Optical Properties and Electronic Energy Relaxation of Metallic Au₁₄₄(SR)₆₀ Nanoclusters

Electronic energy relaxation of Au₁₄₄(SR)₆₀^q ligand-protected nanoclusters, where SR = SC₆H₁₃ and <i>q</i> = −1, 0, +1, and +2, was examined using femtosecond time-resolved transient absorption spectroscopy. The observed differential transient spectra contained three distinct components: (1) transient bleaches at 525 and 600 nm, (2) broad visible excited-state absorption (ESA), and (3) stimulated emission (SE) at 670 nm. The bleach recovery kinetics depended upon the excitation pulse energy and were thus attributed to electron–phonon coupling typical of metallic nanostructures. The prominent bleach at 525 nm was assigned to a core-localized plasmon resonance (CLPR). ESA decay kinetics were oxidation-state dependent and could be described using a metal-sphere charging model. The dynamics, emission energy, and intensity of the SE peak exhibited dielectric-dependent responses indicative of Superatom charge transfer states. On the basis of these data, the Au₁₄₄(SR)₆₀ system is the smallest-known nanocluster to exhibit quantifiable electron dynamics and optical properties characteristic of metals

Structural Basis for Ligand Exchange on Au₂₅(SR)₁₈

The single-crystal X-ray structure of Au₂₅(SC₂H₄Ph)₁₆(pBBT)₂ is presented. The crystallized compound resulted from ligand exchange of Au₂₅(SC₂H₄Ph)₁₈ with pBBT as the incoming ligand, and for the first time, ligand exchange is structurally resolved on the widely studied Au₂₅(SR)₁₈ compound. A single ligand in the asymmetric unit is observed to exchange, corresponding to two ligands in the molecule because of the crystallographic symmetry. The ligand-exchanged Au₂₅ is bonded to the most solvent-exposed Au atom in the structure, making the exchange event consistent with an associative mechanism. The apparent nonexchange of other ligands is rationalized through possible selective crystallization of the observed product and differential bond lengths

Electrophoretic Mechanism of Au₂₅(SR)₁₈ Heating in Radiofrequency Fields

Gold nanoparticles in radiofrequency (RF) fields have been observed to heat. There is some debate over the mechanism of heating. Au₂₅(SR)₁₈ in RF is studied for the mechanistic insights obtainable from precise synthetic control over exact charge, size, and spin for this nanoparticle. An electrophoretic mechanism can adequately account for the observed heat. This study adds a new level of understanding to gold particle heating experiments, allowing for the first time a conclusive connection between theoretical and experimentally observed heating rates

Structural Basis for Ligand Exchange on Au₂₅(SR)₁₈

The single-crystal X-ray structure of Au₂₅(SC₂H₄Ph)₁₆(pBBT)₂ is presented. The crystallized compound resulted from ligand exchange of Au₂₅(SC₂H₄Ph)₁₈ with pBBT as the incoming ligand, and for the first time, ligand exchange is structurally resolved on the widely studied Au₂₅(SR)₁₈ compound. A single ligand in the asymmetric unit is observed to exchange, corresponding to two ligands in the molecule because of the crystallographic symmetry. The ligand-exchanged Au₂₅ is bonded to the most solvent-exposed Au atom in the structure, making the exchange event consistent with an associative mechanism. The apparent nonexchange of other ligands is rationalized through possible selective crystallization of the observed product and differential bond lengths