Ag nanocluster assembly and manufacturing method thereof

Abstract

To provide an aggregate of Ag nanoclusters that features the structured and periodic arrangement of the Ag nanoclusters, demonstrating outstanding thermal stability.SOLUTION: An aggregate of Ag nanoclusters comprises Ag nanoclusters, comprising two or more Ag atoms, connected and aggregated through an organic compound as a linker. The linker comprises C-C triple bonds, with pyridine ligands at every terminus.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an Ag nanocluster assembly in which Ag nanoparticles are regularly aggregated. More specifically, the present invention relates to an Ag nanocluster assembly that has excellent thermal stability compared to conventional techniques while maintaining the properties of a nanocluster assembly in which Ag nanoclusters are regularly and suitably dispersed. [Background technology]

[0002] By reducing metals to nanometer-scale particles, quantum size effects can be exploited to reveal various properties not found in bulk materials, such as photoresponsiveness (photoluminescence), fluorescence, light scattering and reflection, and plasmon resonance. In particular, ultrafine particles consisting of several to several hundred metal atoms, known as metal nanoclusters, have been reported to exhibit even more pronounced quantum size effects. Therefore, metal nanoclusters are being considered for use in a variety of fields, including light-emitting elements and fluorescent materials in display devices and biomarkers, as well as electrode and wiring materials for various electronic and semiconductor devices. Furthermore, because ultrafine metal particles increase the metal surface area, which leads to improved catalytic activity, metal nanoclusters are also being considered for use as catalysts for various chemical reactions.

[0003] Many of the reported uses of metal nanoclusters to date involve their dispersion in an appropriate dispersion medium (generally a liquid solvent). Specifically, the metal nanoclusters are immobilized by applying a dispersion liquid containing the metal nanoclusters to a support such as a catalyst or marker, or to a device substrate.

[0004] In recent years, several studies have been reported on metal nanocluster aggregates as a new application of metal nanoclusters. Metal nanocluster aggregates are structures formed by linking multiple metal nanoclusters together using a bridging agent called a linker. In the metal nanocluster dispersion described above, the metal nanoclusters are irregularly and randomly dispersed in the dispersion medium, and this state remains the same after the dispersion is applied to a support or other surface. Even in this state, individual metal nanoclusters can still exhibit their desired properties to some extent. However, to effectively utilize the properties of metal nanoclusters with reproducibility and uniformity, it is preferable to arrange the metal nanoclusters in a regular and periodic manner. Therefore, by using metal nanoclusters as aggregates that have been pre-assembled in a regular pattern, the properties of the metal nanoclusters can be improved.

[0005] An example of a prior study on nanocluster assemblies is the Ag (silver) nanoparticle assembly described in Patent Document 1. In this prior art, Ag nanoparticles (Ag nanoclusters) protected in advance with a dispersant such as PVP are produced by a wet reduction method, and these are then linked with a sulfur compound such as cysteine ​​as a linker to form an Ag nanoparticle assembly.

[0006] The Ag nanocluster assembly of Patent Document 1 can be said to be a structure that meets the definition in the sense that it is an assembly of metal nanoclusters. However, this prior art does not mention the periodicity or regularity of the Ag nanoclusters bonded by the linker. The linker that forms the metal nanocluster assembly is an organic compound that has a ligand that can bond with the metal nanocluster and can link and arrange the particles together. In this sense, the linker in the Ag nanocluster assembly of Patent Document 1 also meets these requirements. However, in addition to functioning as a cross-linking material, the linker must also have the function of regularly arranging the metal nanoclusters. Patent Document 1 does not form a regular array of metal nanoclusters using the linker.

[0007] On the other hand, the Ag nanocluster assembly described in Non-Patent Document 1 is an example of an accurate study of the function of linkers in metal nanocluster assemblies, taking into account the formation of regularity and periodicity. This document reports an attempt to form an Ag nanocluster assembly using 4,4'-bipyridine (Chemical Formula 1 below) as a linker. Non-Patent Document 1 reveals that the linker 4,4'-bipyridine self-organizes Ag nanoclusters to form an Ag nanocluster assembly. Note that self-organization here refers to the autonomous formation of an assembly with a regular, ordered structure during the process of Ag nanoclusters bonding with the linker. Furthermore, it has been shown that the Ag nanocluster assembly described in Non-Patent Document 1 can maintain a stable periodic and ordered structure even in the atmosphere.

[0008] [ka] [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5581480 Specification [Non-patent literature]

[0010] [Non-Patent Document 1] Ren-Wu Huang et.al, “Hypersensitive dual-function luminescence switching of asilver-chalcogenolate cluster-based metal-organic framework.”, Nature chemistry, 9.7 (2017), p689-697. Summary of the Invention [Problem to be solved by the invention]

[0011] Although there have been several studies on metal nanocluster assemblies, such as those mentioned above, the current situation is that there are few. In particular, there are few rigorous studies that consider the regularity and periodicity of the metal nanoclusters that make up the assembly. Furthermore, there are even fewer studies that consider not only the regular and periodic arrangement of metal nanoclusters but also practical applications such as post-manufacture stability. For example, the Ag nanocluster assembly described in Non-Patent Document 1 above can maintain a stable periodic structure in the air at room temperature, but there is a risk of decomposition when heated. Ensuring thermal stability is an unavoidable challenge when using metal nanocluster assemblies in the various fields mentioned above.

