Diversification of Metallic Molecules through Derivatization Chemistry of Au25 Nanoclusters

Computational and Experimental Elucidation of the Charge-Dependent Acid-Etching Dynamics and Electrocatalytic Performance of Au25(SR)18 q(q = -1, 0, +1) Nanoclusters

Using thiolate-protected Au25(SR)18 nanocluster (NC) with different charge states as the test candidate, how the charge effect affects the etching dynamics of thiolate ligands in acid and the electrocatalytic performance is explored. The ab initio molecular dynamics (AIMD) simulations revealed the charge-dependent reaction kinetics in acid, where the anionic and neutral Au25(SCH3)18 q (q = -1, 0) favorably react with the acid and partially remove the thiolate ligands via two-step proton attack, while the cationic Au25(SCH3)18 + NC is acid-resistant with no tendency for -SR removal. Density functional theory (DFT) calculations further predict that the dethiolated Au sites exhibit enhanced catalytic activity for CO2 electroreduction to CO, with the anionic Au25 - showing significantly superior activity. Acid etching and electrocatalytic experiments further confirmed partial removal of thiolate ligands in Au25(SCH3)18 q (q = -1, 0), with dethiolated Au25 NCs showing enhanced catalytic performance in CO2 electroreduction, particularly Au25 - exhibiting better activity than Au25 0. This work revealed an interesting charge state-mediated interface dynamics and electrocatalytic behaviors in Au25 NCs, which can be applied to modulate the interface and catalytic properties of other atomically precise metal nanoclusters.

Tuning Atomically Precise Gold Nanoclusters for Selective Electroreduction of CO2

The electroreduction of greenhouse gas CO2 into high-value-added chemicals using renewable electricity is a promising way to mitigate climate change and realize carbon cycling. Atomically precise thiolate-protected gold nanoclusters have shown great potential for selective electrochemical conversion of CO2 toward CO due to their quantum confinement effect and unique electronic structures. Additionally, the atomic precision of gold nanocluster is advantageous for investigating the CO2 reduction mechanism, which is typically challenging to understand due to the complexity of the catalytic interface, and unknown structure of the active site in more conventional catalysts. By summarizing CO2 reduction catalyzed by gold nanoclusters, we aim to identify key factors that contribute to the activity, selectivity, and stability of nanocluster catalysts, as well as elucidate the CO₂ reduction pathway, thereby contributing to the design of more active and selective nanocluster catalysts for CO2 reduction.

Ultrasmall metal nanoclusters as efficient luminescent probes for bioimaging

Ultrasmall metal nanoclusters (NCs, <2 nm) have emerged as a novel class of luminescent probes due to their atomically precise size and tailored physicochemical properties. The rapid advancements in the design and utilization of metal NC-based luminescent probes are facilitated by the atomic-level manipulation of metal NCs. This review article explores (i) the engineering of metal NCs' functions for bioimaging applications, and (ii) the diverse uses of metal NCs in bioimaging. We begin by presenting an overview of the engineering functions of metal NCs as luminescent probes for bioimaging applications, highlighting key strategies for enhancing NCs' luminescence, biocompatibility and targeting capabilities towards biological specimens. Our discussion then centers on the bioimaging applications of metal NCs in subcellular organelles, individual cells, tissues, and entire organs. Finally, we offer a perspective on the challenges and potential developments in the future use of metal NCs for bioimaging applications.

Encapsulation of an Au25 Nanocluster inside a Porphyrin Nanoring Enhances Singlet Oxygen Generation and Photo-Electrocatalytic CO2 Reduction

The synthesis of molecular host-guest complexes with enhanced performance, relative to those of their components, is a central theme in supramolecular chemistry. Here we explore a host-guest system consisting of an atomically precise gold nanocluster bound inside a zinc porphyrin nanoring. UV/Vis absorption and fluorescence titrations with different sized nanorings revealed strong binding between a pyridinethiol-coated Au25 nanocluster and a nanoring consisting of six zinc porphyrin units, and complexation is confirmed by mass spectrometry. Formation of this assembly enhances the stability of the gold nanocluster. The host-guest complex also exhibits remarkable activity and selectivity for photochemical CO2 to CO conversion and singlet oxygen generation.

