Photon Upconversion Materials

Abstract

To provide a photon upconversion material that is practical and can be applied to solid films. [Solution] The photon upconversion material of the present invention is an acceptor compound having a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit (where, one of the aromatic ring units is bonded to a group having a chain length of 4 atoms or more, such as sp 3 The compound comprises a carbon atom, a silicon atom bonded to a group having a chain length of 4 or more atoms, a nitrogen atom bonded to a group having a chain length of 4 or more atoms, or a boron atom bonded to a group having a chain length of 4 or more atoms, and a donor compound that imparts triplet energy to the acceptor compound.

Description

[Technical Field]

[0001] This invention relates to a photon upconversion material useful as a source of ultraviolet light. [Background technology]

[0002] Photon upconversion (UC) is a technology that converts low-energy light into high-energy light, and is attracting attention as an energy generation technology that can improve the efficiency of solar energy utilization devices, including solar cells, organic photoreactions, and artificial photosynthesis. As a material system that drives photon upconversion, a photon upconversion composition is known, which combines a donor that functions as a triplet sensitizer and an acceptor that functions as a light emitter. In this composition, when the donor is excited to an excited singlet state by irradiation with excitation light, it undergoes intersystem crossing to an excited triplet state, and its triplet energy is transferred to the acceptor. In the acceptor, which has become an excited triplet state after receiving energy, the triplet states of the two molecules meet, causing triplet-triplet annihilation (TTA), and one of the molecules transitions to an excited singlet state with higher energy than the excited triplet state and emits light (photon upconversion emission). In this composition, photon upconversion by such triplet-triplet annihilation (TTA-UC) can convert the irradiated light into light with higher energy (light with a shorter wavelength). [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] N. Harada et al., J. Mater. Chem. C, 2023, 11, 8002-8006. [Overview of the project] [Problems that the invention aims to solve]

[0004] To date, research on such photon upconversion compositions has mainly focused on solution-type compositions in which donor and acceptor compounds are dissolved in organic solvents. More recently, research has also been conducted on liquid-doped film type photon upconversion materials in which donor and acceptor compounds are dispersed in a non-volatile viscous medium (see Non-Patent Literature 1). However, liquid-doped films require the use of viscous mediums that are difficult to handle, and their photon upconversion efficiency tends to change depending on dissolved oxygen and temperature, posing challenges in terms of stability. In this context, the inventors diligently pursued research with the aim of providing a photon upconversion material that is practical and can also be applied to solid films. [Means for solving the problem]

[0005] As a result of diligent research to solve the above problems, the present inventors have adopted a compound having a π-conjugated condensed polycyclic structure as an acceptor compound, and by introducing a group having a chain length of 4 atoms or more into the π-conjugated condensed polycyclic structure, the threshold excitation intensity I of the photon upconversion solution can be improved. th We found that the threshold excitation intensity (I) is significantly reduced, resulting in remarkably high UC efficiency. Furthermore, photon upconversion materials using these acceptor compounds also exhibit a low threshold excitation intensity (I) even when formed as solid films. th It was also found to exhibit UC emission and to have high practical applicability. It was completely unexpected that introducing a group with a chain length of 4 atoms or more into the π-conjugated condensed polycyclic structure of the acceptor compound significantly improved the UC properties, resulting in UC emission even in the solid state. This invention is proposed based on these findings and specifically has the following configuration.

[0006] [1] Acceptor compounds having a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit (where any of the aromatic ring units is bonded to a group having a chain length of 4 atoms or more, such that sp 3A photon upconversion material comprising carbon, a silicon atom bonded to a group having a chain length of 4 or more atoms, a nitrogen atom bonded to a group having a chain length of 4 or more atoms, or a boron atom bonded to a group having a chain length of 4 or more atoms), and a donor compound that gives triplet energy to the acceptor compound. [2] As the ring skeleton constituent atoms of the π-conjugated condensed polycyclic structure, the sp 3 The photon upconversion material according to [1], comprising carbon, the silicon atom, the nitrogen atom or the boron atom. [3] As the ring skeleton constituent atoms of the π-conjugated condensed polycyclic structure, the sp 3 The photon upconversion material according to [2], comprising two of carbon, the silicon atom, the nitrogen atom or the boron atom. [4] The photon upconversion material according to any one of [1] to [3], wherein the aromatic ring unit is a benzene ring. [5] The photon upconversion material according to any one of [1] to [4], wherein the π-conjugated condensed polycyclic structure contains two benzene rings. [6] The photon upconversion material according to any one of [3] to [5], wherein the π-conjugated condensed polycyclic structure has an indenoindene skeleton. [7] The photon upconversion material according to any one of [1] to [6], wherein the group having a chain length of 4 or more atoms is an alkyl group having a chain length of 4 or more atoms or an alkoxy group having a chain length of 4 or more atoms. [8] The photon upconversion material according to [1], wherein the acceptor compound is a compound represented by the following general formula (1). [Chemical formula] [In general formula (1), X 1 and X 2 each independently represent a carbon atom, a silicon atom, a nitrogen atom or a boron atom. When X 1 is a carbon atom or a silicon atom, n1 is 2, and X 1When is a nitrogen atom or a boron atom, n1 is 1. 2 When is a carbon atom or a silicon atom, n2 is 2, and X 2 When is a nitrogen atom or a boron atom, n2 is 1. 11 and R 12 Each of these independently represents a group having a hydrogen atom or a chain length of 4 or more atoms, but R 11 At least one of the following, and R 12 At least one of them is a group having a chain length of 4 atoms or more. 13 and R 14 Each of these independently represents a substituent. n3 and n4 each independently represent an integer between 0 and 4. [9] The photon upconversion material according to any one of [1] to [8], wherein the molecular size of the donor compound is less than 1.5 times the molecular size of the acceptor compound.

[10] The photon upconversion material according to any one of [1] to [9], wherein the content of the donor compound is in the range of 0.01 to 10.0% in molar ratio with respect to the content of the acceptor compound.

[11] A solid photon upconversion material as described in any one of items [1] to

[10] .

[12] The photon upconversion material described in

[11] , which does not contain a non-volatile solvent.

[13] A crystalline photon upconversion material as described in

[11] .

[14] The photon upconversion material described in

[11] , which is in the form of a film.

[15] A photon upconversion laminate having a structure in which a solid layer made of the photon upconversion material described in any one of items

[11] to

[14] is laminated with a layer containing a low oxygen permeable polymer.

[16] Having a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit, Each of the aforementioned aromatic ring units has a group with a chain length of 4 atoms or more bonded to it, such as sp 3A compound comprising a carbon atom, a silicon atom bonded to a group with a chain length of four or more atoms, a nitrogen atom bonded to a group with a chain length of four or more atoms, or a boron atom bonded to a group with a chain length of four or more atoms. [Effects of the Invention]

[0007] The photon upconversion material of the present invention exhibits photon upconversion luminescence in both solution and solid states, and therefore can also be constructed as a solid photon upconversion material. The photon upconversion material of the present invention, especially the solid form, can be applied to various elements that constitute functional elements using solid films or laminates of solid films, and thus has high practicality. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the UC emission mechanism of the photon upconversion material of the present invention. [Figure 2] This is the UC emission spectrum measured for UC film 1 containing compound A2 and compound D1, with varying excitation light intensities. [Figure 3] These are the X-ray diffraction patterns of UC film 1 containing compound A2 and compound D1, A2 film made of compound A2, and crystalline powder of compound A2. [Figure 4] This figure shows the single-crystal X-ray structural analysis results of compound A2. [Modes for carrying out the invention]

[0009] The present invention will be described in detail below. The following descriptions of constituent elements may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In this specification, numerical ranges expressed using "~" mean a range that includes the numbers written before and after "~" as the lower and upper limits. Furthermore, the isotopes of hydrogen atoms present in the molecule of the compound used in the present invention are not particularly limited; for example, all hydrogen atoms in the molecule 1H is fine, or part or all of it 2 H (Deuterium D) is also acceptable. In this specification, "visible light" means light with a wavelength in the range of over 400 nm and up to 800 nm, and "ultraviolet light" means light with a wavelength in the range of 200 nm and up to 400 nm.

[0010] <Photon Upconversion Materials> The photon upconversion material of the present invention is an acceptor compound having a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit (where any of the aromatic rings has a group with a chain length of 4 atoms or more bonded to it). 3 The compound comprises a carbon atom, a silicon atom bonded to a group with a chain length of 4 or more atoms, a nitrogen atom bonded to a group with a chain length of 4 or more atoms, or a boron atom bonded to a group with a chain length of 4 or more atoms, and a donor compound that imparts triplet energy to the acceptor compound. In the present invention, "photon upconversion material" refers to a material that absorbs light supplied to it and emits light of a shorter wavelength. Thus, the "photon upconversion material" in the present invention exhibits the function of converting supplied light into light of a shorter wavelength. In the photon upconversion material of the present invention, the source light that is converted into "light of a shorter wavelength" is light whose wavelength overlaps with the wavelength region (absorption wavelength range) in which the photon upconversion material exhibits light absorption, and specifically, light whose wavelength overlaps with the wavelength region (absorption wavelength range) in which the donor compound described later exhibits light absorption. This source light is preferably light in the wavelength region longer than the ultraviolet light region, and more preferably visible light. Furthermore, the "light of a shorter wavelength" to be converted is preferably ultraviolet light. The source light and the converted light may be light with a single emission maximum wavelength, or they may be composite light containing multiple lights with different emission maximum wavelengths. In one preferred embodiment of the present invention, the photon upconversion material is a material that absorbs visible light and emits ultraviolet light.

