Occurrence of unusually wide thermal range enantiotropic twist grain boundary TGBC* phases in unsymmetrical cholesterol and oxadiazole based liquid crystalline dimers

Abstract

We report the occurrence of the liquid crystalline twist grain boundary phase with smectic C* blocks (TGBC*) over a very wide thermal range (∼100 °C) in cholesterol based liquid crystalline dimers comprised of an oxadiazole unit. These novel materials have been synthesized by connecting the 5-phenyl substituted oxadiazole unit to a cholesterol unit through a thio-alkyl spacer at one end and the terminal O-alkyl substituted phenyl benzoate unit through an imine linkage, at the other. The range of the TGBC* phase is found to be dramatically dependent on the length of the terminal O-alkyl chain. Interestingly, these homologues, having either TGBC*-N*-BP or TGBC*-N* phase sequence, exhibit the TGBC* phase enantiotropically. We also suggest that the specific form of oxadiazole is perhaps responsible for the phenomenon observed.