Concomitant Near-Infrared Photothermy and Photoluminescence of Rod-Shaped Au52(PET)32 and Au66(PET)38 Synthesized Concurrently.

Gold nanoclusters exhibiting concomitant photothermy (PT) and photoluminescence (PL) under near-infrared (NIR) light irradiation are rarely reported, and some fundamental issues remain unresolved for such materials. Herein, we concurrently synthesized two novel rod-shaped Au nanoclusters, Au52(PET)32 and Au66(PET)38 (PET = 2-phenylethanethiol), and precisely revealed that their kernels were 4 × 4 × 6 and 5 × 4 × 6 face-centered cubic (fcc) structures, respectively, based on the numbers of Au layers in the [100], [010], and [001] directions. Following the structural growth mode from Au52(PET)32 to Au66(PET)38, we predicted six more novel nanoclusters. The concurrent synthesis provides rational comparison of the two nanoclusters on the stability, absorption, emission and photothermy, and reveals the aspect ratio-related properties. An interesting finding is that the two nanoclusters exhibit concomitant PT and PL under 785 nm light irradiation, and the PT and PL are in balance, which was explained by the qualitative evaluation of the radiative and non-radiative rates. The ligand effects on PT and PL were also investigated.

Atomically Precise Nanometer-Sized Pt Catalysts with an Additional Photothermy Functionality.

Atomically precise ~1-nm Pt nanoparticles (nanoclusters, NCs) with ambient stability are important in fundamental research and exhibit diverse practical applications (catalysis, biomedicine, etc.). However, synthesizing such materials is challenging. Herein, by employing the mixture ligand protecting strategy, we successfully synthesized the largest organic-ligand-protected (~1-nm) Pt23 NCs precisely characterized with mass spectrometry and single-crystal X-ray diffraction analyses. Interestingly, natural population analysis and Bader charge calculation indicate an alternate, varying charge -layer distribution in the sandwich-like Pt23 NC kernel. Pt23 NCs can catalyze the oxygen reduction reaction under acidic conditions without requiring calcination and other treatments, and the resulting specific and mass activities without further treatment are sevenfold and eightfold higher than those observed for commercial Pt/C catalysts, respectively. Density functional theory and d-band center calculations interpret the high activity. Furthermore, Pt23 NCs exhibit a photothermal conversion efficiency of 68.4 % under 532-nm laser irradiation and can be used at least for six cycles, thus demonstrating great potential for practical applications.

Bottom-Up Construction of Metal-Organic Framework Loricae on Metal Nanoclusters with Consecutive Single Nonmetal Atom Tuning for Tailored Catalysis.

The introduction of single or multiple heterometal atoms into metal nanoparticles is a well-known strategy for altering their structures (compositions) and properties. However, surface single nonmetal atom doping is challenging and rarely reported. For the first time, we have developed synthetic methods, realizing "surgery"-like, successive surface single nonmetal atom doping, replacement, and addition for ultrasmall metal nanoparticles (metal nanoclusters, NCs), and successfully synthesized and characterized three novel bcc metal NCs Au38I(S-Adm)19, Au38S(S-Adm)20, and Au38IS(S-Adm)19 (S-Adm: 1-adamantanethiolate). The influences of single nonmetal atom replacement and addition on the NC structure and optical properties (including absorption and photoluminescence) were carefully investigated, providing insights into the structure (composition)-property correlation. Furthermore, a bottom-up method was employed to construct a metal-organic framework (MOF) on the NC surface, which did not essentially alter the metal NC structure but led to the partial release of surface ligands and stimulated metal NC activity for catalyzing p-nitrophenol reduction. Furthermore, surface MOF construction enhanced NC stability and water solubility, providing another dimension for tunning NC catalytic activity by modifying MOF functional groups.

Controlled Sequential Doping of Metal Nanocluster.

Atomically precise doping of metal nanoclusters provides excellent opportunities not only for subtly tailoring their properties but also for in-depth understanding of composition (structure)-property correlation of metal nanoclusters and has attracted increasing interest partly due to its significance for fundamental research and practical applications. Although single and multiple metal atom doping of metal nanoclusters (NCs) has been achieved, sequential single-to-multiple metal atom doping is still a big challenge and has not yet been reported. Herein, by introducing a second ligand, a novel multistep synthesis method was developed, controlled sequential single-to-multiple metal atom doping was successfully achieved for the first time, and three doped NCs Au25Cd1(p-MBT)17(PPh3)2, Au18Cd2(p-MBT)14(PPh3)2, and [Au19Cd3(p-MBT)18]- (p-MBTH: para-methylbenzenethiol) were obtained, including two novel NCs that were precisely characterized via mass spectrometry, single-crystal X-ray crystallography, and so forth. Furthermore, sequential doping-induced evolutions in the atomic and crystallographic structures and optical and catalytic properties of NCs were revealed.