[0011] In this specification, the conversion of light absorbed by a photon upconversion material into shorter wavelength light and its emission is referred to as "photon upconversion emission" or "UC emission," the light emitted by photon upconversion emission (light with a shorter wavelength than the irradiated light) is referred to as "UC light," and the efficiency of converting the light irradiated onto the photon upconversion material into UC light is referred to as "upconversion efficiency" or "UC efficiency." For information on how to measure UC efficiency, please refer to the section on examples.

[0012] The "photon upconversion material" of the present invention comprises at least a donor compound and an acceptor compound. The "donor compound" in the present invention absorbs light supplied to the photon upconversion material and becomes excited, transferring the energy of its excited triplet state to the acceptor compound (sensitizer). The "acceptor compound" in the present invention receives energy from the excited triplet state donor compound, undergoes photon upconversion by triplet-triplet annihilation (TTA-UC), and emits photon upconversion light through radiative deactivation from the excited singlet state generated by this process (UC emitter). The mechanism of UC emission in photon upconversion materials will be explained with reference to Figure 1. Here, the acceptor compound is at its lowest excited singlet energy level E S1,A The lowest excited singlet energy level E of the donor compound S1,D Higher than its lowest excited triplet energy level E T1,A The lowest excited triplet energy level E of the donor compound T1,D A case lower than this is shown as a preferred example. Furthermore, the present invention relates to the lowest excited triplet energy level E of the acceptor compound. T1,A The lowest excited triplet energy level E of the donor compound T1,D It can function even if it is higher than that. Lowest excited triplet energy level E of the acceptor compound T1,A and the lowest excited triplet energy level E of the donor compound T1,DThe difference is preferably within 0.20 eV. In Figure 1, the light supplied to the photon upconversion material is assumed to be excitation light for the donor compound, i.e., light whose wavelength overlaps with the absorption wavelength range of the donor compound. In Figure 1, "TTA" indicates triplet-triplet annihilation. First, when excitation light is shone onto a photon upconversion material containing a donor compound and an acceptor compound, as shown in Figure 1, the molecules of the donor compound (donor molecules) absorb the light and enter an excited singlet state (S 1,D After being excited to ), intersystem crossing occurs and an excited triplet state (T 1,D The donor molecule transitions to the excited triplet state (T). The energy of the donor molecule, now in the excited triplet state, is transferred to the acceptor compound molecule (acceptor molecule). This results in the excited triplet state (T). 1,A In the acceptor compound that has reached this state, the triplet states of the two molecules meet, causing triplet-triplet annihilation, and one of the molecules enters an excited singlet state (S 1,A ) transitions to ). That is, photon upconversion occurs due to triplet-triplet annihilation of the acceptor molecule. The acceptor molecule, now in the excited singlet state, is deactivated by emitting fluorescence (UC light), causing the photon upconversion material to emit UC light. At this time, the excited singlet state (S) produced by the photon upconversion via triplet-triplet annihilation 1,A ) has an energy level of S 1,D Because it is higher than the energy level of S 1,A Radiative deactivation from this source allows us to obtain UC light, which has higher energy (shorter wavelength) than the excitation light. Here, the fact that the emission obtained from the photon upconversion material is photon upconversion emission due to triplet-triplet annihilation is because the lifetime of the photon upconversion emission is milliseconds ~ 10 -1The delayed fluorescence is on the order of milliseconds, which can be confirmed by the fact that the slope of the fitting line of the plot changes from 2 to 1 in a log-log plot of the photon upconversion emission intensity dependent on the excitation light intensity. Here, the excitation light intensity at which the slope of the fitting line of this log-log plot changes from 2 to 1 is defined as the "threshold excitation intensity I th " and the threshold excitation intensity I th For information on the measurement method, please refer to the description in the Examples section.

[0013] The acceptor compound and donor compound included in the photon upconversion material of the present invention will be described in detail below. In the following explanation, unless otherwise specified, "alkyl group," "alkoxy group," and "aryl group" refer to substituents within the following ranges. The "alkyl group" may be linear, branched, or cyclic. The preferred number of carbon atoms is 1 to 20, more preferably 1 to 10, and even more preferably 1 to 6. Specific examples of alkyl groups include methyl, ethyl, n-propyl, and isopropyl groups, but the "alkyl group" is not limited to these specific examples. At least one hydrogen atom of the alkyl group may be substituted with a substituent. The "alkoxy group" may be linear or branched. The preferred number of carbon atoms is 1 to 20, more preferably 1 to 10, and even more preferably 1 to 6. Specific examples of alkoxy groups include methoxy, ethoxy, n-propoxy, and isopropoxy groups, but the "alkoxy group" is not limited to these specific examples. At least one hydrogen atom of the alkoxy group may be substituted with a substituent. An "aryl group" may consist of a monocyclic aromatic ring, a fused ring formed by the fusion of two or more aromatic rings, or a linked ring formed by the linkage of two or more aromatic rings. When two or more aromatic rings are linked, they may be linked in a linear chain or in a branched chain. The number of carbon atoms in the aromatic ring constituting the aryl group is preferably 6 to 22, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. Specific examples of aryl groups include phenyl, naphthalenyl, and biphenyl groups, but the "aryl group" is not limited to these specific examples. At least one hydrogen atom of the aryl group may be substituted with a substituent.

[0014] [Acceptor compounds] The acceptor compound used in this invention has a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit, and a group having a chain length of 4 atoms or more is bonded to one of the aromatic ring units contained in the π-conjugated condensed polycyclic structure (sp). 3 It has a structure in which carbon, a silicon atom bonded to a group with a chain length of 4 or more atoms, a nitrogen atom bonded to a group with a chain length of 4 or more atoms, or a boron atom bonded to a group with a chain length of 4 or more atoms are bonded. In this invention, "π-conjugated condensed polycyclic structure" means a condensed polycyclic structure in which two or more rings are fused together, and all the rings constituting the condensed polycyclic structure are π-conjugated. Here, "π-conjugation" may be π-conjugation formed by the alternating arrangement of multiple bonds (double bonds, triple bonds) and single bonds, or it may include π-conjugation formed by the sequential arrangement of atoms with lone pairs of electrons in p orbitals, single bonds, and multiple bonds. In this invention, the "aromatic ring unit" in "a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit" means an aromatic ring (an aromatic ring for each monoring) as a unit constituting the π-conjugated condensed polycyclic structure. Furthermore, in the following description, a ring as a unit constituting the π-conjugated condensed polycyclic structure may be referred to as a "constituent ring." The number of rings (constituent rings) constituting the π-conjugated condensed polycyclic structure is, for example, 2 to 12, and may also be, for example, 2 to 7 or 2 to 6, or 2 to 5 or 2 to 4. At least one of the rings constituting the π-conjugated condensed polycyclic structure is an aromatic ring (aromatic ring unit). The number of aromatic ring units contained in the π-conjugated condensed polycyclic structure may be one or two or more, and all of the rings constituting the π-conjugated condensed polycyclic structure may be aromatic ring units. In other words, the π-conjugated condensed polycyclic structure may contain both aromatic rings and alicyclic rings as constituent rings, or may consist only of aromatic rings. However, the alicyclic ring here has p-orbital electrons that are π-conjugated with the p-orbital electrons of the adjacent ring, and for example, has a double bond positioned between a double bond and a single bond of the adjacent ring. The number of ring members of each constituent ring constituting the π-conjugated condensed polycyclic structure is not particularly limited, but is preferably 5 or 6. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound includes at least one 6-membered ring as a constituent ring. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound includes at least one 5-membered ring and at least one 6-membered ring as constituent rings. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound includes a 6-membered ring that is an aromatic ring as a constituent ring. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound includes a 5-membered ring that is an alicyclic ring and a 6-membered ring that is an aromatic ring as constituent rings. Here, the π-conjugated condensed polycyclic structure may be a π-conjugated condensed polycyclic hydrocarbon structure consisting of a structure in which two or more hydrocarbon rings are fused, or it may be a π-conjugated condensed polycyclic heterocyclic structure containing a heteroatom as a ring member.

[0015] For a description of the number and types of constituent rings in the π-conjugated condensed polycyclic hydrocarbon structure and the aromatic ring units, please refer to the description of "π-conjugated condensed polycyclic structure" above. The number of carbon atoms in the π-conjugated condensed polycyclic hydrocarbon structure is, for example, 9 to 50, and may also be, for example, 9 to 22, 9 to 18, or 10 to 18. An example of an aromatic ring that can constitute a π-conjugated condensed polycyclic structure is a benzene ring, and an example of an alicyclic ring that can constitute a π-conjugated condensed polycyclic structure is an alicyclic hydrocarbon ring having a π-conjugated system within the ring, such as a cycloalkadiene ring such as a cyclopentadiene ring, a cycloalkatriene ring, or a cycloalkatetraene ring. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound has a structure in which a benzene ring and a cyclopentadiene ring are condensed with sharing edges. In a preferred aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound has an indenoindene skeleton. In one aspect of the present invention, the π-conjugated condensed polycyclic structure has a structure in which two or more benzene rings are condensed with sharing an edge.

