Direct versus ligand-exchange synthesis of [PtAg(BDT)(TPP)] nanoclusters: effect of a single-atom dopant on the optoelectronic and chemical properties.

Heteroatom doping of atomically precise nanoclusters (NCs) often yields a mixture of doped and undoped products of single-atom difference, whose separation is extremely difficult. To overcome this challenge, novel synthesis methods are required to offer monodisperse doped NCs. For instance, the direct synthesis of PtAg NCs produces a mixture of [Ag(BDT)(TPP)] and [PtAg(BDT)(TPP)] NCs (TPP: triphenylphosphine; BDT: 1,3-benzenedithiolate). Here, we designed a ligand-exchange (LE) strategy to synthesize single-sized, Pt-doped, superatomic Ag NCs [PtAg(BDT)(TPP)] by LE of [PtAgCl(TPP)] NCs with BDTH (1,3-benzenedithiol). The doped NCs were thoroughly characterized by optical and photoelectron spectroscopy, mass spectrometry, total electron count, and time-dependent density functional theory (TDDFT). We show that the Pt dopant occupies the center of the PtAg cluster, modulates its electronic structure and enhances its photoluminescence intensity and excited-state lifetime, and also enables solvent interactions with the NC surface. Furthermore, doped NCs showed unique reactivity with metal ions - the central Pt atom of PtAg could not be replaced by Au, unlike the central Ag of Ag NCs. The achieved synthesis of single-sized PtAg clusters will facilitate further applications of the LE strategy for the exploration of novel multimetallic NCs.