Ligand Modification of Au25 Nanoclusters for Near-Infrared Photocatalytic Oxidative Functionalization

Au6Cu2 Clusters with High Electron Affinity and Oxygen-Mimetic Properties for Hypoxic Tumor Radiosensitization

Hypoxia-induced radioresistance primarily contributes to the failure of radiotherapy because it hinders the effective fixation of DNA damage. Despite the considerable antitumor activity of chemical molecules such as electron-affinic nitroimidazoles affirmed by clinical studies, their dose-dependent side effects and low radiotherapy efficacy have become major drawbacks. In this study, we synthesized nitrobenzene-functionalized Au6Cu2 (NO2-Au6Cu2) clusters, integrating metal clusters with chemical radiosensitizers. The ligand 4-nitrophenylacetylene's hypoxia-selective toxicity arises from reductase-mediated radical generation under hypoxia, depleting GSH and compromising radiotherapy ROS clearance. Our findings indicate that the electron affinity of interfacial ligands has a significant effect on the electron affinity and hypoxic cytotoxicity of metal clusters. Experimental results demonstrated that NO2-Au6Cu2 clusters exhibit a high sensitization enhancement ratio by leveraging the properties of gold clusters to augment radiotherapy and the oxygen-mimetic property of chemical molecules to impair DNA repair pathways. This research introduces a novel strategy for developing highly efficient metal cluster-based hypoxic radiosensitizers.

An atomically precise alloy AgCu cuboid nanocluster with a cubic core: gram scale synthesis, total structure, electronic structure, and catalytic performance

Although atomically precise noble metal nanoclusters (NMNCs) are highly desirable to unravel the size and structure-activity relationships in catalysis, their synthesis in a controlled way at the atomic level is challenging. Herein, we report the structure and gram scale synthesis of a highly symmetric 2-phenylethanethiol (PETH) and triphenylphosphine (PPh3)-protected AgCu alloy nanocluster (NC) [Ag4Cu28H6(PET)16Cl8(PPh3)8][BF4]2 with a cuboid shape, denoted as Ag4Cu28. This was accomplished via a facile one-pot reduction method. The Ag4Cu28 NC consists of an Ag4Cu4 metal core, six hydrides, four Cu4Cl2 units, eight PET ligands, and four Cu2(PET)2(PPh3)2 motifs. High-resolution electrospray ionization mass spectrometry (HRESI MS) and density functional theory (DFT) calculations support this crystal structure. Moreover, Ag4Cu28 exhibits excellent catalytic activity (k = 7.86 min-1) in the hydrogenation of hazardous nitroarenes. This intriguing NC delivers a unique opportunity to explore the gram scale synthesis of alloy nanoclusters and to expand the research on Cu and Ag-based NCs.

Maneuvering the Electronic State and Active Site of Assembled-Gold Nanoclusters through Polyoxometalate Implantation for Heterogeneous Green-Light Photocatalysis

Gold nanoclusters (AuNCs) exhibit unique molecule-like optical and electronic properties, making them promising candidates for photocatalysis. However, their application as primary photocatalysts in heterogeneous systems is limited by rapid electron recombination, small size, and high solubility. To overcome these limitations, we developed an approach combining AuNCs assemblies with electron trap centers to enhance charge separation and electron transfer. Using a depletion-driven assembly method, Keggin-type polyoxometalates (POMs), Na10SiW9O34 (SiW9), were uniformly embedded within spherical assemblies of glutathione-protected AuNCs, forming gold superclusters (AuSCs). The resulting AuSCs@SiW9 exhibited complete photoluminescence quenching, enhanced metallicity, and stabilized photogenerated electrons via SiW9, enabling their use as primary photocatalysts. The AuSCs@SiW9 efficiently catalyzed the functionalization of terminal aryl alkyne with N-bromosuccinimide (NBS), achieving a tribromoketones yield of 94%, significantly outperforming AuSCs with lower or higher metallicity (38 and 65%, respectively). Mechanistic studies revealed that the improved gold metallicity in AuSCs@SiW9 promotes charge transfer complex formation with NBS, while SiW9 stabilizes photogenerated electrons, enhancing electron density under light irradiation. The AuSCs@SiW9 exhibited strong visible-light absorption, photostability, and solvent dispersibility, enabling recyclability for up to five cycles and scalability for broader applications. This strategy positions gold as a viable primary photocatalyst, expanding its potential in heterogeneous photocatalysis toward synthesizing small molecules.

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.

Generalizable Organic-to-Aqueous Phase Transfer of a Au18 Nanocluster with Luminescence Enhancement and Robust Photocatalysis in Water

For the majority of gold nanoclusters (NCs), their water insolubility, low photoluminescence (PL) intensity, and less understood photostability are three critical factors that limit their application in the biomedical and photocatalysis fields. In this study, we report a polymer wrapping method for phase transfer of organic soluble NCs into aqueous phase without degrading the electronic and optical properties, and such materials are further demonstrated for robust photocatalysis in water. We first synthesized a Au18(DMBT)14 NC (DMBT = 2,4-dimethylbenzenethiolate) and found that the aromatic ligands confer a greatly enhanced antioxidation capability of the NC compared to the Au18(CHT)14 counterpart (CHT = cyclohexanethiolate), with the critical role of aromatic ligand interactions identified by X-ray crystallography. The organic soluble Au18(DMBT)14 was successfully transferred into the aqueous phase by an amphiphilic polymer (Pluronic F127, abbrev. F127) wrapping method, producing Au18-D@F127 nanoparticles [each containing a few NCs; Au18-D is an abbreviation for Au18(DMBT)14] with a 10-fold enhancement in PL intensity, and similar results were also obtained for Au18(CHT)14. This method is broadly applicable to various NCs, rendering their water solubility and significantly enhancing the PL intensity of otherwise weakly emissive gold NCs. The exceptional antioxidation stability of Au18(DMBT)14 enables the application of Au18-D@F127 NPs for the photocatalytic activation of persulfate ions and subsequent photodegradation of water pollutants efficiently.

