Stable dye-encapsulated indium–organic framework as dual-emitting sensor for the detection of Hg2+/Cr2O72− and a wide range of nitro-compounds

Abstract

A water-stable porous anionic metal–organic framework (MOF), [(CH₃)₂NH₂][In(TNB)_4/3]·(2DMF)(3H₂O) (1, H₃TNB = 4,4′,4′′-nitrilotribenzoicacid), was synthesized. Through ion-exchange method, one dual-emitting composite 1⊃DSM was prepared with the encapsulation of cationic dye 4-[p-(dimethylamino)styryl]-1-ethylpyridinium (DSM). 1⊃DSM exhibits sensitive quenching response towards Hg²⁺ and Cr₂O₇²⁻ ions in aqueous solution. In particular, the detection limit of Hg²⁺ is as low as 1.75 ppb, which is among the lowest values for MOF-based probes. Moreover, 1⊃DSM shows remarkable sensitivity for nitro-explosives in a wide scope, particularly for phenol hydroxyl-containing nitro-explosives. Furthermore, 1⊃DSM has a broad response to nitroimidazole-based antibiotics at low concentrations. As a result, the incorporation of DSM into MOF could strikingly improve the sensitivity and range of the detection. In addition, the orbital energy theoretical calculation and UV-Vis absorption experiments confirmed that the quenching performances could be mainly attributed to the electron transfer and resonance energy transfer effect between the framework, DSM and the analytes.