Pd8 Nanocluster with Nonmetal-to-Metal- Ring Coordination and Promising Photothermal Conversion Efficiency.

Constructing ambient-stable, single-atom-layered metal-based materials with atomic precision and understanding their underlying stability mechanisms are challenging. Here, stable single-atom-layered nanoclusters of Pd were synthesized and precisely characterized through electrospray ionization mass spectrometry and single-crystal X-ray crystallography. A pseudo-pentalene-like Pd8 unit was found in the nanocluster, interacting with two syn PPh units through nonmetal-to-metal -ring coordination. The unexpected coordination, which is distinctly different from the typical organoring-to-metal coordination in half-sandwich-type organometallic compounds, contributes to the ambient stability of the as-obtained single-atom-layered nanocluster as revealed through theoretical and experimental analyses. Furthermore, quantum chemical calculations revealed dominant electron transition along the horizontal x-direction of the Pd8 plane, indicating high photothermal conversion efficiency (PCE) of the nanocluster, which was verified by the experimental PCE of 73.3 %. Therefore, this study unveils the birth of a novel type of compound and the finding of the unusual nonmetal-to-metal -ring coordination and has important implications for future syntheses, structures, properties, and structure-property correlations of single-atom-layered metal-based materials.

Lattice Compression Revealed at the ≈1†nm Scale.

Lattice tuning at the ≈1 nm scale is fascinating and challenging; for instance, lattice compression at such a minuscule scale has not been observed. The lattice compression might also bring about some unusual properties, which waits to be verified. Through ligand induction, we herein achieve the lattice compression in a ≈1 nm gold nanocluster for the first time, as detected by the single-crystal X-ray crystallography. In a freshly synthesized Au52 (CHT)28 (CHT=S-c-C6 H11 ) nanocluster, the lattice distance of the (110) facet is found to be compressed from 4.51 to 3.58 Šat the near end. However, the lattice distances of the (111) and (100) facets show no change in different positions. The lattice-compressed nanocluster exhibits superior electrocatalytic activity for the CO2 reduction reaction (CO2 RR) compared to that exhibited by the same-sized Au52 (TBBT)32 (TBBT=4-tert-butyl-benzenethiolate) nanocluster and larger Au nanocrystals without lattice variation, indicating that lattice tuning is an efficient method for tailoring the properties of metal nanoclusters. Further theoretical calculations explain the high CO2 RR performance of the lattice-compressed Au52 (CHT)28 and provide a correlation between its structure and catalytic activity.

Sandwich-Kernelled AgCu Nanoclusters with Golden Ratio Geometry and Promising Photothermal Efficiency.

Metal nanoclusters have recently attracted extensive interest from the scientific community. However, unlike carbon-based materials and metal nanocrystals, they rarely exhibit a sheet kernel structure, probably owing to the instability caused by the high exposure of metal atoms (particularly in the relatively less noble Ag or Cu nanoclusters) in such a structure. Herein, we synthesized a novel AgCu nanocluster with a sandwich-like kernel (diameter≈0.9 nm and length≈0.25 nm) by introducing the furfuryl mercaptan ligand (FUR) and the alloying strategy. Interestingly, the kernel consists of a centered silver atom and two planar Ag10 pentacle units with completely mirrored symmetry after a rotation of 36 degrees. The two Ag10 pentacles and some extended structures show an unreported golden ratio geometry, and the two inner five-membered rings and the centered Ag atom form an unanticipated full-metal ferrocene-like structure. The featured kernel structure causes the dominant radial direction transition of excitation electrons, as determined via time-dependent density functional theory calculations, which affords the protruding absorption at 612 nm and contributes to the promising photothermal conversion efficiency of 67.6 % of the as-obtained nanocluster, having important implications for structure-property correlation and the development of nanocluser-based photothermal materials.

Regulating the Electronic Structure of Metal Nanoclusters by Longitudinal Single-Dithiolate Substitution.

