Superatomic interconversion causes reversible on-off luminescence of doped silver nanoclusters

Abstract

Superatomic metal nanoclusters (NCs) often exhibit typically enhanced stability, granted by electron-shell closure and ligand protection, but also result in a considerable challenge for achieving reversible structural interconversion between homologous systems. Here we report two classes of superatomic NCs, [M1Ag14(DPPP)6Cl4]2+ and [M1Ag18(DPPP)6Cl8]2+ (M = Pd, Pt; DPPP = 1,3-bis(diphenylphosphine)propane), which undergo reversible stimuli-responsive transformation triggered simply by UV light and polar solvents, accompanied by a 48-fold increase or decrease in the luminescence intensity. These superatoms feature the same icosahedral M@Ag12 core and a closed shell of eight electrons pertaining to superatomic electronic configuration of 1S21P6. The rigid structure of [M1Ag14(DPPP)6Cl4]2+, with its uniform μ₄-Ag coordination, suppresses non-radiative decay to "turn on" emission. In contrast, the flexible structure of [M1Ag18(DPPP)6Cl8]2+ facilitates vibrational energy dissipation and consequently quenches the luminescence. Femtosecond transient absorption spectroscopy revealed a shell-mediated emission mechanism, in which the surface rigidification switches the electronic configuration from the singlet state (M1Ag18) to the triplet state (M1Ag14). Furthermore, dopant-dependent HOMO-LUMO gaps and core-shell charge distribution dictate their stability and transformation kinetics. This work underscores the potential of surface engineering and heteroatom doping to regulate photophysical behaviors of superatoms, thereby paving the way for the rational design of stimuli-responsive luminescent nanomaterials.