JP7735689B2 - Compound having a pyrromethene skeleton, light-emitting device material containing the same, and light-emitting device using the same - Google Patents

Description

The present invention relates to a compound having a pyrromethene skeleton, a light-emitting device material containing the compound, and a light-emitting device, display device, and lighting device using the compound.

Organic thin-film light-emitting devices emit light when electrons injected from the cathode and holes injected from the anode recombine in the light-emitting layer sandwiched between the two electrodes. These devices have features such as the ability to be made thin, low driving voltage, high brightness, and the ability to emit multicolor light.

Among the three primary colors of light, green light is being studied as a useful light color. One method for achieving green light is to incorporate a small amount of a green fluorescent material as a dopant into a host material. One such technique is a light-emitting device material containing a compound with a specific pyrromethene skeleton and a molecular weight of 450 or greater (see, for example, Patent Document 1). Another proposed organic electroluminescence device includes an anode, an emitting layer, and a cathode, where the emitting layer contains a first compound and a second compound, the first compound being a delayed fluorescent compound, and the second compound being a compound with a pyrromethene skeleton (see, for example, Patent Document 2).

WO 2009/116456 International Publication No. 2016/056559

High device efficiency is desirable for organic thin-film light-emitting devices from the perspectives of improving brightness and saving power. Power saving has become a particularly important issue for mobile display devices, which have seen increasing use in recent years, and higher device efficiency is required. However, the technology described in Patent Document 1 has the problem that pyrromethene compounds and thermally activated delayed fluorescent materials are prone to quenching due to interactions with surrounding molecules, resulting in insufficient device efficiency. On the other hand, when aryl groups are introduced into pyrromethene compounds to reduce interactions with surrounding molecules, the conjugated structure of the pyrromethene skeleton is extended, shifting the emission wavelength to longer wavelengths. As a result, the technology described in Patent Document 2 has the problem of insufficient color purity of green emission.

In view of the problems with the prior art, the present invention aims to provide a compound that can be used to obtain light-emitting device materials with excellent device efficiency and color purity.

The present invention relates to a compound having a pyrromethene skeleton represented by general formula (1).

In the above general formula (1), one to three of R ¹ , R ³ , R ⁴ and R ⁶ are represented by the following general formula (2), and the others are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, alkoxy groups, alkylthio groups, aryl ether groups, aryl thioether groups, hydroxyl groups, halogens, cyano groups, aldehyde groups, acyl groups, ester groups, amide groups, sulfonyl groups, sulfonate ester groups, sulfonamide groups, amino groups, nitro groups and silyl groups. These groups may further have a substituent.

^R2 and ^R5 may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, and a silyl group. These functional groups may further have a substituent.

^R7 is selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, and a silyl group. These groups may further have a substituent.

^L1 and ^L2 may be the same or different and are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, hydroxyl groups, thiol groups, alkoxy groups, cycloalkoxy groups, alkylthio groups, aryl ether groups, aryl thioether groups, aryl groups, heteroaryl groups, halogens, and cyano groups, and these groups may further have a substituent.

In the above general formula (2), *** represents the bond to the carbon atom.

^R21 and ^R25 may be the same or different and are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, alkoxy groups, alkylthio groups, aryl groups, heteroaryl groups, aryl ether groups, aryl thioether groups, hydroxyl groups, halogens, cyano groups, aldehyde groups, acyl groups, ester groups, amide groups, sulfonyl groups, sulfonate ester groups, sulfonamide groups, amino groups, nitro groups, silyl groups, and ring structures between adjacent groups. These groups may further have a substituent.

R ²² to R ²⁴ may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an arylthioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, a silyl group, and a ring structure between adjacent groups. These groups may further have a substituent.

This invention makes it possible to obtain light-emitting device materials with excellent device efficiency and color purity.

Preferred embodiments of the compound having a pyrromethene skeleton according to the present invention, the light-emitting device material containing the compound, and the light-emitting device, display device, and lighting device using the compound are described in detail below. However, the present invention is not limited to the following embodiments, and can be modified and implemented in various ways depending on the purpose and application.

<Compounds having a pyrromethene skeleton>
The compound having a pyrromethene skeleton according to the present invention has a structure represented by the following general formula (1). Because such a pyrromethene compound has a strong and highly planar skeleton, it exhibits a high fluorescence quantum yield. Furthermore, it is possible to obtain a light-emitting device material having a small full width at half maximum of the peak of the fluorescence spectrum, and excellent device efficiency and color purity.

In the above general formula (1), one to three of R ¹ , R ³ , R ⁴ , and R ⁶ are represented by the following general formula (2), and the remaining groups are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, alkoxy groups, alkylthio groups, aryl ether groups, aryl thioether groups, hydroxyl groups, halogens, cyano groups, aldehyde groups, acyl groups, ester groups, amide groups, sulfonyl groups, sulfonate ester groups, sulfonamide groups, amino groups, nitro groups, and silyl groups. These groups may further have a substituent. Furthermore, R ¹ , R ³ , R ⁴ , and R ⁶ do not form a ring structure with adjacent groups.

In the above general formula (2), *** represents the bond to the carbon atom.

^R21 and ^R25 may be the same or different and are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, alkoxy groups, alkylthio groups, aryl groups, heteroaryl groups, aryl ether groups, aryl thioether groups, hydroxyl groups, halogens, cyano groups, aldehyde groups, acyl groups, ester groups, amide groups, sulfonyl groups, sulfonate ester groups, sulfonamide groups, amino groups, nitro groups, silyl groups, and ring structures between adjacent groups. These groups may further have a substituent.

R ²² to R ²⁴ may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, a silyl group, and a ring structure between adjacent groups. These groups may further have a substituent.

In general formula (1), R ¹ , R ³ , R ⁴ , and R ⁶ are groups that can extend the conjugated structure of the pyrromethene skeleton and thereby contribute to the emission wavelength. In order to adjust the peak wavelength of the fluorescence spectrum to a range suitable for green emission and obtain green emission with excellent color purity, it is preferable to suppress conjugation extension in a compound having a pyrromethene skeleton. On the other hand, in order to improve device efficiency, it is preferable to have multiple groups with large steric hindrance, thereby suppressing quenching with medium molecules in a thin film state and aggregation between compounds, thereby suppressing concentration quenching. Therefore, the present invention is characterized in that one to three of R ¹ , R ³ , R ⁴ , and R ⁶ are groups represented by general formula (2). The group represented by general formula (2) has substituents at positions R ²¹ and R ²⁵ , and therefore has a twisted structure with respect to the pyrromethene skeleton in the structure represented by general formula (1). Therefore, despite being an aryl group, it is possible to suppress conjugation extension of the pyrromethene skeleton, thereby obtaining green emission with excellent color purity. In addition, the group represented by general formula (2) has a large steric hindrance, which can improve the device efficiency. It is preferable to have two or more groups represented by general formula (2). On the other hand, if four groups represented by general formula (2) are present, the emission wavelength becomes longer due to the extension of the conjugated structure, and the color purity decreases.

From the viewpoint of further improving color purity by reducing the half width of the fluorescence spectrum, ^R21 and ^R25 are preferably a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, or a ring structure formed between adjacent groups.

Among R ¹ , R ³ , R ⁴ and R ⁶ , the groups other than the group represented by general formula (2) are as described above. By having these groups, the device efficiency can be improved by steric hindrance. From the viewpoint of further improving color purity and device efficiency, a substituted or unsubstituted alkyl group or a substituted or unsubstituted cycloalkyl group is preferred.

It is preferable that at least one of ^R3 and ^R4 is a group represented by general formula (2), and ^R1 and ^R6 are selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups, and sharp green light emission with a small half-width can be obtained. From the viewpoint of further reducing the half-width and further improving the device efficiency, it is preferable that both ^R3 and ^R4 are groups represented by general formula (2).

It is also preferable that at least one of ^R1 and ^R6 is a group represented by general formula (2), and ^R3 and ^R4 are selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups, thereby obtaining sharp green light emission with a small half-width. From the viewpoint of further reducing the half-width and further improving the device efficiency, it is preferable that both ^R1 and ^R6 are groups represented by general formula (2).

In the general formula (1), ^R2 and ^R5 may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, and a silyl group. These groups may further have a substituent, provided that they do not form a ring structure with the adjacent group.

At least one of ^R2 and ^R5 is preferably a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted cycloalkyl group, which allows for sharp green light emission with a small half-width. This also improves the stability of the compound and facilitates synthesis. It is more preferable that both ^R2 and ^R5 are a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted cycloalkyl group.

