Surface-coated ionic crystal, method for producing surface-coated ionic crystal, and surface coating agent

Abstract

To provide an ionic crystal using a new method that can further improve the heat resistance of the ionic crystal. [Solution] A surface-coated ionic crystal in which the surface of an ionic crystal is coated with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion.

Description

[Technical Field]

[0001] The present invention relates to surface-coated ionic crystals, a method for producing surface-coated ionic crystals, and a surface coating agent. [Background technology]

[0002] Ionic crystals are known to have a variety of applications. For example, perovskite nanoparticles, a type of ionic crystal, are known as quantum dot nanoparticles and are attracting particular attention as wavelength conversion materials. Quantum dot nanoparticles are semiconductor crystals composed of approximately 10 to 50 atoms. By changing the particle size of the nanoparticles, the band gap changes, making it possible to adjust the emission wavelength from the nanoparticles. Furthermore, quantum dot nanoparticles have the characteristics of a narrow full width at half maximum (FWHM) of emission spectra, high fluorescence quantum yield, and the ability to absorb light across a wide range of wavelengths. Utilizing these characteristics, quantum dot nanoparticles are used in applications such as displays, solar cells, and bioimaging. Perovskite nanoparticles can be color-tuned by changing both their composition and particle size, and they also have the characteristics of a narrow FWHM of emission spectra and high fluorescence quantum yield.

[0003] On the other hand, ionic crystals have the disadvantage of being prone to surface defects. For example, perovskite nanoparticles are unstable under conditions such as polar solvents like water, heat, light, and oxygen. Under these conditions, defects form on the nanoparticle surface, resulting in a decrease in the stability of the ionic crystal and a decrease in the fluorescence quantum yield.

[0004] Techniques to overcome these challenges by modifying the surface of nanoparticles with coating agents are known. A common technique involves using a combination of long-chain amines such as oleylamine and long-chain acids such as oleic acid as coating agents. However, these coating agents have weak coordination ability to the nanoparticle surface, resulting in insufficient durability of the nanoparticles obtained through modification.

[0005] Therefore, Non-Patent Document 1 discloses that the durability of nanoparticles against polar solvents can be improved by using a coating agent having a zwitterionic structure, such as sulfobetaine. This effect is thought to be due to a chelating effect caused by the interaction of the cation and anion portions within the molecule with the nanoparticle surface.

[0006] Furthermore, Non-Patent Document 2 discloses the use of a polymer having a zwitterionic structure for surface coating of perovskite nanoparticles. Non-Patent Document 2 confirms that surface coating of nanoparticles with a polymer having a zwitterionic structure maintains the luminescence intensity of the nanoparticles in water for about one week, and significantly improves the water resistance of the nanoparticles.

[0007] Similarly, Patent Document 1 discloses the use of a polymer having a zwitterionic structure, such as phosphorylcholine, as a surface coating for perovskite nanoparticles. This has been shown to maintain a high fluorescence quantum yield (approximately 90%) even after heating at 80°C for 16 hours. Improvements in resistance to polar solvents such as isopropanol, as well as resistance to light, have also been confirmed.

[0008] Furthermore, there are known examples of improving the durability of nanoparticles by utilizing the chelating effect with coating agents that have multiple cationic coordination sites within the same molecule. Non-patent document 3 describes how coating perovskite nanoparticles with a molecule in which two alkylamino groups and a long-chain alkyl group are bonded to a nitrogen atom resulted in the ionic crystalline phase of the nanocrystals being maintained for 20 days even when heated at 85°C in 30-40% humidity, confirming that the resulting nanoparticles exhibited high heat resistance. This effect is thought to be due to the strengthened interaction with the nanoparticle surface caused by biposition by the coating agent with two cationic coordination sites.

[0009] Furthermore, Patent Document 2 discloses the use of a polymer having monomers with two zwitterionic sulfobetaine structures as constituent components in image forming materials and lithographic printing plates. This makes it possible to obtain lithographic printing plates that have both developability and abrasion resistance. It is speculated that this effect is due to the fact that the constituent units having two sulfobetaine structures become more hydrophobic and water permeability decreases as they undergo thermal decomposition in the exposed area, and that polymerization is promoted because the resulting thermal decomposition products contain radical chemical species, thereby improving the curability of the image. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Japanese Patent Publication No. 2023-81338 [Patent Document 2] Japanese Patent Publication No. 2012-31400 [Non-patent literature]

[0011] [Non-Patent Document 1] ACS Energy Lett. 2018, 3, 641-646 [Non-Patent Document 2] Angew. Chem. Int. Ed. 2020, 59, 10802-10806 [Non-Patent Document 3] ACS Energy Lett. 2022, 7, 1963-1970. [Overview of the project] [Problems that the invention aims to solve]

[0012] However, conventional techniques using the aforementioned coating agents have not been able to adequately maintain the heat resistance of ionic crystals such as perovskite nanoparticles, and further improvement in heat resistance is desired.

[0013] One aspect of the present invention aims to provide an ionic crystal using a new method capable of further improving the heat resistance of the ionic crystal.

Means for Solving the Problems

[0014] In order to solve the above problems, the present invention has the following aspects. [1] A surface-coated ionic crystal, wherein the surface of the ionic crystal is coated with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in the side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in the side chain portion.

