Solvatochromism and quantum mechanical investigation of disazo pyridone dye

Disazo pyridone dye, 4‐methyl‐2,6‐dioxo‐5‐(2‐(4‐(phenyldiazenyl)phenyl)hydrazono)‐1,2,5,6‐tetrahydropyridine‐3‐carbonitrile, is synthesised and thoroughly characterised by a combination of experimental and computational approaches. Fourier Transform‐infrared and nuclear magnetic resonance (NMR) spectra prove the existence of the hydrazone form in the solid state and in dimethyl sulphoxide, which is also supported by vibrational and NMR theoretical studies. Ultraviolet (UV) spectral properties, as well as solvatochromism in 19 solvents of different polarity, are investigated. In most of the solvents, the dye is solely present in the hydrazone form, whereas in certain solvents, an acid–base equilibrium exists. Excellent agreement between computational and experimental UV–visible data was established. Frontier Molecular Orbital analysis was performed and proved the existence of intramolecular charge transfer through the dye molecule. A molecular electrostatic potential surface was plotted over the optimised geometry to lighten the reactivity of the investigated molecule.