A comprehensive review of atomically precise metal nanoclusters with emergent photophysical properties towards diverse applications

Atomically precise metal nanoclusters (MNCs) composed of a few to hundreds of metal atoms represent an emerging class of nanomaterials with a precise composition. With the size approaching the Fermi wavelength of electrons, their energy levels are well-separated, leading to molecule-like properties, like discrete single electronic transitions, tunable photoluminescence (PL), inherent structural anisotropy, and distinct redox behavior. Extensive synthetic efforts and electronic structure revelation have expanded applicability of MNCs in catalysis, optoelectronics, and biology. This review highlights the intriguing photophysical and electrochemical behaviors of MNCs and their regulatory parameters and applications. Initially, we present a brief discussion on the evolution of MNCs from gas-phase naked metal clusters to monolayer ligand-protected MNCs along with representative studies on their electronic structure. Due to their quantized molecular orbitals, they often exhibit PL, which can be regulated based on their capping ligands, number of atoms, crystal packing, presence of heterometal, and surrounding environment. Apart from PL, the relaxation pathways of MNCs on an ultrafast time scale have been extensively studied, which significantly differ from that of plasmonic metal nanoparticles. Moreover, their interaction with high-intensity light results in unique non-linear optical properties. The synergy between MNCs in a hierarchical self-assembled structure has been exploited to enhance their PL by precisely tuning their non-covalent interactions. Moreover, several NC-based hybrids have been designed to exhibit efficient electron or energy transfer in the photoexcited state. In the next section, we briefly focus on the redox behavior of NCs and facile electron transfer to suitable substrates, which result in enzyme-like catalytic activity. Utilizing these photophysical and electrochemical behaviors, NCs are widely employed in catalysis, optical sensing, and light-harvesting applications, which are also discussed in this review. In the final section, conclusions and open questions for the NC research community are included. This review will provide a comprehensive view of the emerging physicochemical properties of MNCs, thereby enabling an understanding for their precise modulation in future.

Loading Lewis Acid/Base Pair on Metal Nanocluster for Catalytic Ugi Reaction

Constructing structurally robust and catalytically active metal nanoclusters for catalyzing multi-component reactions is an interesting while challenging task. Inspired by Lewis acid and Lewis base catalysis, we realized the combination of both Lewis acid and Lewis base sites on the surface of a stable gold nanocluster Au35Cd2. The catalytic potential of Au35Cd2 in four-component Ugi reaction was explored, demonstrating high activity and exceptional recyclability. In-depth mechanism studies indicate that the catalytic synergy of the Lewis acid/base pair is crucial for the high efficiency of Au35Cd2-catalyzed Ugi reaction. Bearing the stable structure, multiple activation sites and hierarchical chirality, Au35Cd2 is expected to display further interesting catalytic performance such as asymmetric catalysis.

Phosphonate-Substituted Pyrazinoporphyrin - a General Photocatalyst for Efficient Sulfoxidation

An exceptional efficiency of pyrazine-annelated porphyrin as a general photocatalyst for the oxidation of organic sulfides is demonstrated. It is shown that phosphonate-substituted pyrazinoporphyrin 2H-1 brings together sufficient photostability and high efficiency in the aerobic photooxidation of a series of various sulfides. The influence of the reaction conditions onto the efficiency of homogeneous sulfide photooxidation in the presence of the photosensitizer (PS) was investigated and strong dependence on the solvent system was observed. The use of methanol is required for the photocatalytic sulfoxidation and the ratio of the alcohol/other solvent can significantly affect the conversion and selectivity of the reaction. The application of the prepared PS in 0.001 mol % loading allowed achieving complete conversion (97-100 %, turnover number up to 1,00,000, turnover frequency up to 6250 h-1) of substrates bearing substituents of different nature, namely aromatic and aliphatic sulfides with donor or acceptor substituents and substituents prone to oxidation, as well as cyclic sulfides. The selectivity of the of the corresponding sulfoxides formation of 96-100 % was revealed. Finally, a gram-scale synthesis of several sulfoxides was successfully performed with the PS under investigation, providing desired products in 66-96 % yield with over 98 % purity.

Sintering Ag33 Nanoclusters on TiO2 Nanoparticles as an Efficient Catalyst for Nitroarene Reduction

Polydispersed Ag species-modified TiO2 samples with abundant oxygen vacancies were successfully prepared through the calcination of atomically precise Ag33 nanocluster-loaded TiO2 at an optimal temperature under a nitrogen atmosphere. The ligands of the Ag33 nanoclusters are removed by extracting lattice oxygen from TiO2 during the calcination, leading to the formation of CO2, SO2, and H2O vapor. This process simultaneously induces Ag species sintering on the surface of TiO2. The resulting nanocomposites exhibited excellent catalytic activity for the reduction of nitroarenes with NaBH4 as the reductant. This is attributed to the produced Ag species on the oxygen-deficient TiO2, which act as active centers for the catalytic process.

Atomically Precise Cu Nanoclusters: Recent Advances, Challenges, and Perspectives in Synthesis and Catalytic Applications

Atomically precise metal nanoclusters are an emerging type of nanomaterial which has diverse interfacial metal-ligand coordination motifs that can significantly affect their physicochemical properties and functionalities. Among that, Cu nanoclusters have been gaining continuous increasing research attentions, thanks to the low cost, diversified structures, and superior catalytic performance for various reactions. In this review, we first summarize the recent progress regarding the synthetic methods of atomically precise Cu nanoclusters and the coordination modes between Cu and several typical ligands and then discuss the catalytic applications of these Cu nanoclusters with some explicit examples to explain the atomical-level structure-performance relationship. Finally, the current challenges and future research perspectives with some critical thoughts are elaborated. We hope this review can not only provide a whole picture of the current advances regarding the synthesis and catalytic applications of atomically precise Cu nanoclusters, but also points out some future research visions in this rapidly booming field.

