Compounds, light-emitting materials, and photoelectric conversion elements

Abstract

This invention provides a novel compound that exhibits luminescence properties in the long-wavelength region within the near-infrared area. [Solution] Compound represented by the following formula (1): [Formula 1] JPEG2026114573000020.jpg50169 In formula (1) above, A is selected from aromatic hydrocarbon rings and aromatic heterocycles, L represents a monovalent tridentate ligand, R1 is selected from a hydrogen atom, alkyl group, halogen atom, alkylcarbonyl group, arylcarbonyl group, alkoxyl group, alkenyl group, alkynyl group, cyano group, and aryl group, and X represents an oxygen atom or a sulfur atom.

Description

[Technical Field]

[0001] This disclosure relates to compounds, light-emitting materials, and photoelectric conversion elements. [Background technology]

[0002] Patent document 1 describes an organoiridium complex having a thiadiazopyridine ligand. Non-patent documents 1 to 3 describe Ir complexes having a tridentate ligand containing 2,5-diphenylpyridine. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] U.S. Patent Publication No. 2019-0218240 [Non-patent literature]

[0004] [Non-Patent Document 1] AJ Wilkinson et al "Luminescent Complexes of Iridium(III) Containing N∧C∧N-Coordinating Terdentate Ligands" Inorg. Chem. 2006, 45, 8685-8699 [Non-Patent Document 2] AJ Wilkinson et al "Synthesis and Luminescence of a Charge-Neutral, Cyclometalated Iridium(III) Complex Containing N∧C∧N- and C∧N∧C-Coordinating Terdentate Ligands" Inorg. Chem. 2004, 43, 6513-6515 [Non-Patent Document 3] W. Cheung et al "Synthesis, structure and reactivity of iridium complexes containing a bis-cyclometalated tridentate C^N^C ligand" Dalton Trans., 2021, 50, 8512-8525 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] Currently, inorganic LEDs are mainly used as light sources that emit light in the near-infrared region, but organic EL light sources, which can be applied to a wider range of shapes, are expected to be more widely used.

[0006] The organoiridium complex having a thiadiazopyridine ligand described in Patent Document 1 is desired to have a further extension of its emission wavelength in order to be put into practical use as a luminescent dye. In addition, the Ir complex having a tridentate ligand containing 2,5-diphenylpyridine described in Non-Patent Documents 1 to 3 emit light in the visible range, and a further extension of its emission wavelength is desired.

[0007] This disclosure aims to provide a novel compound having emission properties in the long wavelength range in the near-infrared region. [Means for solving the problem]

[0008] In order to solve the aforementioned problems, the Discloser conducted thorough research and found that the above problems can be solved by an iridium complex having a tridentate ligand.

[0009] In other words, the gist of this disclosure is as follows: [1] A compound represented by the following formula (1); [ka] In the above formula (1), A is selected from an aromatic hydrocarbon ring having 6 to 20 carbon atoms and an aromatic heterocyclic ring having 2 to 19 carbon atoms, which may have a substituent; L represents a monovalent tridentate ligand; R1 is selected from a hydrogen atom, an alkyl group which may have a substituent, a halogen atom, an alkylcarbonyl group which may have a substituent, an arylcarbonyl group which may have a substituent, an alkoxyl group which may have a substituent, an alkenyl group which may have a substituent, an alkynyl group which may have a substituent, a cyano group, and an aryl group which may have a substituent; X represents an oxygen atom or a sulfur atom, a compound. [2] The L is a tridentate ligand represented by the following formula (2);

Chemical formula

Chemical formula

[0010] According to one aspect of this disclosure, it is possible to provide novel compounds having emission properties in the long wavelength range in the near-infrared region and related technologies. [Modes for carrying out the invention]

[0011] <Iridium complexes (compounds)> A compound relating to one aspect of this disclosure is an iridium complex (compound) represented by the following formula (1); [ka] In equation (1) above, A represents an aromatic hydrocarbon ring or an aromatic heterocycle; L represents a monovalent tridentate ligand; R1 is selected from a hydrogen atom, an alkyl group, a halogen atom, an alkylcarbonyl group, an arylcarbonyl group, an alkoxyl group, an alkenyl group, an alkynyl group, a cyano group, and an aryl group; X represents either an oxygen atom or a sulfur atom.

