Effect of mesogenic linkages on two novel aromatic series-based liquid crystals: synthesis, theoretical and comparative studies

Abstract

ABSTRACT Two novel groups of rod-like homologue molecules, one group (group A) having benzothiazole-aromatic mesogenic units and the other (group B) with only aromatic mesogenic units, were designed and synthesised. Both groups (compounds A and B) involve azomethine (−CH=N−), ester (−COO−), azo (−N=N−) and amide (−NH−CO−) linking groups at the different positions in their molecular structures. The structures of the synthesised compounds were elucidated using different analytical techniques (1H, 13C NMR, FT−IR, mass spectra and melting points). In order to verify the influence of the central linkages and their positions on physicothermal and mesomorphic properties, different types of linking groups including −CH=N−, −COO-, −N=N− and −NH−CO− were analytically and thermally investigated. Thermal analyses and mesomorphic properties of both series are discussed in terms of the linkages nature, comprising geometrical structure, interactions polarisability, subtle change in shape and their effective positions. The results revealed that the synthesised compounds (groups A and B) showed the only enantiotropic nematic mesophase in certain temperature regions except compounds A4 and A6. The change of the type linkages and their positions in some compounds (groups A and B) was theoretically investigated to verify if the theoretical calculations show an agreement with the experimental findings.