A Single Model for the Excited-State Dynamics of Au₁₈(SR)₁₄ and Au₂₅(SR)₁₈ Clusters

Excited-state properties of photonic materials play an important part in dictating the photocatalytic activity. Thiol-protected gold clusters, like Au₁₈(SR)₁₄ and Au₂₅(SR)₁₈, are an emerging material of interest with unique optical and electronic properties. Au₁₈(SR)₁₄ clusters, in particular, have shown promise as one of the highest efficiency clusters in light harvesting, with a high emission quantum yield. In this work, the excited-state properties of Au₁₈(SR)₁₄ are studied in-depth by ultrafast pump/probe spectroscopy for the first time. A single model describing the optical characteristics of thiol-protected Au₁₈(SR)₁₄ and Au₂₅(SR)₁₈ clusters is offered. Excited-state dynamics analysis suggests that there are state-resolved relaxations due to the presence of multiple excited states. The populations of these excited states are shown to be solvent- and ligand-dependent.