[0012] In one embodiment, the tridentate ligand represented by formula (1) has an oxadiazolopyridine structure or a thiadiazolopyridine structure having a carboxyl group, and the nitrogen atom of these structures, the carboxyl group, and A coordinate to iridium (Ir). By having an oxadiazolopyridine structure or a thiadiazolopyridine structure, the emission wavelength of this compound can be shifted to longer wavelengths in the near-infrared region.

[0013] Furthermore, the presence of a carboxyl group in iridium complexes can lower the energy of the lowest unoccupied orbital (LUMO) of the tridentate ligand, thereby shifting the emission wavelength of iridium complexes to longer wavelengths in the near-infrared region.

[0014] When A is selected from an aromatic hydrocarbon ring, examples of aromatic hydrocarbon rings include aromatic hydrocarbon groups having 6 to 20 carbon atoms, which may be monocyclic, fused, or linked rings, and may be substituted with substituents. Examples of such aromatic hydrocarbon rings include phenyl, naphthyl, anthryl, phenantrenyl, pyrenyl, perilenyl, and fluoranthenyl groups, with selection from phenyl, 1-naphthyl, and 2-naphthyl groups being more preferable. In this specification, aromatic hydrocarbon rings and aromatic heterocyclic rings (aromatic hydrocarbon groups and aromatic heterocyclic groups) may be described as monovalent groups for convenience, but unless otherwise specified, the meaning may also include groups with two or more valents. For example, a phenyl group refers to a group consisting of a monovalent benzene ring, but depending on the structure of the iridium complex, a phenyl group may more appropriately mean a divalent benzene ring structure. Furthermore, when the description of the bonding site in aromatic hydrocarbon rings and aromatic heterocycles is omitted, it implies that the bonding site is not specified for the group. However, it is also possible to selectively derive the bonding site depending on the structure of the aromatic hydrocarbon ring and aromatic heterocycle, for example, the 1,2-phenyl group (phenylene group).

[0015] Furthermore, when A is selected from aromatic heterocycles, examples of such aromatic heterocycles include aromatic hydrocarbon groups having 2 to 19 carbon atoms, which may be monocycles, fused rings, or linking rings, and may be substituted with substituents. Examples of such aromatic heterocycles include those containing a sulfur atom, an oxygen atom, or a nitrogen atom. Examples of aromatic heterocycles containing a sulfur atom include a thiophenyl group (the description of the bonding site is omitted below), a benzothienyl group, a dibenzothienyl group, and a benzothienobenzothienyl group, with 2-thienyl groups and 2-dibenzothienyl groups being more preferred. Furthermore, when selected from aromatic heterocycles containing an oxygen atom, examples of aromatic heterocycles containing an oxygen atom include a furanyl group, a benzofuranyl group, and a dibenzofuranyl group, with 2-furanyl groups and 2-dibenzofuranyl groups being more preferred. Aromatic heterocycles containing a nitrogen atom include, for example, a pyrrolyl group, a benzopyrrolyl group, a carbazoyl group, and a pyridyl group, with 2-benzopyrrolyl groups and 2-carbazoyl groups being more preferred.

[0016] In formula (1), R1 may be selected from, for example, a hydrogen atom, an alkyl group, a halogen atom, an alkylcarbonyl group, an arylcarbonyl group, an alkoxyl group, an alkenyl group, an alkynyl group, a cyano group, and an aryl group. When R1 is selected from an alkyl group, the alkyl group may be a C1 to C18 alkyl group, and may be linear, branched, or cyclic, and may be substituted with substituents. When R1 is selected from a halogen atom, examples include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and it is more preferable to select from a fluorine atom and a chlorine atom.

[0017] When R1 is selected from alkylcarbonyl groups, examples include alkylcarbonyl groups having alkyl residues with 1 to 18 carbon atoms, where the alkyl residues are linear, branched, or cyclic and may be substituted with substituents. Examples of such alkylcarbonyl groups, though not limited to them, include acetyl, ethylcarbonyl, propylcarbonyl, butylcarbonyl, cyclohexylcarbonyl, benzyloxy, and norbornyl groups.

[0018] When R1 is selected from arylcarbonyl groups, examples include arylcarbonyl groups having 6 to 20 carbon atoms, and the aryl group of the arylcarbonyl group may be, for example, a phenyl group, a 1-naphthyl group, a 2-naphthyl group, and a 2-phenantyl group, and may be substituted with substituents. When R1 is selected from heteroarylcarbonyl groups, examples include heteroarylcarbonyl groups having 4 to 20 carbon atoms, and although not limited to such heteroarylcarbonyl groups, examples include a thienylcarbonyl group.

