Liquid Crystal Induced Large‐Area Continuous Covalent Organic Framework Films for High‐Performance Humidity Sensors

Large-area, continuous covalent organic framework (COF) films are in high demand for the fabrication of high-performance humidity sensors. However, conventional synthetic approaches of COF films are still plagued by drawbacks, such as harsh reaction conditions, film fragility, and time-consuming processes. Herein, we report a novel liquid crystal (LC)-assisted fabrication of large-area COF films, which exhibits remarkable universality for the synthesis of distinct types of COF films. Mechanistic investigations reveal that non-covalent interactions induced by LC molecules facilitate the dense packing and ordered self-assembly of organic precursors, thereby overcoming the bottleneck of large-scale film fragmentation. Featuring a response time of 4.45 s (15%-90% RH), recovery time of 1.95 s (90%-15% RH), and sensitivity of 13.90 mΩ/%RH, the COF film-based humidity sensor exhibits fast response and excellent durability. Overall, this work provides a versatile strategy to synthesize large-area COF films, enabling the construction of high-performance humidity sensors and thereby offering guidance for the development of high-performance active layers for humidity sensors.