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.