Synergistic coordination of diphosphine with primary and tertiary phosphorus centers: Ultrastable icosidodecahedral Ag30 nanoclusters with metallic aromaticity

As versatile ligands with extraordinary coordination capabilities, RPH2 (R = alkyl or aryl) are rarely used in constructing metal nanoclusters due to their volatility, toxicity, spontaneous flammability, and susceptibility to oxidation. In this work, we designed a primary and tertiary phosphorus-bound diphosphine chelator (2-Ph2PC6H4PH2) to create ultrastable silver nanoclusters with metallic aromaticity. By controlling the deprotonation rate of 2-Ph2PC6H4PH2 and adjusting the templates, we successfully synthesized two near-infrared emissive nanoclusters, Ag30 and Ag32, which have analogous icosidodecahedral Ag30 shells with an Ih symmetry. Deprotonated ligand (2-Ph2PαC6H4Pβ2-) exhibits a coordination mode of μ5-η1(Pβ),η2(Pα,Pβ), which endows a unique metallic aromaticity to Ag30 and Ag32. The solution-processed organic light-emitting diodes based on Ag30 achieve an external quantum efficiency of 15.1%, representing the breakthrough in application of silver nanoclusters to near-infrared-emitting devices. This work represents a special ligand system for synthesizing ligand-protected coinage metal nanoclusters and opens up horizons of creating nanoclusters with distinct geometries and metal aromaticity.

Atomically Precise Ternary Cluster: Polyoxometalate Cluster Sandwiched by Gold Clusters Protected by N-Heterocyclic Carbenes

Coinage metal (Au, Ag, Cu) cluster and polyoxometalate (POM) cluster represent two types of subnanometer "artificial atoms" with significant potential in catalysis, sensing, and nanomedicine. While composite clusters combining Ag/Cu clusters with POM have achieved considerable success, the assembly of gold clusters with POM is still lagging. Herein, we first designedly synthesized two cluster structural units: an Au3O cluster stabilized by diverse N-heterocyclic carbene (NHC) ligands and an amine-terminated POM linker. The subsequent reaction involved amine substitution in the POM linker for the central O atom in the Au3O cluster, resulting in the first ternary composite cluster-a POM cluster sandwiched by two Au clusters protected by NHCs. Single-crystal X-ray diffraction and other characteristic methods characterized their atomically precise structures. Furthermore, altering the NHC ligands decreased the number of gold atoms in the sandwich structures, accompanying the different protonated degrees of amine ligand in the terminal end of the POM linker. These composite clusters showed excellent performances in catalytic H2O2 conversion through the synergistic effect between gold clusters and POM clusters. This work opens a new avenue to functional composite metal clusters and would promote their enhanced catalysis applications through intercluster synergistic interactions within composite systems.

Photosynthesis of Au8Cu6 nanocluster for photocatalysis in oxidative functionalization of alkynes

Ligand-protected metal nanoclusters provide an ideal platform for investigating photoredox catalysis. The central challenge is balancing their stability and catalytic activity. Here we show a photochemical reduction-oxidation cascade method for synthesizing an Au8Cu6 nanocluster, which features a robust structure and active surface. Photoredox catalytic activity of Au8Cu6 is developed for the functionalization of alkynes under oxidative conditions. Mechanism studies based on the precise structure reveal the catalytic process of the Au8Cu6 nanocluster. Oxidant-dependent selectivity of Au8Cu6 catalysis is developed for chemodivergent synthesis of mono- and di-functionalized products in high efficiency. The results will stimulate more research on metal nanocluster synthesis and catalysis.

Synthesis of a Gold-Silver Alloy Nanocluster within a Ring-Shaped Polyoxometalate and Its Photocatalytic Property

Alloying is an effective method for modulating metal nanoclusters to enrich their structural diversity and physicochemical properties. Recent investigations have demonstrated that polyoxometalates (POMs) can act as effective multidentate ligands for silver (Ag) nanoclusters to endow them with synergistic properties, reactivity, catalytic properties, and stability. However, the application of POMs as ligands has been confined predominantly to monometallic nanoclusters. Herein, we report a synthetic method for fabricating surface-exposed gold (Au)-Ag alloy nanoclusters within a ring-shaped POM ([P8W48O184]40-). Reacting an Ag nanocluster stabilized by the ring-shaped POM with Au ions (Au+) was found to substitute several Ag atoms at the core of the nanocluster with Au atoms. The resultant {Au8Ag26} alloy nanocluster demonstrated superior photocatalytic activity and stability compared to the pristine Ag nanocluster in the aerobic oxidation of α-terpinene under visible-light irradiation. These findings provide fundamental insights into the formation and catalytic properties of POM-stabilized alloy nanoclusters and advance exploration into the synthesis and applications of diverse metal nanoclusters.

Modulating Decarboxylative Oxidation Photocatalysis by Ligand Engineering of Atomically Precise Copper Nanoclusters

Copper nanoclusters (Cu NCs) characterized by their well-defined electronic and optical properties are an ideal platform for organic photocatalysis and exploring atomic-level behaviors. However, their potential as greener, efficient catalysts for challenging reactions like decarboxylative oxygenation under mild conditions remains unexplored. Herein, we present Cu13(Nap)3(PPh3)7H10 (hereafter Cu13Nap), protected by 1-naphthalene thiolate (Nap), which performs well in decarboxylative oxidation (90% yield) under photochemical conditions. In comparison, the isostructural Cu13(DCBT)3(PPh3)7H10 (hereafter Cu13DCBT), stabilized by 2,4-dichlorobenzenethiolate (DCBT), yields only 28%, and other previously reported Cu NCs (Cu28, Cu29, Cu45, Cu57, and Cu61) yield in the range of 6-18%. The introduction of naphthalene thiolate to the surface of Cu13 NCs influences their electronic structure and charge transfer in the ligand shell, enhancing visible light absorption and catalytic performance. Density functional theory (DFT) and experimental evidence suggest that the reaction proceeds primarily through an energy transfer mechanism. The energy transfer pathway is uncommon in the context of previous reports for decarboxylative oxidation reactions. Our findings suggest that strategically manipulating ligands holds significant potential for creating composite active sites on atomically precise copper NCs, resulting in enhanced catalytic efficacy and selectivity across various challenging reactions.