[0016] For a description of the number and types of constituent rings in a π-conjugated condensed polycyclic heterocyclic structure, and for an explanation of aromatic ring units, please refer to the description of "π-conjugated condensed polycyclic structure" above. A π-conjugated condensed polycyclic heterocyclic structure may have a structure in which one or more heterocyclic rings are fused with one or more hydrocarbon rings, or it may consist of a structure in which two or more heterocyclic rings are fused. Examples of heteroatoms constituting the heterocyclic rings include silicon atoms, nitrogen atoms, oxygen atoms, sulfur atoms, boron atoms, and phosphorus atoms. The number of carbon atoms in a π-conjugated condensed polycyclic heterocyclic structure is, for example, 5 to 50, but may also be, for example, 5 to 21, 6 to 17, or 9 to 17. Examples of heterocycles that can constitute a π-conjugated condensed polycyclic heterocyclic structure include pyrrole rings, pyrazole rings, imidazole rings, triazole rings, pyridine rings, pyridazine rings, pyrimidine rings, pyrazine rings, triazine rings, thiophene rings, furan rings, oxazole rings, isoxazole rings, oxadiazole rings, thiazole rings, isothiazole rings, thiadiazole rings, borepin rings, phospholine rings, and silacicopenta-2,4-diene rings. For examples of hydrocarbon rings that can constitute a condensed polycyclic heterocyclic structure, refer to the above description of aromatic rings and alicyclic rings that can constitute a condensed polycyclic hydrocarbon structure. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound includes at least one benzene ring as an aromatic ring unit, preferably at least two benzene rings.

[0017] Furthermore, the acceptor compound used in this invention is an sp group in which a group having a chain length of 4 atoms or more is bonded to any of the aromatic ring units contained in the π-conjugated condensed polycyclic structure. 3 It contains a carbon atom, a silicon atom bonded to a group with a chain length of 4 or more atoms, a nitrogen atom bonded to a group with a chain length of 4 or more atoms, or a boron atom bonded to a group with a chain length of 4 or more atoms. Here, sp 3 Carbon is a carbon atom that has four single bonds. In this invention, "a group having a chain length of 4 or more atoms" refers to sp 3This refers to a group having an atomic chain in which, when the first atom is covalently bonded to a carbon, silicon, nitrogen, or boron atom, and the number of atoms covalently bonded in series from this first atom is counted in the same direction, there are four or more atoms. The covalent bond may be a single bond, a double bond, or a triple bond, but preferably all bonds between atoms in the atomic chain are single bonds. In this specification, the group of atoms covalently bonded in series from the first atom is called an "atomic chain," and an sp group is a group having a chain length of four or more atoms. 3 Carbon, silicon atoms bonded to a group with a chain length of 4 or more atoms, nitrogen atoms bonded to a group with a chain length of 4 or more atoms, and boron atoms bonded to a group with a chain length of 4 or more atoms are sometimes collectively referred to as "specific atomic chain bonded atoms." Here, the atomic chain of a group with a chain length of 4 or more atoms may contain two or more types of atoms. If the atomic chain contains two or more types of atoms, and the total number of atoms of those two or more types is 4 or more, then it falls under the category of "a group with a chain length of 4 or more atoms" in this invention. Therefore, for example, the "isobutyl group" has an atomic chain of *-CCCH as shown in the formula below, and thus falls under the category of "a group with a chain length of 4 or more atoms" in this invention. In the formula below, * is sp 3 This indicates the bond position to a carbon, silicon, nitrogen, or boron atom.

[0018] [ka]

[0019] The chain length of the "group having a chain length of 4 or more atoms" is, for example, 4 to 25 atoms, and may also be 4 to 10 atoms, 4 to 8 atoms, or 4 to 6 atoms. The atomic chain of the "group having a chain length of 4 or more atoms" may be linear or branched, but branched is preferred. It is thought that the branched atomic chain more effectively suppresses intermolecular interactions that reduce luminescence efficiency, and tends to result in a higher fluorescence quantum yield. Alkyl groups can be cited as an example of a "group having a chain length of 4 or more atoms." For the chain length and type (linear, branched) of alkyl groups as "groups having a chain length of 4 or more atoms," please refer to the explanation of "groups having a chain length of 4 or more atoms" above. The number of carbon atoms in an alkyl group is, for example, 4 to 20, but may also be, for example, 4 to 10 or 4 to 6. Specific examples of alkyl groups include n-propyl group, n-butyl group, isobutyl group, sec-butyl group, n-pentyl group, isopentyl group, neopentyl group, sec-pentyl group, 3-pentyl group, tert-pentyl group, n-hexyl group, isohexyl group, 2-ethylbutyl group, and 2,2-diethylbutyl group. As an example of a "group having a chain length of 4 or more atoms," a chain-like organic group in which at least one methylene group of an alkyl group is replaced with a divalent group containing a heteroatom can also be cited. Examples of divalent groups include oxygen atoms and sulfur atoms, with oxygen atoms being preferred. For the chain length and type (linear, branched) of the chain-like organic group, please refer to the explanation of "groups having a chain length of 4 or more atoms" above. The methylene group that is replaced with a heteroatom among the methylene groups constituting the alkyl group is not particularly limited, but sp 3 A methylene group (sp) directly bonded to a carbon, silicon, nitrogen, or boron atom. 3 It is preferable that the group is a methylene group containing a carbon atom bonded by a single bond to a carbon, silicon, nitrogen, or boron atom. In other words, the chain-like organic group as a "group having a chain length of 4 atoms or more" is preferably an alkoxy group. The number of carbon atoms in the alkoxy group is, for example, 3 to 20, and may also be, for example, 3 to 10 or 4 to 6. Specific examples of alkoxy groups include ethoxy group, n-propyloxy group, n-butyloxy group, isobutyloxy group, sec-butyloxy group, tert-butyloxy group, n-pentyloxy group, isopentyloxy group, neopentyloxy group, sec-pentyloxy group, 3-pentyloxy group, tert-pentyloxy group, n-hexyloxy group, isohexyloxy group, 2-ethylbutyloxy group, and 2,2-diethylbutyloxy group. In one aspect of the present invention, the "group having a chain length of 4 atoms or more" in the acceptor compound is selected from the group consisting of alkyl groups having a chain length of 4 atoms or more and alkoxy groups having a chain length of 4 atoms or more, and is preferably selected from the group consisting of alkyl groups having a chain length of 4 atoms or more.

[0020] In the acceptor compound used in this invention, a sp group having a chain length of 4 atoms or more is bonded to it. 3 A carbon atom, a silicon atom bonded to a group having a chain length of 4 or more atoms, a nitrogen atom bonded to a group having a chain length of 4 or more atoms, or a boron atom bonded to a group having a chain length of 4 or more atoms (a specific atomic chain bond atom) is bonded to one of the aromatic ring units contained in the π-conjugated condensed polycyclic structure. The aromatic ring units to which the specific atomic chain bond atom is bonded may be all of the aromatic ring units contained in the π-conjugated condensed polycyclic structure, or some of the aromatic ring units. Furthermore, the number of specific atomic chain bond atoms bonded to each aromatic ring unit may be one or two or more. When there are a total of two or more specific atomic chain bond atoms bonded to the aromatic ring units of the π-conjugated condensed polycyclic structure, these specific atomic chain bond atoms may be the same or different from each other. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound contains at least two aromatic ring units, and at least one specific atomic chain bond atom is bonded to each of these two aromatic ring units. In one aspect of the present invention, the π-conjugated condensed polycyclic structure of the acceptor compound contains at least two aromatic ring units, one of which is bonded to two specific atomic chain-bonding atoms. Furthermore, sp at specific atomic chain bonding atoms 3Carbon, silicon, nitrogen, and boron atoms may exist as ring skeleton constituent atoms of a π-conjugated condensed polycyclic structure and be bonded to aromatic ring units contained in that π-conjugated condensed polycyclic structure (hereinafter referred to as "first embodiment"), or they may exist outside the π-conjugated condensed polycyclic structure (i.e., not as constituent atoms of the π-conjugated condensed polycyclic structure) and be bonded to ring skeleton constituent atoms of aromatic rings contained in that π-conjugated condensed polycyclic structure (hereinafter referred to as "second embodiment"). In a preferred embodiment of the first embodiment, sp groups with a chain length of 4 or more atoms are bonded as ring skeleton constituent atoms of the π-conjugated condensed polycyclic structure. 3 The compound contains a carbon atom, a silicon atom bonded to a group having a chain length of 4 atoms or more, a nitrogen atom bonded to a group having a chain length of 4 atoms or more, or two boron atoms bonded to a group having a chain length of 4 atoms or more. In a preferred embodiment of the first embodiment, the π-conjugated condensed polycyclic structure contains two benzene rings. In a more preferred embodiment of the first embodiment, the π-conjugated condensed polycyclic structure has an indenoindene skeleton. An example of an acceptor compound of the first embodiment is a compound represented by the following general formula (1), and an example of an acceptor compound of the second embodiment is a compound represented by the following general formula (2).

[0021] [ka]

[0022] In general formulas (1) and (2), X 1 ~X 4 Each of these independently represents a carbon atom, a silicon atom, a nitrogen atom, or a boron atom. 1 When is a carbon atom or a silicon atom, n1 is 2, and X 1 When is a nitrogen atom or a boron atom, n1 is 1. 2 When is a carbon atom or a silicon atom, n2 is 2, and X 2 When is a nitrogen atom or a boron atom, n2 is 1. 3 When is a carbon atom or a silicon atom, n5 is 3, and X 3 When n5 is a nitrogen atom or a boron atom, n5 is 2. 4When is a carbon atom or a silicon atom, n6 is 3, and X 4 When n6 is a nitrogen atom or a boron atom, n6 is 2. 11 , R 12 , R 15 , R 16 Each of these independently represents a group having a hydrogen atom or a chain length of 4 or more atoms, but R 11 At least one of R 12 At least one of R 15 At least one of the following, and R 16 At least one of them is a group having a chain length of 4 atoms or more. 11 , R 12 , R 15 , R 16 Preferably, all of these are groups having a chain length of 4 atoms or more. The π-conjugated condensed polycyclic structure of the compound represented by general formula (1) or (2) may have further rings fused to it, forming a π-conjugated condensed polycyclic structure as a whole. For an explanation of "groups having a chain length of 4 atoms or more," refer to the description of "groups having a chain length of 4 atoms or more" for the π-conjugated condensed polycyclic structure described above. In one aspect of the present invention, the acceptor compound is represented by general formula (1), and X 1 and X 2 The compound is a carbon atom, and more preferably, the acceptor compound is represented by general formula (1), X 1 and X 2 is a carbon atom, R 11 and R 12 The compound is an alkyl group having a chain length of 4 atoms or more, or an alkoxy group having a chain length of 4 atoms or more.

