Recyclable luminescent metal–organic frameworks with self-formed diketone-like sites for cascade ratiometric detection

The development of recyclable cascade sensing platforms capable of sequential detection and regeneration remains a critical challenge for sustainable technologies, owing to limitations in cross-sensitivity control, synthetic complexity, and material irreversibility. Herein, we report a self-assembled luminescent metal-organic framework, Cd-TCAT (TCAT = 4,4',4''-tricarboxyltriphenylamine/4<i>H</i>-1,2,4-triazole-3-amine), featuring <i>in situ</i>-generated diketone-like sites within its channels. These sites enable exceptional Tb³⁺ sensitization, yielding a 14.2-fold enhancement in the fluorescence intensity ratio (<i>I</i>₅₄₅/<i>I</i>₄₃₀). Mechanistic studies combining spectral analysis and DFT calculations reveal that the pre-organized diketone motifs selectively coordinate Tb³⁺, optimizing energy transfer for luminescence amplification. The resulting Tb³⁺@Cd-TCAT complex further acts as a cascade sensor, exhibiting ratiometric selectivity toward cysteine (Cys) over 20 natural amino acids through reversible host-guest interactions, which simultaneously regenerates the pristine MOF. Remarkably, this dual-functional platform maintains sensing efficiency after five reuse cycles, representing a recyclable MOF-based system for ratiometric cascade detection. This work establishes a design paradigm for engineering self-functionalized MOFs with tailored active sites to address multi-analyte sensing and sustainability demands.