[0015] [2] The first repeating unit has a side chain portion represented by the following general formula (1), and the second repeating unit has a side chain portion represented by the following general formula (2),

Chemical formula

[0016] [3] The first repeating unit is represented by the following general formula (3),

Chemical formula

[0017] [4] The ionic crystal is a perovskite crystal, or any one of the surface-coated ionic crystals of [1] to [3].

[0018] [5] The ionic crystal is a perovskite nanoparticle, a surface-coated ionic crystal of any one of [1] to [4].

[0019] A photo-functional material containing one of the surface-coated ionic crystals from [6][1] to [5].

[0020] [7] A method for producing a surface-coated ionic crystal, comprising a contact step of bringing an ionic crystal into contact with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion.

[0021] [8] A surface coating agent for an ionic crystal, comprising a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion. [Effects of the Invention]

[0022] According to one aspect of the present invention, it is possible to provide an ionic crystal using a novel method that can further improve the heat resistance of the ionic crystal. [Modes for carrying out the invention]

[0023] As a result of diligent research, the present inventors have discovered that the heat resistance of the surface-coated ionic crystal is improved by coating the surface of the ionic crystal with both a polymer containing repeating units, which are repeating units having two or more zwitterionic structures in their side chain portions (so-called polydentate zwitterionic polymers), and a polymer containing repeating units, which are repeating units having only one zwitterionic structure in their side chain portions (so-called monodentate zwitterionic polymers). This has led to the completion of the present invention.

[0024] The inventors hypothesize the following principle for obtaining such effects: A polydentate zwitterionic polymer has multiple zwitterionic structures that function as coordination sites for ionic crystals, allowing it to strongly coordinate to the ionic crystal through chelation. However, the side chain portions of a polydentate zwitterionic polymer are rigid and have a large excluded volume. Therefore, when an ionic crystal is coated with only a polydentate zwitterionic polymer, the rigid side chain portions tend to exclude each other, resulting in low coverage. On the other hand, while monodentate zwitterionic polymers have weaker coordination ability to ionic crystals, they have more flexible side chains with smaller excluded volumes compared to polydentate zwitterionic polymers. Therefore, by coating an ionic crystal with a combination of a polydentate zwitterionic polymer and a monodentate zwitterionic polymer, the side chains of the monodentate zwitterionic polymer fill the gaps between the side chains of the polydentate zwitterionic polymer, allowing each side chain portion to coordinate to the ionic crystal. This achieves both strong coordination to the ionic crystal and high coverage, thus improving the heat resistance of the resulting surface-coated ionic crystal.

[0025] [Surface-coated ionic crystals] A surface-coated ionic crystal according to one embodiment of the present invention will be described in detail below. Hereinafter, the surface-coated ionic crystal according to one embodiment of the present invention may be abbreviated as "this coated ionic crystal". This coated ionic crystal is a surface-coated ionic crystal in which the surface of the ionic crystal is coated with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion.

[0026] [Ionic crystals] This coated ionic crystal contains an ionic crystal as its nucleus. The cations and anions contained in the ionic crystal are not particularly limited and may be any combination of inorganic cations and organic cations, as well as inorganic anions and organic anions. Examples of cations include lead and CH3NH3. + NH2CHNH2 + Examples include cadmium and zinc. Examples of anions include halogens, selenium, and sulfur.

[0027] Examples of ionic crystals include semiconducting nanocrystals. Examples of semiconducting nanocrystals include perovskite crystals, zincblende crystals, and wurtzite crystals. Among these, perovskite crystals, while conventionally highly functional, tend to develop surface defects. However, this embodiment makes it possible to reduce surface defects and obtain a surface-coated perovskite crystal with high heat resistance and high functionality. Therefore, the ionic crystal is preferably a perovskite crystal. Examples of zincblende crystals include compounds represented by CdSe, CdS, or ZnS. Examples of wurtzite crystals include compounds represented by CdSe, CdS, or ZnS. These ionic crystals can be used as quantum dots.

[0028] Perovskite crystals are ionic crystals having a perovskite-type structure. Perovskite crystals may be those known in the art, for example, compounds represented by the general formula ABX3 or A2BX4. In the formula, A is a monovalent cation occupying the A site (hereinafter referred to as the "A site cation"), B is a divalent cation occupying the B site (hereinafter referred to as the "B site cation"), and X is a monovalent anion occupying the X site (hereinafter referred to as the "X site anion"). Each of the A site cation, B site cation, and X site anion may be a single chemical species or a combination of two or more chemical species.

[0029] A site cation is at least one of an organic cation and an inorganic cation. An example of an inorganic cation is an alkali metal ion. An example of an alkali metal ion is Cs + , Rb + , K + kaNa + , and Li + Examples include nitrogen-containing organic cations at site A. Examples of nitrogen-containing organic cations include ammonium cations, alkylammonium cations, alkylammonium halogenated cations, amidinium cations, guanidium cations, imidazolium cations, pyridinium cations, pyrrolidinium cations, and protonated thiourea cations.

[0030] Examples of B-site cations include divalent cations of transition metals. Examples of divalent cations of transition metals include Pb 2+ , Ge 2+ Sn 2+ Sb 2+ , Bi 2+ Cu 2+ Ni 2+ Co 2+ Fe 2+ Mn 2+ , Cr 2+ , Pd 2+ , Cd 2+ ,EU 2+ Yb 2+ , and Ag 2+ These are some examples.

