Terminal-substituted benzoxazole based Schiff-base Mesogens and their Cu(II) complexes: Synthesis and structural characterization

Three homologous series of 3‑hydroxy-4-(((-4-benzoxazol-2-yl)phenyl)imino)methyl)phenyl-4-alkoxybenzoate (with ester linkage) and 5-(alkoxy)-2-(((4-(5-benzoxazol-2-yl)phenyl)imino)methylphenol (without ester linkage) Schiff based derivatives, bearing different substituents at 5 position i.e., 5-methylbenzoxazole, benzoxazole and 5-chlorobenzoxazole units at the end of the molecule and their Copper complexes were synthesised. The molecular structure of all the compounds were elucidated by different spectroscopic techniques such as FT-IR, 1H & 13C NMR and mass spectrometry together with elemental analysis. Their phase transition behaviour was investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The structure-property relationships, compounds bearing a variety of polar substituents and changing the spacer from ester linked to without ester-linked has been studied. Substituents with stronger electron-withdrawing properties gave a wider mesomorphic temperature domain, in the order Cl > CH3 >H.