Pyrimidine compound and organic electroluminescent element

Abstract

One purpose of the present invention is to provide a compound which is suitable for use as a material for a capping layer in an organic EL element, has a high refractive index in a wavelength range from 450 nm to 750 nm, and has a low extinction coefficient. Another purpose of the present invention is to provide an organic EL element having an improved light extraction efficiency due to use of the compound.　The present invention is a pyrimidine compound represented by general formula (1). (In formula (1), Ar1 to Ar3 may be the same as or different from one another and each independently represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic ring group or the like; L1 to L3 may be the same as or different from one another and each independently represent a single bond, a substituted or unsubstituted bivalent aromatic hydrocarbon group or the like; and p, q and r may be the same as or different from one another and each independently represent an integer of 1 to 2; in which at least one of Ar1 to Ar3 represents an aromatic heterocyclic ring group such as a substituted or unsubstituted benzoxazolyl group.)

Description

Pyrimidine compounds and organic electroluminescent devices

[0001] The present invention relates to a compound suitable for a self-luminous electronic element suitable for various display devices, particularly a compound suitable for an organic electroluminescence element (hereinafter abbreviated as organic EL element), and to an organic EL element, an electronic element and an electronic device using the compound.

[0002] Organic EL elements are self-luminous elements, and therefore are brighter and more visible than liquid crystal elements, and are capable of producing clearer displays, and therefore have been the subject of vigorous research.

[0003] In 1987, C. W. Tang et al. of Eastman Kodak Company made organic EL devices practical by developing a layered structure element in which various roles are assigned to each material. They layered a phosphor capable of transporting electrons and an organic material capable of transporting holes, and by injecting both charges into the phosphor layer to emit light, they achieved 1000 cd / m at a voltage of 10 V or less. ２ Such high brightness is achieved (see, for example, Patent Documents 1 and 2).

[0004] To date, many improvements have been made to the practical application of organic EL elements, and the role of each layer in the laminated structure has been further subdivided. An anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode are sequentially provided on a substrate to form a light-emitting element with a bottom emission structure that emits light from the bottom, thereby achieving high efficiency and durability (see, for example, Non-Patent Document 1).

[0005] In recent years, light-emitting devices with a top-emission structure that uses a metal with a high work function as the anode and emits light from the top have come into use. In a bottom-emission structure in which light is extracted from the bottom where the pixel circuit is located, the area of ​​the light-emitting section is limited, whereas a light-emitting device with a top-emission structure has the advantage that the light is extracted from the top and is not blocked by the pixel circuit, allowing for a larger light-emitting section. In light-emitting devices with a top-emission structure, a semi-transparent electrode such as LiF / Al / Ag (see, for example, Non-Patent Document 2), Ca / Mg (see, for example, Non-Patent Document 3), or LiF / MgAg is used as the cathode.

[0006] In such light-emitting devices, when light emitted from the light-emitting layer is incident on another film at an angle greater than a certain value, it is totally reflected at the interface between the light-emitting layer and the other film. As a result, only a portion of the emitted light can be utilized. In recent years, in order to improve the light extraction efficiency, light-emitting devices have been proposed in which a "capping layer" with a high refractive index is provided on the outside of a semi-transparent electrode with a low refractive index (see, for example, Non-Patent Documents 2 and 3).

[0007] As an effect of the capping layer in a top-emission light-emitting device, Ir(ppy) ３ In a light-emitting device using ZnSe as the light-emitting material, the current efficiency was 38 cd / A when there was no capping layer, whereas in a light-emitting device using ZnSe with a thickness of 60 nm as the capping layer, the efficiency was improved by approximately 1.7 times to 64 cd / A. Furthermore, it has been shown that the maximum points of the transmittance of the semi-transparent electrode and the capping layer do not necessarily coincide with the maximum points of the efficiency, and that the maximum point of the light extraction efficiency is determined by the interference effect (see, for example, Non-Patent Document 3).

[0008] Conventionally, the use of a high-resolution metal mask has been proposed for forming a capping layer, but there is a problem that when used under high-temperature conditions, the metal mask becomes distorted due to heat, resulting in reduced alignment accuracy. Therefore, ZnSe, which has a high melting point of 1100°C or higher (see, for example, Non-Patent Document 3), cannot be deposited in the correct position using a high-resolution metal mask, which may adversely affect the light-emitting element. Furthermore, even when formed by sputtering, the film adversely affects the light-emitting element, so capping layers made of inorganic constituent materials are not suitable for use.

[0009] In addition, tris(8-hydroxyquinoline)aluminum (hereinafter referred to as Alq) is used as a capping layer for adjusting the refractive index. ３ It has also been proposed to use Alq ３is known as an organic EL material that is generally used as a green light-emitting material or an electron transport material, and has weak absorption around 450 nm, which is close to the emission wavelength of blue light-emitting materials. Therefore, in the case of blue light-emitting devices, it has also had problems such as a decrease in color purity and a decrease in light extraction efficiency.

[0010] In order to improve the device characteristics of organic EL devices and to significantly improve the light extraction efficiency, materials for the capping layer are required that have a high refractive index, a low extinction coefficient, and excellent thin film stability and durability.

[0011] US5792557US5639914International Publication No. 2014 / 009310US2014 / 0225100 A1

[0012] Proceedings of the 9th Seminar of the Japan Society of Applied Physics, pages 55-61 (2001) Appl. Phys. Let. , 78, 544 (2001) Appl. Phys. Let. , 82, 466 (2003) Tetrahedron, 58, 9633 (2002) Appl. Phys. Let. , 98, 083302 (2011)

[0013] An object of the present invention is to provide a compound that has a high refractive index and a low extinction coefficient in the wavelength range of 450 nm to 750 nm, and is suitable as a material for the capping layer of an organic EL device, and to provide an organic EL device that uses the compound and thereby has improved light extraction efficiency.

