Flexible Films of Covalent Organic Frameworks with Ultralow Dielectric Constants under High Humidity

Abstract Covalent organic framework (COF) films combine the processability of polymers with the porosity and atomic precision of crystalline porous materials, properties that are long‐sought‐after in electronics yet hard to realize. Herein, we prepared four flexible COF films with different alkoxy side chains via interfacial polymerization. The COF films exhibit an ultralow dielectric constant ( κ =1.19±0.04 at 10 5 Hz), small dielectric loss (<0.02, 10 3 –10 6 Hz), high breakdown voltage (>63 kV cm −1 ) and low leakage current (10 −10 A cm −2 at 1 kV cm −1 ). They have considerable mechanical strength, and ability to withstand high humidity (RH 70 % for 10 days) and repeated bending (1000 times) without losing their dielectric properties. Extension of the alkoxy chains reduces the film's κ and enhances its moisture resistance, while incorporation of guest molecules further increase the κ value up to 43 times.