Vibrational spectroscopic (FT-IR and FT-Raman) studies, natural bond orbital analysis and molecular electrostatic potential surface of Isoxanthopterin

•Structural parameters were determined by DFT calculations.•Vibrational assignments were performed using FTIR and FT-Raman spectra.•The electronic properties and NBO analysis were carried out.•1H and 13C NMR chemical shifts were calculated using GIAO method.

The FTIR and FT-Raman spectra of Isoxanthopterin have been recorded in the region 4000–450 and 4000–100 cm−1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of Isoxanthopterin were obtained by the density functional theory (DFT) using 6-311++G(d,p) basis set. The harmonic vibrational frequencies were scaled and compared with experimental values. The observed and the calculated frequencies are found to be in good agreement. The 1H and 13C nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. 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), related properties (β, α0 and Δα) and the Mulliken charges of the molecule were also computed using DFT calculations. 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 the σ* and π* antibonding orbitals and second order delocalization energies (E2) confirms the occurrence of intramolecular charge transfer (ICT) within the molecule. 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 excitation wavelength in the UV–visible region.

Graphical abstractThe optimized geometry, frequency and intensity of the vibrational bands. 1H and 13C chemical shifts of Isoxanthopterin were obtained by the density functional theory using 6-311++G** basis set. The electronic properties and NBO analysis are carried out to examine the stability and charge delocalization within the molecule. The non-linear optical properties were also discussed.Figure optionsDownload full-size imageDownload as PowerPoint slide