New Schiff’s base liquid crystals with biphenyl/ benzoylphenyl tail substitutes: synthesis, characterisation, mesomorphic behaviour and DFT calculation

Abstract

A novel series of nematic liquid crystals with rod-like structures, derived from [1,1’−biphenyl]- 4-yl(E)-4-((4-n-alkoxybenzylidene) amino) benzoate (XnI) and 4 -benzoylphenyl (E)-4-((4-(n-alkoxy) benzylidene) amino) benzoate (XnII) have been successfully synthesised, where n ranges from 4, 6, 8 & 10. Proton magnetic resonance, mass and infrared spectroscopy were used to analysed and characterised. Differential scanning calorimetry (DSC) and polarising optical microscopy (POM) were used to examine the liquid crystal behaviour of all produced substances. All homologous series XnI and XnII compounds displayed a nematic mesophase. The impact of molecular flexibility, the range of transition temperatures and the comparative research were all systematically investigated. The X4I–X10I homologues exhibit an enantiotropic nematic mesophase within the temperature range of 177–148°C, while the X4II–X10II homologues show a nematic mesophase at temperatures between 169 and 122°C. XnI & XnII compounds studied using Gauss View 6 software and were subjected to geometry optimisation using the Density Functional Theory (DFT) calculations at the B3LYP/6 –31+G(d,p) level of theory as implemented in Gaussian 16 quantum chemistry package. The band gap values, calculated by the difference of the energy values of HOMO and LUMO, were higher for the XnI series as compared to the XnII compounds.