Synthesis of Au13-based building block clusters for programmed dimer formation and Au13 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 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 a building block molecule which 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.