[0012] The present invention was made against the background described above and relates to an Ag nanocluster assembly that uses Ag nanoclusters among metal nanocluster assemblies. The object of the present invention is to provide an assembly in which Ag nanoclusters are regularly and periodically arranged, which has superior thermal stability to those reported so far. [Means for solving the problem]

[0013] To address the above-mentioned issues, the present inventors investigated the use of organic compounds containing pyridine ligands, the same as the linker (4,4'-bipyridine) described in Non-Patent Document 1, as linkers for constructing Ag nanocluster assemblies. The premise of the present invention is to periodically and regularly assemble Ag nanoclusters when constructing Ag nanocluster assemblies. This is because pyridine ligands have good bonding properties with Ag nanoclusters and, as described above, exhibit favorable self-organization properties during the bonding process with Ag nanoparticles. Meanwhile, the thermal decomposition of Ag nanocluster assemblies is a phenomenon that occurs in relation to the stability of the organic compound that serves as the linker and the bonding strength between the linker and the Ag particles. After extensive research from these perspectives, the present inventors discovered that the thermal stability of Ag nanocluster assemblies can be improved by using an organic compound with pyridine ligands at the ends and triple bonds connecting them as the linker, leading to the present invention.

[0014] The present invention, which solves the above-mentioned problems, provides an Ag nanocluster assembly obtained by assembling Ag nanoclusters, each containing two or more Ag atoms, via a linker made of an organic compound, wherein the linker is an organic compound represented by Chemical Formula 2 or Chemical Formula 3 below, all of whose ends are pyridine ligands. The configuration and manufacturing method of the Ag nanocluster assembly according to the present invention will be described in detail below.

[0015] [ka] In the above formula, the two pyridine ligands are bonded by a carbon-carbon triple bond, and each of the two pyridine ligands may independently have a substituent.

[0016] [ka] In the above formula, n is the number of pyridine ligands and is an integer of 2 to 8. The group X is any of carbon, nitrogen, and phosphorus, or an aliphatic hydrocarbon group having from 1 to 6 carbon atoms which may have a substituent, or a monocyclic, linked, or fused ring aromatic hydrocarbon group having from 6 to 42 carbon atoms (each of these groups may independently have a substituent), or a monocyclic, linked, or fused ring heteroaromatic group having from 3 to 68 carbon atoms (each of these groups may independently have a substituent). The pyridine ligand and the group X are bonded via a carbon-carbon triple bond. The n pyridine ligands may each independently have a substituent.

[0017] The structure and manufacturing method of the Ag nanocluster aggregate according to the present invention will be described below.

[0018] I. Structure of Ag nanocluster assembly according to the present invention As described above, the Ag nanocluster assembly according to the present invention is composed of Ag nanoclusters made up of Ag atoms and linkers. Each of these will be described in detail below.

[0019] (i) Ag nanoclusters Ag is a metal that not only has the excellent electrical conductivity required for electrodes and wiring, but also has catalytic properties such as photocatalysis. When Ag is made into nanoparticles, it also exhibits unique properties such as photoresponsiveness (photoluminescence properties) and plasmon resonance. In the present invention, we focus on these properties of Ag to integrate Ag nanoclusters.

[0020] The Ag nanocluster constituting the Ag nanocluster assembly according to the present invention is composed of two or more Ag atoms, preferably 4 to 78 Ag atoms, more preferably 4 to 30 Ag atoms.

[0021] Furthermore, Ag nanoclusters may be composed only of Ag atoms, but may also contain atoms of other elements. For example, atoms of elements that bond strongly with Ag, such as S (sulfur), O (oxygen), N (nitrogen), C (carbon), Cu (copper), and Au (gold), contribute to the stability of Ag nanoclusters, optimization of the number of Ag atoms constituting the nanocluster, high activation, and high durability. The Ag nanoclusters composed of 4 to 78 Ag elements described above may contain 1 to 43 atoms of other elements.

[0022] Furthermore, Ag nanoclusters may be bound with organic ligands other than the pyridine ligand, which is the main component of the linker. These organic ligands are derived from complexing agents used in synthesizing the Ag complexes that are synthesized as precursors when producing Ag nanoclusters before they are bound to the linker, or from modifiers and protectants used to adjust the shape of the produced Ag nanoclusters and prevent their aggregation. These organic ligands may remain bound to the Ag nanoclusters even after they are aggregated.

[0023] Examples of organic ligands that can be bound to the Ag nanoclusters of the present invention include thiol group-containing ligands, ethynyl group-containing ligands, carboxylate group-containing ligands, etc. Specific examples of these organic ligands will be described later in the description of the production method.

