Molecular clustering behaviour in the cybotactic nematic phase of a spin-labelled liquid crystal

Abstract

A newly synthesised liquid crystalline nitroxide radical (LC-NR) with a terminal trifluoromethyl group as spin-labelled LC compounds exhibits an anomalous phase transition behaviour. It is likely attributed to non-covalent interactions between the trifluoromethyl groups of the adjacent molecules. X-ray diffractometry of the LC-NR suggests the existence of a cybotactic nematic (N_cyb) phase with a transient and local layer order between the normal nematic (N) and smectic A (SmA) phases. The EPR spectroscopy of the spin-labelled LC implies no discontinuity in magnetic susceptibility around the N-to-N_cyb phase transition. Intermolecular contacts between nitroxide radicals seem to change continuously. These results imply that the interactions between trifluoromethyl groups induce the cybotactic clusters, where molecules move in and out.