Synthesis of Au ₁₃ -based building block clusters for programmed dimer formation and Au ₁₃ cluster dimer photoexcitation properties

Recently, there has been increasing attention on the fabrication of ligand-protected metal clusters composed of a finite number of noble metal atoms and on their precise assembly to elicit novel properties that are not observed in individual metal clusters. In the present study, we investigated (1) the behavior of ligand exchange reactions and (2) the selective and efficient formation of dimers composed of Au₁₃ clusters. Specifically, we focused on a gold cluster consisting of 13 atoms coordinated to diphosphine ligands (dppe) and either chloride (Cl) or acetylide, i.e., [Au₁₃(dppe)₅X₂]³⁺ (X = Cl or acetylide). The findings showed that Au₁₃ clusters containing the counter anion Cl^- undergo a transformation under specific conditions, where Cl^- acts as a ligand (rather than an anion) directly coordinated to the Au₁₃ surface. The introduction of two types of ligands-chelating ligands that coordinate to the Au₁₃ cluster surface and end-capping ligands that suppress polymerization-enabled the synthesis of building block molecules that are programmed to selectively and spontaneously form Au₁₃-based dimers upon the addition of metal ions. The designed building block clusters indeed selectively and efficiently formed stable dimers composed of two Au₁₃ clusters in the presence of iron ions. Furthermore, in the Au₁₃-based dimer, the phosphorescent Au₁₃ moiety is directly connected to a coordination site that exhibits quenching effects, enabling rapid intramolecular photoinduced charge transfer even with a small driving force.