Chiral Hydride Cu18 Clusters Transform to Superatomic Cu15Ag4 Clusters: Circularly Polarized Luminescence Lighting

All-Alkynyl Protected Rod-Shaped Au9(AgCu)126 Nanocluster with Remarkable Photothermal Conversion

High-nuclearity intermetallic nanoclusters are important for investigating the evolution of alloy materials from atoms to plasmonic alloy nanoparticles. However, the synthesis of large-size alloy nanoclusters (∼2 nm) is still challenging. In this work, an all-alkynyl protected trimetallic nanocluster of unprecedented size, Au9Ag126- xCux(PhCC)68(BF4)5 (x = 0-20) (1) (PhCC = phenylacetylene), has been synthesized and its total structure determined by single crystal X-ray diffraction (SCXRD). The metal core of 1 is rod-like in structure, with a length of 1.92 nm and a width of 1.45 nm. Cluster 1 contains a concentric metal kernel in the manner of shell-by-shell arrangements of Au3Ag34@Au6Ag64@(AgCu)28 protected by 68 PhCC ligands with 15 distinct alkynyl-metal binding configurations. Theoretic calculation reveals that 1 features a HOMO-LUMO energy gap of 0.29 eV. This suggests that 1 is situated at the boundary of the transition from a molecular to a metallic state. Remarkably, compared to other reported Au/Ag/Cu/Pd based nanoclusters, 1 exhibits significantly enhanced photothermal conversion capability. A substantial temperature rise of ∼51.5 °C within 5 min (λex = 660 nm, 0.5 W cm-2) and a record high photothermal conversion efficiency of 84.7% at 12 µM in N,N-dimethylformamide (DMF) were observed. Time-resolved transient absorption (TA) spectroscopy reveals that the electron-phonon coupling (τe-ph) of excited 1 occurs on the femtosecond timescale, resulting in an ultrafast electronic relaxation process and excellent photothermal performance. Cluster 1, when employed as a photothermal material, shows promise in biothermal therapy, photothermal catalysis, and photothermal imaging.

Observation of a Novel Interligand Chiral Arrangement in Metal Nanoclusters and Its Implication in Resisting Racemization

Given the scientifically significant importance of studying the chirality of clusters, the challenges of synthesizing chiral clusters are progressively surmounted. However, the racemization of clusters is unavoidable, and it limits the development of their follow-on chiral applications. To address this issue, chiral thiols are synthesized and used for the construction of high-stability optically pure nanoclusters in this work. As a result, a pair of chiral nanoclusters, Au24Cd2(SR)14, is obtained with excellent stability under thermal, acidic, alkaline, oxidizing, and reducing environments. Unexpectedly, it can also maintain its optical activity with the introduction of Cu2+ ions and chiral ligand with opposite configuration. Structural relationship analysis indicates that the excellent stability is mainly dependent on the hierarchical assembly of the nanoclusters, in which the chiral assembly of chiral ligands (a new pattern of chiral arrangement of intramolecular ligands on the surface of clusters) may be a key factor.

Metal Nanoclusters as Highly Efficient, Versatile Type-II Photoinitiators via Generating Radicals from Non-Conventional Hydrogen Donors

Development of highly efficient photocatalysis or photoinitiation systems that are applicable to various types of illumination source is critical to virtually all the light-driven applications. Here, we report a generalizable strategy to achieve highly sensitive, versatile photoinitiation systems based on the combination of metal nanoclusters with non-conventional hydrogen donors (co-initiators). Discovery of this type-II photoinitiation pathway in metal nanoclusters not only improves their two-photon initiation sensitivity by up to three-orders-of-magnitude, it further opens the door for metal nanoclusters to trigger the photopolymerization using the low-power UV light-emitting diodes. Different from molecular type-II photoinitiators, we found that the selection rules of hydrogen donors for metal nanoclusters are largely dependent on their ligand structures. More importantly, using electron paramagnetic resonance and mass spectroscopy, we for the first time demonstrate that the photoexcited metal nanoclusters can function as versatile hydrogen atom abstractors which generate various types of previously unreported thiyl and nitrogen-centered radicals. This finding indicates the broad opportunity of the future application of metal nanoclusters in light-driven organic synthesis and radical chemistry.

Silyl- and germyl-bridged neutral square-planar Ag4 clusters with short Ag-Ag distances exhibiting red emission

We report silyl- and germyl-bridged neutral square-planar Ag4 clusters with very short Ag-Ag distances (2.695 and 2.704 Å), as revealed by single-crystal X-ray diffraction analysis. On the basis of the results of theoretical calculations, we attribute these short distances to attractive Ag-Ag interactions that reduce the optical energy gap, resulting in a red emission reaching wavelengths of up to 700 nm. These wavelengths are among the longest observed for emissions from Ag4 clusters.

