Spectroscopic characterization and quantum chemical investigation of molecular structure and vibrational spectra of phthalazine-1(2H)-one

Abstract

In this study, vibrational and electronic transition analysis of phthalazine-1(2H)-one have been presented using experimental techniques FT-IR, FT-Raman and density functional theory (DFT) calculation. The structural properties of the molecule in the ground state have been calculated using DFT employing B3LYP/6-311++G(d,p) basis set. Optimized geometrical parameters have been interpreted and compared with the experimental values. The complete assignments have been performed on the basis of the experimental data and potential energy distribution (PED) of the vibrational modes. The calculated HOMO and LUMO energies and energy difference (ΔE_HOMO‒LUMO = − 4.876 eV), confirm that charge transfers occur within the molecule. The stability of the molecule arising from hyperconjugative interactions and the charge delocalization has been analyzed using natural bond orbital’s analysis (NBO). The specific heat, Gibb’s free energy, and entropy of molecule have been calculated as a function of temperature by using statistical mechanics coupled with quantum chemical calculation. Observed vibrational wave numbers have been compared with calculated values, and found to be in agreement with experimental results. The study of dielectric properties like dielectric constant at microwave frequency, static dielectric constant and dielectric constant at optical frequency of Phthalazine-1(2H)-one have been determined. The dielectric relaxation studies provide information about the molecular structure and intermolecular interaction between phthalazine-1(2H)-one and alcohol mixture.