[0014] The physical properties of a compound suitable for the capping layer of an organic EL device include (1) a high refractive index, (2) a low extinction coefficient, (3) the ability to be vapor-deposited, (4) a stable thin film state, and (5) a high glass transition temperature. The physical properties of the organic EL device to be provided by the present invention include (1) a high light extraction efficiency, (2) no decrease in color purity, (3) light transmission without change over time, and (4) a long life.

[0015] In order to achieve the above object, the present inventors have focused on the advantage that pyrimidine skeleton compounds have excellent thin film stability and durability, and by optimizing molecular design, have developed a material that has a high refractive index in the wavelength range of 450 nm to 750 nm and a low extinction coefficient. Furthermore, they have produced organic EL devices using the compound and diligently evaluated the device's characteristics, which have led to the completion of the present invention, as they have been able to solve the conventional problems.

[0016] That is, according to the present invention, there are provided a pyrimidine compound represented by the following general formula (1) and an organic EL device.

[0017] 1) A pyrimidine compound represented by the following general formula (1):

[0018] (In formula (1), Ar １ ~Ar ３ may be the same or different and each represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, or a substituted or unsubstituted fused polycyclic aromatic group; L １ ~L ３ may be the same or different and each represent a single bond, a substituted or unsubstituted divalent aromatic hydrocarbon group, a substituted or unsubstituted divalent aromatic heterocyclic group, or a substituted or unsubstituted divalent fused polycyclic aromatic group, and p, q, and r may be the same or different and each represent an integer of 1 to 2. １ ~Ar ３ At least one of the groups is a substituted or unsubstituted benzoxazolyl group, a substituted or unsubstituted benzothiazolyl group, a substituted or unsubstituted benzofuranyl group, or a substituted or unsubstituted benzothienyl group.

[0019] 2) L in the general formula (1) １ ~L ３ may be the same or different and are a single bond, a divalent group obtained by removing two hydrogen atoms from substituted or unsubstituted benzene, a divalent group obtained by removing two hydrogen atoms from substituted or unsubstituted biphenyl, or a divalent group obtained by removing two hydrogen atoms from substituted or unsubstituted naphthalene.

[0020] 3) L in the general formula (1) １ ~L ３ may be the same or different and are a single bond, a divalent group obtained by removing two hydrogen atoms from unsubstituted benzene, a divalent group obtained by removing two hydrogen atoms from unsubstituted biphenyl, or a divalent group obtained by removing two hydrogen atoms from unsubstituted naphthalene.

[0021] 4) L in the general formula (1) １ ~L ３ may be the same or different and are a single bond, an unsubstituted 1,4-phenylene group, an unsubstituted 4,4'-biphenylylene group, an unsubstituted 2,6-naphthylene group, or an unsubstituted 2,7-naphthylene group.

[0022] 5) The pyrimidine compound according to any one of 1) to 4), wherein p, q, and r in the general formula (1) are 1.

[0023] 6) Ar in the general formula (1) １ ~Ar ３ at least one of the groups represented by the formula (I) is an unsubstituted benzoxazolyl group, an unsubstituted benzothiazolyl group, an unsubstituted benzofuranyl group, or an unsubstituted benzothienyl group.

[0024] 7) Ar in the general formula (1) １ ~Ar ３ 7) The pyrimidine compound according to 6), wherein at least one of the groups represented by the formula (I) is an unsubstituted 2-benzoxazolyl group, an unsubstituted 2-benzothiazolyl group, an unsubstituted 2-benzofuranyl group, or an unsubstituted 2-benzothienyl group.

[0025] 8) Ar in the general formula (1) １ ~Ar ３ 8) The pyrimidine compound according to 7), wherein any two of the following are an unsubstituted 2-benzoxazolyl group, an unsubstituted 2-benzothiazolyl group, an unsubstituted 2-benzofuranyl group, or an unsubstituted 2-benzothienyl group.

[0026] 9) Ar in the general formula (1) １~Ar ３ is an unsubstituted 2-benzoxazolyl group, an unsubstituted 2-benzothiazolyl group, an unsubstituted 2-benzofuranyl group, or an unsubstituted 2-benzothienyl group.

[0027] 10) The pyrimidine compound according to any one of 1) to 9), which has a refractive index of 1.70 or more in the wavelength range of 450 nm to 750 nm.

[0028] 11) An organic EL device having at least an anode electrode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode electrode, and a capping layer in this order, wherein the capping layer contains the pyrimidine compound according to any one of 1) to 10).

[0029] 12) An organic EL device, wherein the capping layer is a mixed layer containing two or more types of compounds, or a laminate of two or more layers each containing a different compound, and at least one of these compounds contains the pyrimidine compound described in any one of 1) to 10).

[0030] 13) An electronic device having a pair of electrodes and at least one organic layer sandwiched between them, wherein the organic layer contains the pyrimidine compound according to any one of 1) to 10).

[0031] 14) An electronic device using the electronic element according to 13).

[0032] Ar in general formula (1) １ ~Ar ３Specific examples of the "aromatic hydrocarbon group", "aromatic heterocyclic group" or "condensed polycyclic aromatic group" in the "substituted or unsubstituted aromatic hydrocarbon group", "substituted or unsubstituted aromatic heterocyclic group" or "substituted or unsubstituted condensed polycyclic aromatic group" represented by the formula (I) include a phenyl group, a biphenylyl group, a terphenylyl group, a naphthyl group, an anthracenyl group, a phenanthrenyl group, a fluorenyl group, a spirobifluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, a triphenylenyl group, a pyridyl group, a pyrimidinyl group, a triazinylinyl group, a Examples of the aryl group include an aryl group having 6 to 30 carbon atoms, such as a phenyl group, a furyl group, a pyrrolyl group, a thienyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, a quinoxalinyl group, a quinazolinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, a naphthyridinyl group, a phenanthrolinyl group, an acridinyl group, and a carbolinyl group, and a heteroaryl group having 2 to 20 carbon atoms.

