Isomeric trimesogens exhibiting modulated nematic mesophases

Abstract

Modulated nematic phases, in which the constituent molecules possess some form of superstructure in addition to the average orientational organization and lack positional order present in classical nematic phases, are of current fascination in liquid crystal research. Most of the recent focus has been on the twist-bend nematic phase. This phase exhibits phenomena that are of fundamental importance to science; the spontaneous formation of a helical pitch of nanometre scale in a fluid and the spontaneous breaking of mirror symmetry leading to the emergence of chiral domains in an achiral system. In this communication we report on the synthesis of two liquid-crystalline trimesogens whose structures are an extension of the known dimeric material CB6OCB. One material (A6₃) exhibits a nematic phase with a twist-bend modulation (N_TB phase), whereas a structurally isomeric material (B6₃) exhibits an unusual nematic like mesophase which we believe is a candidate for being a new form of modulated nematic. Whereas the properties of dimeric LCs are somewhat indifferent to chemical composition, the stark difference in behaviour between the two materials herein shows that oligomers may exhibit an unexpected sensitivity to molecular structure.