In the general formula (1), ^R7 is selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, and a silyl group. These functional groups may further have a substituent, provided that they do not form a ring structure with adjacent groups.

In the pyrromethene skeleton, the site substituted by ^R7 may be referred to as a "bridgehead position" hereinafter. From the viewpoint of electrical stability or thermal stability, ^R7 is preferably a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. A substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group is more preferred, as it is possible to further improve the fluorescence quantum yield and obtain sharp green light emission with a narrow half-width. Specific examples include a substituted or unsubstituted phenyl group, a substituted or unsubstituted naphthyl group, a substituted or unsubstituted phenanthryl group, and a substituted or unsubstituted dibenzofuranyl group, with a substituted or unsubstituted phenyl group or a substituted or unsubstituted naphthyl group being more preferred.

^L1 and ^L2 may be the same or different and are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, hydroxyl groups, thiol groups, alkoxy groups, cycloalkoxy groups, alkylthio groups, aryl ether groups, aryl thioether groups, aryl groups, heteroaryl groups, halogens, and cyano groups. These functional groups may further have a substituent.

From the viewpoints of luminescence characteristics and thermal stability, ^L1 and ^L2 are preferably an alkyl group, an alkoxy group, an aryl ether group, a halogen, or a cyano group. Furthermore, from the viewpoints of further improving the fluorescence quantum yield and improving durability by stabilizing the excited state, an electron-withdrawing group is more preferred. Examples of the electron-withdrawing group include a fluorine atom, a fluorine-containing alkyl group, a fluorine-containing alkoxy group, a fluorine-containing aryl ether group, and a cyano group. Among these, a fluorine atom or a cyano group is preferred, and a fluorine atom is more preferred. ^L1 and ^L2 may be the same or different, but are preferably the same from the viewpoint of ease of synthesis.

In all of the above groups, hydrogen may be replaced with deuterium. The same applies to the compounds or partial structures described below.

In addition, for all of the above groups, when substituted, the substituent is preferably an alkyl group, cycloalkyl group, heterocyclic group, alkenyl group, cycloalkenyl group, alkynyl group, alkoxy group, alkylthio group, aryl group, heteroaryl group, aryl ether group, aryl thioether group, hydroxyl group, halogen, cyano group, aldehyde group, acyl group, ester group, amide group, sulfonyl group, sulfonate ester group, sulfonamide group, amino group, silyl group, siloxanyl group, or oxo group, with specific substituents specified as preferred in the description of each substituent being more preferred. These substituents may also be further substituted with the substituents described above.

In addition, for all of the above groups, "unsubstituted" means that the atoms bonded to the target basic skeleton or functional group are only hydrogen atoms or deuterium atoms.

An alkyl group refers to a saturated aliphatic hydrocarbon group such as a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, or tert-butyl group, and may be substituted or unsubstituted. If substituted, the additional substituents are not particularly limited, and examples include alkyl groups, halogens, aryl groups, and heteroaryl groups, as will be described below. The number of carbon atoms in the alkyl group is not particularly limited, but is preferably in the range of 1 to 20, more preferably 1 to 8, in terms of availability and cost.

A cycloalkyl group refers to a saturated alicyclic hydrocarbon group such as a cyclopropyl group, cyclohexyl group, norbornyl group, or adamantyl group, which may be substituted or unsubstituted. The number of ring carbon atoms is not particularly limited, but is preferably in the range of 3 to 20.

A heterocyclic group refers to an aliphatic ring containing atoms other than carbon within the ring, such as a pyran ring, piperidine ring, or cyclic amide, and may be substituted or unsubstituted. The number of ring carbon atoms is not particularly limited, but is preferably in the range of 2 to 20.

An alkenyl group refers to an unsaturated aliphatic hydrocarbon group containing a double bond, such as a vinyl group, allyl group, or butadienyl group, which may be substituted or unsubstituted. The number of carbon atoms in the alkenyl group is not particularly limited, but is preferably in the range of 2 to 20.

A cycloalkenyl group refers to an unsaturated alicyclic hydrocarbon group containing a double bond, such as a cyclopentenyl group, cyclopentadienyl group, or cyclohexenyl group, which may be substituted or unsubstituted. The number of ring carbon atoms is not particularly limited, but is preferably in the range of 3 to 20.

An alkynyl group refers to an unsaturated aliphatic hydrocarbon group containing a triple bond, such as an ethynyl group, which may be substituted or unsubstituted. The number of carbon atoms in the alkynyl group is not particularly limited, but is preferably in the range of 2 to 20.

An alkoxy group refers to a group in which an aliphatic hydrocarbon group, such as a methoxy group, ethoxy group, or propoxy group, is bonded via an ether bond. This aliphatic hydrocarbon group may be substituted or unsubstituted. The number of carbon atoms in the alkoxy group is not particularly limited, but is preferably in the range of 1 to 20.

An alkylthio group is an alkoxy group in which the oxygen atom in the ether bond is replaced with a sulfur atom. The hydrocarbon group of the alkylthio group may be substituted or unsubstituted. The number of carbon atoms in the alkylthio group is not particularly limited, but is preferably in the range of 1 to 20.

The aryl group may be a single ring or a fused ring, and may refer to an aromatic hydrocarbon group such as a phenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthryl group, an anthracenyl group, a benzophenanthryl group, a benzanthracenyl group, a chrysenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, a benzofluoranthenyl group, a dibenzoanthracenyl group, a perylenyl group, or a helicenyl group. Among these, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a phenanthryl group, an anthracenyl group, a pyrenyl group, a fluoranthenyl group, or a triphenylenyl group is preferred. The aryl group may be substituted or unsubstituted. In the present invention, groups in which multiple phenyl groups are bonded via single bonds, such as a biphenyl group or a terphenyl group, are considered to be phenyl groups having an aryl group as a substituent. The number of ring carbon atoms is not particularly limited, but is preferably in the range of 6 to 40, more preferably 6 to 30. Furthermore, in the case of a phenyl group, when two adjacent carbon atoms in the phenyl group each have a substituent, the substituents may together form a ring structure.

Heteroaryl groups may be either monocyclic or condensed rings, and examples thereof include pyridyl, furanyl, thiophenyl, quinolinyl, isoquinolinyl, pyrazinyl, pyrimidyl, pyridazinyl, triazinyl, naphthyridinyl, cinnolinyl, phthalazinyl, quinoxalinyl, quinazolinyl, benzofuranyl, benzothiophenyl, indolyl, dibenzofuranyl, dibenzothiophenyl, carbazolyl, and benzocathol. This refers to a cyclic aromatic group having one or more atoms other than carbon and hydrogen, i.e., heteroatoms, in the ring, such as a rubazolyl group, a carbolinyl group, an indolocarbazolyl group, a benzofurocarbazolyl group, a benzothienocarbazolyl group, a dihydroindenocarbazolyl group, a benzoquinolinyl group, an acridinyl group, a dibenzoacridinyl group, a benzimidazolyl group, an imidazopyridyl group, a benzoxazolyl group, a benzothiazolyl group, or a phenanthrolinyl group. The heteroatom is preferably a nitrogen atom, an oxygen atom, or a sulfur atom. The heteroaryl group may be substituted or unsubstituted. The number of ring carbon atoms is not particularly limited, but is preferably 2 to 40, more preferably 2 to 30.

An aryl ether group refers to a group, such as a phenoxy group, to which an aromatic hydrocarbon group is bonded via an ether bond. The aromatic hydrocarbon group may be substituted or unsubstituted. The number of carbon atoms in the aryl ether group is not particularly limited, but is preferably in the range of 6 to 40.

An aryl thioether group is an aryl ether group in which the oxygen atom in the ether bond is replaced with a sulfur atom. The aromatic hydrocarbon group in the aryl thioether group may be substituted or unsubstituted. The number of carbon atoms in the aryl thioether group is not particularly limited, but is preferably in the range of 6 to 40.

Halogen refers to an atom selected from fluorine, chlorine, bromine and iodine.

A cyano group is a group with the structure -C≡N, where it is the carbon atom that bonds to other groups.

An aldehyde group is a group with the structure -C(=O)H. Here, it is the carbon atom that bonds to other groups.

An acyl group refers to a group in which an alkyl group, cycloalkyl group, alkenyl group, alkynyl group, aryl group, or heteroaryl group is bonded via a carbonyl group, such as an acetyl group, propionyl group, benzoyl group, or acrylyl group, and these substituents may be further substituted. The number of carbon atoms in the acyl group is not particularly limited, but is preferably 2 to 40, more preferably 2 to 30.