Expanding the Toolbox of Oxidants: Controllable Etching of Ultrasmall Au Nanoparticles toward Tailorable NIR-II Luminescence and Ligand-Mediated Biodistribution and Clearance

Oxidant-driven and controllable etching of small-sized nanoparticles (NPs, d < 3 nm) and tailorable modulation of their optical properties are challenging due to the high reactivity and complicated surface chemistry. Herein, we present a facile strategy for highly controllable oxidative etching of ultrasmall AuNPs and tailorable modulation of luminescence. The proper choice of a moderate oxidant, ClO-, could not only selectively etch the Au(I)-thiolate motifs from the nanoparticle surface at the subnanometer scale but also retained a stable metallic core structure without aggregation, which impressively prompted the wide-range luminescent switching from the visible to second near-infrared (NIR-II) region. The resultant oxidized AuNPs displayed highly luminescent NIR-II emission with a quantum yield of 3.0%, excellent monodispersed stability, ideal biocompatibility, and tunable shielding effects against protein adsorption. With those outstanding features, oxidized AuNPs could be utilized as nanoprobes for long-lasting and in vivo bioimaging of associated metabolic behaviors with distinguishable organ-specific targeting capabilities and ligand-mediated kinetics in nanoparticle clearance. These findings expand the toolbox of oxidants for the controllable synthesis of NIR-II nanoprobes and open up a path for exploring diverse ligand interactions on ultrasmall AuNPs with organs or tissues that might advance their monitoring applications for a wide range of clinically important diseases.

When Metal Nanoclusters Meet Smart Synthesis

Atomically precise metal nanoclusters (MNCs) represent a fascinating class of ultrasmall nanoparticles with molecule-like properties, bridging conventional metal-ligand complexes and nanocrystals. Despite their potential for various applications, synthesis challenges such as a precise understanding of varied synthetic parameters and property-driven synthesis persist, hindering their full exploitation and wider application. Incorporating smart synthesis methodologies, including a closed-loop framework of automation, data interpretation, and feedback from AI, offers promising solutions to address these challenges. In this perspective, we summarize the closed-loop smart synthesis that has been demonstrated in various nanomaterials and explore the research frontiers of smart synthesis for MNCs. Moreover, the perspectives on the inherent challenges and opportunities of smart synthesis for MNCs are discussed, aiming to provide insights and directions for future advancements in this emerging field of AI for Science, while the integration of deep learning algorithms stands to substantially enrich research in smart synthesis by offering enhanced predictive capabilities, optimization strategies, and control mechanisms, thereby extending the potential of MNC synthesis.

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.

Axially Coordinated Gold Nanoclusters Tailoring Fe-N-C Nanozymes for Enhanced Oxidase-Like Specificity and Activity

Metal-organic frameworks (MOF) derived nitrogen-doped carbon-supported monodisperse Fe (Fe-N-C) catalysts are intensively studied, but great challenges remain in understanding the relationship between the coordination structure and the performance of Fe-N-C nanozymes. Herein, a novel nanocluster ligand-bridging strategy is proposed for constructing Fe-S1 N4 structures with axially coordinated S and Au nanoclusters on ZIF-8 derived Fe-N-C (labeled Aux /Fe-S1 N4 -C). The axial Au nanoclusters facilitate electron transfer to Fe active sites, utilizing the bridging ligand S as a medium, thereby enhancing the oxygen adsorption capacity of composite nanozymes. Compared to Fe-N-C, Aux /Fe-S1 N4 -C exhibits high oxidase-like specificity and activity, and holds great potential for detecting acetylcholinesterase activity with a detection limit of 5.1 µU mL-1 , surpassing most reported nanozymes.

Surface-Ligand Tuned Reversible Transformations in Aqueous Environments Between CdSe Magic-Size Clusters and Their Precursor Compounds

That magic-size clusters (MSCs) have their counterpart precursor compounds (PCs) has not been generally accepted by expertise circles. Here, experimental evidence to support this new concept is presented. With aqueous-phase CdSe MSCs as a model system, it is shown that when the MSCs are dispersed in water containing a certain amount of L-cysteine (Cys), the MSCs disappear slowly. Upon the addition of CdCl2 , the MSCs recover. It is proposed that after dispersing, the MSCs transform to their quasi-isomeric, non-absorbing PCs upon Cys addition. In the presence of CdCl2 , the PCs transform back to the MSCs due to Cys elimination. The surface ligand Cys of the MSCs plays a significant role in the reversible transformations. The present study provides compelling evidence that absorbing MSCs have their non-absorbing PCs. The study findings suggest that the transformation between two MSCs that display absorption spectral shifts in a stepwise pattern is assisted by their PCs.

