Ultrastable Lanthanide Metal–Organic Frameworks for Smartphone-Assisted Ratiometric Fluorescent Sensing of Toluenediamines and Tunable Luminescence

Lanthanide metal–organic frameworks (Ln-MOFs) have excellent optical properties and structural diversity, providing a unique platform for the development of fluorescent sensing and optical materials. In the work described herein, a series of isostructural 3D Ln-MOFs [Ln(L)(H 2 O)]·2H 2 O (Ln = Eu ( 1 ), Gd ( 2 ), Tb ( 3 ), H 3 L = 3,3′,3″-[1,3,5-benzenetriyltris(carbonylimino)]tris-benzoate) are fabricated under solvothermal conditions. The good thermal, water, and acid–base stabilities of 3 are prerequisites for fluorescent sensing applications. 3 can be used as a ratiometric broad-spectrum fluorescent sensor for toluenediamines (TDAs) in real urine with the advantages of visualization, ultrasensitivity, and selectivity. Interestingly, a smartphone-assisted intelligent sensing platform manifests promising results for the detection of TDAs, providing a chance for further development of portable diagnostic tools. In addition, by tuning the ratios of Eu 3+ /Tb 3+ and Eu 3+ /Gd 3+ /Tb 3+, nine bimetallic-doped Eu x Tb 1– x ( x = 0.10–0.90, 4 – 12 ) and one trimetallic-doped Gd 0.95 Tb 0.015 Eu 0.035 ( 13 ) were obtained. 4 – 12 exhibit a gradient of luminescent colors from yellow-green to pink with different ratios of Eu 3+ and Tb 3+ ions. Meanwhile, the trimetallic-doped Gd 0.95 Tb 0.015 Eu 0.035 ( 13 ) shows near-white-light emission with a quantum yield of 8.76%. Interestingly, the inks made with 1 – 13 are invisible under ambient light but show visual color-tunable luminescence under a 254 nm UV lamp, which may facilitate their anti-counterfeiting applications.