Quantum chemical calculations on NBO, NLO, Spectroscopic (UV-Visible, IR, Raman, 1H and 13C NMR) analysis, HOMO-LUMO and ESP map of fluorescent molecule by Semi-empirical and Hartree-Fock optimization methods

Abstract

Quantum chemical calculations of 4-(5-methyl-3-phenyl-benzofuran-2-yl)-6-chloro-chromen-2-one (MPBClC) fluorescent molecules has been carried out using Gaussian 16 software. They exhibit antimicrobial properties and have shown promising anti-fungal activity. Semi-empirical and Hartree-fock method are the convenient tools to study optimized geometry and ground state dipole moment. The proton transfer within the selected donor-acceptor depicting large energy of stabilization for the molecules are given by NBO analysis. NLO properties are used to determine the polarizability and hyper polarizability of the molecules. Various photophysical properties were studied from spectroscopic analysis of UV-Visible, NMR, IR and Raman spectra using DFT method at 6-31G/B3LYP basis set. UV-Visible spectra obtained from TD-DFT method are parameters like absorption maxima, oscillator strength and excited state energies. The excited state dipole moment obtained from TD-DFT method is higher than the ground state dipole moment. Absorption maxima of molecules observed is around 330 nm-370 nm. IR and Raman vibrational spectroscopy have been studied in the regions 3500-50 cm^-1. The ¹H and ¹³C NMR shielding values were evaluated from NMR spectra using GIAO method. ¹H NMR shielding values were higher than ¹³C NMR. Molecular orbital viz., HOMO-LUMO and ESP maps are useful for the study of charge transfer and charge distribution within the molecule.