Recent progress in atomically precise silver nanocluster-assembled materials.

In the dynamic landscape of nanotechnology, atomically precise silver nanoclusters (Ag NCs) have emerged as a novel and promising category of materials with their fascinating properties and enormous potential. However, recent research endeavors have surged towards stabilizing Ag-based NCs, leading to innovative strategies like connecting cluster nodes with organic linkers to construct hierarchical structures, thus forming Ag-based cluster-assembled materials (CAMs). This approach not only enhances structural stability, but also unveils unprecedented opportunities for CAMs, overcoming the limitations of individual Ag NCs. In this context, this review delves into the captivating realm of atomically precise nitrogen-based ligand bonded Ag(I)-based CAMs, providing insights into synthetic strategies, structure-property relationships, and diverse applications. We navigate the challenges and advancements in integrating Ag(I) cluster nodes, bound by argentophilic interactions, into highly connected periodic frameworks with different dimensionalities using nitrogen-based linkers. Despite the inherent diversity among cluster nodes, Ag(I) CAMs demonstrate promising potential in sensing, catalysis, bio-imaging, and device fabrication, which all are discussed in this review. Therefore, gaining insight into the silver nanocluster assembly process will offer valuable information, which can enlighten the readers on the design and advancement of Ag(I) CAMs for state-of-the-art applications.

A thiolated copper-hydride nanocluster with chloride bridging as a catalyst for carbonylative C-N coupling of aryl amines under mild conditions: a combined experimental and theoretical study.

Atomically precise copper nanoclusters (Cu NCs), an emerging class of nanomaterials, have garnered significant attention owing to their versatile core-shell architecture and their potential applications in catalytic reactions. In this study, we present a straightforward synthesis strategy for [Cu29(StBu)12(PPh3)4Cl6H10][BF4] (Cu29) NCs and explore their catalytic activity in the carbonylative C-N coupling reaction involving aromatic amines and N-heteroarenes with dialkyl azodicarboxylates. Through a combination of experimental investigations and density functional theory studies, we elucidate the radical mechanisms at play. The crucial step in the catalytic process is identified as the decomposition of diisopropyl azodicarboxylates on the surface of Cu29 NCs, leading to the generation of oxyacyl radicals and the liberation of nitrogen gas. Subsequently, an oxyacyl radical abstracts a hydrogen atom from aniline, initiating the formation of an aminyl radical. Finally, the aminyl radical reacts with another oxyacyl radical, culminating in the synthesis of the desired carbamate product. This detailed analysis provides insights into the intricate catalytic pathways of Cu29 NCs, shedding light on their potential for catalyzing carbonylative C-N coupling reactions.

Two-Dimensional Silver-Chalcogenolate-Based Cluster-Assembled Material: A p-type Semiconductor.

We have synthesized and characterized a new two-dimensional honeycomb architecture resembling a single-layer of atomically precise silver cluster-assembled material (CAM), [Ag12(StBu)6(CF3COO)6(4,4'-azopyridine)3] (Ag12-azo-bpy). The interlayer noncovalent van der Waals interactions within the single-crystals were successfully disrupted, leading to the creation of this unique structure. The optimized Ag12-azo-bpy CAM demonstrates a valence band that is localized on the Ag12 cluster node situated near the Fermi energy level. This localization induces electron injection from the linker to the cluster node, facilitating efficient charge transportation along the plane. Exploiting this single-layer structure as a distinctive platform for p-type channel material, it was employed in a field-effect transistor configuration. Remarkably, the transistor exhibits a high hole mobility of 1.215 cm2 V-1 s-1 and an impressive ON/OFF current ratio of ∼4500 at room-temperature.

Surface Engineering of Atomically Precise M(I) Nanoclusters: From Structural Control to Room Temperature Photoluminescence Enhancement.

