A Molecular Tetrad That Generates a High-Energy Charge-Separated State by Mimicking the Photosynthetic Z-Scheme

The oxygenic photosynthesis of green plants, green algae, and cyanobacteria is the major provider of energy-rich compounds in the biosphere. The so-called “Z-scheme” is at the heart of this “engine of life”. Two photosystems (photosystem I and II) work in series to build up a higher redox ability than each photosystem alone can provide, which is necessary to drive water oxidation into oxygen and NADP+ reduction into NADPH with visible light. Here we show a mimic of the Z-scheme with a molecular tetrad. The tetrad Bodipy–NDI–TAPD–Ru is composed of two different dyes—4,4-difluoro-1,3,5,7-tetramethyl-2,6-diethyl-4-bora-3a,4a-diaza-s-indacene (Bodipy) and a RuII(bipyridine)3 (Ru) derivative—which are connected to a naphthalene diimide (NDI) electron acceptor and tetraalkylphenyldiamine (TAPD) playing the role of electron donor. A strong laser pulse excitation of visible light where the two dye molecules (Ru and Bodipy) absorb with equal probability leads to the cooperative formation of a highly energetic char...