Combined spectroscopic and DFT studies on 6-bromo-4-chloro-3-formyl coumarin

• The FT-IR, FT-Raman and UV–Visible spectra of 6B4C3FC.
• The temperature dependence of the thermodynamic properties were investigated.
• The atomic charge and charge delocalization of the molecule have been analyzed.
• The reactivity sites have been identified using MEP analysis.

The FTIR and FT-Raman spectra of 6-bromo-4-chloro-3-formyl coumarin (6B4C3FC) have been recorded in the region 4000–400 and 4000–100 cm−1, respectively. The optimized geometry, frequency and intensity of the vibrational bands were obtained by the density functional theory (DFT) using 6-31G(d,p) basis set. The harmonic vibrational frequencies were scaled and compared with experimental values. The observed and the calculated frequencies were found to be in good agreement. The UV–Visible spectrum was also recorded and compared with the theoretical values. The calculated HOMO and LUMO energies show that charge transfer occurs within molecule. The first order hyperpolarizability (β0) of 6B4C3FC is 21 times greater than that of urea. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. Information about the charge density distribution of the molecule and its chemical reactivity has been obtained by mapping molecular electrostatic potential surface. In addition, the non-linear optical properties were discussed from the dipole moment values and the excitation wavelength in the UV–Visible region.

A complete vibrational analysis is performed by combining the experimental and theoretical information using Pulay’s density functional theory (DFT) based on scaled quantum mechanical approach. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes.Figure optionsDownload as PowerPoint slide