Dual-Function Metal–Organic Framework Membrane for High Proton Conduction and Photoswitch Sensor with a Large ON/OFF Ratio

Intelligent proton-conducting metal–organic framework (MOF) membranes, with dynamically and remotely controllable proton conduction, exhibit considerable potential for advanced applications such as sensors. In this study, a unique TCPP∈Im-UiO-66 synthesized by porphyrin (TCPP) and imidazole (im) ligands was used to prepare photoacid-doped TCPP∈Im-UiO-66@PCN (PCN = photoacid) material by the photoacid impregnation method. To improve proton conductivity and practicality, the TCPP∈Im-UiO-66@PCN hybrid membrane was fabricated by blending with sulfonated poly(ether sulfone) (SPES). Under light exposure, the PCN structure transforms from the open-loop spiropyran (MC) form to the closed-loop spiropyran (SP) form. When exposed to 375 nm ultraviolet light at room temperature, the proton transport channels formed by PCN in the composite membrane will be cut off. The TCPP∈Im-UiO-66@PCN film of the 5% composite film shows obvious light response behavior, which is 0.12 S·cm –1 in the absence of light and 0.017 S·cm –1 in the illumination. The optimal 5 wt % composite membrane achieves a maximum proton conductivity ON/OFF switching ratio of 7.1, which represents the largest photoswitching ratio among all prepared membranes. Therefore, our research has developed a stable proton-conducting membrane integrated with photoacids, which not only offers a new strategy for proton exchange membranes in fuel cells but also provides a novel approach for applications in remote photoproton sensing.