Luminescent ionic crystal

Abstract

To provide a photon conversion luminescent material that exhibits high emission efficiency.SOLUTION: A luminescent ionic crystal comprising: a luminescent molecular ion having an ionic site and a luminescent site; and a counter ion of the luminescent molecular ion, wherein the intermolecular distance between the luminescent molecular ions is 3 angstroms or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to photon conversion materials, and more particularly to photon conversion luminescent ionic crystals and light emitters containing the same. [Background technology]

[0002] Technologies for efficiently converting and controlling light sources in the ultraviolet to near-infrared range to a desired wavelength are of industrial importance, and are expected to dramatically improve the efficiency of, for example, artificial photosynthesis, solar cells such as perovskite solar cells, photocatalysts, display elements such as displays, as well as bioimaging technology and optical diagnosis and treatment. Wavelength conversion in organic materials occurs when a material in its ground state absorbs light, becomes excited, and then emits light as it relaxes back to its ground state, but the emitted light has a longer wavelength than the absorbed light. This phenomenon is called fluorescence or down-conversion, and has been known for a long time. In contrast to down-conversion, up-conversion emission is also technically possible. When organic materials are used, up-conversion occurs via the triplet-triplet annihilation (TTA) mechanism. Photon up-conversion (TTA-UC) based on triplet-triplet annihilation consists of a system containing a sensitizer that functions as a donor and an emitter that functions as an acceptor. First, a donor molecule (S) absorbs excitation light on the longer wavelength side and becomes excited into a singlet state. D ) undergoes intersystem crossing (ISC) and transitions to an excited triplet state (T D The triplet energy is transferred from the donor molecule in this excited triplet state to the acceptor molecule (triplet-triplet energy transfer (TTET)), generating a triplet excited state in the acceptor molecule (T A When TTA occurs due to the diffusion and collision of acceptor molecules in this triplet excited state, one of the two colliding molecules will reach a higher excited singlet state (S A) and upconversion light emission occurs. In any luminescence phenomenon, the superiority of a material is determined by how efficiently the luminescent material emits light. Polyaromatic ring compounds, such as naphthalene and anthracene, are commonly used organic luminescent materials. The optical properties of luminescent materials are evaluated by measuring the maximum emission wavelength and half-width of the emission wavelength using fluorescence or phosphorescence spectroscopy, and by measuring the quantum yield using absolute quantum yield measurements. For these measurements, evaluation samples are prepared by dispersing the luminescent material in a sufficiently diluted organic solvent. This is because the maximum luminescence efficiency is observed when the polyaromatic ring molecules are completely dispersed and do not interact with each other. On the other hand, in highly concentrated solutions, solid states including crystalline and amorphous phases, and films doped with polymers, non-covalent bonds such as π-π stacking occur between the polyaromatic ring molecules, resulting in close intermolecular distances and resulting in aggregation and excimer formation. These act as quenching sites for luminescence, resulting in a significant decrease in luminescence efficiency compared to when the material is dispersed in a dilute solvent. For this reason, for practical applications such as solar cells, it is most desirable to provide the luminescent material in a form in which the luminescent molecules are sufficiently dispersed, but this is practically difficult due to the presence of an organic solvent. As a means of suppressing interactions between luminescent molecules, such as aggregation, in solid or film form, a method has been researched in which functional groups with large steric hindrance are added to the luminescent molecules, increasing their molecular volume and suppressing non-covalent bonds. While this method is known to be effective in suppressing aggregation of luminescent molecules, the large molecular volume also gives the molecules fluidity (liquidity), which may result in, for example, phase separation in the film material or softening of the film itself, negatively affecting its properties as a matrix. Furthermore, in upconversion emission, triplet energy transfer often does not occur efficiently because the intermolecular distance is often too great, which is a factor hindering luminescence efficiency. Against this background, energy transfer without forming aggregation or excimers has been studied. There has been a demand for the development of a solid-state material with excellent luminous efficiency, which maintains an appropriate intermolecular distance so as not to impede efficiency, and is sufficiently stable as a luminescent material.

[0003] A composition for forming an upconversion luminescent body has been proposed that uses a matrix resin in addition to a donor compound and an acceptor compound which is an ionic liquid, and that allows the production of molded bodies such as films by thermal or photo-curing, and that has high luminous efficiency and excellent storage stability (Patent Document 1).

