Regulating Conformational Locking in Covalent Organic Framework for Selective and Recyclable Photocatalytic Transformation.

The exploration of new properties and functionality of covalent organic frameworks (COFs) rely mostly on the covalent modification of the starting building blocks or linkages. Noncovalent forces that guide the assembly and adhesion of layers to develop two-dimensional (2D) COFs and improve their bulk properties and functionalities, however, are rarely explored. Herein, the "conformational lock" (CL) effect in 2D hydrazine-linked COFs with intralayer F-H interaction is discovered and regulated to stabilize interlayer adhesion and develop a facile strategy to increase their stability, promote selectivity and efficiency in reactive singlet oxygen (O)-triggered photocatalytic transformation when acting as photocatalysts. The CL strategy endows the fluorinated COFs with an efficient intersystem crossing process for O generation and strong interlayer π-π stacking interaction. The 4F-COF with the strongest F-H noncovalent interaction exhibits the highest photocatalytic conversion and selectivity (exceeding 98%) in typical O-dependent transformations, even over 7 continuous photocatalytic cycles. This work demonstrates that promoting intralayer noncovalent interaction in 2D-COFs can impart high photocatalytic activity and stability, and would vigorously inspire their developments in heterogeneous catalysis.