An ester group refers to a group in which, for example, an alkyl group, cycloalkyl group, aryl group, or heteroaryl group is bonded via an ester bond, and these substituents may be further substituted. The number of carbon atoms in the ester group is not particularly limited, but is preferably in the range of 1 to 20. More specific examples include methyl ester groups such as a methoxycarbonyl group, ethyl ester groups such as an ethoxycarbonyl group, propyl ester groups such as a propoxycarbonyl group, butyl ester groups such as a butoxycarbonyl group, isopropyl ester groups such as an isopropoxymethoxycarbonyl group, hexyl ester groups such as a hexyloxycarbonyl group, and phenyl ester groups such as a phenoxycarbonyl group.

An amide group refers to a group in which, for example, an alkyl group, cycloalkyl group, aryl group, or heteroaryl group is bonded via an amide bond, and these substituents may be further substituted. The number of carbon atoms in the amide group is not particularly limited, but is preferably in the range of 1 to 20. More specific examples include methylamide groups, ethylamide groups, propylamide groups, butylamide groups, isopropylamide groups, hexylamide groups, and phenylamide groups.

The sulfonyl group refers to a group formed by bonding, for example, an alkyl group, a cycloalkyl group, an aryl group, or a heteroaryl group via an -S(=O) ₂ - bond, and these substituents may be further substituted. The number of carbon atoms in the sulfonyl group is not particularly limited, but is preferably in the range of 1 to 20.

The sulfonate ester group refers to a group in which, for example, an alkyl group, a cycloalkyl group, an aryl group, or a heteroaryl group is bonded via a sulfonate ester bond. Here, the sulfonate ester bond refers to an ester bond in which the carbonyl portion, i.e., —C(═O)—, is replaced with a sulfonyl portion, i.e., —S(═O) ₂ —. These substituents may be further substituted. The number of carbon atoms in the sulfonate ester group is not particularly limited, but is preferably in the range of 1 to 20.

A sulfonamide group refers to a group in which, for example, an alkyl group, a cycloalkyl group, an aryl group, or a heteroaryl group is bonded via a sulfonamide bond. Here, the sulfonamide bond refers to an ester bond in which the carbonyl moiety, i.e., —C(═O)—, is replaced with a sulfonyl moiety, i.e., —S(═O) ₂ —. These substituents may be further substituted. The number of carbon atoms in the sulfonamide group is not particularly limited, but is preferably in the range of 1 to 20.

The amino group is a substituted or unsubstituted amino group. In the case of substitution, examples of the substituent include an aryl group, a heteroaryl group, a straight-chain alkyl group, and a branched alkyl group. Preferred aryl and heteroaryl groups are a phenyl group, a naphthyl group, a pyridyl group, and a quinolinyl group. These substituents may be further substituted. The number of carbon atoms is not particularly limited, but is preferably in the range of 2 to 50, more preferably 6 to 40, and particularly preferably 6 to 30.

A silyl group refers to a group to which a substituted or unsubstituted silicon atom is bonded, and examples include alkylsilyl groups such as trimethylsilyl, triethylsilyl, tert-butyldimethylsilyl, propyldimethylsilyl, and vinyldimethylsilyl, and arylsilyl groups such as phenyldimethylsilyl, tert-butyldiphenylsilyl, triphenylsilyl, and trinaphthylsilyl. The substituent on the silicon may be further substituted. There are no particular restrictions on the number of carbon atoms in the silyl group, but it is preferably in the range of 1 to 30.

A siloxanyl group refers to a silicon compound group connected via an ether bond, such as a trimethylsiloxanyl group. The substituent on the silicon may be further substituted.

An oxo group is a group in which an oxygen atom is double-bonded to a carbon atom, i.e., the structure is =O.

In the present invention, the structure represented by the following structural formula (3) is referred to as a pyrromethene skeleton.

Examples of compounds having a pyrromethene skeleton represented by general formula (1) are shown below, but are not limited to these.

Compounds having a pyrromethene skeleton represented by general formula (1) can be produced by referring to methods described in, for example, J. Org. Chem., vol. 64, No. 21, pp. 7813-7819 (1999), Angew. Chem., Int. Ed. Engl., vol. 36, pp. 1333-1335 (1997), and Org. Lett., vol. 12, pp. 296 (2010).

Furthermore, methods for introducing aryl or heteroaryl groups into the pyrromethene skeleton include, for example, a method in which a carbon-carbon bond is generated by a coupling reaction between a halogenated derivative of a pyrromethene boron complex and a boronic acid or boronic acid ester derivative in the presence of a metal catalyst such as palladium. Furthermore, methods for introducing amino or carbazolyl groups into the pyrromethene skeleton include, for example, a method in which a carbon-nitrogen bond is generated by a coupling reaction between a halogenated derivative of a pyrromethene boron complex and an amine or carbazole derivative in the presence of a metal catalyst such as palladium.

The resulting compound having a pyrromethene skeleton is preferably purified using organic synthesis techniques such as recrystallization or column chromatography, and then further purified by heating under reduced pressure, commonly known as sublimation purification, to remove low-boiling components and improve purity. The heating temperature in sublimation purification is not particularly limited, but is preferably 330°C or lower, and more preferably 300°C or lower, from the viewpoint of preventing thermal decomposition of the compound having a pyrromethene skeleton.

The purity of the compound having a pyrromethene skeleton is preferably 99% by weight or more from the viewpoint of stabilizing the light-emitting device characteristics.

In order to further improve the color purity of green light emitted from the compound having a pyrromethene skeleton represented by general formula (1), the peak wavelength is preferably 500 nm or more and 550 nm or less. The fluorescence spectrum of the compound having a pyrromethene skeleton represented by general formula (1) can be measured using a fluorescence spectrophotometer in a diluted solution of toluene at a concentration of 10 ^mol /L.

In order to set the peak wavelength within the above range, it is preferable that one to three of R ¹ , R ³ , R ⁴ and R ⁶ are groups represented by the general formula (2), and R ²¹ and R ²⁵ are substituted or unsubstituted alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted aryl groups, substituted or unsubstituted heteroaryl groups, or ring structures formed between adjacent groups.

In order to further improve color purity, the fluorescence spectrum of the compound having a pyrromethene skeleton represented by general formula (1) preferably has a half-value width of 45 nm or less, and more preferably 35 nm or less.

In order to set the half width within the above range, it is preferable that both ^R3 and ^R4 , or both ^R1 and ^R6 , are groups represented by general formula (2). In particular, when used in top-emission organic electroluminescent devices, which are mainstream in display devices and lighting devices, the improvement in brightness and color purity due to the resonance effect of the microcavity structure is more pronounced as the fluorescence spectrum becomes sharper, thereby enabling further improvement in device efficiency.

The efficiency of a light-emitting device depends on the fluorescence quantum yield of the light-emitting device material. Therefore, a fluorescence quantum yield of nearly 100% is desired for light-emitting device materials. The fluorescence quantum yield of a compound having a pyrromethene skeleton represented by general formula (1) is preferably 90% or more, and more preferably 95% or more. Here, the fluorescence quantum yield of a compound having a pyrromethene skeleton represented by general formula (1) can be measured using an absolute quantum yield measurement device using a diluted solution of toluene at a concentration of 10 ⁻⁵ mol/L.

<Light-emitting element materials>
The light-emitting device material in the present invention refers to a material that includes a compound having a pyrromethene skeleton represented by general formula (1) and is used in any layer of a light-emitting device. Examples include materials used in the hole injection layer, hole transport layer, light-emitting layer, electron transport layer, and/or protective film (cap layer) of an electrode, which will be described later. Among these, the light-emitting device material is preferably used in the light-emitting layer because of its high device efficiency, color purity, and thin film stability.

The light-emitting element material may contain other components in addition to the compound having a pyrromethene skeleton represented by general formula (1). Examples of other components include the materials exemplified below as components of the hole injection layer, hole transport layer, light-emitting layer, electron transport layer, and/or electrode protective film (cap layer).

<Light-emitting element>
Next, an embodiment of the light-emitting device of the present invention will be described. The light-emitting device of the present invention has a light-emitting layer containing the light-emitting device material described above between an anode and a cathode, and emits light when exposed to electrical energy.

The light-emitting element of the present invention may be either a bottom-emission type or a top-emission type. The light-emitting element of the present invention is more preferably a top-emission type, as it has a narrow half-width of the fluorescence spectrum and excellent color purity. Due to the resonance effect of the microcavity, the narrower the half-width of a top-emission light-emitting element, the higher the luminous efficiency. Therefore, it is possible to achieve both high levels of color purity and luminous efficiency.

