Vibrational and Electronic Absorption Spectroscopy of 2,3-Benzofluorene and Its Cation

Benzofluorene (C17H12) has been studied in argon matrices via Fourier transform infrared and UV?visible absorption spectroscopy. The analysis of the infrared absorption spectra of neutral and cationic 2,3-benzofluorene was supported by density functional theory (DFT) B3LYP/6-311+G** calculations of the harmonic-mode frequencies. Extensive time-dependent DFT calculations of the electronic vertical excitation energies with BLYP/6-31++G** and B3LYP/6-31++G** functionals/basis sets and the Casida?Salahub asymptotic correction were performed to assign the observed electronic absorption bands of the neutral species. Although the observed low-energy absorption bands are predicted well by theory, the higher-energy bands (Sn ? S0 transitions, n ≥ 4) have been assigned only tentatively. However, the observed electronic absorption bands for the parent, singly dehydrogenated cationic and neutral species are in accord with TDDFT (BLYP/6-31G**) results. The possibility that the 2,3-benzofluorene cation contributes to the unidentified infrared (UIR) bands observed from interstellar space is discussed briefly. Benzofluorene (C17H12) has been studied in argon matrices via Fourier transform infrared and UV?visible absorption spectroscopy. The analysis of the infrared absorption spectra of neutral and cationic 2,3-benzofluorene was supported by density functional theory (DFT) B3LYP/6-311+G** calculations of the harmonic-mode frequencies. Extensive time-dependent DFT calculations of the electronic vertical excitation energies with BLYP/6-31++G** and B3LYP/6-31++G** functionals/basis sets and the Casida?Salahub asymptotic correction were performed to assign the observed electronic absorption bands of the neutral species. Although the observed low-energy absorption bands are predicted well by theory, the higher-energy bands (Sn ? S0 transitions, n ≥ 4) have been assigned only tentatively. However, the observed electronic absorption bands for the parent, singly dehydrogenated cationic and neutral species are in accord with TDDFT (BLYP/6-31G**) results. The possibility that the 2,3-benzofluorene cation contributes to the unidentified infrared (UIR) bands observed from interstellar space is discussed briefly.