Defects as electronic design elements in metal organic frameworks for photocatalysis

Defect engineering is widely applied to improve the photocatalytic performance of metal–organic frameworks (MOFs), but its role is often interpreted from a structural perspective rather than an electronic one. This review examines defect formation in MOFs from a coordination chemistry standpoint, focusing on how variations in metal–ligand environments influence electronic structure and charge-transfer behavior. The interplay between metal nodes, organic linkers, and defect types is analyzed to clarify their impact on orbital alignment and electronic coupling. Charge-transfer pathways, including ligand-to-metal (LMCT), metal-to-ligand (MLCT), metal-to-metal (MMCT), and ligand-to-ligand (LLCT) processes, are discussed in relation to defect-induced structural distortions. Synthetic strategies such as modulated synthesis, mixed-linker approaches, ligand functionalization, and post-synthetic modification are evaluated based on their ability to generate and regulate defects. Defect density influences photocatalytic behavior in a non-linear manner, reflecting the balance between improved charge separation and reduced electronic connectivity. Current limitations in correlating defect structures with electronic properties are addressed, highlighting the need for improved control and characterization. This review outlines a framework that connects coordination environment, electronic structure, and charge-transfer processes in defect-engineered MOFs.