Mesomorphic study and DFT simulation of calamitic Schiff base liquid crystals with electronically different terminal groups and their binary mixtures

Abstract

Two series of Schiff bases liquid crystals with electronically different terminal substituents, 4-(alkoxy)phenylimino)methyl)benzonitrile (In-a) and N-(4-(hexyloxy)benzylidene)-4-(alkoxy)benzenamine (In-6), were synthesise. Their molecular geometries were elucidated via FT-IR, ¹ H-NMR and elemental analysis. Mesomorphic and optical properties were investigated by differential scanning calorimetry (DSC) and polarised optical microscopy (POM). The effect of electronic nature of in the attached terminals, extra-conjugation E- withdrawing (CN) and E-donating (hexyloxy), is investigated. All members of the investigated compounds were enantiotropically mesomorphic comprising mono or dimorphic phases depending on the electronic and complexity nature of attached terminals. Computational parameters of both series were related with the experimental findings of the mesophase stability and the length of alkoxy chains to investigate the effect of the terminals on the stability of possible architectures. Density functional theory (DFT) calculations revealed that all investigated members are non-co-planar with twist angles between the rings around the CH = N linkage. The relations of the experimentally mesophase range and stability of the enhanced phases with simulated parameters were studied to conclude that these factors contributed in different extent to affect the mesomorphic behaviour. The binary phase diagrams were constructed between In-6 components and achieved very low melting temperatures at their eutectic mixtures.