Liquid-crystalline dimers containing cholesteryl groups and azobenzene moieties with branched allyl chain: synthesis and properties

Abstract

ABSTRACT A series of liquid-crystalline dimers containing a cholesteryl group and a azobenzene moiety with branched allyl chain were synthesised, all exhibiting chiral nematic phase (N*). The chemical structure and liquid crystal properties of the dimers were characterised by FTIR, 1 H-NMR, DSC, POM and XRD. The isotropization temperatures of the dimers were in a decreasing trend with increasing the length of the flexible spacer while anomalies occurred in the melting temperatures and crystallinities of the dimers. Nevertheless, it is in evidence that increasing the flexible spacer length is feasible to reduce the crystallinity of the dimer and then subcool the dimer to glass state to maintain the selective reflection. Besides, it was shown that the dimer with increased flexible spacer length tended to attain selective reflection at longer wavelengths.