Real-Time Visualization of Active Species in a Single-Site Metal–Organic Framework Photocatalyst

In this work, we report a new single-site photocatalyst (Co-Ru-UIO-67(bpy)) based on a metal–organic framework platform with incorporated molecular photosensitizer and catalyst. We show that this catalyst not only demonstrates exceptional activity for light-driven H2 production but also can be recycled without loss of activity. Using the combination of optical transient absorption spectroscopy and in situ X-ray absorption spectroscopy, we not only captured the key CoI intermediate species formed after ultrafast charge transfer from the incorporated photosensitizer but also identified the rate-limiting step in the catalytic cycle, providing insight into the catalysis mechanism of these single-site metal–organic framework photocatalysts.