JP2022132743A - Compound, and light-emitting element material and light-emitting element using the same - Google Patents

Abstract

To provide a compound having green light-emitting characteristics, a light-emitting element material, and a light-emitting element.SOLUTION: The compound has a structure represented by formula (1) (X1 and X2 are each independently an aryl group or an alkyl group and may be bonded to R1, R6, R7 and/or R8 via a linking group or a single bond; A1-A3 are each independently a group having a positive substituent constant σp value in Hammett equation, H, a phenyl group or an alkyl group; and R1-R8 are each independently H, 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 or the like).SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to novel compounds and light-emitting device materials, light-emitting devices, display devices, and lighting devices using the same.

An organic thin film light-emitting device that emits light by recombination of electrons injected from the cathode and holes injected from the anode in the light-emitting layer sandwiched between the two electrodes can be made thinner and has a low driving voltage. , high luminance, and the ability to emit light in multiple colors.

In order to further increase the color gamut of organic light-emitting devices, efforts are being made to develop materials with a narrow half-value width. As such a technique, for example, polycyclic aromatic compounds in which a plurality of aromatic rings are connected via boron atoms and nitrogen atoms (see, for example, Patent Document 1 and Non-Patent Document 1) have been proposed.

WO2015/102118

"Advanced. Materials", 2016, vol. 28, p. 2777-2781

The polycyclic aromatic compounds described in Patent Literature 1 and Non-Patent Literature 1 have high luminance as blue light-emitting materials, but their emission wavelengths are insufficient as green light-emitting materials. Accordingly, an object of the present invention is to provide a compound having green light emission properties.

The present invention is a compound having a structure represented by the following general formula (1).

In general formula (1) above, X ¹ and X ² are each independently an aryl group or an alkyl group, and are bonded to R ¹ , R ⁶ , R ⁷ and/or R ⁸ via a linking group or a single bond. You may These groups may further have a substituent.

A ¹ to A ³ are each independently a group having a positive substituent constant σp value in Hammett's rule, a hydrogen atom, a phenyl group or an alkyl group. However, at least one of A ¹ and A ² is a group having a positive substituent constant σp value in Hammett's rule. The phenyl group and alkyl group may further have a substituent.

R ¹ to R ⁸ each independently represent 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 or an arylthioether group. These groups may further have a substituent.

The compound of the present invention has green emission characteristics with a longer wavelength than conventionally known polycyclic aromatic compounds. The compound of the present invention can provide a light-emitting device material and a light-emitting device that emit green light with excellent color purity.

The contents of the present invention will be described in detail below. The present invention is not limited to the embodiments and specific examples described below.

[Compound having a structure represented by general formula (1)]
The compound of the present invention has a structure represented by the following general formula (1). A compound having a structure represented by the following general formula (1) exhibits a high fluorescence quantum yield because it has a rigid and highly planar skeleton. Moreover, since the peak half width in the emission spectrum is small, the color purity can be improved.

In the above general formula (1), X ¹ and X ² are each independently an aryl group or an alkyl group, and are bonded to R ¹ , R ⁶ , R ⁷ and/or R ⁸ via a linking group or a single bond. You may In addition, the aryl group or alkyl group may further have a substituent. By introducing an aryl group or ^an alkyl group into the positions of ^X1 and X2, electrical stability and thermal stability can be improved without affecting the wavelength.

A ¹ to A ³ are each independently a group having a positive substituent constant σp value in Hammett's rule, a hydrogen atom, a phenyl group or an alkyl group. However, at least one of A ¹ and A ² is a group having a positive substituent constant σp value in Hammett's rule. The phenyl group and alkyl group may further have a substituent. Here, the "substituent constant σp value in Hammett's rule" (hereinafter sometimes simply referred to as "σp value") is defined by L. P. It was proposed by Hammett and represents a per-substituent reaction constant that quantifies the effect of a substituent on the reaction rate or equilibrium of para-substituted benzene derivatives. The "σp value" in the present invention is Hansch, C.; et. al. , "Chemical Reviews", 1991, vol. 91, p. 165-195. A group with a positive σp value tends to exhibit electron-withdrawing properties (acceptor properties).

R ¹ to R ⁸ each independently represent 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 or an arylthioether group. These groups may further have a substituent.

As a means for causing a polycyclic aromatic compound to emit green light as described in Patent Document 1, a method of extending the conjugation and lengthening the emission wavelength is conceivable. However, since the polycyclic aromatic compound forms a specific excited state using the multiple resonance effect, it has been difficult to increase the wavelength by simply extending the conjugated system. Therefore, in the present invention, as shown in the general formula (1), a group having a positive σp value indicating electron-withdrawing property, a hydrogen atom, a phenyl group, or an alkyl group is added to a specific position of A ¹ to A ³ . A group having a positive σp value is introduced into A ¹ and/or A ² . By introducing these groups into the p-position of boron, the lowest unoccupied molecular orbital extends to a group with a positive σp value, making it possible to lengthen the wavelength.

^{The isotopic} species of the hydrogen atoms present in the molecule of the compound of the present invention is not particularly limited. D).

In the following description, "unsubstituted" in the case of "substituted or unsubstituted" means that a hydrogen atom or deuterium atom is attached.

The alkyl group is, for example, a saturated aliphatic hydrocarbon group such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, which is a substituent may or may not have The number of carbon atoms in the alkyl group is not particularly limited, but is preferably from 1 to 20, more preferably from 1 to 8, from the viewpoint of availability and cost. The number of carbon atoms as used herein includes the number of carbon atoms contained in the substituents bonded to the alkyl group, and the same applies to other substituents defining the number of carbon atoms.

