Synthesis, spectroscopic and physicochemical investigations of environmentally benign heterocyclic Schiff base derivatives as antibacterial agents on the bases of in vitro and density functional theory

► Synthesis of novel Schiff bases under microwave irradiation. ► Spectroscopic and physicochemical investigations of Schiff bases. ► The antibacterial activity of these compounds was tested in vitro by minimum inhibitory concentration (MIC). ► The results showed that compound 1 is better inhibitors of both types of the bacteria. ► Based on the density functional theory calculations, DFT/6-31G∗ basis set. A series of Schiff bases were synthesized by the reaction of 4-dimethylamino-benzaldehyde and corresponding active amines under microwave irradiation. Results obtained from spectroscopic (FT-IR, 1H NMR, 13C NMR, GC–MS) and elemental analyses of synthesized compounds were in a very good agreement with their chemical structures. UV–Vis and fluorescence spectroscopy measurements provided that all compounds are good absorbent and fluorescent. Fluorescence polarity study demonstrated that these compounds were sensitive to the polarity of the microenvironment provided by different solvents. In addition, spectroscopic and physicochemical parameters, including singlet absorption, extinction coefficient, Stokes shift, oscillator strength and dipole moment, were investigated in order to explore the analytical potential of synthesized compounds. The antibacterial activity of these compounds was first studied in vitro by the disk diffusion assay against two Gram-positive and two Gram-negative bacteria. The minimum inhibitory concentration was then determined with the reference of standard drug tetracycline. The results displayed that compound 1 was better inhibitors of both types of the bacteria (Gram-positive and Gram-negative) than tetracycline. Based on the density functional theory calculations, LUMO and density of compounds (1–5) were calculated to support the antibacterial activities.