[0031] Examples of X-site anions include halogens, -CN (cyanide), -SCN (thiocyanate), -NSC (isothiocyanate), and -S (sulfide). The X-site anion is preferably a halogen, and more preferably Cl, Br, or I.

[0032] Examples of perovskite crystals include CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3SnI3, CH3NH3SnBr3, CH3NH3SnCl3, and CH3NH3PbI(3-x) Cl x CH3NH3PbI (3-x) Br x CH3NH3PbBr (3-x) Cl x CH3NH3Pb (1-y) Sn y I3, CH3NH3Pb (1-y) Sn y Br3, CH3NH3Pb (1-y) Sn y Cl3, CH3NH3Pb (1-y) Sn y I (3-x) Cl x CH3NH3Pb (1-y) Sn y I (3-x) Br x CH3NH3Pb (1-y) Sn y Br (3-x) Cl x Examples include the following. Here, x is an arbitrary value between 0 and 3, and y is an arbitrary value between 0 and 1. In addition, compounds in which CFH2NH3, CF2HNH3, CF3NH3, NH2CH=NH3, Cs, or Rb are used instead of CH3NH3 in the above compounds can also be given as examples of perovskite crystals. Preferably, CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbCl3, CH3NH3PbI (3-x) Cl x CH3NH3PbI (3-x) Br x CH3NH3PbBr (3-x) Cl x CH3NH3Pb (1-y) Sn y Br3, CH3NH3Pb (1-y) Sn y Cl3, CH3NH3Pb (1-y) Sn y I (3-x) Cl x CH3NH3Pb (1-y) Sn y I (3-x) Br x CH3NH3Pb (1-y) Sn y Br (3-x) Cl xFurthermore, compounds in which NH2CH=NH3, Cs, or Rb are used instead of CH3NH3 in the above compounds are examples of perovskite crystals. More preferably, CH3NH3PbI3, CH3NH3PbBr3, CH3NH3PbI (3-x) Cl x CH3NH3PbI (3-x) Br x CH3NH3PbBr (3-x) Cl x Furthermore, compounds in which NH2CH=NH3, Cs, or Rb are used instead of CH3NH3 in the above compounds are cited as examples of perovskite crystals.

[0033] Conventionally, the larger the specific surface area of ​​an ionic crystal, the more susceptible it is to decomposition and degradation due to aggregation caused by defects on the surface of the ionic crystal. In this embodiment, improved heat resistance can be achieved even for ionic crystals with a large specific surface area, thus providing significant benefits compared to conventional techniques even for such ionic crystals. The ionic crystal is preferably a nanoparticle. Nanoparticles generally refer to particles with an average particle diameter of 100 nm or less, and have a particle diameter that allows for quantum size effects. The average particle diameter of the nanoparticles is preferably 0.5 nm or more, more preferably 2 nm or more, more preferably 20 nm or less, and more preferably 50 nm or less. In this specification, the average particle diameter (volume average diameter) is obtained, for example, by measuring the particle diameter of each particle using a transmission electron microscope or scanning electron microscope and calculating the volume average diameter.

[0034] Among nanoparticles, perovskite nanoparticles have conventionally been highly functional but prone to surface defects. However, according to this embodiment, defects are reduced by improving their heat resistance, and highly functional surface-coated perovskite nanoparticles can be obtained. Therefore, the ionic crystal is preferably a perovskite nanoparticle. Here, the perovskite nanoparticle may have the average particle size of the preferred ionic crystal described above.

[0035] [First Polymer] This coated ionic crystal includes a first polymer that coats the surface of the ionic crystal. The first polymer is a polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in the side chain portion. The first repeating unit is composed of one main chain portion and one or more side chain portions bonded to the main chain portion. In the present specification, one zwitterionic structure refers to a structure including a pair of zwitterionic portions composed of one anionic portion and one cationic portion. Further, "having two or more zwitterionic structures in the side chain portion" means that in one repeating unit, two or more zwitterionic structures are present in one side chain bonded to the main chain portion.

[0036] Examples of the anionic portion included in the zwitterionic structure of the first repeating unit include -SO3 - , -PO2 - -, -PO3 - , and -COO - . Examples of the cationic portion included in the zwitterionic structure of the first repeating unit include a quaternary ammonium ion (-N + R3). Examples of the quaternary ammonium ion include an imidazolium ion, a pyrazolium ion, a pyridinium ion, a quinolinium ion, an isoquinolinium ion, a pyrimidinium ion, and a pyrazinium ion. Examples of the zwitterionic structure of the first repeating unit include a sulfobetaine structure, a phosphobetaine structure, and a carboxybetaine structure, and preferably, a sulfobetaine structure or a phosphobetaine structure.

[0037] The number of zwitterionic structures in the side chain portion of the first repeating unit is two or more, and from the viewpoint that the zwitterionic structure can be coordinated more strongly to the surface of the ionic crystal by the chelate effect, it is preferably two. Further, the number of zwitterionic structures in the side chain portion of the first repeating unit is preferably five or less, and more preferably three or less, from the viewpoint of suppressing the amount of water adsorbed to the zwitterionic structure.

[0038] The first repeating unit may have a side chain portion represented by the following general formula (1).

[0039]

Chem.

