Mesomorphic, micro-Raman and DFT studies of new calamitic liquid crystals; methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino]benzoates

The mesomorphic properties of newly synthesized homologous series of calamitic liquid crystals; methyl 4-[4-(4-alkoxy benzoyloxy)benzylideneamino]benzoates, H2n+1CnOC6H4COOC6H4C(H)=N C6H4COOCH3; n = 6, 8, 10, 12, 14, 16 (MABBAB-n) containing ester and Schiff base groups as linker have been studied by temperature dependent micro-Raman study, differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). All members of this series exhibit enantiotropic smectic A (SmA) mesophase with oily streak and focal conic textures. Analyses of Raman marker bands of phenyl rings, Schiff base and ester groups of MABBAB-10 confirm the phase transitions. The Raman study also gives an evidence of breaking of weak intermolecular hydrogen bonds associated with ester groups and formation of new hydrogen bonds through C=N bond at Cr -> SmA phase transition. The monomer and dimer were optimized and vibrational assignment of MABBAB-10 was also done with density functional theoretical (DFT) technique to understand the experimental results. (C) 2014 Elsevier B.V. All rights reserved.