The performance of a water-soluble cobalt porphyrin ([{meso-tetra­(4-sulfonatophenyl)­porphyrinato}­cobalt­(III)], CoTPPS) as a catalyst for the photoreduction of CO2 in fully aqueous media has been investigated under visible light irradiation using [Ru­(bpy)3]2+ as a photosensitizer and ascorbate as a sacrificial electron donor. CO is selectively produced (>82%) with high efficiency (926 TONCO; TONCO = turnover number for CO). Upon optimization, selectivities of at least 91% are achieved. Efficiencies up to 4000 TONCO and 2400 h–1 TOFCO (TOFCO = turnover frequency for CO) are reached at low catalyst loadings, albeit with loss in selectivity. This work successfully demonstrates the ability of CoTPPS to perform highly efficient photoreduction of CO2 in water while retaining its high selectivity for CO formation.

In order to realizea rtificial photosynthetic devices for splitting water to H 2 and O 2 (2 H 2 O + hn!2H 2 + O 2 ), it is desirable to use awider wavelength range of light that extends to alower energy region of the solar spectrum. Here we report at riruthenium photosensitizer [Ru 3 (dmbpy) 6 (m-HAT)] 6+ (dmbpy = 4,4'-dimethyl-2,2'-bipyridine,H AT = 1, 4,5,8,9,12-hexaazatriphenylene) + , [4] with bpy = 2,2'-bipyridine and ppy = 2-phenylpyridinate), and acatalyst (e.g., colloidal Pt, [5] Pt II , [6] Rh II [7] and Co II [8] complexes). As shown in Scheme 1, either an oxidative or reductive quenching process triggers the lightdriven electron transfer (ET) processes.I ns pite of the great advancement so far in this area, little efforts have been made to develop PSs capable of driving ET events by making use of awider wavelength range of the solar spectrum. Forinstance, one of the well-known PSs,[ Ru(bpy) 3 ] 2+ ,c an absorb light in the 280-600 nm range,w hich covers only 19.1 %o ft he total solar irradiance on the basis of the integrated photon flux. [9] However,the integrated photon flux can be almost doubled if the 280-800 nm domain (39.6 %ofthe total solar irradiance) could be fully used by the PS when driving H 2 evolution. In this context, Hanan et al. employed qpy (4,4':2,2'':4'',4'''-quarterpyridine) instead of bpy,and showed that [Ru(qpy) 3 ] 2+ (see Figure 1A)i sc apable of absorbing longer wavelength light and can actually drive photochemical H 2 evolution even

A new photo-charge separator (PCS) consisting of a [Ru(bpy) ] (bpy=2,2'-bipyridine) chromophore and six viologen (MV ) acceptors, [Ru(bpyMV2) ] , is synthesized and its application in the photocatalytic H evolution reaction is reported. The present PCS possesses shorter linkers for connecting the Ru chromophore and the MV 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 H 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.

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+).