[0023] The π-conjugated polycyclic structure of the acceptor compound may have at least one hydrogen atom substituted with a substituent. In general formulas (1) and (2), R 13 , R 14 , R 17 , R 18Each is independently a substituent, and n3, n4, n7, and n8 are each independently an integer of any one of 0 to 4. The substituent is not particularly limited, and examples thereof include an alkyl group (for example, having 1 or 2 carbon atoms), an alkoxy group (for example, having 1 or 2 carbon atoms), an alkynyl group (for example, having 2 carbon atoms), an amino group, a methylamino group, a dimethylamino group, a cyano group, a carboxyl group, a sulfo group, a phosphoric acid group, a trimethylsilyl group, and a triisopropylsilylethynyl group. It is preferable that the substituent does not have a chain length of 4 atoms or more.

[0024] Hereinafter, specific examples of the acceptor compound will be illustrated, but the acceptor compounds that can be used in the present invention should not be construed as being limited to these specific examples.

[0025] [Chemical formula]

[0026] The acceptor compound used in the present invention is preferably a compound that satisfies at least one of the following conditions (A) to (D), and more preferably a compound that satisfies all of the conditions (A) to (D). (A) Having a long excited triplet state lifetime τ T,A (B) The lowest excited singlet state energy level E S1,A and the lowest excited triplet state energy level E T1,A satisfy the following formula. E S1,A < (2 × E T1,A ) (C) High singlet generation efficiency f by triplet-triplet annihilation. (D) Having a high fluorescence quantum yield Φ F,A

[0027] The acceptor compound having a long excited triplet state lifetime τ defined by condition (A) T,A is in an excited triplet state (T 1,A ​It is more likely to cause photon upconversion by triplet-triplet annihilation than to deactivate to the ground state (S0). Therefore, the threshold excitation light intensity I of the photon upconversion material th can be lowered. The excited triplet lifetime τ T,A is preferably longer than 1 ms (millisecond), and more preferably longer than 1.5 ms.

[0028] The acceptor compound satisfying condition (B) has the lowest excited singlet energy level E T1,A lower than twice the value of the lowest excited triplet energy level E S1,A . Therefore, the remaining 1 molecule in triplet-triplet annihilation easily transitions to the excited singlet state (S 1,A ), and photon upconversion can occur more reliably. Therefore, by using such an acceptor compound, the UC efficiency of the photon upconversion material can be increased.

[0029] The acceptor compound with a high singlet generation efficiency f defined by condition (C) easily generates the excited singlet state (S 1,A ) in triplet-triplet annihilation. Therefore, by using such an acceptor compound, the UC efficiency of the photon upconversion material can be increased. The singlet generation efficiency f is preferably 0.1 or more, and more preferably 0.3 or more.

[0030] The acceptor compound with a high fluorescence quantum yield Φ F,A defined by condition (D) easily undergoes radiative deactivation from the excited singlet state (S 1,A ). Therefore, by using such an acceptor compound, the UC efficiency of the photon upconversion material can be increased. The fluorescence quantum yield Φ F,A of the acceptor compound is preferably 50% or more, and more preferably 80% or more.

[0031] (Synthesis method of the compound represented by general formula (1)) Compounds represented by general formula (1) can be synthesized using known reactions such as electrophilic substitution reactions. For example, a compound represented by general formula (1) and X 1 and X 2 is a carbon atom, R 11 and R 12 Compounds in which the alkyl group has a chain length of 4 atoms or more can be synthesized, for example, by reacting 5,10-dihydroindeno[2,1-a]indene, which has been lithiated by reaction with an organolithium compound, with an alkyl halide. For specific conditions and procedures of the synthesis method, please refer to the section on examples.

[0032] [Donor compound] The donor compound used in the present invention is more preferably a compound that satisfies at least one of the following conditions (E) to (H), and more preferably a compound that satisfies all of conditions (E) to (H). (E) Having a large absorption coefficient ε at the excitation wavelength. (F) High intersystem crossing efficiency Φ ISC Having. (G) Lowest excited triplet energy level E of the acceptor compound T1,A The lowest excited triplet energy level E is higher than T1,D Having. (H) Excitation triplet lifetime τ sufficient for triplet sensitization of the acceptor compound T,D Having.

[0033] A donor compound with a large absorption coefficient ε at the excitation wavelength defined by condition (E) can efficiently transition from the ground state (S0) to the excited singlet state (S1) by supplying excitation light, thus providing a threshold excitation intensity I for photon upconversion materials. th This can be made lower. The absorption coefficient ε of the donor compound at the excitation wavelength is 10 4 M -1 ·cm -1 It is preferable that it be higher than this. Here, "threshold excitation intensity I thThis value represents the excitation light intensity at the inflection point of a log-log graph showing the dependence of UC emission intensity on excitation light intensity. A lower value indicates that the excitation light intensity required for UC emission is lower, or in other words, that UC emission occurs more efficiently.

[0034] Intersystem crossover efficiency Φ as defined by condition (F) ISC Donor compounds with high S 1,D ) to excited triplet state (T 1,D This allows for efficient transition to ) and increases the UC efficiency of photon upconversion materials. Intersystem crossover efficiency of the donor compound Φ ISC It is preferable that the percentage be 70% or more, and more preferably 90% or more.

[0035] The lowest excited triplet energy level E of the acceptor compound, as defined by condition (G). T1,A The lowest excited triplet energy level E is higher than T1,D Donor compounds possessing this property can efficiently transfer excitation triplet energy to acceptor compounds. Therefore, by using such donor compounds, the UC efficiency of photon upconversion materials can be increased. Lowest excited triplet energy level E of the donor compound T1,D and the lowest excited triplet energy level E of the acceptor compound T1,A The difference (E T1,D -E T1,A The voltage is preferably 0.01 to 1 eV, more preferably 0.01 to 0.5 eV, and even more preferably 0.01 to 0.2 eV.

[0036] A sufficient excitation triplet lifetime τ as defined by condition (H) T,D The donor compound having the excited triplet state (T 1,D Excitation triplet energy transfer to the acceptor compound is more likely than deactivation from the ) state to the ground state (S0). Therefore, by using such donor compounds, the UC efficiency of photon upconversion materials can be increased. Excitation triplet lifetime τ T,DIt is preferable that the interval be longer than 1 ms, and more preferably longer than 2 ms.

[0037] For example, compounds having a coumarin skeleton (coumarin compounds) can be used as donors. An example of a coumarin compound that can be used as a donor is the compound represented by the following general formula (3).

[0038] General formula (3) [ka]

[0039] In general formula (3), R 1 ~R 6 Each of these independently represents a hydrogen atom or a substituent. 1 ~R 6 They may be identical or different from one another. R 1 ~R 5 Examples of substituents that can be taken include halogen atoms (e.g., fluorine, chlorine, bromine, iodine), alkyl halides (e.g., trifluoromethyl group), aryl halides (e.g., bromophenyl group), primary amino groups, secondary amino groups (e.g., alkylamino groups, arylamino groups), tertiary amino groups (e.g., dialkylamino groups, diarylamino groups, alkylarylamino groups), thiocarbonyl groups, hydroxyl groups, alkyl groups, cyano groups, imine groups, benzothiazole groups, benzoxazole groups, benzimidazole groups, furan groups, pyrrole groups, thiophene groups, oxazole groups, imidazole groups, and thiazole groups. R 6 Examples of substituents that can be formed include halogen atoms (e.g., fluorine atoms, chlorine atoms, bromine atoms, iodine atoms), alkoxy groups, alkyl groups, amino groups, alkylamino groups, phenylamino groups, pyridyl groups, and hydroxyl groups. R 1 and R 2 , R 2 and R 3 , R 3 and R 4, R 4 and R 5 These elements may be bonded to each other to form a ring. The ring may be an aromatic ring or an alicyclic ring. Examples of rings include a benzene ring, a polycyclic aromatic ring formed by the fusion of two or more benzene rings (e.g., a naphthalene ring, an anthracene ring), a cyclohexadiene ring, a cyclohexene ring, a cyclopentaene ring, a dihydrofuran ring, a heterocyclic ring (e.g., a furan ring, a pyrrole ring, a thiophene ring, an oxazole ring, an imidazole ring, a thiazole ring, a benzothiazole ring, a benzoxazole ring, a benzimidazole ring, a piperidine ring, a pyrrolidine ring, or a ring formed by the fusion of two or more of these), and a BODIPY ring (boron-dipyrromethene ring). For details and specific examples of compounds represented by general formula (1), refer to WO2023 / 037848A1

[0028] to

[0030] .

