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

Two new homologous series of Schiff's base derivatives with lateral methyl substitution having central cinnamates VIn and benzoates VIIn 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 VIn and VIIn are mesogenic. The homologues VI1 to VI12 exhibited enantiotropic nematic mesophase, homologues VI7 to VI18 exhibited smectic A mesophase, homologues VI7 to VI12 exhibited both enantiotropic smectic A and nematic mesophase. Homologues VII1 to VII12 exhibited enantiotropic nematic mesophase, homologues VII8 to VII18 exhibited smectic A mesophase, homologues VII8 to VII12 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.