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

Sayed Z. Mohammady,Yeldez El Kilany,Mohamed A. Zakaria,Daifallah M. Aldhayan,Mohsen M. T. El-Tahawy,Mohamed Hagar,Mohammed T. Alazmid,Khulood A. Abu Al-Ola

doi:10.3390/cryst12020136

Sayed Z. Mohammady, Yeldez El Kilany + Show 6 more

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https://doi.org/10.3390/cryst12020136

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Abstract

Supramolecular, low-melting (near or below 0.0 °C) ionic liquid crystals with two rings of Schiff bases were prepared and studied. The Schiff bases were synthesized using 4-substituted aniline derivatives and 4-pyridine carbaldehyde and then mixed in equimolar amounts with linear 1-bromoalkanes of different chain lengths, namely C6, C8, and C14. The mesomorphic behavior and thermal properties of the compounds were determined by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). Only the ionic liquids analogous with 1-bromotetradecane exhibit mesomorphic behavior. All, except the smectic A (SmA) monomorphic fluorine-substituted complex, show dimorphic enantiotropic mesophases, namely SmA followed by nematic (N) mesophases depending on the temperature rise. The DSC and POM results for the induced mesophases were then treated with density functional theory calculations (DFT). The results showed that both the polarity of the polar groups and the length of the alkyl groups strongly influence the mesomorphic properties of the ionic liquids.

Highlights

IntroductionIonic liquids (ILs) can be defined as ionic materials possessing low melting points of less than 100 ◦ C
Ionic liquids (ILs) play an important role as starting materials for N-heterocyclic carbenes, which can be used in a variety of catalytic reactions [10,11,12,13]
The IL analogues composed of Schiff bases with the 1-bromotetradecane exhibit mesomorphic behavior

Summary

Introduction

Ionic liquids (ILs) can be defined as ionic materials possessing low melting points of less than 100 ◦ C. ILs possess a large number of different physicochemical properties that qualify these materials for specific applications and often lead to significant results when applied compared to their behavior in conventional solvents [4,5]. ILs reveal stability towards thermal degradation [7,8,9]. They can be used as ideal substitutes for conventional organic solvents. They exhibit exceptional solubility properties for inorganic, organic and organometallic compounds. ILCs are gaining popularity since they are projected to combine the numerous intriguing technical applications of ILs and LCs [14,15]

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