Absorption and fluorescence spectral properties of azo dyes based on 3-amido-6-hydroxy-4-methyl-2-pyridone: Solvent and substituent effects.

A series of nine 5-(4-substituted phenylazo)-3-amido-6-hydroxy-4-methyl-2-pyridones were synthesized and characterized by FT–IR, 1H and 13C NMR, UV–Vis, and PL spectroscopy. Photophysical properties of the dyes were examined in solvents of various polarities and at different pH values. The solvent effects on the absorbance and emission spectral shift were analyzed using Lippert–Mataga, Reichardt–Dimroth and Kamlet-Taft equations. Moreover, UV–Vis absorption and emission frequencies were correlated with Hammett substituent constants applying the linear free energy relationships. DFT calculations of the investigated dyes were accomplished to determine their structural and electronic properties. Image 1 • The absorption and emission spectra of nine arylazo pyridone dyes were recorded. • The solvent effects on the absorbance and emission spectral shift were analyzed. • The conformational analysis showed that the investigated dyes are in hydrazone form. • The existence of two conformational forms of hydrazone tautomer was confirmed. • Excellent correlations between computational and experimental data were established. [ABSTRACT FROM AUTHOR]