[0033] L in general formula (1) １ ~L ３ The "divalent aromatic hydrocarbon group", "divalent aromatic heterocyclic group" or "divalent fused polycyclic aromatic group" in the "substituted or unsubstituted divalent aromatic hydrocarbon group", "substituted or unsubstituted divalent aromatic heterocyclic group" or "substituted or unsubstituted divalent fused polycyclic aromatic group" represented by the following general formula (1) can be used: １ ~Ar ３ Examples of such divalent groups include those obtained by removing one hydrogen atom from an "aromatic hydrocarbon group," "aromatic heterocyclic group," or "condensed polycyclic aromatic group" represented by the following formula:

[0034] Ar in general formula (1) １ ~Ar ３ and L １ ~L ３Specific examples of the "substituent" in the "substituted aromatic hydrocarbon group", "substituted aromatic heterocyclic group", or "substituted fused polycyclic aromatic group" represented by the above formula include a deuterium atom, a cyano group, a nitro group; a halogen atom such as a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom; a silyl group such as a trimethylsilyl group or a triphenylsilyl group; a linear or branched alkyl group having 1 to 6 carbon atoms such as a methyl group, an ethyl group, or a propyl group; a linear or branched alkyloxy group having 1 to 6 carbon atoms such as a methyloxy group, an ethyloxy group, or a propyloxy group; an alkenyl group such as a vinyl group or an allyl group; an aryloxy group such as a phenyloxy group or a tolyloxy group; an arylalkyloxy group such as a benzyloxy group or a phenethyloxy group; a phenyl group, a biphenylyl group, a terphenylyl group, a naphthyl group,

[0039] Examples of the aromatic hydrocarbon groups or condensed polycyclic aromatic groups include a pyridyl group, an anthracenyl group, a phenanthrenyl group, a fluorenyl group, a spirobifluorenyl group, an indenyl group, a pyrenyl group, a perylenyl group, a fluoranthenyl group, and a triphenylenyl group; a pyridyl group, a thienyl group, a furyl group, a pyrrolyl group, a quinolyl group, an isoquinolyl group, a benzofuranyl group, a benzothienyl group, an indolyl group, a carbazolyl group, a benzoxazolyl group, a benzothiazolyl group, a quinoxalinyl group, a quinazolinyl group, a benzimidazolyl group, a pyrazolyl group, a dibenzofuranyl group, a dibenzothienyl group, and a carbolinyl group, as well as an aryl group having 6 to 30 carbon atoms or a heteroaryl group having 2 to 20 carbon atoms, and these substituents may be further substituted with the substituents exemplified above. In addition, benzene rings substituted with these substituents, or multiple substituents substituted on the same benzene ring, may be bonded to each other via a single bond, a substituted or unsubstituted methylene group, an oxygen atom, or a sulfur atom to form a ring.

[0035] Ar in general formula (1) １ ~Ar ３Among these, it is preferred that at least two of them are substituted or unsubstituted benzoxazole groups, substituted or unsubstituted benzothiazole groups, substituted or unsubstituted benzofuranyl groups, or substituted or unsubstituted benzothienyl groups, and it is also preferred that all of them are substituted or unsubstituted benzoxazole groups, substituted or unsubstituted benzothiazole groups, substituted or unsubstituted benzofuranyl groups, or substituted or unsubstituted benzothienyl groups.

[0036] Ar in general formula (1) １ ~Ar ３ Among these, at least one is preferably an unsubstituted benzoxazolyl group, an unsubstituted benzothiazolyl group, an unsubstituted benzofuranyl group, or an unsubstituted benzothienyl group, and more preferably an unsubstituted 2-benzoxazolyl group, an unsubstituted 2-benzothiazolyl group, an unsubstituted 2-benzofuranyl group, or an unsubstituted 2-benzothienyl group.

[0037] Ar in general formula (1) １ ~Ar ３ Among these, it is preferable that any two of them are unsubstituted 2-benzoxazolyl groups, unsubstituted 2-benzothiazolyl groups, unsubstituted 2-benzofuranyl groups, or unsubstituted 2-benzothienyl groups, and it is also preferable that all of them are unsubstituted 2-benzoxazolyl groups, unsubstituted 2-benzothiazolyl groups, unsubstituted 2-benzofuranyl groups, or unsubstituted 2-benzothienyl groups.

[0038] L in general formula (1) １ ~L ３ may be the same or different from each other and are preferably a single bond, a divalent group obtained by removing two hydrogen atoms from unsubstituted benzene, a divalent group obtained by removing two hydrogen atoms from unsubstituted biphenyl, or a divalent group obtained by removing two hydrogen atoms from unsubstituted naphthalene, and more preferably a single bond, a divalent group obtained by removing two hydrogen atoms from unsubstituted benzene, a divalent group obtained by removing two hydrogen atoms from unsubstituted biphenyl, or a divalent group obtained by removing two hydrogen atoms from unsubstituted naphthalene.

[0039] L in general formula (1) １ ~L３ may be the same or different from each other and are preferably a single bond, an unsubstituted 1,4-phenylene group, an unsubstituted 4,4'-biphenylylene group, an unsubstituted 2,6-naphthylene group, or an unsubstituted 2,7-naphthylene group, more preferably a single bond, an unsubstituted 1,4-phenylene group, or an unsubstituted 4,4'-biphenylylene group, and particularly preferably a single bond or an unsubstituted 1,4-phenylene group.

[0040] It is preferred that p, q, and r in general formula (1) all be 1.

[0041] In the organic EL device, the thickness of the capping layer is preferably in the range of 30 nm to 120 nm, and more preferably in the range of 40 nm to 80 nm.

