JP2022032989A - Light-emitting element material formed by pyrromethene boron complex and light-emitting element using the same - Google Patents

Abstract

To provide a light-emitting element material capable of obtaining a light-emitting element with excellent element efficiency and durability.SOLUTION: The invention provide a light-emitting element material formed by an asymmetric pyrromethene boron complex, having a specific substituent group at a specific position of a pyrromethene skelton.SELECTED DRAWING: None

Description

The present invention relates to a light emitting device material composed of a pyrromethene boron complex and a light emitting device using the same.

The 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 drive voltage. It has features such as high brightness and multicolor emission. In particular, by combining a host material and a dopant material in the light emitting layer, it is possible to obtain a highly efficient light emitting element exhibiting the three primary colors of blue, green, and red.

As a dopant material capable of providing a light emitting device having high brightness and high purity, a pyrromethene boron complex having various structures has been reported so far (see, for example, Patent Document 1). Further, in recent years, aiming at higher device efficiency, a light emitting device in which a TADF (Thermally Activated Fluorescence) material and a pyrromethene boron complex are combined has been studied (see, for example, Patent Documents 2 and 3). ).

International Publication No. 2009/116456 International Publication No. 2016/056559 International Publication No. 2019/013063

According to the studies by the present inventors, in a light emitting device using a dopant material, recombination of electrons and holes may occur on the dopant material (pyromethene boron complex), which causes element efficiency and durability of the light emitting device. It became clear that there is a problem that the value decreases. Therefore, an object of the present invention is to provide a light emitting device material capable of obtaining a light emitting device having excellent device efficiency and durability.

The present invention is a light emitting device material containing a pyrromethene boron complex represented by the following general formula (1).

In the above general formula (1), R ¹ to R ⁴ may be the same or different, and are independently selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. .. One of R ⁵ and R ⁶ is a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted alkynyl group. , Hydroxyl, thiol group, substituted or unsubstituted alkoxy group, substituted or unsubstituted alkylthio group, substituted or unsubstituted arylether group, substituted or unsubstituted arylthioether group, substituted or unsubstituted heterocyclic group, substituted Alternatively, it is selected from the group consisting of an unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siroxanyl group and a substituted or unsubstituted boryl group, and the other is a hydrogen atom, a substituted or unsubstituted alkyl group. , Substituent or unsubstituted cycloalkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted cycloalkenyl group, substituted or unsubstituted alkynyl group, hydroxyl group, thiol group, substituted or unsubstituted alkoxy group, substituted or Unsubstituted alkylthio group, substituted or unsubstituted arylether group, substituted or unsubstituted arylthioether group, substituted or unsubstituted aryl group, substituted or unsubstituted heteroaryl group, substituted or unsubstituted heterocyclic group, It is selected from the group consisting of a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siroxanyl group and a substituted or unsubstituted boryl group. However, R ⁵ and R ⁶ are different groups.

X ¹ and X ² may be the same or different, substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted aryloxy group, hydroxyl group, It is selected from the group consisting of halogen atoms and cyano groups.

^R7 is selected from the group consisting of substituted or unsubstituted aryl groups and substituted or unsubstituted heteroaryl groups.

The light emitting device material of the present invention makes it possible to obtain a light emitting device having excellent device efficiency and durability.

Hereinafter, preferred embodiments of the light emitting device material and the light emitting device made of the pyrromethene boron complex according to the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be variously modified and implemented according to an object and an application.

<Pyromethene boron complex>
The pyrromethene boron complex used in the present invention is represented by the following general formula (1).

In the above general formula (1), R ¹ to R ⁴ may be the same or different, and are independently selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. .. By selecting these substituents, it is possible to suppress energy deactivation due to intramolecular rotation and improve device efficiency and durability.

One of R ⁵ and R ⁶ is a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted alkynyl group. , Hydroxyl, thiol group, substituted or unsubstituted alkoxy group, substituted or unsubstituted alkylthio group, substituted or unsubstituted arylether group, substituted or unsubstituted arylthioether group, substituted or unsubstituted heterocyclic group, substituted Alternatively, it is selected from the group consisting of an unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siroxanyl group and a substituted or unsubstituted boryl group, and the other is a hydrogen atom, a substituted or unsubstituted alkyl group. , Substituent or unsubstituted cycloalkyl group, substituted or unsubstituted alkenyl group, substituted or unsubstituted cycloalkenyl group, substituted or unsubstituted alkynyl group, hydroxyl group, thiol group, substituted or unsubstituted alkoxy group, substituted or Unsubstituted alkylthio group, substituted or unsubstituted arylether group, substituted or unsubstituted arylthioether group, substituted or unsubstituted aryl group, substituted or unsubstituted heteroaryl group, substituted or unsubstituted heterocyclic group, It is selected from the group consisting of a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siroxanyl group and a substituted or unsubstituted boryl group. By selecting these substituents, it is possible to suppress the interaction between the pyrromethene boron complexes due to steric hindrance and improve the device efficiency.

However, R ⁵ and R ⁶ are different groups. Here, in this description, the "different group" refers to a group having a different structure from each other. For example, a methyl group and an ethyl group are contained in the same alkyl group, but they have different structures and therefore fall under the category of "different groups" in this description.

As described above, recombination of electrons and holes may occur on the dopant material (pyromethene boron complex), and it is conceivable that the electrons are trapped in the light emitting device material as a factor. For example, in a light emitting device material in which a pyrromethene boron complex and a TADF material are combined, it is desirable that electron and hole recombination occur in the TADF material, but when the LUMO level of the dopant material is deep, the dopant from the TADF material is desired. Electron transfer to the material is likely to occur, and electron trapping reduces the device efficiency and durability of the light emitting device. Therefore, in the present invention, as a result of studying to make the LUMO level of the pyrromethene boron complex in the light emitting element material shallow to suppress electron transfer, an asymmetric ^pyromethene boron complex having R5 and ^R6 as different groups is used. It has been found that the electron trap by the pyrromethene boron complex in the light emitting element material can be suppressed and the element efficiency and durability of the light emitting element can be improved.

In the present invention, one of R ⁵ and R ⁶ is preferably selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. By selecting these substituents, intramolecular rotation can be suppressed, the fluorescence quantum yield can be improved, and device efficiency can be further improved. Further, by selecting these substituents, it is possible to suppress vibrational relaxation in the excited state of the pyrromethene boron complex, reduce the half width of the emission spectrum, and improve the color purity. Further, in this case, it is more preferable that the other is hydrogen.

X ¹ and X ² may be the same or different, substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted aryl ether group, hydroxyl group, It is selected from the group consisting of halogen atoms and cyano groups. Among these, at least one alkyl group substituted with at least one halogen can be used because the electron attraction can reduce the electron density of the pyrromethene skeleton, stabilize the excited state, and further improve the device efficiency and durability. It is preferably an alkoxy group substituted with one halogen, an aryl ether group substituted with at least one halogen, an aryl group substituted with at least one halogen, a halogen atom, or a cyano group. Further, it is more preferable that X ¹ and X ² are fluorine atoms from the viewpoint that the excited state can be more stabilized to obtain a higher fluorescence quantum yield and the durability can be further improved.

