Crystal Structure of Au30-xAgx(S-tBu)18 and Effect of the Ligand on Ag Alloying in Gold Nanomolecules

Triplet-triplet annihilation-based photon upconversion using nanoparticles and nanoclusters

The phenomenon of photon upconversion (UC), generating high-energy photons from low-energy photons, has attracted significant attention. In particular, triplet-triplet annihilation-based UC (TTA-UC) has been achieved by combining the excitation states of two types of molecules, called the sensitizer and emitter (or annihilator). With TTA-UC, it is possible to convert weak, incoherent near-infrared (NIR) light, which constitutes half of the solar radiation intensity, into ultraviolet and visible light that are suitable for the operation of light-responsive functional materials or devices such as solar cells and photocatalysts. Research on TTA-UC is being conducted worldwide, often employing materials with high intersystem crossing rates, such as metal porphyrins, as sensitizers. This review summarizes recent research and trends in triplet energy transfer and TTA-UC for semiconductor nanoparticles or nanocrystals with diameters in the nanometer range, also known as quantum dots, and for ligand-protected metal nanoclusters, which have even smaller well-defined sub-nanostructures. Concerning nanoparticles, transmitter ligands have been applied on the surface of the nanoparticles to efficiently transfer triplet excitons formed inside the nanoparticles to emitters. Applications are expanding to solid-state UC devices that convert NIR light to visible light. Additionally, there is active research in the development of sensitizers using more cost-effective and environmentally friendly elements. Regarding metal nanoclusters, methods have been established for the evaluation of excited states, deepening the understanding of luminescent properties and excited relaxation processes.

Construction of novel Ag(0)-containing silver nanoclusters by regulating auxiliary phosphine ligands

Controlled synthesis of metal clusters through minor changes in surface ligands holds significant interest because the corresponding entities serve as ideal models for investigating the ligand environment's stereochemical and electronic contributions that impact the corresponding structures and properties of metal clusters. In this work, we obtained two Ag(0)-containing nanoclusters (Ag17 and Ag32) with near-infrared emissions by regulating phosphine auxiliary ligands. Ag17 and Ag32 bear similar shells wherein Ag17 features a trigonal bipyramid Ag5 kernel while Ag32 has a bi-icosahedral interpenetrating an Ag20 kernel. Ag17 and Ag32 showed a near-infrared emission (NIR) of around 830 nm. Benefiting from the rigid structure, Ag17 displayed a more intense near-infrared emission than Ag32. This work provides new insight into the construction of novel superatomic silver nanoclusters by regulating phosphine ligands.

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

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

Ion mobility-tandem mass spectrometry of bulky tert-butyl thiol ligated gold nanoparticles

Gold nanoparticles (AuNPs) synthesized in the 1-3 nm range have a specific number of gold core atoms and outer protecting ligands. They have become one of the "hot topics" in recent decades because of their interesting physical and chemical properties. The characterization of their structures is usually achieved by crystal X-ray diffraction although the structures of some AuNPs remain unknown because they have not been successfully crystallized. An alternative method for studying the structure of AuNPs is electrospray ionization-ion mobility-tandem mass spectrometry (ESI-IM-MSMS). This research evaluated how effectively ESI-IM-MSMS using the commercially available Waters Synapt XS instrument yielded useful structural information from two AuNPs; Au23 (S-tBu)16 and Au30 (S-tBu)18 . The study used the maximum range of available collision energies along with ion mobility separation to measure the energy-dependence of the product ions and their drift times which is a measure of their spatial size. For Au23 (S-tBu)16 , the dissociation gave the masses of the outer protecting monomeric [RS-Au-SR] and trimeric [SR-Au-SR-Au-SR-Au-SR] staples where R = tBu, and complete dissociation of the outer layer Au and tBu groups to reveal the Au15 S8 core. For Au30 (S-tBu)18 , the dissociation products was primarily through the loss of the partial ligands S-tBu and tBu from the outer protecting layer and the loss of single Au4 (S-tBu)4 unit. These results showed the that ESI-IM-MSMS analysis of the smaller Au23 (S-tBu)16 gave information on all it major structural components whereas for Au30 (S-tBu)18 , the overall structural information was limited to the ligands of the outer layer.

A heteroleptic fused bi-cuboctahedral Cu21S2 cluster

A new dicationic cluster, [Cu₂₁S₂{S₂CNⁿBu₂}₉(C₂Ph)₆]²⁺, where the Cu21S2 kernel consists of two S@Cu₁₂ cuboctahedra sharing a triangular Cu₃ face is reported. Its waist part is bridged by three dithiocarbamate ligands, each in a hexaconnective, hexametallic (μ₃, μ₃) coordination pattern, an unprecedented feature in Cu nanocluster chemistry.

Alloying and dealloying of Au18Cu32 nanoclusters at precise locations via controlling the electronegativity of substituent groups on thiol ligands

The doping site of metals in an alloy nanocluster plays a key role in determining the cluster properties. Herein, we found that alloying engineering was achieved by replacing Cu at specific positions in the second layer Cu₂₀ shell of the [Au18Cu32(SR-O)36]2- or [Au18Cu32(SR-F)36]3- (SR-O = -S-PhOMe; SR-F = -SC₆H₃^3,4F₂) nanocluster with Au to generate a core-shell [Au20.31Cu29.69(SR-O)36]2- protected by mercaptan ligands with electron-donating substituents, which could be stable obtained compared with the alloyed nanocluster with electron-withdrawing substituent ligands. Moreover, dealloying engineering was accomplished by an electron-withdrawing substituent ligand exchange strategy (i.e., [Au18Cu32(SR-F)36]2-). The abovementioned reaction was analyzed using single-crystal X-ray crystallography, electrospray ionization mass spectrometry, and X-ray photoelectron spectroscopy and monitored via time-dependent ultraviolet-visible absorption spectroscopy. This reversible and precise location of alloying and dealloying provides the possibility for studying the relationship between the structure and properties of nanoclusters at the atomic level.

Total Structure of Bimetallic Core-Shell [Au42 Cd40 (SR)52 ]2- Nanocluster and Its Implications

Bimetallic core-shell nanostructures hold great promise in elucidating the bimetallic synergism. However, it remains a challenge to construct atomically precise core-shell with high-valence active metals on the gold surface. In this work, we report the total structure of a [Au₄₂ Cd₄₀ (SR)₅₂ ]^2- core-shell nanocluster and multiple implications. Single crystal X-ray diffraction (SCXRD) reveals that the structure possesses a two-shelled Au₆ @Au₃₆ core and a closed cadmium shell of Cd₄₀ , and the core-shell structure is then protected by 52 thiolate (-SR) ligands. The composition of the nanocluster is further confirmed by electrospray ionization mass spectrometry (ESI-MS). A catalytic test for styrene oxidation and a comparison with relevant nanoclusters reveal the surface effect on the catalytic activity and selectivity.