[0019] When R1 is selected from alkoxyl groups, examples include alkoxyl groups having 1 to 18 carbon atoms and aryloxy groups. Examples of alkoxyl groups include methoxy, ethoxy, propoxy, butoxy, and cyclohexanoxy groups, and examples of aryloxy groups include phenoxy and naphthyloxy groups. These alkoxyl groups may be substituted with substituents.

[0020] When R1 is selected from alkenyl groups, examples include alkenyl groups having 2 to 18 carbon atoms, which may be linear or branched and may be substituted with substituents. Examples of such alkenyl groups include vinyl groups, allyl groups, and methylethynyl groups.

[0021] When R1 is selected from aryl groups, examples include aryl groups having 6 to 20 carbon atoms, which may be substituted with substituents. Examples of such aryl groups include phenyl, naphthyl, anthryl, phenantrenyl, pyrenyl, and fluoranthenyl groups, and it is more preferable that R1 be selected from phenyl, 1-naphthyl, and 2-naphthyl groups.

[0022] If A and R1 have substituents, the substituents can be selected from, for example, alkyl groups, halogen atoms, alkylcarbonyl groups, arylcarbonyl groups, alkoxyl groups, alkenyl groups, alkynyl groups, cyano groups, and aryl groups, and these substituents may be selected from the groups exemplified as R1 above.

[0023] X represents either an oxygen atom or a sulfur atom, and a sulfur atom is more preferable from the viewpoint of obtaining a stronger emission spectrum on the longer wavelength side.

[0024] The following are preferred examples of iridium complexes represented by formula (1).

[0025] [ka]

[0026] The above shows preferred examples of iridium complexes (compounds) represented by formula (1), but the tridentate ligand L of the iridium complex is not limited to 1,3-(2'-pyridyl)-2,4-dimethylbenzene. The iridium complex may have one tridentate ligand having an oxadiazolopyridine structure or a thiadiazolopyridine structure as represented by formula (1), and one tridentate ligand L. These tridentate ligands may be combined as appropriate, and the following iridium complexes can also be given as examples.

[0027] [ka]

[0028] The tridentate ligand L present in iridium complexes will be explained in more detail below.

[0029] (L: tridentate ligand) In formula (1) above, L represents a tridentate ligand, which can be selected from ligands represented by formula (2) below, for example. That is, an iridium complex according to one embodiment may be a compound coordinated by two tridentate ligands. Because L is a tridentate ligand, it can coordinate more strongly to the iridium ion than an iridium complex coordinated by a bidentate ligand, thereby improving the heat resistance and luminescence efficiency due to vibration suppression of the iridium complex.

[0030] [ka]

[0031] In formula (2) above, R2 and R4 are each independently selected from an aromatic hydrocarbon ring, an aromatic heterocycle, and a carboxyl group, and the tridentate ligand may be a monovalent tridentate ligand, that is, either R2 or R4 may be a carboxyl group. Furthermore, R2 and R4 may each be independently selected from an aromatic hydrocarbon ring and an aromatic heterocycle. For example, by selecting a carboxyl group for either R2 or R4, the emission wavelength of the iridium complex according to one embodiment can be shifted to a longer wavelength in the near-infrared region. Also, for example, by selecting a carboxyl group for either R2 or R4, the hydrophilicity of the iridium complex can be increased.

[0032] The presence of at least two of the groups R2, R3, and R4 being aromatic heterocycles allows the iridium complex to be neutral, thereby improving its sublimation properties. This makes it easier to increase the purity of the iridium complex through purification.

[0033] When R2 or R4 is selected from an aromatic hydrocarbon ring, it is selected from an aromatic hydrocarbon ring having 6 to 20 carbon atoms, and examples of such aromatic hydrocarbon rings include a phenyl group, naphthyl group, anthryl group, phenantrenyl group, pyrenyl group, perilenyl group, and fluoranthenyl group, and it is more preferable that it be selected from a phenyl group, a 1-naphthyl group, and a 2-naphthyl group.

[0034] When R2 or R4 is selected from an aromatic heterocycle, it is selected from aromatic heterocycles having 2 to 19 carbon atoms, and the aromatic heterocycle may include, for example, at least one heteroatom selected from a sulfur atom, an oxygen atom, and a nitrogen atom. When R2 or R4 is selected from an aromatic heterocycle containing a sulfur atom, examples of the aromatic heterocycle containing a sulfur atom include a thienyl group, a benzothienyl group, and a dibenzothienyl group, and it is more preferable that it be a 2-thienyl group, a 2-benzothienyl group, a 3-dibenzothienyl group, or a 4-dibenzothienyl group.