^R7 is selected from the group consisting of substituted or unsubstituted aryl groups and substituted or unsubstituted heteroaryl groups. As described above, the pyrromethene boron complex represented by the general formula (1) preferably has a shallow LUMO level. From this point of view, when R ⁷ contains an electron-deficient heteroaryl group, it is preferable that the heteroaryl group does not directly bind to the pyrromethene skeleton. Here, the electron-deficient heteroaryl group means a monovalent group derived from an electron-deficient aromatic heterocycle. From the same viewpoint, when R ⁷ contains a phenyl group having an electron-withdrawing group, it is preferable that the phenyl group does not directly bind to the pyrromethene skeleton.

Examples of the electron-deficient heteroaryl group include a pyridine ring, a pyrazine ring, a pyridazine ring, a pyrimidine ring, a triazine ring, a quinoline ring, an isoquinoline ring, a quinoxaline ring, a quinazoline ring, a naphthylidine ring, an acridine ring, a phenazine ring, and a benzoquinoline ring. , A monovalent group derived from a benzoisoquinoline ring, a phenanslidine ring, a phenanthroline ring, a benzoquinone ring, a coumarin ring, an anthraquinone ring, a fluorenone ring and the like.

Examples of the electron-withdrawing group include a carbonyl group, a sulfonyl group, a cyano group, and a halogen.

In the present description, "unsubstituted" means that the atom bonded to the basic skeleton or functional group of interest is only a hydrogen atom or a deuterium atom.

Further, in all the groups, hydrogen may be deuterium. The same applies to the compounds described below or their partial structures.

The alkyl group refers to a saturated aliphatic hydrocarbon group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a sec-butyl group and a tert-butyl group, which is a substituent. It may or may not have. The additional substituent when substituted is not particularly limited, and examples thereof include an alkyl group, a halogen, an aryl group, a heteroaryl group, and the like, and this point is also common to the following description. The number of carbon atoms of the alkyl group is not particularly limited, but is preferably 1 or more and 20 or less, and more preferably 1 or more and 8 or less from the viewpoint of availability and cost.

The cycloalkyl group means, 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 carbon atoms in the alkyl group moiety is not particularly limited, but is preferably in the range of 3 or more and 20 or less.

The alkenyl group refers to an unsaturated aliphatic hydrocarbon group containing a double bond such as a vinyl group, an allyl group, or a butazienyl group, which may or may not have a substituent. The number of carbon atoms of the alkenyl group is not particularly limited, but is preferably in the range of 2 or more and 20 or less.

The cycloalkenyl group refers to an unsaturated alicyclic hydrocarbon group containing a double bond such as a cyclopentenyl group, a cyclopentadienyl group, a cyclohexenyl group, etc., which may have a substituent. You don't have to.

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

The alkoxy group is, for example, a functional group to which an aliphatic hydrocarbon group is bonded via an ether bond such as a methoxy group, an ethoxy group, or a propoxy group, and even if the aliphatic hydrocarbon group has a substituent. You do not have to have it. The number of carbon atoms of the alkoxy group is not particularly limited, but is preferably in the range of 1 or more and 20 or less.

The alkylthio group is one in which the oxygen atom of the ether bond of the alkoxy group is replaced with a sulfur atom. The hydrocarbon group of the alkylthio group may or may not have a substituent. The number of carbon atoms of the alkylthio group is not particularly limited, but is preferably in the range of 1 or more and 20 or less.

The aryl ether group refers to a functional group to which an aromatic hydrocarbon group is bonded via an ether bond, for example, a phenoxy group, and the aromatic hydrocarbon group may or may not have a substituent. good. The number of carbon atoms of the aryl ether group is not particularly limited, but is preferably in the range of 6 or more and 40 or less.

The arylthio ether group is one in which the oxygen atom of the ether bond of the aryl ether group is replaced with a sulfur atom. The aromatic hydrocarbon group in the arylthioether group may or may not have a substituent. The number of carbon atoms of the arylthioether group is not particularly limited, but is preferably in the range of 6 or more and 40 or less.

The heterocyclic group refers to an aliphatic ring having an atom other than carbon such as a pyran ring, a piperidine ring, and a cyclic amide in the ring, which may or may not have a substituent. .. The number of carbon atoms of the heterocyclic group is not particularly limited, but is preferably in the range of 2 or more and 20 or less.

The amino group is a substituted or unsubstituted amino group. Examples of the substituent in the case of substitution include an aryl group, a heteroaryl group, a linear alkyl group and a branched alkyl group. As the aryl group and the heteroaryl group, a phenyl group, a naphthyl group, a pyridyl group and a quinolinyl group are preferable. These substituents may be further substituted. The number of carbon atoms 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.

The silyl group indicates a functional group to which a substituted or unsubstituted silicon atom is bonded, and is, for example, an alkylsilyl group such as a trimethylsilyl group, a triethylsilyl group, a tert-butyldimethylsilyl group, a propyldimethylsilyl group, or a vinyldimethylsilyl group. , And arylsilyl groups such as phenyldimethylsilyl group, tert-butyldiphenylsilyl group, triphenylsilyl group and trinaphthylsilyl group. Substituents on silicon may be further substituted. The number of carbon atoms of the silyl group is not particularly limited, but is preferably in the range of 1 or more and 30 or less.

The siroxanyl group refers to a silicon compound group via an ether bond such as a trimethylsyloxanyl group. Substituents on silicon may be further substituted.

The boryl group is a substituted or unsubstituted boryl group. Examples of the substituent in the case of substitution include an aryl group, a heteroaryl group, a linear alkyl group, a branched alkyl group, an aryl ether group, an alkoxy group and a hydroxyl group, and among them, an aryl group and an aryl ether group are preferable.

The aryl group is, 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, an anthrasenyl group, a benzophenanthril group, a benzoanthrase. Aromatic hydrocarbon groups such as an Nyl group, a chrysenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, a benzofluoranthenyl group, a dibenzoanthrasenyl group, a peryleneyl group and a helisenyl group are shown. Of these, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a phenanthryl group, an anthrasenyl group, a pyrenyl group, a fluoranthenyl group and a triphenylenyl group are preferable. The aryl group may or may not have a substituent. The number of carbon atoms of the aryl group is not particularly limited, but is preferably in the range of 6 or more and 40 or less, and more preferably 6 or more and 30 or less. Further, in the case of a phenyl group, if there are substituents on two adjacent carbon atoms in the phenyl group, the substituents may form a ring structure with each other.

The heteroaryl group is, for example, a pyridyl group, a furanyl group, a thiophenyl group, a quinolinyl group, an isoquinolinyl group, a pyrazinyl group, a pyrimidyl group, a pyridadinyl group, a triazinyl group, a naphthyldinyl group, a cinnolinyl group, a phthalazinyl group, a quinoxalinyl group, a quinazolinyl group, and the like. Benzofuranyl group, benzothiophenyl group, indolyl group, dibenzofuranyl group, dibenzothiophenyl group, carbazolyl group, benzocarbazolyl group, carbolinyl group, indolocarbazolyl group, benzoflocarbazolyl group, benzothienocarba Non-carbon such as zolyl group, dihydroindenocarbazolyl group, benzoquinolinyl group, acridinyl group, dibenzoacrydinyl group, benzoimidazolyl group, imidazolypyridyl group, benzoxazolyl group, benzothiazolyl group, phenanthrolinyl group Indicates a cyclic aromatic group having one or more of the atoms in the ring. However, the naphthyldinyl group is any of 1,5-naphthyldinyl group, 1,6-naphthyldinyl group, 1,7-naphthyldinyl group, 1,8-naphthyldinyl group, 2,6-naphthyldinyl group and 2,7-naphthyldinyl group. Indicates. The heteroaryl group may or may not have a substituent. The number of carbon atoms of the heteroaryl group is not particularly limited, but is preferably in the range of 2 or more and 40 or less, and more preferably 2 or more and 30 or less.