[0004] To avoid the use of volatile solvents, taking into consideration the influence of residual oxygen, which can cause the deactivation of TTA-UC, and the potential for practical applications, solid materials have been proposed in which donor and acceptor molecules are dispersed in a soft polymer matrix, such as ethylene oxide-epichlorohydrin copolymer or polyurethane (Non-Patent Documents 1 to 3, etc.). In addition, a method has been proposed in which a structure having reducing ability is incorporated to lower the oxygen concentration in the system (Non-Patent Documents 4, 5, etc.). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-80335 [Non-patent literature]

[0006] [Non-Patent Document 1] Castellano et al., J. Am. Chem. Soc., 129, 12652 (2007) [Non-patent document 2] Castellano et al., Chem. Mater., 24, 2250 (2012) [Non-patent document 3] A. Monguzzi et al., Advanced Energy Materials, 3, 680 (2013) [Non-patent document 4] F. Li et. al., J. Am. Chem. Soc., 135, 5029 (2013) [Non-patent document 5] F. Marsico et al., J. Am. Chem. Soc., 136, 12652 (2007) Summary of the Invention [Problem to be solved by the invention]

[0007] However, although the use of the above-mentioned polymer matrix prevents a decrease in oxygen diffusion, it also reduces the diffusion coefficient of the donor and acceptor molecules, resulting in a decrease in quantum yield and the risk of aggregation and phase separation of the donor and acceptor molecules over time. Furthermore, even in the method utilizing reducing ability, there is a concern that the method lacks long-term stability. [Means for solving the problem]

[0008] The present inventors have found that a novel photon conversion luminescent material with high luminous efficiency can be obtained by using a luminescent ionic crystal having the following configuration.

[0009] That is, as a first aspect, the present invention relates to a luminescent ionic crystal comprising a luminescent molecular ion having an ionic moiety and a luminescent moiety, and a counter ion of the luminescent molecular ion, wherein the intermolecular distance between the luminescent molecular ions is 3 angstroms or more. As a second aspect, the present invention relates to the luminescent ionic crystal according to the first aspect, wherein the ionic moiety is at least one anion species selected from the group consisting of carboxylate, sulfate, sulfonate, thiocyanate, nitrate, aluminate, borate, phosphate, amide, antimonate, imide, and methide, or at least one cation species selected from the group consisting of imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium. As a third aspect, the ionic moiety is the anion species, and the counter ion is at least one selected from the group consisting of imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium. The present invention relates to a luminescent ionic crystal according to the second aspect, wherein the cation species is also a type of cation species. As a fourth aspect, the present invention relates to the luminescent ionic crystal according to the first aspect, wherein the luminescent moiety is a naphthalene structure, an anthracene structure, a tetracene structure, a pyrene structure, a perylene structure, a biphenyl structure, a terphenyl structure, a perylene diimide structure, a naphthalene diimide structure, or a BODIPY (boron dipyrromethane) structure. A fifth aspect relates to the luminescent ionic crystal according to the first aspect, which absorbs light to enter an excited singlet state and emits light having a longer wavelength than the irradiated light. As a sixth aspect, the present invention relates to a light-emitting body comprising the luminescent ionic crystal according to the first aspect and a sensitizer, which further comprises a sensitizer that functions as a donor molecule that absorbs light and becomes an excited triplet state, and wherein the luminescent molecular ions undergo triplet energy transfer from the sensitizer to become an excited singlet state and emit light. As a seventh aspect, the present invention relates to a luminescent material comprising the luminescent ionic crystal according to the sixth aspect and a sensitizer, wherein the sensitizer is a compound having a porphyrin structure, a phthalocyanine structure, a fullerene structure, or a 2-phenylpyridinato structure. As an eighth aspect, the present invention relates to the luminescent ionic crystal according to the first aspect, wherein the luminescent molecular ions have an intermolecular distance of 3 to 20 angstroms. As a ninth aspect, the present invention relates to a light-emitting body including the luminescent ionic crystal according to the sixth aspect and a sensitizer, wherein the molar ratio of the sensitizer to the luminescent molecular ions is 1:100 to 1:100,000. As a tenth aspect, the present invention relates to a photon conversion luminescent material comprising the luminescent ionic crystal according to any one of the first to fifth and eighth aspects or the luminescent material according to any one of the sixth, seventh and ninth aspects, and emitting light of a wavelength different from that of irradiated light. As an eleventh aspect, the present invention relates to a photon down-conversion method, which comprises irradiating the luminescent ionic crystal according to the fifth aspect with light to generate light having an energy lower than that of the irradiated light. As a twelfth aspect, the present invention relates to a photon up-conversion method for irradiating the light emitter according to the sixth aspect with light to generate light with higher energy than the energy of the irradiated light. As a thirteenth aspect, the present invention relates to a method for producing the luminescent ionic crystal according to any one of the first to fifth and eighth aspects or the luminescent body according to any one of the sixth, seventh and ninth aspects, comprising a step of dissolving the luminescent molecular ion and a counter ion of the luminescent molecular ion in a solvent, followed by crystallization. As a fourteenth aspect, the present invention relates to a method for improving luminous efficiency by dissolving an amorphous aggregate containing luminescent molecular ions and counter ions of the luminescent molecular ions in a solvent, and then crystallizing the aggregate. As a fifteenth aspect, the present invention relates to a method for controlling the intermolecular distance between luminescent molecular ions by using a counter ion of the luminescent molecular ions. [Effects of the Invention]

