New Schiff’s base cinnamates/benzoates liquid crystals with lateral methyl substitutes: characterisation, mesomorphic behaviour and DFT calculation

Abstract

ABSTRACT Two new homologous series of Schiff’s base derivatives with lateral methyl substitution having central cinnamates VI n and benzoates VII n moiety were prepared. All the compounds were characterised with infrared, proton magnetic resonance and ultraviolet spectroscopy. Liquid crystalline phase and their transition enthalpies were studied using a polarised optical microscope (POM) and differential scanning calorimetry (DSC), respectively. The electrostatic potential of compounds was measured using DFT calculation. All compounds of both the Series VI n and VII n are mesogenic. The homologues VI 1 to VI 12 exhibited enantiotropic nematic mesophase, homologues VI 7 to VI 18 exhibited smectic A mesophase, homologues VI 7 to VI 12 exhibited both enantiotropic smectic A and nematic mesophase. Homologues VII 1 to VII 12 exhibited enantiotropic nematic mesophase, homologues VII 8 to VII 18 exhibited smectic A mesophase, homologues VII 8 to VII 12 exhibited both enantiotropic smectic A and nematic mesophase. The phase transition of the present two series is compared with each other and with three structurally related compounds to evaluate the effect of central linkage and lateral substitution on their mesophase behaviour.