Synthesis and study the liquid crystalline behaviors of double Schiff bases bearing ester linkage as a central core

Abstract

ABSTRACT Two series of 12 homologues, 4-(((4-substituentphenyl)imino)methyl)phenyl 4-((4-(alkoxy) benzylidene)amino)benzoate (Dn, X = –OCH3 and En, X = –-Br), have been synthesised. The two series have different alkoxy terminal chains (OC n H2 n +1, n = 3, 4, 6, 7, 9, 12) on one side of their structures while other side in the series (Dn and En) was substituted by methoxy and Bromo group, respectively. The structures of the synthesised derivatives have been identified using Fourier transform infrared spectrometry (FT-IR) and nuclear magnetic resonance for H and C (1H-NMR, 13C-NMR) and the elemental analysis (CHN). The texture of liquid crystalline phases of the mesogens has been observed by optical polarised microscopy (OPM) while the details of the thermal transition of compounds were investigated by differential scanning calorimetry (DSC). The obtained liquid crystalline results showed that the derivatives of series (Dn) display a broad range of nematic mesophase (N) while the mesogens of (En) series appeared nematic and smectic mesophases. All the studied homologues show a wide range of liquid crystalline mesophases, the stability of mesomorphic behaviour of these compounds was dependent mainly on the length of terminal alkoxy chain (the number of carbon atoms) chain and the effect of substituent groups (OCH3 and Br).