A ratiometric fluorescent sensor with dual response of Fe³⁺/Cu²⁺ based on europium post-modified...

In this work, a sulfone-functionalized metal organic frameworks (MOFs) (CAU-11) formulated as [Al(OH)(SDBA)]·0.25DMF (H₂SDBA = 4, 4'-sulfonyldibenzoic acid) has been successfully constructed under solvothermal conditions. Next, a europium ion post-functionalized compound (Eu³⁺@CAU-11) with bright red fluorescence has been obtained by postsynthetic modification (PSM). Because of its excellent luminescence and robust framework, we design this compound as a ratiometric fluorescent probe (I_L/I_Eu) for sensing application. In the investigation process, what is surprising is that Fe³⁺ can quench the fluorescence of Eu³⁺@CAU-11 both in aqueous solutions and in N, N-dimethylformamide (DMF) while Cu²⁺ can only quench the fluorescence of it in DMF. It represents a rare example of a sensor based on a metal-organic framework which can dually sense and distinguish two quenching metal ions in different solutions simultaneously. To better explain this phenomenon, the probable sensing mechanism of the two metal ions has also been discussed in this paper. More importantly, we have designed this ratiometric fluorescent sensor as a combinational molecular logic gate for further logical application because of its sample synthesis process and favorable luminescent properties.