[0010] The present invention employs an "ionic crystal" form as a photon conversion material, enabling precise control of the arrangement of chromophores. This makes it possible to suppress quenching due to aggregation of luminescent molecules, which has been a problem in the past, and provides a light-emitting material with high luminous efficiency and controllable luminous properties. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 shows the fluorescence spectrum of upconversion emission in response to laser excitation of the solid composed of the ionic crystal and donor molecules of Example 2. In FIG. [Figure 2] FIG. 2 shows the fluorescence spectrum of upconversion emission in response to laser excitation of the solid composed of the ionic crystal and donor molecules of Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0012] The challenges of achieving the aforementioned appropriate intermolecular distance and stabilizing the light emitter in photon conversion materials are largely due to the tendency of light-emitting molecules to aggregate, and the fact that designing a molecular structure that resolves this tendency and leads to a crystalline solid has yet to be explored. To address this issue, the present inventors have found that by providing an ionic moiety to a polyaromatic ring luminescent molecule using an ionic functional group and selecting a counter ion that is bulky but has excellent crystallinity as a counter ion for the ionic moiety, it is possible to solve the above-mentioned issue and produce a solid ionic crystal that has excellent luminescence properties in both down-conversion and up-conversion. The present invention will be described in detail below.

[0013] [Luminescent ionic crystals] The luminescent ionic crystal of the present invention is characterized by comprising a luminescent molecular ion having an ionic site and a luminescent site, and a counter ion of the luminescent molecular ion. The luminescent ionic crystal of the present invention is expected to realize both down-conversion luminescence, in which the luminescent ionic crystal absorbs light to become an excited singlet state and emits light of a longer wavelength than the irradiated light, and up-conversion luminescence, in which the luminescent molecular ion undergoes triplet energy transfer from the sensitizer to become an excited singlet state and emits light, when combined with a sensitizer described later that absorbs light to become an excited triplet state. In the photon down-conversion method of the present invention, the luminescent ionic crystal of the present invention is a method of irradiating the luminescent ionic crystal with light to generate light of an energy lower than the energy of the irradiated light, and the photon up-conversion method is a method of generating light of an energy higher than the energy of the irradiated light. The present invention will be described in detail below, focusing on (photon) upconversion.

[0014] [Luminescent ionic crystals for upconversion luminescence] In upconversion luminescence, the luminescent ionic crystal of the present invention corresponds to an acceptor compound. As shown in the mechanism of photon upconversion (TTA-UC) consisting of triplet-triplet annihilation described above, the acceptor compound in this mechanism refers to a compound having an acceptor moiety (luminescent moiety) that can accept energy from the donor moiety of a donor compound (sensitizer) described below to form a triplet excited state. In the present invention, the acceptor compound is defined as a compound that receives triplet energy transfer from the donor compound, becomes excited into a singlet state, and functions as a light emitter. The luminescent ionic crystal (acceptor compound) of the present invention is capable of forming an excited singlet state by triplet-triplet annihilation (TTA) between luminescent moieties (acceptor moieties) that are in a triplet excited state, and its structure is not particularly limited as long as it is in the form of an ionic crystal as described below. In addition, a sensitizer, which will be described later, may be present in the vicinity of the luminescent ionic crystal, or the luminescent ionic crystal may have a sensitizer included in its crystal structure.

[0015] Specific examples of the luminescent moiety of the luminescent ionic crystal include luminescent moieties (hereinafter also referred to as acceptor moieties) containing aromatic rings, such as luminescent moieties (acceptor moieties) containing fused aromatic rings or ring-assembly aromatic rings in which two or more aromatic rings are assembled. More specifically, luminescent moieties (acceptor moieties) containing a naphthalene structure, anthracene structure, tetracene structure, pyrene structure, perylene structure, biphenyl structure, terphenyl structure, perylene diimide structure, naphthalene diimide structure, or BODIPY (boron dipyrromethene; 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene) structure are preferably used. Note that the "moiety" in the luminescent moiety (acceptor moiety) refers to an atomic group. Specific examples of structures that can be preferably employed as the light-emitting moiety (acceptor moiety) are given below, but the present invention should not be construed as being limited to these specific examples.

