Ligand displacement method

Abstract

The first ligand coordinated to the nanoparticles is replaced with a monodentate second ligand that renders the nanoparticles non-dispersible in a solvent by coordination to the nanoparticles. The nanoparticles coordinated with the second ligand are separated as a first solid by solid-liquid separation, and a second ligand solution comprising a desired target ligand and a third organic solvent is added to the first solid to replace the second ligand with the target ligand.

Description

Technical Field

[0001] This invention relates to a ligand replacement method for replacing ligands on the surface of nanoparticles. Background Technology

[0002] Nanoparticles, such as quantum dots and inorganic nanoparticles with charge carrier transport capabilities, are used in various fields, including light-emitting elements, solar cells, and wavelength conversion devices. These nanoparticles are commercially available, for example, as nanoparticle dispersions containing them. Furthermore, the synthesis of these nanoparticles can be achieved, for example, using wet methods, by coordinating ligands (surface modification) onto the surface of the nanoparticles, thereby controlling the particle size. Ligands also act as dispersants to improve the dispersibility of these nanoparticles. In addition, ligands are used to improve the surface stability and storage stability of these nanoparticles.

[0003] Nanoparticle films containing these nanoparticles are typically formed by coating a nanoparticle dispersion containing these nanoparticles and then drying it. Therefore, in order to disperse synthetically or commercially available ligand-coordinated nanoparticles in any solvent, it is necessary to replace the ligands coordinated to the nanoparticles with ligands suitable for the solvent being used.

[0004] Furthermore, the chemical properties required by the ligands used in the synthesis or preservation of nanoparticles sometimes differ from those required for the intended use of these nanoparticles. In such cases, it is necessary to replace the ligands coordinated to the nanoparticles with ligands suitable for the intended use of these nanoparticles.

[0005] For example, Patent Document 1 discloses the formation of nanoparticles with the second ligand bound to their surface using a first solvent containing nanoparticles with a first ligand bound to their surface, and a second solvent containing nanoparticles with a second ligand bound to their surface and immiscible with the first solvent. Furthermore, Patent Document 1 discloses that the first solvent is at least one selected from, for example, 1-octadecene, toluene, and hexane, and the second solvent is at least one selected from, for example, water, PEGMEA (propylene glycol monomethyl ether acetate), and ethanol. Existing technical documents Patent documents

[0006] Patent Document 1: International Publication No. 2019 / 203240 Summary of the Invention The technical problem to be solved by the present invention

[0007] Thus, in ligand substitution, phase-separated ligand substitution with polar solvents is generally used.

[0008] After such ligand substitution, a liquid phase (first solvent phase) containing nanoparticles with the second ligand bound to the surface and a liquid phase (second solvent phase) containing the first ligand are obtained. Therefore, in order to separate the nanoparticles with the second ligand bound to the surface, liquid-liquid separation of the first solvent phase and the second solvent phase is required.

[0009] Such separation between liquid phases (liquid-liquid separation) is not easy and requires considerable effort. Furthermore, it is difficult to completely separate the liquid phases from each other, necessitating repeated washing to remove the first ligand. Therefore, the aforementioned nanoparticles are prone to degradation.

[0010] Especially when the ligands coordinated to the nanoparticles and the ligands to be replaced are in solvents of the same polarity that are miscible with each other (e.g., both are nonpolar solvents or both are polar solvents), two ligand replacements are required.

[0011] For example, when the nanoparticles mentioned above are quantum dots, quantum dots are generally difficult to disperse in polar solvents but readily disperse in non-polar solvents. To replace the ligand (first ligand) of the quantum dots dispersed in a non-polar solvent with another ligand suitable for dispersing the quantum dots in a non-polar solvent, firstly, the first ligand is temporarily replaced with a ligand (intermediate ligand) suitable for dispersing the quantum dots in a polar solvent (typically water). Then, this intermediate ligand is replaced with a target ligand (target ligand) suitable for dispersing the quantum dots in a non-polar solvent. In this case, two ligand replacements are performed, each requiring liquid-liquid separation.

[0012] Thus, in ligand substitution, solvents with opposite polarities are used before and after the ligand. When the first ligand and the target ligand are ligands that disperse the nanoparticles in solvents with the same polarity when they are coordinated with the nanoparticles, ligand substitution cannot be performed directly from the first ligand to the target ligand. Therefore, in order to perform ligand substitution from the first ligand to any target ligand, one or more liquid-liquid separations are required, depending on the polarity of the solvent in which the nanoparticles are dispersed for each ligand.

[0013] Furthermore, when the aforementioned nanoparticles are quantum dots as described above, the polar solvent is typically an aqueous solvent containing water, or a mixture of water and other solvents (e.g., alcohol-based polar solvents). For example, Patent Document 1 discloses that the reaction solution obtained after ligand substitution separates into two phases: an aqueous phase and an organic solvent phase. However, quantum dots are easily degraded by water. Such degradation of nanoparticles can lead to specific reductions, such as a decrease in quantum yield and a decrease in luminescence properties.

[0014] One aspect of this disclosure is made in view of the aforementioned problems, and its objective is to provide a ligand replacement method that can perform replacement of a desired target ligand without the use of aqueous solvents or liquid-liquid separation, and can suppress the degradation of nanoparticles accompanying ligand replacement compared to existing methods. Technical solutions for solving technical problems

[0015] To address the aforementioned issues, one aspect of the ligand substitution method disclosed herein includes: a first ligand substitution step, in which a first nanoparticle dispersion containing nanoparticles, a first ligand, and a first organic solvent is mixed with a first ligand solution containing a monodentate second ligand and a second organic solvent, thereby substituting the first ligand with the second ligand, wherein the second ligand is coordinated to the nanoparticles, preventing the nanoparticles from dispersing in the solvent; a first separation step, in which the nanoparticles coordinated with the second ligand are separated from the liquid phase as a first solid by solid-liquid separation; a second ligand substitution step, in which a second ligand solution containing a desired target ligand and a third organic solvent is added to the first solid, thereby substituting the second ligand with the target ligand; a second separation step, in which the nanoparticles coordinated with the target ligand, separated in the second separation step, are separated into a fourth organic solvent. Beneficial effects

[0016] According to one aspect of this disclosure, a ligand replacement method can be provided that can perform replacement of a desired target ligand without the use of an aqueous solvent or liquid-liquid separation, and can suppress the degradation of nanoparticles accompanying ligand replacement compared to existing methods. Attached Figure Description

[0017] Figure 1 This is a flowchart of a ligand replacement method implemented in a sequential manner. Figure 2 It is a schematic representation Figure 1 An explanatory diagram of a portion of the ligand replacement method shown. Figure 3 It means Figure 1 and Figure 2 The flowchart shown is an example of the first separation process. Figure 4 It is a schematic representation Figure 1 An explanatory diagram of another part of the ligand replacement method shown. Figure 5 It is a schematic representation Figure 1 An explanatory diagram of another part of the ligand replacement method shown. Figure 6It is a flowchart showing, in sequence, the method of separating nanoparticles with target ligands from a nanoparticle dispersion containing nanoparticles with target ligands and dispersing them in a target solvent. Figure 7 This is an illustration of an existing method for manufacturing a target nanoparticle dispersion by replacing the first ligand of nanoparticles disposed in a first nanoparticle dispersion with a target ligand. Figure 8 This is an illustration of another existing method for producing a target nanoparticle dispersion by replacing the first ligand of nanoparticles disposed in a first nanoparticle dispersion with a target ligand. Detailed Implementation

[0018] Hereinafter, one embodiment of the present disclosure will be described in detail. In addition, in the following description, unless otherwise specified, the reference to "A to B" regarding two quantities A and B means "more than A and less than B".

[0019] The ligand substitution method of this embodiment replaces the ligand (first ligand) of nanoparticles contained in any nanoparticle dispersion (first nanoparticle dispersion) with a desired target ligand that eliminates the need for the use of an aqueous solvent and liquid-liquid separation. Here, "target ligand" refers to any ligand that is ultimately substituted. The target ligand used is one that enables the nanoparticles to be dispersed in a desired organic solvent.

[0020] When the first ligand and the target ligand are ligands that disperse nanoparticles in a solvent with the same polarity when they are coordinated with nanoparticles, ligand substitution cannot be directly performed from the first ligand to the target ligand. Therefore, in order to substitute the first ligand of nanoparticles contained in any nanoparticle dispersion as described above with any target ligand, it is necessary to temporarily substitute the first ligand with an intermediate ligand and then substitute the intermediate ligand with the target ligand.

[0021] Furthermore, here, the intermediate ligand refers to the ligand that is temporarily substituted to replace the first ligand with the target ligand. By ultimately replacing the first ligand with the target ligand, a desired nanoparticle dispersion in a desired organic solvent (target solvent) can be obtained. Furthermore, the target solvent refers to any organic solvent in which the nanoparticles coordinated with the target ligand are ultimately dispersed.

[0022] In this embodiment, a monodentate ligand (second ligand) is used as the intermediate ligand, which significantly reduces the dispersibility of the nanoparticles in any solvent by coordinating with the nanoparticles. If the first ligand is replaced with the second ligand, the nanoparticles cannot be dispersed in the solvent. In other words, the second ligand used in this embodiment prevents the nanoparticles from dispersing in the solvent by coordinating with the nanoparticles.

[0023] In this embodiment, "dispersion" means that the above-mentioned nanoparticles are dispersed in a colloidal state. Furthermore, "dispersion liquid" means "colloidal solution".

[0024] Furthermore, in this embodiment, "coordination" means that the ligand is adsorbed onto the surface of the nanoparticle (in other words, the ligand modifies (surface modifies) the surface of the nanoparticle). Additionally, "adsorption" here means that the concentration of the ligand on the surface of the nanoparticle is increased compared to the surrounding area. This adsorption can be chemisorption, where a chemical bond exists between the nanoparticle and the ligand, or it can be physisorption or electrostatic adsorption. As long as the ligand can have a chemical effect on the surface of the nanoparticle through adsorption, it can be bound by coordination bonds, covalent bonds, ionic bonds, hydrogen bonds, etc., or it may not be necessary for the ligand to bind. Furthermore, in this embodiment, not only molecules or ions coordinated to the surface of the nanoparticle, but also molecules or ions that can be coordinated but are not, are referred to as "ligands".