[0035] Furthermore, when R2 or R4 is selected from an aromatic heterocycle containing an oxygen atom, examples of aromatic heterocycles containing an oxygen atom include a furanyl group, a benzofuranyl group, and a dibenzofuranyl group, with 2-furanyl, 2-benzofuranyl, 3-dibenzofuranyl, and 4-dibenzofuranyl groups being more preferred.

[0036] Furthermore, when R2 or R4 is selected from an aromatic heterocycle containing a nitrogen atom, examples of aromatic heterocycles containing a nitrogen atom include imidazolyl, pyrazolyl, triazolyl, benzimidazolyl, indolyl, pyridyl, quinolyl, and isoquinolyl groups, with 2-pyridyl, 2-quinolyl, and 2-isoquinolyl groups being more preferred.

[0037] Furthermore, R2 and R4 may each independently contain two or more heteroatoms. Examples of aromatic heterocycles containing two or more heteroatoms include oxazolyl groups, benzoxazolyl groups, thiazolyl groups, benzothiazolyl groups, diazoyl groups, and benzodiazoyl groups, with 2-oxazolyl groups, 2-benzoxazolyl groups, 2-thiazolyl groups, and 2-benzothiazolyl groups being more preferred.

[0038] R3 is selected from aromatic hydrocarbon groups and aromatic heterocycles bonded to a monocyclic ring of six or five members, or a fused ring containing part of such monocyclic rings, with R2 and R4 bonded at the 1,3 positions. R3 coordinates the π-conjugated electrons of the aromatic hydrocarbon or the lone pair of electrons of the heteroatom located between R2 and R4 to the iridium ion.

[0039] When R3 is selected from an aromatic hydrocarbon ring, examples of such aromatic hydrocarbon rings include a 1,3-phenylene group and a 1,3-naphthylene group, and it is more preferable that the 1,3-phenylene group and the 1,3-naphthylene group have substituents at either the 4th or 6th position or both.

[0040] When R3 is selected from an aromatic heterocycle, the aromatic heterocycle may include, for example, at least one heteroatom selected from a sulfur atom and a nitrogen atom. When R3 is selected from an aromatic heterocycle containing a sulfur atom, the aromatic heterocycle containing a sulfur atom may include, for example, a thienylene group, and more preferably a 2,4-thienylene group.

[0041] Furthermore, if R3 is selected from an aromatic heterocycle containing a nitrogen atom, examples of aromatic heterocycles containing a nitrogen atom include pyridylene groups, quinolylene groups, and isoquinolylene groups.

[0042] R3 may contain two or more heteroatoms. Examples of aromatic heterocycles containing two or more heteroatoms include oxazolylene groups, benzooxazolylene groups, thiazoylene groups, and benzothiazoylene groups.

[0043] R2, R2, and R4 may each have substituents independently, and these substituents may represent, for example, an alkyl group, a haloalkyl group, an alkoxyl group, or a phenyl group, and adjacent substituents may form a ring.

[0044] When the substituents R2, R2, and R4 are selected from alkyl groups, alkoxyl groups, and phenyl groups, these substituents may be independently selected from the alkyl groups, alkoxyl groups, and phenyl groups exemplified as R1 above. Furthermore, when the substituents R2, R2, and R4 are haloalkyl groups, examples include haloalkyl groups having 1 to 6 carbon atoms, which may be linear, branched, or cyclic, and which may be substituted with at least one halogen atom selected from fluorine, chlorine, bromine, and iodine atoms.

[0045] A preferred example of a tridentate ligand represented by equation (2) is shown below.

[0046] [ka]

[0047] The L represented by formula (1) is not limited to the example compounds above, but may be selected from the tridentate ligands represented by formula (2-1) below. [ka] In formula (2-1) above, the tridentate ligand is a tridentate ligand in which two 2-pyridyl groups and a 1,3-phenylene group are bonded, R 21 ~R 41 '' is a substituent, each independently representing a deuterium atom, a halogen atom, an alkyl group, a haloalkyl group, an alkoxyl group, or a phenyl group, and adjacent substituents may form a ring, with p and r representing integers from 0 to 4, and q representing an integer from 0 to 3.

[0048] When L represented by formula (1) is the formula (2-1), the emission wavelength of the iridium complex can be shifted to a longer wavelength side in the near-infrared region, and the iridium complex can be purified to a high purity by sublimation purification.

