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

Abstract

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 P_s, and the carborane derivative 4A which significantly increased the normalized P_s and γ_s values. In contrast to the hydrocarbon analogs, carborane esters lower the tilt angle.