[0040] Furthermore, specific examples of donors that can be used in the present invention include compounds containing the following heavy metals. [ka] [ka]

[0041] Furthermore, the following heavy metal-free compounds can also be cited as specific examples of donors that can be used in the present invention. [ka] JPEG2026136669000009.jpg220170

[0042] (Lowest excited singlet energy level E S1 and the lowest excited triplet energy level E T1 (Measurement method) The lowest excited singlet energy level E of the compound used in the present invention S1This is obtained by measuring the fluorescence spectrum of the compound in solution and converting the wavelength of the shortest wavelength fluorescence peak into an energy value using the following conversion formula. Also, the lowest excited triplet energy level E of the compound used in this invention T1 The phosphorescence spectrum is obtained by measuring the phosphorescence spectrum of a compound in solution and converting the wavelength of the phosphorescence peak into an energy value using the following conversion formula. The solvent used to prepare the compound in solution should be one that can dissolve the compound (e.g., tetrahydrofuran). The concentration of the solution should be such that the spectrum can be measured (e.g., 100 μM). The emission spectrum can be measured using a xenon lamp as the excitation light source and a JASCO FP-8700 from JASCO Corporation. Conversion formula: E S1 [eV]=1239.85 / λ F Conversion formula: E T1 [eV]=1239.85 / λ P In the above equation, λ F λ is the fluorescence peak wavelength [nm], P This is the phosphorescent light peak wavelength [nm].

[0043] [Ratio and content of donor and acceptor compounds] In the photon upconversion material of the present invention, the molar ratio of the donor compound to the acceptor compound [(moles of donor compound / moles of acceptor compound) × 100] is preferably 0.01 to 20%, more preferably 0.01 to 10%, even more preferably 0.1 to 10%, and even more preferably 1 to 5%. When the absorbance of the donor compound at the emission wavelength of the acceptor compound is small, the concentration of the donor compound can be increased to allow for greater absorption of excitation light.

[0044] [Other ingredients] The photon upconversion material of the present invention may consist only of an acceptor compound and a donor compound, or it may contain other components. Examples of other components include colorants and antioxidants. Furthermore, the solution-type photon upconversion material contains a solvent in addition to the acceptor compound and the donor compound. As the solvent, an organic solvent capable of dissolving the acceptor compound and the donor compound can be appropriately selected from known organic solvents such as hydrocarbon solvents, ether solvents, halogenated hydrocarbon solvents, ketone solvents, alcohol solvents, nitrile solvents, ester solvents, carbonate solvents, and amide solvents.

[0045] The photon upconversion material of the present invention does not need to contain heavy metals. Here, "heavy metals" in "heavy metal-free" refers to heavy metals with a specific gravity of 4 g / cm³. 3 This refers to the metals mentioned above. "Heavy metal-free" means that the compound is substantially free of heavy metals in any form, whether as constituent elements or as elemental heavy metals, and does not exclude the presence of heavy metals as unavoidable impurities. Here, "substantially free of heavy metals" means that the heavy metal content in the composition is 0.1 ppm or less.

[0046] [Forms of Photon Upconversion Materials] The photon upconversion material of the present invention exhibits photon upconversion luminescence in both solution and solid states. Therefore, the photon upconversion material of the present invention may be used as a solution in which the donor compound and acceptor compound are dissolved in a solvent, or as a solid. Here, "solid" means a material that is in a solid state at room temperature (25°C) at 1 atmosphere. The solution, which is a photon upconversion material of the present invention, has an atom (a specific atomic chain bond atom) to which a group with a chain length of 4 or more atoms is bonded, on one of the aromatic ring units contained in the π-conjugated condensed polycyclic structure of the acceptor compound. Compared to a case where such an atomic chain bond atom is not bonded to the π-conjugated condensed polycyclic structure of the acceptor compound, the threshold excitation intensity I thThe coefficient is significantly lower, resulting in extremely high UC efficiency. Furthermore, the photon upconversion material of the present invention is also characterized by exhibiting UC emission in the solid state. This is presumed to be because the steric hindrance of groups with a chain length of 4 atoms or more introduced into the π-conjugated condensed polycyclic structure of the acceptor compound moderately suppresses intermolecular interactions that reduce luminescence efficiency. Therefore, the photon upconversion material of the present invention can also be a solid photon upconversion material. Solid photon upconversion materials offer a high degree of freedom in device design when applied to devices, and can be applied to various devices in which functional elements are composed of films or film laminates, thus offering high practicality. Here, the solid photon upconversion material is preferably a crystalline solid, preferably a solid in the form of a film, and more preferably a crystalline solid film. The crystalline nature of the photon upconversion material can be confirmed by observing diffraction peaks originating from the crystal in the X-ray diffraction spectrum. Because the photon upconversion material is a crystalline solid, triplet exciton diffusion from the donor compound to the acceptor compound is expected to be rapid, and the threshold excitation intensity I th This will be advantageous for reduction. It is preferable that the crystalline solid photon upconversion material has the same crystallinity as the acceptor compound. The fact that the photon upconversion material has the same crystallinity as the acceptor compound can be confirmed by measuring the X-ray diffraction spectra of the crystalline powders of the photon upconversion material and the acceptor compound, and observing the diffraction peak of the photon upconversion material in the region overlapping with the diffraction peak of the acceptor compound.

[0047] Solid films of photon upconversion materials can be formed using a wet process, for example, by supplying a solution containing an acceptor compound and a donor compound onto a substrate to form a solution film, and then volatilizing and removing the solvent from this solution film to obtain the film. The wet process here can be carried out by conventional methods, such as drop casting, spin coating, slit coating, inkjet (spray) printing, gravure printing, offset printing, and flexographic printing, but is not limited to these methods. The solvent used in the solution of the acceptor compound and donor compound is also not particularly limited, and an appropriate solvent that can dissolve the acceptor compound and donor compound can be appropriately selected from among the organic solvents commonly used in wet processes. The thickness of the solid film is not particularly limited and can be appropriately selected according to the application. The thickness of the solid film is, for example, 10 nm to 100 μm, and may be, for example, 10 nm to 100 nm or 100 nm to 1 μm, or 1 μm to 100 μm. Furthermore, the photon upconversion material of the present invention is preferably a solid and does not contain non-volatile solvents. Here, "non-volatile solvent" means a solvent with a vapor pressure of 10 Pa or less at 20°C. Specifically, examples include glycerin, diethylene glycol, polyethylene glycol, polypropylene glycol, ethylene glycol, propylene glycol, butylene glycol, triethylene glycol, thiodiglycol, hexylene glycol, 2-pyrrolidone, etc. Also, "does not contain non-volatile solvents" means that the non-volatile solvent content is 10 ppm or less.

[0048] (Molecular sizes of acceptor and donor compounds) To achieve highly efficient photon upconversion, it is preferable that the molecular sizes of the acceptor compound and the donor compound do not differ significantly. In particular, in crystalline solid photon upconversion materials, if the dimensions of the donor and acceptor molecules do not differ significantly, disorder in the crystal structure is suppressed, enabling highly efficient photon upconversion. The molecular size of each acceptor and donor compound can be indicated by "the distance R to the atom furthest from the center of mass of the molecule," and in this specification, "molecular size" refers to this "distance R." "Distance R" can be estimated from the most stable structure in the ground state, obtained by density functional theory. The ratio of the distance R of the donor compound to the distance R of the acceptor compound is R. D / R A It is preferably less than 1.5, more preferably less than 1.4, even more preferably less than 1.3, and even more preferably less than 1.2.

[0049] <Usage of visible light / ultraviolet light conversion type photon upconversion materials> In a preferred embodiment of the present invention, the photon upconversion material is a visible light / ultraviolet light conversion type photon upconversion material in which, when irradiated with visible light, the photon upconversion function is activated and ultraviolet light is emitted as UC light. With this visible light / ultraviolet light conversion type photon upconversion material, visible light can be converted to ultraviolet light by irradiating it with visible light using, for example, the following method. In other words, the irradiated visible light may be a single light with a maximum emission wavelength at a specific wavelength in the visible region, a composite light composed of multiple visible light sources with different maximum emission wavelengths, or a composite light composed of light with continuous wavelengths in the visible region. Furthermore, the light irradiated onto the photon upconversion material may include light other than visible light. Examples of irradiation sources include sunlight, LEDs, Xe lamps, and lasers. The irradiation intensity may range from 0.1 to 1000 mW / cm². 2Preferably, the range is 0.5 to 100 mW / cm². 2 It is more preferable that the power is 1-50 mW / cm². 2 It is even more preferable that this is the case. The irradiation time is not particularly limited; for example, it should be 1 minute or more. In visible light / ultraviolet light conversion type photon upconversion materials, irradiation with visible light causes the emission of ultraviolet light as unintended ultraviolet (UC) light. This emission should be observed in the ultraviolet region (wavelength range of 200-400 nm). The specific absorption and emission wavelength ranges vary depending on the application and purpose of the UC light. For example, when using UC light with photocatalysts such as titanium dioxide, which do not absorb in the visible to near-infrared region, it is particularly preferable that the absorption of the irradiated light is observed in the range of 400-800 nm, and the emission of ultraviolet light is observed in the range of 300-400 nm. Here, "absorption of irradiated light is observed in the range of 400-800 nm" means that the wavelength range in which the absorbance of the material is 0.01 or higher is 400-800 nm, and "ultraviolet emission is observed in the range of 300-400 nm" means that the emission maximum wavelength of the ultraviolet light is in the range of 300-400 nm, or the emission maximum wavelength is near 300-400 nm, and an emission intensity of 50% or more of the intensity at that emission maximum wavelength is observed at 300 nm or 400 nm. Ultraviolet light obtained in a manner in which ultraviolet emission is observed within this range can be effectively utilized for photocatalysis. When using UC light for curing photocurable resins, it is preferable that the emission of UC light is observed in the range of 300-360 nm, in which many initiators show strong absorption. The wavelength of UC light can be controlled by adjusting the combination of donor and acceptor compounds that constitute the photon upconversion material.

