Ultrafast Electron Dynamics in Thiolate-Protected Plasmonic Gold Clusters: Size and Ligand Effect

The influence of passivating ligands on electron–phonon relaxation dynamics of the smallest-sized gold clusters was studied using ultrafast transient absorption spectroscopy and theoretical modeling. The electron dynamics in Au279, Au329, and Au329 passivated with 4-tert-butylbenzene thiol (TBBT), phenylethane thiol (SC2Ph), and hexane thiol (SC6), respectively, were investigated. These clusters were chosen as they are the smallest gold clusters reported till-date to show plasmonic behavior. Ultrafast transient absorption measurements were also carried out on Au∼1400 (SC6) and Au∼2000 (SC6) to understand the influence of the size on electron–phonon relaxation with the same passivating ligand. The study has revealed interesting aspects on the role of ligands on electron–phonon relaxation dynamics wherein the aromatic passivating ligands, SC2Ph and TBBT, have shown smaller power dependence and broader surface plasmon bleach, indicating dampened plasmon resonance, whereas the cluster with aliphatic passivati...