Surfactants Mediated Synthesis of Highly Crystalline Thin Films of Imine‐Linked Covalent Organic Frameworks on Water Surface

Main observation and conclusion Imine‐linked covalent organic frameworks (COFs) have attracted extensive attention due to designable structures, tunable properties, and excellent thermal and chemical stability. They were typically obtained as insoluble and unprocessable powders, which seriously limits their full promise. Progress has been made in the synthesis of thin films of imine‐linked COFs by interfacial synthesis. However, the synthesis of highly crystalline, self‐supporting thin films of COFs remains challenging. Here, we employed a surfactants‐mediated method to synthesize such films at an air‐water interface, showed the films could be transferred onto arbitrary substrates on demand, and demonstrated the generality of the methodology with two different COFs. We found that the length of hydrophobic segments of surfactants played a key role in determination of the crystallinity and single crystalline domain size of the films. This work provides a feasible strategy to generate highly crystalline thin films of COFs.