Synthesis, characterisation and mesomorphic properties of unsymmetrical N-(o-hydroxybenzylidene)-N '-(4-n-alkoxybenzylidene)azines and their copper (II) complexes

A new series of mesogenic unsymmetrical azines, N-(o-hydroxybenzylidene)-N'-(4-n-alkoxybenzylidene)azines, HOC6H4CH=N-N=CHC6H4OCmH2m+1 (m = 6, 7, 8, 9, 10, 11, 12, 14 and 16) and their copper (II) complexes have been prepared. They were characterised by elemental analyses, Fourier transform infrared (FT-IR), far infrared (IR), (1)Hand C-13 nuclear magnetic resonance (NMR) spectra, ultraviolet (UV)-visible, electron spin resonance (ESR) and magnetic susceptibility measurements. The copper (II) complexes are square planar and the unpaired electron is present in the dx(2)-y(2) orbital. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry and polarising optical microscopy. All of the unsymmetrical azines, except m - 7, exhibit mesogenic nature. The azine (m = 8) shows monotropic nematic mesophase, whereas all other azines exhibit features of a smectic A mesophase in the cooling cycle. The copper (II) complexes of the azines show only an isotropic phase at higher temperatures (similar to 180 degrees C) and no mesogenic nature is observed.