Spectral (FT-IR, FT-Raman, UV, and fluorescence), DFT, and solid state interaction analyses of (E)-4-(3,4-dimethoxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one

Abstract

Here, the authors report a combined experimental and theoretical study on the molecular structure and vibrational spectral analyses of (E)-4-(3,4-dimethoxybenzylideneamino)-1,5-dimethyl-2-phenyl-1H-pyrazol-3(2H)-one (DMBADPP), a pyrazolone-based bioactive molecule. Density functional theory (DFT) calculations were carried out to obtain the ground state optimized geometry of the molecule using the B3LYP method and the 6-311G(d,p) basis set. Calculated results agreed well with X-ray data. The vibrational spectra of DMBADPP were calculated at the same level of theory and theoretical scaled vibrational frequencies and assignments were found to agree well with experimental FT-IR and FT-Raman values. Partial atomic charge and molecular electrostatic potential (MEP) surface map analyses were performed to study reactive sites. Calculated frontier molecular orbitals (FMOs) energies and chemical reactivity parameters indicated that the DMBADPP exhibits high polarizability and low kinetic susceptibility. Excitation energy, wavelength, and oscillator strength were calculated using the Time Dependant-DFT/B3LYP/6-311G(d,p) method and compared with experimental UV–Vis spectra obtained in ethanol. However, UV–Vis and fluorescence spectroscopic experiments showed that DMBADPP has good absorption and fluorescent properties and a large Stokes shift. In addition, the solid state behaviors of molecules in crystals were analyzed quantitatively and qualitatively using 3D Hirshfeld surface analysis and associated 2D fingerprint plots.