A cycloalkyl group is, for example, a saturated alicyclic hydrocarbon group such as a cyclopropyl group, a cyclohexyl group, a norbornyl group, and an adamantyl group, which may or may not have a substituent. The number of ring-forming carbon atoms is not particularly limited, but is preferably in the range of 3 or more and 20 or less.

A heterocyclic group is, for example, a pyran ring, a piperidine ring, an aliphatic ring having a non-carbon atom in the ring such as a cyclic amide, which may or may not have a substituent. . Although the number of ring-forming atoms is not particularly limited, it is preferably in the range of 3 or more and 20 or less.

The alkenyl group is, for example, an unsaturated aliphatic hydrocarbon group containing a double bond such as a vinyl group, an allyl group, a butadienyl group, etc., which may or may not have a substituent. Although the number of carbon atoms in the alkenyl group is not particularly limited, it is preferably in the range of 2 or more and 20 or less.

A cycloalkenyl group is an unsaturated alicyclic hydrocarbon group containing a double bond such as, for example, a cyclopentenyl group, a cyclopentadienyl group, a cyclohexenyl group, which may or may not have a substituent. You don't have to. The number of ring-forming carbon atoms is not particularly limited, but is preferably in the range of 3 or more and 20 or less.

An alkynyl group is, for example, an unsaturated aliphatic hydrocarbon group containing a triple bond such as an ethynyl group, which may or may not have a substituent. Although the number of carbon atoms in the alkynyl group is not particularly limited, it is preferably in the range of 2 or more and 20 or less.

An aryl group includes, for example, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthryl group, anthracenyl group, a benzophenanthryl group, and a benzoanthracene. It represents an aromatic hydrocarbon group such as a nyl group, a chrysenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, a benzofluoranthenyl group, a dibenzoanthracenyl group, a perylenyl group, and a helicenyl group. It may or may not have a substituent. Among these, phenyl group, biphenyl group, terphenyl group, naphthyl group, fluorenyl group, phenanthryl group, anthracenyl group, pyrenyl group, fluoranthenyl group and triphenylenyl group are preferred. The number of ring-forming carbon atoms is not particularly limited, but is preferably 6 or more and 40 or less, more preferably 6 or more and 30 or less.

Moreover, in the substituted phenyl group, when there are substituents on two adjacent carbon atoms in the phenyl group, the substituents may form a ring structure. The resulting group, depending on its structure, is a "substituted phenyl group", an "aryl group having a structure in which two or more rings are condensed", or a "structure in which two or more rings are condensed." any one or more of "heteroaryl group having".

The heteroaryl group includes, for example, pyridyl group, furanyl group, thiophenyl group, quinolinyl group, isoquinolinyl group, pyrazinyl group, pyrimidyl group, pyridazinyl group, triazinyl group, napthyridinyl group, cinnolinyl group, phthalazinyl group, quinoxalinyl group, quinazolinyl group, benzofuranyl group, benzothiophenyl group, indolyl group, dibenzofuranyl group, dibenzothiophenyl group, carbazolyl group, benzocarbazolyl group, carbolinyl group, indolocarbazolyl group, benzoflocarbazolyl group, benzothienocarba non-carbon groups such as zolyl, dihydroindenocarbazolyl, benzoquinolinyl, acridinyl, dibenzoacridinyl, benzimidazolyl, imidazopyridyl, benzoxazolyl, benzothiazolyl, phenanthrolinyl represents a cyclic aromatic group having one or more atoms in the ring. However, the naphthyridinyl group is any of 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 and a 2,7-naphthyridinyl group. or A heteroaryl group may or may not have a substituent. The number of ring-forming atoms is not particularly limited, but is preferably 3 or more and 40 or less, more preferably 3 or more and 30 or less.

An alkoxy group is, for example, a functional group in which an aliphatic hydrocarbon group is bonded via an ether bond such as a methoxy group, an ethoxy group, or a propoxy group, which may or may not have a substituent. good too. Although the number of carbon atoms in the alkoxy group is not particularly limited, it is preferably in the range of 1 or more and 20 or less.

An alkylthio group is an alkoxy group in which the oxygen atom of the ether bond is substituted with a sulfur atom. It may or may not have a substituent. Although the number of carbon atoms in the alkylthio group is not particularly limited, it is preferably in the range of 1 or more and 20 or less.

An aryl ether group is, for example, a group in which an aromatic hydrocarbon group is bonded via an ether bond, such as a phenoxy group, which may or may not have a substituent. Although the number of carbon atoms in the aryl ether group is not particularly limited, it is preferably in the range of 6 or more and 40 or less.

An arylthioether group is an arylether group in which the oxygen atom of the ether bond is substituted with a sulfur atom. It may or may not have a substituent. Although the number of carbon atoms in the arylthioether group is not particularly limited, it is preferably in the range of 6 or more and 40 or less.

In all the above groups, substituents when substituted include alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, hydroxyl groups, thiol groups, Alkoxy group, alkylthio group, arylether group, arylthioether group, halogen, cyano group, aldehyde group, acyl group, carboxyl group, ester group, amide group, acyl group, sulfonyl group, sulfonate ester group, sulfonamide group, amino A group, a nitro group, a silyl group, a siloxanyl group, and a boryl group are preferred, and specific substituents that are preferred in the description of each substituent are preferred. In addition, these substituents may be further substituted with the above substituents.

