Host material for organic electroluminescent element and organic electroluminescent element in which same is used

Abstract

An organic EL element, in which a host material for an organic electroluminescent element according to the present invention is used, can have a high luminous efficiency.　Specifically disclosed is a host material for an organic electroluminescent element represented by general formula (1), or a mixed host material for an organic electroluminescent element, the mixed host material being composed of two or more organic compounds and being characterized by containing a first compound represented by general formula (1) at a concentration of 5 mass% to 95 mass% inclusive. The ring A and the ring E are each independently represented by general formula (1a) or (1b), and are each condensed at an arbitrary position with an adjacent ring. X1, X2, Y1, and Y2 each independently represent N-Ar1, O, or S. Each Ar1 independently represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, or the like, R1 to R5 each independently represent deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, or the like, a to e each represent a number of substitution, and B represents a boron atom.

Description

Host material for organic electroluminescent device and organic electroluminescent device using the same

[0001] The present invention relates to a host material for an organic electroluminescent device and an organic electroluminescent device using the same.

[0002] When a voltage is applied to an organic EL element, holes are injected from the anode and electrons are injected from the cathode into the light-emitting layer. The injected holes and electrons then recombine in the light-emitting layer, generating excitons. At this time, due to the statistical law of electron spin, singlet excitons and triplet excitons are generated in a ratio of 1:3. It is said that the internal quantum efficiency of fluorescent organic EL elements that use emission from singlet excitons is limited to 25%. On the other hand, it is known that the internal quantum efficiency of phosphorescent organic EL elements that use emission from triplet excitons can be increased to 100% if intersystem crossing from singlet excitons is efficiently performed.

[0003] In recent years, technology for extending the lifetime of phosphorescent organic EL elements has progressed, and they are being applied to displays of mobile phones, etc. However, with regard to blue organic EL elements, practical phosphorescent organic EL elements have not yet been developed, and there is a demand for the development of blue organic EL elements that are highly efficient and have a long lifetime.

[0004] More recently, highly efficient delayed fluorescence organic EL elements utilizing delayed fluorescence have been developed. For example, Patent Document 1 discloses an organic EL element utilizing the TTF (Triple-Triple Fusion) mechanism, which is one of the mechanisms of delayed fluorescence. The TTF mechanism utilizes the phenomenon in which singlet excitons are generated by the collision of two triplet excitons, and is thought to theoretically increase the internal quantum efficiency to 40%. However, since the efficiency is lower than that of phosphorescent organic EL elements, further improvements in efficiency are required.

[0005] On the other hand, Patent Document 2 discloses an organic EL device utilizing the thermally activated delayed fluorescence (TADF) mechanism. The TADF mechanism utilizes the phenomenon of reverse intersystem crossing from triplet excitons to singlet excitons in a material with a small energy difference between the singlet level and the triplet level, and is thought to theoretically increase the internal quantum efficiency to 100%.

[0006] Here, Non-Patent Document 1 discloses a device using a predetermined mixed host (SiTrz2Cz and SiCzCz) in addition to a predetermined phosphorescent dopant, TADF dopant.

[0007] Furthermore, Patent Document 3 discloses a device using a compound containing a boron atom as a light-emitting material.

[0008] Furthermore, Patent Documents 4 and 5 disclose devices that use a compound containing a boron atom as a light-emitting material and a compound in which a plurality of carbazoles are linked together as a host.

[0009] Furthermore, Patent Document 6 discloses the use of a compound containing a boron atom as a host material, but the properties are insufficient.

[0010] WO2010 / 134350 publication WO2011 / 070963 publication WO2015 / 102118 publication WO2022 / 45272 publication WO2021 / 200252 publication JP2023024320 publication

[0011] Kim et al., Sci. Adv. 8, eabq1641 (2022)

[0012] In order to apply organic EL elements to display elements such as flat panel displays and light sources, it is necessary to improve the luminous efficiency of the elements and at the same time ensure sufficient stability during operation. An object of the present invention is to provide a practically useful organic EL element having highly efficient characteristics, and a compound suitable for such an element.

[0013] The present invention provides a host material for organic electroluminescent elements represented by the following general formula (1), or a mixed host material comprising two or more organic compounds, characterized in that the mixed host material for organic electroluminescent elements contains a first compound represented by the following general formula (1) in a concentration of 5 mass % or more and 95 mass % or less: Here, ring A and ring E are each independently represented by the above general formula (1a) or (1b), and are fused to the adjacent ring at any position. １ , X ２ , Y １ , and Y ２ are each independently N-Ar １ , O, or S. X １ , X ２ , Y １ , and Y ２ At least two of these are preferably represented by S. Also, B represents a boron atom.

