Experimental and computational studies of laterally ethoxy Schiff base-ester liquid crystalline magnets

Abstract

ABSTRACT A series of liquid crystals 4-X-(3’-ethoxy-4’-alkyoxyphenyimino)anilines with elongated molecular axis through the introduction of alkoxy chains containing different substituents (X = CH3, OCH3 and Cl) were synthesised. The thermal–optical behaviours ofthese organic magnets were characterised by differential scanning calorimetry and polarised optical microscopy. Elemental analysis, FT-IR and 1H-NMR were employed to elucidate the molecular structures of the target compounds. Experimental data show that the nematic phase temperature range increases in the order of CH3 < Cl < OCH3. The laterally ethoxy Schiff base-ester liquid crystal with the most electronegative Cl atom is presumed to outweigh both analogues containing CH3 and OCH3, leading to the highest clearing temperature (Tc) value, but the present work proved that the presence of the O atom from OCH3 is inclined to orientate in a parallel arrangement that increases the length-to-breadth ratio and the polarisability of the molecule. Computational studies on the different substituents against its kinetic stability were carried out based on the variation in the energy value of HOMO–LUMO gap (ΔEgap). A relationship between the energy gap and the substituents under the present study shows that when the ΔEgap increases from OCH3 < Cl < CH3, the chemical reactivity decreases, leading to the lowering of the clearing temperature.