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.

Keywords:

• columnar mesophase
• polyalkynylbenzene
• Sonogashira coupling
• 2-ethylhexane
• branching effect

Acknowledgements

S.K.V. is grateful to Professor Kattera A. Suresh for his sustaining support for the research work. The authors are grateful to Professor Kenji Ema, Department of Physics, Tokyo Institute of Technology, for providing a highly sensitive (homemade) DSC instrument facility.