[0050] <Other uses of conversion-type photon upconversion materials> Other examples of conversion-type photon upconversion materials include photon upconversion materials that convert long-wavelength visible light to short-wavelength visible light. In this case, "visible light" in the above <Method of Use of Visible Light / Ultraviolet Light Conversion Type Photon Upconversion Material> can be read as "long-wavelength visible light," and "ultraviolet light" can be read as "short-wavelength visible light." Other examples of conversion-type photon upconversion materials include photon upconversion materials that convert near-infrared light to visible light. In this case, "visible light" can be read as "near-infrared light" and "ultraviolet light" as "visible light" in the above <Method of Use of Visible Light / Ultraviolet Light Conversion Type Photon Upconversion Materials>.

[0051] <Photon Upconversion Laminate> The photon upconversion laminate of the present invention is a laminate having a structure in which a solid layer made of a photon upconversion material and a layer containing a low oxygen permeable polymer are stacked. For a description of photon upconversion materials, please refer to the "Description of Photon Upconversion Materials" section. For solid layers, please refer specifically to the "Solid Photon Upconversion Materials" section under "Forms of Photon Upconversion Materials." The "low oxygen permeable polymer" in this invention has an oxygen permeability coefficient of 1 × 10⁻⁶ at 30°C. -15 cm 3 cm / cm 2 This refers to materials with an oxygen permeability of less than or equal to sPa. Examples of low-oxygen-permeable polymers include polyvinyl alcohol, polyacrylonitrile, polyvinylidene chloride, and polyacrylonitrile. Laminates formed by stacking a solid layer of photon upconversion material with a layer containing a low-oxygen-permeable polymer exhibit uninterrupted emission even when fabricated under atmospheric conditions, making them highly practical. Here, the solid layer made of the photon upconversion material and the layer containing the low oxygen permeable polymer may be alternately laminated, with at least one of them being two or more layers. The thickness of the solid layer made of the photon upconversion material and the layer containing the low oxygen permeable polymer can be appropriately selected depending on the application, and can be in the range of 10 to 100 μm, for example. [Examples]

[0052] The features of the present invention will be further described in detail below with reference to examples and comparative examples. The materials, amounts used, proportions, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following specific examples. In the following examples, an absolute emission quantum yield analyzer (Hamamatsu Photonics: C9920-01) was used to measure the emission quantum yield, and a 445 nm laser (RGB photonics: Lambda beam), a multi-channel spectrometer (Otsuka Electronics: MCPD-9800), a photodiode sensor (OPHIR Photonics: PD300-UV), and a CCD beam profiler (OPHIR Photonics: SP620) were used to evaluate the UC characteristics. A 425 nm short-pass filter was used to cut off the excitation light when evaluating the UC characteristics. Density functional theory calculations were performed using B3LYP as the functional, with 6-311G(d,p) as the basis set for structural optimization and 6-311++G(d,p) as the basis set for energy calculations. X-ray diffraction measurements were performed using a benchtop X-ray diffractometer (Bruker: D2 phaser), and single-crystal X-ray structure analysis was performed using a single-crystal X-ray structure analyzer (Rigaku: Synergy-R / DW). In this example, the threshold excitation intensity I of the photon upconversion material (sample to be measured) th and UC efficiency η UC , the excited triplet lifetime τ of the compound (the compound being measured) TThe following method was used to determine this. Furthermore, the maximum value around 370 nm in the measured emission spectrum was considered to be the peak of UC emission.

[0053] (1) Threshold excitation intensity I th The excitation light intensity applied to the sample under measurement was changed, and the UC emission spectrum was measured for each excitation light intensity. The UC emission intensity was plotted on a log-log graph with the vertical axis and the excitation light intensity on the horizontal axis. In this log-log plot, the slope of the line that linearly fits the plot changes from 2 to 1. Therefore, the excitation light intensity at the point where the fitting line in the region with a slope of 2 intersects with the fitting line in the region with a slope of 1 is defined as the threshold excitation intensity I. th This was done. Furthermore, if a region with a slope of 2 cannot be detected, the following calculation formula is used: th This was calculated. For details of this calculation method, please refer to Y. Murakami and K. Kamada, Phys. Chem. Chem. Phys., 2021, 23, 18268-18282.

[0054]

number

[0055] In the equation, x represents the excitation light intensity, y represents the UC emission intensity, and a and b represent constants. Threshold excitation intensity I th It is preferable that the light intensity is below the excitation wavelength range of the solar spectrum.

[0056] (2) UC efficiency η UC UC efficiency of the sample to be measured in solution η UC This was calculated using a standard sample with a known absolute luminescence quantum yield, based on the relative luminescence intensity to the luminescence intensity of that standard sample, using the following formula.

number

[0057] In the formula, Φ represents the emission quantum yield, A represents the absorbance, I represents the excitation light intensity, E represents the spectral integral of the UC emission, and n represents the refractive index of the solvent. The subscripts Φ, A, I, and E represent the sample having that characteristic value, "std" is the standard sample, and "UC" is the sample being measured. For example, Φ std This represents the emission quantum yield of the standard sample. Here, the standard sample is a 20 μM tetrahydrofuran solution of coumarin 6 (Φ std =91%) was used. Furthermore, the UC efficiency η of the solid film sample to be measured UC This value was calculated by doubling the absolute UC quantum yield measured with an absolute luminescence quantum yield measuring device and normalizing the maximum value to 100%.

[0058] (3) Excited triplet lifetime τ T teeth Excited triplet lifetime τ of the compound being measured T This was calculated by measuring the transient decay curve of the emission intensity of the sample under measurement and performing tail fitting of delayed emission using the following formula.

[0059]

number

[0060] In the equation, τ UC UC luminescence lifetime, τ T These represent the excited triplet lifetimes, respectively. Excited triplet lifetime τ of the acceptor compound T,A The longer the interval, the higher the threshold excitation light intensity I th The value tends to decrease. Therefore, τ T,A It is preferable that it be long.

[0061] [Acceptor compounds and donor compounds] The acceptor and donor compounds used in each example and comparative example are shown below. Acceptor compound [ka]

[0062] Donor compounds [ka]

[0063] Here, commercially available comparative compounds A1 and D1 (both manufactured by Tokyo Chemical Industry Co., Ltd.), comparative compound A2 (manufactured by Sigma-Aldrich), compounds D2 and D3 (both manufactured by NARD Laboratories), and compound D4 (manufactured by Ossila) were used, while compounds A1 to A4 were synthesized using the following procedure.

[0064] (Synthesis Example 1) Synthesis of Compound A1 [ka]

[0065] 5,10-Dihydroindeno[2,1-a]indene (2.04 g, 10.00 mmol) was placed in a three-necked flask and dissolved in anhydrous tetrahydrofuran (50.0 mL) under a nitrogen atmosphere. This flask was left to stand in a -78°C chilling solution (dry ice / acetone) for 30 minutes. Then, n-butyllithium n-hexane solution (concentration: 2.6 mol / L, amount added: 15.00 mL, 39.0 mmol) was slowly added dropwise to the solution in the flask and left to stand for 15 minutes. 1-iodopropane (3.8 mL, 39.1 mmol) was slowly added to this solution, the flask was purged with nitrogen, and the mixture was allowed to return to room temperature and stirred for 68.5 hours. Concentrated hydrochloric acid (4.0 mL) and sodium thiosulfate (10 mL) were added to this reaction solution and stirred for 1 hour. Extraction was then performed with hexane and water, and the solvent of the organic layer was removed by vacuum distillation. The obtained crude product was purified using an open column (silica gel column) with n-hexane as the developing solvent, and recrystallization with methanol was performed twice. Through these steps, compound A1 was obtained in a yield of 0.070 g and 2%. 1H-NMR (400 MHz, CYCLOHEXANE-D12) δ 7.17-7.27 (4H), 7.10-7.17 (2H), 7.02-7.10 (2H), 1.88-2.17 (8H), 0.77-0.99 (4H), 0.58-0.75 (16H) Elemental analysis, calculated for C 28 H 36 : H 9.74 C 90.26; found H 9.86, C 90.03.

[0066] (Synthesis Example 2) Synthesis of Compound A2 [ka]

[0067] 5,10-Dihydroindeno[2,1-a]indene (1.01 g, 4.96 mmol) was placed in a three-necked flask and dissolved in anhydrous tetrahydrofuran (10.0 mL) under a nitrogen atmosphere. This flask was left to stand in a -98°C chilling solution (liquid nitrogen / methanol) for 30 minutes. Then, n-butyllithium solution in n-hexane (concentration: 2.6 mol / L, amount added: 5.00 mL, 13.0 mmol) was slowly added dropwise to the solution in the flask, and isobutyl bromide (1.86 g, 13.6 mmol) was slowly added. After purging the flask with nitrogen, the flask was allowed to return to room temperature and the solution was stirred for 13 hours. Concentrated hydrochloric acid (0.40 mL) and sodium thiosulfate (10 mL) were added to this reaction solution and stirred for 1 hour. The solvent was then removed by distillation under reduced pressure, and the target product was extracted using a phase separator. The resulting crude product was purified by flash column chromatography using n-hexane as the developing solvent, and recrystallization was performed with acetone. Through the above process, compound A2 was obtained in a yield of 0.29 g and 14%. 1 H-NMR (400 MHz, Cyclohexane-D12 ,TMS): δ (ppm) 7.21-7.33 (4H), 7.12-7.18 (2H), 7.02-7.08 (2H), 2.04-2.13 (4H), 1.91-2.00 (4H), 0.95-1.13 (4H), 0.53-0.71 (12H), 0.27-0.44 (12H). Elemental analysis, calculated for C 32 H 44 : H 10.35 C 89.65; found H 10.36, C 89.54.

