Synergistic humidity-responsive mechanical motion and proton conductivity in a cationic covalent organic framework

The development of flexible, humidity-responsive actuator materials is critical for advanced sensors and electronic systems. Current fabrication methods are complex and harsh. We present a novel approach that uses one-step synthesis at room temperature to prepare a self-standing cationic covalent organic framework (TG-DFP COF) film. Because hydrogen bonding and ionic surface coverage are present throughout the COF network, this material facilitates the rapid adsorption and desorption of water vapor, leading to an ultrafast actuating response rate of less than 1 s. At high humidity, the entrapped water molecules enhance the hydrogen-bonding interactions, leading to an impressive proton conductivity of 2.8 mS cm−1, which is among the highest reported for cationic COFs. This study demonstrates a unique 2D-ordered system that combines high proton conductivity and shape-changing ability with remarkable stability. [Display omitted] •Self-standing cationic covalent organic framework (COF) film•Ultrafast humidity-responsive actuation•In humidity, the COF film shows high proton conductivity of 2.8 mS cm−1 Moisture as an energy source to trigger the mechanical motion of materials is an emerging research area of interest for the development of smart switches and soft robots. Covalent organic frameworks (COFs) provide a superior platform to tune their structures with suitably responsive units and make them stimuli responsive. Hydrophobic COFs lack the ability to engage in polar interactions and limit the fabrication of moisture-sensitive actuators. To overcome this challenge, we have developed a cationic, flexible COF film pre-functionalized with a water-sensitive guanidinium moiety. By exploiting the role of H bonding in extended structure, we have successfully addressed two important problems. Anion-water H bonding enables a fast activation of mechanical motion. H-bonded water molecules allow the creation of efficient pathway for proton conduction. The designed COF paves the way for innovative advances in the field of moisture-responsive conductive smart materials. We showcase the synthesis of a flexible robust cationic COF film at room temperature. The film displays rapid and reversible actuation in response to changes in relative humidity over multiple cycles. The presence of anion-water hydrogen bonding facilitates effective proton-transport channels within the COF network, which leads to high proton conductivity in humid conditions.