[0025] In this embodiment, as described above, taking advantage of the fact that the nanoparticles coordinated with the second ligand cannot be dispersed in any solvent, solid-liquid separation is performed on the nanoparticles coordinated with the second ligand, and ligand replacement is performed with the target ligand. Therefore, without the use of aqueous solvents and liquid-liquid separation, the first ligand of the nanoparticles coordinated in the first nanoparticle dispersion can be replaced with the desired target ligand.

[0026] Figure 1 This is a flowchart illustrating the ligand replacement method of this embodiment in the order of the procedures.

[0027] The aforementioned first nanoparticle dispersion comprises the aforementioned nanoparticles, the aforementioned first ligand, and a first organic solvent. For example... Figure 1 As shown, in the ligand replacement method of this embodiment, firstly, the first nanoparticle dispersion is diluted with the first organic solvent to make the concentration of the nanoparticles in the first nanoparticle dispersion reach the desired concentration (step S1, dilution process).

[0028] Next, the first nanoparticle dispersion and the first ligand solution containing the second ligand and the second organic solvent are mixed to replace the first ligand with the second ligand (ligand replacement) (step S2, first ligand replacement process).

[0029] Next, the nanoparticles with the second ligand coordinated thereto are separated from the liquid phase as a solid (first solid) by solid-liquid separation (step S3, first separation process).

[0030] Next, a second ligand solution containing the desired target ligand and a third organic solvent is added to the first solid, thereby replacing the second ligand with the target ligand (step S4, second ligand replacement step). This allows the first ligand located on the nanoparticles to be replaced with the target ligand.

[0031] Next, the nanoparticles coordinated with the target ligand are separated as the second solid (step S5, second separation process).

[0032] Next, the nanoparticles that were separated in step S5 and coordinated with the target ligand are dispersed in a fourth organic solvent (step S6, redispersion process).

[0033] Through the above operations, a desired nanoparticle dispersion (target nanoparticle dispersion) can be produced by replacing the first ligand with the target ligand and finally dispersing the nanoparticles in the fourth organic solvent, which is the desired organic solvent.

[0034] The following is for reference Figures 2-6 The steps described above will be explained in more detail.

[0035] Figure 2 It is a schematic representation Figure 1 An explanatory diagram of a portion of the ligand replacement method shown. Figure 2 express Figure 1 Steps S2 and S3 are shown.

[0036] In this embodiment, as described above, in Figure 2 Before step S2, in step S1, the first nanoparticle dispersion 11 is diluted in such a way that the concentration of the first nanoparticle dispersion 11 used in step S2 becomes the desired concentration. Thus, the concentration of the first nanoparticle dispersion 11 is adjusted.

[0037] like Figure 2 As shown, the first nanoparticle dispersion 11 comprises nanoparticles 12, a first ligand 13, and a first organic solvent 14. At least a portion of the first ligand 13 in the first nanoparticle dispersion 11 is coordinated with the nanoparticles 12.

[0038] The nanoparticles 12 used in this embodiment are not particularly limited as long as they have a nanoparticle size that requires ligand substitution. Examples of nanoparticles 12 include quantum dots (hereinafter referred to as "QD") or inorganic nanoparticles with charge carrier transport capabilities.

[0039] QDs are generally inorganic nanoparticles with a particle size of several nm to tens of nm. Because their composition originates from semiconductor materials, QDs are also called semiconductor nanoparticles. Furthermore, due to their specific crystal structure, QDs are also called nanocrystals. In addition, QDs emit fluorescence, and because of their nanoscale size, they are also called fluorescent nanoparticles or QD phosphor particles. Therefore, the QD emitting layer is also called the QD phosphor layer.

[0040] A QD (Quasi-Device) may also comprise a semiconductor material, for example, composed of at least one element selected from the group consisting of Cd (cadmium), S (sulfur), Te (tellurium), Se (selenium), Zn (zinc), In (indium), N (nitrogen), P (phosphorus), As (arsenic), Sb (antimony), Al (aluminum), Ga (gallium), Pb (lead), Si (silicon), Ge (germanium), and Mg (magnesium). Furthermore, a typical QD contains Zn. Therefore, a QD can, for example, be a semiconductor material containing Zn.

[0041] Furthermore, QDs can be nucleated, core-shell, or multi-shell. They can also be two-component, three-component, or four-component nucleated structures. Additionally, QDs can contain doped nanoparticles or have a tilted structure. Depending on the particle size and composition, QDs can vary the emission wavelength.

[0042] Furthermore, examples of nanoparticles with charge carrier transport capabilities include inorganic nanoparticles with hole transport capabilities and inorganic nanoparticles with electron transport capabilities. Inorganic nanoparticles with hole transport capabilities are used as hole transport materials. Inorganic nanoparticles with electron transport capabilities are used as electron transport materials.

[0043] Examples of inorganic nanoparticles with hole transport capabilities include particles composed of p-type semiconductor materials. Examples of p-type semiconductor materials include: metal oxides, group IV semiconductors, group II-VI compound semiconductors, group III-V compound semiconductors, amorphous semiconductors, and thiocyanate compounds. Examples of metal oxides include: nickel oxide (NiO), titanium oxide (TiO2), molybdenum oxide (MoO2, MoO3), magnesium oxide (MgO), and nickel lanthanate (LaNiO3). Examples of group IV semiconductors include: silicon (Si) and germanium (Ge). Examples of group II-VI compound semiconductors include: zinc sulfide (ZnS) and zinc selenide (ZnSe). Examples of group III-V compound semiconductors include: aluminum arsenide (AlAs), gallium arsenide (GaAs), indium arsenide (InAs), aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), and gallium phosphide (GaP). Examples of the aforementioned amorphous semiconductors include, for example, p-type hydrogenated amorphous silicon and p-type hydrogenated amorphous silicon. Examples of the aforementioned thiocyanate compounds include, for example, copper thiocyanate and other thiocyanates. These materials may be used individually or in appropriate mixtures of two or more.

[0044] Furthermore, inorganic nanoparticles with electron transport capabilities include particles composed of n-type semiconductor materials. Examples of such n-type semiconductor materials include: metal oxides, group II-VI compound semiconductors, group III-V compound semiconductors, group IV-IV compound semiconductors, and amorphous semiconductors. Examples of such metal oxides include: zinc oxide (ZnO), zinc magnesium oxide (ZnMgO), titanium oxide (TiO2), indium oxide (In2O3), tin oxide (SnO, SnO2), and cerium oxide (CeO2). Examples of such group II-VI compound semiconductors include: zinc sulfide (ZnS) and zinc selenide (ZnSe). Examples of such group III-V compound semiconductors include: aluminum arsenide (AlAs), gallium arsenide (GaAs), indium arsenide (InAs), aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), and gallium phosphide (GaP). Examples of the aforementioned group IV-IV compound semiconductors include silicon germanium (SiGe) and silicon carbide (SiC). Examples of the aforementioned amorphous semiconductors include n-type hydrogenated amorphous silicon. Only one of these materials may be used, or two or more may be appropriately mixed.

[0045] The first ligand 13 is any ligand contained in the first nanoparticle dispersion 11 that has a coordinating functional group (adsorption group) capable of coordinating with the nanoparticle 12.

[0046] As described above, ligands are used to improve the particle size control, surface stability, storage stability, or dispersion stability of nanoparticles during synthesis. Therefore, nanoparticle dispersions, whether synthesized or commercially available, generally contain ligands. At least a portion of the ligand is coordinated to the nanoparticles.

[0047] As described above, the first nanoparticle dispersion 11 can be, for example, a nanoparticle dispersion obtained through synthesis or a commercially available nanoparticle dispersion. Therefore, the first ligand 13 is not particularly limited. The first ligand 13 can be a monomer, an oligomer, or a polymer.

[0048] Representative examples of such orientational functional groups include at least one functional group selected from the group consisting of thiol, amino, carboxyl, phosphonic acid, and phosphonic groups.

[0049] Furthermore, examples of the aforementioned first ligand 13 include oleic acid, dodecanoic acid, dodecylthiol, dodecylamine, trioctylphosphine, and trioctylphosphine oxide. Only one of these first ligands 13 may be used, or a mixture of two or more may be used.

[0050] The first organic solvent 14 described above can be any organic solvent capable of dissolving or dispersing the first ligand 13 and dispersing the nanoparticles 12 with the first ligand 13 coordinated thereto. Therefore, the first organic solvent 14 is appropriately selected according to the type of nanoparticles 12 and the type of first ligand 13, and there are no particular limitations as long as the organic solvent meets the above conditions.

[0051] When the nanoparticles 12 are, for example, QD, a nonpolar organic solvent is generally used as the first organic solvent 14. Furthermore, when the nanoparticles 12 are, for example, inorganic nanoparticles with carrier transport capabilities, a polar organic solvent is generally used as the first organic solvent 14. However, this is not a limitation.

[0052] Although the concentration of the first nanoparticle dispersion 11 used in step S2 also depends on the type of the first ligand 13, it is preferably in the range of 0.001 mg / mL or more and 100 mg / mL or less, and more preferably in the range of 0.01 mg / mL or more and 20 mg / mL or less.

[0053] The higher the concentration of the first nanoparticle dispersion 11, the more difficult it is for the first ligand 13 to detach from the nanoparticle 12 and be replaced. Therefore, ligand replacement may not be possible depending on the type of ligand or nanoparticle. On the other hand, the lower the concentration of the first nanoparticle dispersion 11, the easier it is for the ligand to be replaced. However, if the nanoparticle 12 has low stability, the increased time without ligand protection may lead to a decrease in properties.

[0054] Therefore, in step S1 above, it is preferable to dilute the first nanoparticle dispersion 11 with the first organic solvent 14 so that the concentration of nanoparticles 12 in the first nanoparticle dispersion 11 is within the above-mentioned range. The dilution in step S1 is not necessarily necessary, but by performing the above dilution, the ligand substitution in step S2 can be performed efficiently.

[0055] like Figure 2 As shown in step S2, in step S2, the first nanoparticle dispersion 11 and the first ligand solution 21 are mixed by stirring in container 1, which serves as a reaction vessel.

[0056] The first ligand solution 21 contains a second ligand 22 and a second organic solvent 23.

