The polymorphic phases of the hexaalkanoyloxytriphenylene liquid crystals, as studied by deuterium NMR spectroscopy

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Abstract
Deuterium NMR spectra are reported for several specifically deuterated hexaalkanoyloxytriphenylenes in their corresponding liquid crystalline phases. The higher homologs of this series are polymorphic and exhibit a variety of discotic mesophases, including both biaxial (D0 and D1) and uniaxial (D2) columnar phases. The ordering characteristics of these phases are studied using the quadrupolar splittings of the aromatic and aliphatic deuterons. The results show that during the transition from the biaxial D1 to the axial D2 phase the major susceptibility tensor switch orientation, apparently due to strong tilting of the molecules with respect to the columnar axis in the biaxial phase. Characteristic features which appear in the spectra of these phases are interpreted in terms of intercolumnar jumps of mesogen molecules.