Synthesis, mesomorphic properties and DFT calculations of new coumarin Schiff base-ester liquid crystals

Abstract

ABSTRACT In the present work, two series of Coumarin based Schiff base-esters mesogenic compounds have been synthesised. The first series (KSC-(6–18)) comprises of Schiff base of alkoxy 4-formylbenzoate and 7-alkoxy-3-aminocoumarin with symmetric variation of alkoxy chain at the both ends that have been designed and prepared. In the second series (KC-(6–18)), octyloxy chain on coumarin end was kept constant with variation at the other end. All new mesogens were characterised using various analytical techniques including FTIR, NMR, elemental and mass spectral analysis. The textures of the mesomorphic properties were investigated using polarising optical microscope (POM) and differential scanning calorimetry (DSC). In series (KSC-(6–18)), on varying the alkyl chain length at the both end of molecules systematically, an enantiotropic smectic A phase behaviour was observed for compounds with chain lengths (n = 6, 8, 10, 12). Compounds of the (KSC-(6–18)) series with (n = 14, 16, 18) were non-mesogenic. In the (KC-(6–18)) series with octyloxy chain at coumarin end, an enantiotropic smectic A mesophase was observed for all compounds (n = 6-18). The DFT calculations have been carried out and the theoretical study was discussed in terms of dipole moment, molecular electrostatic potentials, frontier molecular orbitals and geometrical structure along with aspect ratio.