[0057] The second ligand 22 is a monodentate ligand that prevents the nanoparticles 12 from dispersing in a solvent by being configured on them. By being configured on the nanoparticles 12, the second ligand 22 significantly reduces the dispersibility of the nanoparticles 12 in any solvent.

[0058] The second ligand 22 is a monodentate ligand as described above, having a coordinating functional group capable of coordinating with nanoparticle 12.

[0059] As the aforementioned orientation functional group, any functional group capable of coordinating with nanoparticle 12 is acceptable. Therefore, as the aforementioned coordination functional group, examples of the coordination functional groups exemplified above can be listed (e.g., at least one functional group selected from the group consisting of thiol group, amino group, carboxyl group, phosphonic acid group, and phosphine group).

[0060] The second ligand 22 described above has a coordinating functional group capable of coordinating with the nanoparticle 12, and the main chain backbone shown below preferably has 1 or more and 8 or less carbon atoms, more preferably 1 or more and 5 or less.

[0061] In addition, the second ligand 22 may or may not contain a ring (ring structure).

[0062] As in the case where the second ligand 22 is a chain compound, in the absence of a ring, the carbon chain containing the most carbon atoms in the carbon chain that connects the carbon of the aforementioned coordinating functional group to the carbon of the terminal group with the shortest distance is used as the main chain backbone.

[0063] On the other hand, when the second ligand 22 is a cyclic compound such as an alicyclic compound or an aromatic compound, if the ring contains no substituents (side chains, branches) other than the coordinating functional group or the substituent containing the coordinating functional group, then the carbon in the ring located at the opposite pole of the carbon bonded to the coordinating functional group or the substituent containing the coordinating functional group becomes the carbon furthest from the carbon bonded to the coordinating functional group. Furthermore, the movement of cyclic carbon chains is restricted compared to chain-like carbon chains. Therefore, when the second ligand 22 contains a ring, it will not become a carbon chain that affects the number of carbon atoms in the carbon chain contained in the ring, thus affecting the dispersibility of the nanoparticles.

[0064] Therefore, in the case where the second ligand 22 contains a ring, the carbon chain containing more carbon in (i) and (ii) below is used as the main chain backbone.

[0065] (i) Along the aforementioned ring, a carbon chain is formed with the shortest distance connecting the carbon containing the aforementioned coordinating functional group to the carbon in the aforementioned ring that is located at the opposite pole (hereinafter referred to as "the carbon at the opposite pole").

[0066] (ii) When the aforementioned ring is bonded with the aforementioned coordinating functional group or a substituent other than the substituent containing the aforementioned coordinating functional group, the carbon chain that connects the carbon bonded with the aforementioned coordinating functional group to the end of the carbon bonded to the aforementioned ring along the shortest distance contains the largest number of carbons.

[0067] In addition, in (i) and (ii), "carbon with the above-mentioned coordinating functional group" means carbon with the above-mentioned coordinating functional group bonded to the above-mentioned ring when the above-mentioned ring is bonded to the above-mentioned ring, and means carbon with the above-mentioned coordinating functional group bonded to the substituent when the above-mentioned ring is bonded to the substituent.

[0068] That is, when the second ligand 22 contains a ring, the first carbon atom bonded to the coordinating functional group or a substituent containing the coordinating functional group is taken as the first carbon atom. When calculating the number of carbon atoms in the ring along the ring number, the maximum number of carbon atoms in the ring is the number from the carbon atom bonded to the carbon atom at the anti-polar position. For example, when the second ligand 22 contains a benzene ring, the carbon at the p-position (4-position) is the anti-polar carbon, and the maximum number of carbon atoms in the benzene ring is 4.

[0069] In the absence of any substituents other than the coordinating functional group or the substituent containing the coordinating functional group bonded to the ring, the number of carbon atoms in the carbon chain that connects the carbon chain from the carbon bonded to the carbon at the opposite pole (i.e., the carbon at the opposite pole of the carbon in the ring that is bonded to the coordinating functional group or the substituent containing the coordinating functional group) along the ring with the shortest distance becomes the number of carbon atoms in the main chain backbone.

[0070] On the other hand, when the aforementioned ring is bonded with the aforementioned coordinating functional group or a substituent other than a substituent containing the aforementioned coordinating functional group, the number of carbon atoms in the carbon chain that connects along the aforementioned ring with the shortest distance from the carbon bonded with the aforementioned coordinating functional group to the carbon at the aforementioned para pole position is compared with the number of carbon atoms in the carbon chain that connects along the aforementioned ring with the shortest distance from the carbon bonded with the aforementioned coordinating functional group to the carbon at the end of the carbon bonded to the aforementioned ring, which is the carbon at the end of the substituent other than a substituent containing the aforementioned coordinating functional group, and the number of carbon atoms with the highest number is set as the number of carbon atoms in the main chain backbone.

[0071] That is, the path that connects the carbon with the aforementioned coordinating functional group to the carbon at the aforementioned para pole along the aforementioned ring with the shortest distance is taken as the first path, and the path that connects the carbon with the aforementioned coordinating functional group to the carbon at the end of the ring, which is attached to the aforementioned coordinating functional group or a substituent other than the substituent containing the aforementioned coordinating functional group, is taken as the second path. When comparing the two paths, if the second path is longer than the first path, then the second path is the main chain backbone.

[0072] Furthermore, under no circumstances does the aforementioned main chain backbone contain the aforementioned coordination functional group itself. Therefore, even if the aforementioned coordination functional group contains carbon, the number of carbon atoms in the aforementioned main chain backbone does not include the number of carbon atoms in the aforementioned coordination functional group.

[0073] Examples of such second ligands 22 include ethyl mercaptan (ethanethiol), 1-propanethiol, 1-butanethiol, 1-pentanethiol, 2-methyl-1-butanethiol, o-toluenethiol, m-toluenethiol, p-toluenethiol, 2,4-dimethylbenzenethiol, 3,4-dimethylbenzenethiol, 2,5-dimethylbenzenethiol, 3,5-dimethylbenzenethiol, and 3-methylcyclopentanethiol, which have a thiol group and whose main chain backbone has 1 or more but less than 8 carbon atoms. Thiols; amines such as methylamine, pentanamine, and p-toluidine, which have one amino group and whose main chain backbone has 1 to 8 carbon atoms; carboxylic acids such as valeric acid and benzoic acid, which have one carboxyl group and whose main chain backbone has 1 to 8 carbon atoms; phosphonic acids such as ethylphosphonic acid, which have one phosphonic acid group and whose main chain backbone has 1 to 8 carbon atoms; and phosphines such as trimethylphosphine, which have one phosphine group and whose main chain backbone has 1 to 8 carbon atoms. These second ligands 22 can be used individually or in appropriate combinations of two or more.

[0074] As described above, the second ligand 22 can also be an aliphatic ligand such as a straight-chain alkyl thiol, straight-chain alkylamine, straight-chain alkylcarboxylic acid, straight-chain alkylphosphonic acid, or straight-chain alkylphosphinolic acid. Furthermore, the second ligand 22 can also be an aromatic ligand such as a benzenethiol, aniline, benzenecarboxylic acid, benzenephosphonic acid, or benzenephosphinolic acid, or an alicyclic ligand. Additionally, it can have branches and substituents, respectively.

[0075] The following example illustrates how the number of carbon atoms in the main chain skeleton of the second ligand 22 described above is counted. First, pentamidine, as a ligand of a straight-chain alkylamine system, is used as an example. Since pentamidine does not contain a ring, the main chain skeleton is the carbon chain with the most carbon atoms in the carbon chain that connects the carbon of the coordinating functional group to the carbon of the terminal group with the shortest distance. Therefore, the number of carbon atoms in the main chain skeleton of pentamidine is 5, as shown in equations (A) (1) to (5) below.

[0076] [Chemical Formula 1] Next, we will take 2-methyl-1-butanethiol, a branched aliphatic ligand, as an example. In 2-methyl-1-butanethiol, the carbon chain connecting the carbon with the coordinating functional group to the terminal carbon along the shortest distance has: a carbon chain (first carbon chain) having 4 carbon atoms represented by (1) to (4) in formula (B); and a carbon chain (second carbon chain) having 3 carbon atoms represented by (1) to (2), (3)' in formula (B). In this case, the first carbon chain has more carbon atoms than the second carbon chain; therefore, the first carbon chain becomes the backbone, and the carbon chains branching from this backbone, having carbons represented by (3)', become branches. Therefore, the backbone of 2-methyl-1-butanethiol has 4 carbon atoms.

[0077] [Chemical Formula 2] Next, we will take p-toluenethiol, an aromatic ligand (specifically a benzenethiol-based ligand) with a substituent other than the aforementioned coordinating functional group attached to the benzene ring, as an example. As shown in formula (C), p-toluenethiol has a coordinating functional group directly attached to the benzene ring, and the carbon in the benzene ring has a substituent other than the coordinating functional group at its counter potential. Therefore, the carbon chain that connects the carbon with the coordinating functional group to the carbon at the end of the aforementioned substituent other than the coordinating functional group along the benzene ring with the shortest distance forms the main chain backbone.

[0078] As a carbon chain that connects the carbon of the coordinating functional group of p-toluenethiol to the end of a substituent other than the coordinating functional group along the benzene ring with the shortest distance, there exist: a carbon chain having carbons shown in (1) to (5) in the following formula (C) (first carbon chain); and a carbon chain having carbons shown in (1), (2)', (3)', (4) and (5) in the following formula (C) (second carbon chain). In this case, the number of carbon atoms in the first carbon chain and the number of carbon atoms in the second carbon chain are the same, and any carbon chain can be regarded as the main chain backbone. In this case, the number of carbon atoms in the main chain backbone of p-toluenethiol is always 5.

[0079] [Chemical Formula 3] Next, we will take o-toluenethiol, a benzenethiol-based ligand with a substituent other than the aforementioned coordinating functional group bonded to the benzene ring, as an example. As shown in formula (D), o-toluenethiol has a coordinating functional group directly bonded to the benzene ring, and has a substituent other than the coordinating functional group in the middle of the path along the benzene ring connecting the carbon with the coordinating functional group and the carbon at the para-polar (p-position) position with the shortest distance.