Halogen denotes fluorine, chlorine, bromine or iodine.

A cyano group is a group whose structure is represented by -C≡N. It is the carbon atom that is bonded to the other group here.

An aldehyde group is a functional group whose structure is represented by -C(=O)H. Here, it is a carbon atom that binds to other functional groups. The number of carbon atoms in an acyl group representing a group in which an alkynyl group, an aryl group, or a heteroaryl group is bonded is not particularly limited, but is preferably 2 or more and 40 or less, more preferably 2 or more and 30 or less.

An ester group is a functional group in which, for example, an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or the like is bonded via an ester bond. The number of carbon atoms in the ester group is not particularly limited, but is preferably in the range of 1 to 20. More specifically, a methyl ester group such as a methoxycarbonyl group, an ethyl ester group such as an ethoxycarbonyl group, a propyl ester group such as a propoxycarbonyl group, a butyl ester group such as a butoxycarbonyl group, and an isopropyl group such as an isopropoxymethoxycarbonyl group. Examples include an ester group, a hexyl ester group such as a hexyloxycarbonyl group, and a phenyl ester group such as a phenoxycarbonyl group.

An amide group is a functional group in which, for example, an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or the like is bonded via an amide bond. Although the number of carbon atoms in the amide group is not particularly limited, it is preferably in the range of 1 or more and 20 or less. More specific examples include a methylamido group, an ethylamido group, a propylamido group, a butylamido group, an isopropylamido group, a hexylamido group, a phenylamido group and the like.

A sulfonyl group is, for example, a group in which an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or the like is bonded via a -S(=O) ₂ - bond. The number of carbon atoms in the sulfonyl group is not particularly limited, but is preferably in the range of 1 to 20.

A sulfonate group is, for example, a group in which an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or the like is bonded via a sulfonate bond. Here, the sulfonate ester bond refers to an ester bond in which the carbonyl portion, ie, —C(=O)—, is substituted with a sulfonyl portion, ie, —S(=O) ₂ —. The number of carbon atoms in the sulfonate group is not particularly limited, but is preferably in the range of 1 or more and 20 or less.

A sulfonamide group is, for example, a group in which an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, or the like is bonded via a sulfonamide bond. A sulfonamide bond as used herein refers to an ester bond in which the carbonyl portion, ie, —C(=O)—, is substituted with a sulfonyl portion, ie, —S(=O) ₂ —. Although the number of carbon atoms in the sulfonamide group is not particularly limited, it is preferably in the range of 1 or more and 20 or less.

An amino group is a substituted or unsubstituted amino group. The number of carbon atoms in the amino group is not particularly limited, but is preferably 2 or more and 50 or less, more preferably 6 or more and 40 or less, and particularly preferably 6 or more and 30 or less.

A silyl group is a functional group to which a substituted or unsubstituted silicon atom is bonded, and examples thereof include alkylsilyl groups such as trimethylsilyl group, triethylsilyl group, tert-butyldimethylsilyl group, propyldimethylsilyl group and vinyldimethylsilyl group. and arylsilyl groups such as a phenyldimethylsilyl group, a tert-butyldiphenylsilyl group, a triphenylsilyl group and a trinaphthylsilyl group. Although the number of carbon atoms in the silyl group is not particularly limited, it is preferably in the range of 1 or more and 30 or less.

A siloxanyl group indicates a silicon compound group through an ether bond such as a trimethylsiloxanyl group.

A boryl group is a substituted or unsubstituted boryl group. Preferred substituents for substitution are aryl groups and aryl ether groups.

In all the above groups, the substituents when substituted include alkyl groups, cycloalkyl groups, heterocyclic groups, alkenyl groups, cycloalkenyl groups, alkynyl groups, aryl groups, heteroaryl groups, hydroxyl groups, thiol groups, group, alkoxy group, alkylthio group, arylether group, arylthioether group, halogen, cyano group, aldehyde group, acyl group, carboxyl group, ester group, amide group, acyl group, sulfonyl group, sulfonate ester group, sulfonamide group , an amino group, a nitro group, a silyl group, a siloxanyl group, and a boryl group are preferred, and specific substituents that are preferred in the description of each substituent are preferred. In addition, these substituents may be further substituted with the above substituents.

Groups with a positive substituent constant σp value in Hammett's rule include, for example, a group containing a cyano group, a carbonyl group, a sulfonyl group, a substituted or unsubstituted heteroaryl group, a quinone ring or a pyrone ring, a substituted or unsubstituted Examples include a monovalent group having a structure in which a substituted benzene ring is condensed and having one hydrogen atom removed from the benzene ring. The heteroatom contained in the heteroaryl group includes, for example, a nitrogen atom, an oxygen atom, a sulfur atom, a boron atom and the like, with a nitrogen atom being more preferred. The heteroaryl group preferably contains at least one nitrogen atom as a ring member, for example, a group consisting of a 5- or 6-membered ring containing a nitrogen atom as a ring member, a 5-membered ring containing a Groups having a structure in which a substituted or unsubstituted benzene ring is fused to a 6-membered ring, and the like are included. More specifically, a pyridine ring, a pyrazine ring, a pyrimidine ring, a pyridazine ring, a monovalent group obtained by removing one hydrogen atom from a triazine ring, a group having a structure in which these aromatic heterocycles are condensed, A group having a structure in which a benzene ring is fused to an aromatic hetero ring of is preferable. Examples of substituents include alkyl groups having 1 to 20 carbon atoms, aryl groups having 6 to 40 carbon atoms, cyano groups, halogen atoms, and heteroaryl groups having 5 to 40 carbon atoms. Among these substituents, those substitutable by a substituent may be substituted.

