Colloidal nanoparticles are being intensely pursued in current nanoscience research. Nanochemists are often frustrated by the well-known fact that no two nanoparticles are the same, which precludes the deep understanding of many fundamental properties of colloidal nanoparticles in which the total structures (core plus surface) must be known. Therefore, controlling nanoparticles with atomic precision and solving their total structures have long been major dreams for nanochemists. Recently, these goals are partially fulfilled in the case of gold nanoparticles, at least in the ultrasmall size regime (1–3 nm in diameter, often called nanoclusters). This review summarizes the major progress in the field, including the principles that permit atomically precise synthesis, new types of atomic structures, and unique physical and chemical properties of atomically precise nanoparticles, as well as exciting opportunities for nanochemists to understand very fundamental science of colloidal nanoparticles (such as the s...

Atomically Precise Colloidal Metal Nanoclusters and Nanoparticles: Fundamentals and Opportunities

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Atomically precise pieces of matter of nanometer dimensions composed of noble metals are new categories of materials with many unusual properties. Over 100 molecules of this kind with formulas such as Au25(SR)18, Au38(SR)24, and Au102(SR)44 as well as Ag25(SR)18, Ag29(S2R)12, and Ag44(SR)30 (often with a few counterions to compensate charges) are known now. They can be made reproducibly with robust synthetic protocols, resulting in colored solutions, yielding powders or diffractable crystals. They are distinctly different from nanoparticles in their spectroscopic properties such as optical absorption and emission, showing well-defined features, just like molecules. They show isotopically resolved molecular ion peaks in mass spectra and provide diverse information when examined through multiple instrumental methods. Most important of these properties is luminescence, often in the visible–near-infrared window, useful in biological applications. Luminescence in the visible region, especially by clusters prot...

Atomically Precise Clusters of Noble Metals: Emerging Link between Atoms and Nanoparticles

Due to their atomically precise structures and intriguing chemical/physical properties, metal nanoclusters are an emerging class of modular nanomaterials. Photo-luminescence (PL) is one of their most fascinating properties, due to the plethora of promising PL-based applications, such as chemical sensing, bio-imaging, cell labeling, phototherapy, drug delivery, and so on. However, the PL of most current nanoclusters is still unsatisfactory-the PL quantum yield (QY) is relatively low (generally lower than 20%), the emission lifetimes are generally in the nanosecond range, and the emitted color is always red (emission wavelengths of above 630 nm). To address these shortcomings, several strategies have been adopted, and are reviewed herein: capped-ligand engineering, metallic kernel alloying, aggregation-induced emission, self-assembly of nanocluster building blocks into cluster-based networks, and adjustments on external environment factors. We further review promising applications of these fluorescent nanoclusters, with particular focus on their potential to impact the fields of chemical sensing, bio-imaging, and bio-labeling. Finally, scope for improvements and future perspectives of these novel nanomaterials are highlighted as well. Our intended audience is the broader scientific community interested in the fluorescence of metal nanoclusters, and our review hopefully opens up new horizons for these scientists to manipulate PL properties of nanoclusters. This review is based on publications available up to December 2018.

Tailoring the photoluminescence of atomically precise nanoclusters.

ConspectusA comprehensive understanding of chemical bonding and reactions at the surface of nanomaterials is of great importance in the rational design of their functional properties and applicatio...

Surface Chemistry of Atomically Precise Coinage-Metal Nanoclusters: From Structural Control to Surface Reactivity and Catalysis.

Quantum Mechanical Studies of Large Metal, Metal Oxide, and Metal Chalcogenide Nanoparticles and Clusters.

