The influence of lateral hydroxyl group and molecular flexibility on the mesogenic behaviour of a new homologous series based on thiophene-chalcone: Synthesis, characterization, crystal structure and DFT study

Abstract

A new homologous series of rod shaped calamite liquid crystals based on thiophene-chalcone has been prepared by condensation of 2-hydroxy-4-n-alkoxybenzaldehyde (n = 2 to 8, 10, 12, 14, 16, 18) with (E)-1-(4-aminophenyl)-3-(thiophen-2-yl)prop-2-en-1-one. FT-IR, 1H NMR, 13C NMR and mass spectroscopy were used to characterize synthesized compounds. The liquid crystal behaviour of all synthetic compounds was investigated using Differential Scanning Calorimeter (DSC) and Polarizing Optical Microscope (POM). Lower members of the homologous series, n-heptyloxy (E7) to n-dodecyloxy (E12), are nematogenic, and higher members, n-tetradecyloxy (E14) to n-octadecyloxy (E18), are smectogenic, whereas n-ethoxy (E2) to n-pentyloxy (E5) derivatives is non-mesogenic, and n-hexyloxy (E6) exhibited monotropic nematic phase. The n-pentyloxy derivative (E5) crystallizes under monoclinic, space group P2/c with unit cell dimensions a = 16.1723(9) Å, b = 5.8603(3) Å, c = 22.4320(12) Å, β = 100.153(2), V = 2092.69(9) Å3. The ethoxy derivative (E2) was subjected to DFT (density functional theory) level computations and complete geometric optimization utilizing B3LYP/6–311G (d, p) basis sets and results were compared with structurally similar compound.