[0024] (ii) Linker As described above, the linker is a key component of the present invention for periodically and regularly assembling Ag nanoclusters, with the premise that it acts as a cross-linking agent for Ag nanoclusters (metal nanoclusters). The Ag nanocluster assembly of the present invention has pyridine ligands at all ends and uses an organic compound represented by Chemical Formula 2 or 3 above as a linker, which has carbon-carbon triple bonds in its structure with the pyridine ligands.

[0025] The pyridine ligands placed at all ends of the organic compound that serves as the linker are the ligands that bind to the Ag nanoclusters. The linker, having pyridine ligands at all ends, acts as a cross-linking agent that bonds Ag nanoparticles together. The application of pyridine ligands ensures the periodicity and regularity of the Ag nanocluster assembly.

[0026] Furthermore, in the linker of the Ag nanocluster assembly according to the present invention, when a pair of pyridine ligands are bonded together (Chemical Formula 2), or when n pyridine ligands are bonded to the group X located between them (at the center) (Chemical Formula 3), the bond is a carbon-carbon triple bond. The pyridine ligand of the linker of the present invention contains a triple bond in order to improve the thermal stability of the Ag nanocluster assembly. A triple bond has very large bond energy and a rigid structure that is less susceptible to rotation and bending than a single bond. Furthermore, because a triple bond has high electron-withdrawing properties and a short bond distance, it also has the effect of improving the bond strength between the Ag nanocluster and the pyridine ligand. Due to these effects, the Ag nanocluster assembly using the above linker of the present invention has improved thermal stability.

[0027] The linker used in the present invention is an organic compound (4-(2-pyridin-4-ylethynyl)pyridine) in which two pyridine ligands are bonded by a triple bond as shown in Chemical Formula 2, or an organic compound in which n pyridine ligands located at all terminals are bonded to a group X by a triple bond as shown in Chemical Formula 3.

[0028] The number n of pyridine ligands in Chemical Formula 3 is 2 or more and 8 or less. In order to have pyridine ligands at all terminals while having a triple bond, two or more pyridine ligands are necessary. Furthermore, when an organic compound having more than eight pyridine ligands is used as a linker, crystallization becomes difficult due to steric hindrance, so the number of pyridine ligands is set to 8 or less. The number n of pyridine ligands is more preferably 2 or more and 4 or less.

[0029] Furthermore, the n pyridine ligands in Chemical Formula 2 and Chemical Formula 3 may each independently have a substituent. Examples of the substituent include linear or branched alkyl groups having 1 to 20 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, i-butyl, etc.), alkene groups, alkenyl groups, alkoxy groups, hydroxy groups, cyano groups, carboxy groups, amide groups, nitro groups, carbonyl groups, aldehyde groups, sulfonyl groups, sulfinyl groups, ester groups, silyl groups, siloxanyl groups, and halogen groups such as fluorine atoms, chlorine atoms, and bromine atoms.

[0030] In the organic compound serving as a linker of the present invention, the group X is any of carbon, nitrogen, or phosphorus, or an aliphatic hydrocarbon group having from 1 to 6 carbon atoms which may have a substituent, or a monocyclic, linked, or fused ring aromatic hydrocarbon group having from 6 to 42 carbon atoms (each of these groups may independently have a substituent), or a monocyclic, linked, or fused ring heteroaromatic group having from 3 to 68 carbon atoms (each of these groups may independently have a substituent). The group X will be described in detail below.

[0031] When the group X is an aliphatic hydrocarbon group having 1 to 6 carbon atoms, the group X is preferably an aliphatic hydrocarbon group composed of carbon, oxygen, nitrogen, and sulfur. Examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups and unsaturated aliphatic hydrocarbon groups. The aliphatic hydrocarbon group may be linear, branched, or cyclic. Examples of the saturated aliphatic hydrocarbon group include alkyl groups, alkoxy groups, and cycloalkyl groups. Examples of the unsaturated aliphatic hydrocarbon group include alkenyl groups, alkynyl groups, and cycloalkenyl groups.

[0032] When the group X is a monocyclic, linked, or fused-ring aromatic hydrocarbon group having from 6 to 42 carbon atoms, examples of the group X include a phenyl group, a biphenylyl group, a terphenyl group, a naphthalenyl group, a phenylnaphthyl group, a naphthylphenyl group, an anthracenyl group, a pyrenyl group, a phenanthrenyl group, a perylenyl group, a triphenylenyl group, a tetracenyl group, a benzanthracenyl group, a chrysenyl group, and a benzophenanthrenyl group.

[0033] Furthermore, when the group X is a monocyclic, linked, or fused-ring heteroaromatic group having from 3 to 68 carbon atoms, examples of the group X include a pyridyl group, a bipyridyl group, a triazinyl group, a pyrrolyl group, an imidazolyl group, a thiazolyl group, a benzothiadiazole group, a furanyl group, a benzofuranyl group, a dibenzofuranyl group, a thienyl group, a benzothienyl group, a dibenzothienyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a quinolinyl group, an isoquinolinyl group, a carbazolyl group, a pyridyl-phenyl group, a phenyl-pyridyl group, a pyridyl-biphenylyl group, a pyrimidyl-phenyl group, a bicyclo[1.1.1]pentenyl group, a porphyrinyl group, a phthalocyanyl group, and a phenyl-pyrimidyl group.

