Preparation and DFT Study for New Three-Ring Supramolecular H-Bonded Induced Liquid Crystal Complexes.

Sayed Z Mohammady,Daifallah M Aldhayan,Mohamed Hagar

doi:10.3389/fchem.2021.679528

Sayed Z Mohammady, Daifallah M Aldhayan + Show 1 more

Open Access

https://doi.org/10.3389/fchem.2021.679528

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Abstract

Supramolecular three-ring Schiff base novel liquid crystal complexes have been prepared and investigated. Schiff bases of para-substituted aniline derivatives and para-pyridine carbaldehyde have been prepared and then mixed in equimolar quantities with para-alkoxy benzoic acids. On one side, the alkoxy chain length varies from 8 to 16 carbon atoms. On the other side, terminal small compact groups substituting aniline with various polarities are used. Hydrogen-bonding interaction was elucidated by FTIR spectroscopy. The mesomorphic thermal and optical characteristics of the samples were obtained by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). All samples exhibit enantiotropic mesophases. Experimental results obtained for the induced mesophases were correlated with density functional theory (DFT) theoretical calculations. The results revealed that both the polar compact groups’ polarity and the alkoxy chain lengths contribute strongly to mesomorphic characteristics and thermal stabilities of the mesophases. Surprisingly, the observed values of enthalpy changes associated with the crystalline mesomorphic transitions lie in the range of 2.2–12.5 kJ/mol. However, the enthalpy changes corresponding to the mesomorphic–isotropic transitions vary from 0.9 to 13.9 kJ/mol, depending on the polarity of para-attached groups to the aniline moiety.

Highlights

The supramolecular aggregation arises from the binding of a group of molecules of a well-defined structure
Among the second-order bonding types, hydrogen bonds play a pivotal role in supramolecular assemblies, and this has resulted in their widespread use for the synthesis of Liquid crystals (LCs)
The observed values associated with the crystalline mesomorphic transitions are considerably small (∼2.2–12.5 kJ/mol), indicating a weak hydrogen bonding in the crystalline solid compared to the literature values for crystalline mesomorphic transitions (∼20–100 kJ/mol)

Summary

Introduction

The supramolecular aggregation arises from the binding of a group of molecules of a well-defined structure. These molecules are grouped together by second-order (noncovalent) bonds, for example, hydrogen bonds, halogen bonds, pi agglutination, van der Waals forces, coordination bonds, and dipole–dipole interactions (Borissova et al, 2008) (Arunan et al, 2011) (Shimizu and Ferreira Da Silva, 2018). Liquid crystals (LCs) are considered among the most important formative materials that can be produced by supramolecular assembly (Park et al, 2015) (Sun et al, 2015) (Alnoman et al, 2020) (Scholte et al, 2020). The most common method of preparing two-component self-assembly is mixing followed by two-component reaction

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