Functionalization of Cluster-Nodes in a Metal-Organic Framework for Light-Manipulating Proton Conduction

Light-responsive proton conductors, which emulate biological proton pumps, have garnered significant research attention due to their wide-ranging applications in bioelectronics and smart devices. Herein, we demonstrate the first example of functionalization in the cluster-nodes of a metal-organic framework (MOF) for attaining light-responsive proton conduction. Specifically, the photoactive molecules of azobenzene-4,4′-dicarboxylic acid (AZOA) are grafted onto the Zr₆(μ₃-O)₄(μ₃-OH)₄ nodes of MOF-808 through the partial substitution of the terminal formates, giving MOF-808-AZOA. Remarkably, MOF-808-AZOA exhibits switchable proton conduction in responsive to UV light, featuring a substantial ON/OFF ratio, rapid response time, and good reversibility. Molecular simulations indicate that the light-responsive proton conduction in MOF-808-AZOA is attributed to differential interactions between the terminated formates and the −COOH group in AZOA with its cis- or trans-configuration. Given the diversity of cluster-based MOFs, this study opens up a promising avenue for realizing stimuli-responsive proton-conducting MOFs through cluster-node functionalization.