[0042] The compound of the present invention represented by the general formula (1) has (1) a high refractive index in the wavelength range of 450 nm to 750 nm, (2) a low extinction coefficient, (3) can be vapor-deposited, (4) is stable in a thin film state, and (5) has high heat resistance. Therefore, by providing the compound as a capping layer on the outer side of a transparent or semi-transparent electrode of an organic EL element, the light extraction efficiency can be significantly improved.

[0043] FIG. 1 shows the structures of compounds (1-1) to (1-12) as exemplary compounds of the present invention. FIG. 2 shows the structures of compounds (1-13) to (1-24) as exemplary compounds of the present invention. FIG. 3 shows the structures of compounds (1-25) to (1-36) as exemplary compounds of the present invention. FIG. 4 shows the structures of compounds (1-37) to (1-48) as exemplary compounds of the present invention. FIG. 5 shows the structures of compounds (1-49) to (1-60) as exemplary compounds of the present invention. FIG. 6 shows the structures of compounds (1-61) to (1-72) as exemplary compounds of the present invention. FIG. 7 shows the structures of compounds (1-73) to (1-84) as exemplary compounds of the present invention. FIG. 8 shows the structures of compounds (1-85) to (1-96) as exemplary compounds of the present invention. FIG. 9 shows the structures of compounds (1-97) to (1-108) as exemplary compounds of the present invention. FIG. 10 shows the structures of compounds (1-109) to (1-120) as exemplary compounds of the present invention. FIG. 11 shows the structures of compounds (1-121) to (1-132) as exemplary compounds of the present invention. FIG. 1 is a diagram showing the structures of compounds (1-133) to (1-144) as examples of compounds of the present invention. FIG. 2 is a diagram showing the structures of compounds (1-145) to (1-156) as examples of compounds of the present invention. FIG. 3 is a diagram showing the structures of compounds (1-157) to (1-168) as examples of compounds of the present invention. FIG. 4 is a diagram showing the structures of compounds (1-169) to (1-180) as examples of compounds of the present invention. FIG. 5 is a diagram showing the structures of compounds (1-181) to (1-189) as examples of compounds of the present invention. FIG. 6 is a diagram showing the structures of compounds (1-190) to (1-197) as examples of compounds of the present invention. FIG. 7 is a diagram showing an example of the configuration of an organic EL element of the present invention.

[0044] The pyrimidine compound represented by the general formula (1) is a novel compound, and can be synthesized, for example, by a known coupling reaction using a palladium catalyst or the like (see, for example, Non-Patent Document 4).

[0045] Among the pyrimidine compounds represented by the general formula (1), specific examples of preferred compounds are shown in FIGS. 1 to 17, but the compounds are not limited to these.

[0046] The purification of the compound represented by the general formula (1) is not particularly limited, and can be performed by known methods used for purifying organic compounds, such as purification by column chromatography, adsorption purification using silica gel, activated carbon, activated clay, etc., recrystallization purification using a solvent, crystallization purification, and sublimation purification, and the compound can be identified by NMR analysis. It is preferable to measure the melting point, glass transition point (Tg), refractive index, and extinction coefficient as physical property values. The melting point is an index of vapor deposition property, the glass transition point (Tg) is an index of stability of the thin film state, and the refractive index and extinction coefficient are indexes for improving light extraction efficiency.

[0047] The melting point and glass transition point (Tg) can be measured using a powder with a high-sensitivity differential scanning calorimeter (DSC3100SA, manufactured by Bruker AXS).

[0048] The refractive index and extinction coefficient can be measured by forming an 80 nm thin film on a silicon substrate and using a spectrophotometer (F10-RT-UV, manufactured by Filmetrics).

[0049] The structure of the organic EL element may be, for example, a top-emission light-emitting element, which is composed of an anode, a hole transport layer, an emitting layer, an electron transport layer, a cathode, and a capping layer, which are arranged in this order on a glass substrate. Other examples include an organic EL element having a hole injection layer between the anode and the hole transport layer, an electron blocking layer between the hole transport layer and the emitting layer, a hole blocking layer between the emitting layer and the electron transport layer, and an electron injection layer between the electron transport layer and the cathode. In these multilayer structures, one organic layer can serve multiple roles, such as a hole injection layer and a hole transport layer, a hole transport layer and an electron blocking layer, a hole blocking layer and an electron transport layer, or an electron transport layer and an electron injection layer. It is also possible to use a structure in which two or more organic layers having the same function are stacked, such as a structure in which two hole transport layers are stacked, a structure in which two light-emitting layers are stacked, a structure in which two electron transport layers are stacked, or a structure in which two capping layers are stacked.

[0050] The total thickness of the layers of the organic EL element is preferably 200 nm to 750 nm, more preferably 350 nm to 600 nm. The thickness of the capping layer is preferably, for example, 30 nm to 120 nm, more preferably 40 nm to 80 nm. In this case, good light extraction efficiency can be obtained. The thickness of the capping layer can be appropriately changed depending on the type of light-emitting material used in the light-emitting element, the thickness of the organic EL element other than the capping layer, and the like.

[0051] For the anode of an organic EL element, an electrode material with a large work function, such as ITO or gold, is used.

