Dual-Emission SG7@MOF Sensor via SC–SC Transformation: Enhancing the Formation of Excimer Emission and the Range and Sensitivity of Detection

In this study, a water stable metal–organic framework FIR-53 is applied as a single-crystal container for anion exchange. The exceptional chemical stability and low crystallographic symmetry of FIR-53 makes it possible to determine anionic guests. Through ion exchange and single-crystal to single-crystal (SC–SC) transformation, 8-hydroxypyrene-1,3,6-trisulfonate (SG7, solvent green 7, ion form as SG73–) is introduced into the pores of FIR-53 to obtain SG7@FIR-53. Because of the spatial confinement and partition effect, SG7@FIR-53 shows the bright exciter emission of SG7 ions. Interestingly, the composite SG7@FIR-53 exhibits a sensitive fluorescence quenching response against Cr2O72– and MnO4– in aqueous solution. Especially, the detection limit toward MnO4– is as low as 0.12 ppb, which is the smallest value to date. Moreover, the prepared SG7@FIR-53 film also displays a broad response to nitro explosives in vapor/aqueous phase. Compared with the results of FIR-53, the range and sensitivity were greatly improved.