Efficient Light-Driven Multi-Electron Accumulation on Viologens by Molecular Control Over Photochemical Reaction Pathways

Achieving multiple photo-induced charge accumulations on the same acceptor is one option to propel photochemical reactions that demand highly reducing or oxidizing conditions. By switching the initial light-driven process from an oxidative to a reductive quenching pathway via mutual redox potential control over Ru(II) polypyridyl chromophores and sacrificial electron donors (SEDs), acceleration of complete single electron reduction of methyl viologen (MV2+) and polymer-bound viologens by a factor of up to 2,200 as well as a rapid subsequent second reduction of MV∙+ to MV0 was achieved in homogeneous solution. Ab initio molecular dynamics (AIMD) allowed the conformer space to be mapped and to shed light on the thermodynamics of the photochemical intermediates involved in the formation of the two-electron reduced methyl viologen (MV0). These results provide a toolbox of structurally simple compounds for the modular construction of efficient artificial photosynthesis schemes.