Ferroelectric and antiferroelectric odd–even behavior in a tricarbosilane-terminated liquid crystal homologous series

Abstract

A new class of polyphilic mesogens composed of a tolanphenyl carboxylate core, a chiral alkoxy tail, and a tricarbosilane terminated alkoxy tail was synthesized, and shown to self-organize into nanophase segregated, smectic liquid crystalline (LC) phases. It was found that the number of carbons in the alkyl spacer between the tricarbosilane and the core controlled the observed phase with perfect fidelity: odd-carbon spacers gave antiferroelectric phases, and even-carbon spacers gave ferroelectric phases. Even more interestingly, homologues with odd carbon number show the rare and useful chiral orthoconic antiferroelectric SmC_A* phase, where the optic axis tilt alternates from layer to layer between +45° and −45°, making the molecular directors in adjacent layers orthogonal. The even-carbon homologues exhibit the SmC* phase with close to 45° tilt. The findings demonstrate that the supramolecular self-organization of polyphilic mesogens may be controlled by the length of hydrocarbon spacers.