Examples of the group with a positive σp value include the groups shown below. Among the groups exemplified below, those having a ring structure are bonded by replacing the hydrogen atom of any one of the methine groups (-CH=) constituting the ring structure. The left and right lines of CO of the carbonyl group (--CO--) and the left and right lines of SO ₂ of the sulfonyl group ( _--SO.sub.2-- ) each represent a single bond (bond). A carbonyl group (—CO—) and a sulfonyl group (—SO ₂ —) are directly bonded to one single bond or connected to A ¹ to A ³ via a linking group, and the other single bond has an atomic group are combined. Atom groups include substituted or unsubstituted alkyl groups, aryl groups, heteroaryl groups, and the like. The alkyl group preferably has 1 to 20 carbon atoms, the aryl group preferably has 6 to 40 carbon atoms, and the heteroaryl group preferably has 5 to 40 carbon atoms.

Among these, groups having a positive σp value are represented by the following structural formulas (a-1) to (a-8) from the viewpoint of ease of synthesis and excellent electrical and thermal stability. It is preferable to have a partial structure represented by either. That is, the compound of the present invention has a partial structure in which at least one of A ¹ and A ² in the general formula (1) is represented by any one of the following structural formulas (a-1) to (a-8) It is preferred to have

Moreover, from the viewpoint of improving the luminous efficiency, the compound of the present invention preferably has a structure represented by the following general formula (2) or (3).

In general formulas (2) to (3) above, R ²¹ to R ²⁸ and R ³¹ to R ³⁸ each independently represent a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, a cycloalkenyl group, It is an alkynyl group, an alkoxy group, an alkylthio group, an aryl group, a heteroaryl group, an aryl ether group, an arylthioether group, or a ring structure between adjacent groups. These groups may further have a substituent.

Y ¹ to Y ⁴ are each independently a single bond, —O—, —S—, or a divalent substituent having a structure represented by the following general formula (4).

In general formula (4) above, R ¹⁰¹ and R ¹⁰² are each independently a hydrogen atom, an alkyl group or an aryl group. These groups may further have a substituent, and may form a ring structure between ^R101 and ^R102 .

Examples of compounds having a structure represented by general formula (1) are shown below, but are not limited thereto.

A compound having a structure represented by general formula (1) is described in, for example, "Advanced. Materials", 2016, vol. 28, p. 2777-2781 can be referred to.

The obtained compound having a structure represented by the general formula (1) is purified by organic synthesis such as recrystallization and column chromatography, and then further purified by heating under reduced pressure, which is generally called sublimation purification. It is preferable to remove low boiling point components to improve purity.

The purity of the compound having the structure represented by formula (1) is preferably 99% by weight or more from the viewpoint of stabilizing the characteristics of the light-emitting device.

In the fluorescence spectrum of the compound represented by formula (1), the peak wavelength is preferably 470 nm or more and 550 nm or less from the viewpoint of further improving the color purity of green emission. Here, the fluorescence spectrum of the compound represented by general formula (1) can be measured using a fluorescence spectrophotometer using a diluted solution with a concentration of 10 ⁻⁵ mol/L in toluene as a solvent.

<Light emitting element material>
The light-emitting element material in the present invention represents a material that contains a compound having a structure represented by general formula (1) and is used in any layer of the light-emitting element. For example, materials used for a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, and/or a protective film (cap layer) for electrodes, which will be described later, can be used. Among these, it is preferably used for the light-emitting layer because it has high device efficiency and color purity.

The light emitting device material may contain other components together with the compound having the structure represented by general formula (1). Other components include, for example, those exemplified as materials constituting the hole injection layer, hole transport layer, light emitting layer, electron transport layer and/or electrode protective film (cap layer) described later.

<Light emitting element>
Next, embodiments 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 by electrical energy.

The light emitting device of the present invention may be of either bottom emission type or top emission type. A top-emission type light-emitting device has a higher luminous efficiency with a narrower half width due to the resonance effect of the microcavity. Therefore, both color purity and luminous efficiency can be achieved at a higher level.

The layer structure between the anode and the cathode in such a light-emitting element includes, in addition to the structure consisting only of the light-emitting layer, 1) light-emitting layer/electron transport layer, 2) hole transport layer/light-emitting layer, and 3) hole transport layer. layer/emissive layer/electron transport layer, 4) hole injection layer/hole transport layer/emissive layer/electron transport layer, 5) hole transport layer/emissive 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, 8) positive Layered structures such as hole-injection layer/hole-transport layer/electron-blocking layer/light-emitting layer/hole-blocking layer/electron-transporting layer/electron-injecting layer can be mentioned.

Furthermore, a tandem type in which a plurality of the above laminated structures are laminated via an intermediate layer may be used. The intermediate layer generally includes an intermediate electrode, an intermediate conductive layer, a charge generation layer, an electron extraction layer, a connection layer, an intermediate insulating layer, and the like, and known material configurations can be used. As a preferred specific example of the tandem type, 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 Laminate constructions such as layer/electron injection layer are included.

