Synthesis, characterization, solvatochromic, computational and antibacterial studies of a series of new 4-imino-3-(2-heteroarylhydrazono) chroman-2-one dyes

Herein, 4-aminocoumarin was synthesized and reacted with some diazonium salts derived from substituted 2aminothiazoles to produce corresponding new azo dyes. These newly synthesized compounds were fully characterized by FT-IR and NMR spectroscopies and mass spectral analysis. The results testified that the obtained products exclusively exist in the hydrazone tautomeric form both in solid and solution states, and no spectral evidence of an azo structure was detected. The visible absorption spectral changes of the dyes were also studied in acetic acid, ethanol, chloroform, acetonitrile, dimethyl formamide, and dimethyl sulfoxide in the region of 300-600 nm, and the results were discussed according to possible electronic transitions in the compounds. The visible spectral behavior of ethanol-water solutions (50:50, v: v) of the dyes was also examined at different pH values at ambient temperature. Furthermore, the geometries of the proposed azo and hydrazone tautomeric forms of the dyes were optimized at B3LYP/6-311++G (d, p) level of theory. DFT calculations have been performed to evaluate the stability of the proposed azo and hydrazone tautomeric forms of the prepared dyes both in the gas phase and in solution, and the outcomes were compared with spectroscopic findings. Besides, antibacterial activities of the dyes dissolved in DMSO were evaluated using the well diffusion method against Staphylococcus aureus (ATCC 25923) and Escherichia coli (ATCC 25922) bacterial strains.