Molecular structure, spectroscopic characterization, HOMO and LUMO analysis of 3,3′-diaminobenzidine with DFT quantum chemical calculations

• Monomeric conformations of 3,3-diaminobenzidine were investigated.
• The compound was characterized by FT-IR, FT-Raman, and UV spectroscopies.
• The vibrational frequencies, electronic absorption wavelengths were calculated by DFT method and discussed.

In this work, infrared, Raman and UV spectra of 3,3′-diaminobenzidine (3,3-DAB) were carried out by using density functional theory (DFT)/B3LYP method with 6-311G(d,p) basis set. FT-IR and FT-Raman spectra were recorded in the region 4000–400 and 4000–50 cm−1, respectively. The geometrical parameters, energies and wavenumbers were obtained and fundamental vibrations were assigned on the basis of the potential energy distribution (PED) of the vibrational modes. The UV spectrum of the investigated compound was recorded in the range of 200–400 nm in ethanol and water solutions. The electronic properties, such as excitation energies, absorption wavelengths, HOMO and LUMO energies were performed by DFT/B3LYP approach and the results were compared with experimental observations. Thermodynamic properties, Mulliken atomic charges and molecular electrostatic potential (MEP) were calculated for the title molecule. Also the nonlinear optical properties of 3,3-DAB molecule were explored theoretically. As a result, the calculated results were compared with the observed values and generally found to be in good agreement.

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