Abstract Homology is well known in organic chemistry; however, it has not yet been reported in nanochemistry. Herein, we introduce the concept of kernel homology to describe the phenomenon of metal nanoclusters sharing the same “functional group” in kernels with some similar properties. To illustrate this point, we synthesized two novel gold nanoclusters, Au 44 (TBBT) 26 and Au 48 (TBBT) 28 (TBBTH=4‐tert‐butylbenzenethiol), and solved their total structures by X‐ray crystallography, which reveals that they have the same Au 23 bi‐icosahedron capped with a similar bottom cap (Au 6 and Au 8 , respectively) in the kernels. The two novel gold nanoclusters, together with the existing Au 38 (PET) 24 nanocluster (PETH=phenylethanethiol), have the same “functional group”—Au 23 —in their kernels and have some similar properties (e.g., electrochemical properties); therefore, they are comparable to the homologues in organic chemistry.
Crystallization-induced photoluminescence weakening was recently revealed in ultrasmall metal nanoparticles. However, the fundamentals of the phenomenon are not understood yet. By obtaining conformational isomer crystals of gold nanoclusters, we investigate crystallization-induced photoluminescence weakening and reveal that the shortening of interparticle distance decreases photoluminescence, which is further supported by high-pressure photoluminescence experiments. To interpret this, we propose a distance-dependent non-radiative transfer model of excitation electrons and support it with additional theoretical and experimental results. This model can also explain both aggregation-induced quenching and aggregation-induced emission phenomena. This work improves our understanding of aggregated-state photoluminescence, contributes to the concept of conformational isomerism in nanoclusters, and demonstrates the utility of high pressure studies in nanochemistry.
This paper reports the synthesis of a new class of NaLnF4–Ag (Ln = Nd, Sm, Eu, Tb, Ho) hybrid nanorice and its application as a surface-enhanced Raman scattering (SERS) substrate in chemical analyses. Rice-shaped NaLnF4 nanoparticles as templates are prepared by a modified hydrothermal method. Then, the NaLnF4 nanorice particles are decorated with Ag nanoparticles by magnetron sputtering method to form NaLnF4–Ag hybrid nanostructures. The high-density Ag nanogaps on NaLnF4 can be obtained by the prolonging sputtering times or increasing the sputtering powers. These nanogaps can serve as Raman 'hot spots', leading to dramatic enhancement of the Raman signal. The NaLnF4–Ag hybrid nanorice is found to be robust and is an efficient SERS substrate for the vibrational spectroscopic characterization of molecular adsorbates; the Raman enhancement factor of Rhodamine 6G (R6G) absorbed on NaLnF4–Ag nanorice is estimated to be about 1013. Since the produced NaLnF4–Ag hybrid nanorice particles are firmly fastened on a silicon wafer, they can serve as universal SERS substrates to detect target analytes. We also evaluate their SERS performances using 4-mercaptopyridine (Mpy), and 4-mercaptobenzoic acid (MBA) molecules, and the detection limit for Mpy and MBA is as low as 10−12 M and 10−10 M, respectively, which meets the requirements of the ultratrace detection of analytes. This simple and highly efficient approach to the large-scale synthesis of NaLnF4–Ag nanorice with high SERS activity and sensitivity makes it a perfect choice for practical SERS detection applications.
Among many outstanding findings associated with the quantum size effect, one of the most exciting is the discovery of the antigalvanic reaction (AGR), which is the opposite of the classic galvanic reaction (GR) that has a history of nearly 240 years. The GR, named after Italian scientist Luigi Galvani, involves the spontaneous reduction of a noble-metal cation by a less noble metal in solution driven by the difference in electrochemical potentials. Classic galvanic reduction has been widely applied and has recently received particular interest in nanoscience and nanotechnology. However, the opposite of GR, that is, reduction of metal ions by less reactive (or more noble) metals, has long been regarded as a virtual impossibility until the recent surprising findings regarding atomically precise ultrasmall metal nanoparticles (nanoclusters), which bridge the gap between metal atoms (complexes) and metal nanocrystals and provide opportunities for novel scientific findings due to their well-defined compositions and structures. The AGR is significant not only because it is the opposite of the classic galvanic theory but also because it opens extensive applications in a large range of fields, such as sensing and tuning the compositions, structures, and properties of nanostructures that are otherwise difficult to obtain. Starting with the proposal of the general AGR concept in 2012 by Wu, a new era began, in which AGR received widespread attention and was extensively studied. After years of effort, great advances have been achieved in the research on AGR, which will be reviewed below. In this Account, we first provide a short introduction to the AGR concept and then discuss the driving force of the AGR together with the effecting factors, including the ligand, particle size, solvent, metal ion precursor, and ion dose. Subsequently, the application of the AGR in engineering atomically precise alloy (bimetallic and trimetallic) and monometallic nanoclusters is described, and tuning the properties of the parent nanoclusters is also included. In particular, four alloying modes (namely, (i) addition, (ii) replacement, (iii) replacement and structural transformation, and (iv) nonreplacement and structural transformation) associated with the AGR are discussed. After that, the applications of the AGR in metal ion sensing and antioxidation are reviewed. Finally, future prospects are discussed, and some challenging issues are presented at the end of this Account. It is expected that this Account will stimulate more scientific and technological interests in the AGR, and exciting progress in the understanding and application of the AGR will be made in the coming years.
