Near-Infrared Light-Driven Hydrogen Evolution from Water Using a Polypyridyl Triruthenium Photosensitizer.

In order to realize artificial photosynthetic devices for splitting water to H2 and O2 (2 H2 O+hν→2 H2 +O2 ), it is desirable to use a wider wavelength range of light that extends to a lower energy region of the solar spectrum. Here we report a triruthenium photosensitizer [Ru3 (dmbpy)6 (μ-HAT)]6+ (dmbpy=4,4'-dimethyl-2,2'-bipyridine, HAT=1,4,5,8,9,12-hexaazatriphenylene), which absorbs near-infrared light up to 800 nm based on its metal-to-ligand charge transfer (1 MLCT) transition. Importantly, [Ru3 (dmbpy)6 (μ-HAT)]6+ is found to be the first example of a photosensitizer which can drive H2 evolution under the illumination of near-infrared light above 700 nm. The electrochemical and photochemical studies reveal that the reductive quenching within the ion-pair adducts of [Ru3 (dmbpy)6 (μ-HAT)]6+ and ascorbate anions affords a singly reduced form of [Ru3 (dmbpy)6 (μ-HAT)]6+ , which is used as a reducing equivalent in the subsequent water reduction process.