Photophysical Properties of (Dimethylamino)anthraquinones: Radiationless Transitions in Solvent and Polyelectrolyte Media

Substitution of 9,10-anthraquinone with dialkylamino groups in the 2(6) positions results in either highly solvent-sensitive fluorescence emission from an intramolecular charge transfer state or, for a symmetrical substitution pattern, an intensely absorbing triplet transient. For the 2-dimethylamino derivative 1, the fluorescence quantum yield is strongly dependent on solvent polarity, consistent with the imposition of a nonradiative decay channel involving motion of the amine moiety that is favored in more polar media. The emission yield is uniformly low for the symmetrical bis-substituted derivative 2 due to a competitive intersystem crossing which yields strongly absorbing triplet transients that decay in the microsecond regime