Thermally Activated Delayed Fluorescence-Based Near-Infrared-II Luminescence and Controlled Size Growth of Silver Nanoclusters

Due to the significant relationships between structure and properties, the controlled construction of atomically precise metal clusters presents both a formidable challenge and great importance. The innovative synthesis of well-defined silver nanoclusters with near-infrared II (NIR-II) luminescent properties may inspire further exploration of functional metal nanoclusters for bioimaging applications. In this study, we employed the multidentate chelating nitrogen ligand 3,5-di(2-pyridyl)pyrazole (Hbpypz) to construct three unprecedented silver nanoclusters: [Ag27(bpypz)14]3+ (Ag27), [Ag62(bpypz)18]6+ (Ag62), and [Ag91(bpypz)24]5+ (Ag91). Single-crystal X-ray analysis indicated that these cluster structures stem from Ag13 units, exhibiting cluster-of-cluster configurations. By modulating the stoichiometry of the chelating ligand and silver centers, we achieved controlled size growth and reversible cluster-to-cluster conversions among these silver nanoclusters. Notably, the Ag27 nanocluster exhibits an interesting thermally activated delayed fluorescence (TADF) based luminescence in the second near-infrared (NIR-II) region and demonstrates high catalytic efficiency in the oxidative coupling of benzylamines via a singlet oxygen (1O2) oxidation mechanism.

Site-specific substitution in atomically precise carboranethiol-protected nanoclusters and concomitant changes in electronic properties

We report the synthesis of [Ag17(o1-CBT)12]3- abbreviated as Ag17, a stable 8e⁻ anionic cluster with a unique Ag@Ag12@Ag4 core-shell structure, where o1-CBT is ortho-carborane-1-thiol. By substituting Ag atoms with Au and/or Cu at specific sites we created isostructural clusters [AuAg16(o1-CBT)12]3- (AuAg16), [Ag13Cu4(o1-CBT)12]3- (Ag13Cu4) and [AuAg12Cu4(o1-CBT)12]3- (AuAg12Cu4). These substitutions make systematic modulation of their structural and electronic properties. We show that Au preferentially occupies the core, while Cu localizes in the tetrahedral shell, influencing stability and structural diversity of the clusters. The band gap expands systematically (2.09 eV for Ag17 to 2.28 eV for AuAg12Cu4), altering optical absorption and emission. Ultrafast optical measurements reveal longer excited-state lifetimes for Cu-containing clusters, highlighting the effect of heteroatom incorporation. These results demonstrate a tunable platform for designing nanoclusters with tailored electronic properties, with implications for optoelectronics and catalysis.

Doping Copper(I) in Ag7 Cluster for Circularly Polarized OLEDs with External Quantum Efficiency of 26.7

Hetero-metal doping or substitution to create alloy clusters is a highly appealing strategy for improving physicochemical characteristics as well as tailoring optical and electronic properties, although high-yield synthesis of alloy clusters with precise positioning of doped metals is a daunting challenge. Herein, we manifest rational synthesis of chiral alloy cluster enantiomers R/S-Ag6Cu in 85 %-87 % yield by replacing one Ag(I) atom with Cu(I) in homometallic clusters R/S-Ag7, achieving circularly polarized luminescence (CPL) with a quantum yield beyond 90 %. As a small energy gap (ca. 0.07 eV) between S1 and T1 states facilitates thermally activated delay fluorescence (TADF) through reverse intersystem crossing (RISC), the photoluminescence (PL) of R/S-Ag7 and R/S-Ag6Cu at ambient temperature originates mostly from TADF (85 % and 86 %) in place of phosphorescence (15 % and 14 %). Relative to those of R/S-Ag7, copper(I) doping not only triples PL quantum yields of R/S-Ag6Cu due to accelerating ISC (intersystem crossing) and RISC, but also doubles CPL asymmetry factors of R/S-Ag6Cu ascribed to rigidizing cluster structure through stronger Ag-Cu interaction apart from dramatically improving thermodynamic stability. Solution-processable circularly polarized organic light-emitting diodes (CP-OLEDs) demonstrate high-efficiency circularly polarized electroluminescence (CPEL) with external quantum efficiency (EQE) of 26.7 %, which is superior to most of red-emitting OLEDs through solution process.

