Unlocking luminescence by decoupling quenching vibrations in Au21SR17 nanoclusters: backbone flexibility versus ligand dynamics

Abstract

We designed a vibrationally decoupled model system, the non-emissive Au₂₁Cys₁₇, featuring a structurally identified flexible Au₄S₅ segment exclusively within its backbone. Glycerol switched on its emission via a dual mechanism: local hydrogen-bonding that rigidifies the flexible Au₄S₅ segment at low concentration and bulk viscous damping of ligand vibrations that dominates at high concentrations. The emissive Au₂₂SG₁₈, lacking such a flexible site, responds only to viscosity. This work provides the first direct experimental discrimination between backbone- and ligand-dominated quenching pathways and establishes site-specific staple rigidity as a critical design principle for luminescent nanomaterials.