Heterometal Doping Modulates Luminescent and Chiroptical Behavior in Superatomic M₁Ag₁₄ (M = Pd, Pt) Clusters

Abstract

Incorporating lower-valent heterometal dopants into ligand-protected superatomic metal clusters is a key strategy for tuning their optical properties and stability. However, the precise doping effects in such clusters remain poorly understood. In this study, three pairs of 8-electron superatomic alloy clusters stabilized by diphosphine ligands: one pair with 1,3-bis(diphenyphosphino)propane ligand ([M1Ag14(DPPP)6Cl4](OTf)2, abbr. M1Ag14; M = Pd, Pt) is presented, while the other two pairs with chiral 2,4-bis(diphenylphosphino)pentane ligand (R/S-Pe-Pd1Ag14 and R/S-Pe-Pt1Ag14) synthesized by replacement of ligand. The regulatory mechanism of the single central atom substituting to the clusters' optical properties is systematically investigated, including absorption, photoluminescence, and chiroptical activity, demonstrating that Pt doping increases the HOMO–LUMO energy gap and boosts the photoluminescence quantum yield (PLQY) of Pt₁Ag₁₄, while Pd doping uniquely extends the emission lifetime of Pd₁Ag₁₄ by reducing radiative decay rates–deviating from the energy gap law. Femtosecond-to-nanosecond transient absorption spectroscopy further clarifies the luminescence mechanism and excited-state dynamics of M₁Ag₁₄, revealing the origin of both triplet-state emission and the remarkable aggregation-induced PL enhancement. Besides, the enantiomeric R/S-Pe-M₁Ag₁₄ clusters display strong chiroptical activity mediated by the central dopant atom via modulation of electric-magnetic dipole transition competition.