[0052] Materials that can be used as hole injection layers for organic EL devices include arylamine compounds having a structure in which three or more triphenylamine structures are linked in a molecule by a single bond or a divalent group not containing a heteroatom, such as starburst triphenylamine derivatives, various triphenylamine tetramers, porphyrin compounds such as copper phthalocyanine, acceptor heterocyclic compounds such as hexacyanoazatriphenylene, and coating-type polymer materials. These materials can be formed into films alone or mixed with other materials to form a single layer, or they can be laminated with other layers formed alone, mixed with other layers, or mixed with other layers formed alone. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0053] Materials that can be used for the hole transport layer of organic EL devices include benzidine derivatives such as N,N'-diphenyl-N,N'-di(m-tolyl)benzidine (hereinafter abbreviated as TPD), N,N'-diphenyl-N,N'-di(α-naphthyl)benzidine, and N,N,N',N'-tetrabiphenylylbenzidine, as well as 1,1-bis[4-(di-4-tolylamino)phenyl]cyclohexane. In particular, it is preferable to use an arylamine compound having two triphenylamine structures linked in the molecule by a single bond or a divalent group not containing a heteroatom, such as N,N,N',N'-tetrabiphenylylbenzidine. It is also preferable to use an arylamine compound having three or more triphenylamine structures linked in the molecule by a single bond or a divalent group not containing a heteroatom, such as various triphenylamine trimers and tetramers. These materials may be formed as a film alone, or may be mixed with other materials to form a single layer, or may be laminated with layers formed alone, layers formed as a mixture, or layers formed as a mixture with layers formed alone. Furthermore, a coating-type polymer material such as poly(3,4-ethylenedioxythiophene) / poly(styrene sulfonate) can be used as the hole injection / transport layer. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0054] Furthermore, as materials for the hole injection layer and the hole transport layer, materials that are typically used for the layers can be doped with P dopants such as trisbromophenylaminehexachloroantimony and radialene derivatives (see, for example, Patent Document 3), as well as polymer compounds having a structure of a benzidine derivative such as TPD in their partial structure.

[0055] It is also possible to laminate an electron-blocking layer on the organic EL device. Examples of materials that can be used for the electron-blocking layer include carbazole derivatives such as 4,4',4''-tri(N-carbazolyl)triphenylamine (hereinafter abbreviated as TCTA), 9,9-bis[4-(carbazol-9-yl)phenyl]fluorene, 1,3-bis(carbazol-9-yl)benzene (hereinafter abbreviated as mCP), and 2,2-bis(4-carbazol-9-ylphenyl)adamantane, and compounds having a triphenylsilyl group and a triarylamine structure, such as 9-[4-(carbazol-9-yl)phenyl]-9-[4-(triphenylsilyl)phenyl]-9H-fluorene, which have an electron-blocking effect. These materials may be formed into a film by themselves, or may be mixed with other materials to form a single layer, or may be laminated with other layers formed by mixing them, or with other layers formed by mixing them, or with other layers formed by mixing them. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0056] Alq is used as a material for the light-emitting layer of an organic EL element. ３Examples of materials that can be used include metal complexes of quinolinol derivatives such as quinolinol derivatives, various metal complexes, anthracene derivatives, bisstyrylbenzene derivatives, pyrene derivatives, oxazole derivatives, and polyparaphenylenevinylene derivatives. The light-emitting layer may also be composed of a host material and a dopant material. Anthracene derivatives are preferred as host materials, but other examples include the above-mentioned light-emitting materials, heterocyclic compounds having an indole ring as a fused ring substructure, heterocyclic compounds having a carbazole ring as a fused ring substructure, carbazole derivatives, thiazole derivatives, benzimidazole derivatives, and polydialkylfluorene derivatives. Examples of dopant materials that can be used include quinacridone, coumarin, rubrene, perylene, and derivatives thereof, benzopyran derivatives, rhodamine derivatives, and aminostyryl derivatives, with green light-emitting materials being particularly preferred. These may be formed alone, or may be mixed with other materials to form a single layer, or may be stacked with other layers formed alone, other layers formed as a mixture, or a layer formed alone and a layer formed as a mixture.

[0057] It is also possible to use a phosphorescent emitter as the light-emitting material. As the phosphorescent emitter, a phosphorescent emitter of a metal complex such as iridium or platinum can be used. For example, Ir(ppy) ３ green phosphorescent emitters such as FIrpic and FIr6; blue phosphorescent emitters such as Btp ２ A red phosphorescent emitter such as Ir(acac) can be used, and a green phosphorescent emitter is particularly preferred. As the host material, a hole-injecting / transporting host material such as 4,4'-di(N-carbazolyl)biphenyl, TCTA, or mCP can be used, and as an electron-transporting host material such as p-bis(triphenylsilyl)benzene or 2,2',2"-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole) can be used.

[0058] The phosphorescent light-emitting material is preferably doped into the host material by co-evaporation in a range of 1 to 30 weight percent based on the total weight of the light-emitting layer in order to avoid concentration quenching.

[0059] Furthermore, materials that emit delayed fluorescence, such as CDCB derivatives such as PIC-TRZ, CC2TA, PXZ-TRZ, and 4CzIPN, can also be used as light-emitting materials (see, for example, Non-Patent Document 5). These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and ink-jet printing.

[0060] It is also possible to laminate a hole-blocking layer on an organic EL device. Examples of materials that can be used for the hole-blocking layer include phenanthroline derivatives such as bathocuproine, metal complexes of quinolinol derivatives such as aluminum(III) bis(2-methyl-8-quinolinato)-4-phenylphenolate (hereinafter abbreviated as BAlq), various rare earth complexes, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, and benzoazole derivatives, all of which have hole-blocking properties. These materials can also be used as materials for the electron-transporting layer. These materials can be formed into films alone or mixed with other materials to form a single layer. They can also be used as a laminate structure consisting of layers formed alone, layers formed in a mixture, or layers formed in a mixture with other layers. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0061] Alq is used as an electron transport layer for an organic EL device. ３Metal complexes of quinolinol derivatives such as BAlq, various metal complexes, triazole derivatives, triazine derivatives, pyrimidine derivatives, oxadiazole derivatives, pyridine derivatives, benzimidazole derivatives, benzoazole derivatives, thiadiazole derivatives, anthracene derivatives, carbodiimide derivatives, quinoxaline derivatives, pyridoindole derivatives, phenanthroline derivatives, and silole derivatives can be used. These materials can be formed into films alone, or they can be mixed with other materials to form a single layer, or they can be laminated with other layers formed alone, other layers formed as a mixture, or layers formed as a mixture with other layers formed alone. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0062] The electron injection layer of an organic EL device can be made of alkali metal salts such as lithium fluoride and cesium fluoride, alkaline earth metal salts such as magnesium fluoride, metal complexes of quinolinol derivatives such as lithium quinolinol, metal oxides such as aluminum oxide, and metals such as ytterbium (Yb), samarium (Sm), calcium (Ca), strontium (Sr), and cesium (Cs). The electron injection layer can be omitted by selecting the electron transport layer and the cathode appropriately.

