Regulating Ligand‐to‐Metal Charge Transfer in UiO‐66(Zr)‐NH ₂ With Site‐Isolated Cu ⁺ Centers for Efficient Photocatalytic H ₂ O ₂ Generation

Site‐isolated metal centers within metal‐organic frameworks (MOFs) offer a promising strategy to regulate charge–transfer dynamics and enhance photocatalysis. Here, we investigate the influence of atomically dispersed Cu ions on the photophysics and photocatalytic activity of the zirconium‐based MOF UiO‐66(Zr)‐NH 2 . Cu was incorporated via wet impregnation, producing Cu@UiO‐66(Zr)‐NH 2 composites with preserved crystallinity. Structural and spectroscopic analyses confirm that Cu is stabilized predominantly as site‐isolated Cu + species interacting with the amino‐functionalized linker. Photoluminescence studies reveal that Cu incorporation introduces an additional ligand‐to‐Cu charge–transfer pathway that competes with the intrinsic ligand‐to‐cluster transfer to the Zr 6 O 4 (OH) 4 nodes, resulting in strong photoluminescence quenching. Time‐resolved photoluminescence and transient infrared spectroscopy demonstrate that Cu sites efficiently capture photogenerated electrons, suppressing energy dissipation and accelerating charge‐separation processes. These electronic effects significantly enhance photocatalytic oxygen reduction for H 2 O 2 production under simulated solar irradiation. The H 2 O 2 yield upon using 5 mg of MOF increased from ∼1.5 µmol h −1 for pristine UiO‐66(Zr)‐NH 2 to ∼8.2 µmol h −1 for the 7 wt% Cu‐loaded material. Mechanistic investigations indicate Cu + centers promote oxygen adsorption and activation, favoring the two‐electron oxygen reduction pathway. This work demonstrates that site‐isolated Cu ions can modulate ligand‐to‐metal charge–transfer processes in MOFs, offering a rational strategy to design efficient photocatalysts.