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

The cyano group is a functional group whose structure is represented by −C≡N. Here, it is the carbon atom that binds to other functional groups.

In the present invention, the structure represented by the following structural formula (2) is referred to as a pyrromethene skeleton.

An example of the pyrromethene boron complex represented by the general formula (1) is shown below, but the present invention is not limited thereto.

The molecular weight of the pyrromethene boron complex represented by the general formula (1) is preferably 380 or more from the viewpoint of thermal stability, and thermal decomposition can be suppressed and the device efficiency can be improved more stably. The molecular weight is more preferably 400 or more.

The pyrromethene boron complex represented by the general formula (1) is, for example, J. Am. Org. Chem. , Vol. 64, No. 21, pp. 7813-7819 (1999), Angew. Chem. , Int. Ed. Engl. , Vol. 36, pp. 1333-1335 (1997), Org. Let. , Vol. 12, pp. It can be manufactured with reference to the method described in 296 (2010) and the like. As a method for synthesizing a pyrromethene boron complex from pyrrole having a different structure, for example, Tetrahedron Letter. , Vol. 56, pp. Examples thereof include the methods described in 3919-3922 (2015), JP-A-2010-83875, and the like.

The obtained pyromethene boron complex is subjected to organic synthetic purification such as recrystallization and column chromatography, and then purified by heating under reduced pressure, which is generally called sublimation purification, to remove low boiling point components and improve the purity. It is preferable to let it. The heating temperature in the sublimation purification is not particularly limited, but is preferably 330 ° C. or lower, more preferably 300 ° C. or lower, from the viewpoint of preventing thermal decomposition of the pyrromethene boron complex. The purity of the pyrromethene boron complex is preferably 99% by weight or more from the viewpoint of stabilizing the characteristics of the light emitting device.

It is preferable that the pyrromethene boron complex represented by the general formula (1) exhibits light emission observed in a region having a peak wavelength of 500 nm or more and 550 nm or less by using excitation light. Hereinafter, the emission observed in the region where the peak wavelength is 500 nm or more and 550 nm or less is referred to as “green emission”. From the viewpoint of expanding the color gamut and improving the color reproducibility, it is more preferable to have the peak wavelength in the wavelength range of 510 nm or more and 540 nm or less. Here, the emission spectrum of the pyrromethene boron complex represented by the general formula (1) can be measured using a fluorescence spectrophotometer using a diluted solution having a concentration of ^10-5 mol / L using toluene as a solvent. can.

The pyrromethene boron complex represented by the general formula (1) preferably has a sharp emission spectrum from the viewpoint of further improving the color purity. In particular, when used in top-emission type light-emitting elements, which are the 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 light emission spectrum becomes sharper. The element efficiency can be further improved. From this viewpoint, the half width of the emission spectrum is preferably 45 nm or less, more preferably 35 nm or less, and further preferably 30 nm or less.

The device efficiency of the light emitting device depends on the fluorescence quantum yield of the light emitting device material. Therefore, a fluorescence quantum yield close to 100% is desired for the light emitting device material. The fluorescence quantum yield of the pyrromethene boron complex represented by the general formula (1) is preferably 80% or more, more preferably 85% or more. Here, the fluorescence quantum yield of the pyrromethene boron complex represented by the general formula (1) is determined by using a diluted solution having a concentration of ^10-5 mol / L using toluene as a solvent and using an absolute quantum yield measuring device. Can be measured.

<Light emitting element material>
The light emitting device material according to the present invention comprises a pyrromethene boron complex represented by the general formula (1), and represents a material used for any layer of the light emitting device. That is, the light emitting device material means the use of the pyrromethene boron complex represented by the above-mentioned general formula (1). Examples of the light emitting element material include a hole injection layer, a hole transport layer, an electron blocking layer, a light emitting layer, an electron transport layer, an electron injection layer, a hole blocking layer, and / or a protective film (cap layer) for an electrode, which will be described later. Examples include the materials used in. Among these, it is suitably used for a light emitting layer because it has high device efficiency, color purity and thin film stability.

<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 above-mentioned light emitting device material between the anode and the cathode, and emits light by electric energy.

The light emitting element of the present invention may be either a bottom emission type or a top emission type. The light emitting device of the present invention is more preferably a top emission type because the half width of the light emitting spectrum is narrow and the color purity is excellent. In the top emission type light emitting element, the element efficiency increases as the half width is narrower due to the resonance effect of the microcavity. Therefore, both color purity and device efficiency can be achieved at a higher level.

In such a light emitting element, the layer structure between the anode and the cathode consists of only a light emitting layer, 1) a light emitting layer / an electron transport layer, 2) a hole transport layer / a light emitting layer, and 3) a 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, 8) positive Examples thereof include a laminated structure such as a pore injection layer / a hole transport layer / an electron blocking layer / a light emitting layer / a hole blocking layer / an electron transport layer / an electron injection layer.

Further, the above-mentioned laminated structure may be a tandem type in which a plurality of the above laminated structures are laminated via an intermediate layer. Examples of the intermediate layer include 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. Preferred specific examples of the tandem type are 9) hole transport layer / light emitting layer / electron transport layer / charge generation layer / hole transport layer / light emitting layer / electron transport layer, 10) hole injection layer / hole transport layer / Two or more light emitting layers between the anode and the cathode, such as a 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. A laminated structure including one or more charge generating layers as an intermediate layer between each light emitting layer and the light emitting layer can be mentioned. As the material constituting the intermediate layer, a pyridine derivative, a phenanthroline derivative and the like are preferable.

Further, each of the above layers may be either a single layer or a plurality of layers, and may be doped. Further, an element configuration including an anode, one or more organic layers including a light emitting layer, a cathode, and a layer using a capping material for improving element efficiency due to an optical interference effect can also be mentioned.

Specific examples of the configuration of the light emitting element will be given below, but the configuration of the present invention is not limited thereto.

(substrate)
It is preferable to form the light emitting element on the substrate in order to maintain the mechanical strength of the light emitting element, have little thermal deformation, and have a barrier property to prevent water vapor and oxygen from entering the light emitting layer. The substrate is not particularly limited, and examples thereof include a glass plate, a ceramic plate, a resin film, a resin thin film, and a metal thin plate. Among these, a glass substrate is preferably used from the viewpoint of being transparent and easy to process. In particular, in the case of a bottom emission type light emitting element that extracts light 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 preferably used for this purpose. As the resin film, a heat-resistant film is used, and specific examples thereof include a polyimide film and a polyethylene naphthalate film.

Further, various wirings, 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, but in the case of a bottom emission type light emitting device, a transparent or translucent electrode is preferable, and a top emission type light emitting device is used. In this case, it is preferably a reflective electrode.

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

The material of the reflective electrode is preferably one that does not absorb all light and has a high reflectance, and examples thereof include metals such as aluminum, silver, and platinum.

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

The film thickness of the anode is not particularly limited, but is preferably several nm to several hundred nm.