[0080] As a carbon chain that connects the coordinating functional group of o-toluene mercaptan to the carbon at the p-position along the benzene ring with the shortest distance, there exist: a carbon chain having carbons represented by (1) to (4) in the following formula (D) (first carbon chain); and a carbon chain having carbons represented by (1), (2)', (3)', and (4) in the following formula (D) (second carbon chain). In this case, all carbon chains have 4 carbon atoms.

[0081] On the other hand, the carbon chain in o-toluenethiol, which connects the carbon of the carbon with the coordinating functional group to the carbon of the end of the substituent other than the coordinating functional group along the benzene ring with the shortest distance, is a carbon chain (third carbon chain) having carbons represented by (1), (2)', and (3)" in the following formula (D), and the carbon chain has 3 carbon atoms.

[0082] In addition, as a carbon chain consisting of a carbon with a coordinating functional group and a carbon with a substituent other than the coordinating functional group attached to the benzene ring, there are carbon chains constituting the third carbon chain described above, having 3 carbon atoms in the following formula (D) with carbons represented by (1), (2)', and (3)" and carbon chains having 6 carbon atoms in the following formula (D) with carbons represented by (1) to (4), (3)', and (2)'.

[0083] However, as described above, in this embodiment, when counting the number of carbons constituting the ring along the aforementioned ring, the maximum number of carbon atoms from the carbon with the aforementioned coordinating functional group to the carbon at the antipolar position is taken as the maximum number of carbon atoms in the aforementioned ring. The number of carbon atoms, 6, exceeds the maximum number of carbon atoms in the benzene ring, 4. Furthermore, the path connecting the carbons shown in (1) to (4), (3)', and (2)' in the following formula (D) is not a path that connects the carbon with the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group along the benzene ring with the shortest distance. In other words, the carbon chain with the carbons shown in (1) to (4), (3)', and (2)' in the following formula (D) is not a carbon chain that connects the carbon with the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group along the benzene ring with the shortest distance.

[0084] Therefore, in the benzene ring of o-toluenethiol, the first or second carbon chain connecting the carbon with the coordinating functional group to the p-position carbon along the benzene ring with the shortest distance forms the backbone of o-toluenethiol. In this case, the backbone of o-toluenethiol always has 4 carbon atoms.

[0085] [Chemical Formula 4] Similarly, m-toluenethiol, a ligand of the benzenethiol system, which has a substituent other than the aforementioned coordinating functional group bonded to the benzene ring, is shown in formula (E). The coordinating functional group is directly bonded to the benzene ring, and the substituent other than the coordinating functional group is present in the middle of the path in the benzene ring that connects the carbon with the coordinating functional group and the carbon at the para-polar (p-position) position along the shortest distance of the benzene ring.

[0086] As a carbon chain in the benzene ring of m-toluenethiol, which connects the carbon with the coordinating functional group to the carbon at the p-position along the benzene ring in the shortest distance, there exist: a carbon chain having carbons shown in (1) to (4) in the following formula (E) (first carbon chain); and a carbon chain having carbons shown in (1), (2)', (3)', and (4) in the following formula (E) (second carbon chain). In this case, the number of carbon atoms in any carbon chain is 4.

[0087] Furthermore, a carbon chain that connects the carbon of m-toluene mercaptan with a coordinating functional group along the benzene ring to the carbon at the end of a substituent other than the coordinating functional group at the shortest distance becomes a carbon chain (third carbon chain) having carbons represented by (1), (2)', (3)', and (4)' in the following formula (E), which has 4 carbon atoms.

[0088] Therefore, in this case, the number of carbon atoms in the first carbon chain, the second carbon chain, and the third carbon chain are the same, and any carbon chain can be considered as the backbone. In this case, as mentioned above, the number of carbon atoms in the backbone of m-toluenethiol is 4 in any case.

[0089] [Chemical Formula 5] Next, we will take 2,4-dimethylbenzylthiol, a ligand of the benzene-thiol system, which has two substituents other than the aforementioned coordinating functional groups attached to the benzene ring, as an example. As shown in formula (F), 2,4-dimethylbenzylthiol has a coordinating functional group directly attached to the benzene ring, and has substituents other than the coordinating functional group at the midway along the path connecting the carbon with the coordinating functional group and the carbon at the para-polar (p-position) position in the benzene ring, as well as at the para-polar position of the coordinating functional group.

[0090] As shown in equation (F), when there is a substituent other than the coordinating functional group at the para position of the coordinating functional group in the benzene ring, the carbon chain connecting the carbon of the coordinating functional group to the carbon at the para position along the benzene ring with the shortest distance is naturally longer than the carbon chain in the benzene ring that connects the carbon of the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group attached to the carbon at the para position with the shortest distance along the benzene ring.

[0091] As a carbon chain in the benzene ring of 2,4-dimethylbenzenethiol, which connects the carbon with the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group at the p-position along the shortest distance of the benzene ring, there exist: carbon chains (first carbon chains) represented by (1) to (5) in the following formula (F); and carbon chains (second carbon chains) represented by (1), (2)', (3)', (4), and (5) in the following formula (F). In this case, the number of carbon atoms in any carbon chain is 5.

[0092] In addition to the p-position (4-position), 2,4-dimethylbenzenethiol also has substituents other than coordinating functional groups at the o-position (2-position). The carbon chain of 2,4-dimethylbenzenethiol, which connects the carbon with the coordinating functional group along the benzene ring at the shortest distance from the carbon with the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group at the o-position, becomes the carbon chain (third carbon chain) with carbons shown in (1), (2)', and (3)" in the following formula (F).

[0093] Therefore, the first or second carbon chain of 2,4-dimethylbenzenethiol, which connects the carbon with the coordinating functional group along the benzene ring at the shortest distance to the carbon at the end of the substituent other than the coordinating functional group at the p-position, forms the main chain backbone of 2,4-dimethylbenzenethiol. In this case, the main chain backbone of 2,4-dimethylbenzenethiol always has 5 carbon atoms.

[0094] [Chemical Formula 6] Next, we will take 2,5-dimethylbenzylthiol, a ligand of the benzene-thiol system, which has two substituents other than the aforementioned coordinating functional groups bonded to the benzene ring, as an example. As shown in formula (G), 2,5-dimethylbenzylthiol has a coordinating functional group directly bonded to the benzene ring, and has two substituents other than the coordinating functional group in the middle of the path in the benzene ring that connects the carbon with the coordinating functional group and the carbon at the para-polar (p-position) position along the shortest distance of the benzene ring.

[0095] As a carbon chain in the benzene ring of 2,5-dimethylbenzenethiol, which connects the carbon atoms of the coordinating functional groups along the benzene ring in the shortest distance from the carbon atom to the end of the substituent other than the coordinating functional group at the p-position, there exist: a carbon chain having carbon atoms as shown in (1) to (4) in formula (G) (first carbon chain); and a carbon chain having carbon atoms as shown in (1), (2)', (3)', and (4) in formula (F) (second carbon chain). In this case, the number of carbon atoms in any carbon chain is 4.

[0096] The carbon chain of 2,5-dimethylbenzenethiol, which is a carbon chain that connects the carbon of the benzene ring along the benzene ring at the shortest distance from the carbon of the carbon with the coordinating functional group to the carbon of the carbon other than the coordinating functional group at the o position (2 position), is the carbon chain (third carbon chain) with carbons shown in (1), (2)', (3)" in the following formula (G).

[0097] The carbon chain of 2,5-dimethylbenzenethiol, which consists of a carbon atom of a coordinating functional group connected along the benzene ring at the shortest distance to the end of a substituent other than the coordinating functional group at the m-position (5-position), is a carbon chain (fourth carbon chain) having carbon atoms represented by (1), (2), (3), (4)' in the following formula (G), which has 4 carbon atoms.

[0098] Therefore, in this case, the first, second, and fourth carbon chains mentioned above each have the same number of carbon atoms, and any one of them can be considered as the main chain backbone. In this case, the main chain backbone of 2,5-dimethylbenzenethiol always has 4 carbon atoms.

[0099] [Chemical Formula 7] Next, benzoic acid, which has a carbon-containing coordinating functional group bonded to the benzene ring and serves as an aromatic ligand (specifically, a ligand of the phenylcarboxylic acid system), will be used as an example. As shown in formula (H), benzoic acid has a coordinating functional group directly bonded to the benzene ring, but does not have substituents other than the coordinating functional group. Therefore, the number of carbon atoms in the carbon chain that connects the carbon with the coordinating functional group to the carbon at its para (p) position along the benzene ring with the shortest distance becomes the number of carbon atoms in the main chain skeleton. The coordinating functional group of benzoic acid itself has carbon, but as mentioned above, the coordinating functional group is not included in the main chain skeleton. Therefore, the carbon chain (first carbon chain) with carbons shown in (1) to (4) in formula (H) or the carbon chain (second carbon chain) with carbons shown in (1), (2)', (3)', and (4) in formula (H) becomes the main chain skeleton of benzoic acid. In this case, the main chain backbone of benzoic acid has 4 carbon atoms regardless.

[0100] [Chemical Formula 8] Next, we will take 3-methylcyclopentanethiol, a ligand in an alicyclic system that incorporates a substituent other than a coordinating functional group, as an example. 3-methylcyclopentanethiol is shown in formula (I). Since the coordinating functional group is directly bonded to cyclopentane (a 5-membered ring), and the anti-polar position of the coordinating functional group in cyclopentane has a substituent other than the coordinating functional group, the carbon chain connecting the carbon containing the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group along the ring with the shortest distance forms the main chain backbone.

[0101] As a carbon chain in cyclopentane that connects a carbon with a coordinating functional group to a carbon with a substituent other than the coordinating functional group, there exist: a carbon chain (first carbon chain) having 3 carbon atoms of carbons represented by (1) to (3) in the following formula (I); and a carbon chain (second carbon chain) having 4 carbon atoms of carbons represented by (1), (2)', (3)', and (3) in the following formula (I).

[0102] However, the para position of the coordinating functional group in cyclopentanethiol is 3, and the maximum number of carbon atoms in cyclopentane that forms part of the main chain backbone is 3. The number of carbon atoms 4 exceeds the maximum number of carbon atoms 3 in cyclopentane. Furthermore, the paths connecting the carbons shown in (1), (2)', (3)', and (3) in formula (I) below are not the shortest path along the ring connecting the carbon with the coordinating functional group to the carbon at the end of the substituent other than the coordinating functional group.

