Generating hydrated electrons through photoredox catalysis with 9-anthrolate†
Hydrated electrons are among the strongest reductants known. Adding the ascorbate dianion as a sacrificial donor turns the photoionization of 9-anthrolate in water into a catalytic cycle for their in situ production with near-UV light (355 nm). The photoionization step is exclusively biphotonic and occurs via the first excited singlet state of the catalyst. Neither triplet formation nor any photochemical side reactions interfere. The ionization by-product, the anthroxy radical, is inert towards the ascorbate monoanion but is rapidly reduced by the dianion, thereby recovering the starting catalyst. A sufficient amount of the sacrificial donor makes that reduction quantitative and leads to a sustainable generation of hydrated electrons, as is evidenced by electron yields greatly surpassing the catalyst concentration. Control experiments established that the superincrease is indeed due to the catalyst regeneration and not to an ionization of other species involved in the reaction.