Recent Progress in Atomically Precise Cu-M Alloy Nanoclusters

Metal nanoclusters (NCs) with dimensions of approximately 3 nm serve as a crucial link between metal-organic complexes and metal nanoparticles, garnering significant interest due to their distinctive molecule-like characteristics. These include well-defined molecular structures, clear HOMO-LUMO transitions, quantized charge, and robust luminescence emission. Atomically precise alloy NCs, in contrast to homometallic NCs, exhibit a wealth of structures and intriguing properties, with their novel attributes often intricately tied to the positions of alloyed elements within the structure, facilitating the exploration of structure-property relationships. A notable subgroup within this category comprises Cu-M (where M represents metals such as Au, Ag, Rh, Ir, Pd, Pt, Zn, Al etc.) alloy NCs. In this review, we initially outline recent advancements in the development of efficient synthetic techniques for Cu-M alloy NCs, emphasizing the underlying physical and chemical properties that enable precise control over their sizes and surface characteristics. Subsequently, we delve into recent progress in structural elucidation techniques for Cu-M alloy NCs. This structural insight is instrumental in comprehensively understanding the structure-property correlations at the molecular level. Finally, we showcase various examples of Cu-M alloy NCs to illustrate their photoluminescent and catalytic properties, shedding light on their diverse functionalities and potential applications.

Thiacalix[4]arene-Stabilized Sb/Ag Bimetallic Nanoclusters: Elucidating the Effects of Sb Doping on Electrocatalytic CO2 Reduction in Ag Clusters

Accurately identifying the metal doping effects within heterogeneous catalysts presents a formidable challenge due to the complex nature of controlling the interfacial chemistry at the molecular level. Herein, we use two sets of atomically precise nanoclusters to demonstrate the impact of Sb doping on the electrocatalytic CO2 reduction activity in Ag nanoclusters. Leveraging the unique properties of the thiacalix[4]arene, we have pioneered a methodology for incorporating catalytic Ag1+ and Sb3+ sites, culminating in the synthesis of the pioneering Sb-Ag bimetallic cluster, Sb2Ag11. We refined this structure by replacing the two Sb3+ sites with Na+ sites, resulting in a Na2Ag10 cluster. Broadening our investigative scope, we isolated the core components from both Sb2Ag11 and Na2Ag10 and obtained two clusters: Sb2Ag4 and Ag4. The subtle compositional variations between two pairs of structurally analogous clusters, Sb2Ag11 and Na2Ag10, as well as Sb2Ag4 and Ag4, create opportunities to investigate how the Sb doping impacts the catalytic activity of Ag clusters. Clearly, compared to the undoped clusters, those doped with Sb exhibit higher catalytic current densities and enhanced CO selectivity. The theoretical calculations suggest that Sb doping can enhance the adsorption barrier of *H, thereby inhibiting hydrogen evolution activity and conversely promoting eCO2RR to CO activity.

Highly efficient circularly polarized electroluminescence based on chiral manganese(ii) complexes

Currently reported circularly polarized luminescent devices are primarily based on rare earth and noble metal complexes or lead perovskite materials. Reports on electroluminescent devices employing eco-friendly luminescent materials are notably scarce. In this study, we strategically designed and synthesized manganese complexes featuring Binapo as the chiral ligand. The complex structure reveals a tetrahedral coordination configuration, with the R/S configurations exhibiting a mirror relationship. Leveraging the strong ligand field and chiral structural characteristics of Binapo, the enantiomers display red emission and exhibit significant circularly polarized luminescence with a circularly polarized luminescence asymmetric factor (g lum) of 5.1 × 10-3. The circularly polarized electroluminescent performance was investigated by using a solution processing method and host-guest doping strategy. Our efforts resulted in device performance with an external quantum efficiency (EQE) exceeding 4%, and its electroluminescent asymmetric factor (g EL) reached an impressive -8.5 × 10-3. This surpasses the performance of most devices relying on platinum (Pt) and iridium (Ir) metal complexes and perovskite related materials. Our work establishes a pathway for the development of cost-effective and environmentally friendly chiral electroluminescent materials and devices.

Anomalous Structural Transformation of Cu(I) Clusters into Multifunctional CuAg Nanoclusters

We report an anomalous structural transformation of a Cu(I) cluster into two different types of copper-silver (CuAg) alloy nanoclusters. Different from previous reports, we demonstrate that under specifically designed reaction conditions, the Ag-doping could induce a substantial growth of the starting Cu15 and a Ag13Cu20 nanocluster was obtained via the unexpected insertion of an Ag13 kernel inside the Cu(I)-S shell. Ag13Cu20 demonstrates high activity to initiate the photopolymerization of previously hard-to-print inorganic polymers in 3D laser microprinting. Interestingly, a slight modification of the reaction condition leads to the formation of another Ag18-xCuxS (8≤x) nanocluster templated by a central S2- anion, which possesses a unique electronic structure compared to conventional template-free CuAg nanoclusters. Overall, this work unveils the intriguing doping chemistry of Cu clusters, as well as their capability to create different types of alloy nanoclusters with previously unobtainable structures and multifunctionality.