As the method for forming the anode, the optimum method can be selected according to the material for forming the anode, and examples thereof include a sputtering method, a vapor deposition method, and an inkjet method. For example, a sputtering method is preferably used when the anode is formed of a metal oxide, and a thin-film deposition method is preferably used when the anode is formed of a metal. The film thickness of the anode is not particularly limited, but is preferably several nm to several hundred nm.

(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 can efficiently inject electrons into the light emitting layer, but in the case of a bottom emission type light emitting device, it is preferably a reflective electrode, and in the case of a top emission type light emitting device, it is translucent. It is preferably an electrode.

Generally, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, alloys of these metals with low-working functional metals such as lithium, sodium, potassium, calcium and magnesium, and multilayer laminates. , Zinc oxide, indium tin oxide (ITO), indium zinc oxide (IZO) and other conductive metal oxides are preferred. Among these, aluminum, silver, and magnesium are preferable as the main components from the viewpoints of electric resistance value, ease of film formation, film stability, device efficiency, and the like. Further, when it is composed of magnesium and silver, electron injection into the electron transport layer and the electron injection layer becomes easy, and the driving voltage can be reduced, which is preferable.

(Protective layer)
For cathode protection, it is preferable to laminate a protective layer (cap layer) on the cathode. The material constituting the protective layer is not particularly limited, and is, for example, metals such as platinum, gold, silver, copper, iron, tin, aluminum and indium, alloys using these metals, silica, titania and silicon nitride. Examples thereof include organic polymer compounds such as inorganic substances, polyvinyl alcohol, polyvinyl chloride, and hydrocarbon-based 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 having light transmission 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 one layer or a plurality of layers may be laminated. When the hole injection layer is present between the hole transport layer and the anode, it can be driven at a lower voltage and the durability can be further improved. Further, the carrier balance of the element can be improved, and the element efficiency can be further improved.

A preferable example of the hole injection material is an electron donating hole injection material (donor material). These are materials whose HOMO level is shallower than that of the hole transport layer and which is 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 (1-naphthyl). Aromatic amine materials such as phenyl) amino) triphenylamine (1-TNATA), carbazole derivatives, pyrazoline derivatives, stilben compounds, hydrazone compounds, benzofuran derivatives, thiophene derivatives, oxadiazole. Examples thereof include heterocyclic compounds such as derivatives, phthalocyanine derivatives, and porphyrin derivatives, polycarbonate and styrene derivatives having the monomer on the side chain, polythiophene such as PEDOT / PSS, polyaniline, polyfluorene, polyvinylcarbazole, and polysilane. To. Two or more of these may be used. Further, a plurality of materials may be laminated to form a hole injection layer.

Further, another preferable example of the hole injection material is an electron acceptor 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 donor material with the acceptor material. The acceptor material is a material that forms a charge transfer complex between the adjacent hole transport layers when used alone and with the donor material when used by doping with the donor material. It is more preferable to use such a material because it contributes to the improvement of the conductivity of the hole injection layer and the decrease of the driving voltage of the device, and the effect of further improving the device efficiency and durability can be obtained. Acceptor materials include metal oxides such as molybdenum oxide, vanadium oxide, tungsten oxide, 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), Tetra Examples thereof include cyanoquinodimethane derivatives, radialene derivatives, n-type organic semiconductor compounds such as fluorinated copper phthalocyanine, and fullerene. When the hole injection layer contains an acceptor compound, the hole injection layer may be one layer or may be configured by laminating a plurality of layers.

(Hole transport layer and electron blocking layer)
The hole transport layer is a layer that transports holes injected from the anode to the light emitting layer, and the electron blocking layer is a layer that efficiently blocks the movement of electrons. Both the hole transport layer and the electron blocking layer may be a single layer or may be configured by laminating a plurality of layers. It is formed by laminating or mixing the hole transporting materials of. Further, it is preferable that the hole transport material has high hole injection efficiency and efficiently transports the injected holes. For that purpose, it is required to be a substance having an appropriate ionization potential, a high hole mobility, excellent stability, and less likely to generate impurities as traps.

The substance satisfying such conditions is not particularly limited, but for example, a benzidine derivative, an aromatic amine-based material group called starburst arylamine, a carbazole derivative, a pyrazoline derivative, a stilben-based compound, a hydrazone-based compound, and the like. Heterocyclic compounds such as benzofuran derivatives, dibenzofuran derivatives, thiophene derivatives, benzothiophene derivatives, dibenzothiophene derivatives, fluorene derivatives, spirofluorene derivatives, oxadiazole derivatives, phthalocyanine derivatives, porphyrin derivatives, and the above-mentioned monomers are side chains in polymer systems. Examples thereof include the polycarbonate and styrene derivatives, polythiophene, polyaniline, polyfluorene, polyvinylcarbazole and polysilane having the above.

(Light emitting layer)
The light emitting layer is a layer that emits light by the excitation energy generated by the recombination of holes and electrons. The light emitting layer may be composed of a single material, but it is preferable to have a first compound and a second compound which is a dopant exhibiting strong light emission from the viewpoint of color purity. As the first compound, for example, a host material responsible for charge transfer and a TADF material can be mentioned as suitable examples.

The pyrromethene boron complex represented by the general formula (1) has a particularly excellent fluorescence quantum yield, the peak wavelength of the emission spectrum is suitable for green emission, the half width is narrow, and the color purity is excellent. Therefore, it is preferable to use it as a second compound which is a dopant of the light emitting layer. The content of the second compound is preferably 5% by weight or less, more preferably 2% by weight or less in the light emitting layer from the viewpoint of further suppressing the concentration quenching phenomenon. 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, more preferably 0.5% by weight or more.

The host material is not particularly limited, but is, for example, a compound having a fused aryl ring such as naphthacene, pyrene, anthracene, and fluoranthene, a derivative thereof, N, N'-dinaphthyl-N, N'-diphenyl-4,4'-. Aromatic amine derivatives such as diphenyl-1,1'-diamine, metal chelated oxynoid compounds such as tris (8-quinolinate) aluminum (III), bisstyryl derivatives such as distyrylbenzene derivatives, tetraphenylbutadiene derivatives, and inden. Derivatives, coumarin derivatives, oxadiazole derivatives, pyrolopyridine derivatives, perinone derivatives, pyrolopyrrole derivatives, thiadiazolopyridine derivatives, dibenzofuran derivatives, carbazole derivatives, indolocarbazole derivatives, triazine derivatives, polyphenylene vinylene derivatives, poly in polymer systems. Examples thereof include a paraphenylene derivative, a polyfluorene derivative, a polyvinylcarbazole derivative, and a polythiophene derivative. Two or more kinds of these may be used, or two or more kinds of host materials may be laminated. Among these, carbazole derivatives, anthracene derivatives, and naphthacene derivatives are preferable.

As the dopant material, a fluorescent light emitting material other than the pyrromethene boron complex represented by the general formula (1) may be contained. Specifically, compounds having a fused 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 stylben derivatives. , Ardazine derivative, pyromethene derivative, diketopyrrolo [3,4-c] pyrrole derivative, coumarin derivative, azole derivative and its metal complex, aromatic amine derivative and the like. Two or more of these may be used.

Further, a phosphorescent light emitting material may be contained as the dopant material. The phosphorescent material comprises at least one metal selected from the group consisting of iridium (Ir), ruthenium (Ru), palladium (Pd), platinum (Pt), osmium (Os), and renium (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 thereto.

