In-Situ Assembly of Self-Photosensitizing Crystalline Copper(I) Coordination Networks for Photocatalytic CO₂ Reduction

Crystalline coordination networks (CCNs) offer rigid and highly organized structures that stabilize metal ions in unique coordination geometries, oxidation states, and electronic configurations, enabling unexpected catalytic properties. In this study, we introduce two photocatalytic CCNs, CuTTC-E and CuTTC-M, synthesized from noncatalytic Cu-(I) ions and nonphotosensitizing trithiocyanuric acid (TTC) linkers, without reliance on precious metals or expensive photosensitizing ligands. Structural analysis revealed that CuTTC-E features [Cu^IS₃Cl] secondary building units (SBUs) that are catalytically active for CO₂ reduction to CO. Mechanistic investigations showed that the proximity of TTC linkers to [Cu^IS₃Cl] in the CuTTC-E facilitates rapid electron transfer, effectively transforming the short-lived TTC linker into a functional photosensitizer. This design resulted in CuTTC-E achieving 10 times higher photocatalytic efficiency than the homogeneous control (Cu⁺ and Me₃TTC), with 100% selectivity toward CO. Notably, the synthesis and catalytic testing of CuTTC-M were integrated into a one-pot process, further simplifying its application. This strategy was successfully extended to other MTTC (M = Zn, Ag, Cd) CCNs, demonstrating its versatility and scalability. These findings illustrate how assembling metal ions and organic linkers into MOFs fundamentally transforms their catalytic properties and establishes a robust framework for developing cost-effective and highly selective photocatalysts.