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.