Electron transport chain-inspired photodiode-like junction in metal-organic framework for directional multi-electron transfer in photocatalysis†

Abstract

It is highly desirable to mimic the ratchet-like multi-electron transfer of the electron transport chain (ETC) by artificial systems and impose dual-mode anaerobic denitrification and aerobic oxidation on organic compounds to produce value-added fine chemicals. But the extreme complexity of biological structures hampered their direct mimics. In this article, we report a new continuous and directional photoinduced-electron transfer (PET) method to mimic the ETC process of natural enzymes using metal-organic framework (MOF) as the platform, phenothiazine (PTH) ligand decorated with carboxylate coordination terminal was introduced into iron porphyrin PCN−222(Fe) by use of solvent-assisted ligand incorporation (SALI) process, electron-donating (D) PTH moiety and electron-accepting (A) iron porphyrin were spatially separated by the insulator-like high-polar Zr−carboxylate cluster. This D−A junction facilitated the photodiode-like directional electron transfer from PTH to the iron-porphyrin, thereby preventing back-electron transfer. The locally excessive distribution of PTH motifs, compared to neighboring iron-porphyrins, favored continuous electron injection. These advantages facilitated the more efficient photocatalytic performance of PTH@PCN−222(Fe) in the reduction of nitroarenes in N₂ and the oxidation of benzylamines in O₂ compared with the homogeneous mode. Femtosecond transient absorption (fs-TA) demonstrated more efficient intra-framework photoinduced electron transfer (PET) within PTH@PCN−222(Fe) compared to other counterparts, further indicating the superiority of this bioinspired supramolecular strategy.