It is significant but challenging to understand the property evolution of metal nanoclusters by orientated regulation of the electronic structure. Previous research has demonstrated that the optical properties of metal nanoclusters with anisotropic structures are greatly impacted by their longitudinal electronic structure. However, the manipulation of optical properties of metal nanoclusters by regulating their electronic structure through longitudinal dithiolate substitutions has not yet been reported. In this study, we first achieved the longitudinal single-dithiolate replacement of metal nanoclusters and obtained two novel nanoclusters: Au28(SPh-tBu)18(SCH2SCH2S) and Au28(SPh-tBu)18(SCH2CH2CH2S). Both experimental and theoretical results demonstrated the regulation of the electronic structure (dipole moment) in the z (longitudinal) and x directions, resulting in absorption redshift and photoluminescence (polarity) enhancement. These findings not only deepen the understanding of the property-electronic structure correlation of metal nanoclusters but also provide guidance for their subtle property tuning.

Surface Site-Specific Replacement for Catalysis Selectivity Switching.

Surface atom replacement in materials without other composition/structure changes is challenging but is important for fundamental scientific research and for practical applications. In particular, for nanoparticles including nanoclusters, surface metal site-specific replacement with atomic precision has not yet been achieved. In this study, we for the first time achieved surface site-specific antigalvanic replacement with the remaining composition/structure and surface replacement-dependent selectivity in the electrocatalytic reduction of CO2. Density functional theory (DFT) calculations describe the catalysis selectivity switch induced by replacing Ag with Cu and explain why Cu replacement facilitates C2 production. Also, CO2 electroreduction to C2 on well-defined metal nanoclusters is first reported in this study.

Synthesizing Photoluminescent Au28 (SCH2 Ph-t Bu)22 Nanoclusters with Structural Features by Using a Combined Method.

We present a method for atomically precise nanocluster synthesis. As an illustration, we introduced the reducing-ligand induction combined method and synthesized a novel nanocluster, which was determined to be Au28 (SCH2 Ph-t Bu)22 with the same number of gold atoms as existing Au28 (SR)20 nanoclusters but different ligands (hetero-composition-homo-size). Compared with the latter, the former has distinct properties and structures. In particular, a novel kernel evolution pattern is reported, i.e., the quasi-linear growth of Au4 -tetrahedron by sharing one vertex and structural features, including a tritetrahedron kernel with two bridging thiolates and two Au6 (SCH2 Ph-t Bu)6 hexamer chair-like rings on the kernel surface were also first reported, which endow Au28 (SCH2 Ph-t Bu)22 with the best photoluminescence quantum yield among hydrophobic thiolated gold nanoclusters so far, probably due to the enhanced charge transfer from the bi-ring to the kernel via Au-Au bonds.

Unravelling the Structure of a Medium-Sized Metalloid Gold Nanocluster and its Filming Property.

Unravelling the structure of thiolated metalloid gold nanoclusters in the medium-sized range by single crystal X-ray crystallography (SCXC) is challenging. Herein, we successfully synthesized a novel Au67 (SR)35 nanocluster, and unravelled its single crystal structure by SCXC, which features a mix-structured Au48 kernel protected by one Au4 (SR)5 staple and fifteen Au(SR)2 staples. Unprecedentedly, this structure can be thermally induced to aggregate into larger nanoparticles and self-deposit to form a gold nanoparticles film onto the walls of a vial or other substrates such as quartz, mica or ceramic, which can be developed into a facile, substrate-universal and scalable filming method. The film exhibits high sensitivity, uniformity and recyclability as a surface-enhanced Raman scattering (SERS) substrate and can be applied for detecting multiple organic pollutants.

Traceless Removal of Two Kernel Atoms in a Gold Nanocluster and Its Impact on Photoluminescence.

Removing or adding kernel atoms of metal nanoclusters (NCs) without leaving a trace is a substantial challenge because the kernel atoms are inside and covered by the outer staples. However, such kernel tuning is very important for improving the properties and acquiring an in-depth understanding of the kernel-property correlation. Photoluminescence (PL) is one of the most intriguing characteristics of metal NCs but has not been well understood until now. Inspired by these challenges/questions, we conducted this study and, for the first time, achieved the traceless removal of two kernel atoms in a gold nanocluster by applying a simple thermal treatment and revealed its impact on PL. Further, we demonstrated that the kernel Au-Au bond length can be an indicator for a comparison of the PL or kernel charge state between nanoclusters with similar kernel structures and sizes.

Distance makes a difference in crystalline photoluminescence.

