A combined experimental and theoretical studies on FT-IR, FT-Raman and UV–vis spectra of 2-chloro-3-quinolinecarboxaldehyde

• Vibrational spectra of 2-chloro-3-quinolinecarboxaldehyde recorded and analyzed.
• The vibrational assignments with PED were computed using DFT method.
• The MEP, NLO and HOMO, LUMO energy gap were theoretically predicted.
• The redistribution of electron density (ED) and E(2) energies had been calculated by NBO.

In the present study, the FT-IR and FT-Raman spectra of 2-chloro-3-quinolinecarboxaldehyde (2Cl3QC) have been recorded in the region 4000–400 and 3500–50 cm−1, respectively. The fundamental modes of vibrational frequencies of 2Cl3QC are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-31G(d,p) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The predicted first hyperpolarizability also shows that the molecule might have a reasonably good non-linear optical (NLO) behavior. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the molecule. Stability of the molecule arising from hyper conjugative interactions, charge delocalization have been analyzed using natural bond orbitals (NBO) analysis. The results show that charge in electron density (ED) in the π∗ antibonding orbitals and E(2) energies confirms the occurrence of ICT (intra-molecular charge transfer) within the molecule. UV–visible spectrum of the title molecule has also been calculated using TD-DFT/CAM-B3LYP/6-31G(d,p) method. The calculated energy and oscillator strength almost exactly reproduces reported experimental data.

The vibrational and electronic spectra of 2-chloro-3-quinolinecarbaxaldehyde (2Cl3QC) are reported and discussed. Using DFT employing B3LYP exchange correlation with the normal basis level 6-31G(d,p) the structural properties and vibrational frequencies of 2Cl3QC have been investigated. NLO, NBO and HOMO–LUMO analysis have been carried out. There is good agreement between experimental and theoretical results.Figure optionsDownload as PowerPoint slide