Multiple emitting species and competing intramolecular fluorescence quenching in 9,9′-dianthrylmethanol and model compounds

In addition to the anthracene-type emission, 9,9′-dianthrylmethanol (A1OHA) shows a structureless long-wavelength fluorescence band, which undergoes a red-shift as well as an increase of its relative intensity with increasing solvent polarity. A parallel intramolecular fluorescence quenching process is investigated by the study of two reference compounds, 9-hydroxymethylanthracene and 9-ethoxymethylanthracene. In spite of the lack of the additional fluorescence band in this case, the quenching still persists. It might be caused by the formation of an intramolecular nonemissive exciplex but it cannot be the source for the observed additional red-shifted structureless emission band of the bichromophoric compound. The latter has been accounted for by a polar excited state product resulting from a charge separation process.