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

In order to realize artificial photosynthetic devices for splitting water to H 2 and O 2 (2 H 2 O+ hν →2 H 2 +O 2 ), 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 [Ru 3 (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, [Ru 3 (dmbpy) 6 (μ‐HAT)] 6+ is found to be the first example of a photosensitizer which can drive H 2 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 [Ru 3 (dmbpy) 6 (μ‐HAT)] 6+ and ascorbate anions affords a singly reduced form of [Ru 3 (dmbpy) 6 (μ‐HAT)] 6+ , which is used as a reducing equivalent in the subsequent water reduction process.