Further, each of the above layers may be either a single layer or multiple layers, and may be doped. Moreover, in addition to the above layers, a protective layer (cap layer) may be further provided, and the light emission efficiency can be further improved by the optical interference effect.

Specific examples of the structure of the light-emitting element are given below, but the structure of the present invention is not limited thereto.

(substrate)
It is preferable to form the light-emitting element over a substrate in order to maintain the mechanical strength of the light-emitting element, reduce thermal deformation, and have barrier properties to prevent water vapor and oxygen from entering the light-emitting layer. Examples of the substrate include, but are not limited to, a glass plate, a ceramic plate, a resin film, a resin thin film, a metal thin plate, and the like. Among these substrates, a glass substrate is preferably used because it is transparent and easy to process. In particular, in the case of a bottom-emission type light-emitting device in which light is extracted through a substrate, a glass substrate having high transparency is preferable. In addition, flexible displays and foldable displays are increasing mainly in mobile devices such as smartphones, and resin films and resin thin films obtained by curing varnish are suitably used for these applications. A heat-resistant film is used as the resin film, and specific examples thereof include a polyimide film and a polyethylene naphthalate film.

Various wirings, circuits, and TFT switching elements for driving the organic EL may be provided on the surface of the substrate.

(anode)
An anode is preferably formed on the substrate. Various wiring, 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 is a material that can efficiently inject holes into the organic layer. In this case, it is preferably a reflective electrode.

Examples of materials for the transparent or translucent electrode include conductive metal oxides such as zinc oxide, tin oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO), gold, silver, aluminum, chromium, and the like. and conductive polymers such as polythiophene, polypyrrole and polyaniline. However, when a metal is used, it is preferable to make the film thickness thin so that light can be semi-transmitted. Among these, indium tin oxide (ITO) is more preferable from the viewpoint of transparency and stability.

As a material for the reflective electrode, it is preferable to use a material that does not absorb all light and has a high reflectance. Examples thereof include metals such as aluminum, silver, and platinum.

Two or more kinds of these electrode materials may be used, and a plurality of materials may be laminated.

Although the film thickness of the anode is not particularly limited, it is preferably several nanometers to several hundreds of nanometers.

As for the method of forming the anode, an optimum method can be selected according to the material for forming the anode, and examples thereof include a sputtering method, a vapor deposition method, an inkjet method, and the like. For example, a sputtering method is preferably used when forming an anode from a metal oxide, and a vapor deposition method is preferably used when forming an anode from a metal. Although the film thickness of the anode is not particularly limited, it is preferably several nanometers to several hundreds of nanometers.

(cathode)
The cathode is formed on the surface opposite to the anode with the organic layer interposed therebetween, and is particularly 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 is a material that can efficiently inject electrons into the light-emitting layer. It is preferably an electrode.

In general, metals such as platinum, gold, silver, copper, iron, tin, aluminum, and indium, alloys of these metals with low work function metals such as lithium, sodium, potassium, calcium, and magnesium, and multi-layer laminated films , zinc oxide, indium tin oxide (ITO), and conductive metal oxides such as indium zinc oxide (IZO) are preferred. Among these, aluminum, silver, and magnesium are preferable as the main component from the viewpoints of electrical resistance, ease of film formation, film stability, luminous efficiency, and the like. Moreover, when it is composed of magnesium and silver, electron injection into the electron transport layer and the electron injection layer is facilitated, and the driving voltage can be reduced, which is preferable.

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

(hole injection layer)
The hole injection layer is a layer that 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 a plurality of layers. The presence of a hole injection layer between the hole transport layer and the anode is preferable because it not only enables the device to be driven at a lower voltage and extends the durability life, but also improves the carrier balance of the device and the luminous efficiency.

A preferred example of the hole injection material is an electron-donating hole injection material (donor material). These materials have a HOMO level shallower than that of the hole transport layer and are close to the work function of the anode, so that the energy barrier with the anode can be reduced. Specifically, benzidine derivatives, 4,4′,4″-tris(3-methylphenyl(phenyl)amino)triphenylamine (m-MTDATA), 4,4′,4″-tris(1-naphthyl ( Aromatic amine materials such as starburst arylamines such as phenyl)amino)triphenylamine (1-TNATA), carbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole Derivatives, phthalocyanine derivatives, heterocyclic compounds such as porphyrin derivatives, polymer systems such as polycarbonates and styrene derivatives having the aforementioned monomers in side chains, polythiophenes such as PEDOT/PSS, polyanilines, polyfluorenes, polyvinylcarbazoles, and polysilanes. be. You may use 2 or more types of these. Alternatively, a hole injection layer may be formed by laminating a plurality of materials.

Another preferred example of the hole injection material is an electron-accepting hole injection material (acceptor material). Here, the hole injection layer may be composed of the acceptor material alone, or may be used by doping the acceptor material into the donor material. The acceptor material is a material that forms a charge-transfer complex with the adjacent hole-transport layer when used alone, or with the donor material when doped with the donor material. The use of such a material is more preferable because it contributes to the improvement of the conductivity of the hole injection layer and the reduction of the driving voltage of the device, and the effects such as the improvement of the luminous efficiency and the durability of the device can be obtained. 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), 1,4,5, 8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN6), 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), fluorine Examples include n-type organic semiconductor compounds such as copper phthalocyanine, fullerenes, and the like. When the hole injection layer contains the acceptor compound, the hole injection layer may consist of one layer or may be formed by laminating a plurality of layers.