[0014] Ar １ each independently represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. １ preferably represents a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 or 3 of these aromatic groups. １ , or Y ２ is N-Ar １ and Ar １ is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, １ is the Ar １ may be condensed with an adjacent ring to form a ring.

[0015] R １ ~R ５R each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. １ ~R ５ preferably represents a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two or three of these aromatic groups, and more preferably represents a substituted or unsubstituted triarylsilyl group having 18 to 24 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two or three of these aromatic groups.

[0016] a and d each represent the number of substitutions of 0 to 4, and preferably 0 to 2; b and c each represent the number of substitutions of 0 to 2, and preferably 0 or 1; and e each represent the number of substitutions of 0 to 3, and preferably 0 or 1.

[0017] In addition, some or all of the hydrogen atoms in the compound represented by the general formula (1) may be substituted with deuterium atoms.

[0018] The host material for an organic electroluminescent device represented by the general formula (1) or the first compound is preferably represented by the following general formula (3). Here, X １ , X ２ , Y １ , Y ２ , R １ ~R ５ , a to e have the same meanings as in general formula (1). In addition, some or all of the hydrogen atoms in the compound represented by general formula (3) may be substituted with deuterium atoms.

[0019] The mixed host material for organic electroluminescent devices preferably further contains a second compound represented by the following general formula (2): When the mixed host material for organic electroluminescent devices contains a first and a second compound, it is preferable that the first compound is contained as an electron-transporting host and the second compound is contained as a hole-transporting host. Here, f represents the number of substitutions and is 0 to 3, preferably 0 to 2. g represents the number of substitutions and is 0 to 4, preferably 0 to 3. m represents the number of repetitions and is 2 or 3, preferably 2. n represents the number of substitutions and is 1 or 2.

[0020] Ar ２ represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and aromatic heterocyclic groups. ２ is preferably a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two or three of these aromatic groups, and more preferably a substituted or unsubstituted triarylsilyl group having 18 to 24 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two or three of these aromatic groups.

[0021] R ６ , R ７ R each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. ６ , R ７R preferably represents a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 of these aromatic groups. ６ , R ７ More preferably, represents a substituted or unsubstituted triarylsilyl group having 18 to 24 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 of these aromatic groups.

[0022] However, in the general formula (2), Ar ２ , R ６ , and R ７ In addition, some or all of the hydrogen atoms in the compound represented by the general formula (2) may be substituted with deuterium atoms.

[0023] The mixed host material for organic electroluminescent elements containing the first compound represented by the general formula (1) and the second compound represented by the general formula (2) preferably satisfies the following conditions (i) and (ii), and more preferably further satisfies the following condition (iii): (i) the excited singlet energy S1 of both the first compound represented by the general formula (1) and the second compound represented by the general formula (2) is 3.2 eV or more, (ii) when the concentration of the first compound represented by the general formula (1) is A% by mass and the concentration of the second compound represented by the general formula (2) is B% by mass, the difference between the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for organic electroluminescent elements containing A in a concentration of 5% by mass or more and B in a concentration of 95% by mass or less and the maximum emission wavelength of the fluorescent emission spectrum of a mixture containing A in a concentration of less than 5% by mass and B in a concentration of more than 95% by mass is 40 nm or more. (iii) The maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for an organic electroluminescent device is 455 nm or less.

[0024] The present invention also provides an organic electroluminescent device comprising one or more organic layers between an anode and a cathode facing each other, wherein at least one of the organic layers contains a mixed host material for an organic electroluminescent device comprising a first compound represented by general formula (1) in a concentration of 5% by mass or more and 95% by mass or less.

[0025] The organic layer containing the mixed host material for organic electroluminescent devices is preferably an emitting layer. The emitting layer preferably further contains a thermally activated delayed fluorescent material or a phosphorescent material as a luminescent dopant, and more preferably contains both a thermally activated delayed fluorescent material and a phosphorescent material. Preferably, the thermally activated delayed fluorescent material is contained as the luminescent dopant. The thermally activated delayed fluorescent material is preferably a thermally activated delayed fluorescent material containing a boron atom, and the phosphorescent material is preferably a phosphorescent material containing a platinum atom. However, the thermally activated delayed fluorescent material containing a boron atom is a different compound from the first compound represented by the general formula (1).