Recent progress in atomically precise metal nanoclusters for photocatalytic application

Photocatalysis is a widely recognized green and sustainable technology that can harness inexhaustible solar energy to carry out chemical reactions, offering the opportunity to mitigate environmental issues and the energy crisis. Photocatalysts with wide spectral response and rapid charge transfer capability are crucial for highly efficient photocatalytic activity. Atomically precise metal nanoclusters (NCs), an emerging atomic-level material, have attracted great interests owing to their ultrasmall size, unique atomic stacking, abundant surface active sites, and quantum confinement effect. In particular, the molecule-like discrete electronic energy level endows them with small-band-gap semiconductor behavior, which allows for photoexcitation in order to generate electrons and holes to participate in the photoredox reaction. In addition, metal NCs exhibit strong light-harvesting ability in the wide spectral UV-near IR region, and the diversity of optical absorption properties can be precisely regulated by the composition and structure. These merits make metal NCs ideal candidates for photocatalysis. In this review, the recent advances in atomically-precise metal NCs for photocatalytic application are summarized, including photocatalytic water splitting, CO2 reduction, organic transformation, photoelectrocatalytic reactions, N2 fixation and H2O2 production. In addition, the strategy for promoting photostability, charge transfer and separation efficiency of metal NCs is highlighted. Finally, a perspective on the challenges and opportunities for NCs-based photocatalysts is provided.

Chiral Inversion of Au40(SR)24 Nanocluster Driven by Rotation of Gold Tetrahedra in the Kekulé-like Core

Studying the chiral characteristics and chiral inversion mechanisms of gold nanoclusters is important to promote their applications in the field of chiral catalysis and chiral recognition. Herein, we investigated the chiral inversion process of the Au40(SR)24 nanocluster and its derivatives using density functional theory calculations. The results showed that the chiral inversion process can be achieved by rotation of tetrahedra units in the gold core without breaking the Au-S bond. This work found that Au40 nanoclusters protected by different ligands have different chiral inversion mechanisms, and the difference is mainly attributable to the steric effects of the ligands. Moreover, the chiral inversion of the derivative clusters (Au34, Au28, and Au22) of the Au40 nanocluster can also be accomplished by the rotation of the Au4 tetrahedra units in the gold core. The energy barrier in the chiral inversion process of gold nanoclusters increases with the decrease of Au4 tetrahedra units in the gold core. This work identifies a chiral inversion mechanism with lower reaction energy barriers and provided a theoretical basis for the study of gold nanocluster chirality.

Enantioselective Synthesis of Homochiral Hierarchical Nd8Fe3-Oxo Cluster from Racemic Nd9Fe2-Oxo Cluster

Enantioselective synthesis of homochiral rare earth clusters is still a great challenge. In this work, we developed an efficient "cluster to cluster" approach, that is, a pair of enantiomerical R/S-{Nd8Fe3}-oxo clusters were successfully obtained from the presynthesized racemic {Nd9Fe2}-oxo cluster. R/S-hydrobenzoin ligands trigger the transformation of the pristine clusters by an SN2-like mechanism. Compared to the pristine cluster with an achiral core, the new cluster exhibits hierarchical chirality, from ligand chirality to interface chirality, then to helix chirality, and finally to supramolecular double helix chirality. The spectral experiments monitored the transformation and confirmed distinctly structure-related optical activity. The enantiomeric pure cluster also exhibits a potential asymmetric catalytic activity.

"Visualizing" the partially reversible conversion of gold nanoclusters via the Au23(S-c-C6H11)17 intermediate

Transformation chemistry of atomically precise metal nanoclusters has emerged as a novel strategy for fundamental research on the structure-property correlations of nanomaterials. However, a thorough understanding of the transformation mechanism is indeed necessary to understand the structural growth patterns and corresponding property evolutions in nanoclusters. Herein, we present the ligand-exchange-induced transformation of the [Au23(SR)16]- (8e-) nanocluster to the [Au25(SR')18]- (8e-) nanocluster, through the Au23(SR)17 (6e-) intermediate species. Identification of this key intermediate through a partially reversible transformation helped in a detailed investigation into the transformation mechanism with atomic precision. Moreover, photophysical studies carried out on this Au23(SR)17 species, which only differs by a single ligand from that of the [Au23(SR)16]- nanocluster reveal the property evolutions at the slightest change in the nanocluster structure.

Planar Core and Macrocyclic Shell Stabilized Atomically Precise Copper Nanocluster Catalyst for Efficient Hydroboration of C-C Multiple Bond

Atomically precise metal nanoclusters (NCs) have become an important class of catalysts due to their catalytic activity, high surface area, and tailored active sites. However, the design and development of bond-forming reaction catalysts based on copper NCs are still in their early stages. Herein, we report the synthesis of an atomically precise copper nanocluster with a planar core and unique shell, [Cu45(TBBT)29(TPP)4(C4H11N)2H14]2+ (Cu45) (TBBT: 4-tert-butylbenzenethiol; TPP: triphenylphosphine), in high yield via a one-pot reduction method. The resulting structurally well-defined Cu45 is a highly efficient catalyst for the hydroboration reaction of alkynes and alkenes. Mechanistic studies show that a single-electron oxidation of the in situ-formed ate complex enables the hydroboration via the formation of boryl-centered radicals under mild conditions. This work demonstrates the promise of tailored copper nanoclusters as catalysts for C-B heteroatom bond-forming reactions. The catalysts are compatible with a wide range of alkynes and alkenes and functional groups for producing hydroborated products.

NIR-II emissive anionic copper nanoclusters with intrinsic photoredox activity in single-electron transfer

Ultrasmall copper nanoclusters have recently emerged as promising photocatalysts for organic synthesis, owing to their exceptional light absorption ability and large surface areas for efficient interactions with substrates. Despite significant advances in cluster-based visible-light photocatalysis, the types of organic transformations that copper nanoclusters can catalyze remain limited to date. Herein, we report a structurally well-defined anionic Cu40 nanocluster that emits in the second near-infrared region (NIR-II, 1000-1700 nm) after photoexcitation and can conduct single-electron transfer with fluoroalkyl iodides without the need for external ligand activation. This photoredox-active copper nanocluster efficiently catalyzes the three-component radical couplings of alkenes, fluoroalkyl iodides, and trimethylsilyl cyanide under blue-LED irradiation at room temperature. A variety of fluorine-containing electrophiles and a cyanide nucleophile can be added onto an array of alkenes, including styrenes and aliphatic olefins. Our current work demonstrates the viability of using readily accessible metal nanoclusters to establish photocatalytic systems with a high degree of practicality and reaction complexity.

