Watching Intermolecular Light-Induced Charge Accumulation on Naphthalene Diimide by Tris(bipyridyl)ruthenium(II) Photosensitizer

Performing photocatalytic reactions to produce solar fuels requires the coupling of multiple photoinduced one-electron transfer steps on multielectronic catalysis. Understanding the light-driven charge accumulation in photocatalytic systems is of pivotal importance in the optimization process. Herein, we investigated the elementary steps of light-induced two-electron accumulation on a multicomponent system consisted of three archetypal molecules commonly used in photophysical studies, [Ru(bpy)(3)](2+), ascorbate as a reversible electron donor, and naphthalene diimide as a two-electron acceptor. Remarkably, accumulative charge separation was observed in both single-pulse and double-pulse experiments in a reversible manner, indicating a very high efficiency of charge transfer reactions. The doubly reduced state of similar to 100 mu s lifetime was obtained with a formation yield of 4.2%. Rate constants of all elementary steps in the formation and the relaxation of the doubly reduced state were determined with the aid of a newly developed numerical simulation method for this photosystem. To the best of our knowledge, this is the first investigation of charge accumulation with only a single-pulse excitation in a multicomponent system.