In such light-emitting elements, the layer configuration between the anode and cathode may be a configuration consisting of only the light-emitting layer, or may be a laminate configuration such as 1) light-emitting layer/electron transport layer, 2) hole transport layer/light-emitting layer, 3) hole transport layer/light-emitting layer/electron transport layer, 4) hole injection layer/hole transport layer/light-emitting layer/electron transport layer, 5) hole transport layer/light-emitting layer/electron transport layer/electron injection layer, 6) hole injection layer/hole transport layer/light-emitting layer/electron transport layer/electron injection layer, 7) hole injection layer/hole transport layer/light-emitting layer/hole blocking layer/electron transport layer/electron injection layer, or 8) hole injection layer/hole transport layer/electron blocking layer/light-emitting layer/hole blocking layer/electron transport layer/electron injection layer.

Furthermore, a tandem type may be used in which multiple layers of the above-mentioned laminated structure are laminated via intermediate layers. Examples of intermediate layers generally include intermediate electrodes, intermediate conductive layers, charge generation layers, electron extraction layers, connection layers, and intermediate insulating layers, and known material structures can be used. A preferred example of a tandem type is a laminated structure such as 9) hole injection layer/hole transport layer/light-emitting layer/electron transport layer/electron injection layer/charge generation layer/hole injection layer/hole transport layer/light-emitting layer/electron transport layer/electron injection layer.

Furthermore, each of the above layers may be a single layer or multiple layers, and may be doped. Furthermore, each of the above layers may include an anode, one or more organic layers including an emitting layer, and a cathode, and may also include a device configuration that further includes a protective film (cap layer) to improve luminous efficiency due to the optical interference effect.

Specific examples of the configuration of the light-emitting element are given below, but the configuration of the present invention is not limited to these.

(substrate)
It is preferable to form the light-emitting element on a substrate in order to maintain the mechanical strength of the light-emitting element, minimize thermal deformation, and provide barrier properties that prevent water vapor and oxygen from penetrating the light-emitting layer. The substrate is not particularly limited, but examples include glass plates, ceramic plates, resin films, thin resin films, and thin metal plates. Among these, glass substrates are preferably used because of their transparency and ease of processing. In particular, for bottom-emission light-emitting elements that extract light through the substrate, highly transparent glass substrates are preferred. Furthermore, flexible displays and foldable displays are becoming increasingly common, primarily in mobile devices such as smartphones, and for these applications, resin films and thin resin films obtained by curing varnish are preferably used. Heat-resistant films are used as resin films, and specific examples include polyimide films and polyethylene naphthalate films.

In addition, various wiring, circuits, and TFT switching elements for driving the organic EL may be provided on the surface of the substrate.

(anode)
The anode is preferably formed on the substrate. Various wirings, circuits, and switching elements may be interposed between the substrate and the anode. The material used for the anode is not particularly limited as long as it can efficiently inject holes into the organic layer. In the case of a bottom-emission light-emitting element, it is preferably a transparent or semi-transparent electrode, and in the case of a top-emission light-emitting element, it is preferably a reflective electrode.

Examples of materials for transparent or translucent electrodes include conductive metal oxides such as zinc oxide, tin oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); metals such as gold, silver, aluminum, and chromium; and conductive polymers such as polythiophene, polypyrrole, and polyaniline. However, when using metals, it is preferable to make the film thin so that light can be semi-transmitted. Of these, indium tin oxide (ITO) is more preferred from the standpoints of transparency and stability.

The material for the reflective electrode is preferably one that does not absorb any light and has high reflectivity, such as metals such as aluminum, silver, and platinum.

Two or more of these electrode materials may be used, or multiple materials may be layered.

The thickness of the anode is not particularly limited, but a thickness of several nanometers to several hundred nanometers is preferable.

The anode formation method can be selected optimally depending on the material used, but examples include sputtering, vapor deposition, and inkjet printing. For example, sputtering is preferred when forming the anode from metal oxide, and vapor deposition is preferred when forming the anode from metal. There are no particular restrictions on the thickness of the anode, but a thickness of several nanometers to several hundred nanometers is preferable.

(cathode)
The cathode is formed on the surface opposite to the anode with the organic layer sandwiched therebetween, and is preferably formed on the surface of the electron transport layer or the electron injection layer. The material used for the cathode is not particularly limited as long as it can efficiently inject electrons into the light emitting layer, but in the case of a bottom emission type light emitting element, it is preferably a reflective electrode, and in the case of a top emission type light emitting element, it is preferably a semi-transparent electrode.

Generally, metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium; alloys or multilayer laminates of these metals with low work function metals such as lithium, sodium, potassium, calcium, and magnesium; and conductive metal oxides such as zinc oxide, indium tin oxide (ITO), and indium zinc oxide (IZO) are preferred. Among these, aluminum, silver, and magnesium are preferred as the main components from the standpoints of electrical resistance, ease of film formation, film stability, and luminous efficiency. Furthermore, a composition of magnesium and silver is preferred because it facilitates electron injection into the electron transport layer and electron injection layer, thereby reducing the driving voltage.

(protective layer)
For cathode protection, it is preferable to laminate a protective layer (cap layer) on the cathode. Materials constituting the protective layer are not particularly limited, but examples include metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium, alloys using these metals, inorganic substances such as silica, titania, and silicon nitride, and organic polymer compounds such as polyvinyl alcohol, polyvinyl chloride, and hydrocarbon-based polymer compounds. However, in the case of a top-emission light-emitting device, the material used for the protective layer is preferably selected from materials that are optically transparent in the visible light region.

(Hole injection layer)
The hole injection layer is inserted between the anode and the hole transport layer to facilitate hole injection. The hole injection layer may be a single layer or a laminate of multiple layers. The presence of the hole injection layer between the hole transport layer and the anode is preferable because it not only enables lower voltage driving and improves durability and lifespan, but also improves the carrier balance of the device and the luminous efficiency.

A preferred example of a hole injection material is an electron-donating hole injection material (donor material). These materials have a shallower HOMO level than the hole transport layer and a work function close to that of the anode, thereby reducing the energy barrier with the anode. Specific examples include aromatic amine materials such as benzidine derivatives, starburst arylamines such as 4,4',4"-tris(3-methylphenyl(phenyl)amino)triphenylamine (m-MTDATA) and 4,4',4"-tris(1-naphthyl(phenyl)amino)triphenylamine (1-TNATA), and other starburst arylamines; heterocyclic compounds such as carbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole derivatives, phthalocyanine derivatives, and porphyrin derivatives; and polymers such as polycarbonates and styrene derivatives having the above-mentioned monomers in their side chains, polythiophenes such as PEDOT/PSS, polyaniline, polyfluorene, polyvinylcarbazole, and polysilane. Two or more of these materials may be used. Furthermore, a hole injection layer may be formed by laminating multiple materials.

Another preferred example of a hole injection material is an electron-accepting hole injection material (acceptor material). The hole injection layer may be composed of an acceptor material alone, or the donor material may be doped with an acceptor material. When used alone, the acceptor material forms a charge-transfer complex with the adjacent hole transport layer, and when used as a dopant in a donor material, it forms a charge-transfer complex with the donor material. The use of such materials is more preferred because they improve the conductivity of the hole injection layer, contribute to lowering the device's driving voltage, and provide benefits such as improved luminous efficiency and extended durability. Examples of acceptor materials include metal oxides such as molybdenum oxide, vanadium oxide, tungsten oxide, and ruthenium oxide; charge-transfer complexes such as tris(4-bromophenyl)aminium hexachloroantimonate (TBPAH); n-type organic semiconductor compounds such as 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN6), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), and fluorinated copper phthalocyanine; and fullerenes. When the hole injection layer contains an acceptor compound, the hole injection layer may be a single layer or may be configured by stacking multiple layers.

(Hole transport layer)
The hole transport layer is a layer that transports holes injected from the anode to the light emitting layer, and may be a single layer or a laminate of multiple layers.

The hole transport layer is formed using one type of hole transport material alone, or by laminating or mixing two or more types of hole transport materials. It is also preferable that the hole transport material have high hole injection efficiency and efficiently transport the injected holes. To achieve this, the material must have an appropriate ionization potential, high hole mobility, excellent stability, and be less likely to generate impurities that can become traps.

Substances that satisfy these conditions include, but are not limited to, heterocyclic compounds such as benzidine derivatives, aromatic amine materials known as starburst arylamines, carbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, dibenzofuran derivatives, thiophene derivatives, benzothiophene derivatives, dibenzothiophene derivatives, fluorene derivatives, spirofluorene derivatives, oxadiazole derivatives, phthalocyanine derivatives, and porphyrin derivatives; and polymers such as polycarbonates and styrene derivatives having the above-mentioned monomers in their side chains, polythiophenes, polyanilines, polyfluorenes, polyvinylcarbazoles, and polysilanes.

