Substituent effects on triplet yields in aminoanthraquinones : radiationless deactivation via intermolecular and intramolecular hydrogen bonding

Abstract

The dependence of the triplet quantum yields of monosubstituted and disubstituted aminoanthraquinones on the number of substituents and on their position was studied. Using fluorescence lifetimes, fluorescence quantum yields and triplet quantum yields, the rate constants of the intersystem crossing into the triplet state and of the internal conversion into the ground state were evaluated. For monosubstituted aminoanthraquinones the individual contributions of various mechanisms to the internal conversion have been estimated. In quenching the excited singlet state, intermolecular hydrogen bonding to the solvent is more efficient by an order of magnitude than intramolecular hydrogen bonding.