Experimental and theoretical insight into the electronic properties of 4‐aryl‐5‐arylazo‐3‐cyano‐6‐hydroxy‐2‐pyridone dyes

In this paper, spectroscopic and quantum mechanical investigation of nine 4‐aryl‐5‐arylazo‐3‐cyano‐6‐hydroxy‐2‐pyridone dyes was performed, and obtained density functional theory (DFT) results were compared with experimental data. The structural and spectroscopic properties of azo‐2‐pyridone dyes were studied by DFT using B3LYP, CAM‐B3LYP, and M06‐2X methods with a 6‐311++G(d,p) basis set. Comparison of results reveals that the scaled theoretical vibrational frequencies of azo dyes are in good agreement with experimental data. The time‐dependent DFT calculated and experimental ultraviolet‐visible (UV‐vis) absorption spectra are also in good agreement. The effect of electron‐donating –OCH₃ and electron‐withdrawing –NO₂ groups on the structural parameters, vibrational frequencies, UV‐vis absorption, and natural bond orbital (NBO) atomic charges were thoroughly analysed. Vibrational, UV‐vis, and NBO analyses confirm that investigated dyes exist in the hydrazo tautomeric form in the solid state and ethanol solution. These analyses signify the occurrence of intramolecular charge transfer in these azo‐pyridone dyes.