However, from the viewpoint of further improving the color purity, it is preferable that the dopant material is only the pyrromethene boron complex represented by the general formula (1).

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

The TADF material promotes the inverse intersystem crossing from the triplet excited state to the singlet excited state by reducing the energy gap between the singlet excited state and the triplet excited state, and increases the probability of singlet excitation. It is an improved material. By utilizing delayed fluorescence due to this TADF mechanism, the theoretical internal efficiency can be increased to 100%. Furthermore, when Felster-type energy transfer occurs from the singlet excited state of the first compound having thermal activated delayed fluorescence to the singlet excited state of the second compound, the singlet excited state of the second compound occurs. Fluorescence emission is observed. Here, when the second compound is a fluorescent light emitting material having a sharp light emitting spectrum, it is possible to obtain an excellent light emitting device with higher element efficiency and color purity. As described above, when the light emitting layer contains a thermally activated delayed fluorescent material, the device efficiency is further improved and the power consumption of the display is reduced. The thermally activated delayed fluorescent material may be a single material that exhibits thermal activated delayed fluorescence, or a material that exhibits thermal activated delayed fluorescence with a plurality of materials as in the case of forming an exhibix complex. May be.

The thermally activated delayed fluorescent compound may be a single material or a plurality of materials, and known materials can be used. Specific examples thereof include benzonitrile derivatives, triazine derivatives, disulfoxide derivatives, carbazole derivatives, indolocarbazole derivatives, dihydrophenazine derivatives, thiazole derivatives, oxadiazole derivatives and the like. The thermally activated delayed fluorescent compound is not particularly limited, and examples thereof include 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). When the first compound is a thermally activated delayed fluorescent compound, the light emitting layer further contains the third compound, and the excitation singlet energy of the third compound is the excitation singlet energy of the first compound. Is preferably larger than. As a result, the third compound can have a function of confining the energy of the light emitting material in the light emitting layer, and can efficiently emit light.

The third compound is preferably an organic compound having a high charge transporting ability and a high glass transition temperature. The third compound is not particularly limited, and examples thereof include the following.

(Electron transport layer and hole blocking layer)
The electron transport layer is a layer in which electrons are injected from the cathode and further transports electrons, and the hole blocking layer is a layer that efficiently blocks the movement of holes. The electron transport material used for the electron transport layer and the hole blocking layer has a high electron affinity, a high electron mobility, excellent stability, and a substance that does not easily generate impurities that act as traps. Required. Further, a compound having a molecular weight of 400 or more is preferable from the viewpoint of suppressing deterioration of the film quality due to crystallization.

Examples of the electron transport material include polycyclic aromatic ring derivatives, styryl-based aromatic ring derivatives, quinone derivatives, phosphoroxide derivatives, quinolinol complexes such as tris (8-quinolinolate) aluminum (III), benzoquinolinol complexes, hydroxyazole complexes, and azomethine complexes. , Troporon metal complexes and various metal complexes such as flavonol metal complexes. From the viewpoint of reducing the driving voltage and further improving the device efficiency, it is preferable to use a compound having a heteroaryl group containing electron-accepting nitrogen. Here, the electron-accepting nitrogen represents a nitrogen atom forming a multiple bond with an adjacent atom. Since the heteroaryl group containing electron-accepting nitrogen has a large electron affinity, it becomes easy to inject electrons from the cathode, and lower voltage drive becomes possible. In addition, the supply of electrons to the light emitting layer is increased, and the recombination probability is increased, so that the device efficiency is further improved. Examples of the compound having a heteroaryl group structure containing electron-accepting nitrogen include a pyridine derivative, a triazine derivative, a pyrazine derivative, a pyrimidine derivative, a quinoline derivative, a quinoxaline derivative, a quinazoline derivative, a naphthylidine derivative, a benzoquinoline derivative, a phenanthroline derivative, and an imidazole. Examples thereof include derivatives, oxazole derivatives, thiazole derivatives, triazole derivatives, oxadiazole derivatives, thiadiazol derivatives, benzimidazole derivatives, benzoxazole derivatives, benzthiazole derivatives, phenanthroimidazole derivatives, oligopyridine derivatives such as bipyridine and tarpyridine. Two or more of these may be used.

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

The electron transport layer may contain a donor material. Here, the donor material is a compound that facilitates electron injection 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 an alkali metal such as Li, an inorganic salt containing an alkali metal such as LiF, a complex of an alkali metal such as lithium quinolinol and an organic substance, an alkaline earth metal, and an alkaline earth metal. Examples thereof 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. Two or more of these may be used. Among these, metallic lithium, rare earth metals, and lithium quinolinol (Liq) are preferable.

(Charge generation layer)
The charge generation layer in the present invention is a layer that generates or separates charges by applying a voltage and injects charges into adjacent layers. The charge generation layer may be formed of one layer, or a plurality of layers may be laminated. Generally, a layer that easily generates electrons as a charge is called an n-type charge generation layer, and a layer that easily generates holes is called a p-type charge generation layer. The charge generation layer is preferably composed of a double layer, and more preferably a pn junction type charge generation layer composed of an n-type charge generation layer and a p-type charge generation layer. The pn junction type charge generation layer generates a charge by applying a voltage in a light emitting element or separates the charge into holes and electrons, and these holes and electrons are separated into a hole transport layer and an electron transport layer. Is injected into the light emitting layer via. Specifically, in a light emitting element in which a plurality of light emitting layers are laminated, it functions as a charge generation layer which is an intermediate layer. The n-type charge generation layer supplies electrons to the first light emitting layer existing on the anode side, and the p-type charge generation layer supplies holes to the second light emitting layer existing on the cathode side. Therefore, the element efficiency in the light emitting element in which a plurality of light emitting layers are laminated can be further improved, the driving voltage can be reduced, and the durability of the element can be further improved.

The n-type charge generation layer consists of an n-type dopant and an n-type host, and conventional materials can be used for these. For example, as the n-type dopant, the donor material exemplified as the material of the electron transport layer is preferably used. Among these, alkali metals or salts thereof and rare earth metals are preferable, and metallic lithium, lithium fluoride (LiF), lithium quinolinol (Liq), and metallic ytterbium are more preferable. Further, as the n-type host, those exemplified as the electron transport material are preferably used. Among these, a triazine derivative, a phenanthroline derivative, and an oligopyridine derivative are preferable, a phenanthroline derivative and a terpyridine derivative are more preferable, and a phenanthroline derivative represented by the following general formula (3) is further preferable. That is, the light emitting device of the present invention preferably contains a phenanthroline derivative represented by the general formula (3) in the charge generation layer.

In the above general formula (3), Ar ¹ is selected from the group consisting of a p-valent aromatic hydrocarbon group and a p-valent aromatic heterocyclic group. p is a natural number of 1 to 3. R ⁸ to R ¹⁵ may be the same or different from each other, 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. Of Ar ¹ , the substitution position with p phenanthrolyl groups is an arbitrary position.