(Light-emitting layer)
The light-emitting layer is a layer that emits light by excitation energy generated by the recombination of holes and electrons. The light-emitting layer may be composed of a single material, but from the viewpoint of color purity, it is preferable to have a first compound and a second compound that is a dopant exhibiting strong light emission. Suitable examples of the first compound include a host material responsible for charge transfer and a thermally activated delayed fluorescent compound.

Compounds having a pyrromethene skeleton represented by general formula (1) are preferably used as the second compound, which is a dopant in the light-emitting layer, because they have particularly excellent fluorescence quantum yield, a peak wavelength in their fluorescence spectrum that is suitable for green emission, a narrow half-width, and excellent color purity. From the viewpoint of further suppressing concentration quenching, the content of the second compound in the light-emitting layer is preferably 5% by weight or less, and more preferably 2% by weight or less. On the other hand, from the viewpoint of more efficient energy transfer, the content of the second compound in the light-emitting layer is preferably 0.1% by weight or more, and more preferably 0.5% by weight or more.

Host materials include, but are not limited to, compounds with fused aryl rings such as naphthacene, pyrene, anthracene, and fluoranthene, and their derivatives; aromatic amine derivatives such as N,N'-dinaphthyl-N,N'-diphenyl-4,4'-diphenyl-1,1'-diamine; metal-chelating oxinoid compounds such as tris(8-quinolinato)aluminum(III); bisstyryl derivatives such as distyrylbenzene derivatives; tetraphenylbutadiene derivatives; indene derivatives; coumarin derivatives; oxadiazole derivatives; pyrrolopyridine derivatives; perinone derivatives; pyrrolopyrrole derivatives; thiadiazolopyridine derivatives; dibenzofuran derivatives; carbazole derivatives; indolocarbazole derivatives; triazine derivatives; and polymer-based materials such as polyphenylenevinylene derivatives, polyparaphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, and polythiophene derivatives. Two or more of these host materials may be used, or two or more host materials may be layered. Among these, carbazole derivatives, anthracene derivatives, and naphthacene derivatives are preferred.

The dopant material may contain a fluorescent material other than the compound having a pyrromethene skeleton represented by general formula (1). Specific examples include compounds having fused aryl rings such as naphthacene, pyrene, anthracene, and fluoranthene, and derivatives thereof; compounds having heteroaryl rings and derivatives thereof; distyrylbenzene derivatives; aminostyryl derivatives; tetraphenylbutadiene derivatives; stilbene derivatives; aldazine derivatives; pyrromethene derivatives; diketopyrrolo[3,4-c]pyrrole derivatives; coumarin derivatives; azole derivatives and metal complexes thereof; and aromatic amine derivatives. Two or more of these may also be used.

The dopant material may also contain a phosphorescent material. The phosphorescent material is preferably a metal complex compound containing at least one metal selected from the group consisting of iridium (Ir), ruthenium (Ru), palladium (Pd), platinum (Pt), osmium (Os), and rhenium (Re). From the viewpoint of highly efficient luminescence, an iridium complex or a platinum complex is more preferable. The ligand preferably has a nitrogen-containing heteroaryl group such as a phenylpyridine skeleton, a phenylquinoline skeleton, or a carbene skeleton, but is not limited to these.

However, from the viewpoint of further improving color purity, it is preferable that the dopant material be solely a compound having a pyrromethene skeleton represented by general formula (1).

In addition to the host material or dopant material described above, the light-emitting layer may further contain a third component to adjust the carrier balance within the light-emitting layer or to stabilize the layer structure of the light-emitting layer. However, it is preferable to select a material as the third component that does not interact with the host material and dopant material.

Thermally activated delayed fluorescent materials, commonly referred to as TADF (thermally activated delayed fluorescence) materials, are materials that promote reverse intersystem crossing from the triplet excited state to the singlet excited state by reducing the energy gap between the singlet and triplet excited states, thereby increasing the probability of singlet exciton generation. By utilizing delayed fluorescence via this TADF mechanism, theoretical internal efficiency can be increased to 100%. Furthermore, when Förster-type energy transfer occurs from the singlet excited state of a first compound with thermally activated delayed fluorescent properties to the singlet excited state of a second compound, fluorescence emission from the singlet excited state of the second compound is observed. When the second compound is a fluorescent material with a sharp fluorescence spectrum, light-emitting devices with superior device efficiency and color purity can be obtained. Thus, the inclusion of a thermally activated delayed fluorescent material in the light-emitting layer further improves device efficiency and contributes to lower display power consumption. The thermally activated delayed fluorescence material may be a material that exhibits thermally activated delayed fluorescence from a single material, or may be a material that exhibits thermally activated delayed fluorescence from multiple materials, such as when an exciplex complex is formed.

The thermally activated delayed fluorescent compound may be a single material or multiple materials, and known materials can be used. Specific examples include benzonitrile derivatives, triazine derivatives, disulfoxide derivatives, carbazole derivatives, indolocarbazole derivatives, dihydrophenazine derivatives, thiazole derivatives, and oxadiazole derivatives. Examples of such thermally activated delayed fluorescent compounds include, but are not limited to, the following:

It is preferable that the first compound is a thermally activated delayed fluorescent compound, and the second compound is a compound having a pyrromethene skeleton represented by the general formula (1) above. Furthermore, when the first compound is a thermally activated delayed fluorescent compound, it is preferable that the emitting layer further contains a third compound, and that the singlet energy of the third compound is greater than the singlet energy of the first compound. This allows the third compound to have the function of trapping the energy of the emitting material within the emitting layer, enabling efficient light emission.

The third compound is preferably an organic compound with high charge transport capability and a high glass transition temperature. The third compound is not particularly limited, but examples include the following:

The third compound may be composed of a single material or two or more materials. When two or more materials are used as the third compound, a combination of an electron-transporting third compound and a hole-transporting third compound is preferable. By combining the electron-transporting third compound and the hole-transporting third compound in an appropriate mixing ratio, the charge balance in the light-emitting layer can be adjusted, the unevenness of the light-emitting region can be suppressed, and the reliability and durability of the light-emitting device can be improved. An exciplex may be formed between the electron-transporting third compound and the hole-transporting third compound.

Examples of the third electron-transporting compound include compounds containing a π-electron-deficient heteroaromatic ring. Specific examples include 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7), 9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (CO11), 2,2',2''-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazo[4-( ... heterocyclic compounds having a polyazole skeleton such as 2-[3-(dibenzothiophen-4-yl)phenyl]-1-phenyl-1H-benzimidazole (mDBTBIm-II); 2-[3-(dibenzothiophen-4-yl)phenyl]dibenzo[f,h]quinoxaline (2mDBTPDBq-II), 2-[3'-(dibenzothiophen-4-yl)biphenyl-3-yl]dibenzo[f,h]quinoxaline (2mDBTBPDBq-II), 2-[4-(3,6-diphenyl-9H-carbazol-9-yl)phenyl]dibenzo[f,h]quinoxaline (2CzPDBq-II) heterocyclic compounds having a quinoxaline skeleton or a dibenzoquinoxaline skeleton, such as 4,6-bis[3-(phenanthrene-9-yl)phenyl]pyrimidine (4,6mPnP2Pm), 4,6-bis[3-(9H-carbazol ... Examples include heterocyclic compounds having a diazine skeleton (pyrimidine skeleton or pyrazine skeleton) such as 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (4,6mCzP2Pm) and 4,6-bis[3-(4-dibenzothienyl)phenyl]pyrimidine (4,6mDBTP2Pm-II); and heterocyclic compounds having a pyridine skeleton such as 3,5-bis[3-(9H-carbazol-9-yl)phenyl]pyridine (3,5DCzPPy), 1,3,5-tri[3-(3-pyridyl)phenyl]benzene (TmPyPB), and 3,3',5,5'-tetra[(m-pyridyl)-phen-3-yl]biphenyl (BP4mPy).

Examples of the third hole-transporting compound include compounds containing a π-electron-rich heteroaromatic ring. Specific examples include 1,3-bis(N-carbazolyl)benzene, 4,4'-di(N-carbazolyl)biphenyl (CBP), 3,3'-di(N-carbazolyl)biphenyl (mCBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (TCPB), 9-[4-(10-phenyl-9-anthracenyl)phenyl]-9H-carbazole (CzPA), 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, 9-phenyl-9H-3-(9-phenyl-9H-carbazol-3-yl)carbazole, and 3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino] Examples include compounds having a carbazole skeleton such as 9-phenylcarbazole (PCzPCA2), 3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole (PCzPCN1), 9-([1,1-biphenyl]-4-yl)-9'-([1,1':4',1"-terphenyl]-4-yl)-9H,9'H-3,3'-bicarbazole, 9-([1,1':4',1"-terphenyl]-4-yl)-9'-(naphthalen-2-yl)-9H,9'H-3,3'-bicarbazole, and 9,9',9"-triphenyl-9H,9'H,9"H-3,3':6',3"-tricarbazole.

