Delocalized Orbitals over Metal Clusters and Organic Linkers Enable Boosted Charge Transfer in Metal–Organic Framework for Overall CO2 Photoreduction

• Published in: Angewandte Chemie International Edition 2024-11, Vol.63 (47), p.e202411508-n/a
• Main Authors: Liu, Hai‐Xiong, Zhou, Zi‐Jian, Xie, Lei, Liu, Chen, Cai, Lei, Wu, Xin‐Ping, Liu, Tian‐Fu
• Format: Article
• Language: English
• Subjects: Active sites; Carbon dioxide; Charge transfer; delocalized orbitals; direct charge transfer; Electron transfer; Electrons; Energy charge; Energy levels; Excitation; internal charge-separated state; Metal clusters; Metal-organic frameworks; metal–organic framework; Orbitals; overall CO2 photoreduction; Photocatalysis; Photoreduction; Photosensitivity; Recombination
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202411508

The conversion of CO2 to C2 through photocatalysis poses significant challenges, and one of the biggest hurdles stems from the sluggishness of the multi‐electron transfer process. Herein, taking metal–organic framework (MOF, PFC‐98) as a model photocatalyst, we report a new strategy to facilitate charge separation. This strategy involves matching the energy levels of the lowest unoccupied node and linker orbitals of the MOF, thereby creating the lowest unoccupied crystal orbital (LUCO) delocalized over both the node and linker. This feature enables the direct excitation of electrons from photosensitive linker to the catalytic centers, achieving a direct charge transfer (DCT) pathway. For comparison, an isoreticular MOF (PFC‐6) based on analogue components but with far apart frontier energy level was synthesized. The delocalized LUCO caused the presence of an internal charge‐separated (ICS) state, prolonging the excited state lifetime and further inhibiting the electron‐hole recombination. The presence of ICS state prolongs the excited state lifetime and further inhibits the electron‐hole recombination. Moreover, it also induced abundant electrons accumulating at the catalytic sites, enabling the multi‐electron transfer process. As a result, the material featuring delocalized LUCO exhibits superior overall CO2 photocatalytic performance with high C2 production yield and selectivity. Delocalized orbitals over the skeleton were constructed through regulating the linker units in a metal–organic framework, enabling electron transfer via the direct charge transfer (DCT) pathway. The presence of an internal charge‐separated state and the electron‐rich catalytic sites significantly improved the generation of C2 products in the overall CO2 photoreduction.