[0034] The groups X may each independently have a substituent, such as a linear or branched alkyl group having 1 to 20 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, or i-butyl group), an alkene group, alkenyl group, alkoxy group, hydroxy group, cyano group, carboxy group, amide group, nitro group, carbonyl group, aldehyde group, sulfonyl group, sulfinyl group, ester group, silyl group, siloxanyl group, or a halogen group such as a fluorine atom, chlorine atom, or bromine atom, etc.

[0035] The organic compounds in which the number n of pyridine ligands is 2 to 4 and which are suitable as linkers for the Ag nanocluster assembly according to the present invention are as follows:

[0036] (ii-1) Linker consisting of two pyridine ligands The linker having two pyridine ligands (n=2) is an organic compound represented by Chemical Formula 2 (4-(2-pyridin-4-ylethynyl)pyridine: Chemical Formula 4 below) and an organic compound represented by Chemical Formula 5 below.

[0037] [ka]

[0038] [ka]

[0039] In the organic compound represented by the above formula, the pyridine ligand and X1 are bonded via a carbon-carbon triple bond. The group X1 is preferably carbon, an aliphatic hydrocarbon group having from 1 to 6 carbon atoms which may have a substituent, a monocyclic, linked, or fused ring aromatic hydrocarbon group having from 6 to 22 carbon atoms (each of these groups may independently have a substituent), or a monocyclic, linked, or fused ring heteroaromatic group having from 3 to 44 carbon atoms (each of these groups may independently have a substituent).

[0040] In this organic compound, when the group X1 is an aliphatic hydrocarbon group having from 1 to 6 carbon atoms, the group X1 is preferably an aliphatic hydrocarbon group composed of carbon, oxygen, nitrogen, and sulfur. Examples of the aliphatic hydrocarbon group include saturated aliphatic hydrocarbon groups and unsaturated aliphatic hydrocarbon groups. The aliphatic hydrocarbon group may be linear, branched, or cyclic. Examples of the saturated aliphatic hydrocarbon group include alkyl groups, alkoxy groups, and cycloalkyl groups. Examples of the unsaturated aliphatic hydrocarbon group include alkenyl groups, alkynyl groups, and cycloalkenyl groups.

[0041] Furthermore, when the group X1 is a monocyclic, linked, or fused-ring aromatic hydrocarbon group having 6 to 22 carbon atoms, examples of the group X1 include a phenyl group, a biphenylyl group, a terphenyl group, a naphthalenyl group, a phenylnaphthyl group, a naphthylphenyl group, an anthracenyl group, a pyrenyl group, a phenanthrenyl group, a perylenyl group, a triphenylenyl group, a tetracenyl group, a benzanthracenyl group, a chrysenyl group, and a benzophenanthrenyl group.

[0042] Furthermore, when the group X1 is a monocyclic, linked, or fused-ring heteroaromatic group having 3 to 44 carbon atoms, examples of the group X1 include a pyridyl group, a bipyridyl group, a triazinyl group, a pyrrolyl group, an imidazolyl group, a thiazolyl group, a benzothiadiazole group, a furanyl group, a benzofuranyl group, a dibenzofuranyl group, a thienyl group, a benzothienyl group, a dibenzothienyl group, a pyridinyl group, a pyrimidinyl group, a pyrazinyl group, a quinolinyl group, an isoquinolinyl group, a carbazolyl group, a pyridyl-phenyl group, a phenyl-pyridyl group, a pyridyl-biphenylyl group, a pyrimidyl-phenyl group, a bicyclo[1.1.1]pentenyl group, a porphyrinyl group, a phthalocyanyl group, and a phenyl-pyrimidyl group.

[0043] The groups X1 may each independently have a substituent, such as a linear or branched alkyl group having 1 to 20 carbon atoms (e.g., methyl, ethyl, n-propyl, i-propyl, n-butyl, sec-butyl, tert-butyl, or i-butyl), an alkene group, alkenyl group, alkoxy group, hydroxy group, cyano group, carboxy group, amide group, nitro group, carbonyl group, aldehyde group, sulfonyl group, sulfinyl group, ester group, silyl group, siloxanyl group, or a halogen group such as a fluorine atom, chlorine atom, or bromine atom.

[0044] Furthermore, the two pyridine ligands may each independently have a substituent, the range of which is preferably the same as that of the group X1 above.

[0045] Specific examples of the linker of the present invention having two pyridine ligands include the following organic compounds.

[0046] [ka]

[0047] [ka]

[0048] [ka]

[0049] (ii-2) Linker consisting of three pyridine ligands Examples of linkers having three pyridine ligands (n=3) include the organic compounds shown below.

