A multifunctional material of a terbium-based metal-organic framework showing fluorescence detection of Hg2+ and proton conductivity.

A novel terbium-based metal-organic framework, namely {[(CH3CH2)2NH2]2[Tb2(TTDI)2(H2O)1.7 (HCOOH)0.3]·DEF·3H2O}n (Tb-MOF, H4TTDI = 5-[5-(3,5-dicarboxyphenyl) thieno [3,2-b] thiophen-2-yl] benzene-1,3-dicarboxylic acid) was synthesized and characterized. The Tb-MOF is a three-dimensional porous framework based on binuclear clusters and crystallizes in the triclinic P1̄ space group. Fluorescence sensing experiments indicated that the Tb-MOF can recognize Hg2+ ions in aqueous solutions by the fluorescence quenching effect with a detection limit of 0.94 μM. The fluorescence quenching effect in the presence of Hg2+ ions primarily arises from the interaction between S in the ligand and Hg2+ ions. Additionally, the Tb-MOF displays proton conduction properties with a maximum proton conductivity of 5.99 × 10-4 S cm-1 at 50 °C and 98% relative humidity, and the proton conduction behavior follows the Grotthuss mechanism. Therefore, the Tb-MOF is a potential bifunctional material with fluorescence sensing of Hg2+ and proton conduction.