Photocatalytic H2 Evolution Using a Ru Chromophore Tethered to Six Viologen Acceptors.

A new photo-charge separator (PCS) consisting of a [Ru(bpy)3 ]2+ (bpy=2,2'-bipyridine) chromophore and six viologen (MV2+ ) acceptors, [Ru(bpyMV2)3 ]14+ , is synthesized and its application in the photocatalytic H2 evolution reaction is reported. The present PCS possesses shorter linkers for connecting the Ru chromophore and the MV2+ acceptors in comparison with our previous PCSs (Inorg. Chem. Front., 2016, 3, 671-680) and shows a consecutive photo-driven electron transfer in the presence of a sacrificial electron donor [ethylenediaminetetraacetic acid (EDTA)], leading to a multi-electron storage over the PCS. This behavior can also be coupled with the catalytic H2 evolution by the presence of a colloidal Pt catalyst. More importantly, the present PCS exhibits a much higher durability during the photolysis, which is attributed to the higher rate in the catalytic process. The high durability is also attributed to its bulky framework preventing undesirable side reactions.

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.

Pt(II)-Catalyzed photosynthesis for H2 evolution cycling between singly and triply reduced species.

A PtCl2(bpy) derivative tethered to two viologen (MV(2+)) moieties drives photochemical H2 evolution via forming a three-electron-reduced species possessing a bpy(-)˙-based (or MV(0)-based) reducing equivalent. Such species can only form after one electron reduction of both the MV(2+) sites because of rapid intramolecular electron transfer from bpy(-)˙ to MV(2+).