Electron transport chain-inspired photodiode-like junction in a 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. However, the extreme complexity of biological structures hampers their direct mimicry. 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 frameworks (MOFs) as the platform. A phenothiazine (PTH) ligand decorated with a carboxylate coordination terminal was introduced into iron porphyrin PCN–222(Fe) using the solvent-assisted ligand incorporation (SALI) process. The electron-donating (D) PTH moiety and electron-accepting (A) iron porphyrin were then spatially separated by an insulator-like high-polar Zr–carboxylate cluster. This D–A junction facilitated photodiode-like directional electron transfer from PTH to iron-porphyrin, thereby preventing back-electron transfer. The locally excessive distribution of PTH motifs, compared with that of neighboring iron-porphyrins, favored continuous electron injection. These advantages enabled PTH@PCN–222(Fe) to exhibit more efficient photocatalytic performance than the homogeneous system in both the reduction of nitroarenes under N₂ atmosphere and the oxidation of benzylamines under O₂ atmosphere. Femtosecond transient absorption (fs-TA) demonstrated more efficient intra-framework photoinduced electron transfer (PET) within PTH@PCN–222(Fe) compared with other counterparts, further indicating the superiority of this bioinspired supramolecular strategy.