Enhancement of Intrinsic Proton Conductivity and Aniline Sensitivity by Introducing Dye Molecules into the MOF Channel

The encapsulation of dyes into metal-organic frameworks (MOFs) has generated a variety of platforms for luminescence, but little attention has been paid to their application in proton conduction. Here, a cationic MOF {{[In₃OL_1.5(H₂O)₃](NO₃)}·(DMA)₃·(CH₃CN)₆·(H₂O)₃₀} _n (FJU-10, H₄L = 4,4',4″,4‴-(1,4-phenylenbis(pyridine-4,2,6-triyl))-tetrabenzoic acid, DMA = N, N-dimethylacetamide) was synthesized, and the dye molecule 8-hydroxy-1,3,6-pyrenetrisulfonic acid trisodium salt (HPTS) was further added to the MOF growth solution, but during the reaction, HPTS was nitrated and nitrated HPTS was encapsulated into the FJU-10 to obtain dye@FJU-10. As a result, the intrinsic proton conductivity of dye@FJU-10 is nearly 5 times higher than that of FJU-10 at 90 °C. Dye@FJU-10 exhibits more sensitive fluorescence quenching toward aniline than FJU-10 in DMF solution (the detection limits of FJU-10 and dye@FJU-10 are as low as 0.58 and 0.62 μM, respectively). Here, it is demonstrated for the first time that intrinsic proton conductivity can be effectively improved by encapsulating a nitrated HPTS dye into an MOF.