The deexcitation of the S<SUB>1</SUB> state of aminoanthraquinones: a steadystate and timeresolved study

The non-radiative processes of deactivation from the lowest singlet excited state of aminoanthraquinones have been studied using steady-state and time-resolved methods. The fluorescence decay rate constant, kf correlates well with the solvent polarity parameter, ET(30), in nonhydrogen bonding solvents. Large deuterium isotope effects in fluorescence lifetimes (&#964;f) and quantum yields (&#934;f) are observed in the case of 1-amino (AAQ) and 1-methylaminoanthraquinones (MAQ), where the S1 state is mainly deactivated through internal conversion to the ground state. The temperature-dependence of the fluorescence quantum yields of various aminoanthraquinones was also investigated. The &#934;f and &#964;f exhibited strong temperature-dependence in the case of 1-acetylaminoanthraquinone (ACAQ). In the case of ACAQ, the intersystem crossing to the triplet state is a major deactivation channel from the S1 and in this derivative a close-lying T2 state seems to be responsible for the high kisc rate. The fluorescence properties of 1,5-diaminoanthraquinone (DAQ) are affected by intermolecular hydrogen bonding with alcohols. Increasingn-alkyl chain length in the case of l-(n-alkyl)aminoanthraquinones from methyl to butyl does not produce any change in the fluorescence properties, whereas a hydroxypropyl substitution results in a small decrease of &#934;f and &#964;f in these compounds, indicating an interaction of the hydroxyl group with the carbonyl group of the aminoanthraquinones