Ratiometric fluorescence sensing and colorimetric decoding methanol by a bimetallic lanthanide-organic framework

Ratiometric fluorescence sensor has drawn much attention due to its decreased environment influence and easy-to-differentiate color and intensity change. In this work, a bimetallic metal-organic framework (MOF), namely {(Me2NH2)[Tb0.9Eu0.1(OBA)2]∙(Hatz)∙(H2O)1.5}n (1, H2OBA = 4,4′-oxybis(benzoate) acid, Hatz = 3-amino-1,2,4-triazole) with a yellow-emission signal has been successfully fabricated by appealing to the lanthanide doping strategy. In this MOF, the emission band of OBA2− ligand matches well with the excitation energy of lanthanide ions (Eu3+ and Tb3+) which leads to high energy transfer from the ligand to the lanthanide ions to provide dual emission peaks for the both Eu3+ and Tb3+ ions. This MOF shows high fluorescence stability with the ratio of its two emission peaks (545 nm and 618 nm) do not change with the change of Ln-MOF sensor concentration used as the merit of ratiometric fluorescence detection. Subsequently, we choose this MOF as a fluorescent sensor for various volatile organic molecules, and the results show that it is capable of decoding methanol with an obvious color change and unique emission intensity ratio of Tb3+ ion to Eu3+ ion, both in the solution and vapor state. Good detection reproducibility and fast response could be achieved in this sensor.