Mesomorphic Behaviour and DFT Insight of Arylidene Schiff Base Liquid Crystals and Their Pyridine Impact Investigation

Abstract

A new series of Schiff base liquid crystal have been prepared and studied. Schiff bases of p-alkyl aniline derivatives and 4-phenyl pyridine-4′-carbaldehyde were prepared. The terminal alkyl groups substituting aniline are of varied chain length, namely C8, C12 and C14. The structures of the compounds were elucidated by 1H NMR and 13C NMR. The mesomorphic thermal and optical characteristics of the samples were determined via differential thermal analysis (DSC) and polarization optical microscopy (POM). All compounds exhibit enantiotropic dimorphic mesophase behaviour, referred to as smectic X1 (SmX1) and smectic X2 (Sm A). Experimental results obtained for the mesophases were correlated with density functional theory (DFT) theoretical calculations. The results of the new series are further compared to two series of compounds bearing pyridine (two ring Schiff bases) and biphenyl, respectively, in their mesogens. The series of compounds of one pyridine ring are generally not mesomorphic. The results indicate that the alkyl chain length has a strong impact on the mesomorphic characteristics and thermal stabilities of the different mesophases. As a trend, the temperature ranges of both of smectic mesophases of all compounds are higher in new compounds bearing the 4-phenyl pyridine moiety. In addition, the total mesophase range is generally higher in the new compounds when compared to their biphenyl analogues. Finally, theoretical DFT calculations were performed to illustrate the experimental finding of the mesomorphic behaviour in terms of the molecular geometry and aromaticity, π–π stacking and LOL-π.

Polar Alkoxy Group and Pyridyl Effects on the Mesomorphic Behavior of New Non-Symmetrical Schiff Base Liquid Crystals

“…This elevation in pi-pi stacking can explain the promoted SmB and SmA mesomorphic order rather than the nematic one even for the sample bearing relatively short hexyloxy chain length (3.d). Comparing the effect in the present study with LC having 4-phenyl pyridine and terminated with alkyl groups, the effects of introducing the above explained two factors were more pronounced [48].…”

“…• C kJ/mol It is worth noting that this study presents a continuation of our systematic work in which we investigate the effect of conjugation length on the mesomorphic behavior on model examples of LCs. In a recent article, we have investigated the effect of introducing 4phenyl pyridine moiety on LC molecules terminated with alkyl group [48]. The mesophases of new compounds were verified by observing their textures through POM (Figure 2).…”

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

“…The variation in aspect ratio of the compounds (length-to-width ratio) with the mesomorphic temperature range of the SmA and N mesophases of the compounds is displayed in Figure 4a,b. It is well known that the intermolecular interaction increases upon the elevation of aspect ratio [37][38][39][40]. At high aspect ratios, the area of the intermolecular interaction increases.…”

Synthesis and Mesogenic Properties of New Aromatic Schiff Base’s Esters

“…LCs have received an overwhelming response due to their very promising applications in various technological fields such as display devices, organic light emitting diodes, anisotropic networks, photoconductors, semiconductor materials, lubricating agents and LC sensors [1][2][3][4][5]. An effective way to develop new low-cost LC material with unique properties is the modification of molecular structure which has proven to be one of the finest strategies [6]. This has led to the synthesis of numerous mesogens, especially thermotropic type.…”

“…It has a stepped core struc-ture, but it can maintain linearity of the molecule. Hence, it provides higher stability and allow mesophase formation [6,7]. Much works has been emphasized on Schiff base system ever since the discovery of room temperature MBBA [8].…”