Abstract
Covalent organic frameworks (COFs) are attractive candidates for the next generation films in technical applications. However, due to their crystallization nature, insolubility in common solvents as well as infusible at high temperatures make it challenging to grow them spontaneously or process them into films. Herein, we report an efficient strategy to fabricate COF films based on a modulator-solvent induced polymerization process. The addition of modulator slows down the nucleation rate during the initial stages of COF growth, resulting in the formation of fluidic precursors that are easy to process. Subsequently, a suitable drying process is introduced to balance the evaporation rate of solvent and the crystallization rate of modulator induced, resulting in the formation of COF films with a mixture of amorphous and crystalline structures. This strategy is universal for the fabrication of several types of COF films with large-scale and freestanding state. Moreover, COF films with asymmetric structure can function as organic vapor-triggered actuators, offering excellent repeatability and reversibility. By introducing functional molecules such as fluorescence, chirality and catalyst during the nucleation process, versatile functional COF films can be easily fabricated, which endow them with broader application prospects.