesogens on mesophase stability are consistent with their relative molecular sizes.