Guest-Regulated Charge Separation in a Porphyrin Metallacage for Visible-Light Photocatalytic Oxidative Cyclization.

The regulation of charge separation within well-defined molecular systems remains a central challenge in the development of efficient photocatalysts. Herein, a supramolecular photocatalytic platform based on a porphyrin-based metallacage is established, in which charge separation is modulated through guest encapsulation rather than structural reconstruction of the host framework. Encapsulation of planar electron-accepting guests within the confined cavity induces efficient photoinduced electron transfer from the excited porphyrin panels, leading to the formation of long-lived charge-separated states. Comprehensive spectroscopic, electrochemical, and theoretical studies reveal that the electronic nature and spatial arrangement of the encapsulated guest play decisive roles in determining the efficiency and lifetime of charge separation, as well as the subsequent reactive oxygen species generation pathways. As a result, the optimized host-guest system exhibits markedly enhanced photocatalytic activity and selectivity in oxidative cyclization reactions under visible-light irradiation. This work demonstrates a guest-regulated strategy for controlling charge separation in discrete metallacages, providing a versatile and modular approach for the design of high-performance supramolecular photocatalysts.