ConspectusUnderstanding the structural architecture of nanoparticles is essential for investigating their fundamental properties because these materials have become more desirable in modern nanoscience research. Designing a proper synthetic strategy to control their growth with atomic precision is crucial. The polydispersed nature of the nanoparticles makes determining their precise structural information challenging. Metal nanoclusters (NCs) have emerged as a promising solution to this problem as they bridge the gap between metal nanoparticles and discrete molecular complexes. Well-ordered molecular structures provide opportunities to look at structure-property correlations and find quantum confinement effects at the atomic level that reveal their similarity to molecular-like properties. While most M(0)/(I)-based NCs exhibit exceptional photoluminescence (PL) emission at room temperature, M(I)-based NCs are less likely to exhibit PL emissions due to their electronic environment. Developments in the field of metal nanoparticles have made it intriguing to achieve room-temperature PL emission in M(I) NCs. Efforts have focused on developing efficient methods for preparing luminescent M(I) NCs to better comprehend fundamental aspects of their PL emission properties. We provide an overview of various synthetic strategies for preparing NCs and their selective functionalization for generating room-temperature PL emissions. Our focus has been creating an Ag(I) NC with a core-shell architecture, as this unique structural design complements the charge transition phenomenon. The molecular structure obtained from single-crystal X-ray diffraction (SCXRD) and associated theoretical calculation revealed that our effort results in a unique hexagonal closed pack core and Keplerate shell containing [S@Ag50S12(StBu)20]4+ NC where the charge transition between the core and the metal-ligand shell facilitates emission properties. We also explored the approach of host-guest supramolecular adduct formations to engineer the surface of ligands that reduce nonradiative relaxation rates by restricting surface molecular vibrations and controlling the generation of PL emission. To do this, we capped precisely structured [Cl@Ag16S(S-Adm)8(CF3COO)5(DMF)3(H2O)2]·DMF with ß-cyclodextrin via adamantane moieties. We also describe the effects of bimetallic cluster formation on increasing surface rigidity and modulating the frontier molecular orbital arrangement, which helps to attain synergy to generate room-temperature PL emission. We focused on the structural integrity of Ag(I) NCs, allowing us to incorporate heterometal atoms at peripheral positions that lead to the formation of [CO2@Ag20Cu2S2(StBu)10(CF3COO)8(DMA)4]·(DMA). We also explored the impact of introducing extra ligands into the Ag(I) cluster node on the generation of PL emission at room-temperature. These strategies are not limited to Ag NCs. We discussed the possibility of combining core-shell architecture and surface modifications to enhance PL emission in [Cu18H3(S-Adm)12(PPh3)4Cl2] NC at room temperature. SCXRD studies revealed its distinct core-shell architecture that ensures electronic transitions and that transition is controlled by the imposed surface rigidity that yields a higher PL emission. We believe that this innovative structural engineering holds potential for the advancement of NC research, and this Account will inspire the scientific community to synthesize functional M(I) NCs.

Luminescent [CO2@Ag20(SAdm)10(CF3COO)10(DMA)2] nanocluster: synthetic strategy and its implication towards white light emission.

Owing to the quantized size and associated discrete energy levels, atomically precise silver nanoclusters (Ag NCs) hold great potential for designing functional luminescent materials. However, the thermally activated non-radiative transition of Ag(I)-based NCs has faded the opportunities. To acquire the structurally rigid architecture of cluster nodes for constraining such transitions, a new synthetic approach is unveiled here that utilizes a neutral template as a cluster-directing agent to assemble twenty Ag(I) atoms that ensure the maximum number of surface-protecting ligand attachment possibilities in a particular solvent medium. The solvent polarity triggers the precise structural design to circumvent the over-reliance of the templates, which results in the formation of [CO2@Ag20(SAdm)10(CF3COO)10(DMA)2] NC (where SAdm = 1-adamantanethiolate and DMA = N,N-dimethylacetamide) exhibiting an unprecedented room-temperature photoluminescence emission. The high quantum yield of the generated blue emission ensures its candidature as an ideal donor for artificial light-harvesting system design, and it is utilized with the two-step sequential energy transfer process, which finally results in the generation of ideal white light. For implementing perfect white light emission, the required chromophores in the green and red emission regions were chosen based on their effective spectral overlap with the donor components. Due to their favorable energy-level distribution, excited state energy transfers occurred from the NC to ß-carotene at the initial step, then from the conjugate of the NC and ß-carotene to another chromophore, Nile Blue, at the second step via a sequential Förster resonance energy transfer pathway.

