Silicon-containing bis-azomethines: Synthesis, structural characterization, evaluation of the photophysical properties and biological activity

• An original diamine containing dimethylsilane unit was obtained and characterized.
• Azomethines of salicylaldehyde and its OH- and CH3O-substituted derivatives were obtained.
• Schiff bases proved to be good UV light absorbing and fluorescent materials.
• The photophysical sensitivity to the solvent polarity was studied.
• Two azomethines proved antimicrobial activity better than standard compounds.

A new diamine, (dimethylsilanediyl)bis(methylene)bis(4-aminobenzoate) (1), containing dimethylsilane spacer, was prepared by the condensation of p-aminobenzoic acid with bis(chloromethyl)dimethylsilane. This was subsequently reacted with salicylaldehyde, 3-hydroxy-salicylaldehyde, and 3-methoxy-salicyladehyde, when corresponding Schiff bases (E)-(dimethylsilanediyl)bis(methylene)bis(4-((E)-(2-hydroxybenzilidene)amino)benzoate (2), (E)-(dimethylsilanediyl)bis(methylene)bis(4-((E)-(2-hydroxybenzilidene)amino)benzoate (3), and (E)-(dimethylsilanediyl)bis(methylene) bis(4-((E)-(2-hydroxy-3-methoxybenzilidene)amino)benzoate (4), respectively were formed. All the obtained compounds were structurally characterized by spectral (FT-IR, 1HNMR, 13CNMR) analyses and single crystal X-ray diffraction. Photophysical studies revealed that the new prepared Schiff bases are good UV light absorbing and fluorescent materials. Thus, they exhibit strong UV/Vis-absorption at 250–400 nm and violet or orange emission, in sensitive dependence on the polarity of the solvents and the nature of the substituent (H, OH and OCH3) at the aromatic ring. The antimicrobial activity of these compounds was first studied in vitro by the disk diffusion assay against two species of bacteria and three fungi. The minimum inhibitory concentration was then determined with the reference of standard compounds. The results displayed that Schiff bases 3 and 4 having hydroxy- and methoxy-substituents on the aromatic ring were better inhibitors of both types of species (bacteria and fungi) than standard compounds, Caspofungin and Kanamycin.

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