Unlocking Zenith Electronic State of Ni Sites in Ligand‐Engineered COFs for Efficient •O 2 − ‐Driven Uranium Photoreduction

ABSTRACT Photocatalytic uranium reduction via the superoxide radical (•O 2 − ) pathway is a sustainable route, but its efficiency is constrained by rapid charge recombination and poor O 2 activation. Herein, we develop a ligand engineering strategy to construct a series of Ni‐diketimine‐linked COFs by varying the diketone units directly coordinated to the Ni centers, enabling precise tuning of the Ni electronic state. The acenaphthylene‐1,2‐dione‐derived Ni‐COF‐E reaches a peak optimum within the present series, termed the “Zenith electronic state”, as evidenced by the highest ligand‐to‐metal charge transfer (0.584 e) and the largest charge transfer distance (1.700 Å) among the three Ni‐COFs in the S 1 excited state. This zenith electron density balances efficient photogenerated electron capture with enhanced O 2 adsorption and a lowered barrier for •O 2 − formation, which is corroborated by combined experimental and theoretical analyses. Consequently, Ni‐COF‐E delivers a record •O 2 − generation rate of 8.48 µM h −1 and achieves >99% uranium removal from real wastewater. This work establishes direct ligand engineering as a powerful strategy for tuning single‐metal sites in COFs and positions the Zenith electronic state as a new design principle for •O 2 − ‐mediated photocatalysis.