[0063] Furthermore, as the material for the electron injection layer and the electron transport layer, materials that are normally used for the layers and are doped with N-type metals such as cesium can be used.

[0064] Materials used for the cathode of an organic EL element include metals with low work functions such as aluminum, alloys with even lower work functions such as magnesium-silver alloys, magnesium-calcium alloys, magnesium-indium alloys and aluminum-magnesium alloys, as well as ITO and IZO.

[0065] It is preferable to use the pyrimidine compound represented by the general formula (1) as the capping layer of an organic EL device. These compounds may be formed into a film alone, or may be mixed with other materials to form a single layer, or may be laminated with other layers formed alone, other layers formed as a mixture, or a layer formed as a mixture with other layers formed alone. These materials can be formed into thin films by known methods such as vapor deposition, spin coating, and inkjet printing.

[0066] The pyrimidine compound represented by the general formula (1) preferably has a refractive index of 1.70 or more, particularly preferably 1.85 or more, in the wavelength range of 450 nm to 700 nm.

[0067] Although the organic EL element having a top emission structure has been described above, the present invention is not limited to this and can be similarly applied to an organic EL element having a bottom emission structure or an organic EL element having a dual emission structure that emits light from both the top and bottom. In these cases, it is preferable that the electrode in the direction in which light is extracted from the light-emitting element to the outside be transparent or semi-transparent.

[0068] Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0069] Example 1 Synthesis of 4-(biphenyl-4-yl)-2,6-di{4-(benzoxazol-2-yl)phenyl}-pyrimidine (compound (1-73)) A reaction vessel was charged with 5.0 g of 4-(biphenyl-4-yl)-2,6-dichloropyrimidine, 11.7 g of 2-{4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl}-benzoxazole, 0.4 g of tetrakis(triphenylphosphine)palladium(0), and 5.1 g of potassium carbonate, and the mixture was diluted with toluene / EtOH / H ２The mixture was refluxed and stirred overnight in a 2,000 ml mixed solvent. After allowing to cool, MeOH was added, and the precipitated solid was filtered to obtain a crude product. The obtained crude product was purified by crystallization using a monochlorobenzene / acetone mixed solvent to obtain 8.1 g (yield: 78.9%) of a white powder of 4-(biphenyl-4-yl)-2,6-di{4-(benzoxazol-2-yl)phenyl}-pyrimidine (compound (1-73)).

[0070]

[0071] The structure of the resulting white powder was identified using NMR. １ H-NMR (DMSO-d ６ ), the following 26 hydrogen signals were detected, and the compound was identified as compound (1-73): δ (ppm) = 8.92 (2H), 8.81-8.79 (3H), 8.67 (2H), 8.45 (4H), 7.96 (2H), 7.90-7.82 (6H), 7.56-7.43 (7H).

[0072] Example 2 Synthesis of 2,4,6-tri{4-(benzoxazol-2-yl)phenyl}-pyrimidine (compound (1-92)) A reaction vessel was charged with 4.3 g of 2,4,6-trichloropyrimidine, 25.0 g of 2-{4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl}-benzoxazole, 0.8 g of tetrakis(triphenylphosphine)palladium(0), and 11.4 g of potassium carbonate. ２ The mixture was refluxed and stirred overnight in a 0.2% O mixed solvent. After allowing to cool, the precipitated solid was filtered to obtain a crude product. The obtained crude product was purified by recrystallization using dichlorobenzene to obtain 7.3 g (yield: 47.1%) of a white powder of 2,4,6-tri{4-(benzoxazol-2-yl)phenyl}-pyrimidine (compound (1-92)).

[0073]

[0074] The structure of the resulting white powder was identified using NMR. １ H-NMR (DMSO-d ６), the following 25 hydrogen signals were detected, and the compound was identified as (1-92): δ (ppm) = 8.89 (2H), 8.82 (1H), 8.79 (4H), 8.42 (6H), 7.86-7.81 (6H), 7.51-7.40 (6H).

[0075] Example 3 Synthesis of 4-(biphenyl-4-yl)-2,6-di{4-(benzothiazol-2-yl)phenyl}-pyrimidine (compound (1-145))) A reaction vessel was charged with 5.0 g of 4-(biphenyl-4-yl)-2,6-dichloropyrimidine, 12.3 g of 2-{4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl}-benzothiazole, 0.4 g of tetrakis(triphenylphosphine)palladium(0), and 5.1 g of potassium carbonate, and the mixture was diluted with toluene / EtOH / H ２ The mixture was refluxed and stirred overnight in a 0 mixed solvent. After allowing to cool, MeOH was added, and the precipitated solid was filtered to obtain a crude product. The obtained crude product was purified by crystallization using a monochlorobenzene / acetone mixed solvent to obtain 10.3 g (yield: 95.1%) of a white powder of 4-(biphenyl-4-yl)-2,6-di{4-(benzothiazol-2-yl)phenyl}-pyrimidine (compound (1-145)).

