Photosystem II-Inspired Ce-MOF for Selectively Coupling Photocatalytic Nitro-to-Azoxy Conversion with Water Oxidation.

Abstract

The integration of photocatalytic water oxidation with selective organic transformations remains challenging due to inefficient charge separation and intermediate regulation. Inspired by the spatially separated redox centers of photosystem II (PSII), we developed a cerium(IV)-based metal-organic framework (Ce(IV)-<b>DPA</b>) constructed from anthracene-derived ligands (DPA) and dinuclear Ce₂(μ-O) clusters, which mimic the enzymatic compartmentalization of oxidation and reduction sites and synergistically drive visible-light-induced nitrobenzene-to-azoxybenzene conversion coupled with stoichiometric water oxidation. Single-crystal X-ray diffraction unambiguously identifies nitrobenzene coordination to Ce(IV) centers, establishing rare atomic-resolution evidence for substrate activation in MOF photocatalysis, guiding targeted electron transfer. Through the LMCT process, photogenerated electrons reduce Ce(IV) to Ce(III), driving sequential proton-coupled electron transfers (PCET) for nitrobenzene-to-azoxybenzene conversion with 91% yield and 96% selectivity, while holes oxidize water, outperforming Ce(III)-<b>DPA</b> analogs by 49% in yield. Isotopic tracer studies confirm water as the exclusive proton source, mirroring PSII's PCET mechanism. DFT reveals that the LUMO of Ce(IV)-<b>DPA</b> localizes on the nitro group, enabling directional electron transfer. The synergy of coordination flexibility and framework confinement in Ce(IV)-<b>DPA</b> spatially preorganizes intermediates (e.g., nitrosobenzene/<i>N</i>-phenylhydroxylamine) for selective azoxybenzene coupling, ensuring >95% selectivity and stability over six cycles. By emulating the compartmentalized redox architecture of PSII, this work establishes a Ce(IV)-<b>DPA</b> catalytic paradigm for scalable solar-to-chemical conversion, offering a paradigm for high-value nitrogen chemical production coupling with water oxidation.