Identification of Structural and Spectral Properties of New Mono Azobenzo[c]cinnolines: Experimental and Theoretical Approach

Characterization of new azo compounds is quite challenging due to the formation of azo‐hydrazone tautomers in solvents. The use of theoretical calculations is an important tool in resolving this phenomenon. In this study, new mono azobenzo[ c ]cinnolines were synthesized by coupling 3,8‐dihydroxybenzo[ c ]cinnoline with diazonium salts. Azo dyes ( 1 – 3 ) were characterized by UV–vis, FTIR, NMR, and LC‐MS spectroscopy. The absorption maxima of dyes were investigated for solvent and acid‐base effects. 1D and 2D NMR spectra of dye 1 were also presented, and its molecular structure was comprehensively evaluated. Furthermore, the B3LYP functional with the 6‐311++G(d,p) basis set was used in theoretical calculations to determine the molecular structures, vibrational frequencies, and gauge‐including atomic orbital ( GIAO ) chemical shifts of the tautomers of dye 1 . Additionally, TD‐DFT calculations were performed to specify the absorption spectra of the tautomers. Structural information of the tautomers was assessed by combining spectroscopic analysis with experimental and computational techniques. Supported by 2D NMR and theoretical studies, this study addressed the phenomenon arising from the equilibrium state of azo‐hydrazone tautomers in the NMR spectra of dye 1 . It presents a detailed, up‐to‐date, and original study on the synthesis, spectral characterization, and theoretical analysis of novel mono‐azobenzo[ c ]cinnoline dyes.