A comparative study of the electronic transitions of fluorene and its hetero-analogues dibenzofuran, carbazole, and dibenzothiophene was performed in a wide energy range. Gas phase, crystal phase, and linear dichroism electronic transmittance spectra were measured with synchrotron radiation. Electronic transitions to excited singlet states were predicted with time-dependent density functional theory, TD-B3LYP/6-31+G(d,p). Based on the experimental and theoretical results, symmetry assignments of electronic transitions in the vacuum and near-UV region are suggested. The correspondence between excited states in these molecules, similarities, and differences between their electronic spectra are discussed.
Nguyen, D. D., Trunk, J., Nakhimovsky, L., & Spanget-Larsen, J. (2010). Electronic transitions of fluorene, dibenzofuran, carbazole, and dibenzothiophene: From the onset of absorption to the ionization treshold. Journal of Molecular Spectroscopy, 264(1), 19-25. https://doi.org/10.1016/j.jms.2010.08.009