[0103] Therefore, the carbon chain containing the first carbon chain in formula (I) with carbons shown in (1) to (4) becomes the main chain backbone of 3-methylcyclopentanethiol. Therefore, the main chain backbone of 3-methylcyclopentanethiol has 4 carbon atoms.

[0104] [Chemical Formula 9] Next, we will take 4-phenylbutamine, an aromatic ligand with a substituent containing a coordinating functional group, as an example. 4-Phenylated 4-phenylbutamine has only a -(CH2)4NH2 group, containing an amino group (-NH2) as a coordinating functional group, as a substituent on the benzene ring. Therefore, the number of carbon atoms in the carbon chain connecting the carbon with the amino group to the carbon at the p-position of the substituent in the benzene ring along the shortest distance constitutes the number of carbon atoms in the main chain skeleton. The main chain skeleton contains 4 carbon atoms of the substituent, and the maximum number of carbon atoms in the benzene ring is 4; therefore, the main chain skeleton of 4-phenylbutamine has 8 carbon atoms.

[0105] In addition, the number of carbon atoms in the main chain backbone of the second ligand 22 other than those mentioned above can also be calculated in the same way. An example of the second ligand 22 used in this embodiment is shown in Table 1 along with the number of carbon atoms in its main chain backbone.

[0106] [Table 1] Furthermore, the above example is just one instance, and the second ligand 22 is not particularly limited as long as it is a monodentate ligand that prevents the nanoparticles 12 from being dispersed in the solvent by coordinating with the nanoparticles 12 as described above.

[0107] Wherein, the aforementioned second ligand 22 is preferably at least one ligand selected from the group consisting of the aforementioned ethyl mercaptan, 1-propanethiol, 1-butanethiol, 1-pentanethiol, 2-methyl-1-butanethiol, o-toluenethiol, m-toluenethiol, p-toluenethiol, 2,4-dimethylbenzenethiol, 3,4-dimethylbenzenethiol, 2,5-dimethylbenzenethiol, 3,5-dimethylbenzenethiol, 3-methylcyclopentanethiol, 4-tert-butylbenzenethiol, 4-isopropylbenzenethiol, methylamine, pentylamine, p-toluidine, 4-phenylbutanamine, valeric acid, benzoic acid, ethylphosphonic acid and trimethylphosphine. Furthermore, it is more preferred that the aforementioned second ligand 22 is a ligand having a main chain skeleton with 5 or less carbon atoms, and p-toluenethiol is further preferred.

[0108] The second ligand 22 is soluble or dispersible in the second organic solvent 23, and an organic solvent having a polarity opposite to that of the first organic solvent 14 is used.

[0109] Therefore, as described above, when the nanoparticle 12 is, for example, a QD, and the aforementioned first organic solvent 14 is a non-polar organic solvent, a polar organic solvent is used as the aforementioned second organic solvent 23. Furthermore, when the aforementioned nanoparticle 12 is, for example, an inorganic nanoparticle having carrier transport property, and the aforementioned first organic solvent 14 is a polar organic solvent, a non-polar organic solvent is used as the aforementioned second organic solvent 23.

[0110] As the aforementioned non-polar organic solvent, it is preferable to use an organic solvent having a dielectric constant (Y) of 1.8 or more and 6.1 or less (that is, 1.8≤Y≤6.1). Furthermore, as the aforementioned polar organic solvent, it is preferable to use an organic solvent having a dielectric constant (Y) of more than 6.1 and 50 or less (that is, 6.1<Y≤50).

[0111] Table 2 shows the dielectric constants of main solvents. In addition, in the present embodiment, the dielectric constant refers to the dielectric constant measured around 20°C to 25°C. Generally, publicly disclosed dielectric constants are values measured around 20°C to 25°C, therefore, as the aforementioned dielectric constant, the generally publicly disclosed dielectric constant can be directly used. In addition, there is no particular limitation on the measurement method and measurement device for the dielectric constant. As an example, a dielectric constant meter for liquids can be used.

[0112] [Table 2] As shown in Table 2, examples of the organic solvent satisfying 1.8≤Y≤6.1 include pentane, hexane, heptane, octane, carbon tetrachloride, p-xylene, benzene, toluene, diethyl ether, chloroform, butyl acetate, isobutyl acetate, chlorobenzene, ethyl acetate and the like.

[0113] In addition, as shown in Table 2, examples of organic solvents that satisfy 6.1 < Y ​​≤ 50 include dimethyl ether, tetrahydrofuran (THF), dichloromethane, 1,2-dichloroethane, ethylene glycol monomethyl ether, 1-butanol, 2-propanol, 1-propanol, acetone, acetaldehyde, ethanol, methanol, N,N-dimethylformamide (DMF), acetonitrile, ethylene glycol, and dimethyl sulfoxide (DMSO).

[0114] Although the concentration of the second ligand 22 in the first ligand solution 21 also depends on the type of the first ligand 13 in the first nanoparticle dispersion 11 and the coordination ease of the second ligand 22, it is preferably 1 mg / mL or more, and more preferably 10 mg / mL or more.

[0115] The higher the concentration of the second ligand 22, the easier it is to replace the first ligand 13 with the second ligand 22; therefore, a concentration as high as possible is preferred. Thus, there is no particular upper limit to the concentration of the second ligand 22. From the viewpoint of solubility or dispersibility of the second ligand 22 in the second organic solvent 23 and manufacturing cost, a concentration of 1500 mg / mL or less is preferred, and more preferably, a concentration of 500 mg / mL or less is preferred.

[0116] Furthermore, the supply amount of the second ligand 22 is not particularly limited, for example, as long as it is appropriately set to supply an excess of the second ligand 22 that is disposed on the nanoparticles 12, depending on the type and amount of the nanoparticles 12. Considering each nanoparticle 12, the amount of the supplied second ligand 22 is sufficient regardless of the aforementioned conditions; therefore, the actual amount of the second ligand 22 disposed on the nanoparticles 12 tends to depend on the concentration of the second ligand 22 contained in the first ligand solution 21. Additionally, any remaining second ligand 22 not disposed on the nanoparticles 12 is separated and removed in step S3 (first separation step).

[0117] In step S2, by mixing the first nanoparticle dispersion 11 and the first ligand solution 21, the first ligand 13 located on the nanoparticle 12 can be replaced by the second ligand 22.

[0118] The reaction conditions, such as reaction temperature and reaction time, in step S2 of the ligand substitution reaction are appropriately set according to the types and amounts of the first ligand 13, the second ligand 22, and the second organic solvent 23, until the ligand substitution reaction is completed. Therefore, the above reaction conditions are not particularly limited.

[0119] The higher the reaction temperature of the aforementioned ligand substitution reaction, the more readily the ligand substitution reaction proceeds. However, if the reaction temperature is high, the ligand or nanoparticles 12 used may deteriorate or decompose. Furthermore, if the reaction temperature is high, the second organic solvent 23 may disappear due to its boiling point. Therefore, the reaction temperature depends on the type and amount of the first ligand 13, the second ligand 22, and the second organic solvent 23; for example, it is preferably below 100°C, more preferably below 60°C. In addition, the longer the reaction time, the higher the ligand substitution rate; however, in reactions under preferred conditions, substitution may be essentially completed within minutes. In most cases, even in longer cases, the time required for the substitution to be completed is approximately 24 hours.

[0120] Nanoparticles 12 coordinated with the second ligand 22 are not dispersed in any solvent. Furthermore, nanoparticles 12 coordinated with the second ligand 22 are sometimes referred to below as "second ligand-modified nanoparticles 24". Therefore, second ligand-modified nanoparticles 24 are also not dispersed in the first organic solvent 14 or the second organic solvent 23, and as ligand substitution proceeds, they aggregate and gradually precipitate from the colloidal solution. The precipitated second ligand-modified nanoparticles 24 further aggregate into clumps and precipitate.

[0121] On the other hand, as described above, the first ligand 13 is soluble or dispersed in the first organic solvent 14. Therefore, the first ligand 13, which is freed from the nanoparticle 12 by ligand substitution, dissolves or disperses in the first organic solvent 14.

[0122] Furthermore, as described above, the second ligand 22 is soluble or dispersible in the second organic solvent 23. As described above, in step S2, an excess of the second ligand 22 is supplied to the nanoparticles 12. Therefore, the ligand-substituted reaction solution 25 contains the remaining second ligand 22. The remaining second ligand 22 not ligated to the nanoparticles dissolves or disperses in the second organic solvent 23. Additionally, the remaining second ligand 22 not ligated to the nanoparticles refers to free second ligand 22 not ligated to the nanoparticles 12.

[0123] Therefore, in this embodiment, as Figure 2 As shown in S3, after the above ligand replacement, the second ligand-modified nanoparticles 24 are separated from the liquid phase as a solid (the first solid) through solid-liquid separation.

[0124] Figure 3 It means Figure 1 and Figure 2 A flowchart of an example of the first separation process (step S3) shown in S3. Step S3 may include, for example, the following steps.

[0125] like Figure 3As shown, in step S3, for example, centrifugation is performed to precipitate the precipitated second ligand-modified nanoparticles 24 as a first solid (step S11). Next, the liquid phase (supernatant) is removed by removing the first solid (second ligand-modified nanoparticles 24) remaining as precipitate, and the first solid is separated from the liquid phase by solid-liquid separation (step S12).

[0126] The first organic solvent 14 and the second organic solvent 23 are immiscible (compatible) and separate into two phases: a first organic solvent phase and a second organic solvent phase. The first organic solvent phase contains free first ligand 13. The second organic solvent phase contains free second ligand 22. Therefore, by removing the liquid phase (supernatant) as described above, the first ligand 13 that has been replaced by the ligand and the remaining second ligand 22 can be removed.

[0127] Additionally, at this point, the liquid phase (supernatant) can be removed by adding the first organic solvent 14 and the second organic solvent 23 again to remove the residual precipitate, thereby cleaning the aforementioned first solid. Since the aforementioned first solid is not dispersed in any solvent, the free first ligand 13 and free second ligand 22 remaining in the aforementioned container 1 can be removed by adding the first organic solvent 14 and the second organic solvent 23 to remove the supernatant.

