Chemically-induced discotic liquid crystals: structural studies with NMR spectroscopy

Hughes, J.R., Luckhurst, G.R., Praefcke, K., Singer, D. and Tearle, W.M. (2003) Chemically-induced discotic liquid crystals: structural studies with NMR spectroscopy. Molecular Crystals and Liquid Crystals, 396, 187-225. (doi:10.1080/15421400390213311).

Abstract

Deuterium NMR spectroscopy provides an especially important technique with which to investigate a wide range of liquid crystal behaviour. Here, we describe its use in the structural study of liquid crystals formed from discotic or disc-like molecules and, to illustrate the breadth and power of the NMR method, we have selected two systems in which the liquid crystal phases are chemically induced. The binary mixtures are similar in that one component is a radial multiyne but differ significantly in the nature of the chemical inductor. In one case the inductor is a nitrated fluorenone which has a similar anisotropy to the radial multiyne while for the second system the inductor, a substituted o-xylene is considerably smaller and far less anisotropic. By measuring the deuterium NMR spectra of suitably deuteriated versions of the components we show how it is possible to investigate the orientational order of the components in the various induced phases, their effective molecular symmetry, the molecular geometry, the chain flexibility and orientational order together with the phase symmetry. The results of these investigations are described and explained.

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