Understanding fundamental behavior of luminescent nanomaterials upon photoexcitation is necessary to expand photocatalytic and biological imaging applications. Despite the significant amount of experimental work into the luminescence of Au25(SR)18– clusters, the origin of photoluminescence in these clusters still remains unclear. In this study, the geometric and electronic structural changes of the Au25(SR)18– (R = H, CH3, CH2CH3, CH2CH2CH3) nanoclusters upon photoexcitation are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the optimized excited states of up to 0.33 A impart remarkable effects on the energy levels of the frontier orbitals of Au25(SR)18– nanoclusters. This gives rise to a Stokes shift of 0.49 eV for Au25(SH)18– in agreement with experiments. Even larger Stokes shifts are predicted for longer ligands. Vibrational frequencies in the 75–80 cm–1 range are calculated for the nuclear motion involved in the excited-state nuclear relaxation; th...

Theoretical Insights into the Origin of Photoluminescence of Au25(SR)18- Nanoparticles

Ligand-stabilized gold and silver nanoparticles are of tremendous current interest in sensing, catalysis, and energy applications. Experimental and theoretical studies have closely interacted to elucidate properties such as the geometric and electronic structures of these fascinating systems. In this review, the interplay between theory and experiment is described; areas such as optical absorption and doping, where the theory–experiment connections are well established, are discussed in detail; and the current status of these connections in newer fields of study, such as luminescence, transient absorption, and the effects of solvent and the surrounding environment, are highlighted. Close communication between theory and experiment has been extremely valuable for developing an understanding of these nanocluster systems in the past decade and will undoubtedly continue to play a major role in future years. Expected final online publication date for the Annual Review of Physical Chemistry Volume 69 is April 2...

Connections Between Theory and Experiment for Gold and Silver Nanoclusters

Recent theoretical insights into the origin of photoluminescence of thiolate-protected gold nanoclusters raise the question of whether the observed luminescence mechanism is valid for related silver nanoparticles. To this end, we perform density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations on the Ag25(SR)18– (R = H, PhMe2) nanocluster, which is currently the only thiolate-protected silver cluster that has a matching analogue in gold. The geometric and electronic structural modifications of Ag25(SH)18– upon photoexcitation are found to be similar but less pronounced than those of Au25(SH)18– at the same level of theory. The Stokes shift is calculated to be 0.37 eV and the replacement of R = H model ligands by R = PhMe2 decreases the Stokes shift in contrast to the increase in Stokes shift for aliphatic ligands previously observed in the Au25 system. The calculated emission energy agrees well with the experimental photoluminescence energy when the typical underes...

Origin of Photoluminescence of Ag25(SR)18– Nanoparticles: Ligand and Doping Effect

Photoluminescence of metal nanoparticles has drawn considerable research interest due to their potential fundamental and industrial applications in optoelectronics and biomedicine. However, the origin and underlying mechanism of photoluminescence in these clusters still need to be explored. Herein, the geometrical and electronic structural changes upon photoexcitation in the Au38(SH)24 and Au22(SH)18 nanoclusters are discussed using time-dependent density functional theory (TD-DFT) methods. Geometric relaxations in the Au23 core of Au38(SH)24 up to a maximum of 0.05 A lead to slight electronic structure changes in the optimized singlet excited states with different state symmetries. The observed geometric and electronic structure variations upon photoexcitation are minor compared to the previously studied Au25(SH)18– nanoparticle. These small distortions can be correlated with small Stokes shifts calculated in the range of 0.06–0.09 eV in comparison to 0.49 eV for the Au25(SH)18– nanoparticle. Compared to...

K. L. Dimuthu M. Weerawardene

Papers

Quantum Mechanical Studies of Large Metal, Metal Oxide, and Metal Chalcogenide Nanoparticles and Clusters.

Theoretical Insights into the Origin of Photoluminescence of Au25(SR)18- Nanoparticles

Connections Between Theory and Experiment for Gold and Silver Nanoclusters

Origin of Photoluminescence of Ag25(SR)18– Nanoparticles: Ligand and Doping Effect

Photoluminescence Origin of Au38(SR)24 and Au22(SR)18 Nanoparticles: A Theoretical Perspective