The synthesis, structural characterization and antibacterial properties of some 2-((4-amino-1,2,5-oxadiazol-3-ylimino)methyl)-4-(phenyldiazenyl)phenol

The Schiff base compounds 2-((4-amino-1,2,5-oxadiazol-3-ylimino)methyl)-4-(phenyldiazenyl) phenol (2a–e) were prepared from the reaction of 3,4-diamino-1,2,5-oxadiazole with 2-hydroxy-5-[(E)-(aryldiazenyl)]benzaldehyde (1a–e) in methanol. The structures of all compounds were then characterized by elemental analysis, mass, IR, UV–Vis, 1H and 13C NMR spectroscopy. UV–Vis absorption spectra indicated enol–keto tautomeric and positive solvatochromism in compound 2a–e which is dependent on the substitution, nature of solvent, pH and environment temperature. The Quantum chemical calculations and UV–Vis absorption spectra data show that positive solvatochromism behavior of compounds 2a–e, which could be due to intramolecular hydrogen bond in enol–keto tautomeric and dipole moment changes. The antibacterial activities of compounds were evaluated against both gram-positive and gram-negative bacteria. All the compounds were found to be active against Staphylococcus aureus and Bacillus cereuss. Among them, compound 2b exhibited the most potent antibacterial activity.

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► New 1,2,5-oxadiazole based azo-azomethine dyes.
► Acidity, temperature and medium dependency of solvatochromism in azo-azomethine dyes.
► The effect of dipole moment on enol–keto tautomerism of azo-azomethine dyes.
► Increasing the antibacterial activity of azo-azomethine dyes with electron releasing of substituents.