Photodynamics of the S1 state of some hydroxy- and amino-substituted naphthoquinones and anthraquinones

Abstract

Photodynamics of the S₁ state of the 1,4- and 1,8-disubstituted hydroxyquinones and aminoquinones have been studied in different organic solvents by absorption and fluorescence spectroscopy. The internal conversion process is the major deactivation path for the S₁ state. The solvent and temperature dependence and deuterium isotope effect on the fluorescence dynamics suggest that hydrogen stretching vibrations in different intra- and inter-molecular hydrogen bonds are responsible for very fast non-radiative decay processes. Among the intra-molecular hydrogen-bonded molecules studied only the S₁ state of 1,8-dihydroxy-9,10-anthraquinone showed the evidence of excited-state intramolecular proton-transfer process. Preliminary observations on the interaction of the S₁ state of these quinones with benzene and other aromatic hydrocarbon solvents via the formation of an exciplex have also been reported.