Experimental (FT‒IR, FT‒Raman, and UV‒Vis) and quantum chemical calculations on monomer and dimer structures of l-hydroxy-2-naphthoic acid using the DFT and TD‒DFT methods

Abstract

The fourier transform infrared (FT‒IR) and fourier transform Raman (FT‒Raman) spectra of l-hydroxy-2-naphthoic acid (1H2NA) in solid phase have been experimentally recorded and analyzed in the region 4000‒400 cm⁻¹. DFT/B3LYP/6‒31G (d,p) calculations were used to determine the optimized molecular structure, conformational, non-linear optical (NLO), natural bond orbital (NBO) analysis, molecular surfaces, Mulliken, NBO charges and vibrational studies of 1H2NA. Obtained results on the geometric structure, vibrational frequencies and UV‒Vis spectral analysis are compared with the observed data. The dimeric structure of 1H2NA with the DFT/B3LYP/6‒31G (d,p) level caused by the shifts of O–H and C=O bands in the vibrational spectra were also studied. Moreover, the spectroscopic and theoretical results were compared with the corresponding properties for monomeric and dimeric structures of 1H2NA. The detailed vibrational assignments were performed with the DFT calculation, and the potential energy distribution (PED) was obtained by the vibrational energy distribution analysis (VEDA4) program. TD‒DFT/B3LYP/6‒31G (d,p) calculations with the SCF (self‒consistent field) in gas phase and ethanol solvent in the excited state were employed to investigated UV‒Vis absorption spectra and the major contributions to the electronic transitions were obtained. The NLO properties such as mean polarizability (<α>), the anisotropy of the polarizability (<Δα>) and the mean first‒order hyperpolarizability (<β>) were computed by using finite field method. The computed values of μ, α and β of the title molecule are 2.2744 D, 17.3225 × 10⁻²⁴ esu and 4.222 × 10 ⁻³⁰ esu, respectively. The high β values and non-zero values of μ indicate that the title compound might be a good candidate for NLO material.