Synthesis, Characterization and Solvent Effects on the Electronic Absorption Spectra of Aminopyridine Schiff Bases

Six Schiff bases, namely, N-(2-hydroxylbenzylidene)pyridine-4-amine (IA), N-(2-hydroxylbenzylidene)pyridine-2-amine (IB), N-(5nitro-2-hydroxylbenzylidene)pyridin-4-amine (IIA), N-(5-nitro-2-hydroxylbenzylidene)pyridin-2-amine (IIB), N-(5-bromo-2hydroxylbenzylidene)pyridin-4-amine (IIIA) and N-(5-bromo-2-hydroxylbenzylidene)pyridin-2-amine (IIIB) derived from condensation reactions of 4-aminopyridine or 2-aminopyridine with salicylaldehye, 5-nitrosalicylaldehye and 5-bromosalicylaldehye were synthesized and characterized using elemental analysis, IR, NMR and Raman spectroscopic techniques.The effect of solvent on the electronic absorption spectra was examined in five solvents of different polarities, namely, 1,4-dioxane, chloroform, ethanol, acetonitrile and N,Ndimethyl formamide.The bands involving different electronic transitions were interpreted and regression coefficients calculated for the absorption band involving intermolecular charge transfer transition within the whole Schiff base molecule using an equation that relates the absorption maxima to empirical solvent parameters that depend on the dielectric constant, refractive index and hydrogen bonding ability of the solvents.