The non-radiative processes from the S₁ state of aminoanthraquinones: a steady state and time-resolved study

Abstract

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 k_f correlates well with the solvent polarity parameter E_T(30) in non-hydrogen-bonding solvents. Large deuterium isotope effects in fluorescence lifetimes τ_f and quantum yields φ_f are observed in the case of 1-amino and 1-methylamino anthraquinones, 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. φ_f and τ_f exhibited strong temperature dependences in the case of 1-acetylaminoanthraquinone. In the case of 1-acetylaminoan-thraquinone, 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 k_isc rate.