Influence of the substituents of the thiol ligand on the optical properties of AuCu14

Detailed photophysical processes of two AuCu14 clusters with different substituents (-F or -C(CH3)3) of the thiol ligand were studied in this work. The electronic effect of the substituents led to structural shrinkage, thus enhancing the luminous intensity. The internal conversion (IC) and intersystem crossing (ISC) rates in the AuCu14-C(CH3)3 crystal were slower compared with the AuCu14-F crystal, which was caused by the steric effect.

Circular dichroism and circularly polarized luminescence of ligand-protected molecular metal clusters: insights into structure-chiroptical property relationships

Molecular noble metal clusters are an emerging class of circularly polarized luminescent (CPL) nanomaterials. Many of the ligand-protected metal clusters exhibit discrete electronic absorption bands, which are assigned to their structural components such as metal core, ligands and metal-ligand interfaces. This implies the suitability of the chiroptical spectroscopic approach to unravel the structure-chiroptical property relationships in molecular metal clusters. Due to the tremendous developments in computational methods for investigating chiroptical properties, along with circular dichroism (CD) and CPL spectroscopy, understanding of the structure-chiroptical properties of these clusters is rapidly progressing. This review discusses various strategies such as the use of chiral ligands, metal atom substitution, ligand exchange, co-crystallization with chiral ligands, etc., for inducing and enhancing the CPL of such metal clusters. This review demonstrates the potential of combined CD-CPL spectroscopic investigations and theoretical calculations to unravel the origins of photoluminescence and CPL activity of chiral metal clusters.

Chemical Flexibility of Atomically Precise Metal Clusters

Ligand-protected metal clusters possess hybrid properties that seamlessly combine an inorganic core with an organic ligand shell, imparting them exceptional chemical flexibility and unlocking remarkable application potential in diverse fields. Leveraging chemical flexibility to expand the library of available materials and stimulate the development of new functionalities is becoming an increasingly pressing requirement. This Review focuses on the origin of chemical flexibility from the structural analysis, including intra-cluster bonding, inter-cluster interactions, cluster-environments interactions, metal-to-ligand ratios, and thermodynamic effects. In the introduction, we briefly outline the development of metal clusters and explain the differences and commonalities of M(I)/M(I/0) coinage metal clusters. Additionally, we distinguish the bonding characteristics of metal atoms in the inorganic core, which give rise to their distinct chemical flexibility. Section 2 delves into the structural analysis, bonding categories, and thermodynamic theories related to metal clusters. In the following sections 3 to 7, we primarily elucidate the mechanisms that trigger chemical flexibility, the dynamic processes in transformation, the resultant alterations in structure, and the ensuing modifications in physical-chemical properties. Section 8 presents the notable applications that have emerged from utilizing metal clusters and their assemblies. Finally, in section 9, we discuss future challenges and opportunities within this area.

Chiral Canoe-Like Pd0 or Pt0 Alloyed Copper Alkynyl Nanoclusters Display Near-Infrared Luminescence

Alloying nanoclusters (NCs) has emerged as a widely explored and versatile strategy for tailoring tunable properties, facilitating in-depth atomic-level investigations of structure-property correlations. In this study, we have successfully synthesized six atomically precise copper NCs alloyed with Group 10 metals (Pd or Pt). Notably, the Pd0 or Pt0 atom situated at the center of the distorted hexagonal antiprism Pd0/Pt0@Cu12 cage, coordinated with twelve Cu+ and two tBuC≡C- ligands. Moreover, ligand exchange strategies demonstrated the potential for Cl- and Br- to replace one or two alkynyl ligands positioned at the top or side of the NCs. The chirality exhibited by these racemic NCs is primarily attributed to the involvement of halogens and a chiral (Pd/Pt)@Cu18 skeleton. Furthermore, all the NCs exhibit near-infrared (NIR) luminescence, characterized by emission peaks at 705-755 nm, lifetimes ranging from 6.630 to 9.662 μs, and absolute photoluminescence quantum yields (PLQYs) of 1.75 %-2.52 % in their crystalline state. The experimental optical properties of these NCs are found to be in excellent agreement with the results of theoretical calculations. These alloy NCs not only offer valuable insights into the synthesis of Pd0/Pt0-Cu alloy NCs, but also bridge the gap in understanding the structure-luminescence relationships of Pd0/Pt0-Cu molecules.

