Three-ring mesogens containing p-carboranes: characterization and comparison with the hydrocarbon analogs in the pure state and as additives to a ferroelectric mixture

A series of sixteen three-ring esters of carboxylic acids derived from p-carborane, bicyclo[2.2.2]octane and benzene were synthesized and their mesogenic properties investigated using polarizing microscopy and DSC. The stability of the nematic phases follows the order BCO > Ph > 12-vertex > 10-vertex (or C > D > A > B). The biphenol derivatives 1 and 2 show significantly more rich smectic behavior than the pyrimidinylphenol esters 3 and 4. Most of the esters show the expected effect on FLC properties of a host mixture. The exceptions are BCO derivatives 2C and 4C, which significantly lower the normalized Ps, and the carborane derivative 4A which significantly increased the normalized Ps and γs values. In contrast to the hydrocarbon analogs, carborane esters lower the tilt angle.