[0128] Figure 4 It is a schematic representation Figure 1 An explanatory diagram of another part of the ligand replacement method shown. Figure 4 express Figure 1 Step S4 is shown.

[0129] like Figure 4 As shown, in step S4, the second ligand solution 31 is added to the first solid (second ligand-modified nanoparticles 24) separated in step S3 within container 1, and the mixture is stirred to mix the second ligand solution 31 and the first solid. The second ligand solution 31 contains the desired target ligand 32 and a third organic solvent 33. Thus, the second ligand 22 is replaced with the target ligand 32, dispersing the nanoparticles 12 coordinated to the target ligand 32 in the third organic solvent 33. Furthermore, the nanoparticles 12 coordinated to the target ligand 32 are sometimes referred to below as "target ligand-modified nanoparticles 34".

[0130] The target ligand 32 is any ligand having a coordination functional group capable of coordinating with the nanoparticle 12. The target ligand 32 can be a monomer, an oligomer, or a polymer. Furthermore, in this case, the coordination functional group exemplified above can be used as an example.

[0131] As described above, the first solid substance (second ligand-modified nanoparticles 24) separated in step S3 is a precipitate. Therefore, the third organic solvent 33 is not particularly limited as long as it is an organic solvent that can dissolve or disperse the second ligand 22 and the target ligand 32, and can disperse the target ligand-modified nanoparticles 34.

[0132] Furthermore, in the case where the nanoparticle 12 is, for example, a QD, it also depends on the type of the target ligand 32, but as the aforementioned third organic solvent 33, a nonpolar organic solvent is used, for example. Additionally, in the case where the aforementioned nanoparticle 12 is, for example, an inorganic nanoparticle with carrier transport capabilities, it also depends on the type of the target ligand 32, but as the aforementioned third organic solvent 33, a polar organic solvent is used, for example.

[0133] The concentration of the target ligand 32 in the second ligand solution 31 also depends on the type of the second ligand 22 and the ease of coordination of the target ligand 32, but is preferably 1 mg / mL or more, more preferably 10 mg / mL or more.

[0134] The higher the concentration of the target ligand 32, the easier it is to replace the second ligand 22 with the target ligand 32; therefore, a concentration as high as possible is preferred. Thus, there is no particular upper limit to the concentration of the target ligand 32. From the viewpoint of solubility or dispersibility of the target ligand 32 in the third organic solvent 33 and manufacturing cost, a concentration of 1500 mg / mL or less is preferred, and more preferably, a concentration of 500 mg / mL or less is preferred.

[0135] Furthermore, the supply amount of target ligand 32 can be appropriately set to be an excess of second ligand 22 exceeding the amount of second ligand 22 located on nanoparticles 12, depending on the type and amount of nanoparticles 12, without particular limitation. Considering each nanoparticle 12, the supplied amount of target ligand 32 is sufficient regardless of the aforementioned conditions; therefore, the actual amount of target ligand 32 located on nanoparticles 12 tends to depend on the concentration of target ligand 32 contained in the second ligand solution 31. Additionally, any remaining target ligand 32 not located on nanoparticles 12 is separated and removed in step S5 (second separation step).

[0136] In step S4, by mixing the second ligand solution 31 with the first solid, the second ligand 22 located on the nanoparticle 12 can be replaced with the target ligand 32.

[0137] The reaction conditions, such as reaction temperature and reaction time, in step S4 of the ligand substitution reaction only need to be appropriately set according to the type and amount of the second ligand 22, the target ligand 32, and the third organic solvent 33 to ensure the completion of the ligand substitution reaction. Therefore, the above reaction conditions are not particularly limited.

[0138] The ligand substitution reaction described above also proceeds more readily with higher reaction temperatures. However, if the reaction temperature is too high, the ligand or nanoparticles 12 used may deteriorate or decompose. Furthermore, if the reaction temperature is too high, the second organic solvent 23 may disappear depending on its boiling point. Therefore, the reaction temperature depends on the type and amount of the second ligand 22, the target ligand 32, and the third organic solvent 33; preferably, it is below 100°C, and more preferably below 60°C. Additionally, the longer the reaction time, the higher the ligand substitution rate; however, in reactions under preferred conditions, substitution may be essentially completed within minutes. In most cases, even in longer cases, the time required for substitution to be complete is approximately 24 hours.

[0139] As described above, in step S4, excess target ligand 32 is supplied to the nanoparticles 12. Therefore, as... Figure 4 As shown, the reaction solution 35 after ligand substitution comprises: a third organic solvent 33, nanoparticles 12 coordinated with the target ligand 32 (target ligand-modified nanoparticles 34), a second ligand 22 freed from the nanoparticles 12 through ligand substitution, and the remaining target ligand 32 not coordinated to the nanoparticles 12. Furthermore, the remaining target ligand 32 not coordinated to the nanoparticles 12 refers to the free target ligand 32 not coordinated to the nanoparticles 12. The aforementioned target ligand-modified nanoparticles 34 are dispersed in the aforementioned third organic solvent 33. Additionally, the free second ligand 22 and the free target ligand 32 are dissolved or dispersed in the aforementioned third organic solvent 33.

[0140] Figure 5 It is a schematic representation Figure 1 An explanatory diagram of another part of the ligand replacement method shown. Figure 5 express Figure 1 Steps S5 and S6 are shown.

[0141] like Figure 5 As shown, in step S5, nanoparticles 12 (target ligand-modified nanoparticles 34) coordinated with the target ligand 32 are taken out from the reaction liquid 35 in container 1 obtained by the ligand substitution reaction in step S4, washed, and separated. In step S6, the separated target ligand-modified nanoparticles 34 are redispersed in the solvent by dispersing them in a fourth organic solvent 51, which is the target solvent.

[0142] Figure 6 It is a flowchart showing, in sequence, the method of separating nanoparticles with target ligands from a nanoparticle dispersion containing nanoparticles with target ligands and dispersing them in a target solvent.

[0143] like Figure 6As shown, to separate nanoparticles with target ligands from the above nanoparticle dispersion, typically, firstly, a poor solvent is added to the nanoparticle dispersion and centrifuged to precipitate the nanoparticles with target ligands (step S21). Next, the liquid phase (supernatant) is removed and the solids are separated (step S22). Then, by washing the solids, the nanoparticles with target ligands can be separated. The washing of the solids is performed by repeatedly redispersing the separated solids in an organic solvent (step S23) and then adding a poor solvent, centrifuging, removing the supernatant, and redispersing the solids (step S24). Then, the solids finally separated by the above washing are dispersed in the target solvent (step S25), thereby dispersing the separated nanoparticles with target ligands into the target solvent. Furthermore, step S25 and... Figure 1 and Figure 5 Step S6 corresponds to the step S6 shown in the diagram.

[0144] therefore, Figure 1 and Figure 5 The second separation process (step S5) shown in S5 is carried out, for example, by the following method.

[0145] First, such as Figure 5 and Figure 6 As shown, an organic poor solvent 41 is added to the reaction solution 35 in container 1 obtained through the ligand substitution reaction in step S4, causing the nanoparticles 12 (target ligand modified nanoparticles 34) coordinated with the target ligand 32 to precipitate as a solid (second solid). Then, the precipitated second solid is separated by centrifugation (step S21).

[0146] Then, by removing the liquid phase (supernatant) containing the third organic solvent 33 containing the free second ligand 22 and the free target ligand 32 and the aforementioned undesirable organic solvent 41, the aforementioned second solid (target ligand modified nanoparticles 34) as precipitate is separated (step S22).

[0147] Subsequently, a third organic solvent 33, which serves as a good solvent, is added again to the separated solids (second solids). This causes the target ligand-modified nanoparticles 34, the unremoved second ligand 22 remaining in container 1, and the unremoved target ligand 32 to be redispersed in the third organic solvent 33 (step S23).

[0148] Next, the undesirable organic solvent 41 is added again to the container 1, and centrifugation is performed. This causes the target ligand-modified nanoparticles 34 to precipitate again as a solid (second solid). Then, the second solid, which is the precipitate, is separated again by removing the liquid phase (supernatant) remaining in the container 1, which includes the third organic solvent 33 containing the free second ligand 22 and the free target ligand 32, as well as the undesirable organic solvent 41 (step S24).

[0149] By repeating steps S23 and S24 multiple times, the target ligand-modified nanoparticles 34 can be cleaned (purified). This allows for the separation of the target ligand-modified nanoparticles 34.

[0150] In step S25, as Figure 5 As shown in step S6, a fourth organic solvent 51, serving as the target solvent, is added to the target ligand-modified nanoparticles 34, which are separated as a second solid, thereby dispersing the target ligand-modified nanoparticles 34 in the fourth organic solvent 51. This allows the fabrication of a target nanoparticle dispersion 61 containing the target ligand-modified nanoparticles 34 and the fourth organic solvent 51.

[0151] Furthermore, the target solvent (fourth organic solvent 51) can be any solvent capable of dispersing the target ligand-modified nanoparticles 34. As mentioned above, in the case of nanoparticles 12, for example, QD, it also depends on the type of target ligand 32, but as the fourth organic solvent 51, it is the same as the third organic solvent 33, for example, a nonpolar organic solvent. Moreover, in the case of nanoparticles 12, for example, inorganic nanoparticles with charge carrier transport capabilities, as the fourth organic solvent 51, it is the same as the third organic solvent 33, for example, a polar organic solvent.

[0152] In addition, the first organic solvent 14, the third organic solvent 33, and the fourth organic solvent 51 can be the same as each other or different.

[0153] The concentration of nanoparticles 12 in the target nanoparticle dispersion 61 can be appropriately set according to the application and is not particularly limited. For example, when forming a nanoparticle film by coating using the target nanoparticle dispersion 61, the concentration of nanoparticles 12 in the target nanoparticle dispersion 61 is set in the same way as in the present invention, as long as it has a coatable concentration or viscosity. For example, if the nanoparticles are QD, and a light-emitting layer is formed as a QD film, the concentration of nanoparticles 12 in the target nanoparticle dispersion 61 also depends on the film thickness of the QD film, but is preferably in the range of 0.1 mg / mL or more and 500 mg / mL or less, more preferably in the range of 1 mg / mL or more and 100 mg / mL or less.