Template-assisted alloying of atom-precise silver nanoclusters: a new approach to generate cluster functionality.

To acquire the atomic design of new functional Ag(i) nanoclusters (NCs), a new synthetic approach of site-specific alloying has been unveiled, by which the neutral CO2 templated Ag20 core is confined through Cu containing two peripheral motif units. The impact of surface charge, size and shape of the template on the self-assembly of Ag(i) has been precisely controlled here for the first time and as a result, a similar pentagonal gyrobicupola-like Ag20 core is formed while varying the templates (S2-, CO3 2- and CO2). However, the surface charge generated on the Ag(i) core due to the presence of a neutral template opens up the possibility of this novel alloying process. The introduction of strongly interacted peripheral motif units (DMA-CuS-) on the Ag20 core enforces more rigidity in the skeleton that reduces the probability of non-radiative transition in the excited state by lowering the intramolecular vibration. In addition to this, the incorporation of electron-donating peripheral motif units modulates the frontier molecular arrangement that helps in attaining the synergy which would ultimately turn on the room-temperature emission properties. The electron-donating effect of the peripheral motif units further leads to a sharp reduction of the bandgap and the symmetric position of the heterometal in the cluster minimizes the intercluster distances which further influences the intercluster charge carrier transport. So, the precise structure-property correlation with this novel synthetic approach will pave the way for a well-functioning NC design.

An atomically precise silver nanocluster for artificial light-harvesting system through supramolecular functionalization.

Designing an artificial light-harvesting system (LHS) with high energy transfer efficiency has been a challenging task. Herein, we report an atom-precise silver nanocluster (Ag NC) as a unique platform to fabricate the artificial LHS. A facile one-pot synthesis of [Cl@Ag16S(S-Adm)8(CF3COO)5(DMF)3(H2O)2]·DMF (Ag16) NC by using a bulky adamantanethiolate ligand is portrayed here which, in turn, alleviates the issues related to the smaller NC core designed from a highly steric environment. The surface molecular motion of this NC extends the non-radiative relaxation rate which is strategically restricted by a recognition site-specific supramolecular adduct with ß-cyclodextrin (ß-CD) that results in the generation of a blue emission. This emission property is further controlled by the number of attached ß-CD which eventually imposes more rigidity. The higher emission quantum yield and the larger emission lifetime relative to the lesser numbered ß-CD conjugation signify Ag16 ∩ ß-CD2 as a good LHS donor component. In the presence of an organic dye (ß-carotene) as an energy acceptor, an LHS is fabricated here via the Förster resonance energy transfer pathway. The opposite charges on the surfaces and the matched electronic energy distribution result in a 93% energy transfer efficiency with a great antenna effect from the UV-to-visible region. Finally, the harvested energy is utilized successfully for efficient photocurrent generation with much-enhanced yields compared to the individual components. This fundamental investigation into highly-efficient energy transfer through atom-precise NC-based systems will inspire additional opportunities for designing new LHSs in the near future.

[Cu18H3(S-Adm)12(PPh3)4Cl2]: fusion of Platonic and Johnson solids through a Cu(0) center and its photophysical properties.

Structural elucidation of atom-precise thiolate-protected copper nanoclusters (Cu NCs) containing Cu(0) is quite challenging. Here, we report a new adamantane-thiol-protected NC, [Cu18H3(S-Adm)12(PPh3)4Cl2] (Cu18), which represents the first observation of a rare mononuclear Cu(0)-containing Cu10H3Cl2 core that is constructed via kernel fusion through vertex sharing of the Platonic-solid- and Johnson-solid-geometry-like kernels and hydride-bridging. The unique core is surrounded by a Cu8S12P4 metal-ligand motif shell and adopts a butterfly-like structure. In comparison to its closest structural analogue, the predominant effect of the principal Cu atom vacancy-induced structural rearrangement is evidenced. The occupied orbitals of this NC have a major d-orbital contribution to the distorted Cu6 octahedral kernel, whereas unoccupied orbitals owe a contribution to the distorted Cu5 square-pyramidal kernel. Thus, the charge transfer phenomenon is uniquely instigated between the two fused kernels through Cu(d) → Cu(d) transition via the Cu(0) center. This NC exhibits violet emission due to kernel-dominated relaxation at room temperature, which is further enhanced by confining the surface protecting ligands through recognition-site-specific host-guest supramolecular adduct formation by ß-cyclodextrin. The unique electronic structure of this NC further facilitates its application toward photocurrent generation. Thus, this study offers a unique strategy for the controllable synthesis of a Cu(0)-containing Cu NC, which enables atomic-level insights into their optoelectronic properties.

