Synthesis of silica-stabilized Ag₄₄ clusters aided by a designed mercaptosilane ligand

The novel and precise design of both a microscopic ligand and macroscopic structure has been demonstrated to improve the stability and potential optical applications of Ag44 clusters. The ligand with designed silane substituents on its thiophenol enabled the synthesized [Ag44(SPhSi(OEt)3)30](PPh4)4 clusters to maintain UV-vis absorption for 13 h when heated at 60 °C in air and be readily coated with silica shells via a one-pot reverse microemulsion method. This composite structure overcomes the issue that non-luminescent Ag44 clusters cannot be applied in photothermal and photoacoustic imaging due to their instability.