[0050] [ka]

[0051] In the organic compound represented by the above formula, the pyridine ligand and the group X2 are bonded via a carbon-carbon triple bond. The group X2 is preferably any of carbon, nitrogen, and phosphorus, or an aliphatic hydrocarbon group having from 1 to 6 carbon atoms which may have a substituent, or a monocyclic, linked, or fused ring aromatic hydrocarbon group having from 6 to 30 carbon atoms (each of these groups may independently have a substituent), or a monocyclic, linked, or fused ring heteroaromatic group having from 3 to 27 carbon atoms (each of these groups may independently have a substituent).

[0052] In this organic compound, when the group X2 is an aliphatic hydrocarbon group having 1 to 6 carbon atoms, the scope and specific examples of the group X2 are the same as those of the group X1 described above.

[0053] In this organic compound, when the group X2 is a monocyclic, linked, or fused ring aromatic hydrocarbon group having 6 to 30 carbon atoms, specific examples of the group X2 are the same as the specific examples for the group X1 described above. When the group X2 is a monocyclic, linked, or fused ring heteroaromatic group having 3 to 27 carbon atoms, specific examples of the group X2 are also the same as the specific examples for the group X1 described above.

[0054] Similarly to the group X1, the groups X2 may each independently have a substituent. The range of possible substituents is the same as that of the group X1. Furthermore, the three pyridine ligands may each independently have a substituent. The range of possible substituents is preferably the same as that of the substituents possessed by the group X1.

[0055] Specific examples of linkers with three pyridine ligands include the following organic compounds:

[0056] [ka]

[0057] (ii-3) Linker consisting of four pyridine ligands Examples of linkers having four pyridine ligands (n=4) include the organic compounds shown below.

[0058] [ka]

[0059] In the organic compound represented by the above formula, the pyridine ligand and the group X3 are bonded via a carbon-carbon triple bond. The group X3 is preferably carbon, an aliphatic hydrocarbon group having from 1 to 6 carbon atoms which may have a substituent, a monocyclic, linked, or fused ring aromatic hydrocarbon group having from 6 to 25 carbon atoms (each of these groups may independently have a substituent), or a monocyclic, linked, or fused ring heteroaromatic group having from 3 to 44 carbon atoms (each of these groups may independently have a substituent).

[0060] In this organic compound, when the group X3 is an aliphatic hydrocarbon group having 1 to 6 carbon atoms, the scope and specific examples of the group X1 are the same as those of the group X1 described above.

[0061] In this organic compound, when the group X3 is a monocyclic, linked, or fused ring aromatic hydrocarbon group having 6 to 25 carbon atoms, specific examples of the group X3 are the same as the specific examples for the group X1 described above. In addition, when the group X3 is a monocyclic, linked, or fused ring heteroaromatic group having 3 to 44 carbon atoms, specific examples of the group X3 are the same as the specific examples for the group X1 described above.

[0062] Similarly to the group X1, the group X3 may each independently have a substituent. The range of the substituent is the same as that of the group X1. Furthermore, the four pyridine ligands may each independently have a substituent. The range is preferably the same as that of the substituent of the group X1.

[0063] Specific examples of linkers with four pyridine ligands include the following organic compounds:

[0064] [ka]

[0065] (ii-4) Linker with 5 or more pyridine ligands Representative specific examples of linkers in which the number n of pyridine ligands is 2 to 4 have been given above. In addition to these, examples of linkers in which the number n of pyridine ligands is 5 or more include the following organic compounds in which n=6 and 8.

[0066] [ka]

[0067] The Ag nanocluster assembly of the present invention is an organic-inorganic hybrid material composed of the linker, which is an organic compound, and the Ag nanoclusters, which are metals, as explained above. The Ag nanoclusters are regularly arranged by the linker, which is a bridging material, and can behave as a pseudo-crystal.

[0068] II. Method for producing Ag nanocluster aggregate according to the present invention As described above, an Ag nanocluster assembly is a structure in which Ag nanoclusters containing multiple Ag atoms are assembled via a linker. Therefore, it can be produced by forming an aggregate of multiple Ag atoms and adding a linker to the dispersed aggregate. Examples of this aggregate of multiple Ag atoms include the Ag nanoclusters described above, as well as Ag complexes. That is, the method for producing an Ag nanocluster assembly according to the present invention includes the steps of preparing a dispersion medium in which either Ag nanoclusters containing two or more Ag atoms or Ag complexes containing two or more Ag atoms are dispersed, and adding the linker to the dispersion medium, in which an organic compound represented by Chemical Formula 2 or Chemical Formula 3 is added as the linker.

[0069] Ag complexes are precursors of Ag nanoclusters. They are formed by adding and reacting an organic ligand with a solution of Ag salt (Ag ions). They are composites containing multiple Ag atoms with organic ligands coordinated to Ag. Examples of Ag salts that can be used include silver nitrate, silver chloride, silver sulfide, silver oxalate, silver oxide, and silver carbonate. Suitable organic ligands for forming Ag complexes in the present invention include thiol- and ethynyl-containing ligands. Specific compounds that can be used as organic ligands include tertiary thiol group-containing ligands such as 1-adamantanethiol, tert-butylthiol (tert-butyl mercaptan), 3-mercapto-3-methyl-1-butanol, bicyclo[1.1.1]pentanethiol, 8-mercaptomenthone, and O-carborane-1,2-dithiol, and ethynyl group-containing ligands such as tert-butylacetylene, 1-ethynyladamantane, 3,3-dimethyl-1-pentene, 1-ethynylbicyclo[1.1.1]pentane, and 1-ethynyl-3,5-dimethyladamantane.