[0040] In formula (1), (*) represents the bonding position with the main chain portion. A 1 represents a divalent linking group. A 1 Examples of A include -CO-O-, -CO-NH-, -CO-NR- (where R is an alkyl group having 1 to 20 carbon atoms or a phenyl group), -O-, -CH2O-, or a phenylene group which may have a substituent. Here, as the substituent, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 2 to 20 carbon atoms, or an alkynyl group having 2 to 20 carbon atoms is preferable. These alkyl groups, phenylene groups, and alkynyl groups may be further substituted with any one of a halogen atom, a hydroxy group, a carboxy group, a sulfonato group, a nitro group, a cyano group, an amide group, an amino group, an alkyl group, an alkenyl group, an alkynyl group, an aryl group, a substituted oxy group, a substituted sulfonyl group, a substituted carbonyl group, a substituted sulfinyl group, a sulfo group, a phosphono group, a phosphonato group, a silyl group, and a heterocyclic group.

[0041] In formula (1), B 1 represents an (n1 + 1)-valent linking group. B 1 Examples of B include an organic group composed of at least one or more elements selected from 1 to 60 carbon atoms, 0 to 10 nitrogen atoms, 0 to 50 oxygen atoms, 1 to 100 hydrogen atoms, and 0 to 20 sulfur atoms. More specific examples include the following structures, and organic groups composed of polyvalent phenylene, polyvalent naphthalene, polyvalent anthracene, polyvalent norbornane, and polyvalent adamantane alone or in combination of a plurality thereof.

[0042]

Chem.

[0043] In formula (1), C 1C represents a functional group having a zwitterionic structure. 1 Examples include sulfobetaine structures, phosphobetaine structures, and carboxybetaine structures. n1 represents the number of coordination sites for the ionic crystal in the side chain portion represented by general formula (1), and represents an integer from 2 to 9, preferably from 2 to 5, and more preferably from 2 to 3. In formula (1), n1 C 1 Each of these may be independently represented by the following general formulas (11), (12), or (13).

[0044] [ka]

[0045] In equations (11), (12), and (13), (*) represents B 1 This indicates the bond position with R. 12 , R 13 , R 17 , R 20 , and R 23 R represents an alkylene group. 12 , R 13 , R 17 , R 20 , and R 23 Each of these may be independently linear or branched. 12 , R 13 , R 17 , R 20 , and R 23 Preferably, each of these is an alkylene group having 1 to 4 carbon atoms. Examples of alkylene groups having 1 to 4 carbon atoms include methylene, ethylene, propylene, and various butylene groups.

[0046] In equations (11), (12), and (13), R 14 , R 15 , R 16 , R 18 , R 19 , R 21 , and R 22Each of these independently represents an alkyl group having 1 to 18 carbon atoms. Examples of alkyl groups having 1 to 18 carbon atoms include methyl, ethyl, n-propyl, isopropyl, n-butyl, n-octyl, 2-ethylhexyl, dodecyl, and octadecyl groups. These alkyl groups may be further substituted or bonded to each other to form a ring.

[0047] In equations (12) and (13), Q - Q represents an anion. - An example is -SO3 - , -PO3 - , and -COO - These are some examples.

[0048] Examples of the main chain portion of the first repeating unit include: hydrocarbon groups derived from olefins such as ethylene and propylene; and hydrocarbon groups derived from compounds having (meth)acryloyl groups such as acrylic acid and methacrylic acid. The first repeating unit may also be represented by the following general formula (4).

[0049] [ka]

[0050] In formula (4), R 11 R represents a hydrogen atom or an alkyl group. 11 The alkyl group in is preferably selected from alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, and n-butyl groups. 11 From the viewpoint of ease of polymerization of the copolymer, it is preferably a hydrogen atom or a methyl group, and from the viewpoint of solubility of polymers having a zwitterionic structure, it is preferably a n-propyl group, an isopropyl group, or a n-butyl group.

[0051] In formula (4), Y represents the side chain portion. Examples of Y include alkyl groups having a zwitterionic group as a substituent, aryl groups having a zwitterionic group as a substituent, carboxylic acid ester groups having a zwitterionic group as a substituent, carboxylic acid amide groups having a zwitterionic group as a substituent, and alkoxyl groups having a zwitterionic group as a substituent. It is preferable that Y is represented by the general formula (1) described above.

[0052] From the viewpoint of further improving the heat resistance of the coated ionic crystal, the first repeating unit is preferably represented by the following general formula (3).

[0053] [ka]

[0054] In formula (3), R 5 represents a hydrogen atom or a methyl group. 5 represents a trivalent linking group. 5 An example of this is the following structure.

[0055] [ka]

[0056] D 5 and D 6 Each of these independently represents a divalent linking group. 5 and D 6 Examples include alkylene groups having 1 to 10 carbon atoms, and divalent organic groups having 1 to 20 carbon atoms, which may also contain a ring structure such as xylylene.

[0057] In formula (3), R 6 ~R 9 Each of these independently represents a methyl group, an ethyl group, or an isopropyl group. 5 and E 6 Each of these independently represents an alkylene group with 2 to 5 carbon atoms. 5 and E 6 Examples include methylene groups, ethylene groups, propylene groups, and various butylene groups.

[0058] The first polymer may be a copolymer containing the first repeating unit described above and repeating units other than the first repeating unit. The first polymer may be a block copolymer or a random copolymer. The repeating units other than the first repeating unit are not particularly limited as long as they are repeating units derived from monomers copolymerizable with the monomer that provides the first repeating unit described above. For example, the repeating units other than the first repeating unit may be repeating units that do not have a zwitterionic structure in their side chain portion and may be represented by the following general formula (5).

