Electron-Rich Macrocycle-Based Metal-Organic Frameworks for Efficient Photocatalytic CO₂ Reduction

Metal-organic frameworks (MOFs) are distinguished by their structural diversity, tunable electronic properties, and exceptional performance in various applications. Notably, the electron-donating ability of ligands significantly enhances the ligand-to-metal charge transfer (LMCT) processes within these frameworks, thereby promoting efficient charge migration. Herein, we developed two electron-rich macrocyclic ligands derived from phenothiazine- and phenoxazine-functionalized calix[3]arenes, alongside their corresponding cobalt-coordinated MOFs. Remarkably, the MOF designated as Co-C[3]PTZ-MOF─constructed using the more electron-donating calix[3]phenothiazine ligand (C[3]PTZ-COOH)─exhibited superior photoresponse and enhanced charge-transport characteristics. This optimized material achieved an exceptional CO₂ photoreduction initial efficiency of 17,800 μmol g^-1 h^-1 with 81% CO selectivity. The outstanding photocatalytic performance originates from the strong electron-donating nature of the calix[3]arene-based ligands, which facilitated efficient LMCT processes. This study provides valuable insights for designing high-performance photocatalysts through rational engineering of macrocyclic ligands.