The photoreactions of the title compound with a variety of electron-transfer quenchers (e.g., methionine, triethylamine) in aqueous solution were investigated by laser flash photolysis with FT-EPR and optical detection. These systems proved to be efficient sources of hydrated electrons e(aq)(.-). The complex kinetics of the secondary reactions were modeled numerically, and the deceptively simple, seemingly first-order decay of e(aq)(.-) was analyzed. On the basis of the results of chemical control experiments and the dependence of the electron yield on the intensity of the exciting light, it was established that the pathway to e(aq)(.-) is a two-photon ionization, in which the first photon effects photoinduced electron transfer and the second photon ionizes the resulting radical anion. The novel feature of this mechanism compared to other two-photon ionizations with intervening chemical step is that it constitutes a catalytic cycle with respect to the substrate. Hence, the electron yield is not limited by substrate depletion and can significantly surpass the concentration of the starting material.