[0070] Furthermore, Ag nanoclusters can be formed by the reduction treatment of the above-mentioned Ag salt or Ag complex, or by a ligand exchange method in which other organic ligands are added to the above-mentioned Ag complex.

[0071] In the production of the Ag nanocluster assembly of the present invention, it is preferable to form an Ag nanocluster by a ligand exchange method, in which another organic ligand is added to an Ag complex formed from the above-mentioned organic ligand, and then react it with a linker to form an assembly. Although Ag complexes are composed of multiple atoms, the number of constituent atoms is often not specified. For Ag complexes formed with the above-mentioned thiol group-containing ligands, the number of Ag atoms can be adjusted by adding another organic ligand, and Ag nanoclusters can be synthesized from the Ag complex by ligand exchange. As this other organic ligand, it is preferable to add a carboxylate group-containing ligand such as trifluoroacetic acid or trifluoroacetate salt. The carboxylate group-containing ligand can contribute to maintaining the dispersibility of Ag nanoclusters while generating them from the Ag complex.

[0072] The Ag complex or Ag nanocluster produced as described above is dispersed in a dispersion medium, and an organic compound serving as a linker is added and reacted to form an Ag nanocluster aggregate. Organic solvents such as chloroform, toluene, ethanol, and methanol are preferred as dispersion media for Ag nanoclusters. To obtain a dispersion of Ag nanoclusters in a dispersion medium, the Ag complex formed above may be recovered and dispersed in a dispersion medium, followed by conversion into an Ag cluster. Alternatively, Ag nanoclusters may be produced and dispersed in a dispersion medium.

[0073] When adding a linker, it is preferable to add it as a solution (linker solution) by dissolving it in the same organic solvent as above. The amount of linker added is preferably an excess amount, approximately 10 times the number of moles of Ag in the Ag nanoparticles.

[0074] Ag nanocluster assemblies are formed by adding a linker solution and then reacting the linker with the Ag nanoclusters. The reaction conditions are preferably a reaction temperature of -40°C to 80°C in air or inert gas, and a reaction time of 3 hours or more. Bonding between the linker and Ag nanoparticles proceeds through ligand exchange between the organic ligands bonded to the Ag nanoclusters and the pyridine ligands at the end of the linker. Then, Ag nanocluster assemblies can be obtained through self-organization caused by the reaction between the linker and the Ag nanoclusters.

[0075] After the reaction is complete, the Ag nanocluster aggregate can be separated and recovered by centrifugation and vacuum drying. The Ag nanocluster aggregate can be washed appropriately with alcohol (e.g., methanol). The Ag nanocluster aggregate thus obtained can also be dispersed again in an appropriate dispersion medium for various uses. [Effects of the Invention]

[0076] As described above, the present invention provides an Ag nanocluster assembly in which Ag nanoclusters are periodically and regularly assembled by applying a suitable linker. The Ag nanocluster assembly of the present invention has periodicity and regularity while exhibiting superior thermal stability compared to conventional techniques. As a result, the present invention can improve the applicability to various applications such as catalysts and device elements. [Brief explanation of the drawings]

[0077] [Figure 1] 10 is an SEM image of Ag nanocluster aggregates of Examples 1 and 2. [Figure 2] FIG. 1 shows the results of SC-XRD analysis of the crystal structure of the Ag nanocluster aggregate of Example 1. [Figure 3] FIG. 10 shows the results of SC-XRD analysis of the crystal structure of the Ag nanocluster aggregate of Example 2. [Figure 4] P-XRD diffraction patterns of Ag nanocluster aggregates of Examples 1 and 2. [Figure 5] TG-DTA curves of Ag nanocluster aggregates of Example 1, Example 2, and Comparative Example. [Figure 6] P-XRD diffraction patterns of the Ag nanocluster aggregate of Example 1 after immersion in various solutions and solvents. [Figure 7] P-XRD diffraction patterns of the Ag nanocluster aggregate of Example 2 after immersion in various solutions and solvents. DETAILED DESCRIPTION OF THE INVENTION

[0078] Hereinafter, an embodiment of the present invention will be described. In this embodiment, an Ag nanocluster assembly was produced using 4-(2-pyridin-4-ylethynyl)pyridine (hereinafter, sometimes referred to as ETNbpy) of Chemical Formula 2 and 1,4-bis(pyridin-4-ylethynyl)benzene (hereinafter, sometimes referred to as 2EBbpy) of Chemical Formula 7 as linkers.

