Vibrational and electronic spectra of 9,10-dihydrobenzo(a)pyren-7(8H)-one and 7,8,9,10-tetrahydrobenzo(a)pyrene: An experimental and computational study

The molecular geometries, vibrational and UV–vis spectra of 9,10-dihydrobenzo(a)pyrene-7(8H)-one (9,10-H2BaP) and 7,8,9,10-tetrahydrobenzo(a)pyrene (7,8,9,10-H4BaP) were investigated using density functional theory (DFT-B3LYP), with the triple-ζ 6–311 + G(d,p) and Dunning's cc-pVTZ basis sets. From the comparison of infrared experimental and calculated infrared, and Raman data comprehensive assignments are made. The calculated infrared frequencies below 1800 cm−1 are in good agreement with experimental data, with an average deviation of <4 cm−1. Using the B3LYP/6–311 + G(d,p)//TD-B3LYP/6–311G(d,p) level of theory, transition energies, and oscillator strengths of the 30 lowest electronic absorption bands are assigned to π–π* transitions, with good qualitative agreement between experimental and simulated absorption data. In addition, the HOMO–LUMO gaps and their chemical hardness were analyzed.

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► 9,10-Dihydrobenzo(a)pyren-7(8H)-one and 7,8,9,10-tetrahydrobenzo(a)pyrene are mutagenic and carcinogenic derivatives of benzo(a)pyrene; a model PAH.
► Comprehensive experimental infrared (IR) and Raman assignments of these molecules are interpreted through theoretical DFT calculations (B3LYP/6–311 + G(d,p) and cc-pVTZ).
► Electronic spectra, transition energies, oscillator strengths and the respective HOMO–LUMO energies and hardness are provided.
► Relative stabilities, HOMO–LUMO gaps and implications of the electronic properties are examined and discussed.