[0016] [ka]

[0017] The phrase "the luminescent ionic crystal of the present invention corresponds to an acceptor compound" means that the acceptor compound comprises a luminescent molecular ion having either a cation species or an anion species as an ionic site, and an ion having a counter anion species or a cation species. In the present invention, the acceptor compound is ionic crystalline, so that the acceptor compound is in a solid state and can be dispersed in a matrix resin or a donor compound while maintaining an appropriate intermolecular distance, thereby enabling the acceptor compound to maintain an appropriate intermolecular distance between luminescent molecular ions.

[0018] In the luminescent ionic crystal of the present invention, the intermolecular distance between luminescent molecular ions is 3 angstroms or more, and can be, for example, 3 to 20 angstroms, 3 to 15 angstroms, 3 to 10 angstroms, or 3 to 5 angstroms. Note that the intermolecular distance here refers to the shortest distance between the luminescent molecular ions. The intermolecular distance at which quenching of luminescence due to aggregation is confirmed is generally about 3 angstroms, and in the luminescent ionic crystal of the present invention, the luminescent molecular ions have a larger distance than the above. You can maintain an appropriate distance.

[0019] The "ionic crystal" can be one generally known as an "ionic crystal," and examples thereof include a combination of a cationic species selected from the group consisting of imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium, and an anionic species selected from the group consisting of carboxylate, sulfate, sulfonate, thiocyanate, nitrate, aluminate, borate, phosphate, amide, antimonate, imide, and methide. That is, the luminescent ionic crystal of the present invention (an embodiment in which the acceptor compound is an ionic crystal) can be an embodiment in which either one of these cationic species or anionic species is linked to the luminescent moiety (acceptor moiety) or a molecule having a luminescent moiety (acceptor moiety) to form a luminescent molecular ion, and an ion having a counter anionic species or cationic species is bound via ionic interaction.

[0020] An example of such an embodiment is a luminescent ionic crystal (acceptor compound) in which an ionic crystal is formed from a luminescent molecular ion having the luminescent moiety and any one of the anion species as an ionic moiety, and an ion having, as a counter ion, at least one cationic species selected from the group consisting of imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium, and having a cationic species with a bulky structure such as a triphenyl structure or a tetraphenyl structure. More specific examples of the counter ion include triphenylmethylammonium and tetraphenylphosphonium.

[0021] As an example of the luminescent ionic crystal (acceptor compound), a sulfonate anion (-SO3 - ) and a tetraaromatic ring phosphonium cation (PAr4 + ) tetraaromatic ring methylammonium cation (Ar3C-NH3 + ) and ionic crystals. Counter ions include imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium. More specifically, triphenylmethylammonium and tetraphenylphosphonium are mentioned.

[0022] In the present invention, the luminescent ionic crystal according to the present invention is used as the acceptor compound, but luminescent materials other than crystals, such as amorphous solids (powder, etc.) or liquids, may also be used as long as the effects of the present invention are not impaired. In this case, the acceptor moiety may be a part of the acceptor compound, or the entire acceptor compound may serve as the acceptor moiety.

[0023] [Donor compounds in upconversion luminescence] The structure of the donor compound (donor molecule) used for upconversion luminescence is not particularly limited as long as it has a donor moiety that can supply energy to the acceptor moiety (luminescent moiety) of the acceptor compound (luminescent ionic crystal) and form a triplet excited state at the acceptor moiety (luminescent moiety). In the present invention, the donor compound is defined as a compound that absorbs light to enter an excited triplet state and functions as a sensitizer. The "site" in the donor site means an atomic group, and the "donor site" may be a part of the donor compound, or the entire donor compound (i.e., the sensitizer) may be the "donor site."

[0024] Specific examples of the donor moiety include a donor moiety having a metal atom. Examples of the metal atom include Pt, Pd, Zn, Ru, Re, Ir, Os, Cu, Ni, Co, Cd, Au, Ag, Sn, Sb, Pb, P, and As. The donor moiety preferably includes a porphyrin structure, a phthalocyanine structure, a fullerene structure, or a 2-phenylpyridinato structure, but donor moieties having structures other than these may also be used. Specific examples of structures that can be preferably employed as the donor moiety are given below, but the present invention should not be construed as being limited to these specific examples.

[0025] [ka]

[0026] [ka]

[0027] [ka]

[0028] [ka]

[0029] [ka]

[0030] The molar ratio of the sensitizer (donor moiety) to the luminescent molecular ion (acceptor moiety) can be, for example, 1:100 to 1:100,000, 1:1,000 to 1:50,000, or 1:1,000 to 1:10,000.

[0031] In the present invention, the luminescent ionic crystals can of course exert the effects of the invention by themselves, but the effects are not impaired even if they are dispersed in a matrix resin or the like.