The New Ag-S Cluster [Ag50S13(StBu)20][CF3COO]4 with a Unique hcp Ag14 Kernel and Ag36 Keplerian-Shell-Based Structural Architecture and Its Photoresponsivity.

In metal nanoclusters (NCs), the kernel geometry and the nature of the surface protecting ligands are very crucial for their structural stability and properties. The synthesis and structural elucidation of Ag NCs is challenging because the zerovalent oxidation state of Ag is very reactive and prone to oxidization. Here, we report the NC [Ag50S13(StBu)20][CF3COO]4 with a hexagonal close-packed (hcp) cagelike Ag14 kernel. A truncated cubic shell and an octahedral shell encapsulate the hcp-layered kernel via an interstitial S2- anionic shell to form an Ag36 Keplerian outer shell of the NC. A theoretical study indicates the stability of this NC in its 4+ charge state and the charge distribution between the kernel and Keplerian shell. The unprecedented electronic structure facilitates its application toward sustainable photoresponse properties. The new insights into this novel Ag NC kernel and Keplerian shell structure may pave the way to understanding the unique structure and developing electronic structure-based applications.

Role of Ligand on Photophysical Properties of Nanoclusters with fcc Kernel: A Case Study of Ag14(SC6H4X)12(PPh3)8 (X = F, Cl, Br).

The structure-property correlation of a series of silver nanoclusters (NCs) is essential to understand the origin of photophysical properties. Here, we report a series of face-centered cubic (fcc)-based silver NCs by varying the halogen atom in the thiolate ligand to investigate the influence of the halide atoms on the electronic structure. These are {Ag14(FBT)12(PPh3)8·(solvent)x} (NC-1), Ag14(CBT)12(PPh3)8 (NC-2), and Ag14(BBT)12(PPh3)8 (NC-3), where 4-fluorothiophenol (FBT), 4-chlorothiophenol (CBT), and 4-bromothiophenol (BBT) have been utilized as thiolate ligands, respectively. Interestingly, the optical and electrochemical bandgap values of these NCs nicely correlated with the electronic effect of the halides, which is governed by the intracluster and interclusters π-π interactions. These clusters are emissive at room temperature and the luminescence intensity increases with the lowering of temperature. The short lifetime data suggest that the emission is predominantly originating due to the interband relaxation (d → sp) of the Ag cores. Femtosecond transient absorption (TA) spectra revealed similar types of decay profiles for NC-2 and NC-3 and longer decay time for NC-2. The relaxation dominates the decay profile to the surface states and most of the excited-state energy dissipates via this process. This supports the molecular-like dynamics of these series of NCs with an fcc core. This overview shed light on an in-depth understanding of ligand's role in luminescence and transient absorption spectra.

Solvent-Dependent Photophysical Properties of a Semiconducting One-Dimensional Silver Cluster-Assembled Material.

Unraveling the total structure of the atom-precise silver cluster-assembled materials (CAMs) is extremely significant to elucidating the structure-property correlation, but it is a very challenging task. Herein, a new silver CAM is synthesized by a facile synthetic pathway with a unique distorted elongated square-bipyramid-based Ag11 core geometry. The core is protected by two different kinds of the surface protecting ligands (adamantanethiolate and trifluoroacetate) and connected through a bidentate organic linker. The crystallographic data show that this material embraces a one-dimensional periodic structure that orchestrates by various noncovalent interactions to build a thermally stable supramolecular assembly. Further characterization confirms its n-type semiconducting property with an optical band gap of 1.98 eV. The impact of an adamantanethiol-protected silver core on the optical properties of this type of periodic framework is analyzed by the UV-vis absorbance and emission phenomena. Theoretical calculations predicted that the occupied states are majorly contributed by Ag-S. Solvent-dependent photoluminescence studies proved that a polar solvent can significantly perturb the metal thiolate and thiolate-centered frontier molecular orbitals that are involved in the electronic transitions.