(electron transport layer)
The electron transport layer is a layer into which electrons are injected from the cathode and further transports the electrons. The electron transport material used in the electron transport layer is required to have a large electron affinity, a large electron mobility, excellent stability, and to be a substance that is unlikely to generate impurities that become traps. Furthermore, from the viewpoint of suppressing film quality deterioration due to crystallization, a compound with a molecular weight of 400 or more is preferred.

The electron transport layer in this invention also includes, as a synonym, a hole blocking layer that can efficiently block the movement of holes. The hole blocking layer and electron transport layer may be composed of a single material or a laminate of multiple materials.

Electron transport materials include polycyclic aromatic derivatives, styryl aromatic ring derivatives, quinone derivatives, phosphorus oxide derivatives, and various metal complexes such as quinolinol complexes of tris(8-quinolinolato)aluminum(III), benzoquinolinol complexes, hydroxyazole complexes, azomethine complexes, tropolone metal complexes, and flavonol metal complexes. To reduce driving voltage and further improve device efficiency, it is preferable to use a compound having a heteroaryl group containing electron-accepting nitrogen. Here, electron-accepting nitrogen refers to a nitrogen atom that forms multiple bonds with adjacent atoms. Heteroaryl groups containing electron-accepting nitrogen have a high electron affinity, facilitating electron injection from the cathode and enabling lower-voltage operation. Furthermore, increased electron supply to the light-emitting layer increases the recombination probability, further improving device efficiency. Examples of compounds having a heteroaryl group structure containing electron-accepting nitrogen include pyridine derivatives, triazine derivatives, pyrazine derivatives, pyrimidine derivatives, quinoline derivatives, quinoxaline derivatives, quinazoline derivatives, naphthyridine derivatives, benzoquinoline derivatives, phenanthroline derivatives, imidazole derivatives, oxazole derivatives, thiazole derivatives, triazole derivatives, oxadiazole derivatives, thiadiazole derivatives, benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, phenanthroimidazole derivatives, and oligopyridine derivatives such as bipyridine and terpyridine. Two or more of these may be used.

Furthermore, it is more preferable for the electron transport material to have a condensed polycyclic aromatic skeleton, as this improves the glass transition temperature, increases electron mobility, and reduces the driving voltage. Examples of such a condensed polycyclic aromatic skeleton include a quinolinol skeleton, a triazine skeleton, a fluoranthene skeleton, an anthracene skeleton, a pyrene skeleton, and a phenanthroline skeleton.

The electron transport layer may contain a donor material. Here, a donor material is a compound that improves the electron injection barrier, thereby facilitating electron injection from the cathode or electron injection layer into the electron transport layer, and further improving the electrical conductivity of the electron transport layer.

Preferred examples of donor materials include alkali metals such as Li, inorganic salts containing alkali metals such as LiF, complexes of alkali metals and organic substances such as lithium quinolinol, alkaline earth metals, inorganic salts containing alkaline earth metals, complexes of alkaline earth metals and organic substances, rare earth metals such as Eu and Yb, inorganic salts containing rare earth metals, and complexes of rare earth metals and organic substances. Two or more of these may be used. Of these, metallic lithium, rare earth metals, and lithium quinolinol (Liq) are preferred.

(electron injection layer)
In the present invention, an electron injection layer may be provided between the cathode and the electron transport layer. Generally, the electron injection layer is formed to facilitate the injection of electrons from the cathode to the electron transport layer and is composed of a compound having a heteroaryl ring structure containing electron-accepting nitrogen or the above-mentioned donor material. Two or more of these may be contained. Among these, triazine derivatives, phenanthroline derivatives, and oligopyridine derivatives are preferred, phenanthroline derivatives and terpyridine derivatives are more preferred, and phenanthroline derivatives represented by the following general formula (4) are even more preferred. That is, the light-emitting element of the present invention preferably contains a phenanthroline derivative represented by general formula (4) in the electron injection layer.

In the above general formula (4), Ar ¹ is selected from the group consisting of p-valent aromatic hydrocarbon groups and p-valent aromatic heterocyclic groups, where p is a natural number from 1 to 3. R ³¹ to R ³⁸ may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an aryl group, and a heteroaryl group. The substitution positions of the p phenanthrolyl groups in Ar ¹ may be any positions.

Examples of monovalent aromatic hydrocarbon groups include phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, benzofluorenyl, dibenzofluorenyl, phenanthryl, anthracenyl, benzophenanthryl, benzanthracenyl, chrysenyl, pyrenyl, fluoranthenyl, triphenylenyl, benzofluoranthenyl, dibenzoanthracenyl, perylenyl, and helicenyl groups. Among these, from the standpoint of ease of synthesis and sublimation, phenyl, biphenyl, terphenyl, naphthyl, fluorenyl, phenanthryl, anthracenyl, pyrenyl, fluoranthenyl, and triphenylenyl groups, as well as groups derived from these groups from which at least some of the hydrogen atoms have been removed, are preferred. The aromatic hydrocarbon group may or may not have a substituent. The number of ring carbon atoms is not particularly limited, but is preferably 6 to 40, more preferably 6 to 30. Furthermore, when two adjacent carbon atoms each have a substituent, the substituents may together form a ring structure.

Aromatic heterocyclic groups refer to cyclic aromatic groups having one or more atoms other than carbon within the ring. For example, in the case of monovalent groups, they include pyridyl, furanyl, thiophenyl, quinolinyl, isoquinolinyl, pyrazinyl, pyrimidyl, pyridazinyl, triazinyl, naphthyridinyl, cinnolinyl, phthalazinyl, quinoxalinyl, quinazolinyl, benzofuranyl, benzothiophenyl, indolyl, and dibenzofuranyl. Examples of aromatic heterocyclic groups include a phenyl group, a dibenzothiophenyl group, a carbazolyl group, a benzocarbazolyl group, a carbolinyl group, an indolocarbazolyl group, a benzofurocarbazolyl group, a benzothienocarbazolyl group, a dihydroindenocarbazolyl group, a benzoquinolinyl group, an acridinyl group, a dibenzoacridinyl group, a benzimidazolyl group, an imidazopyridyl group, a benzoxazolyl group, a benzothiazolyl group, and a phenanthrolinyl group. However, the naphthyridinyl group refers to a 1,5-naphthyridinyl group, a 1,6-naphthyridinyl group, a 1,7-naphthyridinyl group, a 1,8-naphthyridinyl group, a 2,6-naphthyridinyl group, or a 2,7-naphthyridinyl group. The aromatic heterocyclic group may or may not have a substituent. The number of ring carbon atoms in the aromatic heterocyclic group is not particularly limited, but is preferably in the range of 2 to 40, more preferably 2 to 30.

The aromatic hydrocarbon group or aromatic heterocyclic group may have further substituents in addition to the phenanthryl group.

From the viewpoint of sublimation properties and thin film formability, p is preferably 2.

An example of a phenanthroline derivative represented by general formula (4) is shown below.

In addition, inorganic insulating or semiconducting materials can also be used for the electron injection layer. Using these materials is preferable because it can prevent short circuits in the light-emitting element and improve electron injection properties.

Preferred insulators are metal compounds such as alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides. Two or more of these may be used.

(Charge Generation Layer)
The charge generation layer in the present invention generally comprises a double layer, specifically, a pn junction charge generation layer comprising an n-type charge generation layer and a p-type charge generation layer. When a voltage is applied to the light-emitting device, the pn junction charge generation layer generates charges or separates the charges into holes and electrons, and injects the holes and electrons into the light-emitting layer via the hole transport layer and electron transport layer. Specifically, it functions as an intermediate charge generation layer in a light-emitting device in which light-emitting layers are stacked. The n-type charge generation layer supplies electrons to the first light-emitting layer located on the anode side, and the p-type charge generation layer supplies holes to the second light-emitting layer located on the cathode side. Therefore, the luminous efficiency of a light-emitting device in which multiple light-emitting layers are stacked can be improved, the driving voltage can be reduced, and the durability of the light-emitting device can also be improved.