[0059] [ka]

[0060] In formula (5), R 21 R represents a hydrogen atom or an alkyl group. 21 The alkyl group in is preferably selected from alkyl groups having 1 to 4 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, and n-butyl groups. 21 From the viewpoint of ease of polymerization of the copolymer, it is preferably a hydrogen atom or a methyl group, and from the viewpoint of solubility of polymers having a zwitterionic structure, it is preferably a n-propyl group, an isopropyl group, or a n-butyl group.

[0061] In formula (5), Z represents an alkyl group, an aryl group, a carboxylic acid ester group, or a carboxylic acid amide group.

[0062] From the viewpoint of ensuring sufficient coordination with ionic crystals, the proportion of the first repeating units among all 100 mol% of the total repeating units constituting the first polymer is preferably 0.05 mol% or more, and more preferably 0.1 mol% or more. Furthermore, from the viewpoint of improving solubility in aprotic solvents, the proportion of the first repeating units among all 100 mol% of the total repeating units constituting the first polymer is preferably 50 mol% or less, and more preferably 10 mol% or less.

[0063] From the viewpoint of increasing the coordination site of the first polymer to the ionic crystal surface and further improving heat resistance, the number-average molecular weight of the first polymer is preferably 1000 or more, and more preferably 10000 or more. Furthermore, from the viewpoint of improving the dispersibility of the coated ionic crystal in the solvent, the number-average molecular weight of the first polymer is preferably 1,000,000 or less, and more preferably 500,000 or less. In this specification, the number-average molecular weight of the polymer is the number-average value of the molecular weight in terms of polystyrene, measured by gel permeation chromatography (GPC).

[0064] From the viewpoint of further improving the heat resistance of the ionic crystal, the content of the first polymer in this coated ionic crystal is preferably 5% by mass or more, and more preferably 10% by mass or more. Furthermore, from the viewpoint of reducing the introduction of moisture due to the uncoordinated zwitterionic structure, the content of the first polymer in this coated ionic crystal is preferably 90% by mass or less, and more preferably 80% by mass or less.

[0065] [Second Polymer] The coated ionic crystal contains a second polymer coating the surface of the ionic crystal. The second polymer is a polymer containing a second repeating unit, which is a repeating unit having only one zwitterionic structure in its side chain portion. The second repeating unit consists of one main chain portion and one or more side chain portions attached to the main chain portion. In this specification, "having only one zwitterionic structure in its side chain portion" means that in one repeating unit, there is only one zwitterionic structure in one side chain attached to the main chain portion.

[0066] The anionic and cationic parts of the zwitterionic structure of the second repeating unit are the same as those described above for the first repeating unit, so their explanation is omitted.

[0067] The second repeating unit may have a side chain portion represented by the following general formula (2). [ka]

[0068] In equation (2), (*) indicates the bond position with the main chain. A 2 represents a divalent linking group. 2 Examples of these groups include -CO-O-, -CO-NH-, -CO-NR- (where R is an alkyl group having 1 to 20 carbon atoms, or a phenyl group), -O-, -CH2O-, or a phenylene group which may have substituents. Preferred substituents are alkyl groups having 1 to 20 carbon atoms, alkenyl groups having 2 to 20 carbon atoms, or alkynyl groups having 2 to 20 carbon atoms. These alkyl groups, phenylene groups, and alkynyl groups may be further substituted with any of the following: halogen atoms, hydroxyl groups, carboxyl groups, sulfonate groups, nitro groups, cyano groups, amide groups, amino groups, alkyl groups, alkenyl groups, alkynyl groups, aryl groups, substituted oxy groups, substituted sulfonyl groups, substituted carbonyl groups, substituted sulfinyl groups, sulfo groups, phosphono groups, phosphonato groups, silyl groups, and heterocyclic groups.

[0069] In formula (2), B 2 represents a divalent linking group. 2 Examples include organic groups composed of at least one element selected from 1 to 60 carbon atoms, 0 to 10 nitrogen atoms, 0 to 50 oxygen atoms, 1 to 100 hydrogen atoms, and 0 to 20 sulfur atoms. More specific examples include the following structures, as well as organic groups composed of polyvalent phenylene, polyvalent naphthalene, polyvalent anthracene, polyvalent norbornane, and polyvalent adamantane, either individually or in combination.

[0070] [ka]

[0071] In formula (2), C 2 C represents a functional group having a zwitterionic structure. 1Examples include sulfobetaine structures, phosphobetaine structures, and carboxybetaine structures. In formula (2), C 2 This may be expressed by general formulas (11), (12), or (13). The explanation of general formulas (11), (12), or (13) is the same as that given above for the first repeating unit, so the explanation is omitted.

[0072] Examples of the main chain portion of the second repeating unit include: hydrocarbon groups derived from olefins such as ethylene and propylene; and hydrocarbon groups derived from compounds having (meth)acryloyl groups such as acrylic acid and methacrylic acid. The second repeating unit may also be represented by general formula (4). The explanation of general formula (4) is the same as that of general formula (4) described above for the first repeating unit, so the explanation is omitted.

