Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13C NMR Spectroscopy.

Abstract

Mesogens that vary in shape anisometry have been investigated by 13C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (Szz) values for the phenyl rings of the rod-like mesogen are 0.65-0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit's phenyl rings, Szz is ~ 0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the Szz value for the side arm phenyl rings is ~ 0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of Szz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of l shape is proposed in the liquid crystalline phase.