Vibrational spectra, molecular structure, natural bond orbital, first order hyperpolarizability, TD-DFT and thermodynamic analysis of 4-amino-3-hydroxy-1-naphthalenesulfonic acid by DFT approach

Vibrational spectral analysis of 4-amino-3-hydroxy-1-naphthalenesulfonicacid (4A3HNSA) molecule were carried out using FT-IR and FT-Raman spectroscopic techniques. The equilibrium geometry, harmonic vibrational wavenumbers, various bonding features have been computed using density functional B3LYP method with 6-31G(d,p) as basis set. The Non-Linear Optical (NLO) behavior of 4A3HNSA has been studied by determination of the electric dipole moment (μ) and hyperpolarizability β using HF/6-31G(d,p) method. Stability of the molecule arising from hyperconjugative interactions, charge delocalization have been analyzed using natural bond orbital (NBO) analysis. The results show that charge in electron density (ED) in σ(*) and π(*) antibonding orbitals and second order delocalization energies (E2) confirms the occurrence of Intramolecular Charge Transfer (ICT) within the molecule. The energy and oscillator strength calculated by Time-Dependent Density Functional Theory (TD-DFT) complements with the experimental findings. The simulated spectra satisfactorily coincide with the experimental spectra.