A Fluorescent Three-Dimensional Covalent Organic Framework Formed by the Entanglement of Two-Dimensional Sheets

Herein, we report the introduction of steric hindrancein molecularbuilding blocks to prevent & pi;& BULL;& BULL;& BULL;& pi; stacking,thus allowing two-dimensional (2D) covalent organic sheets to formthree-dimensional (3D) covalent organic frameworks (COFs) throughentanglement. Starting from the rationally designed precursors containinga bulky anthracene unit in the vertical direction, a highly crystallineCOF (3D-An-COF) was successfully synthesized. Very interestingly,3D-An-COF was determined as an entangled 2D square net (sql) structure, and the high-resolution data (1.1 & ANGS;) obtainedby the continuous rotation electron diffraction technique allowedus to directly locate all non-hydrogen atoms. Structurally, the presenceof an anthracene group outside the C (2h ) symmetry plane strongly reduces the & pi;& BULL;& BULL;& BULL;& pi;interactions and promotes the formation of square entanglements. Inaddition, 3D-An-COF is fluorescent and can be used as a sensor todetect the trace amount of antibiotics in water. This study providesa new strategy for the structural diversification of 3D COFs and willcertainly motivate us to construct more entangled COFs for interestingapplications in the future.