Room-temperature discotic cholesteric and nematic phases: influence of 3,7-dimethyloctane peripheral chain on the molecular self-assembly of radial polyalkynylbenzene

Abstract

A series of novel radial symmetrical and non-symmetrical polyalkynylbenzene-based chiral and achiral disc-shaped materials with respectively five and six 3,7-dimethyloctyl peripheral aliphatic chains are synthesised. The symmetrical and non-symmetrical polyalkynylbenzene are prepared by Pd-catalysed alkynylation of hexaiodobenzene or monoalkoxypentabromobenzene with phenylacetylenes substituted by 3,7-dimethyloctyl peripheral chains. The molecular structures are confirmed by spectroscopic and spectrometric analysis. The phenylacetylene bearing 3,7-dimethyloctyl peripheral aliphatic chains via oxygen (OR) or directly to the phenyl ring (R) functions to balance steric and space-filling effects of the peripheral branched chains. Symmetrical molecules in which the peripheral aliphatic chain directly attaches to the R and OR functional groups exhibit the columnar and the nematic/cholesteric phases, respectively. By introducing non-symmetry to the disc shape, the mesophase is stabilised above and below room temperature. This molecular tailoring significantly affects the intermolecular attraction forces and as a result affects the melting, clearing temperatures and the molecular packing.