[0073] The second polymer may be a copolymer containing the second repeating unit described above and repeating units other than the second repeating unit. The second polymer may be a block copolymer or a random copolymer. The repeating units other than the second repeating unit are not particularly limited as long as they are repeating units derived from monomers copolymerizable with the monomer that provides the second repeating unit described above. For example, the repeating units other than the second repeating unit may be repeating units that do not have a zwitterionic structure in their side chain portion and may be represented by general formula (5). The explanation of general formula (5) is the same as that of general formula (5) described above for the first repeating unit, so the explanation is omitted.

[0074] From the viewpoint of sufficiently strong coordination to ionic crystals, the proportion of the second repeating units among all 100 mol% of the total repeating units constituting the second polymer is preferably 0.5 mol% or more, and more preferably 1.0 mol% or more. Furthermore, from the viewpoint of improving solubility in aprotic solvents, the proportion of the second repeating units among all 100 mol% of the total repeating units constituting the second polymer is preferably 50.0 mol% or less, and more preferably 10.0 mol% or less.

[0075] From the viewpoint of increasing the coordination points of the second polymer to the ionic crystal surface and further improving heat resistance, the number-average molecular weight of the second polymer is preferably 1000 or more, and more preferably 10000 or more. Furthermore, from the viewpoint of improving the dispersibility of the coated ionic crystal in the solvent, the number-average molecular weight of the second polymer is preferably 1,000,000 or less, and more preferably 500,000 or less.

[0076] In this coated ionic crystal, the second polymer may be a single type of polymer or a combination of two or more types of polymers.

[0077] [Combination of the first polymer and the second polymer] The zwitterionic structure of the first polymer and the zwitterionic structure of the second polymer may be the same or different.

[0078] From the viewpoint of further improving the heat resistance of the ionic crystal, the total content of the first polymer and the second polymer in this coated ionic crystal is preferably 80% by mass or more, and more preferably 90% by mass or more. Furthermore, from the viewpoint of reducing the introduction of moisture due to the uncoordinated zwitterionic structure, the total content of the first polymer and the second polymer in this coated ionic crystal is preferably 99% by mass or less, and more preferably 95% by mass or less.

[0079] In this coated ionic crystal, there are no limitations on the ratio of the content of the first polymer to the content of the second polymer, but it is preferable that the ratio of the first polymer to the second polymer is 1:9 to 5:5 by mass.

[0080] [Materials containing surface-coated ionic crystals] This coated ionic crystal has improved heat resistance. Taking advantage of this improved heat resistance, this coated ionic crystal can be used as a component in various materials. That is, a material according to one embodiment of the present invention includes the above-described coated ionic crystal.

[0081] The application of the material is determined according to the properties of the ionic crystals constituting this coated ionic crystal. Alternatively, the ionic crystals constituting this coated ionic crystal may be appropriately selected according to the desired application of the material. An example of the application of the material is a photo-functional material. In this specification, photo-functionality refers to photoresponsiveness, luminescence, or a combination thereof. Here, photoresponsiveness refers to the property that the material shows some kind of response (e.g., photoelectric conversion, wavelength conversion, or improvement of the catalytic activity of the ionic crystal) to light irradiated onto the material from the outside. Luminescence refers to the property that the material shows a response accompanied by luminescence to some kind of action applied to the material from the outside (e.g., electric field, magnetic field, heat, or stress).

[0082] Examples of photo-functional materials include photoelectric conversion elements, electroluminescent devices, and wavelength conversion materials. Furthermore, examples of coated ionic crystals included in photo-functional materials include perovskite crystals, with perovskite nanoparticles being a particularly preferred example.

[0083] In photo-functional materials, components other than the coated ionic crystal (hereinafter referred to as "other components") may be included. Other components can be appropriately selected depending on the application of the photo-functional material. Examples of other components include surfactants, stabilizers, and scattering agents.

[0084] [Method for producing surface-coated ionic crystals] A method for manufacturing a surface-coated ionic crystal according to one embodiment of the present invention will be described in detail below. Hereinafter, the surface-coated ionic crystal according to one embodiment of the present invention may be abbreviated as "this manufacturing method." This manufacturing method includes a contact step of bringing an ionic crystal into contact with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion. This manufacturing method can be used as a method for manufacturing the coated ionic crystal described above. For the sake of convenience in explanation, components having the same function as the components described above will be referred to by the same name and their descriptions will not be repeated.

[0085] [Contact process] This manufacturing method includes a contact step, which involves contacting an ionic crystal with a first polymer and a second polymer. Contact between the ionic crystal and the first and second polymers can be carried out using methods known in the art. For example, the ionic crystal may be mixed into a dispersion in which the first and second polymers are dispersed in a solvent. As another example, the dispersion may be sprayed onto the ionic crystal. In methods using such mixing or spraying for contact, the coated ionic crystal can be obtained by removing the solvent from the surface of the ionic crystal by drying after contact.

[0086] The solvent used in the dispersion can be appropriately selected from known solvents in which the first and second polymers can disperse. Examples of solvents include nonpolar solvents such as toluene and chloroform, and polar solvents such as 2,2,2-trifluoroethanol.

[0087] From the viewpoint of coordination ability to the ionic crystal surface, the total concentration of the first and second polymers in the dispersion is preferably 5 mg / mL or more. Furthermore, from the viewpoint of reducing the amount of water adsorbed on the polymers, the total concentration of the first and second polymers in the dispersion is preferably 50 mg / mL or less.

