Substituent effects on the mesogenic benzylidenes of 4-methylaniline: Synthesis, characterization, DFT, NLO, photophysical, molecular docking, and antibacterial studies

Abstract

Substituted benzylidene anilines forming donor-π-acceptor (D-π-A) molecular systems are the models of molecular mesogenic cores for NLO applications. The effect of the benzylidene substituents on the sensitivity of the electronic properties of the azomethine CN group in the substituted benzylidene anilines p-X-C6H4-CH = N-C6H4-p-Me is investigated by experimental and theoretical studies. Three benzylidene anilines are synthesized from p-toluidine and para substituted benzaldehydes and are characterized by FT-IR and NMR spectra. Density functional theory (DFT) calculations are employed to investigate the structural and electronic featural changes incurred by the benzylidene substituent from their optimized geometry, Mulliken values, and FMOs. Since this type of mesogenic cores exhibit enhanced nonlinear optical behavior, their molecular NLO properties are evaluated from the DFT calculations. The effect of the substituents on the photophysical characteristics of the molecules are studied from the experimental and theoretical absorption and emission spectra of the compounds. The biological activity of these Schiff bases is probed for their in vitro antibacterial activities and for their molecular binding dynamics with falcipian 2 and 3.