Ambient one-step synthesis and direct coating of highly crystalline covalent organic frameworks on arbitrary surfaces

Covalent organic frameworks (COFs) are promising materials for wide-ranging applications. Challenges with coating them onto surfaces have however limited their wider implementation in practice. We report an acoustomicrofluidic nebulization platform that enables rapid, one-step synthesis of highly crystalline COFs and their direct deposition as a coating under ambient conditions. Demonstrated with both two- and three-dimensional imine-based COFs, the method yields uniform COF films with nanometer to micrometer thicknesses, tuned simply by adjusting the nebulization time. Unlike conventional COF coating approaches, this strategy eliminates the need for any postsynthetic substrate heating or processing, thereby offering a general and scalable route for fabricating functional COF coatings on a variety of sensitive and complex substrates, including living tissue. As proof of concept, we demonstrate that COFs can constitute protective coatings on plant leaves for solar ultraviolet shielding, thus highlighting the potential of the platform to extend the deployment of COFs in real-world devices, biological systems, and environmental interfaces.