An Au5Ag12(SR)9(dppf)4 alloy nanocluster: structural determination and optical property and photothermal conversion investigation

Photothermal conversion has garnered significant attention due to its potential for efficient energy conversion and application in targeted therapies. However, controlling photothermal properties at the atomic level remains a challenge in current materials synthesis. In this study, we report the synthesis and structural determination of a phosphine and mercaptan co-protected Au5Ag12(SR)9(dppf)4 (Au5Ag12) nanocluster with an extremely low quantum yield (∼0%). For comparative purposes, we synthesized three alloy nanoclusters of similar size. Notably, Au5Ag12 demonstrates a remarkably superior photothermal conversion performance, significantly outperforming the other clusters. We investigated this variance from both absorption and emission perspectives. This research not only opens new avenues for the application of clusters with extremely low quantum yields, but also provides experimental evidence for understanding the photothermal conversion properties of cluster materials at the atomic level.

Incorporation of the 99TcO4- Anion within the Ag24(C≡CtBu)204+ Cluster Unveiling the Unique Shell-to-Core Charge Transfer

We present the first example of an 99TcO4- anion entrapped within the cavity of a silver cluster, revealing an unprecedented photoinduced charge transfer phenomenon. [Ag24(C≡CtBu)20(99TcO4)]·(BF4)3 (denoted as 99TcO4-@Ag24) was successfully synthesized and structurally characterized. Single-crystal X-ray diffraction and Raman spectroscopy reveal that the tetrahedral structure of the 99TcO4- anion sustains significant symmetry breaking with weakened Tc-O bond strength under confinement within the Ag24(C≡CtBu)204+ cluster. Notably, 99TcO4-@Ag24 exhibits a broadband electronic absorption spectrum in the visible region, which was absent for the other 99TcO4--containing compounds. Density functional theory calculations elucidate that host-guest electrostatic interactions result in an electron polarization effect between the 99TcO4- anion core and the Ag24 cationic shell. The emergence of an absorption band in 99TcO4-@Ag24 is rationalized by intermolecular charge transfer from the Ag24 electronic states to the lowest unoccupied molecular orbitals of 99TcO4- instead of the intramolecular electron transition observed in other 99TcO4--containing compounds.

Transformational Modulation of Fluorescence to Room Temperature Phosphorescence in Metal-Organic Frameworks with Flexible C-S-C Bonds

Photoluminescent metal-organic frameworks (MOFs) have been a subject of considerable interest for many years. However, the regulation of excited states of MOFs at the single crystal level remains restricted due to a lack of control methods. The singlet-triplet emissive property can be significantly influenced by crystal conformational distortions. This review introduces an intelligent responsive MOF material, denoted as LIFM-SHL-3a, characterized by flexible C-S-C bonds. LIFM-SHL-3a integrates elastic structural dynamics with fluorescence and room temperature phosphorescence (RTP) modulation under heating conditions. The deformable carbon-sulfur bond essentially propels the distortion of molecular conformation and alters the stacking mode, as illustrated by single-crystal-to-single-crystal transformation detection. The deformation of flexible C-S-C bonds leads to different noncovalent interactions in the crystal system, thereby achieving modulation of the fluorescence (F) and RTP bands. In the final state structure, the ratio of fluorescence is 66.7%, and the ratio of RTP is 32.6%. This stands as a successful demonstration of modulating F/RTP within the dynamic MOF, unlocking potential applications in optical sensing and beyond. Especially, a PL thermometer with a relative sensitivity of 0.096-0.104%·K-1 in the range of 300-380 K and a H2S probe with a remarkably low LOD of 125.80 nM can be obtained using this responsive MOF material of LIFM-SHL-3a.

Atom-Precise Ligated Copper and Copper-Rich Nanoclusters with Mixed-Valent Cu(I)/Cu(0) Character: Structure-Electron Count Relationships

Copper homometallic and copper-rich heterometallic nanoclusters with some Cu(0) character are reviewed. Their structure and stability are discussed in terms of their number of "free" electrons. In many aspects, this structural chemistry differs from that of their silver or copper homologs. Whereas the two-electron species are by far the most numerous, only one eight-electron species is known, but more electron-rich nanoclusters have also been reported. Owing to the relatively recent development of this chemistry, it is likely that more electron-rich species will be reported in the future.