(Hole transport layer)
The hole-transporting layer is a layer that transports holes injected from the anode to the light-emitting layer. The hole transport layer may be either a single layer or a laminate of a plurality of layers.

The hole-transporting layer is formed using one type of hole-transporting material alone, or by laminating or mixing two or more types of hole-transporting materials. Further, the hole transport material preferably has a high hole injection efficiency and efficiently transports the injected holes. For this purpose, it is required that the material has an appropriate ionization potential, high hole mobility, excellent stability, and does not easily generate trapping impurities.

Substances that satisfy these conditions are not particularly limited, but examples include benzidine derivatives, a group of aromatic amine materials called starburst arylamines, carbazole derivatives, pyrazoline derivatives, stilbene compounds, hydrazone compounds, Heterocyclic compounds such as benzofuran derivatives, dibenzofuran derivatives, thiophene derivatives, benzothiophene derivatives, dibenzothiophene derivatives, fluorene derivatives, spirofluorene derivatives, oxadiazole derivatives, phthalocyanine derivatives, and porphyrin derivatives; Polycarbonate, styrene derivative, polythiophene, polyaniline, polyfluorene, polyvinylcarbazole, polysilane, etc.

(Light emitting layer)
The light-emitting layer is a layer that emits light by excitation energy generated by recombination of holes and electrons. The light-emitting layer may be composed of a single material, but from the viewpoint of color purity, it preferably contains a first compound and a second compound, which are dopants that emit light with a narrow half-value width. Suitable examples of the second compound include a host material responsible for charge transfer and a thermally activated delayed fluorescent compound.

The compound having the structure represented by the general formula (1) has a particularly excellent fluorescence quantum yield, a fluorescence spectrum peak wavelength suitable for green light emission, a narrow half width, and low color purity. Since it is excellent, it is preferably used as the first compound that is a dopant for the light-emitting layer. From the viewpoint of further suppressing the concentration quenching phenomenon, the content of the first compound is preferably 5% by weight or less, more preferably 2% by weight or less, in the light-emitting layer. On the other hand, from the viewpoint of more efficient energy transfer, the content of the first compound in the light-emitting layer is preferably 0.1% by weight or more, more preferably 0.5% by weight or more.

Examples of the host material include, but are not limited to, compounds having condensed aryl rings such as naphthacene, pyrene, anthracene, fluoranthene, derivatives thereof, N,N'-dinaphthyl-N,N'-diphenyl-4,4'- Aromatic amine derivatives such as diphenyl-1,1′-diamine, metal chelated 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; paraphenylene derivatives, polyfluorene derivatives, polyvinylcarbazole derivatives, polythiophene derivatives and the like. Two or more of these may be used, or two or more host materials may be laminated. Among these, carbazole derivatives, anthracene derivatives, and naphthacene derivatives are preferred.

As a dopant material, a fluorescence-emitting material other than the compound having the structure represented by general formula (1) may be contained. Specifically, compounds having a condensed aryl ring such as naphthacene, pyrene, anthracene, and fluoranthene and their derivatives, compounds having a heteroaryl ring and their derivatives, distyrylbenzene derivatives, aminostyryl derivatives, tetraphenylbutadiene derivatives, and stilbene derivatives. , aldazine derivatives, pyrromethene derivatives, diketopyrrolo[3,4-c]pyrrole derivatives, coumarin derivatives, azole derivatives and their metal complexes, and aromatic amine derivatives. You may use 2 or more types of these.

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

However, from the viewpoint of further improving color purity, the dopant material is preferably only a compound having a structure represented by general formula (1).

The light-emitting layer may further contain a third component for adjusting the carrier balance in the light-emitting layer and stabilizing the layer structure of the light-emitting layer, in addition to the above host material or dopant material. However, as the third component, it is preferable to select a material that does not interact with the host material and the dopant material.

A thermally activated delayed fluorescence material is also generally called a TADF (Thermally Activated Delayed Fluorescence) material, and by reducing the energy gap between singlet excited states, a singlet is emitted from a triplet excited state. It is a material that promotes reverse intersystem crossing to an excited state and improves the generation probability of singlet excitons. By utilizing delayed fluorescence by this TADF mechanism, the theoretical internal efficiency can be increased to 100%. Furthermore, when Forster type energy transfer occurs from the singlet excited state of the second compound having thermally activated delayed fluorescence to the singlet excited state of the first compound, the singlet excited state of the first compound fluorescence emission is observed. Here, when the first compound is a fluorescent light-emitting material having a sharp fluorescence spectrum, a light-emitting device with excellent device efficiency and color purity can be obtained. Thus, when the light-emitting layer contains the thermally-activated delayed fluorescent material, the device efficiency is further improved, which contributes to lower power consumption of the display. The thermally activated delayed fluorescence material may be a material that exhibits thermally activated delayed fluorescence with a single material, or a material that exhibits thermally activated delayed fluorescence with a plurality of materials as in the case of forming an exciplex complex. may be

As the heat-activated delayed fluorescence compound, a single material or a plurality of materials may be used, and known materials can be used. Specific examples include benzonitrile derivatives, triazine derivatives, disulfoxide derivatives, carbazole derivatives, indolocarbazole derivatives, dihydrophenazine derivatives, thiazole derivatives, oxadiazole derivatives and the like. Examples of such a heat-activated delayed fluorescent compound include, but are not limited to, the following examples.