Multiple neighboring active sites of an atomically precise copper nanocluster catalyst for efficient bond-forming reactions

Atomically precise copper nanoclusters (NCs) are an emerging class of nanomaterials for catalysis. Their versatile core-shell architecture opens the possibility of tailoring their catalytically active sites. Here, we introduce a core-shell copper nanocluster (CuNC), [Cu29(StBu)13Cl5(PPh3)4H10]tBuSO3 (StBu: tert-butylthiol; PPh3: triphenylphosphine), Cu29NC, with multiple accessible active sites on its shell. We show that this nanocluster is a versatile catalyst for C-heteroatom bond formation (C-O, C-N, and C-S) with several advantages over previous Cu systems. When supported, the cluster can also be reused as a heterogeneous catalyst without losing its efficiency, making it a hybrid homogeneous and heterogeneous catalyst. We elucidated the atomic-level mechanism of the catalysis using density functional theory (DFT) calculations based on the single crystal structure. We found that the cooperative action of multiple neighboring active sites is essential for the catalyst's efficiency. The calculations also revealed that oxidative addition is the rate-limiting step that is facilitated by the neighboring active sites of the Cu29NC, which highlights a unique advantage of nanoclusters over traditional copper catalysts. Our results demonstrate the potential of nanoclusters for enabling the rational atomically precise design and investigation of multi-site catalysts.

Dithiocarbonate-Protected Au25 Nanorods of a Chiral D5 Configuration and NIR-II Phosphorescence

Innovative surface-protecting ligands are in constant demand due to their crucial role in shaping the configuration, property, and application of gold nanoclusters. Here, the unprecedented O-ethyl dithiocarbonate (DTX)-stabilized atomically precise gold nanoclusters, [Au25(PPh3)10(DTX)5Cl2]2+ (Au25DTX-Cl) and [Au25(PPh3)10(DTX)5Br2]2+ (Au25DTX-Br), were synthesized and structurally characterized. The introduction of bidentate DTX ligands not only endowed the gold nanocluster with unique staggered Au25 nanorod configurations but also generated the symmetry breaking from the D5d geometry of the Au25 kernels to the chiral D5 configuration of the Au25 molecules. The chirality of Au25 nanorods was notably revealed through single-crystal X-ray diffraction, and chiral separation was induced by employing chiral DTX ligands. The staggered configurations of Au25 nanorods, as opposed to eclipsed ones, were responsible for the large red shift in the emission wavelengths, giving rise to a promising near-infrared II (NIR-II, >1000 nm) phosphorescence. Furthermore, their performances in photocatalytic sulfide oxidation and electrocatalytic hydrogen evolution reactions have been examined, and it has been demonstrated that the outstanding catalytic activity of gold nanoclusters is highly related to their stability.

Radical reactions enabled by polyfluoroaryl fragments: photocatalysis and beyond

Polyfluoroarenes have been known for a long time, but they are most often used as fluorinated building blocks for the synthesis of aromatic compounds. At the same time, due to peculiar fluorine effect, they have unique properties that provide applications in various fields ranging from synthesis to materials science. This review summarizes advances in the radical chemistry of polyfluoroarenes, which have become possible mainly with the advent of photocatalysis. Transformations of the fluorinated ring via the C-F bond activation, as well as use of fluoroaryl fragments as activating groups and hydrogen atom transfer agents are discussed. The ability of fluoroarenes to serve as catalysts is also considred.

Dynamic surface reconstruction of individual gold nanoclusters by using a co-reactant enables color-tunable electrochemiluminescence

Here we report for the first time the phenomenon of continuously color-tunable electrochemiluminescence (ECL) from individual gold nanoclusters (Au NCs) confined in a porous hydrogel matrix by adjusting the concentration of the co-reactant. Specifically, the hydrogel-confined Au NCs exhibit strong dual-color ECL in an aqueous solution with triethylamine (TEA) as a co-reactant, with a record-breaking quantum yield of 95%. Unlike previously reported Au NCs, the ECL origin of the hydrogel-confined Au NCs is related to both the Au(0) kernel and the Au(i)-S surface. Surprisingly, the surface-related ECL of Au NCs exhibits a wide color-tunable range of 625-829 nm, but the core-related ECL remains constant at 489 nm. Theoretical and experimental studies demonstrate that the color-tunable ECL is caused by the dynamic surface reconstruction of Au NCs and TEA radicals. This work opens up new avenues for dynamically manipulating the ECL spectra of core-shell emitters in biosensing and imaging research.

Near-Infrared Light-Driven Photocatalysis with an Emphasis on Two-Photon Excitation: Concepts, Materials, and Applications

Efficient utilization of sunlight in photocatalysis is widely recognized as a promising solution for addressing the growing energy demand and environmental issues resulting from fossil fuel consumption. Recently, there have been significant developments in various near-infrared (NIR) light-harvesting systems for artificial photosynthesis and photocatalytic environmental remediation. This review provides an overview of the most recent advancements in the utilization of NIR light through the creation of novel nanostructured materials and molecular photosensitizers, as well as modulating strategies to enhance the photocatalytic processes. A special focus is given to the emerging two-photon excitation NIR photocatalysis. The unique features and limitations of different systems are critically evaluated. In particular, it highlights the advantages of utilizing NIR light and two-photon excitation compared to UV-visible irradiation and one-photon excitation. Ongoing challenges and potential solutions for the future exploration of NIR light-responsive materials are also discussed.

