Calamitic liquid crystals involving fused ring and their metallomesogens

Abstract

In this paper, the authors report two different types of terminally substituted homologous series with an ester–azo central linkage involving fused-ring achiral liquid crystals such as 4-((4-chlorophenyl)diazenyl)-3-hydroxyphenyl 6-alkoxy-2-naphthoate (series A) and 4-((4-nitrophenyl)diazenyl)-3-hydroxyphenyl 6-alkoxy-2-naphthoate (series B). Their copper (II) metallomesogens were synthesised and characterised by methods such as elemental analysis, Fourier transform infrared, proton (1H) nuclear magnetic resonance (NMR), carbon-13 (13C) NMR and mass spectroscopic studies. Thermotropic properties were studied by performing polarising optical microscopy and DSC analysis. All liquid crystalline compounds (ligands) display nematic and/or smectic phase/s. Unlike ligands, both types of copper (II) complexes show a solely nematic behaviour. The series B exhibit Sm-form from C7 derivatives where as series A exhibit Sm-form from C8 derivatives. The series B is more thermally stable than series A. The series A exhibit monotropic nematic phase for C4 derivative and monotropic smectic phase for C10 derivative. Whereas series B display monotropic nematic phase for C5 derivative and C12 derive is fully monotropic i.e. both nematic and smectic phase obtained only on cooling cycle.