-SR removal or -R removal? A mechanistic revisit on the puzzle of ligand etching of Au25(SR)18 nanoclusters during electrocatalysis

Accurate identification of active sites is highly desirable for elucidation of the reaction mechanism and development of efficient catalysts. Despite the promising catalytic performance of thiolated metal nanoclusters (NCs), their actual catalytic sites remain elusive. Traditional first-principles calculations and experimental observations suggested dealkylated S and dethiolated metal, respectively, to be the active centers. However, the real kinetic origin of thiolate etching during the electrocatalysis of NCs is still puzzling. Herein, we conducted advanced first-principles calculations and electrochemical/spectroscopic experiments to unravel the electrochemical etching kinetics of thiolate ligands in prototype Au25(SCH3)18 NC. The electrochemical processes are revealed to be spontaneously facilitated by dethiolation (i.e., desorption of -SCH3), forming the free HSCH3 molecule after explicitly including the solvent effect and electrode potential. Thus, exposed under-coordinated Au atoms, rather than the S atoms, serve as the real catalytic sites. The thermodynamically preferred Au-S bond cleavage arises from the selective attack of H from proton/H2O on the S atom under suitable electrochemical bias due to the spatial accessibility and the presence of S lone pair electrons. Decrease of reduction potential promotes the proton attack on S and significantly accelerates the kinetics of Au-S bond breakage irrespective of the pH of the medium. Our theoretical results are further verified by the experimental electrochemical and spectroscopic data. At more negative electrode potentials, the number of -SR ligands decreased with concomitant increase of the vibrational intensity of S-H bonds. These findings together clarify the atomic-level activation mechanism on the surface of Au25(SR)18 NCs.

Stepwise construction of Ag29 nanocluster-based hydrogen evolution electrocatalysts

Although several silver-based nanoclusters have been controllably prepared and structurally determined, their electrochemical catalytic performances have been relatively unexplored (or showed relatively weak ability towards electro-catalysis). In this work, we accomplished the step-by-step enhancement of the electrocatalytic hydrogen evolution reaction (HER) efficiency based on an Ag29 cluster template. A combination of atomically precise operations, including the kernel alloying, ligand engineering, and surface activation, was exploited to produce a highly efficient Pt1Ag28-BTT-Mn(10) nano-catalyst towards HER, derived from both experimental characterization and theoretical modelling. The precision characteristic of the Ag29-based cluster system enables us to understanding the correlations between nanocluster structures and HER performances at the atomic level. Overall, the findings of this work will hopefully provide more opportunities for the customization of new cluster-based nano-catalysts with enhanced electrocatalytic capacities.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Engineering ligand chemistry on Au25 nanoclusters: from unique ligand addition to precisely controllable ligand exchange

Au25 nanoclusters (NCs) protected by 18 thiol-ligands (Au25SR18, SR is a thiolate ligand) are the prototype of atomically precise thiolate-protected gold NCs. Studies concerning the alteration of the number of surface ligands for a given Au25SR18 NC are scarce. Herein we report the conversion of hydrophobic Au25PET18 (PET = 2-phenylethylthiolate) NCs to Au25SR19 [Au25PET18(metal complex)1] induced by ligand exchange reactions (LERs) with thiolated terpyridine-metal complexes (metal complex, metal = Ru, Fe, Co, Ni) under mild conditions (room temperature and low amounts of incoming ligands). Interestingly, we found that the ligand addition reaction on Au25PET18 NCs is metal dependent. Ru and Co complexes preferentially lead to the formation of Au25SR19 whereas Fe and Ni complexes favor ligand exchange reactions. High-resolution electrospray ionization mass spectrometry (HRESI-MS) was used to determine the molecular formula of Au25SR19 NCs. The photophysical properties of Au25PET18(Ru complex)1 are distinctly different from Au25PET18. The absorption spectrum is drastically changed upon addition of the extra ligand and the photoluminescence quantum yield of Au25PET18(Ru complex)1 is 14 times and 3 times higher than that of pristine Au25PET18 and Au25PET17(Ru complex)1, respectively. Interestingly, only one surface ligand (PET) could be substituted by the metal complex when neutral Au25PET18 was used for ligand exchange whereas two ligands could be exchanged when starting with negatively charged Au25PET18. This charge dependence provides a strategy to precisely control the number of exchanged ligands at the surface of NCs.

