Bimetallic Strip-Inspired Dual-Layer Covalent Organic Framework Membrane for Smart Organic Vapor Response

Vapor-driven smart materials show significant advantages in areas such as intelligent control, gas detection, and information transmission. However, their typically singular response mechanisms pose challenges for achieving binary response behaviors within a single system. Drawing inspiration from bimetallic strips, a dual-layer covalent organic framework (DL-COF) membrane is developed with a hierarchical pore structure. This membrane exhibits asymmetric expansion or contraction on either side when exposed to morpholine and 1,4-dioxane vapors, enabling binary response behaviors. The driving forces underlying these binary responses are the shifts in hydrogen bond equilibrium caused by chain-like hydrogen bonding and the swelling effects within the two layers, which have different degrees of crystallinity. The hierarchical pore structure further enhances rapid mass transfer, enabling the DL-COF membrane to achieve an impressive response time of just 0.6 s. By leveraging its distinct responsiveness to different vapors, the DL-COF membrane can be effectively utilized for the visual translation of encrypted information, enabling the reliable decoding of gas-encrypted Morse code from continuous programmatic vapor inputs.