[0079] Example 1 (Linker: ETNbpy) 0.55 g (3.24 mmol) of silver nitrate (AgNO3) was dissolved in 7.5 mL of acetonitrile, and 1.25 mL of tert-butylthiol (HS-tBu) was added to the solution to generate the precursor Ag complex (referred to as AgStBu). The Ag complex was washed with alcohol and then collected by centrifugation and vacuum drying.

[0080] Next, 5 mL of a solution was prepared by dissolving chloroform (CHCl3) in acetonitrile (CH3CN) at a volume ratio of 1:1 as a solvent. 30 mg of the Ag complex prepared above and 22.5 mg of silver trifluoroacetate (CF3COOAg) were added to this solvent, and the mixture was stirred thoroughly to obtain a dispersion of Ag nanoclusters.

[0081] While preparing the Ag nanoclusters as described above, 30 mg of 4-(2-pyridin-4-ylethynyl)pyridine, which serves as a linker, was weighed out and added to 5 mL of the same solvent as above (acetonitrile / chloroform solution) and stirred well to prepare a linker solution.

[0082] The Ag nanocluster dispersion and linker solution were mixed in an ice bath and left in a cool, dark place for 24 hours. After that, the mixture was collected by centrifugation and washed with methanol to obtain an Ag nanocluster aggregate (Ag / ETNbpy).

[0083] Example 2 (Linker: 2EBbpy) As a solvent, 5 mL of a solution was prepared by dissolving dimethylacetamide (DMAc) in toluene at a volume ratio of 1:1. Then, an Ag nanocluster dispersion was obtained in the same manner as in Example 1.

[0084] On the other hand, 45 mg of 1,4-bis(pyridin-4-ylethynyl)benzene, which serves as a linker, was weighed out, and then added to 5 mL of a dimethylacetamide / toluene solution, which is the same solvent as above, and stirred thoroughly to prepare a linker solution.

[0085] Then, similarly to Example 1, the Ag nanoparticle dispersion and the linker solution were mixed and left to stand at 5°C for 24 hours, and the mixture was recovered by centrifugation and washed with methanol to obtain an Ag nanocluster aggregate (Ag / 2EBbpy).

[0086] The appearance of the Ag nanocluster aggregates produced above in Examples 1 and 2 was observed using a scanning electron microscope (SEM). Figure 1 shows SEM images of these examples.

[0087] Next, single-crystal X-ray diffraction analysis (SC-XRD) was performed on the Ag nanocluster aggregates of Examples 1 and 2, and structural analysis was performed based on the diffraction data. The SC-XRD analysis was performed by coating the surface of the sample with a paraffin dispersion and using a single-crystal X-ray diffractometer (XtaLAB Synergy-R / DW manufactured by Rigaku Corporation). The analysis was performed at -173 °C by irradiating the sample with monochromatic X-rays from a monochromatic Cu source equipped with a multilayer mirror to collect diffraction data. The obtained diffraction data was then analyzed using crystal structure analysis software (Olex2) to simulate the structure of the Ag nanocluster aggregates.

[0088] In the structural analysis by SC-XRD, the structure of the Ag nanocluster unit and the periodic structure of the Ag nanocluster aggregate were modeled for the Ag nanocluster aggregate of each Example. The analytical results for Example 1 are shown in Figure 2, and the analytical results for Example 2 are shown in Figure 3.

[0089] Looking at the Ag nanocluster assembly (Ag / ETNbpy) of Example 1 in Figure 2, Figure 2(a) shows that the Ag nanocluster, which is the unit of the assembly, is composed of 14 Ag atoms and 10 S atoms. The Ag atoms are bonded to a skeleton that combines pyramidal and distorted rectangular shapes (Johnson solid, J8). The Ag nanoclusters are also coordinated with organic ligands, such as thiol and trifluoroacetic acid. Figure 2(b) shows that in this Ag nanocluster assembly, the Ag nanoclusters are bonded to four linkers and arranged periodically and at equal intervals. Periodicity and regularity are observed in both two-dimensional (planar) and three-dimensional (layered) structures.

[0090] In the Ag nanocluster assembly (Ag / 2EBbpy) of Example 2 shown in Figure 3, the Ag nanocluster is composed of 12 Ag atoms and 6 S atoms, and it can be seen that the Ag atoms are bonded together in a cuboctahedral framework (Figure 3(a)). In this Ag nanocluster assembly, the Ag nanoclusters are bonded to six linkers to form a regular hexagon, and are arranged periodically and evenly spaced two-dimensionally. This Ag nanocluster assembly also exhibits a periodic layer structure.

[0091] To confirm the above analytical results, powder X-ray diffraction analysis (P-XRD) was performed on the Ag nanocluster aggregates of Examples 1 and 2. In the P-XRD analysis, the Ag nanocluster aggregates were prepared by appropriately grinding them with a glass rod, and then analyzed using a multipurpose X-ray diffractometer (Ultima IV, manufactured by Rigaku Corporation) with a Cu source in the analysis range of 2θ = 5° to 50°. The X-ray diffraction patterns obtained by P-XRD were then referenced to the theoretical diffraction patterns (Common Data Format for Crystallography (CIF)) obtained based on the above SC-XRD analysis results.