It is preferable that the second compound is a thermally activated delayed fluorescent compound, and the first compound is a compound having a structure represented by the general formula (1). Further, when the second compound is a thermally activated delayed fluorescent compound, the light-emitting layer further contains a third compound, and the excited singlet energy of the first compound is S ₁ (1), the second compound When the excited singlet energy of is S ₁ (2) and the excited singlet energy of the third compound is S ₁ (3), the relationship of Formula 1 is preferably satisfied.
S ₁ (3)>S ₁ (2)>S ₁ (1) (Formula 1)
As a result, the third compound can have a function of confining the energy of the light-emitting material in the light-emitting layer, enabling efficient light emission.

The third compound is preferably an organic compound having a high charge-transporting ability and a high glass transition temperature. Examples of the third compound include, but are not particularly limited to, the following.

(Electron transport layer)
The electron transport layer is a layer into which electrons are injected from the cathode and which transports the electrons. The electron-transporting material used in the electron-transporting layer is required to have a high electron affinity, a high electron mobility, excellent stability, and a substance that does not easily generate trapping impurities. From the viewpoint of suppressing film quality deterioration due to crystallization, a compound having a molecular weight of 400 or more is preferable.

The electron-transporting layer in the present invention also includes a hole-blocking layer capable of efficiently blocking the movement of holes. The hole-blocking layer and the electron-transporting layer may be composed of a single material or a laminate of multiple materials.

Examples of electron transport materials include polycyclic aromatic derivatives, styryl aromatic ring derivatives, quinone derivatives, phosphorus oxide derivatives, quinolinol complexes such as tris(8-quinolinolate) aluminum (III), benzoquinolinol complexes, hydroxyazole complexes, and azomethine complexes. , tropolone metal complexes and flavonol metal complexes. From the viewpoint of reducing driving voltage and further improving device efficiency, it is preferable to use a compound having a heteroaryl group containing electron-accepting nitrogen. Here, electron-accepting nitrogen represents a nitrogen atom forming a multiple bond with an adjacent atom. A heteroaryl group containing an electron-accepting nitrogen has a high electron affinity, so that electrons can be easily injected from the cathode, enabling lower voltage driving. In addition, more electrons are supplied to the light-emitting layer, and the recombination probability increases, so that the device efficiency is further improved. Examples of compounds having a heteroaryl group structure containing an electron-accepting nitrogen include pyridine derivatives, triazine derivatives, pyrazine derivatives, pyrimidine derivatives, quinoline derivatives, quinoxaline derivatives, quinazoline derivatives, naphthyridine derivatives, benzoquinoline derivatives, phenanthroline derivatives, and imidazole. derivatives, oxazole derivatives, thiazole derivatives, triazole derivatives, oxadiazole derivatives, thiadiazole derivatives, benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, phenanthroimidazole derivatives, oligopyridine derivatives such as bipyridine and terpyridine. You may use 2 or more types of these.

Further, it is more preferable that the electron transporting material has a condensed polycyclic aromatic skeleton, because the glass transition temperature is improved, the electron mobility is high, and the driving voltage can be reduced. As such a condensed polycyclic aromatic skeleton, a quinolinol skeleton, triazine skeleton, fluoranthene skeleton, anthracene skeleton, pyrene skeleton or phenanthroline skeleton is preferred.

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

Preferred examples of the donor material 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, and alkali earth metals. Examples include inorganic salts, 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. You may use 2 or more types of these. Among 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. In general, the electron injection layer is formed for the purpose of assisting 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-described donor material. .

Inorganic substances such as insulators and semiconductors can also be used for the electron injection layer. By using these materials, it is possible to suppress the short circuit of the light-emitting element and improve the electron injection property, which is preferable.

As such an insulator, metal compounds such as alkali metal chalcogenides, alkaline earth metal chalcogenides, alkali metal halides, and alkaline earth metal halides are preferable. You may use 2 or more types of these.

(Charge generation layer)
The charge generation layer in the present invention generally consists of a double layer, and specifically can be used as a pn junction type charge generation layer consisting of an n-type charge generation layer and a p-type charge generation layer. The pn junction charge generation layer generates charges or separates the charges into holes and electrons when a voltage is applied in the light emitting device, and transfers these holes and electrons to the hole transport layer and the electron transport layer. injected into the light-emitting layer through the layer. Specifically, it functions as an intermediate charge-generating layer in a light-emitting element in which light-emitting layers are stacked. The n-type charge-generating layer supplies electrons to the first light-emitting layer on the anode side, and the p-type charge-generating layer supplies holes to the second light-emitting layer on the cathode side. Therefore, it is possible to improve the luminous efficiency of a light-emitting element in which a plurality of light-emitting layers are stacked, reduce the driving voltage, and improve the durability of the light-emitting element.

The n-type charge generation layer consists of an n-type dopant and a host, which can be conventional materials. Examples of n-type dopants include alkali metals, alkaline earth metals, and rare earth metals. Examples of hosts include triazine derivatives, phenanthroline derivatives, oligopyridine derivatives and the like. You may use 2 or more types of these. Among these, phenanthroline derivatives are preferred.

The p-type charge generation layer consists of a p-type dopant and a host, which can be conventional materials. For example, p-type dopants include tetrafluor-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ), tetracyanoquinodimethane derivatives, radialene derivatives, iodine, FeCl ₃ , FeF ₃ , SbCl ₅ etc. You may use 2 or more types of these. Among these, arylamine derivatives are preferred.