[0076]

[0077] The structure of the resulting white powder was identified using NMR. １ H-NMR (DMSO-d ６ ), the following 26 hydrogen signals were detected, and the compound was identified as (1-145). δ (ppm) = 8.87 (2H), 8.76-8.74 (3H), 8.66 (2H), 8.35 (4H), 8.21 (2H), 8.15 (2H), 7.96 (2H), 7.83 (2H), 7.61 (2H), 7.56-7.50 (4H), 7.45 (1H).

[0078] Example 4 Synthesis of 2,4,6-tri{4-(benzothiazol-2-yl)phenyl}-pyrimidine (compound (1-163)) A reaction vessel was charged with 2.0 g of 2,4,6-trichloropyrimidine, 11.4 g of 2-{4-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl}-benzothiazole, 0.4 g of tetrakis(triphenylphosphine)palladium(0), and 6.0 g of potassium carbonate. ２ The mixture was refluxed and stirred overnight in a 2,4,6-tri{4-(benzothiazol-2-yl)phenyl}-pyrimidine (compound (1-163)) mixed solvent. After allowing to cool, MeOH was added, and the precipitated solid was filtered to obtain a crude product. The obtained crude product was purified by recrystallization using dichlorobenzene to obtain 6.7 g (yield: 86.8%) of a white powder of 2,4,6-tri{4-(benzothiazol-2-yl)phenyl}-pyrimidine (compound (1-163)).

[0079]

[0080] The structure of the resulting white powder was identified using NMR. １ H-NMR (DMSO-d ６ ), the following 25 hydrogen signals were detected, and the compound was identified as (1-163): δ (ppm) = 8.90 (2H), 8.84 (1H), 8.78 (4H), 8.38 (6H), 8.22 (3H), 8.16 (3H), 7.64-7.60 (3H), 7.55-7.51 (3H).

[0081] [Example 5] The melting point and glass transition point (Tg) of the compounds obtained in the above examples were measured using a high-sensitivity differential scanning calorimeter (DSC3100SA, manufactured by Bruker AXS). The measurement results are shown in Table 1.

[0082]

[0083] From the above results, it can be seen that the compounds obtained in the examples have high melting points and either no glass transition point or a glass transition point of 100° C. or higher, which indicates that the thin film state is stable.

[0084] Example 6 Using the compound obtained in the above example, a vapor-deposited film having a thickness of 80 nm was formed on a silicon substrate, and the refractive index n and extinction coefficient k at wavelengths of 450 nm and 750 nm were measured using a spectrophotometer (F10-RT-UV, manufactured by Filmetrics). ３ The measurement was also carried out for a comparative compound (2-1) of the following structural formula (see, for example, Patent Document 4). The measurement results are summarized in Table 2.

[0085]

[0086]

[0087] As shown in Table 2, the compound of the present invention exhibits a saturation of Alq at wavelengths between 450 nm and 750 nm. ３ and refractive indexes equal to or greater than those of the comparative compound (2-1). By using the compound of the present invention as a constituent material of the capping layer, it is expected that the light extraction efficiency of an organic EL device will be improved.

[0088] Example 7 As shown in FIG. 18 , a reflective ITO electrode was previously formed as a metal anode 2 on a glass substrate 1, and a hole injection layer 3, a hole transport layer 4, a light-emitting layer 5, an electron transport layer 6, an electron injection layer 7, a cathode 8, and a capping layer 9 were deposited in this order on the substrate to prepare an organic EL device.

[0089] Specifically, a glass substrate 1 on which a 50 nm thick ITO film, a 100 nm thick silver alloy reflective film, and a 5 nm thick ITO film were sequentially formed was subjected to ultrasonic cleaning in isopropyl alcohol for 20 minutes and then dried for 10 minutes on a hot plate heated to 250°C. After that, UV ozone treatment was performed for 2 minutes, and the ITO-coated glass substrate was mounted in a vacuum deposition machine and the pressure was reduced to 0.001 Pa or less. Subsequently, a hole injection layer 3 was formed covering the transparent anode 2 by binary deposition of an electron acceptor (Acceptor-1) of the following structural formula and a compound (3-1) of the following structural formula at a deposition rate ratio of Acceptor-1:Compound (3-1) = 3:97, resulting in a thickness of 10 nm. On this hole injection layer 3, a hole transport layer 4 was formed of a compound (3-1) of the following structural formula to a thickness of 140 nm. On this hole transport layer 4, a light-emitting layer 5 was formed by binary deposition of a compound (3-2) having the following structural formula and a compound (3-3) having the following structural formula at a deposition rate ratio of (3-2):(3-3)=5:95 to a thickness of 20 nm. On this light-emitting layer 5, a compound (3-4) having the following structural formula and a compound (3-5) having the following structural formula were formed by binary deposition of a compound (3-4):(3-5) having the following structural formula at a deposition rate ratio of (3-4):(3-5)=50:50 to a thickness of 30 nm. On this electron transport layer 6, lithium fluoride was formed as an electron injection layer 7 to a thickness of 1 nm. On this electron injection layer 7, a magnesium-silver alloy was formed as a cathode 8 to a thickness of 12 nm. Finally, a capping layer 9 was formed by deposition of the compound (1-73) of Example 1 to a thickness of 60 nm. The characteristics of the produced organic EL devices were measured in the atmosphere at room temperature, and the measurement results of the light-emitting characteristics when a DC voltage was applied are summarized in Table 3.

[0090]

[0091] An organic EL device was fabricated under the same conditions as in Example 7, except that compound (1-92) of Example 2 was used instead of compound (1-73) of Example 1 for capping layer 9. The characteristics of the fabricated organic EL device were measured in the atmosphere at room temperature, and the measurement results of the light-emitting characteristics when a DC voltage was applied are summarized in Table 3.

[0092] An organic EL device was fabricated under the same conditions as in Example 7, except that the compound (1-145) of Example 3 was used as the capping layer 9 instead of the compound (1-73) of Example 1. The characteristics of the fabricated organic EL device were measured in the atmosphere at room temperature, and the measurement results of the light-emitting characteristics when a DC voltage was applied are summarized in Table 3.