Crystallization-induced photoluminescence weakening was recently revealed in ultrasmall metal nanoparticles. However, the fundamentals of the phenomenon are not understood yet. By obtaining conformational isomer crystals of gold nanoclusters, we investigate crystallization-induced photoluminescence weakening and reveal that the shortening of interparticle distance decreases photoluminescence, which is further supported by high-pressure photoluminescence experiments. To interpret this, we propose a distance-dependent non-radiative transfer model of excitation electrons and support it with additional theoretical and experimental results. This model can also explain both aggregation-induced quenching and aggregation-induced emission phenomena. This work improves our understanding of aggregated-state photoluminescence, contributes to the concept of conformational isomerism in nanoclusters, and demonstrates the utility of high pressure studies in nanochemistry.

A Dual Purpose Strategy to Endow Gold Nanoclusters with Both Catalysis Activity and Water Solubility.

Gold nanoclusters have attracted extensive interest for catalysis applications in recent years due to their ultrasmall sizes and well-defined compositions and structures. However, at least two challenges exist in this emerging field. First, the steric hindrance of the ligands inhibits the catalysis activity, and second, the mechanism underlying water-phase catalysis using gold nanoclusters is often ambiguous. Herein, we introduce a "kill two birds with one stone" strategy to address these two challenges via the use of host-guest chemistry. As an illustration, a novel adamantanethiolate-protected Au40(S-Adm)22 nanocluster was synthesized, bound with γ-CD-MOF, and then transferred to the HRP-mimicking reaction system. The as-obtained catalyst exhibits excellent water solubility and catalytical activity, totally different from the virgin Au40(S-Adm)22 nanoclusters. Further, the detailed HRP-mimicking catalysis mechanism was proposed and supported by DFT calculation. Another interesting finding is the unique structure of Au40(S-Adm)22, which can be regarded as an Au13 icosahedron unit derived structure but different from the widely reported icosahedron contained nanocluster where the Au13 icosahedrons are often centered. These novel, intriguing results have important implication for the property tuning and practical application of metal nanoclusters in the future.

Kernel Homology in Gold Nanoclusters.

Homology is well known in organic chemistry; however, it has not yet been reported in nanochemistry. Herein, we introduce the concept of kernel homology to describe the phenomenon of metal nanoclusters sharing the same "functional group" in kernels with some similar properties. To illustrate this point, we synthesized two novel gold nanoclusters, Au44 (TBBT)26 and Au48 (TBBT)28 (TBBTH=4-tert-butylbenzenethiol), and solved their total structures by X-ray crystallography, which reveals that they have the same Au23 bi-icosahedron capped with a similar bottom cap (Au6 and Au8 , respectively) in the kernels. The two novel gold nanoclusters, together with the existing Au38 (PET)24 nanocluster (PETH=phenylethanethiol), have the same "functional group"-Au23 -in their kernels and have some similar properties (e.g., electrochemical properties); therefore, they are comparable to the homologues in organic chemistry.

Real-Time X-ray Imaging Reveals Interfacial Growth, Suppression, and Dissolution of Zinc Dendrites Dependent on Anions of Ionic Liquid Additives for Rechargeable Battery Applications.

The dynamic interfacial growth, suppression, and dissolution of zinc dendrites have been studied with the imidazolium ionic liquids (ILs) as additives on the basis of in situ synchrotron radiation X-ray imaging. The phase contrast difference of real-time images indicates that zinc dendrites are preferentially developed on the substrate surface in the ammoniacal electrolytes. After adding imidazolium ILs, both nucleation overpotential and polarization extent increase in the order of additive-free < EMI-Cl < EMI-PF6 < EMI-TFSA < EMI-DCA. The real-time X-ray images show that the EMI-Cl can suppress zinc dendrites, but result in the formation of the loose deposits. The EMI-PF6 and EMI-TFSA additives can smooth the deposit morphology through suppressing the initiation and growth of dendritic zinc. The addition of EMI-DCA increases the number of dendrite initiation sites, whereas it decreases the growth rate of dendrites. Furthermore, the dissolution behaviors of zinc deposits are compared. The zinc dendrites show a slow dissolution process in the additive-free electrolyte, whereas zinc deposits are easily detached from the substrate in the presence of EMI-Cl, EMI-PF6, or EMI-TFSA due to the formation of the loose structure. Hence, the dependence of zinc dendrites on anions of imidazolium IL additives during both electrodeposition and dissolution processes has been elucidated. These results could provide the valuable information in perfecting the performance of zinc-based rechargeable batteries.