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.

Stepwise Amplification of Circularly Polarized Luminescence in Chiral Metal Cluster Ensembles

Chiral metal-organic frameworks (MOFs) are usually endowed by chiral linkers and/or guests. The strategy using chiral secondary building units in MOFs for solving the trade-off of circularly polarized luminescence (CPL)-active materials, high photoluminescence quantum yields (PLQYs) and high dissymmetry factors (|g_lum |) has not been demonstrated. This work directionally assembles predesigned chiral silver clusters with ACQ linkers through reticular chemistry. The nanoscale chirality of the cluster transmits through MOF's framework, where the linkers are arranged in a quasi-parallel manner and are efficiently isolated and rigidified. Consequently, this backbone of chiral cluster-based MOFs demonstrates superb CPL, high PLQYs of 50.3%, and |g_lum | of 1.2 × 10^-2 . Crystallographic analyses and DFT calculations show the quasi-parallel arrangement manners of emitting linkers leading to a large angle between the electric and magnetic transition dipole moments, boosting CPL response. As compared, an ion-pair-direct assembly without interactions between linkers induces one-ninth |g_lum | and one-sixth PLQY values, further highlighting the merits of directional arrangement in reticular nets. In addition, a prototype CPL switching fabricated by a chiral framework is controlled through alternating ultraviolet and visible light. This work is expected to inspire the development of reticular chemistry for high-performance chiroptical materials.

Luminescent Gold Nanoparticles with Controllable Hydrophobic Interactions

The construction of luminescent gold nanoparticles (AuNPs) with highly redshifted emission in the second near-infrared window (NIR-II) and good biocompatibility is still challenging. Herein, using an amphiphilic block copolymer (ABC) template with controllable hydrophobic interactions in the diverse forms of unimers and micelles, we report a facile strategy for redshifting the emission and enhancing the biological interactions of luminescent AuNPs. While the uniform clusters of NIR-II AuNPs are formed in situ inside the hydrophobic cores of ABC micelles with strong interparticle hydrophobic interactions and enhanced emission at 1080 nm with a high quantum yield (QY) of 1.6%, the rigid NIR-II AuNPs are generated with strong intraparticle hydrophobic interactions as ABC unimers on the surface, leading to a redshifted emission of 1280 nm with a QY of 0.25% and enhancing the affinities toward injured intestinal mucosa in colitis imaging. These findings open new possibilities for the design of highly redshifted luminescent AuNPs with enhanced biological interactions.

Snapshots of key intermediates unveiling the growth from silver ions to Ag70 nanoclusters

Nanoclusters (NCs) are considered as initial states of condensed matter, and unveiling their formation mechanism is of great importance for directional synthesis of nanomaterials. Here, we initiate the reaction of Ag(i) ions under weak reducing conditions. The prolonged reaction period provides a unique opportunity for revealing the five stages of the growth mechanism of 20-electron superatomic Ag70 NCs by a time-dependent mass technique, that is, aggregate (I) → reduction (II) → decomposition and recombination (III) → fusion (IV) → surface recombination and motif enrichment (V), which is different from the formation process applicable to the gold clusters. More importantly, the key intermediates, Ag14 without free electrons (0e) in the first (stage I) and Ag24 (4e) in the second (stage II), were crystallized and structurally resolved, and the later transformation rate towards Ag70 was further controlled by modulating solvents for easy identification of more intermediates. In a word, we establish a reasonable path of gradual expansion in size and electrons from Ag(i) ions to medium-sized 20e Ag70. This work provides new insights into the formation and evolution of silver NCs, and unveils the corresponding optical properties along with the process.