[0093] An organic EL device was fabricated under the same conditions as in Example 7, except that the compound (1-163) of Example 4 was used as the capping layer 9 instead of the compound (1-73) of Example 1. The characteristics of the fabricated organic EL device were measured in the atmosphere at room temperature, and the measurement results of the light-emitting characteristics when a DC voltage was applied are summarized in Table 3.

[0094] Comparative Example 1 For comparison, in Example 7, Alq was used as the capping layer 9 instead of the compound (1-73) in Example 1. ３ The organic EL device was fabricated under the same conditions as above, except that the layer was formed to a thickness of 60 nm. The characteristics of the fabricated organic EL device were measured in the atmosphere at room temperature, and the measurement results of the light-emitting characteristics when a DC voltage was applied are summarized in Table 3.

[0095] For comparison, an organic EL device was fabricated under the same conditions as in Example 7, except that compound (2-1) was formed to a thickness of 60 nm as capping layer 9 instead of compound (1-73) in Example 1. The characteristics of the fabricated organic EL device were measured in air at room temperature, and the measurement results of the light-emitting characteristics when a DC voltage was applied are summarized in Table 3.

[0096] The organic EL elements fabricated in the examples and comparative examples were used to measure the element lifespan, and the results are summarized in Table 2. The element lifespan was 10 mA / cm ２ The time required for the initial luminance to decay to 95% of 100% when the device was driven at a constant current of 100% was measured.

[0097]

[0098] As shown in Table 3, the current density was 10 mA / cm ２The driving voltage at this time was almost the same for the devices of Comparative Examples 1 and 2 and the devices of Examples 7 to 10, whereas the devices of Examples showed significant improvements in all of the luminance, luminous efficiency, power efficiency, and device life compared to the devices of Comparative Examples. This indicates that the compound represented by general formula (1) of the present invention is a material that can be suitably used for the capping layer, and that increasing the refractive index of the capping layer can significantly improve the light extraction efficiency of the organic EL device.

[0099] The compound of the present invention has a high refractive index, can significantly improve light extraction efficiency, and is stable in a thin film state, making it an excellent compound suitable for use in organic EL devices. Furthermore, organic EL devices fabricated using the compound of the present invention can achieve high efficiency. Furthermore, the use of the compound of the present invention, which has no absorption in the blue, green, and red wavelength regions, is particularly suitable for displaying clear, bright images with good color purity. For example, the compound can be expected to be used in home appliances and lighting.

[0100] REFERENCE SIGNS LIST 1 Glass substrate 2 Transparent anode 3 Hole injection layer 4 Hole transport layer 5 Light-emitting layer 6 Electron transport layer 7 Electron injection layer 8 Cathode 9 Capping layer

Claims

1. A pyrimidine compound represented by the following general formula (1): 【Chemistry 1】 (In formula (1), Ar １ ~Ar ３ may be the same or different and each represent a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted benzoxazolyl group, or a substituted or unsubstituted benzothiazolyl group, L １ ~L ３ may be the same or different and each represent a single bond, a substituted or unsubstituted divalent aromatic hydrocarbon group, a substituted or unsubstituted divalent aromatic heterocyclic group, or a substituted or unsubstituted divalent fused polycyclic aromatic group; p, q, and r each represent an integer of 1 to 2, which may be the same or different from each other. However, Ar １ ~Ar ３ At least two of the groups are substituted or unsubstituted benzoxazolyl groups or substituted or unsubstituted benzothiazolyl groups.

2. L in the general formula (1) １ ~L ３ may be the same or different and are each a single bond, a divalent group obtained by removing two hydrogen atoms from substituted or unsubstituted benzene, a divalent group obtained by removing two hydrogen atoms from substituted or unsubstituted biphenyl, or a divalent group obtained by removing two hydrogen atoms from substituted or unsubstituted naphthalene.

3. L in the general formula (1) １ ~L ３ may be the same or different and are each a single bond, a divalent group obtained by removing two hydrogen atoms from unsubstituted benzene, a divalent group obtained by removing two hydrogen atoms from unsubstituted biphenyl, or a divalent group obtained by removing two hydrogen atoms from unsubstituted naphthalene.

4. L in the general formula (1) １ ~L ３ may be the same or different and are each a single bond, an unsubstituted 1,4-phenylene group, an unsubstituted 4,4'-biphenylylene group, an unsubstituted 2,6-naphthylene group, or an unsubstituted 2,7-naphthylene group.

5. The pyrimidine compound according to claim 1, wherein p, q, and r in the general formula (1) are 1.

6. Ar in the general formula (1) １ ~Ar ３ 2. The pyrimidine compound according to claim 1, wherein any two of the following are unsubstituted 2-benzoxazolyl groups or unsubstituted 2-benzothiazolyl groups:

7. Ar in the general formula (1) １ ~Ar ３ The pyrimidine compound according to claim 1, wherein is an unsubstituted 2-benzoxazolyl group or an unsubstituted 2-benzothiazolyl group.

8. 2. The pyrimidine compound according to claim 1, which has a refractive index of 1.70 or more in the wavelength range of 450 nm to 750 nm.

9. An organic electroluminescence device having at least an anode electrode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode electrode, and a capping layer in this order, wherein the capping layer contains the pyrimidine compound according to any one of claims 1 to 8.

10. The organic electroluminescence element according to claim 9, wherein the capping layer is a mixed layer containing two or more types of compounds or a laminate consisting of two or more layers each containing a different compound, and at least one of these compounds is the pyrimidine compound according to any one of claims 1 to 8.

11. 9. An electronic device having a pair of electrodes and at least one organic layer sandwiched between them, wherein the organic layer contains the pyrimidine compound according to claim 1.

12. An electronic device using the electronic element according to claim 11.

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