2D NMR, Solvatochromic Behaviour and DFT Studies of Some Azo-quinoline Derivatives

In this study, the chemical structures of three azo-quinoline derivatives (S1, S2, and S5) were unequivocally established using comprehensive 2D NMR techniques, including COSY, HSQC, HMBC, and TOCSY.Their solvatochromic behaviour was investigated in seven solvents of varying polarity.Both S1 and S5 showed moderate correlations (R 2 ) of 0.45 and 0.681 with solvent polarity function and dispersive effects respectively.DFT/TD-DFT calculations at the B3LYP/6-311++G (d, p) level showed S5 as having the smallest gas-phase HOMO-LUMO energy gap (2.71 eV) and the most elongated N=N bond (1.3277 Å), indicating enhanced conjugation.The excellent agreement between the computed and experimental absorption maxima for S2 validated the computational protocol.These structure-property correlations provide a pedestal for designing quinoline-based chemosensors and optoelectronic materials.