(Method for manufacturing light-emitting element)
A method for forming each layer constituting the light-emitting element may be either a dry process or a wet process, and examples thereof include resistance heating deposition, electron beam deposition, sputtering, molecular lamination, coating, inkjet, and printing. . Among these, resistance heating vapor deposition is preferable from the viewpoint of device characteristics.

Although the thickness of the organic layer depends on the resistance value of the light-emitting substance and cannot be limited, it is preferably 1 to 1000 nm. Each of the light-emitting layer, the electron transport layer, and the hole transport layer preferably has a film thickness of 1 nm or more and 200 nm or less, more preferably 5 nm or more and 100 nm or less.

(Characteristics of light-emitting element)
A light emitting device according to an embodiment of the present invention has a function of converting electrical energy into light. Here, direct current is mainly used as electric energy, but pulse current and alternating current can also be used. The current value and voltage value are not particularly limited, and the required characteristic values differ depending on the purpose of the device. However, from the viewpoint of power consumption and life of the device, it is preferable to obtain high luminance at a low voltage.

In the light-emitting device according to the embodiment of the present invention, from the viewpoint of improving color purity, the half-value width is preferably 45 nm or less, more preferably 35 nm or less, and 30 nm from the viewpoint of further improving color purity in the fluorescence spectrum by energization. More preferred are:

(Use of light-emitting element)
The light-emitting elements according to the embodiments of the present invention can achieve both high luminous efficiency and high color purity, and can be made thinner and lighter. It is suitably used for devices and the like. The display device includes, for example, a matrix and/or segmented display. Backlights are mainly used for the purpose of improving the visibility of display devices such as displays that do not emit light by themselves. is mentioned. Among these, the light-emitting device of the present invention can be made thinner and lighter, and is therefore preferably used for liquid crystal displays, especially for backlights for personal computers, for which thinning is being considered. Lighting devices include, for example, medical lighting and interior lighting, and can achieve both low power consumption, vivid emission colors, and high designability.

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

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

(Excitation singlet energy S ₁ )
General-purpose quantum chemical calculation program "Gaussian 16" program package (Gaussian
Co., Ltd.) was used to perform structural optimization with B3LYP/6-311G(d). Based on the optimized structure, the excited singlet energy S ₁ was calculated and converted to wavelength.

(Examples 1-3, Comparative Examples 1-2)
Compounds D-1 to D-5 shown in Table 1 were evaluated for singlet excitation energy S ₁ by the method described above. The evaluation results are shown in Table 1, and the structures of D-1 to D-5 are shown below.

As can be seen from Table 1, the compounds of Examples 1 to 3 have longer emission wavelengths than the compounds of Comparative Examples 1 and 2, and results suitable for green emission were obtained.

Claims (11)

A compound having a structure represented by the following general formula (1).

(In general formula (1) above, X ¹ and X ² are each independently an aryl group or an alkyl group, and are connected to R ¹ , R ⁶ , R ⁷ and/or R ⁸ via a linking group or a single bond. These groups may further have a substituent.
A ¹ to A ³ are each independently a group having a positive substituent constant σp value in Hammett's rule, a hydrogen atom, a phenyl group or an alkyl group. However, at least one of A ¹ and A ² is a group having a positive substituent constant σp value in Hammett's rule. The phenyl group and alkyl group may further have a substituent.
R ¹ to R ⁸ each independently represent 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 or an arylthioether group. These groups may further have a substituent. ) A group having a positive substituent constant σp value in Hammett's rule has a partial structure represented by any one of the following structural formulas (a-1) to (a-8), and among A ¹ and A ² , The compound according to claim 1, at least one of which has a partial structure represented by any one of the following structural formulas (a-1) to (a-8).

3. The compound according to claim 1 or 2, having a structure represented by the following general formula (2) or (3).

(In general formulas (2) to (3) above, R ²¹ to R ²⁸ and R ³¹ to R ³⁸ are each independently a hydrogen atom, an alkyl group, a cycloalkyl group, a heterocyclic group, an alkenyl group, or 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, or a ring structure between adjacent groups These groups may further have substituents. .
Y ¹ to Y ⁴ are each independently a single bond, —O—, —S—, or a divalent substituent having a structure represented by the following general formula (4). )

(In general formula (4) above, R ¹⁰¹ and R ¹⁰² are each independently a hydrogen atom, an alkyl group or an aryl group. These groups may further have a substituent, and R ¹⁰¹ and A ring structure may be formed between R ¹⁰² . A light-emitting device material comprising the compound according to any one of claims 1 to 3. A light-emitting device that emits light by electrical energy, comprising a light-emitting layer containing the light-emitting device material according to claim 4 between an anode and a cathode. 6. The light-emitting device according to claim 5, wherein the light-emitting layer contains a first compound and a second compound, and the compound according to any one of claims 1 to 4 as the first compound. 7. The light-emitting device according to claim 6, wherein the second compound comprises a thermally activated delayed fluorescent compound. Further containing a third compound, the excited singlet energy of the first compound is S ₁ (1), the excited singlet energy of the second compound is S ₁ (2), and the excited singlet energy of the third compound 8. The light-emitting device according to claim 7, wherein the relationship of formula ₁ is satisfied when S1(3) is satisfied.
S ₁ (3)>S ₁ (2)>S ₁ (1) (Formula 1) The light emitting device according to any one of claims 5 to 8, which is a top emission type organic electroluminescent device. A display device comprising the light emitting device according to any one of claims 5 to 9. A lighting device comprising the light emitting element according to any one of claims 5 to 9.