Dysprosium(III) Metal–Organic Framework Demonstrating Ratiometric Luminescent Detection of pH, Magnetism, and Proton Conduction

A multifunctional metal–organic framework, (Hdmbpy)[Dy(H 2 dobdc) 2 (H 2 O)]·3H 2 O ( Dy-MOF, H 4 dobdc = 2,5-dihydroxyterephthalic acid, dmbpy = 4,4′-dimethyl-2,2′-bipyridine), was synthesized and structurally characterized. The metal center Dy III is connected by four carboxyl groups to form the [Dy 2 (CO 2 ) 4 ] binuclear nodes, which are further interconnected by eight separate H 2 dobdc 2– ligands to form a three-dimensional (3D) framework including hydrophilic triangular channels and abundant hydrogen-bonding networks. Dy-MOF has good stability in aqueous solution as well as in harsh acidic or alkaline solutions (pH range: 2.0–12.0). Furthermore, the luminescence signal of Dy-MOF undergoes a visualized color change as the acidity of the solution alters, which is the typical behavior of pH ratiometric probe. At a 100% relative humidity, Dy-MOF exhibits a high proton conductivity σ (1.70 × 10 –4 S cm –1 at 303 K; 1.20 × 10 –3 S cm –1 at 343 K) based on the proton hopping mechanism, which can be classified as a superionic conductor with σ exceeding 10 –4 S cm –1 . Additionally, the ferromagnetic interaction and magnetic relaxation behavior are simultaneously achieved in Dy-MOF . Herein, the combination of luminescence sensing, magnetism, and proton conduction in a single-phase 3D MOF may offer great potential applications in smart multitasking devices.