Abstract Unravelling the structure of thiolated metalloid gold nanoclusters in the medium‐sized range by single crystal X‐ray crystallography (SCXC) is challenging. Herein, we successfully synthesized a novel Au 67 (SR) 35 nanocluster, and unravelled its single crystal structure by SCXC, which features a mix‐structured Au 48 kernel protected by one Au 4 (SR) 5 staple and fifteen Au(SR) 2 staples. Unprecedentedly, this structure can be thermally induced to aggregate into larger nanoparticles and self‐deposit to form a gold nanoparticles film onto the walls of a vial or other substrates such as quartz, mica or ceramic, which can be developed into a facile, substrate‐universal and scalable filming method. The film exhibits high sensitivity, uniformity and recyclability as a surface‐enhanced Raman scattering (SERS) substrate and can be applied for detecting multiple organic pollutants.
Abstract Can the active kernels in ultrasmall metal nanoparticles (nanoclusters, NCs) react with one another, or can the internanocluster reaction occur when they are in close enough proximity? To resolve this fundamental issue, we investigated the solid‐state internanocluster reaction of the most studied gold NC Au 25 (SR) 18 (SR: thiolate). A novel NC was produced by increasing the pressure to 5 GPa, whose composition was determined to be Au 32 (SC 2 H 4 Ph) 24 by mass spectrometry and thermogravimetric analysis. As revealed by single‐crystal X‐ray crystallography, the structure, a bicuboid Au 14 kernel and three pairs of interlocked trimetric staples, has not been reported and endows the NC with obvious photoluminescence. DFT calculations indicate that the staples contribute substantially to the absorption properties. Further experiments reveal the pressure (internanocluster distance) can tune the internanocluster reaction, and the resulting product is not necessarily the thermodynamic product.
Abstract An assembly strategy for metal nanoclusters using electrostatic interactions with weak interactions, such as C−H⋅⋅⋅π and π⋅⋅⋅π interactions in which cationic [Ag 26 Au(2‐EBT) 18 (PPh 3 ) 6 ] + and anionic [Ag 24 Au(2‐EBT) 18 ] − nanoclusters gather and assemble in an unusual alternating array stacking structure is presented. [Ag 26 Au(2‐EBT) 18 (PPh 3 ) 6 ] + [Ag 24 Au(2‐EBT) 18 ] − is a new compound type, a double nanocluster ion compound (DNIC). A single nanocluster ion compound (SNIC) [PPh 4 ] + [Ag 24 Au(2‐EBT) 18 ] − was also synthesized, having a k‐vector‐differential crystallographic arrangement. [PPh 4 ] + [Ag 24 Au(2,4‐DMBT) 18 ] − adopts a different assembly mode from both [Ag 26 Au(2‐EBT) 18 (PPh 3 ) 6 ] + [Ag 24 Au(2‐EBT) 18 ] − and [PPh 4 ] + [Ag 24 Au(2‐EBT) 18 ] − . Thus, the striking packing differences of [Ag 26 Au(2‐EBT) 18 (PPh 3 ) 6 ] + [Ag 24 Au(2‐EBT) 18 ] − , [PPh 4 ] + [Ag 24 Au(2‐EBT) 18 ] − and the existing [PPh 4 ] + [Ag 24 Au(2,4‐DMBT) 18 ] − from each other indicate the notable influence of ligands and counterions on the self‐assembly of nanoclusters.
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