Examples of the aromatic hydrocarbon group include a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a benzofluorenyl group, a dibenzofluorenyl group, a phenanthryl group, an anthrasenyl group and a benzo in the case of a monovalent group. Examples thereof include a phenanthryl group, a benzoanthrasenyl group, a chrysenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, a benzofluoranthenyl group, a dibenzoanthrasenyl group, a peryleneyl group and a helisenyl group. Among them, from the viewpoint of easiness of synthesis and sublimation, a phenyl group, a biphenyl group, a terphenyl group, a naphthyl group, a fluorenyl group, a phenanthryl group, an anthrasenyl group, a pyrenyl group, a fluoranthenyl group, a triphenylenyl group, and hydrogen atoms thereof. Groups excluding at least one part of the above are preferred. The aromatic hydrocarbon group may or may not have a substituent. The number of carbon atoms is not particularly limited, but is preferably in the range of 6 or more and 40 or less, and more preferably 6 or more and 30 or less. Further, when there are substituents on two adjacent carbon atoms, the ring structure may be formed between the substituents.

The aromatic heterocyclic group refers to a cyclic aromatic group having one or more atoms other than carbon in the ring, and in the case of monovalent, for example, a pyridyl group, a furanyl group, a thiophenyl group, a quinolinyl group, an isoquinolinyl group, a pyrazinyl. Group, pyrimidyl group, pyridazinyl group, triazinyl group, naphthyldinyl group, cinnolinyl group, phthalazinyl group, quinoxalinyl group, quinazolinyl group, benzofuranyl group, benzothiophenyl group, indolyl group, dibenzofuranyl group, dibenzothiophenyl group, carbazolyl group, Benzocarbazolyl group, carborinyl group, indolocarbazolyl group, benzoflocarbazolyl group, benzothienocarbazolyl group, dihydroindenocarbazolyl group, benzoquinolinyl group, acridinyl group, dibenzoacrydinyl group, Examples thereof include a benzoimidazolyl group, an imidazoly pyridyl group, a benzoxazolyl group, a benzothiazolyl group, a phenylanthrolinyl group and the like. However, the naphthyldinyl group is any of 1,5-naphthyldinyl group, 1,6-naphthyldinyl group, 1,7-naphthyldinyl group, 1,8-naphthyldinyl group, 2,6-naphthyldinyl group and 2,7-naphthyldinyl group. Indicates. The aromatic heterocyclic group may or may not have a substituent. The number of carbon atoms of the aromatic heterocyclic group is not particularly limited, but is preferably in the range of 2 or more and 40 or less, and more preferably 2 or more and 30 or less.

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

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

An example of the phenanthroline derivative represented by the general formula (3) is shown below.

The p-type charge generation layer is composed of a p-type dopant and a p-type host, and conventional materials can be used for these. For example, as the p-type dopant, an acceptor material exemplified as a material for a hole injection layer, iodine, FeCl ₃ , FeF ₃ , SbCl ₅ , and the like are preferably used. Specific examples thereof include HAT-CN6, F4-TCNQ, tetracyanoquinodimethane derivative, radialene derivative, iodine, FeCl ₃ , FeF ₃ , SbCl ₅ and the like. Among these, HAT-CN6 and (2E, 2'E, 2''E) -2,2', 2''- (cyclopropane-1,2,3-triylidene) tris (2- (perfluorophenyl) )-Acetonitrile), (2E, 2'E, 2''E) -2,2', 2''- (cyclopropane-1,2,3-triylidene) Tris (2- (4-cyanoperfluorophenyl) -Radialene derivatives such as acetonitrile) are more preferred. A thin film of the p-type dopant may be formed, and the film thickness is preferably 10 nm or less. Further, as the p-type host, an arylamine derivative is preferable.

(Electron injection layer)
In the present invention, an electron injection layer may be provided between the cathode and the electron transport layer. It is preferable to have an electron injection layer and an electron transport layer between the cathode and the light emitting layer in this order from the cathode side. Generally, the electron injection layer is formed for the purpose of assisting the injection of electrons from the cathode into the electron transport layer. Examples of the electron injection material used for the electron injection layer include compounds having a heteroaryl ring structure containing electron-accepting nitrogen, the above-mentioned donor material, and the like. Two or more of these may be contained. Among these, a triazine derivative, a phenanthroline derivative, and an oligopyridine derivative are preferable, a phenanthroline derivative and a terpyridine derivative are more preferable, and a phenanthroline derivative represented by the general formula (3) is further preferable. That is, the light emitting device of the present invention preferably contains a phenanthroline derivative represented by the general formula (3) in the electron injection layer.

Further, an insulator or a semiconductor inorganic substance can be used for the electron injection layer. By using these materials, it is possible to suppress a short circuit of the light emitting element and improve the electron injection property.

As such an insulator, metal compounds such as alkali metal chalcogenide, alkaline earth metal chalcogenide, alkali metal halide, and alkaline earth metal halide are preferable. Two or more of these may be used.

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

The thickness of the organic layer cannot be limited because it depends on the resistance value of the luminescent substance, but is preferably 1 to 1000 nm. The film thicknesses of the light emitting layer, the electron transporting layer, the hole blocking layer, the hole transporting layer, the electron blocking layer, and the charge generating layer are each preferably 1 nm or more and 200 nm or less, and more preferably 5 nm or more and 100 nm or less.

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

From the viewpoint of further enhancing the color purity, the light emitting device according to the embodiment of the present invention preferably has a half width of 45 nm or less, more preferably 35 nm or less, still more preferably 30 nm or less in the fluorescence emission spectrum by energization. ..

(Use of light emitting element)
The light emitting element 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, for example.

The light emitting element according to the embodiment of the present invention is also preferably used as a backlight for various devices and the like. The backlight is mainly used for the purpose of improving the visibility of display devices such as displays that do not emit light by itself, and is used for display devices such as liquid crystal displays, watches, audio devices, automobile panels, display boards and signs. In particular, the light emitting element of the present invention is preferably used for a liquid crystal display, especially a backlight for a personal computer for which thinning is being considered, and it is possible to provide a backlight that is thinner and lighter than the conventional one.

The light emitting element according to the embodiment of the present invention is also preferably used as various lighting devices. The light emitting element according to the embodiment of the present invention can achieve both high element efficiency and high color purity, and can be made thinner and lighter, so that low power consumption and bright light emitting color can be achieved. A lighting device with high design can be realized.

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

First, the evaluation methods in each Example and Comparative Example are described below.

( ^{1 1} H-NMR)
The structure of the pyrometheneboron complex obtained in Example 1 was identified by ¹ H-NMR measurement in a deuterated chloroform solution using superconducting FTNMR EX-270 (manufactured by JEOL Ltd.).

(Absorption spectrum)
A diluted solution of pyrromethene boron complex obtained in each Example and Comparative Example dissolved in toluene at a concentration of ^10-5 mol / L was absorbed using a spectrophotometer (U-3010) manufactured by Hitachi High-Tech Science Co., Ltd. The spectrum was measured and the peak wavelength was determined.

(Emission spectrum)
Using a fluorescence spectrophotometer (FluoroMax-4P) manufactured by Horiba Seisakusho Co., Ltd., a diluted solution having a concentration of ^10-5 mol / L in which the pyrromethene boron complex obtained in each Example and Comparative Example was dissolved in toluene was used. The emission spectrum was measured to determine the peak wavelength and full width at half maximum.

(Fluorescence quantum yield)
Fluorescent quantum of a diluted solution of pyrromethene boron complex obtained in each example and comparative example dissolved in toluene at a concentration of ^10-5 mol / L using an absolute PL quantum yield measuring device manufactured by Hamamatsu Photonics Co., Ltd. Yield QY was measured. The excitation wavelength was 460 nm.

