Electron Injection from Photoexcited Metal-Organic Framework Ligands to Ru-2 Secondary Building Units for Visible-Light-Driven Hydrogen Evolution

We report the design of two new metal organic frameworks (MOFs), Ru-TBP and Ru-TBP-Zn, based on Ru-2 secondary building units (SBUs) and porphyrin-derived tetracarboxylate ligands. The proximity of Ru-2 SBUs to porphyrin ligands (similar to 1.1 nm) facilitates multielectron transfer from excited porphyrins to Ru-2 SBUs to enable efficient visible-light-driven hydrogen evolution reaction (HER) in neutral water. Photophysical and electrochemical studies revealed oxidative quenching of excited porphyrin by Ru-2 SBUs as the initial step of the HER process and the energetics of key intermediates in the catalytic cycle. Our work provides a new strategy to building multifunctional MOFs with synergistic ligands and SBUs for efficient photocatalysis.