Spectroscopic and DFT/TDDFT insights of the novel phosphonate imine compounds

Recently, phosphonate compounds have got immense attention of the scientific community due to their structural properties. These are inserted in a number of chemical moieties and are associated with important pharmacological activities. Herein, we reported synthesis of the imino phosphonate compounds: (E)-diethyl (3-nitrobenzylideneamino)(phenyl)methylphosphonate (DNBMP), (E)-diethyl (4-hydroxybenzylideneamino) (phenyl) methyl phosphonate) (DHBMP), and (E)-diethyl (4-nitrobenzylideneamino)(phenyl)methylphosphonate (DNPMP) with high yields form the condensation reaction of diethyl (alpha-aminobenzyl)phosphonate hydrochloride and the corresponding substituted benzaldehyde. The synthesized compounds were analyzed by various spectroscopic techniques such as NMR, MS, UV-Vis, and IR spectroscopy. Moreover, the computational studies were also performed and the experimental and theoretical investigation results were compared. The geometries of the compounds were optimized with B3LYP/6-311+G (d,p) and absence of imaginary frequency confirmed the stability of DNBMP, DHBMP and DNPMP. The FT-IR, natural bond orbital (NBO) analysis, frontier molecular orbitals (FMOs) and nonlinear (NLO) properties of DNBMP, DHBMP, and DNPMP were performed with former level of theory. In addition, UV-Vis spectra were obtained by Time Dependent Density Functional Theory (TD-DFT) approach with former level in Polarizable Continuum Model (PCM) using different solvents. A comparative investigation of FT-IR and UV-Visible spectra of DNBMP, DHBMP and DNPMP revealed that there is a good agreement between DFT and experimental findings. NBO analysis was employed to calculate the atomic charges as well as bonding interactions of the interesting molecules. NBO findings revealed that non-bonding interactions might be one of the most important reasons for stability of DNBMP, DHBMP and DNPMP. Moreover, the energy value of HOMO/LUMO was found to be -6.977/-3.033 eV with Delta E 3.944 eV (DNBMP), -6.300/-1.274 eV with Delta E 5.026 eV (DHBMP) and -6.993/-3.124 eV with a band gap (Delta E) 3.869 eV (DNPMP) and global reactivity parameters (GRP) were also obtained using the HOMO-LUMO energies. It was observed that DNBMP, DHBMP and DNPMP have greater NLO responses than standard molecules. (C) 2020 Elsevier B.V. All rights reserved.