[0154] In addition, Figure 2 as well as Figures 4-5 In this embodiment, the same container 1 is used in steps S2 to S6 as an example. There are no particular limitations as long as container 1 has resistance to the organic solvent used and heat resistance to high reaction temperatures in the ligand substitution reaction; it can also be a centrifugal container such as a centrifuge tube. However, this embodiment is not limited to this, and the container used for the ligand substitution reaction and the centrifugal container can be different. Furthermore, different containers can be used depending on the process steps.

[0155] Figure 7 and Figure 8 This is an illustrative diagram schematically illustrating a conventional method for manufacturing a target nanoparticle dispersion 61 by replacing a first ligand 13 coordinated to nanoparticles 12 in a first nanoparticle dispersion 11 with a target ligand 32. Additionally, Figure 8 It indicates that in Figure 7 The process following step S105 as shown in S105.

[0156] In existing technologies, such as Figure 7 As shown in step S102, instead of the first ligand solution 21 in step S2 above, an aqueous intermediate ligand solution 121 containing an aqueous solvent dispersion ligand 122 and an aqueous solvent 123 is mixed with the first nanoparticle dispersion 11. Thus, the first ligand 13 is replaced with the aforementioned aqueous solvent dispersion ligand 122 (step S102).

[0157] The first organic solvent 14 and the aqueous solvent 123 are immiscible (compatible), and the reaction solution after ligand substitution is separated into two phases: the first organic solvent phase and the aqueous solvent phase. In step S102, excess aqueous solvent dispersion ligand 122 is supplied to the nanoparticles 12. Therefore, the aqueous solvent 123 of the aqueous solvent phase contains nanoparticles 12 with the aqueous solvent dispersion ligand 122 coordinated as an intermediate ligand and the remaining aqueous solvent dispersion ligand 122 not coordinated to the nanoparticles 12. In addition, the remaining aqueous solvent dispersion ligand 122 not coordinated to the nanoparticles 12 refers to the free aqueous solvent dispersion ligand 122 not coordinated to the nanoparticles 12. On the other hand, the first organic solvent 14 of the first organic solvent phase contains the first ligand 13 that is freed from the nanoparticles 12 through ligand substitution. Hereinafter, the nanoparticles 12 with the aqueous solvent dispersion ligand 122 coordinated as an intermediate ligand are sometimes referred to as "intermediate ligand modified nanoparticles 124".

[0158] Therefore, as follows, Figure 7As shown in step S103, the aqueous solvent phase containing the above-mentioned intermediate ligand modified nanoparticles 124 and free aqueous solvent dispersion ligand 122 is separated from the above-mentioned first organic solvent phase by liquid-liquid separation (step S103).

[0159] As described above, the aqueous solvent 123 of the above-mentioned aqueous solvent phase, in addition to containing the intermediate ligand-modified nanoparticles 124, also contains a free aqueous solvent dispersion ligand 122. Therefore, next, as Figure 7 As shown in step S104, the intermediate ligand-modified nanoparticles 124 are separated (isolated) from the aqueous solvent phase (step S104).

[0160] The separation (deposition) of the aforementioned intermediate ligand-modified nanoparticles 124 was achieved through interaction with... Figure 6 The same process is performed as shown in the flowchart. Specifically, firstly, a poor solvent is added to the aqueous solvent phase (nanoparticle dispersion) separated in step S103, and centrifugation is performed to precipitate the intermediate ligand-modified nanoparticles 124. Next, the liquid phase (supernatant) is removed, and the intermediate ligand-modified nanoparticles 124 are separated as solids. Then, the solids are washed by repeatedly redispersing the separated solids in the aqueous solvent 123, adding a poor solvent, centrifuging, removing the supernatant, and reseparating the solids. Therefore, the above-mentioned intermediate ligand modified nanoparticles 124 were separated.

[0161] Next, as Figure 7 As shown in step S105, the intermediate ligand-modified nanoparticles 124 separated in step 104 above are dispersed in an aqueous solvent 123. Thus, a nanoparticle dispersion 125 containing the intermediate ligand-modified nanoparticles 124 and the aqueous solvent 123 is obtained (step S105).

[0162] As described above, the second ligand 22 coordinates with the nanoparticle 12, preventing the nanoparticle 12 from dispersing in the solvent. However, the second ligand 22 monomer dissolves or disperses in an organic solvent, as described above, forming, for example, a first ligand solution 21. On the other hand, the ligand 122 for aqueous solvent dispersion does not dissolve or disperse in an organic solvent, but dissolves or disperses in an aqueous solvent, as described above, forming, for example, an aqueous intermediate ligand solution 121.

[0163] Therefore, in order to replace the ligand 122 that is coordinated in the aqueous solvent dispersion of nanoparticles 12 with the target ligand 32, it is necessary to disperse the separated intermediate ligand modified nanoparticles 124 in the aqueous solvent 123.

[0164] Next, as Figure 8As shown in S106, a second ligand solution 31 containing the desired target ligand 32 and a third organic solvent 33 is added to the nanoparticle dispersion 125 and stirred, etc., to mix the second ligand solution 31 and the intermediate ligand-modified nanoparticles 124. Thereby, the aqueous solvent dispersion ligand 122 is replaced with the target ligand 32, and the nanoparticles 12 (target ligand-modified nanoparticles 34) coordinated with the target ligand 32 are dispersed in the third organic solvent 33 (step S106).

[0165] The aqueous solvent 123 and the third organic solvent 33 are immiscible (compatible), and the reaction solution after ligand substitution separates into two phases: an aqueous solvent phase and a third organic solvent phase. In step S106, excess target ligand 32 is supplied to the nanoparticles 12. Therefore, the third organic solvent phase 33 contains the target ligand-modified nanoparticles 34 and the remaining target ligand 32 not liganded in the nanoparticles 12. Furthermore, the remaining target ligand 32 not liganded in the nanoparticles 12 refers to the free target ligand 32 not liganded in the nanoparticles 12. On the other hand, the aqueous solvent phase 123 contains the aqueous solvent dispersion ligand 122 that has been released from the nanoparticles 12 through ligand substitution.

[0166] Therefore, as follows, Figure 8 As shown in step S107, the third organic solvent phase containing the above-mentioned target ligand modified nanoparticles 34 and free target ligands 32 is separated from the above-mentioned aqueous solvent phase by liquid-liquid separation (step S107).

[0167] Next, as Figure 8 As shown in step S108, the target ligand modified nanoparticles 34 are removed from the separated third organic solvent phase, washed, and separated (step S108).

[0168] Through with Figure 6 The same process as shown in the flowchart is used to separate the target ligand-modified nanoparticles 34. Specifically, firstly, a poor solvent is added to the third organic solvent phase (nanoparticle dispersion) separated in step S107, and centrifugation is performed to precipitate the target ligand-modified nanoparticles 34. Next, the liquid phase (supernatant) is removed, and the target ligand-modified nanoparticles 34 are separated as solids. Then, the solids are washed by repeatedly redispersing the separated solids in the third organic solvent 33, adding a poor solvent and centrifuging, removing the supernatant, and separating the solids again. Thus, the separation of the target ligand-modified nanoparticles 34 is performed.

[0169] Then, a fourth organic solvent 51, serving as the target solvent, is added to the target ligand-modified nanoparticles 34, which are separated as solids, to disperse the target ligand-modified nanoparticles 34 in the fourth organic solvent 51. This allows the production of a target nanoparticle dispersion 61 containing the target ligand-modified nanoparticles 34 and the fourth organic solvent 51 (step S109). Step S109 is identical to steps S6 and S25 described above.

[0170] For example, when the nanoparticles 12 are QD and the first organic solvent 14 is toluene, in existing methods, the aqueous solvent dispersion ligand 122 uses, for example, diethylaminoethanethiol hydrochloride or tetramethylammonium hydroxide (TMAH). The aqueous solvent 123 uses, for example, water.

[0171] On the other hand, in this embodiment, for example, when the nanoparticle 12 is QD and the first organic solvent 14 is toluene, the second ligand 22 is, for example, p-toluenethiol (p-TT), and the second organic solvent 23 is, for example, methanol. In this embodiment, as an example, the concentration of p-TT in the first ligand solution 21 is set to, for example, 300 mg / mL. Furthermore, in any case, the third organic solvent 33 is, for example, toluene.

[0172] As described above, in the prior art, liquid-liquid separation is required to replace the first ligand 13 with the target ligand 32. Furthermore, as described above, when both the first nanoparticle dispersion 11 and the target nanoparticle dispersion 61 contain a nonpolar solvent as a solvent, the aqueous solvent 123 is used as the solvent in the replacement of the ligand 122, which is an intermediate ligand, with the aqueous solvent for dispersion.

[0173] In contrast, as described above, in the ligand replacement method of this embodiment, steps S2 to S6 are performed instead of steps S102 to S109. As described above, step S2 (first ligand replacement step) involves mixing a first nanoparticle dispersion 11 containing nanoparticles 12, a first ligand 13, and a first organic solvent 14, and a first ligand solution 21 containing a monodentate second ligand 22 that is coordinated to the nanoparticles 12 so that the nanoparticles 12 cannot be dispersed in the solvent, and a second organic solvent 23, thereby replacing the first ligand 13 with the second ligand 22. Step S3 (first separation step) involves separating the nanoparticles 12 (second ligand-modified nanoparticles 24) coordinated with the second ligand 22 from the liquid phase as a first solid by solid-liquid separation. Step S4 (second ligand replacement step) involves adding a second ligand solution 31 containing the desired target ligand 32 and a third organic solvent 33 to the first solid and replacing the second ligand 22 with the target ligand 32. Step S5 (second separation step) is a step of separating the nanoparticles 12 (target ligand modified nanoparticles 34) coordinated with the target ligand 32 as a second solid. Step S6 (redispersion step) is a step of dispersing the target ligand modified nanoparticles 34 separated in the second separation step in a fourth organic solvent 51.