Structure control and evolution of atomically precise gold clusters as heterogeneous precatalysts

Metal clusters have distinct features from single atom and nanoparticle (>1 nm) catalysts, making them effective catalysts for various heterogeneous reactions. Nevertheless, the ambiguity and complexity of the catalyst structure preclude in-depth mechanistic studies. The evolution of metal species during synthesis and reaction processes represents another challenge. One effective solution is to precisely control the structure of the metal cluster, thus offering a well-defined pre-catalyst. The well-defined chemical formula and configurations make atomically precise metal nanoclusters optimal choices. To fabricate an atomically precise metal nanocluster-based heterogeneous catalyst with enhanced performance, careful structural design of both the nanocluster and support material, an effective assembling technique, and a pre-treatment method for these hybrids need to be developed. In this review, we summarize recent advances in in the development of heterogeneous catalysts using atomically precise gold and alloy gold nanoclusters as precursors. We will begin with a brief introduction to the structural properties of atomically precise nanoclusters and structure determination of cluster/support hybrids. We will then introduce heterogeneous catalysts prepared from medium size (tens to hundreds of metal atoms) and low nuclearity nanoclusters. We will illustrate how ligand modification, support-cluster interaction, hybrid fabrication, and heteroatom (Pt, Pd Ag, Cu, Cd, Fe) introduction affect the structural properties and pretreatment/reaction-induced structural evolution of gold nanocluster pre-catalysts. Lastly, we will highlight the synthetic method of NCs@MOF hybrids and their effectiveness in circumventing the adverse cluster structural evolution. These findings are expected to shed light on the structure-activity relationship studies and future catalyst design strategies using atomically precise metal nanocluster pre-catalysts.

Dual Catalysis of Gold Nanoclusters: Photocatalytic Cross-Dehydrogenative Coupling by Cooperation of Superatomic Core and Molecularly Modified Staples

Thiolate-protected gold nanoclusters (AuNCs) have attracted significant attention as nano-catalysts, revealing a superatomic core and gold-thiolate staples as distinct structural units. Here, we demonstrate the unprecedented dual catalytic activity of thiolate-protected [Au25 (SR)18 ]- nanoclusters, involving both photosensitized 1 O2 generation by the Au13 superatomic core and catalytic carbon-carbon bond formation facilitated by Au2 (SR)3 staples. This synergistic combination of two different catalytic units enables efficient cross-dehydrogenative coupling of terminal alkynes and tertiary aliphatic amines to afford propargylamines in high yields of up to 93 %. Mixed-ligand AuNCs bearing both thiolate and alkynyl ligands revealed the intermediacy of the alkynyl-exchanged AuNCs toward both photosensitization and C-C bond-forming catalytic cycles. Density functional theory calculations also supported the intermediacy of the alkynyl-exchanged AuNCs. Thus, the use of ligand-protected metal nanoclusters has enabled the development of an exceptional multifunctional catalyst, wherein distinct nanocluster components facilitate cooperative photo- and chemo-catalysis.

Tailoring Carbon Tails of Ligands on Au52(SR)32 Nanoclusters Enhances the Near-Infrared Photoluminescence Quantum Yield from 3.8 to 18.3

One of the important factors that determine the photoluminescence (PL) properties of gold nanoclusters pertain to the surface. In this study, four Au52(SR)32 nanoclusters that feature a series of aromatic thiolate ligands (-SR) with different bulkiness at the para-position are synthesized and investigated. The near-infrared (NIR) photoluminescence (peaks at 900-940 nm) quantum yield (QY) is largely enhanced with a decrease in the ligand's para-bulkiness. Specifically, the Au52(SR)32 capped with the least bulky p-methylbenzenethiolate (p-MBT) exhibits the highest PLQY (18.3% at room temperature in non-degassed dichloromethane), while Au52 with the bulkiest tert-butylbenzenethiolate (TBBT) only gives 3.8%. The large enhancement of QY with fewer methyl groups on the ligands implies a nonradiative decay via the multiphonon process mediated by C-H bonds. Furthermore, single-crystal X-ray diffraction (SCXRD) comparison of Au52(p-MBT)32 and Au52(TBBT)32 reveals that fewer methyl groups at the para-position lead to a stronger interligand π···π stacking on the Au52 core, thus restricting ligand vibrations and rotations. The emission nature is identified to be phosphorescence and thermally activated delayed fluorescence (TADF) based on the PL lifetime, 3O2 quenching, and temperature-dependent PL and absorption studies. The 1O2 generation efficiencies for the four Au52(SR)32 NCs follow the same trend as the observed PL performance. Overall, the highly NIR-luminescent Au52(p-MBT)32 nanocluster and the revealed mechanisms are expected to find future applications.

A metal-free photoactive nitrogen-doped carbon nanosolenoid with broad absorption in visible region for efficient photocatalysis

Riemann surfaces inspired chemists to design and synthesize such multidimensional curved carbon architectures. It has been predicted that carbon nanosolenoid materials with Riemann surfaces have unique structures and novel physical properties. Here we report the first synthesis of a nitrogen-doped carbon nanosolenoid (N-CNS) using bottom-up approach with a well-defined structure. N-CNS was obtained by a rational Suzuki polymerization, followed by oxidative cyclodehydrogenation. The successful synthesis of N-CNS was fully characterized by GPC, FTIR, solid-state 13C NMR and Raman techniques. The intrinsic single-strand molecular structures of N-CNS helices can be clearly resolved using low-dose integrated differential phase contrast scanning transmission electron microscopy (iDPC-STEM) technique. Possessing unique structural and physical properties, this long π-extended polymer N-CNS can provide new insight towards bottom-up syntheses of curved nanoribbons and potential applications as a metal-free photocatalyst for visible-light-driven H2 evolution and highly efficient photocatalyst for photoredox organic transformations.

