Excited singlet state properties of anthracenedione photosensitizers

The absorption, fluorescence and S1 state kinetics of anthracycline antitumour drugs (e.g. daunomycin, adriamycin) and several imino- and/or amino-substituted derivatives are investigated. The study, which includes all anthracyclines which possess photocytocidal activity, is extended to the disubstituted aminoanthracenedione, mitoxantrone, a red-light-absorbing antitumour drug whose activity, both in vitro and in vivo, is enhanced by photoactivation. The S1 state of the anthracycline imino and amino derivatives, in aqueous buffer at pH 7.4, is characterized by bi-exponential decay kinetics which indicates the presence of two ground state populations differing in the extent of hydrogen bonding. The ammonium group of the sugar moiety of anthracyclines contributes to the quenching of the S1 state population through a prototropic mechanism.