Novel class of water-soluble phosphonate silver cluster assembled material for efficient photoelectric sensing and photoacoustic imaging.

Owing to the atomic precession and exotic photophysical properties, silver cluster assembled materials (CAMs) have been explored for use as functional nanomaterials in recent years. Although a small number of thiolate protected silver CAMs have previously been investigated, the synthesis of thiol-free analogues and their solubility remain challenging. Here, the structure-property correlation of a newly synthesized one-dimensional phenyl phosphonate protected [Ag2(PhPO3H)2(apy)2], (in which, 4,4'-azopyridine = apy) CAM is demonstrated. The multifunctional surface protecting ligand is strategically attached to the core for the first time to tailor the solubility, structural stability and charge transfer mechanism. The small size of the cluster building blocks, along with the choice of organic linker molecules, efficiently stabilize the structure via intra-chain π-π stacking while inter-chains π-π interactions create a two-dimensional supramolecular architecture. The advantageous band structure associated with the charge transfer phenomenon and the high structural stability of the material are guided to explore the sustainable photoresponsive character of this CAM, resulting in the generation of an 82 nA photocurrent. Additionally, the unprecedented water solubility, which is very rare for this class of material, provides opportunities for use in biomedical imaging applications. The measured photoacoustic signal strength confirms the blood vessel mimicking capabilities of the portrayed material at a depth of approximately 3 mm inside chicken breast tissue.

One-Dimensional Silver-Thiolate Cluster-Assembly: Effect of Argentophilic Interactions on Excited-State Dynamics.

We report the synthesis, crystal structure, and electronic structure calculations of a one-dimensional silver-thiolate cluster-assembled and its ultrafast spectroscopic investigation. Experiments and theory find the material to have a significant gap as the HOMO-LUMO absorption corresponds to 2.69 eV, and the defect-free structure is calculated to have a gap of 2.82 eV. Cluster models demonstrate that the gap energy is length-dependent. Theoretical studies identify a nonbonding metallophilic interaction that exists between two Ag atoms in adjacent strings that helps to stabilize the chain structure. Transient absorption spectroscopy reveals that the electron dynamics is a mixture of the behavior of cluster and nanoparticle, with the material having a 346 fs ground-state relaxation like a cluster, and the electron dynamics is dominated by electron-phonon coupling with a decay time of 1.5 ps, unlike the isolated cluster whose decay is mostly radiative.

Defects Engineering on Ceria and C-C Coupling Reactions Using [Au11(PPh3)7I3] Nanocluster: A Combined Experimental and Theoretical Study.

Ligand protected atom-precise gold-based catalysts have been utilized in many essential chemical processes, but their mechanism and the fate of the catalyst during reaction are still unrevealed. Atom-precise cluster without ligands are thus highly desirable to maximize atom efficiency, but making these in solution phase is challenging. In this scenario, catalysts with dispersion on oxide support are highly desirable to understand the role of metal core during catalytic reaction. Here, we report the synthesis of Au11(PPh3)7I3 cluster that consists of an incomplete icosahedron core. During its impregnation process on CeO2 support, all of the ligands were removed from the kernel and the Au11 kernel fits into the defects of ceria (embedded onto the oxygen vacancy of ceria (111) plane). This Au11@CeO2 has high atom efficiency and catalytic activity for Ullmann-type C-C homocoupling reactions for electron rich substrates. Density functional theory calculations showed that hexagonal arrangements of Au11 kernel on (111) plane of CeO2 is the most stable one. Theoretical calculations also proved that the atop gold atom has more favorable interaction with phenyl iodide than the second layer gold atoms of the Au11@CeO2. This demonstrated that the present catalyst mimics the single-atom catalyst-like behavior in facilitating the coupling reactions.