Aqueous photoionizations produce the hydrated electron, which is a super reductant with versatile chemical applications (e.g. reductive decomposition of pollutants). However, all previous procedures had to rely on UV-C radiation, inherently making a solar application impossible. In this thesis, some photoionization mechanisms were elucidated that require ionization wavelengths of the terrestrial solar spectrum and consume only the cheap sacrificial donor ascorbate. The most efficient photoionization can even be driven by green light and proceeds via an aryl radical anion as key intermediate. Moreover, investigations of the cyclic electron donor photoionization have shown that this mechanism is capable of generating the phenoxy radical of the famous radical scavenger resveratrol and of repairing it by co-antioxidants. With this approach, detailed findings on the biologically important repair of the resveratrol radical both in homogeneous solution and in supramolecular systems have been obtained.