Silylated bent-core molecules: the influence of the direction of the carboxyl connecting groups on the mesophase behaviour

Abstract

Novel bent-core molecules based on phenyl benzoate rigid cores and heptamethyltrisiloxane units at one or at both ends of the aliphatic side chains were synthesized and investigated by polarized light microscopy, differential scanning calorimetry, X-ray diffraction and electrooptical methods and the effect of the direction of the carboxyl groups on the mesomorphic self assembly was investigated. A series of distinct liquid crystalline phases was found, among them ferroelectric and antiferroelectric switching and also non-switchable smectic, undulated smectic (USmC) and modulated smectic phases (columnar phases, Col_ob). All polar phases show field-induced inversion of chirality at least in a certain temperature range. Moreover, two non-polar and uniaxial smectic phases were observed, one with a hollow cone-like orientational director distribution (SmC_R) and the other one with a maximum of the director distribution at zero tilt (SmA). These two phases were discussed in relation to the distinct models of de Vries type smectic phases.