[0049] R 21 ~R 41 When ~R is selected from halogen atoms, the halogen atom is selected from a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, and is more preferably a fluorine atom.

[0050] R 21 ~R 41 When ~R is selected from an alkyl group and an alkoxy group, the alkyl group and the alkoxy group include the alkyl group and the alkoxy group exemplified for R1 above. Further, when ~R 21 ~R 41 is selected from a haloalkyl group, the haloalkyl group includes a C1-C6 haloalkyl group exemplified as the substituent of R2, R2, and R4, and may be linear, branched, or cyclic, and is preferably substituted by at least one halogen atom selected from a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0051] q represents an integer of 0 to 3, is preferably 1 or 2, and more preferably 2. When q is 2 and R 31 is bonded to the 4,6 positions of 1,3-di(2'-pyridyl)-4,6-dimethylbenzene, it is possible to prevent the generation of by-products during the synthesis of the iridium complex.

[0052] R 21 ~R 41 may be such that adjacent groups (substituents) are bonded to each other to form a ring. For example, as exemplified below, adjacent R 31 may be bonded to each other to form a 1,3-naphthylene group, and adjacent R 21 to each other, or adjacent R 41The bonding between them may form a 2-quinolyl group or a 2-isoquinolyl group. Also, for example, adjacent R 21 and R 31 or adjacent R 31 and R 41 A 9-benzo[h]quinoline ring may be formed on the tridentate ligand by bonding to it.

[0053] [ka]

[0054] <Applications of Compounds> Near-infrared emission, while invisible to the human eye, can be visualized when combined with machine vision, and is expected to be used in anti-counterfeiting inks and display markers. Furthermore, due to its high skin penetration, it is also expected to be applied in medical fields such as biosensors and bioimaging markers, as well as as a light source for beauty, health promotion, treatment, and plant growth. While various OLED luminescent dyes that emit near-infrared light have been developed, there are few examples of luminescent dyes that emit light efficiently at 790 nm or higher.

[0055] A compound according to one aspect of this disclosure has absorption and emission characteristics in the near-infrared region or above 790 nm, and can be suitably used as a component in applications such as near-infrared luminescence markers, indicators, bioimaging, sensors, wavelength conversion films, light-emitting transistors, organic light-emitting diodes (OLEDs), electrochemiluminescent cells, photodynamic therapy, phototherapy, night vision displays, security, and anti-counterfeiting applications. A photoelectric conversion element is described below as an example of a preferred application.

[0056] <Photoelectric conversion element> A photoelectric conversion element according to one aspect of this disclosure comprises a layer containing an iridium complex (compound) according to one aspect between a pair of electrodes. The photoelectric conversion element may be a light-emitting element that emits light when a voltage is applied between the pair of electrodes.

[0057] The photoelectric conversion element may contain an iridium complex according to one embodiment as a photoelectric conversion layer. Here, the iridium complex may be contained in the photoelectric conversion layer as a light-emitting material or a dopant. In addition to the iridium complex according to one embodiment, the photoelectric conversion layer may also contain, for example, arylamine derivatives, carbazole derivatives, fluorescent dyes, and conjugated polymers such as polyvinylcarbazole. The method for forming the layer containing the iridium complex according to one embodiment is not limited and may be formed by vacuum deposition of the iridium complex or by coating a composition containing the iridium complex.

[0058] The photoelectric conversion element may be, for example, a multilayer photoelectric conversion element comprising other layers stacked on a photoelectric conversion layer, wherein at least one of the multiple layers may contain an iridium complex according to one embodiment. The multilayer photoelectric conversion element may be stacked in the order of hole transport layer, photoelectric conversion layer, electron transport layer, and cathode from the anode side. Here, the multilayer photoelectric conversion element may have multiple hole transport layers or multiple electron transport layers.

[0059] The anode of a photoelectric conversion element is an electrode that supplies holes to the photoelectric conversion layer, and it is effective for it to have a work function of 4.5 eV or more. Examples of materials for the anode include metals, alloys, metal oxides, and electrically conductive compounds. Examples of conductive metal oxides include tin oxide, zinc oxide, indium oxide, and indium tin oxide (ITO), while examples of metals include gold, silver, chromium, and nickel, and examples of electrically conductive compounds include mixtures of inorganic conductive substances such as copper iodide and copper sulfide and organic conductive materials such as polyaniline, polythiophene, and polypyrrol.