(Ionization potential)
The ionization potential Ip of the pyrromethene boron complex obtained in each Example and Comparative Example was measured in the atmosphere using a photoelectron spectroscope (manufactured by RIKEN KEIKI Co., Ltd .: AC-2).

(Electron affinity)
The pyrromethene boron complex obtained in each Example and Comparative Example was vapor-deposited on a quartz plate to prepare a film having a thickness of 30 nm. The absorption spectrum of the obtained film was measured using a spectrophotometer (U-3010) manufactured by Hitachi High-Tech Science Co., Ltd. A tangent line is drawn for the falling edge of the obtained absorption spectrum on the long wavelength side, and the wavelength value λ _edge [nm] at the intersection of the tangent line and the horizontal axis is substituted into the conversion formula 1 shown below to substitute the energy gap Eg. Was calculated.
Conversion formula 1: Eg [eV] = 1239.85 / λ _edge
The value of Ip-Eg was calculated from the values of Ip and Eg measured or calculated by the above method, and used as the electron affinity Af as an index of the LUMO level.

(Characteristics of Thermally Activated Delayed Fluorescence Element)
A voltage was applied to the light emitting elements obtained in each Example and Comparative Example so that the current density was 0.1 mA / cm ² , and light was emitted using a spectral radiance meter CS-1000 manufactured by Konica Minolta Co., Ltd. The spectrum was measured. From the obtained emission spectrum, it was assumed that Lambasian radiation was performed, and the external quantum efficiency EQE was calculated and used as an index of device efficiency.

Further, the emission spectrum when a voltage was applied to the obtained light emitting element so that the current density was 10 mA / cm ² was similarly measured, and the peak wavelength and the half width were calculated.

(durability)
The brightness of the light emitting device was measured using a photodiode while applying a voltage to the light emitting device obtained in each Example and Comparative Example so that the current density was 10 mA / cm ² , and 90% of the initial brightness was measured. The time (LT90) at which the luminance becomes the brightness of the above was measured and used as an index of durability.

The raw materials used in each Example and Comparative Example will be described.

Synthesis Example 1: Synthesis of Compound D-1 2.00 g of 2,4-dimethylpyrrole and dehydrated diethyl ether were placed in a flask and substituted with nitrogen. The mixture was cooled to 0 ° C., 12.9 mL of 1.6 M n-butyllithium was added dropwise, and the mixture was stirred at room temperature for 2 hours. 1.25 g of 2,6-dimethylaniline was added to the reaction solution, and the mixture was stirred at room temperature for 30 minutes. A diethyl ether solution of 15.3 g of aldehyde was added dropwise to the reaction solution, and the mixture was stirred at 35 ° C. for 3 hours. The reaction solution was cooled to room temperature, ammonium chloride solution was added and stirred, and the organic layer was extracted. This organic layer was dried over magnesium sulfate, filtered, and then the solvent was distilled off. The obtained reaction product was purified by silica gelization chromatography to obtain 6.91 g of brown liquid D-1A.

6.59 g of D-1A and 280 mL of toluene were placed in a flask and replaced with nitrogen. 2.63 g of 3-ethyl-2,4-dimethylpyrrole was added to the reaction solution and replaced with nitrogen again. 4.95 g of methanesulfonic acid anhydride was added to the reaction solution, and the mixture was heated and stirred at 80 ° C. for 3 hours under a nitrogen stream. The reaction solution was cooled to room temperature, aqueous sodium hydrogen carbonate was added, and the mixture was stirred to extract the organic layer. This organic layer was dried over magnesium sulfate, filtered, and then the solvent was distilled off to obtain D-1B.

Toluene 300 mL was added to D-1B in the flask and replaced with nitrogen. 12.6 mL of diisopropylethylamine was added, and the mixture was stirred at room temperature for 15 minutes. After adding 8.90 mL of boron trifluoride diethyl ether complex to the reaction solution and stirring at room temperature for 15 hours, water was added and the mixture was stirred to extract the organic layer. This organic layer was dried over magnesium sulfate, filtered, and then the solvent was distilled off. The obtained reaction product was purified by silica gelation chromatography to obtain an orange powder. Further, 40 mL of butyl acetate was added to the obtained powder, and the mixture was heated and stirred at 140 ° C. for 30 minutes and then allowed to cool. The precipitated solid was filtered and vacuum dried to obtain 5.85 g of orange powder. The analysis result of ¹ H-NMR of the obtained powder is as follows, and it was confirmed that the orange powder obtained above was compound D-1 having a pyrromethene skeleton.
^{1 1} H-NMR (CDCl ₃ (d = ppm)): 7.95 (s, 1H), 7.57 (d, 4H), 7.52-7.51 (m, 6H), 5.96 (s) , 1H), 2.57 (s, 6H), 2.17 (s, 6H), 1.48-1.37 (m, 20H), 0.99 (t, 3H).

Sublimation purification was performed to further increase the purity. A metal container containing compound D-1 was placed in a glass tube and sublimated by heating at 250 ° C. under a pressure of 1 × 10-3 Pa using an oil diffusion pump. The solid adhering to the glass tube wall was recovered and analyzed by LC-MS. As a result, the purity was 99%.

The results of evaluation of D-1 after sublimation purification by the above-mentioned method are shown below.
Absorption spectrum (solvent: toluene): λmax 515 nm
Emission spectrum (solvent: toluene): λmax 532 nm, half width 24 nm
Fluorescence quantum yield QY (solvent: toluene, excitation light: 460 nm): 89%
Ionization potential: 5.72 eV
Electron affinity: 3.46 eV
The structures of the pyrromethene boron complexes D-2 to D-10 used in each Example and Comparative Example are shown below.

The characteristics of the pyrromethene boron complexes D-1 to D-10 are shown in Table 1.

In each Example and Comparative Example, the structure of the compound used for the hole injection layer, the hole transport layer, the hole blocking layer, the host material, the TADF material, the electron blocking layer, the electron transport layer, the charge generation layer, and the electron injection layer. Is shown below.

Example 1
A glass substrate (manufactured by Geomatec Co., Ltd., 11Ω / □, sputtered product) on which an ITO transparent conductive film was deposited at 165 nm was cut into 38 mm × 46 mm and etched. The obtained substrate was ultrasonically washed 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 the device was manufactured, installed in a vacuum vapor deposition apparatus, and exhausted until the degree of vacuum in the apparatus became 5 × 10 ^-4 Pa or less. By the resistance heating method, HAT-CN6 was first deposited at 10 nm as a hole injection layer, and then HT-1 was deposited at 30 nm as a hole transport layer. Next, as the light emitting layer, the host material H-1, the compound D-1, and the TADF material compound H-2 are mixed in a weight ratio of 79.0: 1.0: 20 to 30 nm. Vapor deposition to the thickness of. Subsequently, ET-1 was laminated to a thickness of 10 nm as a hole blocking layer, and ET-2 was laminated to a thickness of 40 nm as an electron transporting layer. Next, after depositing 2E-1 at 0.5 nm as an electron injection layer, magnesium and silver were co-deposited at 100 nm to form a cathode, and a 5 mm × 5 mm square light emitting device was produced.

When the obtained light emitting device was evaluated by the above-mentioned method, the emission peak wavelength was 533 nm, the half width was 24 nm, the external quantum efficiency was 15.3%, and the LT90 was 62 hours.

