Vibrational spectroscopic, first-order hyperpolarizability and HOMO, LUMO studies of 1,2-dichloro-4-nitrobenzene based on Hartree–Fock and DFT calculations

The Fourier-transform infrared spectrum of 1,2-dichloro-4-nitrobenzene (DCNB) was recorded in the region 4000–400 cm−1. The Fourier-transform Raman spectrum of DCNB was also recorded in the region 3500–50 cm−1. Quantum chemical calculations of energies, geometrical structure and vibrational wavenumbers of DCNB were carried out by ab initio HF and density functional theory (DFT/B3LYP) method with 6-31+G(d,p) basis set. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (μ) and the first-order hyperpolarizability (β) of the investigated compound were computed using ab initio quantum mechanical calculations. The calculated results also show that the DCNB might have microscopic nonlinear optical (NLO) behavior with non-zero values. A detailed interpretation of the infrared and Raman spectra of DCNB is also reported based on total energy distribution (TED). The calculated HOMO and LUMO energies shows that charge transfer occur within the molecule. The theoretical FT-IR and FT-Raman spectra for the title compound have also been constructed.

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► The substituted benzene derivatives with high optical non-linearities are very promising materials for future optoelectronic and non-linear optical applications.
► The optimized geometries, harmonic vibrational wavenumbers and intensities of vibrational bands of 1,2-dichloro-4-nitrobenzene (DCNB) have been determined using HF and DFT–B3LYP with 6-31+G(d,p) level calculations.
► The normal modes of DCNB have been studied by FTIR and FT-Raman spectroscopies on the basis of CS point group symmetry.
► The lowering of HOMO–LUMO energy gap explains the eventual charge transfer interactions taking place within the molecule.
► Most probably this research work may be useful to the scientists who were doing research in non-linear optical studies.