Proton-induced switching of excitation-wavelength-dependent emission based on mixed-ligand metal-organic frameworks

Stimuli-responsive metal-organic frameworks (MOFs) remain at the forefront of porous materials research due to their sensitive response to various stimuli. Thereinto, the excitation-wavelength-dependent (Ex-De) emission in MOFs has attracted great attention due to the fast and non-invasive manipulation features, yet it still suffers from fixed energy-level structures with restricted emission modulation, limiting applications in high-level anti-counterfeiting. Herein, we propose a strategy to achieve the switching of Ex-De emission behavior in mixed-ligand metal-organic frameworks (ML-MOFs) based on the proton-controlled energy transfer (ET) process. The designed ML-MOFs exhibit competition between ET emission and intrinsic ligand emission, which permits the modulation of relative intensities of these two emissions by adjusting the excitation wavelength, leading to the Ex-De emission behavior. The introduction of amino groups on the acceptor ligand can affect the luminescence efficiency of the acceptor via the protonation/deprotonation effect, which reversibly manipulates the ET process. On this basis, the proton-switched Ex-De emission behavior in ML-MOFs was achieved. Furthermore, we demonstrate high-level anti-counterfeiting applications based on ML-MOFs via dynamic control of Ex-De emission behavior. The results will provide guidance for the design of novel Ex-De emission devices with smart responsiveness. Switchable Ex-De emission of ML-MOFs has been realized via a proton-controlled ET process, enabling the design of high-level anti-counterfeiting applications.