Luminescence modulation of ultrasmall gold clusters by aromatic ligands

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.