Coumarin Schiff base derivatives with asymmetric naphthalene: Synthesis, mesomorphic studies and DFT calculations

Abstract

Coumarin Schiff base derivatives NC(2–16) with 7-(decyloxy)naphthalen-2-yl-4-formylbenzoate have been designed, synthesized and characterized by IR, ¹H NMR, ¹³C NMR, ESI-MS and CHN analysis followed by study of mesomorphic properties using polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) analysis. In this homologous series NC(6–16), decyloxy chain was kept constant and systematic variation was carried out at coumarin end of the molecule. In this series NC(2–16), compounds NC2 to NC5 exhibited enantiotropic smectic A (SmA) with fan shaped texture. On increasing chain length to hexyloxy in compound NC6, enantiotropic SmC mesophase was observed along with SmA mesophase with low stability during cooling cycle. While higher analogous in this series with n = 7,8,10,12,14,16, have exhibited enantiotropic SmC mesophase with various texture including broken fan, sanded and broken focal conic texture. Tilted SmC mesophase for one of the compound is confirmed by VT-XRD analysis. The DFT calculations for all the compounds and literature reference molecules were studied and compared with structural (length, aspect ratio) and electronic (dipole moment, polarizability) parameters followed by discussions. Incorporation of coumarin moiety was found to play role in increasing stability of mesophase due to increase in dipole moment and polarizability.