Heteroligand Metal‐Organic Frameworks With Low Background for Ratiometric Luminescent “Turn on” Sensing of Multiple Targets

ABSTRACT Traditional ratiometric fluorescent metal–organic framework (MOF) sensors are fundamentally constrained by unstable and high background signals, which obscure trace analyte responses and preclude effective self‐calibration. To address this, we engineered heteroligand Zr‐MOFs incorporating aggregation‐induced emission (AIE) ligand (H 4 ETTTC) as the energy/electron donor and aggregation‐caused quenchin g (ACQ) ligand (TCPP) as the energy/electron acceptor. This architecture exploits synergistic Förster resonance energy transfer and photoinduced electron transfer to suppress donor fluorescence, while local aggregation of ACQ molecules quenches acceptor fluorescence, establishing near‐zero background emission critical for high‐fidelity ratiometric sensing. Critically, analyte binding activates concentration‐dependent multicolor responses. Sulfide ion elicits a four‐stage emission transition—from dark to red, yellow, and green—through sequential N─S coordination and Zr‐node displacement. Meanwhile, ammonia triggers progressive chromatic shifts via TCPP deprotonation and H 4 ETTTC hydrogen‐bond–mediated restriction of intramolecular motion, followed by hydrolysis‐mediated ligand release. This system achieves exceptional sensitivity, with lower detection limits compared with conventional single‐ligand MOFs (0.76 µ M sulfide ion; 0.011 m M ammonia), and enables versatile multi‐target detection of sulfide ion, ammonia, biogenic amines, and urease activity. Demonstrated field applications include real‐time food spoilage monitoring (−20°C to 25°C), industrial effluent surveillance, and clinical urease diagnostics, all enabled by robust ΔE‐based quantification.