[0060] The cathode of a photoelectric conversion element is an electrode that supplies electrons to the photoelectric conversion layer. The cathode material can be a metal, alloy, metal halide, metal oxide, electrically conductive compound, or a mixture thereof. Examples of metal halides and metal oxides include fluorides or oxides of alkali metals and alkaline earth metals, while examples of metals and alloys include gold, silver, lead, and lithium-aluminum alloys.

[0061] A photoelectric conversion element may include a hole transport layer between the anode and the photoelectric conversion layer. The hole transport layer is a layer that transports holes supplied from the anode to the photoelectric conversion layer and also blocks electrons supplied from the cathode from being transported to the anode. When there are multiple hole transport layers, the hole transport layer in contact with the anode is sometimes called the hole injection layer.

[0062] Examples of materials for the hole injection layer and hole transport layer include aromatic heterogeneous compounds containing a nitrogen atom as a heterogeneous atom, such as karbazole derivatives, triazole derivatives, oxazole derivatives, and imidazole derivatives; aromatic amine compounds such as phenylenediamine derivatives and arylamine derivatives; silazane derivatives; porphyrin compounds; poly(N-vinylcarbazole) derivatives; aniline copolymers; and conductive polymer oligomers such as thiofuene oligomers. Furthermore, the hole injection layer and hole transport layer may also contain an iridium complex according to one embodiment of this disclosure.

[0063] A photoelectric conversion element may include an electron transport layer between the photoelectric conversion layer and the cathode. The electron transport layer is a layer that transports electrons supplied from the cathode to the photoelectric conversion layer, and also a layer that blocks holes supplied from the anode from being transported to the cathode. When a photoelectric conversion element has multiple electron transport layers, the electron transport layer in contact with the cathode is sometimes called the electron injection layer.

[0064] Examples of materials for the electron injection layer and electron transport layer include aromatic heterogeneous compounds containing nitrogen atoms such as triazole derivatives, oxazole derivatives, oxadiazole derivatives, and imidazole derivatives; quinone derivatives such as fluorenone derivatives, anthraquinodimide derivatives, and diphenylquinone derivatives; carbodiimide derivatives; tetracarboxylic anhydrides having aromatic rings such as naphthalene and perylene; phthalocyanine derivatives and their metal complexes. Furthermore, the electron injection layer and electron transport layer may also contain iridium complexes according to one embodiment of this disclosure.

[0065] The method for forming each of the aforementioned layers is not particularly limited, and various methods such as vacuum deposition, LB method, sputtering method, molecular stacking method, coating method, and inkjet method can be used.

[0066] This disclosure is not limited to the embodiments described above, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of this disclosure. [Examples]

[0067] One embodiment of this disclosure is described below. • Preparation of dpyx (trident ligand L) 1,3-di(2'-pyridyl)-4,6-dimethylbenzene (dpyx) was synthesized according to the following scheme.

[0068] [ka]

[0069] • Preparation of ligands (trisceptor ligands) 1-3 Ligands 1 (4,7-diphenyl-1,2,5-oxadiazolo[3,4-c]pyridine-6-carboxylic acid), 2 (4,7-diphenyl-1,2,5-thiadiazolo[3,4-c]pyridine-6-carboxylic acid), and 3 (4,7-bis(4-methylphenyl)-[1,2,5]thiadiazolo[3,4-c]pyridine-6-carboxylic acid), used in the synthesis of compounds 1-3, were each synthesized using Suzuki coupling, referring to International Publication No. 2016 / 068324.

[0070] <Synthesis Example 1: Synthesis of Ir-dpyx Dimer> Next, the precursor Ir-dpyx dimer was synthesized from iridium chloride n-hydrate and 1,3-di(2'-pyridyl)-4,6-dimethylbenzene according to the following scheme.

[0071] [ka]

[0072] Iridium chloride n-hydrate (Ir purity 52.8%, 1.5 g, 4.12 mmol), 1,3-di(2-pyridyl)-4,6-dimethylbenzene (1.08 g, 4.16 mmol), and 83 mL of methanol were added to a 200 mL four-necked flask to obtain a methanol solution. The resulting methanol solution was subjected to nitrogen bubbling for 30 minutes, followed by reflux under a nitrogen atmosphere for 24 hours. This synthesized the precursor complex. Subsequently, the methanol solution was cooled to precipitate the precursor complex, which was then filtered by suction, washed with ethanol, and vacuum dried. This yielded the Ir-dpyx dimer (orange powder, 1.70 g, yield 79.1%).

