Twin effects of induction and stabilization of the SmA* phase by Cu(ii) using 4,4′-disubstituted salicylideneimine containing [1,2,3]-triazole and cholesterol arms

Abstract

A new series of Cu(II) metallomesogens containing 4,4′-disubstituted salicylideneimine armed with two mesogenic units of [1,2,3]-triazole and cholesterol were synthesized and characterized. Spectroscopic techniques such as UV-visible, FT-IR, ¹H-NMR and elemental analysis were employed to elucidate their molecular structures. Polarizing optical microscopy (POM) and differential scanning calorimetry (DSC) have confirmed that all the complexes and ligands exhibited enantiotropic chiral mesophases. The ligand with the terminal dodecanoate chain exhibited enantiotropic N* and SmC* phases, while the other homologous members with even alkanoate chains ranging from C₁₄H₂₉ to C₂₀H₄₁ exhibited exclusively the SmC* phase. Surprisingly, their corresponding Cu(II) complexes exhibited a new SmA* phase which was absent in their respective ligands. Comparison studies between the present compounds with earlier reported Cu(II) complexes have further uncovered that the incorporation of Cu(II) ions would increase the colinearity and the presence of N atoms in the [1,2,3]-triazole ring could increase the acentral transverse dipole and the permanent dipole in between the molecules. As such it led to the enhancement of the smectogenic properties. Besides, all the Cu(II) complexes reported in this study are thermally more stable than their corresponding ligands.