Selectivity, Thermodynamic and Anisotropic Properties of Substituted Liquid-Crystal Cyanoazoxybenzenes as Stationary Phases for Gas Chromatography

Kuvshinova Sa,Burmistrov Va

doi:10.4172/2157-7064.1000314

Abstract

Herein we discuss physical properties of 4-(ω-hydroxyalkoxy)-4’-cyanoazoxybenzene homologs. 1D and 2D correlation NMR spectroscopy (in particular, 1Ði?½, 15N-HMBC experiment) have allowed elucidation of structure of the prepared rod-like supramolecular cyanoazoxybenzenes. Mesomorphic properties of the compounds have been studied by means of polarization thermomicroscopy and differential scanning calorimetry. All the studied cyanoazoxybenzenes have revealed enantiotropic nematic mesomorphism over wide temperature range. Nematic mesophase of the eighth homolog has possessed large positive dielectric anisotropy. Introduction of small amounts of the prepared cyanoazoxybenzenes as additive has stabilized the mesophase and has increased the dielectric anisotropy of 4-pentyloxy-4’-cyanobiphenyl. Gas-liquid chromatography studies have shown that sorbents based on 4-(2-hydroxyethyloxy)-4’-cyanoazoxybenzene are highly selective towards various structural isomers; that cannot be achieved using conventional nematic liquid crystals. Thermodynamic evidence of specific interactions between the mesogen and the non-mesomorphic sorbate has been discovered.

Highlights

Modern supramolecular chemistry is among most dynamically developing branches of science [1,2,3,4,5]
We have extended the range of conventional reactive polar substituents constituting the discussed systems by synthesis study of mesogenic derivatives of azobenzene, benzylideneaniline, phenylbenzoate, and biphenyls containing aldehyde, aldoxime, epoxy, and other terminal groups [41,42]
Structures of azoxybenzenes Ia-e were elucidated by means of NMR spectroscopy

Summary

Introduction

Modern supramolecular chemistry is among most dynamically developing branches of science [1,2,3,4,5]. DSC data demonstrated that energy of the nematic-isotropic phase transition of supramolecular azoxybenzenes Ia-e was of 2.64-2.87 kJ/ mol, significantly higher than that of the azoxybenzenes not containing terminal OH groups in the aliphatic fragment and not capable of Figure 4: 1Н,15N–HMBC spectrum of isomers of azoxybenzene Id. Chain associate of “head to tail” type Introduction of terminal hydroxyl group increased the Де value up to 11.8 in the case of compound Id. That could be due to both the increase of overall dipole moment of the molecule upon addition of a polar hydroxyl group and significant changes of nature of the association processes in the nematic and isotropic phases of supramolecular azoxybenzenes as compared to their analogs not capable of self-assembly.

Results

Conclusion