[0068] (Synthesis Example 3) Synthesis of Compound A3 [ka]

[0069] 5,10-Dihydroindeno[2,1-a]indene (2.04 g, 10.0 mmol) was placed in a three-necked flask and dissolved in anhydrous tetrahydrofuran (50.0 mL) under a nitrogen atmosphere. This flask was left to stand in a -78°C chilling solution (dry ice / acetone) for 30 minutes. Then, n-butyllithium solution in n-hexane (concentration: 1.6 mol / L, amount added: 25.00 mL, 40.0 mmol) was slowly added dropwise to the solution in the flask. 1-Bromo-2-ethylbutane (5.00 g, 30.3 mmol) was slowly added to this solution, the flask was purged with nitrogen, and the solution was allowed to return to room temperature and stirred for 24 hours. Concentrated hydrochloric acid (4.00 mL) and sodium thiosulfate (10 mL) were added to this reaction solution and stirred for 1 hour, after which the solvent was removed by distillation under reduced pressure. The residue was separated by liquid-liquid extraction with water and toluene, and the organic layer was dehydrated with anhydrous sodium sulfate. The obtained crude product was purified using a flash column with n-hexane as the developing solvent, followed by recrystallization with acetone and then with methanol. Through these steps, compound A3 was obtained in a yield of 0.72 g and 13%. 1 H-NMR (400 MHz, Acetone-D6 ,TMS): δ (ppm) 7.42-7.54 (4H), 7.21-7.31 (2H), 7.11-7.21 (2H), 2.08-2.19 (8H), 0.46-1.14 (44H). Elemental analysis, calculated for C 40 H 60 : H 11.18 C 88.82; found H 11.06, C 88.61.

[0070] (Synthesis Example 4) Synthesis of Compound A4 [ka]

[0071] 5,10-Dihydroindeno[2,1-a]indene (2.04 g, 10.00 mmol) was placed in a three-necked flask and dissolved in anhydrous tetrahydrofuran (50.0 mL) under a nitrogen atmosphere. This flask was left to stand in a -78°C chilling solution (dry ice / acetone) for 30 minutes. Then, n-butyllithium n-hexane solution (concentration: 2.6 mol / L, amount added: 15.00 mL, 39.0 mmol) was slowly added dropwise to the solution in the flask and left to stand for 15 minutes. 1-iodopentane (5.2 mL, 40.0 mmol) was slowly added to this solution, the flask was purged with nitrogen, and the flask was returned to room temperature and stirred for 76 hours. To this reaction solution, concentrated hydrochloric acid (4.1 mL) and aqueous sodium thiosulfate solution (concentration: 4.0 mol / L, amount added: 10.0 mL, 40.0 mmol) were added and the mixture was stirred for 1 hour. Extraction was then performed with tetrahydrofuran and brine, and the solvent of the organic layer was removed by reduced pressure distillation. The resulting crude product was purified using an open column (silica gel column) with n-hexane as the developing solvent, and further purified using a flash column with n-hexane as the developing solvent, followed by recrystallization with methanol. Compound A4 was obtained in a yield of 0.069 g and 1% through the above steps.

[0072] 1 H-NMR (400 MHz, Acetone-D6 ,TMS): δ (ppm) 7.36-7.44 (4H), 7.15-7.30 (4H), 2.07-2.24 (8H), 0.50-1.17 (36H). Elemental analysis, calculated for C 36 H 52 : H 10.81 C 89.19; found H 10.62, C 89.16.

[0073] For each acceptor compound, the excited singlet energy level E was determined by density functional theory. S1,A , excited triplet energy level E T1,A and E T1,A Twice the value of (2 × E T1,A The excited triplet energy levels E of each donor compound are shown in Table 1. T1,D The literature values ​​are shown in Table 2. Furthermore, Table 3 shows the fluorescence quantum yield measured using an absolute emission quantum yield analyzer for the crystalline powder of each acceptor compound and the pulverized powder obtained by grinding this crystalline powder.

[0074] [Table 1]

[0075] [Table 2]

[0076] [Table 3]

[0077] As shown in Table 3, the indenoindene skeleton sp 3In crystalline powders of compounds A1-A4, which have a structure in which a group with a chain length of 4 or more atoms is bonded to carbon, a high fluorescence quantum yield of over 60% was obtained. This suggests that intermolecular interactions that reduce luminescence efficiency are moderately suppressed by the side chains (groups with a chain length of 4 or more atoms). Furthermore, compounds A1 and A2 in particular maintained a high fluorescence quantum yield of over 70% even after operations that reduce crystallinity, such as grinding. From this, it was inferred that photon upconversion materials using compounds A1 and A2 as acceptor compounds can exhibit high UC efficiency even when fabricated using film deposition methods that allow for rapid drying but tend to reduce crystallinity, such as drop casting, spin coating, and spraying.

[0078] (Example 1) Preparation and evaluation of a solution containing compound A2 and compound D1 (UC solution 1) Compounds A2 and D1 were dissolved in tetrahydrofuran in a glove box under an Ar atmosphere to prepare a tetrahydrofuran solution (UC solution 1), which was then injected into a screw-capped quartz cell (optical path length: 1 mm) and sealed. Here, the concentration of compound A2 was 10 mM and the concentration of compound D1 was 100 μM. When the prepared UC solution 1 was irradiated with excitation light at 445 nm, a peak of UC emission (emission maximum wavelength: 369.0 nm) was observed. Furthermore, the threshold excitation intensity I of UC solution 1 was also determined. th This is 3.34 mW / cm². 2 UC efficiency η UC It is 8.79 W / cm² 2 The excitation light intensity is 26.4%, and the excited triplet lifetime τ of compound A2 is 26.4%. T,A The elution interval was 8.10 ms. Compound A2, due to the introduction of an alkyl chain, showed significantly improved solubility compared to comparative compound A1, which lacks an alkyl chain, and exhibited strong UC emission even at a high concentration of 10 mM. Furthermore, the threshold excitation intensity I of UC solution 1 using compound A2 was also determined. th This is the I of comparative UC solution 1 using comparative compound A1. th (110mW / cm 2、 This was significantly lower compared to (see Comparative Example 1 below).

[0079] (Example 2) Preparation and evaluation of a solid film containing compound A2 and compound D1 (drop casting method) A tetrahydrofuran solution of compound A2 and compound D1 was prepared using the same procedure as in Example 1, with the concentration of compound A2 changed to 1 mM and the concentration of compound D1 to 100 μM. This tetrahydrofuran solution was deposited on a quartz substrate by drop casting to produce a solid film (UC film 1). The film was formed. Furthermore, another quartz substrate was placed on top of this UC film 1, and the sides were sealed with a two-component epoxy resin repair adhesive (ThreeBond Corporation, 2086M) to obtain a sealed body. The fabricated UC film 1 was subjected to 445 nm excitation light at 1.1 mW / cm². 2 ~8.9W / cm 2 The UC film was irradiated with varying intensity within the specified range, and the UC emission spectrum was measured for each excitation light intensity. The measured UC emission spectra are shown in Figure 2. Threshold excitation intensity I of UC film 1 th It is 1.1 mW / cm² 2 UC efficiency η UC It is 39 W / cm² 2 The excitation light intensity is 0.065%, and the excited triplet lifetime τ of compound A2 is 0.065%. T,A The duration was 2.73 ms. The irradiation intensity in the 440 nm to 450 nm range of the solar spectrum is typically 1.4 mW / cm². 2 This is the extent of the effect. Therefore, it has been shown that UC film 1 can be used as a solvent-free solid material that can convert visible light to ultraviolet light at an irradiation intensity similar to that of sunlight.

[0080] Furthermore, Figure 3 shows the results of X-ray diffraction measurements of UC film 1, and Figure 4 shows the results of single-crystal X-ray structural analysis of compound A2. Figure 3 shows both the X-ray diffraction pattern of a film (A2 film) prepared by drop-casting a tetrahydrofuran solution of compound A2, and the X-ray diffraction pattern of crystalline powder of compound A2. As shown in Figure 3, a diffraction pattern similar to that of the crystalline powder of compound A2 was observed in UC film 1. This confirmed that UC film 1 is crystalline. Furthermore, from the single-crystal X-ray structure analysis results shown in Figure 4, it was confirmed that compound A2 has a molecular arrangement in which the nearest neighbor distance between carbon atoms forming a π-conjugated plane is approximately 0.4 nm, allowing for the transfer of excitation triplet energy.

[0081] (Examples 3, 4, 5) Preparation and evaluation of solid films containing compound A1, A3, or A4 and compound D1 (drop casting method) In Example 3, compound A1 was used instead of compound A2, and a solid film (UC film 2) was formed using the same procedure as in Example 2 to produce a seal (Example 4). In Example 5, compound A4 was used instead of compound A2, and a solid film (UC film 4) was formed using the same procedure as in Example 2 to produce a seal (Example 5). No UC emission was detected in the solid film (UC film 2) using compound A1. This indicates that a branched alkyl chain is preferable to a linear alkyl chain when introduced into the acceptor compound. When the fabricated UC films 3 and 4 were irradiated with 445 nm excitation light at varying intensity, and the UC emission spectra were measured for each excitation light intensity, the UC emission spectra showing the same trend as in Figure 2 were observed, and the threshold excitation intensity I of UC film 3 using compound A3 was determined. th It is 0.41 W / cm² 2 The excited triplet lifetime τT,A of compound A3 was 2.37 ms. Furthermore, the threshold excitation intensity I of UC film 4 using compound A4 was also determined. th It is 53 mW / cm² 2 , the excited triplet lifetime τ of compound A4 T,A The response time was 0.57 ms.

