Abstract
A new series of mesogenic unsymmetrical azines, N-(o-hydroxybenzylidene)-N′-(4-n-alkoxybenzylidene)azines, HOC6H4CH = N − N = CHC6H4OC m H2m + 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), 1H and 13C 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 (∼180°C) and no mesogenic nature is observed.
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