[0032] [Photon conversion luminous body] The luminescent ionic crystal (and an embodiment of a luminescent material comprising the crystal and the sensitizer) can be a photon conversion luminescent material that emits light of a wavelength different from that of the irradiated light, and such luminescent material is also within the scope of the present invention. In the present invention, the effects of the invention can be achieved not only by using the luminescent ionic crystal alone (or by using the luminescent material comprising the crystal and the sensitizer alone), but also by dispersing the luminescent ionic crystal in a matrix resin or the like without impairing the effects. In other words, the photon conversion luminescent material may contain, in addition to the luminescent ionic crystal (or the crystal and the sensitizer), a matrix resin (and a curing agent, curing aid, etc.) and other components within a range that does not impair the effects of the present invention. Examples of other components include surfactants, adhesion promoters, thickeners, sensitizers, antifoaming agents, leveling agents, coatability improvers, lubricants, stabilizers (antioxidants, heat stabilizers, light resistance stabilizers, etc.), plasticizers, dissolution promoters, fillers (silica, etc.), antistatic agents, colorants (dyes, pigments), etc. Furthermore, for the purpose of adjusting the viscosity of the matrix resin or improving its curability, a curable monomer may be used within a range that does not impair the effects of the present invention. These other components may be used alone or in combination of two or more.

[0033] In an embodiment containing the matrix resin, for example, a composition for forming a light-emitting body is formed which contains the above-mentioned luminescent ionic crystal (or an embodiment of a light-emitting body containing the crystal and the sensitizer), a resin component, a curing agent, etc., and by curing this, a cured product, a photon conversion light-emitting body, can be obtained. For example, a molding composition containing a thermal initiator can be applied to a substrate by casting, potting, dispensing, printing, or other methods, or poured into a casting plate coated with a release agent, pre-cured at a temperature of 100 to 120°C, and then fully cured (post-cured) at a temperature of 120 to 200°C, to obtain a cured product (molded article) in the form of, for example, a film or plate. The heating time is 1 to 12 hours, with the pre-curing and fully curing each lasting about 2 to 5 hours. When a photoinitiator is used for the curing reaction, examples of the light to be irradiated or exposed include gamma rays, X-rays, ultraviolet rays, and visible light. The wavelength of the light is, for example, about 150 to 800 nm, preferably about 150 to 600 nm, more preferably about 200 to 400 nm, and particularly about 300 to 400 nm. In this case, the exposure dose varies depending on the thickness of the coating film, but is, for example, about 2 to 20,000 mJ / cm. 2 , preferably 5 to 5,000 mJ / cm 2 The light source can be selected depending on the type of light to be exposed, and for example, in the case of ultraviolet light, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultra-high-pressure mercury lamp, a deuterium lamp, a halogen lamp, laser light (helium-cadmium laser, excimer laser, etc.), a UV-LED, etc. can be used. When a thermal initiator is used, or when a photoinitiator is used, the coating film is heated as needed after light irradiation, for example, at room temperature (approximately 23° C.) to about 250° C. The heating time can be selected from the range of 3 seconds or more (for example, about 3 seconds to 5 hours), for example, about 5 seconds to 2 hours.

[0034] [Photon upconversion luminous body and photon upconversion method] A photon up-conversion luminescent material, which is one aspect of the photon conversion luminescent material containing the luminescent ion crystal, for example, a photon up-conversion luminescent material formed from a composition for forming a luminescent material containing the luminescent ion crystal, a sensitizer, and a matrix resin (composition for forming a photon up-conversion luminescent material), is a cured product of the composition, and has a function of emitting light with higher energy than the excitation light (light with a shorter wavelength than the irradiated light) when irradiated with excitation light. This light emitter has a function as a converter, and is also included in the scope of the present invention. The present invention also provides a method for achieving photon upconversion using the photon upconversion phosphor, in which the photon upconversion phosphor is irradiated with light to generate light having a higher energy than the energy of the irradiated light.

[0035] Here, the light emitted from the photon upconversion luminescent material may or may not be observable from the outside, depending on the mode of use of the photon upconversion luminescent material of the present invention. An example of a case where the light can be observed from the outside is when light such as visible light or ultraviolet light is emitted to the outside. An example of a case where the light cannot be observed from the outside is when the light emitted from the photon upconversion luminescent material is absorbed by an energy absorbing material present in the vicinity of the photon upconversion luminescent material. By removing such an energy absorbing material, the light emitted from the photon upconversion luminescent material of the present invention can be observed.

[0036] The light emitted from the photon upconversion phosphor of the present invention is light with a shorter wavelength than the wavelength of the excitation light, where the wavelength of the excitation light of the phosphor corresponds to the wavelength of light absorbed by the donor compound in the phosphor, and the wavelength of the light emitted from the phosphor corresponds to the wavelength emitted by the acceptor compound in the phosphor. The degree of wavelength shift from excitation light to emitted light is not particularly limited, but depending on the selection of the donor-acceptor compound, it can be, for example, 20 nm or more, 50 nm or more, or 80 nm or more, or, for example, 200 nm or less, 150 nm or less, or 110 nm or less.