[0174] According to this embodiment, by temporarily replacing the first ligand 13 as an intermediate ligand with the second ligand 22, the second ligand-modified nanoparticles 24 cannot be dispersed in the solvent, enabling solid-liquid separation from the other solution portion (liquid phase). Therefore, it is not necessary to replace the first ligand 13 as an intermediate ligand with the ligand 122 for dispersion in an aqueous solvent, as in the conventional method described above, and to perform liquid-liquid separation using an aqueous solvent 123, replacing the first ligand 13 with the target ligand 32. Therefore, it is not necessary to use water (an aqueous solvent) as a solvent; the first ligand 13 can be replaced with the target ligand 32 using only an organic solvent. Therefore, the degradation of the nanoparticles 12 due to the aqueous solvent can be prevented. Furthermore, the nanoparticles 12 coordinated with the second ligand 22 can be separated by solid-liquid separation as described above, thus making separation easier compared to liquid-liquid separation as in the prior art. Furthermore, it is not necessary to consider the two-phase separation (two-layer separation) of immiscible solvents required in conventional methods, making it easy to apply. Furthermore, compared to existing liquid-liquid separation methods, damage to the nanoparticles 12 caused by repeated removal of residual ligands can be suppressed. Therefore, according to this embodiment, compared to the prior art, the separation process of nanoparticles with intermediate ligands can be simplified, and the separation time can be shortened. In addition, specific reductions such as the decrease in quantum yield and the decrease in luminescence properties accompanying the deterioration of nanoparticles 12 can be suppressed or prevented.

[0175] Furthermore, the types of ligands coordinated with the nanoparticles can be detected, for example, by MS / MS spectroscopy using a TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) device equipped with a tandem mass spectrometer (MS / MS). By using the aforementioned TOF-SIMS device, for example, performing tandem mass spectrometry analysis on nanoparticle-containing films obtained by drying the aforementioned nanoparticle dispersions, the molecular structure of molecules in nanoscale thin film samples can be resolved, and the molecular structure of ligands contained in nanoparticle-containing films can be determined with high precision.

[0176] Furthermore, the replacement of the first ligand 13 coordinated with the nanoparticle 12 with the second ligand 22 can be confirmed by the fact that the nanoparticle 12 coordinated with the second ligand 22 does not disperse in any solvent and precipitates out. Furthermore, the replacement of the second ligand 22 coordinated with the nanoparticle 12 with the target ligand 32 can be confirmed by dispersing the nanoparticle 12 coordinated with the target ligand 32 in a third organic solvent 33.

[0177] Furthermore, depending on the coordinated ligand, the presence or absence of coordination can be confirmed, for example, by using Fourier transform infrared spectroscopy (FT-IR) measurements (hereinafter referred to as "FT-IR measurements"). For example, when the ligand coordinated with nanoparticle 12 has, for example, a carboxyl (-COOH) group, an amino (-NH2) group, or a -PO group present in a phosphonic acid group, the vibrations observed by FT-IR measurements are subtly different in the uncoordinated and coordinated states, and the detection peak shifts. Therefore, it is possible to confirm the coordination of the ligand to nanoparticle 12 or the substitution of the ligand coordinated with nanoparticle 12.

[0178] Furthermore, after ligand replacement, the peak value of the ligand before replacement (the ligand of the replacement source) disappears, and only the ligand after replacement (the ligand of the replacement target site) is present, which confirms that the ligand of the replacement target site is coordinated to the nanoparticle.

[0179] Furthermore, if at least one of the ligands of the substitution source and the ligands of the substitution target has a functional group exhibiting a specific peak value in addition to the coordinating functional group coordinated to nanoparticle 12, coordination can be confirmed by the amount detected. Examples of such functional groups include ether groups, ester groups, and C=C bonds of oleic acid. In particular, ligand substitution can be confirmed when a specific peak present before ligand substitution disappears after ligand substitution, or when a new specific peak is detected after ligand substitution.

[0180] FT-IR can measure each functional group. Furthermore, by comparing the detection peaks, it is possible not only to confirm the presence or absence of coordination and ligand substitution as described above, but also to determine the approximate substitution rate. In addition, when p-toluenethiol is used for the second ligand 22 as described above, if coordination with p-toluenethiol occurs, large absorptions can be observed at wavenumbers of 1500 nm⁻¹ and 800 nm⁻¹.

[0181] Furthermore, as described above, in step S3 (first separation step), for example, the nanoparticles 12 coordinated with the second ligand 22 are precipitated to form a precipitate. Then, by removing the supernatant as the liquid phase, the precipitate, which is the first solid, is subjected to solid-liquid separation. The supernatant includes: a first organic solvent 14 containing the first ligand 13; and a second organic solvent 23 containing the remaining second ligand 22 that is not coordinated with the nanoparticles 12.

[0182] According to this embodiment, by replacing the first ligand 13 with the second ligand 22, the nanoparticles 12 coordinated with the second ligand 22 precipitate and can be separated from the supernatant. Therefore, solid-liquid separation can be easily achieved, for example, by decantation. Alternatively, solid-liquid separation can also be performed using methods such as filtration.

[0183] This disclosure is not limited to the embodiments described above, and various modifications can be made within the scope of the claims. Embodiments obtained by appropriately combining the technical solutions disclosed in different embodiments are also included in the technical scope of this disclosure. Moreover, new technical features can be formed by combining the technical means disclosed in each embodiment. Explanation of reference numerals in the attached figures

[0184] 11: First Nanoparticle Dispersion 12: Nanoparticles 13: First ligand 14: First organic solvent 21: First ligand solution 22: Second ligand 23: Second organic solvent 24: Second ligand modified nanoparticles 31: Second ligand solution 32: Target ligand 33: Third organic solvent 34: Target ligand modified nanoparticles 41: Poor organic solvents 51: Fourth organic solvent

Claims

1. A ligand displacement method characterized in that, The ligand replacement method includes: In the first ligand replacement step, the first nanoparticle dispersion contains nanoparticles, a first ligand, and a first organic solvent. The first ligand solution contains a monodentate second ligand and a second organic solvent. The second ligand coordinates with the nanoparticles, preventing the nanoparticles from dispersing in the solvent. The first nanoparticle dispersion and the first ligand solution are mixed to replace the first ligand with the second ligand; In the first separation step, the nanoparticles coordinated with the second ligand are separated from the liquid phase as a first solid by solid-liquid separation; The second ligand replacement step involves adding a second ligand solution containing the desired target ligand and a third organic solvent to the first solid, thereby replacing the second ligand with the target ligand. The second separation step involves separating the nanoparticles coordinated with the target ligand as a second solid; and The redispersion process disperses the nanoparticles, which are coordinated with the target ligand and separated in the second separation process, into a fourth organic solvent.

2. The ligand replacement method according to claim 1, characterized in that, The second ligand is the following ligand: It possesses coordination functional groups capable of fitting into the nanoparticles. When the second ligand does not contain a ring, the carbon chain with the most carbon atoms in the carbon chain that connects the carbon with the coordinating functional group to the carbon of the terminal group with the shortest distance is used as the main chain backbone. When the second ligand comprises a ring, (i) a carbon chain that connects along the ring from the carbon with the coordinating functional group to the carbon in the ring located at the opposite pole of the carbon with the coordinating functional group or the substituent containing the coordinating functional group, and (ii) when the ring is connected to a substituent other than the coordinating functional group or the substituent containing the coordinating functional group, the carbon chain containing the most carbon atoms in the carbon chain that connects along the ring from the carbon with the coordinating functional group to the end of the carbon with the ring connected to the ring, other than the coordinating functional group or the substituent containing the coordinating functional group, is the main chain backbone, and the main chain backbone has 1 or more and 8 or less carbon atoms.

3. The ligand replacement method according to claim 2, characterized in that, The main chain backbone of the second ligand has 5 or fewer carbon atoms.

4. The ligand replacement method according to claim 1, characterized in that, The second ligand is at least one ligand selected from the group consisting of ethyl mercaptan, 1-propanethiol, 1-butanethiol, 1-pentanethiol, 2-methyl-1-butanethiol, o-toluenethiol, m-toluenethiol, p-toluenethiol, 2,4-dimethylbenzenethiol, 3,4-dimethylbenzenethiol, 2,5-dimethylbenzenethiol, 3,5-dimethylbenzenethiol, 3-methylcyclopentanethiol, 4-tert-butylbenzenethiol, 4-isopropylbenzenethiol, methylamine, pentaneamine, p-toluidine, 4-phenylbutylamine, valeric acid, benzoic acid, ethylphosphonic acid, and trimethylphosphine.

5. The ligand displacement method of claim 1, wherein, The second ligand is p-toluenethiol.

6. The ligand replacement method according to any one of claims 1 to 5, characterized in that, The nanoparticles are quantum dots. The first organic solvent is a non-polar organic solvent, and the second organic solvent is a polar organic solvent.

7. The ligand replacement method according to any one of claims 1 to 5, characterized in that, The nanoparticles are inorganic nanoparticles with charge carrier transport capabilities. The first organic solvent is a polar organic solvent, and the second organic solvent is a non-polar organic solvent.

8. The ligand replacement method according to claim 6, characterized in that, The nonpolar organic solvent is a solvent with a dielectric constant of 1.8 or higher and 6.1 or lower.

9. The ligand replacement method according to claim 6, characterized in that, The polar organic solvent is a solvent with a dielectric constant greater than 6.1 and less than 50.

10. The ligand replacement method according to any one of claims 1 to 5, characterized in that, Prior to the first ligand replacement step, a dilution step is also included, in which the first nanoparticle dispersion is diluted with the first organic solvent so that the concentration of the nanoparticles in the first nanoparticle dispersion is in the range of 0.001 mg / mL or more and 100 mg / mL or less.

11. The ligand replacement method according to claim 10, characterized in that, In the dilution step, the first nanoparticle dispersion is diluted with the first organic solvent so that the concentration of the nanoparticles in the first nanoparticle dispersion is in the range of more than 0.01 mg / mL and less than 20 mg / mL.

12. The ligand replacement method according to any one of claims 1 to 5, characterized in that, In the first separation step, the nanoparticles with the second ligand precipitated are used as precipitates. The precipitates, which are the first solids, are removed by using the supernatant as the liquid phase. The supernatant includes: the first organic solvent containing the first ligand and the second organic solvent containing the remaining second ligands that are not ligated to the nanoparticles.

13. The ligand replacement method according to any one of claims 1 to 5, characterized in that, In the second separation step, the nanoparticles coordinated with the target ligand are precipitated and purified using an organic poor solvent, and then separated as the second solid.

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