Investigation of internal and external potentials acting on benzyl halides dissolved in different nematic solvents

Abstract

The NMR spectra of C6H5CH2X (X=Cl, Br, I) dissolved in three different nematic liquid crystal solvents were analysed to investigate, using the AP-ELS model, the internal and external potentials acting on the solutes. The nematics [ZLI1132, I35 and a zero electric field gradient mixture (55% ZLI1132:EBBA)] were selected to compare the effects depending on the nature of the solvents on both potentials. The internal potential for the rotation around the exocyclic C—C bond shows minima located at γ4=±90° (C—X bond lies in a plane perpendicular to the ring) and torsional barrier increasing with the steric hindrance of the halide (from X=Cl to X=I) and with the polarity of the solvent (I35<the mixture <ZLI1132). Concerning the nature of the interactions responsible for the orientational order of the solutes, the results obtained from the AP method were analysed in a mean field approach testing different hypotheses: it seems that the interaction between the polarizability tensor of the solutes and the electric field squared of the solvents plays a non-negligible role in the orientational mechanism for this kind of compound.