Cerium-Based Metal-Organic Layers Catalyze Hydrogen Evolution Reaction through Dual Photoexcitation

Cerium-based materials such as ceria are increasingly used in catalytic reactions. We report here the synthesis of the first Ce-based metal-organic layer (MOL), Ce-6-BTB, comprising Ce-6 secondary building units (SBUs) and 1,3,5-benzenetribenzoate (BTB) linkers, and its functionalization for photocatalytic hydrogen evolution reaction (HER). Ce-6-BTB was postsynthetically modified with photosensitizing [(MBA)Ir(ppy)(2)]Cl or [(MBA)Ru(bpy)(2)]Cl-2 (MBA = 2-(5'-methyl-[2,2'-bipyridin]-5-yl)acetate, ppy = 2-phenylpyridine, bpy = 2,2'-bipyridine) to afford Ce-6-BTB-Ir or Ce-6-BTB-Ru MOLs, respectively. The proximity of photosensitizing ligands and Ce(6)SBUs in the MOLs facilitates electron transfer to drive photocatalytic HER under visible light with turnover numbers of 1357 and 484 for Ce-6-BTB-Ir and Ce-6-BTB-Ru, respectively. Photophysical and electrochemical studies revealed a novel dual photoexcitation pathway whereby the excited photosensitizers in the MOL are reductively quenched and then transfer electrons to Ce(6)SBUs to generate Ce-III centers, which are further photoexcited to Ce-III* species for HER.