Experimental and theoretical (HOMO, LUMO, NBO analysis and NLO properties) study of 7-hydroxy-4-phenylcoumarin and 5,7-dihydroxy-4-phenylcoumarin

The FT-IR and FT-Raman spectra of 7-hydroxy-4-phenylcoumarin (7-H4PC) and 5,7-dihydroxy-4-phenylcoumarin (5,7-DH4PC) have been measured in the regions 4000–400 cm−1 and 3500–100 cm−1, respectively. The equilibrium geometry, bonding features and harmonic vibrational frequencies have been carried out with the help of density functional theory (DFT) method. The assignments of the vibrational spectra of title compounds have been carried out with the normal coordinate analysis (NCA) following the scaled quantum mechanical force field methodology (SQMFF). UV–Vis spectra of the title compounds were recorded and the electronic properties, such as HOMO and LUMO energies, were performed by Time dependant density functional theory (TD-DFT) using 6-31G(d,p) basis set. The HOMO–LUMO calculations indicating the charge transfer takes place within the molecules. Stability of the molecules arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bonding orbital (NBO) analysis. The theoretical predictions of non-linear optical (NLO) properties have been carried out.