Alkynyl-anchored silver nanoclusters in lanthanide metal-organic framework for luminescent thermometer and CO₂ cycloaddition

In this study, an alkynyl-modified aromatic dicarboxylic acid bifunctional ligand was selected to construct lanthanide compound {[Eu₄(ebdc)₆(4,4-bpy)_0.5(H₂O)_4.5]·(C₂H₅OH)_1.25(H₂O)}_n (Eu-MOF, H₂ebdc = 5-ethynyl-isophthalic acid, 4,4-bpy = 4,4-bipyridine, and MOF = metal-organic framework), of which the uncoordinated alkynyl group would be used to anchor silver nanoclusters (Ag NCs). The Eu-MOF exhibits double emission peaks, located at 492 and 611 nm, respectively, in which the high-energy blue emission is associated with alkynyl-modified ligand while the low-energy red emission belongs to characteristic emission of Eu³⁺, indicating that ligands can effectively sensitize Eu³⁺ luminescence. The intensity ratio of the dual emission fluorescence peaks of Eu-MOF displays a good linear relationship with temperature, which realizes the detection function in the low temperature region of 75–275 K, and the thermal sensitivity reaches 1.5398%·K⁻¹. After anchoring the Ag NCs, the high-energy blue emission is significantly quenched, indicating that the Ag NCs are indeed confined into the framework and interact with the alkynyl group, and thus change the overall electronic distribution. This is the first case of anchoring Ag NCs by a luminescent Eu-MOF and studying nanocluster loading by using spectroscopic properties. In addition, the Ag NCs@Eu-MOF also shows a good catalytic activity for cycloaddition reaction from CO₂ and epoxides. This study not only provides ideas for exploring the changes in optical properties of luminescent MOFs and Ag NCs caused by confinement effect, but also expands their potential applications in various fields.