Highly fluorescent, water-soluble, few-atom noble-metal quantum dots have been created that behave as multielectron artificial atoms with discrete, size-tunable electronic transitions throughout the visible and near infrared. These molecular metals exhibit highly polarizable transitions and scale in size according to the simple relation EFermi/N1/3, predicted by the free-electron model of metallic behavior. This simple scaling indicates that fluorescence arises from intraband transitions of free electrons, and these conduction-electron transitions are the low-number limit of the plasmon—the collective dipole oscillations occurring when a continuous density of states is reached. Providing the missing link between atomic and nanoparticle behavior in noble metals, these emissive, water-soluble Au nanoclusters open new opportunities for biological labels, energy-transfer pairs, and light-emitting sources in nanoscale optoelectronics.

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Highly fluorescent noble-metal quantum dots.

Metal nanoclusters: New fluorescent probes for sensors and bioimaging

This critical review highlights recent advances in using electronic structure methods to study surface-enhanced Raman scattering Examples showing how electronic structure methods, in particular time-dependent density functional theory, can be used to gain microscopic insights into the enhancement mechanism are presented (150 references)

Electronic structure methods for studying surface-enhanced Raman scattering.

Thiolate-protected metal nanoclusters (or thiolated metal NCs) have recently emerged as a promising class of functional materials because of their well-defined molecular structures and intriguing molecular-like properties. Recent developments in the NC field have aimed at exploring metal NCs as novel luminescent materials in the biomedical field because of their inherent biocompatibility and good photoluminescence (PL) properties. From the fundamental perspective, recent advances in the field have also aimed at addressing the fundamental aspects of PL properties of metal NCs, shedding some light on developing efficient strategies to prepare highly luminescent metal NCs. In this Perspective, we discuss the physical chemistry of a recently discovered aggregation-induced emission (AIE) phenomenon and show the significance of AIE in understanding the PL properties of thiolated metal NCs. We then explore the unique physicochemical properties of thiolated metal NCs with AIE characteristics and highlight some re...

Luminescent Metal Nanoclusters with Aggregation-Induced Emission.

Electronic and atomic structure, and magnetism of transition-metal clusters.

The optical absorption spectra of a series of small gold clusters and their cations have been measured, between 1.9 and 5.6 eV, using a method based upon the photodepletion of a molecular beam of their van der Waals complexes containing one and two xenon atoms. This method provides size‐specific information even though the molecular beam contains a wide range of cluster sizes. There is little difference between the spectra of complexes containing one or two xenon atoms. However there is a pronounced odd–even alternation in the spectra of gold clusters with differing numbers of valence s electrons. This alternation is described in terms of a simple electron pairing scheme. The spectrum for Au13 is in reasonable agreement with Dirac scattered‐wave molecular orbital considerations for icosahedral Au13 [A. F. Ramos, R. Arratia‐Perez, and G. L. Malli, Phys. Rev. B 35, 3790 (1987)]. This description of the molecular and electronic structure of small gold clusters in terms of localized molecular orbitals is contrasted with other models based upon jellium potentials and delocalized excitations that have been used to describe small clusters of alkali metals and silver. The bonding in gold clusters is influenced by relativistic effects that increase the degree of sd hybridization in the molecular orbitals. Even though gold clusters can be described in this way, some evidence for electron shells is also presented. Thus, it is concluded that structural motifs other than jellium potentials can lead to shell structure in cluster properties.

K. Athanassenas

Papers

Optical absorption spectra of au7, au9, au11, and au13, and their cations : gold clusters with 6, 7, 8, 9, 10, 11, 12, and 13 s-electrons

Optical Absorption Spectra of Au7, Au9, Au11, and Au13, and Their Cations: Gold Clusters with 6, 7, 8, 9, 10, 11, 12, and 13 s‐Electrons