Molecular structure, spectral (FT-IR, FT-Raman, Uv-Vis, and fluorescent) properties and quantum chemical analyses of azomethine derivative of 4-aminoantipyrine

A detail of the theoretical study on the molecular geometry and the infrared vibrational frequency assignments of (E)-4-(2-methoxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (MBA-dMPP), a bioactive azomethine analog of antipyrine, have been reported and compared with the experimental results. The ground state optimized structure, torsional energies, vibrational wavenumbers, atomic charge analysis, molecular electrostatic potential (MEP) distributions, and energies and maps of frontier molecular orbitals (FMOs) of MBA-dMPP was analyzed using Density Functional Theory (DFT)-B3LYP/6-311G method. Potential energy surface (PES) scans showed that the ground state optimized geometry of MBA-dMPP possesses less torsional energy than that of the crystal structure. Mulliken atomic charge and MEP analyses were carried out to locate the donor-acceptor atoms and reactive sites in the molecule. Calculated quantum chemical descriptors and HOMO-LUMO energies described the molecular properties and reactivity of the studied molecule. We have also calculated average local ionization energy (ALIE) surfaces and Fukui functions to obtain the initial information for the nucleophilic and electrophilic reaction sites of the molecule. Time Dependent (TD)-DFT method was used to calculate electronic transition energy, wavelength, and oscillator strength of MBA-dMPP and to be compared with experimental UV-Vis spectra. The charge transfer mechanism within the molecule is also studied using TD-DFT/B3LYP-/6-311G approach. The fluorescence spectra of MBA-dMPP showed good Stokes shift properties.