Synthesis of Thin Film of a Three‐Dimensional Covalent Organic Framework as Anti‐counterfeiting Label

Comprehensive Summary Film plays a key role in the sustainable development of our society. Freestanding thin films of two-dimensional covalent organic frameworks (COFs) have been produced by interface, spin coating, microwave-assisted synthesis, and screen printing methods and are applied in nanofiltration, molecular separation, photochemical sensing, anion transport, heat conduction, and proton conduction. On the other hand, the synthesis of their three-dimensional (3D) analogues and subsequent integration in devices remains challenging. Herein, self-supporting thin films of a three-dimensional COF with tunable thickness was created by a stearic acid mediated synthesis methodology on water surface at room temperature in air. The film could be transferred onto arbitrary substrate, and when supported on indium tin oxide glass, it exhibited irreversible electrochromism. The optical feature made it act as a one-time anti-counterfeiting label in an electrochemical device. This work will inspire the synthesis of thin films of 3D COFs as well as other 3D materials, and boost their property and application exploration.