Photosensitizing Metal–Organic Layers for Efficient Sunlight-Driven Carbon Dioxide Reduction

Metal–organic layers (MOLs), a free-standing monolayer version of two-dimensional metal–organic frameworks (MOFs), have emerged as a new class of 2D materials for many potential applications. Here we report the design of a new photosensitizing MOL, Hf12-Ru, based on Hf12 secondary building units (SBUs) and [Ru­(bpy)3]2+ (bpy = 2,2′-bipyridine) derived dicarboxylate ligands. After modifying the SBU surface of Hf12-Ru with M­(bpy)­(CO)3X (M = Re and X = Cl or M = Mn and X = Br) derived capping molecules through carboxylate exchange reactions, the resultant Hf12-Ru-Re and Hf12-Ru-Mn MOLs possess both [Ru­(bpy)3]2+ photosensitizers and M­(bpy)­(CO)3X catalysts for efficient photocatalytic CO2 reduction. The proximity of the MOL skeleton to the capping ligands (1–2 nm) facilitates electron transfer from the reduced photosensitizer [Ru­(bpy)3]+ to MI(bpy)­(CO)3X (M = Re, Mn) catalytic centers, resulting in CO2 reduction turnover numbers of 8613 under artificial visible light and of 670 under sunlight. MOLs thus represent a novel platform to assemble multifunctional materials for studying artificial photosynthesis.