[0037] Examples of excitation light (irradiation light) for the light emitter include near-infrared light (approximately 800 to 2,500 nm) and visible light (approximately 400 to 800 nm), and examples of excitation sources (irradiation sources) include, but are not limited to, sunlight, LED, Xe lamp, laser, etc. Furthermore, the excitation (irradiation) time is not particularly limited and can be any time. The wavelength of the light emitted from the light emitter is not particularly limited, and can be, for example, visible light (such as green) or ultraviolet light (approximately 250 to 400 nm).

[0038] The light emitted from the photon upconversion luminescent material of the present invention may be, for example, normal fluorescence or delayed fluorescence. Delayed fluorescence is fluorescence with a longer lifetime than normal fluorescence, and for example, fluorescence with a lifetime of 50 ns (nanoseconds) or longer can be defined as delayed fluorescence. Furthermore, the photon upconversion phosphor of the present invention can emit light with a shorter wavelength than the excitation light even when irradiated with excitation light of low intensity. 2 Below, 10mW / cm 2 Below, 5mW / cm 2 Below, 2mW / cm 2 It can emit light even with the following excitation light.

[0039] The present invention also relates to a method for producing a luminescent material comprising the above-mentioned luminescent ionic crystal or the luminescent ionic crystal and a sensitizer, which method comprises a step of dissolving the luminescent molecular ions and counter ions of the luminescent molecular ions in a solvent, followed by crystallization. Note that the method for producing the luminescent material may further comprise a step of mixing and dissolving the obtained crystals with a sensitizer in a solvent, followed by removing the solvent, after the crystallization step. Furthermore, the present invention also relates to a method for improving luminous efficiency by dissolving an amorphous aggregate containing a luminescent molecular ion and a counter ion of the luminescent molecular ion in a solvent and then crystallizing the aggregate. The present invention also relates to a method for controlling the intermolecular distance between luminescent molecular ions by using a counter ion of the luminescent molecular ion. [Example]

[0040] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0041] In the examples, the apparatus and conditions used for sample preparation and analysis of physical properties are as follows. (1) 1 H NMR measurement Apparatus: Nuclear magnetic resonance apparatus Ascend™ 500, Bruker Internal standard: tetramethylsilane (TMS) (2) Absorption spectrum measurement Equipment: UV-Vis-NIR absorption spectrometer, JASCO, V-670 / V-770 (3) Excitation and emission spectrum measurement Equipment: Excitation and emission spectrum measuring device, JASCO, FP-8700 (4) Absolute quantum yield measurement Apparatus: Absolute quantum yield measurement apparatus, Hamamatsu Photonics Co., Ltd., C9920-02 (5) Microscopic observation Equipment: Optical microscope: Nikon Corporation, ECLIPSE 80i, 80iF-21-1 (6) Upconversion emission spectrum measurement Equipment: Multichannel spectrometer MCPD-7000, Otsuka Electronics Co., Ltd. Excitation source: Laser module: RGB-Lazer systems, NovaPro 730-40 Detector: OTSUKA ELECTRONICS, Photol MCPD-9800(7) Single crystal X-ray structure analysis measurement Equipment: Single crystal X-ray structure analyzer, Rigaku Corporation, MicroMax-007HF

[0042] The compounds used in the examples are as follows: Solvents: dichloromethane, methanol, tetrahydrofuran, ethyl acetate, deuterated dimethyl sulfoxide (deuterated DMSO), all manufactured by Junsei Chemical Co., Ltd. Raw materials: Perylene, TPMA (triphenylmethylamine), PPh4Cl (triphenylphosphonium chloride), all manufactured by Tokyo Chemical Industry Co., Ltd. Trimethylsilylsulfonyl chloride, PdTPBP (palladium (II) meso-tetraphenyltetrabenzoporphyrin, both manufactured by Aldrich)

[0043] [Synthesis Example 1: Production of perylene-3,9-disulfonic acid (PDS-2H)] [ka]

[0044] Perylene (10.1 g, 40.0 mmol) was dissolved in 1200 mL of dry dichloromethane. Trimethylsilylsulfonyl chloride (18.0 g, 100.0 mmol) was added thereto, and the mixture was stirred at room temperature (approximately 23°C) for 6 hours. After the reaction was completed, 20 mL of methanol was added to the mixture, and the mixture was stirred at room temperature for 1 hour to remove unreacted trimethylsilylsulfonyl chloride. The reaction solvent was removed under reduced pressure, and then tetrahydrofuran and ethyl acetate were added to the residue, which was then heated to 65°C and dissolved. After dissolution, the mixture was cooled to room temperature and the target product was recrystallized and purified. The recrystallized product was collected by filtration to obtain the target product, PDS-2H (13.7g, 33.2mmol, 83%). 1 H NMR (500MHz, deuterated DMSO): δ(ppm)=7.58(t,2H), 7.98(d,2H), 8.34(d,2H), 8.41(d,2H), 8.77(d,2H).