The n-type charge generation layer comprises an n-type dopant and a host, and conventional materials can be used for these. Examples of n-type dopants include alkali metals, alkaline earth metals, and rare earth metals. Two or more of these may be used. Among these, alkali metals or their salts, and rare earth metals are preferred, with metallic lithium, lithium fluoride (LiF), lithium quinolinol (Liq), and metallic ytterbium being more preferred. Examples of hosts include triazine derivatives, phenanthroline derivatives, and oligopyridine derivatives. Two or more of these may be used. Among these, triazine derivatives, phenanthroline derivatives, and oligopyridine derivatives are preferred, with phenanthroline derivatives and terpyridine derivatives being more preferred, and phenanthroline derivatives represented by the general formula (4) being even more preferred. That is, the light-emitting element of the present invention preferably contains a phenanthroline derivative represented by the general formula (4) in the charge generation layer.

The p-type charge generation layer comprises a p-type dopant and a host, and conventional materials can be used for these. Examples of p-type dopants include tetrafluorene-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), tetracyanoquinodimethane derivatives, radialene derivatives, iodine, FeCl ₃ , FeF ₃ , and SbCl _5. Two or more of these may be used. Among these, arylamine derivatives are preferred.

(Method for manufacturing light-emitting element)
The method for forming each of the layers constituting the light-emitting device may be either a dry process or a wet process, such as resistance heating evaporation, electron beam evaporation, sputtering, molecular lamination, coating, inkjet printing, etc. Among these, resistance heating evaporation is preferred from the viewpoint of device characteristics.

The thickness of the organic layer cannot be limited because it depends on the resistance value of the light-emitting material, but is preferably 1 to 1,000 nm. The film thickness of the light-emitting layer, electron transport layer, and hole transport layer is preferably 1 nm to 200 nm, and more preferably 5 nm to 100 nm.

(Light Emitting Element Characteristics)
The light-emitting device according to the embodiment of the present invention has a function of converting electrical energy into light. While direct current is primarily used as the electrical energy, pulsed current or alternating current can also be used. There are no particular limitations on the current and voltage values, and the required characteristic values vary depending on the purpose of the device. However, from the viewpoint of the power consumption and lifespan of the device, it is preferable to obtain high brightness at a low voltage.

In the light-emitting element according to the embodiment of the present invention, from the viewpoint of enhancing color purity, in order to further improve the color purity in the fluorescent spectrum when current is applied, the half-value width is preferably 45 nm or less, and more preferably 35 nm or less.

(Use of light-emitting element)
The light-emitting device according to the embodiment of the present invention is suitably used as a display device such as a display that displays in a matrix and/or segment system.

Light-emitting elements according to embodiments of the present invention are also preferably used as backlights for various devices. Backlights are primarily used to improve the visibility of non-self-luminous displays and other display devices, and are used in display devices such as liquid crystal displays, clocks, audio equipment, automotive panels, display boards, and signs. In particular, the light-emitting elements of the present invention are preferably used as backlights for liquid crystal displays, especially for personal computers, where thinner designs are being considered, and can provide backlights that are thinner and lighter than conventional ones.

Light-emitting elements according to embodiments of the present invention are also suitable for use in various lighting devices. Light-emitting elements according to embodiments of the present invention are capable of achieving both high luminous efficiency and high color purity, and can also be made thinner and lighter, making it possible to realize lighting devices that combine low power consumption, vivid luminous colors, and high design flexibility.

The present invention will be explained below using examples, but the present invention is not limited to these examples.

First, the evaluation methods used in each example and comparative example are described below.

( ^1H -NMR)
The compound having a pyrromethene skeleton obtained in Example 1 was subjected to ¹ H-NMR measurement in a deuterated chloroform solution using a superconducting FTNMR EX-270 (manufactured by JEOL Ltd.) to identify its structure.

(Absorption spectrum)
The compounds having a pyrromethene skeleton obtained in each of the Examples and Comparative Examples were dissolved in toluene to prepare diluted solutions with a concentration of 10 ⁻⁵ mol/L. The absorption spectra were measured using a spectrophotometer (U-3010) manufactured by Hitachi High-Tech Science Corporation, and the peak wavelength λmax was determined.

(Fluorescence spectrum)
The compounds having a pyrromethene skeleton obtained in each of the Examples and Comparative Examples were dissolved in toluene to prepare diluted solutions with a concentration of 10 ⁻⁵ mol/L. The fluorescence spectra were measured using a FluoroMax-4P fluorescence spectrophotometer manufactured by Horiba, Ltd., and the peak wavelength λmax and half-width were determined.

(Fluorescence quantum yield)
The compounds having a pyrromethene skeleton obtained in each of the Examples and Comparative Examples were dissolved in toluene to prepare diluted solutions with a concentration of 10 ⁻⁵ mol/L, and the fluorescence quantum yield QY was measured using an absolute PL quantum yield measurement device manufactured by Hamamatsu Photonics K.K.

(Thermal activated delayed fluorescence element characteristics)
The characteristics of the light-emitting devices of Examples 1 to 20 and Comparative Examples 1 and 2 were evaluated by the following method.

A glass substrate (manufactured by Geomatec Co., Ltd., 11 Ω/□, sputtered product) on which a 100 nm ITO transparent conductive film had been deposited was cut into 38 mm x 46 mm pieces and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" (registered trademark) 56 (trade name, manufactured by Furuuchi Chemical Co., Ltd.) and then washed with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before fabricating the device, then placed in a vacuum deposition apparatus and evacuated until the degree of vacuum inside the apparatus reached 5 x 10 ^-4 Pa or less. First, a hole injection layer of 10 nm HAT-CN6 and a hole transport layer of 30 nm HT-1 were vapor-deposited by resistance heating. Next, a 30 nm thick light-emitting layer was formed by vapor-depositing a host material H-1, D-1 to D-22 shown in Table 1, and the TADF material compound H-2 in a weight ratio of 79.0:1.0:20. Next, ET-1 was laminated to a thickness of 10 nm as a hole element layer, and ET-2 was laminated to a thickness of 40 nm as an electron transport layer. Next, 2E-1 was vapor-deposited to a thickness of 0.5 nm as an electron injection layer, and then magnesium and silver were co-deposited to a thickness of 100 nm as a cathode to prepare a 5 × 5 mm square light-emitting device.

A voltage was applied to the obtained light-emitting device so that the current density was 0.1 mA/ ^cm2 , and the spectrum when this was measured using a spectroradiometer CS-1000 manufactured by Konica Minolta, Inc. From the obtained spectrum, the element efficiency EQE was calculated, assuming that Lambertian radiation was performed.

Furthermore, a voltage was applied to the obtained light-emitting device so that the current density was 10 mA/cm ² , and the spectrum was similarly measured. The peak wavelength λmax and half-width were calculated to evaluate the color purity.

(Evaluation of tandem fluorescent light emitting devices)
For Example 21, the characteristics of the tandem light-emitting device were evaluated by the following method.

A glass substrate (manufactured by Geomatec Co., Ltd., 11 Ω/□, sputtered product) with a 100 nm thick ITO transparent conductive film deposited as an anode was cut into 38 mm x 46 mm pieces and etched. The resulting substrate was ultrasonically cleaned for 15 minutes using "Semicoclean" 56 (trade name, manufactured by Furuuchi Chemical Co., Ltd.) and then rinsed with ultrapure water.

This substrate was subjected to UV-ozone treatment for 1 hour immediately before fabricating the device, then placed in a vacuum deposition apparatus and evacuated until the degree of vacuum in the apparatus was 5 × 10 ^-4 Pa or less. Using a resistance heating method, first, 5 nm of HAT-CN6 was deposited as a hole injection layer, followed by 30 nm of HT-1 as a hole transport layer. Next, host materials H-1, D-1, and compound H-2, a TADF material, were deposited to a thickness of 30 nm at a weight ratio of 79.0:1.0:20. Further, 10 nm of ET-1 was deposited as a hole blocking layer, and 35 nm of compound ET-3 was deposited as an electron transport layer. Subsequently, 10 nm of compound ET-3, an n-type host, and metallic lithium, an n-type dopant, were deposited as an n-type charge generation layer at a deposition rate ratio of 99:1. Furthermore, 10 nm of HAT-CN6 was deposited as a p-type charge generation layer. A 30 nm hole-transporting layer and a 30 nm light-emitting layer were formed thereon in the same manner as above. ET-2 was then deposited to a thickness of 10 nm as a hole-blocking layer, followed by ET-3 at a thickness of 35 nm as an electron-transporting layer. Next, 2E-1 was deposited to a thickness of 0.5 nm as an electron-injecting layer, and then magnesium and silver were co-deposited to a thickness of 1000 nm as a cathode, to produce a tandem light-emitting device measuring 5 mm x 5 mm.

