Highly efficient green-light ionization of an aryl radical anion: key step in a catalytic cycle of electron formation

A sustainable generation of hydrated electrons with green light would allow solar-driven applications of this potent reductant, such as the detoxification of halogenated organic waste. Using two-color laser flash photolysis, we have studied the photoionizations of the 1,5-naphthalene disulfonate radical anion and triplet with 532 nm as well as 355 nm. The radical anion is prepared by reducing the triplet with the bioavailable ascorbate monoanion under physiological conditions; its photoionization recovers the starting substrate, so turns the reaction sequence into a catalytic cycle. A comparison of the four ionizations suggests that their efficiency is strongly influenced by the electronic configuration of the state ejecting the electron. The quantum yield for ionizing the radical anion with 532 nm (0.27) is at least four times higher than for the very few known examples of such green-light ionizations and comparable to the most efficient UV ionizations known to date, so this system might represent a breakthrough towards the "green" production of hydrated electrons.