Expanded Synthesis of 3D Covalent Organic Frameworks via Linker Exchange for Efficient Photocatalytic Aerobic Oxidation

Despite recent progress in 3D covalent organic frameworks (3D-COFs), their design and synthesis still pose significant challenges, mainly due to a limited mechanistic understanding of their synthesis. Herein, a linker exchange approach has been utilized to synthesize a series of new 3D-COFs by first preparing an imine-linked 3D-COF followed by exchanging with selected linear diamine linkers. This approach can be widely applicable to different types of diamines, enabling rational-designed synthesis of 3D frameworks that are previously inaccessible via direct polymerization in a one-pot reaction. Mechanistic aspects associated with the improved 3D-COF synthesis via the linker exchange approach, are investigated by density functional theory calculations, in which the possibility of the departure of the leaving linker is a spontaneous process with a decrease in enthalpy. Catalytic and computational results revealed that incorporating benzoxazole moiety into the 3D-COF frameworks enables a significant increase in the capability of visible-light-driven catalysis. The overall findings of the present study will pave the way toward the development of 3D-COFs with tunable structures and functions for other promising and challenging applications.