(Examples 2 to 8, Comparative Examples 1 and 2)
A light emitting device material and a light emitting device were produced in the same manner as in Example 1 except that the compounds shown in Table 2 were used instead of the pyrromethene boron complex D-1 as the dopant material. The evaluation results are shown in Table 2.

Example 9
A glass substrate (manufactured by Geomatec Co., Ltd., 11Ω / □, sputtered product) on which an ITO transparent conductive film was deposited at 165 nm was cut into 38 mm × 46 mm and etched. The obtained substrate was ultrasonically cleaned with "Semicoclean" 56 (trade name, manufactured by Furuuchi Chemical Co., Ltd.) for 15 minutes, and then washed with ultrapure water. This substrate was subjected to UV-ozone treatment for 1 hour immediately before the device was manufactured, installed in a vacuum vapor deposition apparatus, and exhausted until the degree of vacuum in the apparatus became 5 × 10 ^-4 Pa or less. By the resistance heating method, HAT-CN6 was first deposited at 5 nm as a hole injection layer, and then HT-1 was deposited at 50 nm as a hole transport layer. Next, H-1 was used as the hole blocking layer at 10 nm, and the host material H-1 and the compound D-1 were used as the light emitting layer in a weight ratio of 99.5: 0.5 to a thickness of 20 nm. It was vapor-deposited. Further, ET-1 was laminated to a thickness of 10 nm as an electron blocking layer, and compound ET-3 was laminated to a thickness of 35 nm as an electron transporting layer. Subsequently, as the n-type charge generation layer, the compound ET-3, which is an n-type host, and metallic lithium, which is an n-type dopant, were laminated at 10 nm so that the vapor deposition rate ratio was 99: 1. Further, HAT-CN6 was laminated at 10 nm as a p-type charge generation layer. A hole transport layer of 50 nm, a hole blocking layer of 10 mn, and a light emitting layer of 20 nm were formed on the hole transport layer in the same manner as described above. Further, ET-2 was deposited at 10 nm as an electron blocking layer, and ET-3 was deposited at 35 nm as an electron transporting layer. Next, after depositing 2E-1 at 0.5 nm as an electron injection layer, magnesium and silver were co-deposited at 1000 nm to form a cathode, and a tandem type light emitting device of 5 mm × 5 mm square was produced.

When the obtained light emitting device was evaluated by the above-mentioned method, the emission peak wavelength was 533 nm, the half width was 24 nm, the external quantum efficiency was 7.9%, and the LT90 was 92 hours. It was confirmed that the durability was improved as compared with Example 1 in which the light emitting layer was only one layer.

Claims (14)

A light emitting device material composed of a pyrromethene boron complex represented by the following general formula (1).

(In the above general formula (1), R ¹ to R ⁴ may be the same or different, and are independently selected from the group consisting of substituted or unsubstituted alkyl groups and substituted or unsubstituted cycloalkyl groups. One of R ⁵ and R ⁶ is a substituted or unsubstituted alkyl group, a substituted or unsubstituted cycloalkyl group, a substituted or unsubstituted alkenyl group, a substituted or unsubstituted cycloalkenyl group, a substituted or unsubstituted cycloalkenyl group. Alkinyl group, hydroxyl group, thiol group, substituted or unsubstituted alkoxy group, substituted or unsubstituted alkylthio group, substituted or unsubstituted arylether group, substituted or unsubstituted arylthioether group, substituted or unsubstituted heterocyclic group. , Substituted or unsubstituted amino group, substituted or unsubstituted silyl group, substituted or unsubstituted siroxanyl group and substituted or unsubstituted boryl group, the other is hydrogen atom, substituted or unsubstituted. Alkyl groups, substituted or unsubstituted cycloalkyl groups, substituted or unsubstituted alkenyl groups, substituted or unsubstituted cycloalkenyl groups, substituted or unsubstituted alkynyl groups, hydroxyl groups, thiol groups, substituted or unsubstituted alkoxy groups, Substituted or unsubstituted alkylthio group, substituted or unsubstituted aryl ether group, substituted or unsubstituted arylthio ether group, substituted or unsubstituted aryl group, substituted or unsubstituted heteroaryl group, substituted or unsubstituted heterocycle It is selected from the group consisting of a group, a substituted or unsubstituted amino group, a substituted or unsubstituted silyl group, a substituted or unsubstituted siroxanyl group and a substituted or unsubstituted boryl group, except that R ⁵ and R ⁶ are different groups. Is.
X ¹ and X ² may be the same or different, substituted or unsubstituted alkyl group, substituted or unsubstituted aryl group, substituted or unsubstituted alkoxy group, substituted or unsubstituted aryloxy group, hydroxyl group, It is selected from the group consisting of halogen atoms and cyano groups.
^R7 is selected from the group consisting of substituted or unsubstituted aryl groups and substituted or unsubstituted heteroaryl groups. ) The light emitting element material according to claim 1, wherein one of R ⁵ and R ⁶ is selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted cycloalkyl group. The light emitting element material according to claim 2, wherein one of R ⁵ and R ⁶ is selected from the group consisting of a substituted or unsubstituted alkyl group and a substituted or unsubstituted cycloalkyl group, and the other is hydrogen. X ¹ and X ² may be the same or different, at least one halogen substituted alkyl group, at least one halogen substituted aryl group, at least one halogen substituted alkoxy group, at least one. The light emitting element material according to any one of claims 1 to 3, which is selected from the group consisting of an aryl ether group substituted with one halogen, a halogen atom, and a cyano group. The light emitting device material according to claim 4, wherein X ¹ and X ² are fluorine atoms. The light emitting device material according to any one of claims 1 to 5, which has a peak wavelength of a light emitting spectrum in a wavelength range of 500 nm or more and 550 nm or less. A light emitting device that emits light by electric energy and has a light emitting layer containing the light emitting device material according to any one of claims 1 to 6 between an anode and a cathode. The light emitting device according to claim 7, wherein the light emitting layer has a first compound and a second compound which is a dopant, and the second compound is a pyrromethene boron complex represented by the general formula (1). .. The light emitting device according to claim 7 or 8, wherein the first compound is a thermally activated delayed fluorescent compound. The light emitting element according to claim 9, wherein the light emitting layer further contains a third compound, and the singlet energy of the third compound is larger than the singlet energy of the first compound. The light emitting device according to any one of claims 7 to 10, further comprising two or more light emitting layers between the anode and the cathode, and one or more charge generating layers between the respective light emitting layers and the light emitting layers. The light emitting device according to any one of claims 7 to 11, wherein an electron injection layer and an electron transport layer are provided between the cathode and the light emitting layer in this order from the cathode side. The light emitting device according to claim 11 or 12, wherein the charge generation layer and / or the electron injection layer contains a phenanthroline derivative represented by the following general formula (3).

(Ar ¹ is selected from the group consisting of a p-valent aromatic hydrocarbon group and a p-valent aromatic heterocyclic group. P is a natural number of 1 to 3. R ⁸ to R ¹⁵ are the same, respectively. It may be different and is selected from the group consisting of hydrogen atom, alkyl group, cycloalkyl group, heterocyclic group, aryl group and heteroaryl group.) The light emitting device according to any one of claims 7 to 11, which is a top emission type organic electroluminescent element.