[0073] <Example 1: Compound 1> Compound 1, the Ir complex of Example 1, was synthesized from the Ir-dpyx dimer obtained in Synthesis Example 1, following the scheme below.

[0074] [ka]

[0075] Ir-dpyx dimer (505 mg, 0.483 mmol), 4,7-diphenyl-1,2,5-oxadiazolo[3,4-c]pyridine-6-carboxylic acid (ligand 1, 763 mg, 2.41 mmol), silver trifluoromethanesulfonate (408 mg, 1.59 mmol), and benzoic acid (3.535 g, 28.9 mmol) were weighed into a mortar, ground, and mixed to obtain a mixture. The obtained mixture was placed in a 100 mL Schlenk flask, purged with nitrogen three times, and stirred at 135°C for 22.5 hours to obtain a reaction mixture. The reaction mixture was dissolved in dichloromethane, and a sodium bicarbonate aqueous solution was added for liquid-liquid washing. Subsequently, the dichloromethane solution containing the liquid-liquid washed reaction mixture was dried over anhydrous sodium sulfate to remove the solvent. The residue obtained by solvent removal was purified by column chromatography. Silica gel was used as the column support, and a mixed solvent of dichloromethane and ethyl acetate was used as the purification solvent. During column purification, the dichloromethane:ethyl acetate ratio was changed from 75:25 to 65:35. This yielded compound 1 (reddish-brown powder, yield 58.5 mg, 0.076 mmol, yield 7.9%). 1 The H-NMR spectrum is shown below.

[0076] 1 H-NMR(400MHz,CD3Cl):δ=8.69(1H,dd,J=7.9,1.1),8.07(2H,d,J=8.1),7.81-7.84(2H,m),7.63(2H,ddd,J=8.6,7.3,1.7),7.46- 7.58(5H,m),6.94-7.00(2H,m),6.85(2H,ddd,J=7.3,5.8,1.3),6.71(1H,ddd,J=7.5,1.5),6.07(1H,ddd,J=7.8,0.7),2.86(6H,s)

[0077] <Example 2: Compound 2> Compound 2, the Ir complex of Example 2, was synthesized from the Ir-dpyx dimer obtained in Synthesis Example 1, following the scheme below.

[0078] [ka]

[0079] Ir-dpyx dimer (506.3 mg, 0.485 mmol), 4,7-diphenyl-1,2,5-thiadiazolo[3,4-c]pyridine-6-carboxylic acid (ligand 2, 736.4 mg, 2.21 mmol), silver trifluoromethanesulfonate (391 mg, 1.52 mmol), and benzoic acid (3.5 g, 28.7 mmol) were weighed into a mortar, ground, and mixed to obtain a mixture. The obtained mixture was placed in a 100 mL Schlenk flask, purged with nitrogen three times, and stirred at 140 °C for 25 hours to obtain a reaction mixture. The reaction mixture was dissolved in dichloromethane, and aqueous sodium bicarbonate solution was added for liquid-liquid washing. Then, the dichloromethane solution containing the liquid-liquid washed reaction mixture was dried over anhydrous sodium sulfate to remove the solvent. The residue obtained by solvent removal was purified by column (silica gel, dichloromethane:ethyl acetate = 67:33). This yielded compound 2 (reddish-brown powder, yield 106.8 mg, 0.139 mmol, yield 14%). 1 The H-NMR spectrum is shown below.

[0080] 1 H-NMR(400MHz,CD3Cl):δ=9.09(1H,dd,J=8.0,1.0),8.06(2H,d,J=8.4),7.72-7.75(2H,m),7.47-7.63(7H,m),6.9 3-6.96(2H,m),6.80(2H,ddd,J=7.3,5.8,1.3),6.67(1H,ddd,J=7.5,1.5),6.01(1H,ddd,J=7.8,0.9),2.86(6H,s)

[0081] <Example 3: Compound 3> Compound 3, the Ir complex of Example 3, was synthesized from the Ir-dpyx dimer obtained in Synthesis Example 1, following the scheme below. [ka] Ir-dpyx dimer (49.1 mg, 0.047 mmol), 4,7-bis(4-methylphenyl)-[1,2,5]thiadiazolo[3,4-c]pyridine-6-carboxylic acid (ligand 3, 70.0 mg, 0.194 mmol), silver trifluoromethanesulfonate (33.0 mg, 0.129 mmol), and benzoic acid (845.0 mg, 6.92 mmol) were weighed into a mortar, ground, and mixed to obtain a mixture. The obtained mixture was placed in a 50 mL Schlenk flask, purged with nitrogen three times, and stirred at 140°C for 25 hours to obtain a reaction mixture. The reaction mixture was dissolved in dichloromethane, and aqueous sodium bicarbonate solution was added for liquid-liquid washing. Then, the dichloromethane solution containing the liquid-liquid washed reaction mixture was dried over anhydrous sodium sulfate to remove the solvent. The residue obtained by solvent removal was purified by column (silica gel, dichloromethane:ethyl acetate = 67:33). This yielded compound 3 (reddish-brown powder, 7.7 mg, 0.0094 mmol, 10% yield).

