TRIPLET FORMATION IN AMINOANTHRAQUINONES AND ITS IMPORTANCE FOR THE CATALYTIC FADING OF DYE MIXTURES

The catalytic fading of yellow azo dyes in an admixture with blue, red or violet anthraquinone dyes is due to a type II photo-oxygenation during which singlet oxygen is produced by the anthraquinone dye in its triplet state. The triplet quantum yields (which are of decisive importance in the extent of catalytic fading) of all monoaminoanthraquinone and diaminoanthraquinone isomers (model compounds for technical dyestuffs) were measured in toluene. The rate constants of the radiationless deactivation (k(IC)) and of the triplet formation (k(ISC)) were determined from the fluorescence quantum yield, the fluorescence lifetime and the triplet quantum yield. The rate constants of triplet formation (k(ISC)) depend strongly on the position of the substituents and are related to the singlet-triplet separation energies of the excited singlet and triplet states (E(S1) - E(T1)).