[0045] 2) Preparation of PDS-2TPMA: [ka] PDS-2H (5.7 mg, 13.7 μmol) and TPMA (7.7 mg, 29.7 μmol) were added to a glass bottle and dissolved in 2 mL of methanol. The lid of the glass bottle was left open, and the methanol was evaporated in air to obtain the target product, PDS-2TPMA crystals.

[0046] 3) Production of PDS-2PPh4 [ka]

[0047] PDS-2H (5.5 mg, 13.3 μmol) and PPh4Cl (10.4 mg, 27.7 μmol) were added to a glass bottle and dissolved in 2 mL of methanol. The lid of the glass bottle was left open, and the methanol was evaporated in air to obtain the target product, PDS-2PPh4 crystals.

[0048] [Example 1 and Comparative Example 1] Evaluation of absolute quantum yield The absolute quantum yields of the produced compounds (PDS-2TPMA, PDS-2PPh4) and the starting compound PDS-2H were measured. The measurement was performed by placing a few milligrams of the compound (solid) in a quartz container, placing it in the integrating sphere of an absolute quantum yield measurement device, and then irradiating it with 450 nm excitation light to obtain the absolute quantum yield of luminescence. The absolute quantum yield is calculated as the ratio of the number of photons emitted as luminescence to the number of photons of excitation light absorbed by the compound. The results are shown in Table 1.

[0049] Evaluation of absorption spectra The compound (PDS-2TPMA, PDS-2PPh4, or PDS-2H) was sandwiched between glass substrates and placed in a UV-Vis-NIR absorption spectrometer. Air was used as a reference. The results are shown in Table 1.

[0050] Emission spectrum evaluation The compound (PDS-2TPMA, PDS-2PPh4, or PDS-2H) was sandwiched between glass substrates, which were then placed in an excitation / emission spectrum measuring device. The emission spectrum of the compound was obtained, and the maximum absorption wavelength was confirmed. The results are shown in Table 1.

[0051] Evaluation of single crystal X-ray structure analysis The compounds (PDS-2TPMA, PDS-2PPh4, or PDS-2H) were placed in a single-crystal X-ray structure analyzer and subjected to single-crystal X-ray crystal structure analysis to measure the intermolecular distance between PDS molecules and confirm the maximum emission wavelength. Samples in which no clear diffraction peaks were observed were considered to have an amorphous structure. The results are shown in Table 1.

[0052] Table 1 shows the measurement results for each compound. [Table 1]

[0053] PDS-2H, the compound (raw material compound) of Comparative Example 1, had a very low absolute quantum yield of 0.67%, resulting in almost no light emission. In contrast, the Examples exhibited absolute quantum yields that were 15.8 to 22.2 times higher than that of PDS-2H. Furthermore, in PDS-2TPMA and PDS-2PPh4, which were confirmed to have improved absolute quantum yields, the intermolecular distance between PDS molecules in single-crystal X-ray structural analysis was greater than 3 Å, at which point quenching due to aggregation was observed. Furthermore, the maximum absorption and emission wavelengths of the examples (PDS-2TPMA, PDS-2PPh4) were both shifted to shorter wavelengths than those of the comparative example PDS-2H, indicating that the intermolecular distance between these molecules increased due to the introduction of ionic moieties into PDS.

[0054] Example 2: Preparation of test sample (1) for photon upconversion measurement [ka] PDS-2TPMA and PdTPBP (1 / 1000 mol ratio relative to PDS) were added to a glass bottle and dissolved in methanol. The bottle was left open and the methanol was evaporated in air to obtain the target test sample (1) for upconversion measurement.

[0055] Example 3: Preparation of test sample (2) for photon upconversion measurement [ka] PDS-2PPh4 and PdTPBP (1 / 1000 mol ratio relative to PDS) were added to a glass bottle and dissolved in methanol. The lid of the glass bottle was left open, and the methanol was evaporated in air to obtain the target test sample (2) for upconversion measurement.

[0056] Comparative Example 2: Preparation of test sample (3) for photon upconversion measurement [ka] PDS-2H and PdTPBP (1 / 1000 mol ratio relative to PDS) were added to a glass bottle and dissolved in methanol. The bottle was left open, and the methanol was evaporated in air to obtain the target test sample (3) for upconversion measurement.