[0082] (Example 6) Fabrication and evaluation of a laminated film containing a layer (UC layer) with a PVA layer containing compound A2 and compound D1 (spin coating method) Using toluene instead of tetrahydrofuran, toluene solutions of compound A2 and compound D1 were prepared using the same procedure as in Example 1. Here, the concentration of compound A2 was 30 mM and the concentration of compound D1 was 300 μM. A PVA layer was formed by dropwise adding 100 μL of a 4 wt% polyvinyl alcohol aqueous solution onto a quartz substrate and spin-coating at 2000 rpm. A solid UC layer was then formed by dropwise adding 40 μL of the prepared toluene solution and spin-coating at 2000 rpm. This operation was repeated four times to produce a solid laminated film (UC film 5) in which four PVA layers and four UC layers were alternately layered. The spin-coating of the laminated film was performed under atmospheric conditions. The fabricated UC film 5 was exposed to excitation light of 445 nm at 131 W / cm². 2 When the light was irradiated and the emission spectrum was measured, a peak in UC emission (maximum emission wavelength: 370 nm) was confirmed.

[0083] (Examples 7 and 8) Preparation and evaluation of solid films containing compound A2 and compound D3 or D4 (spin coating method) A tetrahydrofuran solution of compound A2 and compound D3 was prepared using the same procedure as in Example 1. Here, the concentration of compound A2 was 100 mM and the concentration of compound D3 was 1 mM. This tetrahydrofuran solution was dropped onto a quartz substrate and a solid film (UC film 6) was formed by spin-coating at 1500 rpm (Example 7). A sealed body was prepared by placing another quartz substrate on top of this UC film 5 and sealing the sides with a two-component epoxy resin repair adhesive (ThreeBond, 2086M). The prepared UC film 6 was exposed to excitation light at 445 nm at 1.7 W / cm². 2 When the light was irradiated and the emission spectrum was measured, a UC emission peak (maximum emission wavelength: 369 nm) was confirmed. Furthermore, compound D4 was used instead of compound D3, and a solid film (UC film 7) was formed using the same procedure to create a encapsulant (Example 8). The fabricated UC film 7 was exposed to excitation light at 445 nm at 1.7 W / cm². 2When the light was irradiated and the emission spectrum was measured, a peak in UC emission (maximum emission wavelength: 370 nm) was similarly confirmed.

[0084] (Comparative Examples 1 and 2) Preparation and evaluation of a solution (comparative solution 1) containing comparative compound A1 or A2 and compound D1. Using comparative compound A1 or comparative compound A2 instead of compound A1, a tetrahydrofuran solution of comparative compound A1 and compound D1 (comparative solution 1) and a tetrahydrofuran solution of comparative compound A2 and compound D1 (comparative solution 2) were prepared using the same procedure as in Example 1. Each solution was then injected into a screw-capped quartz cell and sealed. In comparative solution 1, the concentration of comparative compound A1 was 1 mM and the concentration of compound D1 was 50 μM, while in comparative solution 2, the concentration of comparative compound A2 was 10 mM and the concentration of compound D1 was 100 μM. Threshold excitation intensity I of comparative solution 1 th It is 92.4 mW / cm² 2 UC efficiency η UC It is 4.5 W / cm² 2 The excitation light intensity was 8.4%, and the excited triplet lifetime τ of comparative compound A1 was 8.4%. T,A The threshold excitation intensity I of comparative solution 2 was 1.41 ms. th The reading is 56.8 mW / cm². 2 UC efficiency η UC It is 26 W / cm² 2 The excitation light intensity was 29.09%, and the excited triplet lifetime τ of comparative compound A2 was 29.09%. T,A The response time was 1.02ms.

[0085] (Comparative Examples 3 and 4) Preparation and evaluation of solid films (comparative films 1 and 2) containing comparative compound A1 or A2 and compound D1 (drop casting method) Comparative compound A1 was used instead of compound A1, and a solid film (comparative film 1) was formed using the same procedure as in Example 2 to produce a seal (Comparative Example 3). Furthermore, comparative compound A2 was used instead of compound A1, and a solid film (comparative film 2) was formed using the same procedure as in Example 2 to produce a seal (Comparative Example 4). Comparison film 1 was exposed to 445nm excitation light at 1.8W / cm². 2When the emission spectrum was measured after irradiation, no peak of UC emission was detected. Furthermore, although UC emission was confirmed for comparison film 2, its threshold excitation intensity I th It is 190 mW / cm² 2 UC efficiency η UC It is 57 W / cm² 2 The excited triplet lifetime τ of comparative compound A2 is 0.016%. T,A The response time was 0.40ms.

[0086] [Investigation of molecular size] To achieve highly efficient photon upconversion in the solid state, it is desirable that the sizes of the donor molecule and the acceptor molecule do not differ significantly. Therefore, here, we determine the "distance R to the atom furthest from the center of gravity of the molecule," which is an indicator of molecular size, for both the acceptor compound and the donor compound, and calculate the ratio R of the donor compound's distance to the acceptor compound's distance. D / R A The following was investigated. Table 4 shows the distance R of the acceptor compound estimated based on the most stable ground state structure obtained by density functional theory, and Table 5 shows the distance R of the donor compound. For structural optimization of the acceptor compound, the functional B3LYP and basis set 6-311G(d,p) were used, and for structural optimization of the donor compound, the functional B3LYP and SDD as the basis set for Ir and 6-31G(d,p) as the basis set for C, H, N, O, and S were used.

[0087] [Table 4]

[0088] [Table 5]

[0089] In Example 8, R D / R A A peak in UC emission has been observed in a solid film (UC film 7) combining compound A2 and compound D4, both of which have a ratio of 1.49. From this, RD / R A It was found that a value of less than 1.5 is preferable. [Industrial applicability]

[0090] The photon upconversion material of the present invention exhibits photon upconversion luminescence in both solution and solid states, and can therefore be constructed as a solid film-type photon upconversion material. For this reason, the photon upconversion material of the present invention can be applied to various elements that constitute functional components in films or film laminates, demonstrating high industrial applicability.

Claims

1. An acceptor compound having a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit (where any of the aromatic ring units is bonded to a group having a chain length of 4 atoms or more, i.e., sp ３ A photon upconversion material comprising a carbon atom, a silicon atom bonded to a group having a chain length of four or more atoms, a nitrogen atom bonded to a group having a chain length of four or more atoms, or a boron atom bonded to a group having a chain length of four or more atoms, and a donor compound that imparts triplet energy to the acceptor compound.

2. As the ring skeleton constituent atoms of the π-conjugated condensed polycyclic structure, the sp ３ The photon upconversion material according to claim 1, comprising carbon, the silicon atom, the nitrogen atom, or the boron atom.

3. As the ring skeleton constituent atoms of the π-conjugated condensed polycyclic structure, the sp ３ The photon upconversion material according to claim 2, comprising carbon, two silicon atoms, two nitrogen atoms, or two boron atoms.

4. The photon upconversion material according to claim 1, wherein the aromatic ring unit is a benzene ring.

5. The photon upconversion material according to claim 2, wherein the π-conjugated condensed polycyclic structure contains two benzene rings.

6. The photon upconversion material according to claim 3, wherein the π-conjugated condensed polycyclic structure has an indenoindene skeleton.

7. The photon upconversion material according to claim 1, wherein the group having a chain length of 4 atoms or more is an alkyl group having a chain length of 4 atoms or more, or an alkoxy group having a chain length of 4 atoms or more.

8. The photon upconversion material according to claim 1, wherein the acceptor compound is a compound represented by the following general formula (1). 【Chemistry 1】 In general formula (1), X １ and X ２ each independently represent a carbon atom, a silicon atom, a nitrogen atom or a boron atom. When X １ is a carbon atom or a silicon atom, n1 is 2, and when X １ is a nitrogen atom or a boron atom, n1 is 1. When X ２ is a carbon atom or a silicon atom, n2 is 2, and when X ２ is a nitrogen atom or a boron atom, n2 is 1. R １１ and R １２ each independently represent a hydrogen atom or a group having a chain length of 4 or more atoms, provided that at least one of R １１ , and at least one of R １２ is a group having a chain length of 4 or more atoms. R １３ and R １４ each independently represent a substituent. n3 and n4 each independently represent an integer of any one of 0 to 4.]

9. The photon upconversion material according to claim 1, wherein the molecular size of the donor compound is less than 1.5 times the molecular size of the acceptor compound.

10. The photon upconversion material according to claim 1, wherein the content of the donor compound is in the range of 0.01 to 10.0% in molar ratio relative to the content of the acceptor compound.

11. A photon upconversion material according to any one of claims 1 to 10, which is a solid.

12. The photon upconversion material according to claim 11, which does not contain a non-volatile solvent.

13. A photon upconversion material according to claim 11, having crystalline properties.

14. The photon upconversion material according to claim 11, which is in the form of a film.

15. A photon upconversion laminate having a structure in which a solid layer made of the photon upconversion material according to claim 11 and a layer containing a low oxygen permeable polymer are laminated together.

16. It has a π-conjugated condensed polycyclic structure containing at least one aromatic ring unit, Any of the aforementioned aromatic ring units is bonded to a group having a chain length of 4 atoms or more. ３ A compound comprising a carbon atom, a silicon atom bonded to a group with a chain length of four or more atoms, a nitrogen atom bonded to a group with a chain length of four or more atoms, or a boron atom bonded to a group with a chain length of four or more atoms.

Images