Polymorphic smectic A phases in perfluoroalkylated mesogenic dimers

Abstract

New homologous symmetric dimers are presented in which two-ring monomers are connected by a flexible spacer and perfluorinated chains are introduced in terminal positions. The mesophase behaviour depends on the length and structure of the spacer and on the length of the terminal chains. The most interesting finding is the occurrence of dimorphic SmA phases in the longer chain homologues with odd-numbered spacer. The transition between the dimorphic SmA phases is accompanied by a relatively high enthalpy. Considering the results of XRD measurements and computer simulations, structural models are proposed, based on different conformations of the molecules.