[0057] The emission spectra of the obtained test samples (1) to (3) were measured when irradiated with 635 nm excitation light. The results are shown in Figure 1 (Example 2: PDS-2TPMA, PdTPBP) and Figure 2 (Example 3: PDS-2PPh4, PdTPBP). As shown in Figure 1, upconversion luminescence was observed in the PDS-2TPMA ionic crystal containing PdTPBP, from 470 nm to 560 nm, which is shorter than the excitation light (635 nm). Similarly, as shown in Figure 2, upconversion luminescence was observed in the PDS-2PPh4 ionic crystal containing PdTPBP, from 460 nm to 560 nm, which is shorter than the excitation light (635 nm). On the other hand, in PDS-2H containing PdTPBP, no upconversion luminescence was observed even when the excitation light intensity was increased.

[0058] According to the present invention, it is possible to achieve high luminous efficiency in a solid state, such as a function as a light emitter using a light energy conversion material, or a function of converting low-energy light into high-energy light by photon upconversion technology. Therefore, the present invention can be applied in a variety of fields, and is expected to dramatically improve the efficiency of, for example, artificial photosynthesis, solar cells such as perovskite solar cells, photocatalysts, display elements such as displays, and further bioimaging technology and optical diagnosis and treatment.

Claims

1. A luminescent ionic crystal comprising a luminescent molecular ion having an ionic site and a luminescent site, and a counter ion of the luminescent molecular ion, wherein the intermolecular distance between the luminescent molecular ions is 3 angstroms or more.

2. the ionic moiety is at least one anionic species selected from the group consisting of carboxylate, sulfate, sulfonate, thiocyanate, nitrate, aluminate, borate, phosphate, amide, antimonate, imide, and methide; or 2. The luminescent ionic crystal of claim 1, wherein the luminescent ionic crystal is at least one cationic species selected from the group consisting of imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium.

3. 3. The luminescent ionic crystal of claim 2, wherein the ionic moiety is the anionic species and the counterion is at least one cationic species selected from the group consisting of imidazolium, imidazolinium, pyridinium, pyrazolium, piperidinium, pyrrolidinium, phosphonium, ammonium, and sulfonium.

4. 2. The luminescent ionic crystal according to claim 1, wherein the luminescent moiety is a naphthalene structure, an anthracene structure, a tetracene structure, a pyrene structure, a perylene structure, a biphenyl structure, a terphenyl structure, a perylene diimide structure, a naphthalene diimide structure, or a BODIPY (boron dipyrromethane) structure.

5. 2. The luminescent ionic crystal according to claim 1, which absorbs light to enter an excited singlet state and emits light having a longer wavelength than the irradiated light.

6. 2. A light-emitting body comprising the luminescent ionic crystal and a sensitizer according to claim 1, further comprising a sensitizer that functions as a donor molecule that absorbs light to become an excited triplet state, wherein the luminescent molecular ions undergo triplet energy transfer from the sensitizer to become an excited singlet state and emit light.

7. 7. The luminescent body comprising a luminescent ionic crystal and a sensitizer according to claim 6, wherein the sensitizer is a compound containing a porphyrin structure, a phthalocyanine structure, a fullerene structure, or a 2-phenylpyridinato structure.

8. 2. The luminescent ionic crystal according to claim 1, wherein the intermolecular distance between the luminescent molecular ions is 3 to 20 angstroms.

9. 7. A luminescent material comprising a luminescent ionic crystal and a sensitizer according to claim 6, wherein the molar ratio of said sensitizer to said luminescent molecular ions is 1:100 to 1:100,000.

10. A photon conversion luminescent material comprising a luminescent ionic crystal according to any one of claims 1 to 5 and claim 8 or a luminescent material according to any one of claims 6, 7 and claim 9, and emitting light of a wavelength different from that of irradiated light.

11. A photon down-conversion method comprising irradiating the luminescent ionic crystal according to claim 5 with light to generate light having an energy lower than that of the irradiated light.

12. A photon up-conversion method comprising irradiating the light emitter according to claim 6 with light to generate light having higher energy than the energy of the irradiated light.

13. A method for producing the luminescent ionic crystal according to any one of claims 1 to 5 and claim 8 or the luminescent body according to any one of claims 6, 7 and claim 9, comprising a step of dissolving the luminescent molecular ions and counter ions of the luminescent molecular ions in a solvent and then crystallizing the luminescent ions.

14. A method for improving luminous efficiency by dissolving an amorphous association containing a luminescent molecular ion and a counter ion of the luminescent molecular ion in a solvent and then crystallizing the resulting mixture.

15. A method for controlling the intermolecular distance between luminescent molecular ions by using a counter ion of the luminescent molecular ion.

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