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. The binding of dyes to poly(methacrylic acid) (PMAA) is particularly efficient for the polyelectrolyte in its globular or ''hypercoiled'' conformation in water (acid form, pH 3.0). For bound dye the yield of fluorescence for 1 is increased significantly; the triplet states for 2 are especially long-lived and resist excited-state quenching.