Covalent Organic Framework Colloids With Core-Shell Donor/Acceptor Architecture and Ultralong-Lived Charge-Separated States.

Covalent organic frameworks (COFs) possess structural tunability, high surface area, and extended delocalization of π-electrons but remain limited by challenges in constructing well-defined structures that enable efficient charge separation. Here, we address this limitation through the construction of core-shell colloidal COF particles using isostructural but electronically distinct donor (D) and acceptor (A) COFs. The resulting p-n heterojunction architecture enables efficient spatial separation of photogenerated electrons and holes, while preserving high crystallinity. Nanoscale phase separation is confirmed by high-angle annular dark-field scanning transmission electron microscopy coupled with energy-dispersive X-ray spectroscopy (HAADF-EDS) mapping and X-ray photoelectron spectroscopy (XPS) analysis. Light-induced electron paramagnetic resonance (EPR) measurements reveal enhanced populations and significantly longer lifetimes of charge-separated states in the core-shell COFs compared to their single-phase counterparts, indicating suppressed charge recombination and improved charge separation. The resulting heterostructures show efficient CO2 photoreduction to CO and HCOOH, coupled with H2O oxidation, thereby requiring no sacrificial agents. The results demonstrate the importance of well-defined D/A interfaces in COF photocatalysis.