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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.
Acknowledgements
The authors thank the Head of the Department of Chemistry, Banaras Hindu University (BHU), Varanasi, for providing laboratory facilities. One of the authors (AP) thanks University Grants Commission, New Delhi (UGC) for financial support as a Project Fellow and the BHU for the research scholarship. Thanks are also due to Mr Satish Tiwari for CHN analyses, Mr R.C.P. Bipin for NMR and Mr V.N. Pandey for IR and electronic spectral data. We are thankful to S.A.I.F., Indian Institute of Technology (IIT), Bombay, for recording the ESR spectra.