[0092] Figure 4 shows the P-XRD diffraction patterns and theoretical diffraction patterns of the Ag nanocluster aggregates of Example 1 (Ag / ETNbpy) and Example 2 (Ag / 2EBbpy). In these diffraction patterns, the low-angle region (10° or less) corresponds to the long-term period (the spacing between Ag nanoclusters) in the two-dimensional direction, and the high-angle region (25° or more) corresponds to the atomic spacing in the Ag nanocluster unit. Referring to Figures 4 and 5, the diffraction patterns of the Ag nanocluster aggregates of Example 1 (Ag / ETNbpy) and Example 2 (Ag / 2EBbpy) both have peak positions consistent with the theoretical diffraction patterns. This indicates that the Ag nanocluster aggregates of Examples 1 and 2 have the structures shown in the SC-XRD analysis results (Figures 2 and 3). This confirms that the use of ETNbpy and 2EBbpy as linkers resulted in Ag nanocluster aggregates in which Ag nanoclusters are periodically and regularly arranged.

[0093] [Evaluation of thermal stability] Next, the thermal stability of the Ag nanocluster aggregates of Example 1 (Ag / ETNbpy) and Example 2 (Ag / 2EBbpy) was investigated. Thermal stability was evaluated by TG-DTA (thermogravimetric-differential thermal analysis). The measurement conditions were a temperature increase rate of 5°C / min in an air stream. For comparison, in this investigation, Ag nanocluster aggregates using 4,4'-bipyridine (bpy) as a linker, which is a conventional technology (Non-Patent Document 1), were produced according to the method described in the non-patent document and evaluated in the same manner.

[0094] The TG-DTA curves of each Ag nanocluster aggregate are shown in Figure 5 as the evaluation results. Thermal stability was evaluated by comparing the temperatures at which a 10% weight loss was observed in the TG curves. As a result, the 10% weight loss temperatures were 162°C for Example 1 (Ag / ETNbpy), 174°C for Example 2 (Ag / 2EBbpy), and 152°C for the comparative example (Ag / Bpy). This confirmed that the Ag nanocluster aggregates of Examples 1 and 2 have higher thermal stability than conventional Ag nanocluster aggregates.

[0095] [Evaluation of chemical stability] Furthermore, the chemical stability of the Ag nanocluster aggregates of Example 1 (Ag / ETNbpy) and Example 2 (Ag / 2EBbpy) was examined. In this evaluation test, samples (30 mg) of each Ag nanocluster aggregate were immersed in various solvents and acid (pH 1) or alkali (pH 14) for 5 minutes. Then, P-XRD analysis was performed on each sample, and the presence or absence of decomposition of the Ag nanocluster aggregate was determined from the presence or absence of changes in the diffraction pattern, thereby evaluating the chemical stability.

[0096] The results of this evaluation test are shown in Figure 6 (Example 1) and Figure 7 (Example 2). The test solutions used included solvents such as water and alcohol, as well as alkalis and acids. However, the Ag nanocluster aggregates of Examples 1 and 2 showed no significant changes in their diffraction patterns when immersed in any of the test solutions, confirming that they did not decompose. Therefore, it can be said that the Ag nanocluster aggregates of the present invention also have good chemical stability. [Industrial Applicability]

[0097] As described above, the present invention elucidates a suitable linker that can improve the thermal stability of Ag nanocluster assemblies in which Ag nanoclusters are regularly assembled. The Ag nanocluster assemblies of the present invention are useful in various fields, including electronics, chemistry, and medicine.

Claims

1. An Ag nanocluster assembly obtained by assembling Ag nanoclusters each containing two or more Ag atoms via a linker made of an organic compound, The Ag nanocluster assembly is characterized in that the linker is an organic compound represented by the following Chemical Formula 1 or Chemical Formula 2, and all ends of which are pyridine ligands. 【Chemistry 1】 In the above formula, the two pyridine ligands are joined by a carbon-carbon triple bond. 【Chemistry 2】 In the above formula, n is the number of pyridine ligands, and n = 2. The group X is an unsubstituted benzene ring. The pyridine ligands and the group X are bonded via a carbon-carbon triple bond.

2. A method for producing an Ag nanocluster assembly by regularly assembling Ag nanoclusters each containing two or more Ag atoms via a linker made of an organic compound, comprising: A step of preparing a state in which either an Ag complex containing two or more Ag atoms or an Ag nanocluster containing two or more Ag atoms is dispersed in a dispersion medium; adding the linker to the dispersion medium; An Ag nanocluster assembly characterized in that an organic compound represented by the following Chemical Formula 6 or 7, in which all ends are pyridine ligands, is added as the linker. 【Transformation 6】 In the above formula, the two pyridine ligands are joined by a carbon-carbon triple bond. 【Transformation 7】 In the above formula, n is the number of pyridine ligands, and n = 2. The group X is an unsubstituted benzene ring. The pyridine ligands and the group X are bonded via a carbon-carbon triple bond.

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