Pyridine-Based Three-Ring Bent-Shape Supramolecular Hydrogen Bond-Induced Liquid Crystalline Complexes: Preparation and Density Functional Theory Investigation

Abstract

A series of new supramolecular three-ring bent-shape Schiff base liquid crystal (LC) complexes were prepared and studied. On one side, two alkoxy chain lengths of the carboxylic acids were used, namely eight and sixteen carbons. Moreover, on the other side, terminal small compact groups, which substituted aniline, with different polarities were utilized. Furthermore, the hydrogen-bonding interactions in the formed complexes were elucidated by Fourier-transform infrared (FT–IR) spectroscopy. The mesomorphic thermal and optical characteristics of the samples were determined by differential thermal analysis (DSC) and polarized optical microscopy (POM). The complexes exhibited enantiotropic and dimorphic mesophase behaviors. The results indicate that the polarity of the compact groups and the lengths of the alkoxy chains greatly impacted the mesomorphic characteristics and thermal stabilities of the mesophases. The observed values of the enthalpy changes (ΔH) associated with the crystalline smectic-A (TCr-SmA) transitions were extremely small compared with the conventional values that characterize supramolecular hydrogen-bonded liquid crystalline complexes. ΔH, which corresponded to the nematic isotropic transitions (TN-I), varied from 0.13 to 9.54 kJ/mol depending mainly on the polarity of the groups that were para-attached to the aniline moiety. Finally, the theoretical results obtained by density functional theory (DFT) calculations were discussed. The DFT geometrical structures showed non-coplanar structures. The mesomorphic range was correlated with the calculated dipole moment, polarizability and the aspect ratios of the investigated compounds.

Synthesis and DFT Investigation of New Low-Melting Supramolecular Schiff Base Ionic Liquid Crystals

“…However, the methoxy group of high mesomeric resonance effect with large space filling showed higher overall mesomorphic smectic range than the nematic mesophase. indicated, due to the greater degree of alkyl aggregation of the methoxy chain, the smectic range increases [33,34,41].…”

“…In this contribution, we extended our recent work of supramolecular Schiff baseinduced liquid crystalline materials [33,34] to synthesize functionalized ionic liquid crystal (FILCs) two-ring Schiff bases with melting points close to or lower than 0.0 • C. These Schiff bases were designed using 4-substituted aniline derivatives and 4-pyridine carbaldehyde and finally paired with linear 1-bromoalkanes of various chain lengths. We investigated the mesomorphic behavior and thermal properties of these FILCs using polarized optical microscopy (POM) and differential thermal analysis (DSC).…”