Luminescence is one of the most important properties for metal nanoclusters; however, clearly revealing its origin remains challenging. The different luminescence properties of the two prototypical 8e nanoclusters Au₁₁ and Au₁₃ remain elusive—Au₁₁ is always nonluminescent, whereas Au₁₃ is luminescent. In this work, by using a designed unique aromatic ligand (quinoline-2-thiol), we obtained new atomically precise phosphine-thiolate-protected neutral Au₁₁-SH and cationic Au₁₃-SH. In comparison with the classic phosphine-halide-protected Au₁₁-Cl and Au₁₃-Cl, the Cl-to-thiol alteration triggered room-temperature luminescence of the Au₁₁ core and dramatically modulated that of the Au₁₃ core. Ultrafast ultraviolet/infrared (UV/IR) spectroscopy, which is sensitive to organic aromatic groups, together with ultrafast transient absorption (TA) spectroscopy unprecedently revealed a relaxation process from the ligand to core state affecting the dynamics in excited states and some critical intermediate states favouring efficient room-temperature emission of these nanoclusters. This work provides some new insights into the origin of photoluminescence of metal nanoclusters and opens an avenue to modulate the dynamics of their excited states using aromatic ligands, which would have direct applications in lighting, light harvesting, and photocatalysis.

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.