Deuterium NMR study of a probe molecule dissolved in a carbohydrate liquid crystal

Abstract

A deuterium NMR investigation of C₆D₆ dissolved in the discotic mesogen octa-O-decanoyl-β-cellobiose (Cel-II-10) is reported. The liquid-crystalline phase was found to be uniaxial in agreement with a previous X-ray study. The influence of magnetic field strength and thermal treatment on the mesophase alignment was investigated. From ²H NMR lineshape simulations, the form of the director distribution function was estimated. In contrast to most discotics, the columns of Cel-II-10 orient parallel to the external field indicating that the anisotropic diamagnetic susceptibility of this mesophase is positive. An increase of the quadrupolar splitting of C₆D₆ was observed when the sample was heated. This behaviour is interpreted in terms of a fast dynamic equilibrium between different solvation sites in the carbohydrate liquid crystal. The ²H NMR spectra recorded in the solid phase also indicated an exchange process between several sites.