An In Situ Film to Film Transformation Approach toward Highly Crystalline Covalent Organic Framework Films

Fabrication of highly crystalline covalent organic framework (COF) films with tunable thickness and good substrate adaptability remains a substantial challenge. Here, we have developed an effective approach for fabricating crystalline COF films based on elaborately designed bifunctional A(2)B(2) monomers. Typically, amorphous drop-tasted monomer [e.g., 1,4-bis(4-formylphenyl)-2,5-bis((4-aminophenyl)ethynyl))benzene (BFBAEB)] films were directly transformed into corresponding highly crystalline BFBAEB-COF film upon in situ vapor-assisted self-polycondensation in high yields (93-97%). The thickness of the BFBAEB-COF film could be modulated readily by varying the monomer concentration. These crystalline COF films could be grown on various substrates, including silicon, indium-doped tin oxide (ITO), glass, and gold. Moreover, such an in situ film-to-film transformation approach has been demonstrated as versatile and applicable to different A(2)B(2) monomers. This work provides a novel pathway toward homogeneous and highly crystalline COF films, representing a key step forward to explore the application of COFs. [GRAPHICS] .

Automated summary

This study presents an effective method for fabricating highly crystalline COF films with tunable thickness. The films can be grown on various substrates and offer new possibilities for COF applications.