The molecular mechanism of radiationless deactivation from the excited singlet state of aminoanthraquinones (AAQ) induced by alcohols and hydroperoxides was investigated by time-resolved picosecond fluorescence measurements. AAQ suffered substantial fluorescence quenching with red shifts of their lambda(max) in benzene solution upon addition of alcohol and hydroperoxide. Primary alcohols exhibited the largest quenching effects among 26 alcohols examined, while tertiary alcohols were least effective. The Stern-Volmer constants were well correlated with the C-13 NMR chemical shift of the carbinol carbon atom and the contact molecular surface area of the hydroxyl hydrogen of the quenchers, while it apparently did not depend upon pK(a) values. Contact molecular surface area was revealed to be a good quantitative parameter for the steric effect in the intermolecular hydrogen-bonding interaction. The steric factor was dominant in the fluorescence-quenching process, but the electronic factor becomes evident among the molecules having the same steric factor such as benzyl alcohol derivatives, where the Hammet plot showed a good linearity. Fluorescence decay kinetics clearly showed that two emitting levels were involved such as the fluorescent state in benzene and a fully relaxed state in which reorganization of the surrounding alcohol was established. Estimated lifetimes of the fully relaxed states were longer than those in neat alcohol by a factor of 30. The results were interpreted that there were at least two relaxation pathways by alcohol reorganization through the intermolecular hydrogen bond. A specific reorganization of alcohol to AAQ induced relaxation from the fluorescent state in benzene to a relaxed, emissive state and to another relaxed, nonfluorescent state, The latter leads to an efficient radiationless deactivation. The relaxed emissive state corresponds to the excited state of intermolecular hydrogen-bonded species of AAQ with the alcohol in the ground state in which the hydroxyl group of alcohol interacts through an in-plane mode against the carbonyl oxygen of AAQ. Another relaxed nonfluorescent state is formed through an out-of-plane mode interaction between AAQ and the hydroxyl group of alcohol.