Synthesis, Characterization, and Mesomorphic Investigations of Calamitic Liquid Crystals – methyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino) benzoates and Their Copper(II) and Nickel(II) Complexes

Abstract

A new series of Schiff's base mesogenic ligands with a polar methyl ester as an end group, methyl 4-(4′-(alkoxy)-2 hydroxybenzylideneamino) benzoates, C_nLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) and nickel(II) complexes have been synthesized. They were characterized by elemental analyses, Fourier transform infrared (FT-IR), ¹H and ¹³C nuclear magnetic resonance, and UV-VIS spectroscopy. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The ligands exhibit an enantiotropic SmA mesophase with a high-temperature range and thermal stability. The square planar copper(II) complexes show enantiotropic SmA mesophase, but the nickel(II) complexes are nonmesogenic in nature. The thermal stability of the compounds was also determined by thermo gravimetric analyses. Density functional theory (DFT) calculations were performed using GAUSSIAN-03 program at B3LYP level to obtain the stable electronic structure of the ligand and their metal complexes.

Keywords:

• Density functional theory
• differential scanning calorimetry
• enantiotropic mesophase
• metallomesogen
• polarizing optical microscopy

Acknowledgments

Hemant Kumar Singh (Junior Research Fellow), Sachin Kumar Singh (Senior Research Fellow), and Vijay Kumar (Junior Research Fellow project) are grateful to Council of Scientific and Industrial Research (CSIR), New Delhi, India, for financial support. Bachcha Singh is grateful to CSIR (Project No. 01(2550)12/EMR-II) for providing financial assistance.