[0088] The contact between the ionic crystal and the first polymer, and the contact between the ionic crystal and the second polymer, may be performed simultaneously or sequentially. When contact is performed sequentially, a first dispersion in which the first polymer is dispersed in the solvent and a second dispersion in which the second polymer is dispersed in the solvent may be prepared separately. When contact is performed sequentially, from the viewpoint of efficiently coating the ionic crystal, it is preferable to contact the ionic crystal first with the first polymer and then with the second polymer. Furthermore, contact with at least one of the first and second polymers may be performed two or more times.

[0089] [Surface coating agent] A surface coating agent according to one embodiment of the present invention will be described in detail below. Hereinafter, the surface coating agent according to one embodiment of the present invention may be abbreviated as "this coating agent". This coating agent is a surface coating agent for ionic crystals and comprises a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion. This coating agent is a chemical agent for coating the surface of an ionic crystal. This coating agent can be used in the manufacturing method described above. For the sake of convenience of explanation, components having the same function as the components described above will be referred to by the same name and their descriptions will not be repeated.

[0090] This coating agent comprises a first polymer and a second polymer. Furthermore, from the viewpoint of improving the fluidity of this coating agent, it is preferable that the coating agent further contains a solvent in which the first polymer and the second polymer can be dispersed. That is, in the manufacturing method described above, this coating agent can be used as a dispersion in which the first polymer and the second polymer are dispersed in a solvent. The example of the solvent is the same as the solvent described above for this manufacturing method, so its description is omitted. Also, the concentrations of the first polymer and the second polymer in the dispersion are the same as the concentrations in the dispersion described above for this manufacturing method, so its description is omitted.

[0091] [Additional Notes] The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention. [Examples]

[0092] An embodiment of the present invention is described below. In this embodiment, a polydentate zwitterionic polymer and a monodentate zwitterionic polymer were synthesized, and a surface-coated ionic crystal was produced using the obtained polydentate zwitterionic polymer, monodentate zwitterionic polymer, or a combination thereof. The heat resistance of the obtained surface-coated ionic crystal was evaluated based on the fluorescence quantum yield (PLQY).

[0093] [Synthesis of monomers] (Synthesis of monomer 1a) Using 2-isocyanatoethyl methacrylate, the synthesis was carried out according to US2023 / 0108053, and the methacrylate (monomer 1a) shown in the following formula (1a) was obtained in a yield of 25 mol%.

[0094] (Synthesis of monomer 2a) Using monomer 1a, synthesis was carried out with reference to CN104628938, and the methacrylate (monomer 2a) shown in the following formula (2a) was obtained in a yield of 20 mol%.

[0095] (Synthesis of monomer 1b) Using 2-isocyanatoethyl methacrylate, the synthesis was carried out according to US2023 / 0108053, and the methacrylate (monomer 1b) shown in the following formula (1b) was obtained in a yield of 32 mol%.

[0096] (Synthesis of monomer 2b) Using monomer 1b, synthesis was carried out according to CN104628938, and the methacrylate (monomer 2b) shown in the following formula (2b) was obtained in a yield of 19 mol%.

[0097] [Polymer synthesis] (Polymer 1) Butyl methacrylate (BMA) (95% by mass) and monomer 2a (5% by mass) were copolymerized according to Angew. Chem. Int. Ed. 2020, 59, 10802-10806 to obtain polymer 1. 1 Chemical structure identification using 1H-NMR revealed that the content of repeating units derived from monomer 2a in polymer 1 was 0.18 mol%. Chemical structure identification using GPC revealed that the number-average molecular weight of polymer 1 was 45700.

[0098] A dispersion of polymer 1 at a concentration of 0.1% by mass in N,N-dimethylformamide (DMF) was used as the sample for measuring the number-average molecular weight Mn and polydispersity index PDI. The measurements were performed by gel permeation chromatography (GPC) using N,N-dimethylformamide (DMF) with lithium bromide dissolved to a concentration of 10 nM as the mobile phase and a differential refractometer as the detector. Monodisperse polystyrene was used as the molecular weight standard. The details of the measurement conditions are as follows. The measurement results are shown in Table 1. • Column: Two TSKgelGMHHR-M (7.8mm x 30cm, Tosoh) columns were connected in series. • Mobile phase: DMF with 10 mM lithium bromide dissolved in it. ·Flow rate: 1.0ml / sec ·Temperature: 40℃ • Standard material: Standard polystyrene kit (PStQuick Kit-H, Tosoh)

[0099] (Polymer 2) Polymer 2 was obtained by performing the same procedure as for polymer 1, except that the monomer used in copolymerization was changed from monomer 2a to monomer 2b, and the charge ratio of monomer 2b was set to 11% by mass. The measurement results for polymer 2 are shown in Table 1.

[0100] (Polymer 3) Polymer 3 was obtained by performing the same procedure as for polymer 1, except that the monomer used in copolymerization was changed from monomer 2a to monomer 2b, and the charge ratio of monomer 2b was set to 2.0% by mass. The measurement results for polymer 3 are shown in Table 1.

[0101] (Polymer 4) Polymer 4 was obtained by performing the same procedure as for polymer 1, except that the monomer used for copolymerization was changed from monomer 2a to 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid N,N-dimethyl-N-(2-methacryloxyethyl)-N-(3-sulfopropyl)ammonium betaine (SBMA), and the charging ratio of SBMA was set to 5.7% by mass. The measurement results for polymer 4 are shown in Table 1.