[0082] 1 H-NMR(400MHz,CD3Cl):δ=8.94(1H,d,J=8.0),8.02(2H,d,J=8.0),7.53-7.63(4H,m),7.46(2H,dd,J=6.0,1 .2),7.35(2H,d,J=8.4),6.91(1H,s),6.72-6.79(3H,m),5.79(1H,s),2.84(6H,s),2.45(3H,s),1.99(3H,s)

[0083] <Spectroscopy> UV-vis absorption and emission spectroscopy and Raman spectroscopy were performed on each of the compounds in Examples 1 to 3. For UV-vis absorption and emission spectroscopy, toluene was used as the solvent, and the sample concentration was set to 10. -6 The procedure was performed with an adjustment to M. Table 1 shows the emission spectra observed by UV-vis absorption and emission spectroscopy.

[0084] [Table 1]

[0085] Furthermore, Raman spectroscopy (laser power: 5mW) revealed that for compound 1 in Example 1, an emission spectrum was observed at 870nm when the excitation wavelength was 405nm. For compound 2 in Example 2, an emission spectrum was observed with peak wavelengths of 512nm for fluorescence and 870nm for phosphorescence when the excitation wavelength was 633nm (red excitation). For compound 3 in Example 3, an emission spectrum was observed with peak wavelengths of 512nm for fluorescence and 860nm for phosphorescence when the excitation wavelength was 633nm (red excitation).

[0086] In the compounds of Examples 1 to 3, emission spectra were observed at long wavelengths of 860 to 870 nm in the near-infrared region. These compounds can be suitably used as functional colorants, including luminescent materials in organic light-emitting diodes (OLEDs). [Industrial applicability]

[0087] A compound according to one aspect of this disclosure has absorption and emission properties in the near-infrared region or beyond, and can be suitably used as a component for, for example, near-infrared luminescence markers, indicators, bioimaging, sensors, wavelength conversion films, light-emitting transistors, organic light-emitting diodes (OLEDs), electrochemiluminescent cells, photodynamic therapy, phototherapy, night vision displays, security, and anti-counterfeiting applications.

Claims

1. A compound represented by the following formula (1): 【Chemistry 1】 In the above formula (1), A is selected from aromatic hydrocarbon rings having 6 to 20 carbon atoms and aromatic heterocycles having 2 to 19 carbon atoms; L represents a monovalent tridentate ligand; R １ This is selected from hydrogen atoms, alkyl groups, halogen atoms, alkylcarbonyl groups, arylcarbonyl groups, alkoxyl groups, alkenyl groups, alkynyl groups, cyano groups, and aryl groups; X represents a compound containing either an oxygen atom or a sulfur atom.

2. The L is a tridentate ligand represented by the following formula (2): 【Chemistry 2】 In the above formula (2), R ２ , and R ４ Each is independently selected from an aromatic hydrocarbon ring having 6 to 20 carbon atoms, an aromatic heterocycle having 2 to 19 carbon atoms, and a carboxyl group; R ３ These are selected from aromatic hydrocarbon rings having 6 to 14 carbon atoms and aromatic heterocycles having 2 to 13 carbon atoms; R ２ , R ３ and R ４ The compound according to claim 1, wherein at least two of the atoms are selected from aromatic heterocycles containing nitrogen atoms.

3. The L is a tridentate ligand represented by the following formula (2-1): 【Transformation 3】 In the above formula (2-1), R ２１ , R ３１ , and R ４１ each independently represent a deuterium atom, a halogen atom, an alkyl group, a haloalkyl group, an alkoxyl group, or a phenyl group, and adjacent substituents may form a ring with each other. The compound according to claim 1, wherein p and r represent integers from 0 to 4, and q represents an integer from 0 to 3.

4. A light-emitting material comprising the compound described in any one of claims 1 to 3.

5. A photoelectric conversion element comprising a layer containing the compound described in any one of claims 1 to 3 between a pair of electrodes.

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