Room temperature columnar phase: Influence of 2-ethylhexane peripheral chain on the mesomorphism of polyalkynylbenzene-based disc-shaped molecules

Abstract

A series of novel symmetrical and non-symmetrical polyalkynylbenzene-based chiral and achiral disc-shaped materials with respectively five and six 2-ethylhexyl peripheral aliphatic chains have been synthesised. The symmetrical and non-symmetrical polyalkynylbenzene was prepared by Sonogashira coupling of hexabromobenzene or monofunctionalised pentabromobenzene with phenylacetylenes substituted by 2-ethylhexyl peripheral chains. The molecular structures were confirmed by spectroscopic and spectrometric analysis. The phenylacetylene bearing 2-ethylhexyl peripheral aliphatic chains via oxygen (OR) or sulfur (SR) or ester (CO2R, without branched chain) functions to balance steric and space-filling effects of the peripheral branched chains. Non-symmetrical molecules exhibit the hexagonal and/or rectangular columnar mesophase whereas symmetrical molecules have higher melting temperature. These molecular engineering drastically affects the intermolecular forces of attractions that lead to unusual molecular self-assembly and affect the transition temperatures. Thus, the mesophase is stabilised above and below room temperature.