Synthesis, nonlinear optical analysis and DFT studies of D–π–D and A–π–A configured Schiff bases derived from bis-phenylenediamine

Herein, an integral approach has been made towards the exploration of electronic and structural parameters of four synthesized (DMA with an A–π–A configuration and DMM, DAM, and DMD with a D–π–D configuration) and one designed (DMB-D) novel Schiff base compounds. Bis phenylenediamine derivatives were prepared by condensation of 4,5-dimethyl-o-phenylenediamine (1) with various substituted benzaldehydes (2a–d). The structures of compounds were confirmed by spectroscopic techniques, i.e., UV-visible, FT-IR, and NMR spectroscopy. The DFT-based analysis of entitled compounds was performed via density functional theory utilizing the M06-2X functional in conjugation with the 6-311G(d,p) basis set to acquire geometrical parameters, natural bonding orbital (NBO), the density of states (DOS), non-linear optical (NLO), molecular electrostatic potential (MESP), and natural population analyses. The smallest band gap of (5.446 eV) was noted for DMAvia frontier molecular orbital (FMO) analysis. GRPs were obtained with the aid of E(gap) values as DMA with the lowest band gap displayed a small magnitude of hardness (2.723 eV) and a large magnitude of softness (0.183 eV). The β(tot) values of DMA, DMM, DMB-D, DAM, and DMD were 56.95, 0.43, 2.53, 8.98, and 68.47 times larger than urea (β(tot) = 3.71 × 10(−31) e.s.u.), respectively. The observed fascinating NLO properties of these novel compounds might be helpful for further advancement in non-linear optics.