[0102] [ka]

[0103] [Table 1]

[0104] [Manufacturing of surface-coated ionic crystals] [Example 1] (Ligand washing) A perovskite quantum dot dispersion (Quantum Solutions, ABX3-510) and methyl acetate (Fujifilm Wako Pure Chemical Industries, first grade) were mixed in a 1:1 volume ratio and centrifuged at 6000 rpm for 0.5 hours. The supernatant was removed by decantation, the walls and surface were lightly washed with methyl acetate, and then toluene was added to the residue to redisperse it, followed by ligand washing and obtaining a dispersion.

[0105] (Surface coating) Polymer 1 and Polymer 4 were dissolved in toluene in a mass ratio of 1:9. Using a Dean-Stark apparatus, the mixture was heated under reflux for 2 hours, followed by dehydration to obtain a zwitterionic polymer solution with a total concentration of 15 mg / mL. 45 μL of the ligand-washed dispersion, 200 μL of the zwitterionic polymer solution, and 55 μL of toluene were mixed and stirred at room temperature for 1 hour to obtain the surface-coated solution.

[0106] (Preparation of coated film) 20 μL of the post-coating solution was dropped onto a glass substrate and heated on a hot plate at 80°C for 1 hour to obtain the surface-coated ionic crystal coating film of Example 1.

[0107] [Examples 2-5, Comparative Examples 1-4] Except for changing the type of polymer used and its mass ratio as shown in Table 2, the same procedure as in Example 1 was performed to obtain surface-coated ionic crystal films for Examples 2-5 and Comparative Examples 1-4.

[0108] [Evaluation of heat resistance] PLQY after the heat resistance test was measured using Quantaurus-QY (Hamamatsu Photonics). The excitation wavelength was 450 nm. The heat resistance test was performed by heating the coated film at 180°C for 0.5 hours under yellow light. The evaluation results are shown in Table 2.

[0109] [Table 2]

[0110] 〔result〕 As can be seen from the comparison between Comparative Example 2 and Examples 1-2, the PLQY after heating was higher in Examples 1-2, where the perovskite nanoparticle surface was coated with polymer 4 (monodentate zwitterionic polymer) having only one zwitterionic structure in its side chain, in combination with polymer 1, than in Comparative Example 2, where the perovskite nanoparticle surface was coated with polymer 1 (bidentate zwitterionic polymer) alone, which has two zwitterionic structures in its side chain. A similar trend was observed in the comparison between Comparative Example 3 and Example 3, and between Comparative Example 4 and Examples 4-5. These results demonstrate that coating an ionic crystal with a combination of a multidentate zwitterionic polymer and a monodentate zwitterionic polymer can improve heat resistance compared to coating the ionic crystal with a multidentate zwitterionic polymer alone.

[0111] In Comparative Example 1, perovskite nanoparticles were coated with polymer 4 alone, a monodentate zwitterionic polymer, and a heat resistance test was performed. The PLQY of Examples 1-5 was higher than that of Comparative Example 1. From these results, it can be seen that a mixture of monodentate zwitterionic polymers and bidentate zwitterionic polymers is more effective in improving the heat resistance of ionic crystals than the monodentate zwitterionic polymer in Comparative Example 1. [Industrial applicability]

[0112] This invention can be used, for example, in applications of materials such as photo-functional materials.

Claims

1. The surface of the ionic crystal is coated with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion. Surface-coated ionic crystal.

2. The first repeating unit has a side chain portion represented by the following general formula (1): The second repeating unit has a side chain portion represented by the following general formula (2): 【Chemistry 1】 In general formula (1), (*) indicates the bond position with the main chain, A １ represents a divalent linking group, B １ is (n １ +1) Represents a linking group with a valence of C １ represents a functional group having a zwitterionic structure, n １ The integers 2 through 9 represent integers from 2 to 9. In general formula (2), (*) indicates the bond position with the main chain, A ２ represents a divalent linking group, B ２ represents a divalent linking group, C ２ This represents a functional group having a zwitterionic structure. The surface-coated ionic crystal according to claim 1.

3. The first repeating unit is represented by the following general formula (3): 【Chemistry 2】 In the general formula (3), R ５ represents a hydrogen atom or a methyl group, B ５ represents a trivalent linking group, D ５ and D ６ each independently represent a divalent linking group, R ６ to R ９ each independently represent a methyl group, an ethyl group, or an isopropyl group, E ５ and E ６ each independently represent an alkylene group having 2 to 5 carbon atoms. The surface-coated ionic crystal according to claim 1.

4. The aforementioned ionic crystal is a perovskite crystal. A surface-coated ionic crystal according to any one of claims 1 to 3.

5. The aforementioned ionic crystal is a perovskite nanoparticle. A surface-coated ionic crystal according to any one of claims 1 to 3.

6. A photo-functional material comprising a surface-coated ionic crystal according to any one of claims 1 to 3.

7. The method includes a contact step of bringing an ionic crystal into contact with a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion. A method for producing surface-coated ionic crystals.

8. A surface coating agent for ionic crystals, A surface coating agent comprising a first polymer containing a first repeating unit which is a repeating unit having two or more zwitterionic structures in its side chain portion, and a second polymer containing a second repeating unit which is a repeating unit having only one zwitterionic structure in its side chain portion.

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