Protein-Templated Metal Nanoclusters: Molecular-like Hybrids for Biosensing, Diagnostics and Pharmaceutics

The use of proteins as biomolecular templates to synthesize atomically precise metal nanoclusters has been gaining traction due to their appealing properties such as photoluminescence, good colloidal- and photostability and biocompatibility. The synergistic effect of using a protein scaffold and metal nanoclusters makes it especially attractive for biomedical applications. Unlike other reviews, we focus on proteins in general as the protective ligand for various metal nanoclusters and highlight their applications in the biomedical field. We first introduce the approaches and underlined principles in synthesizing protein-templated metal nanoclusters and summarize some of the typical proteins that have been used thus far. Afterwards, we highlight the key physicochemical properties and the characterization techniques commonly used for the size, structure and optical properties of protein-templated metal nanoclusters. We feature two case studies to illustrate the importance of combining these characterization techniques to elucidate the formation process of protein-templated metal nanoclusters. Lastly, we highlight the promising applications of protein-templated metal nanoclusters in three areas-biosensing, diagnostics and therapeutics.

Manifestation of the interplay between spin-orbit and Jahn-Teller effects in Au25 superatom UV-Vis fingerprint spectra

Atomically precise nanoclusters play an important role in nanoscale catalysis, photonics, and quantum information science. Their nanochemical properties arise from their unique superatomic electronic structures. As the flagship of atomically precise nanochemistry, the Au₂₅(SR)₁₈ nanocluster exhibits tunable spectroscopic signatures that are sensitive to the oxidation state. This work aims to unravel the physical underpinnings of the spectral progression of Au₂₅(SR)₁₈ nanocluster using variational relativistic time-dependent density functional theory. The investigation will focus on the effects of superatomic spin-orbit coupling, its interplay with Jahn-Teller distortion, and their manifestations in the absorption spectra of Au₂₅(SR)₁₈ nanoclusters of different oxidation states.

Body-Centered-Cubic-Kernelled Ag15Cu6 Nanocluster with Alkynyl Protection: Synthesis, Total Structure, and CO2 Electroreduction

While atomically monodisperse nanostructured materials are highly desirable to unravel the size- and structure-catalysis relationships, their controlled synthesis and the atomic-level structure determination pose challenges. Particularly, copper-containing atomically precise alloy nanoclusters are potential catalyst candidates for the electrochemical CO₂ reduction reaction (eCO₂RR) due to high abundance and tunable catalytic activity of copper. Herein, we report the synthesis and total structure of an alkynyl-protected 21-atom AgCu alloy nanocluster [Ag₁₅Cu₆(C≡CR)₁₈(DPPE)₂]^-, denoted as Ag₁₅Cu₆ (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene; DPPE: 1,2-bis(diphenylphosphino)ethane). The single-crystal X-ray diffraction reveals that Ag₁₅Cu₆ consists of an Ag₁₁Cu₄ metal core exhibiting a body-centered cubic (bcc) structure, which is capped by 2 Cu atoms, 2 Ag₂DPPE motifs, and 18 alkynyl ligands. Interestingly, the Ag₁₅Cu₆ cluster exhibits excellent catalytic activity for eCO₂RR with a CO faradaic efficiency (FE_CO) of 91.3% at -0.81 V (vs the reversible hydrogen electrode, RHE), which is much higher than that (FE_CO: 48.5% at -0.89 V vs RHE) of Ag₉Cu₆ with bcc structure. Furthermore, Ag₁₅Cu₆ shows superior stability with no significant decay in the current density and FE_CO during a long-term operation of 145 h. Density functional theory calculations reveal that the de-ligated Ag₁₅Cu₆ cluster can expose more space at the pair of AgCu dual metals as the efficient active sites for CO formation.

Spontaneous Intercluster Electron Transfer X2- + X0 → 2 X- (X = PtAu24(SCnH2n+1)18) in Solution: Promotion by Long Alkyl Chains

In this work, we systematically investigated the ligand effects on spontaneous electron transfer (ET) between alkanethiolate-protected metal clusters in solution. The donor and acceptor clusters used were [PtAu₂₄(SC_nH_2n+1)₁₈]^2- (8e(Cn)) and [PtAu₂₄(SC_mH_2m+1)₁₈]⁰ (6e(Cm)) (n, m = 2-16), which have icosahedral Pt@Au₁₂ cores with eight and six valence electrons, respectively. The ET rate constant (k_ET) from 8e(Cn) to 6e(Cm) in benzene exhibited a novel turnover behavior as a function of the total chain length n + m: the k_ET decreased with n + m in the range of 4-12, whereas it monotonically increased with n + m in the range of 12-32. Electrospray ionization mass spectrometry of the mixture of 8e(Cn) and 6e(Cm) detected the dimer complex 8e(Cn)·6e(Cm), the relative population of which increased with n + m. The activation energy (E_a), determined based on the Arrhenius plots for n = m, monotonically decreased with n (≥ 6). Based on these results, we proposed that the promotion of ET by longer alkanethiolates was ascribed to two effects on the key intermediate 8e(Cn)·6e(Cm): (1) elongation of the lifetime and (2) the contraction of the distance between 8e(Cn) and 6e(Cm) due to the stronger van der Waals interaction between the longer alkyl chains. Such alkyl-chain-promoted ET is specific to ultrasmall clusters in solution because a nonuniform ligand layer could be formed due to the large curvature of the cluster core.

Open Nitrogen Site-Induced Kinetic Resolution and Catalysis of a Gold Nanocluster

The emerging metal nanocluster provides a platform for the investigation of structural features, unique properties, and structure-property correlation of nanomaterials at the atomic level. Construction of open sites on the surface of the metal nanocluster is a long-pursued but challenging goal. Herein, we realized the construction of "open organic sites" in a metal nanocluster for the first time. Specifically, we introduce the PNP (2,6-bis(diphenylphosphinomethyl)pyridine) pincer ligand in the synthesis of the gold nanocluster, enabling the construction of a structurally precise Au₈(PNP)₄ nanocluster. The rigidity and the unique bonding mode of PNP lead to open nitrogen sites on the surface of the Au₈(PNP)₄ nanocluster, which have been utilized as multifunctional sites in this work for efficient kinetic resolution and catalysis. The gold pincer nanocluster and the open nitrogen site-induced performance will be enlightening for the construction of multifunctional metal nanoclusters.