A voltage was applied to the obtained light-emitting device so that the current density was 0.1 mA/ ^cm2 , and the spectrum when this was measured using a spectroradiometer CS-1000 manufactured by Konica Minolta, Inc. From the obtained spectrum, the element efficiency EQE was calculated, assuming that Lambertian radiation was performed.

Furthermore, a voltage was applied to the obtained light-emitting device so that the current density was 10 mA/cm ² , and the spectrum was similarly measured. The peak wavelength λmax and half-width were calculated to evaluate the color purity.

Example 1
A mixed solution of 5.00 g of 3-methylpyrrole, 8.70 g of bis(pinacolato)diboron, 0.34 g of chloro(1,5-cyclooctadiene)iridium(I) (dimer), 0.28 g of 2,6-di-tert-butylpyridine, and 120 ml of heptane was heated and stirred at 80°C for 5 hours under a nitrogen stream. The reaction solution was cooled to room temperature, filtered through Celite, and the solvent was then distilled off to obtain 8.15 g of 2-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaboran-2-yl)-pyrrole.

A mixed solution of 2.5 g of 2-methyl-4-(4,4,5,5-tetramethyl-1,3,2-dioxaboran-2-yl)-pyrrole, 3.06 g of mesityl bromide, 0.28 g of tetrakis(triphenylphosphine)palladium(0), 5.12 g of potassium phosphate, 24 ml of dimethoxyethane, and 3 ml of water was heated to reflux under a nitrogen stream for 2 hours. The reaction solution was cooled to room temperature, filtered through Celite, and the solvent was distilled off to yield 1.75 g of 2-mesityl-4-methylpyrrole.

1.75 g of 2-mesityl-4-methylpyrrole and 0.65 g of 2,4,6-trimethylbenzaldehyde were added to the reaction solution, and 30 mL of dichloromethane and 5 drops of trifluoroacetic acid were added and stirred for 1 hour. 1.64 g of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone was added and stirred for 1 hour. 3.90 mL of diisopropylethylamine and 3.79 mL of boron trifluoride diethyl ether complex were added and stirred for 1 hour, after which the solvent was distilled off, water was added and stirred, the organic layer was separated, and washed with saturated brine. This organic layer was dried over magnesium sulfate, filtered, and the solvent was distilled off. The resulting reaction product was purified by silica gel chromatography to obtain 670 mg of an orange powder. The ¹ H-NMR analysis results of the resulting powder were as follows, confirming that the orange powder obtained above was Compound D-1 having a pyrromethene skeleton.
¹ H-NMR (CDCl ₃ (d=ppm)): 7.01 (s, 2H), 6.79 (s, 4H), 5.92 (s, 2H), 2.37 (s, 3H), 2.22 (s, 6H), 2.20 (s, 6H), 2.08 (s, 12H), 1.48 (s, 6H).

Sublimation purification was carried out to further increase the purity. The metal container containing compound D-1 was placed in a glass tube and heated at 220°C under a pressure of 1 x ^10-3 Pa using an oil diffusion pump to cause sublimation. The solid adhering to the wall of the glass tube was collected and analyzed by LC-MS, revealing a purity of 99%. The results of evaluation of D-1 after sublimation purification using the above-mentioned method are shown below.
Absorption spectrum (solvent: toluene): λmax 507 nm
Fluorescence spectrum (solvent: toluene): λmax 525 nm, half width 30 nm
Fluorescence quantum yield QY (solvent: toluene, excitation light: 460 nm): 100%

(Examples 2 to 20, Comparative Examples 1 and 2)
Instead of compound D-1, the compounds shown in Table 1 were synthesized and evaluated in the same manner as in Example 1. However, for Comparative Example 2, the emission wavelength was significantly different from that of the Examples, making it difficult to compare the device configuration similar to that of the Examples, so device evaluation was not performed. The evaluation results are shown in Table 1.

(Example 21)
When the characteristics of a tandem light-emitting device were evaluated using the compound D-1 by the above-mentioned method, the λmax was 525 nm, the half-value width was 35 nm, and the device efficiency EQE was 35.1%.

The structures of D-1 to D-22 are shown below.

As can be seen from Table 1, in Examples 1 to 20, the device efficiency was significantly improved compared to Comparative Example 1. Furthermore, green light emission with higher color purity was obtained compared to Comparative Example 2. Furthermore, in Example 21, the device efficiency was further improved compared to Example 1, which had only one light-emitting layer.

Claims (18)

A compound having a pyrromethene skeleton represented by the following general formula (1) (excluding the compound represented by the following (2-3)).
(In the above general formula (1), one to three of R ¹ , R ³ , R ⁴ and R ⁶ are represented by the following general formula (2), and the rest are selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. R ² and R ⁵ may be the same or different and are selected from the group consisting of a hydrogen atom, substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups.)
^R7 is selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, and a silyl group. These groups may further have a substituent.
L ¹ and L ² are each a fluorine atom.
In the above general formula (2), *** represents the bond to the carbon atom.
^R21 and ^R25 may be the same or different and are selected from the group consisting of alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, alkoxy groups, alkylthio groups, aryl groups, heteroaryl groups, aryl ether groups, aryl thioether groups, hydroxyl groups, halogens, cyano groups, aldehyde groups, acyl groups, ester groups, amide groups, sulfonyl groups, sulfonate ester groups, sulfonamide groups, amino groups, nitro groups, silyl groups, and ring structures between adjacent groups. These groups may further have a substituent.
R ²² to R ²⁴ may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an aryl thioether group, a hydroxyl group, a halogen atom, a cyano group, an aldehyde group, an acyl group, an ester group, an amide group, a sulfonyl group, a sulfonate ester group, a sulfonamide group, an amino group, a nitro group, a silyl group, and a ring structure between adjacent groups. These groups may further have a substituent.
The compound having a pyrromethene skeleton according to claim 1, wherein in the general formula (2), ^R21 and ^R25 are selected from the group consisting of a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted heteroaryl group, and a ring structure between adjacent groups. The compound having a pyrromethene skeleton according to claim 1 or 2, wherein in the general formula (1), R ⁷ is selected from the group consisting of a substituted or unsubstituted aryl group and a substituted or unsubstituted heteroaryl group. The compound having a pyrromethene skeleton according to any one of claims ¹ to ³ , wherein, in the general formula (1), ^R1 and ^R6 are selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted cycloalkyl group, and at least one of R3 and R4 is a group represented by the general formula (2). The compound having a pyrromethene skeleton according to claim 4, wherein in the general formula (1), ^R3 and ^R4 are groups represented by the general formula (2). The compound having a pyrromethene skeleton according to any one of claims 1 to ³ , wherein, in the general formula (1 ⁾ , ^R3 and ^R4 are selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted cycloalkyl group, and at least one of R1 and R6 is a group represented by the general formula (2). The compound having a pyrromethene skeleton according to claim 6, wherein in the general formula (1), R ¹ and R ⁶ are groups represented by the general formula (2). A compound having a pyrromethene skeleton according to any one of claims 1 to 7, wherein the peak wavelength of the fluorescence spectrum is 500 nm or more and 550 nm or less. A light-emitting device material comprising the compound described in any one of claims 1 to 8. A light-emitting element that emits light when exposed to electrical energy, having a light-emitting layer between an anode and a cathode, the light-emitting element material of claim 9. The light-emitting device according to claim 10 , wherein the light-emitting layer contains a first compound and a second compound, and the second compound contains the compound having a pyrromethene skeleton according to any one of claims 1 to 8. The light-emitting device described in claim 10 or 11, wherein the first compound contains a thermally activated delayed fluorescent compound. The light-emitting device described in claim 12, wherein the light-emitting layer further contains a third compound, and the singlet energy of the third compound is greater than the singlet energy of the first compound. The light-emitting element described in any one of claims 10 to 13, wherein the light-emitting layer is laminated multiple times with a charge-generating layer interposed therebetween. The light-emitting device according to claim 14 , wherein the charge generating layer contains a phenanthroline derivative represented by the following general formula (3):
(In the above general formula (3), Ar ¹ is selected from the group consisting of p-valent aromatic hydrocarbon groups and p-valent heteroaromatic ring groups, where p is a natural number from 1 to 3. R ³¹ to R ³⁸ may be the same or different and are selected from the group consisting of a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an aryl group, and a heteroaryl group. The substitution positions of the p phenanthrolyl groups in Ar ¹ are arbitrary positions.) The light-emitting device according to any one of claims 10 to 15, which is a top-emission organic electroluminescent device. A display device comprising the light-emitting element according to any one of claims 10 to 16. A lighting device comprising the light-emitting element described in any one of claims 10 to 16.