Mobility changes of side chains ascribed to density modulations along columnar structures detected by 2D NMR

Abstract

The molecular dynamics and phase transitions of a columnar liquid crystal based on hexaether-substituted rufigallol mesogens were studied by a combination of X-ray scattering as well as 1D and 2D solid-state NMR spectroscopy. A correlation of the anisotropic molecular motion, with the molecular symmetry and the phase symmetry was established. 2D-exchange NMR spectra revealed a slow dynamic process involving the side chains, which is attributed to changes in the packing density of the molecules along the column. In this way the packing problem of columnar liquid crystals resulting from the incommensurability of the aromatic core moieties and the aliphatic side chains is solved as proposed by de Gennes