Spectroscopic (FT-IR, FT-Raman, UV and NMR) investigation, conformational stability, NLO properties, HOMO–LUMO and NBO analysis of hydroxyquinoline derivatives by density functional theory calculations

• Normal coordinate analysis was carried out to confirm the precision of assignments.
• Structural properties were determined by DFT using B3LYP method with 6-311++G(d,p).
• IR, Raman, NMR and UV–vis techniques were used to understand the dynamical aspects.
• The influences of different halogen atoms and hydroxyl group have been investigated.

The FTIR and FT-Raman spectra of 2-hydroxyquinoline and its derivatives have been recorded in the region 4000–400 cm−1 and 3500–100 cm−1, respectively. The optimized geometry, frequency and intensity of the vibrational bands of these compounds were obtained by the density functional theory using 6-311++G(d,p) basis sets. The harmonic vibrational frequencies were calculated and the scaled values have been compared with experimental FTIR and FT-Raman spectra. A detailed interpretation of the infrared and Raman spectra were also reported based on total energy distribution (TED). The observed and the calculated frequencies are found to be in good agreement. The experimental spectra also coincide satisfactorily with those of theoretically simulated spectra. 1H and 13C NMR spectra were recorded and its corresponding nuclear magnetic resonance chemical shifts of the molecule were also calculated using the gauge independent atomic orbital (GIAO) method. UV–visible spectrum of the compound was recorded and the electronic properties HOMO and LUMO energies were measured by time-dependent (TD-DFT) approach. Molecular stability and bond strength were investigated by applying the natural bond orbital analysis (NBO). The calculated HOMO and LUMO energies show that charge transfer occurs in the molecules. In addition, the non-linear optical properties were discussed from the dipole moment values and excitation wavelength in the UV–visible region.

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