Solvent and Structural Effects on the UV–Vis Absorption Spectra of Some 4,6-Disubstituted-3-Cyano-2-Pyridones

A series of 4,6-disubstituted-3-cyano-2-pyridones was synthesized and their UV–Vis absorption spectra were recorded in the region 200–600 nm in the set of selected solvents. The effects of solvent dipolarity/polarizability and solvent–solute hydrogen-bonding interactions on the spectral shifts were analyzed by means of the linear solvation energy relationship concept of Kamlet and Taft. The influence of solvents as well as substituents on the 2-pyridone/2-hydroxypyridine tautomeric equilibration was evaluated. The absorption band maximum of the 2-hydroxypyridine form is found to appear at a shorter wavelength than that of the 2-pyridone form in all investigated solvents. The replacement of the methyl and phenyl groups at position 6 of the pyridone ring, by a hydroxy group, significantly changes the solvatochromic behavior of the investigated pyridones.