Tailoring the Electron-Phonon Interaction in Au25(SR)18 Nanoclusters via Ligand Engineering and Insight into Luminescence

Understanding the electron-phonon interaction in Au nanoclusters (NCs) is essential for enhancing and tuning their photoluminescence (PL) properties. Among all the methods, ligand engineering is the most straightforward and facile one to design Au NCs with the desired PL properties. However, a systematic understanding of the ligand effects toward electron-phonon interactions in Au NCs is still missing. Herein, we synthesized four Au₂₅(SR)₁₈^- NCs protected by different -SR ligands and carefully examined their temperature-dependent band-gap renormalization behavior. Data analysis by a Bose-Einstein two-oscillator model revealed a suppression of high-frequency optical phonons in aromatic-ligand-protected Au₂₅ NCs. Meanwhile, a low-frequency breathing mode and a quadrupolar mode are attributed as the main contributors to the phonon-assisted nonradiative relaxation pathway in aromatic-ligand-protected Au₂₅ NCs, which is in contrast with non-aromatic-ligand-protected Au₂₅ NCs, in which tangential and radial modes play the key roles. The PL measurements of the four Au₂₅ NCs showed that the suppression of optical phonons led to higher quantum yields in aromatic-ligand-protected Au₂₅ NCs. Cryogenic PL measurements provide insights into the nonradiative energy relaxation, which should be further investigated for a full understanding of the PL mechanism in Au₂₅ NCs.

Photochemical synthesis of 1,2,4-triazoles via addition reaction of triplet intermediates to diazoalkanes and azomethine ylide intermediates

The reactivity of diazoalkanes most commonly proceeds through the formation of carbene intermediates or dipolar cycloaddition reactions. The reaction of diazoalkanes with intermediates with unpaired electrons, however, is much less elaborated. Herein, we report on the photochemical reaction of acceptor-only diazoalkanes with azodicarboxylates. Photoexcitation of the latter results in the formation of a triplet species, which undergoes an addition reaction with diazoalkanes and formation of an azomethine ylide followed by dipolar cycloaddition reaction with organic nitriles to give a 1,2,4-triazole. The application of this transformation was elaborated in a broad and general substrate scope (48 examples), including scale-up via flow chemistry and downstream transformations. Experimental and computational studies were performed to elucidate the reaction mechanism and to rationalize the reaction outcome.

Doping-Mediated Energy-Level Engineering of M@Au12 Superatoms (M=Pd, Pt, Rh, Ir) for Efficient Photoluminescence and Photocatalysis

We synthesized a series of MAu₁₂ (dppe)₅ Cl₂ (MAu₁₂ ; M=Au, Pd, Pt, Rh, or Ir; dppe=1,2-bis(diphenylphosphino)ethane), which have icosahedral M@Au₁₂ superatomic cores, and systematically investigated their electronic structures, photoluminescence (PL) and photocatalytic properties. The energy gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) was expanded when doping an M element positioned at the lower left of the periodic table. The PL quantum yield was enhanced with an increase in the HOMO-LUMO gap and reached 0.46-0.67 for MAu₁₂ (M=Pt, Rh, or Ir) under deaerated conditions. The bright PLs from MAu₁₂ (M=Pt, Rh, or Ir) were assigned to phosphorescence based on quenching by O₂ . MAu₁₂ (M=Pt, Rh, or Ir) acted as a more efficient and stable photocatalyst than Au₁₃ for intramolecular [2+2] cycloaddition of bisenone via the oxidative quenching cycle. This study provides rational guides for designing photoluminescent and photocatalytic gold superatoms by the doping of heterometal elements.

Composition-Dependent Enzyme Mimicking Activity and Radiosensitizing Effect of Bimetallic Clusters to Modulate Tumor Hypoxia for Enhanced Cancer Therapy

Alloying is an efficient chemistry to tailor the properties of metal clusters. As a class of promising radiosensitizers, most previously reported metal clusters exhibit unitary function and cannot overcome radioresistance of hypoxic tumors. Here, atomically precise alloy clusters Pt₂ M₄ (M = Au, Ag, Cu) are synthesized with bright luminescence and adequate biocompatibility, and their composition-dependent enzyme mimicking activity and radiosensitizing effect is explored. Specifically, only the Pt₂ Au₄ cluster displays catalase-like activity, while the others do not have clusterzyme properties, and its radiosensitizing effect is the highest among all the alloy clusters tested. By taking advantage of the sustainable production of O₂ via the decomposition of endogenous H₂ O₂ , the Pt₂ Au₄ cluster modulates tumor hypoxia as well as increases the efficacy of radiotherapy. This work thus advances the cluster alloying strategy to produce multifunctional therapeutic agents for improving hypoxic tumor therapy.

Gold nanoclusters: Photophysical properties and photocatalytic applications

Atomically precise gold nanoclusters (Au NCs) have high specific surface area and abundant unsaturated active sites. Traditionally, Au NCs are employed as thermocatalysts for multielectron transfer redox catalysis. Meanwhile, Au NCs also exhibit discrete energy levels, tunable photophysical and electrochemical properties, including visible to near infrared absorption, microsecond long-lived excited-state lifetime, and redox chemistry. In recent years, Au NCs are increasingly employed as visible to near infrared photocatalysts for their high photocatalytic activity and unique selectivity. This review focuses on the photophysical properties of a variety of Au NCs and their employment as photocatalysts in photocatalytic reactions and related applications including solar energy conversion and photodynamic therapies.

Bridged eosin Y: a visible and near-infrared photoredox catalyst

Herein, a new NIR photoredox catalyst, bridged eosin Y (BEY), has been developed. Its detailed structure and NIR optical properties are clarified by using various spectroscopic methods, X-ray single-crystal structure analysis and DFT calculations. In addition, we demonstrate the photoreaction in colored reagents and high-concentration suspensions to show the advantage of NIR photoredox-catalyzed reactions.

Metal-free polyporphyrin based photocatalysts for the functionalization of C(sp3)–H bonds in water

Insoluble polyporphyrin or water-dispersible nano-polyporphyrin was used to achieve visible light-induced functionalization of C(sp3)–H bonds in water under mild conditions.