Vibrational and electronic spectra of 2-nitrobenzanthrone: An experimental and computational study

• Vibrational (FT-Raman, FT-IR) and electronic UV–Vis spectra of benzanthrone and 2-nitrobenzanthrone were accurately simulated.
• Calculated vibrational frequencies show good agreement to experiment to within ~ 5 cm− 1 and < 20 cm− 1 for frequencies < 1800 cm− 1 and 2700–3200 cm− 1, respectively
• Potential Energy Distributions (% PEDs) was calculated for each normal mode was used to determine the νsNO2/νasNO2.
• Fluorescence quantum yields for 2-nitrobenzanthrone is ~ 3 times lower than that of benzanthrone in polar solvents.
• Nitro group substitution of H (on C-2) in benzanthrone shifts νs(CH) vibrations vis-à-vis benzanthrone by ~+ 30 cm− 1, and electronic spectra is noted.

The environmental pollutant 2-nitrobenzanthrone (2-NBA) poses human health hazards, and is formed by atmospheric reactions of NOX gases with atmospheric particulates. Though its mutagenic effects have been studied in biological systems, its comprehensive spectroscopic experimental data are scarce. Thus, vibrational and optical spectroscopic analysis (UV–Vis, and fluorescence) of 2-NBA was studied using both experimental and density functional theory employing B3LYP method with 6-311 + G(d,p) basis set. The scaled theoretical vibrational frequencies show good agreement to experiment to within ~ 5 cm− 1 and < 20 cm− 1 for frequencies < 1800 cm− 1 and 2700–3200 cm− 1, respectively. In addition, predictions of the DFT frequencies below 1800 cm− 1 yield an overall root mean square (RMS) of ± 20.1 and ± 20.6 cm− 1 for benzanthrone and 2-NBA, respectively. On the basis of normal coordinate analysis complete assignments of harmonic experimental infrared and Raman bands are made. The influence of the nitro group substitution upon the benzanthrone structure and symmetric CH vibrations, and electronic spectra is noted. This study is useful for the development of spectroscopy–mutagenicity relationships in nitrated polycyclic aromatic hydrocarbons.

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