[0026] Furthermore, the present invention relates to a premixed host material for organic electroluminescent devices, which comprises a compound represented by the general formula (1) and a compound represented by the general formula (2). Here, the premixed host material refers to a composition in which the compound represented by the general formula (1) and the compound represented by the general formula (2) are mixed in advance for deposition from a single deposition source in the production of an organic electroluminescent device. Therefore, in the premixed host material for organic electroluminescent devices, it is preferred that the difference in 50% weight loss temperature between the first compound represented by the general formula (1) and the second compound represented by the general formula (2) be 20° C. or less.

[0027] The present invention also provides a method for producing an organic electroluminescent element having one or more organic layers between an anode and a cathode facing each other, wherein at least one of the organic layers is an emitting layer, and the emitting layer is produced by depositing the premixed host material for the organic electroluminescent element from a single deposition source.

[0028] The present invention is characterized in that the host material represented by the general formula (1) or the mixed host material composed of two or more kinds of organic compounds contains a first compound represented by the general formula (1), and an organic EL device using the same can be an organic EL device with high luminous efficiency.

[0029] FIG. 1 is a schematic cross-sectional view showing an example of an organic EL element.

[0030] The present invention relates to a host material represented by the general formula (1) or a mixed host material for organic electroluminescent elements, which is a mixed host material of two or more organic compounds, and which contains a first compound represented by the general formula (1). In this mixed host material for organic electroluminescent elements, the concentration of the compound represented by the general formula (1) is preferably 5% by mass or more and 95% by mass or less, more preferably 15% by mass or more and 85% by mass or less, and even more preferably 30% by mass or more and 70% by mass or less.

[0031] The compound represented by the general formula (1) will be described. The compound represented by the general formula (1) is preferably represented by the general formula (3). In addition, some or all of the hydrogen atoms in the compounds represented by the general formulas (1) and (3) may be substituted with deuterium atoms. Preferably, 40% of the total hydrogen atoms contained in the compounds represented by the general formulas (1) and (3) are deuterated, and more preferably 70%.

[0032] Ar １ each independently represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. １is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 of these aromatic groups, more preferably a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 of these aromatic groups. １ , or Y ２ is N-Ar １ and Ar １ is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, １ is the Ar １ may be condensed with an adjacent ring to form a ring.

[0033] R １ ~R ５ each independently represent deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. Preferably, it is a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 12 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 of these aromatic groups, and even more preferably it is a substituted or unsubstituted triarylsilyl group having 18 to 24 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 11 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 of these aromatic groups.

[0034] a and d represent the number of substitutions from 0 to 4, preferably from 0 to 2. b and c represent the number of substitutions from 0 to 2, preferably from 0 to 1. e represents the number of substitutions from 0 to 3, preferably from 0 to 2.

[0035] Ar １ , R １ ~R ５ is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, it may be any of a linear, branched, and cyclic aliphatic hydrocarbon groups, and specific examples thereof include linear saturated hydrocarbon groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, n-dodecyl, n-tetradecyl, and n-octadecyl groups, branched saturated hydrocarbon groups such as isopropyl, isobutyl, tert-butyl, neopentyl, 2-ethylhexyl, and 2-hexyloctyl groups, and saturated alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, cyclooctyl, 4-butylcyclohexyl, and 4-dodecylcyclohexyl groups. Preferred are methyl, ethyl, n-propyl, n-butyl, tert-butyl, neopentyl, and cyclohexyl groups. Preferably, it is a methyl group, an ethyl group, a tert-butyl group, or a cyclohexyl group.

[0036] Ar １ , R １ ~R ５ Specific examples of when is an unsubstituted triarylsilyl group having 18 to 36 carbon atoms include triphenylsilyl, biphenyldiphenylsilyl, bisbiphenylphenylsilyl, and trisbiphenylsilyl. Preferred are triphenylsilyl, biphenyldiphenylsilyl, and bisbiphenylphenylsilyl. More preferred are triphenylsilyl and biphenyldiphenylsilyl.

[0037] Ar １ , R １ ~R ５ Specific examples of when is an unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms include groups formed by removing one hydrogen atom from benzene, naphthalene, acenaphthene, acenaphthylene, anthracene, chrysene, pyrene, phenanthrene, triphenylene, fluorene, benzo[a]anthracene, etc. Preferred examples include groups formed from benzene, naphthalene, anthracene, chrysene, pyrene, phenanthrene, triphenylene, or fluorene. More preferred examples include a phenyl group or a naphthyl group.

[0038] Ar １ , R １ ~R ５ Specific examples of when is an unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms include groups formed by removing one hydrogen atom from nitrogen-containing aromatic compounds having a pyrrole ring such as pyrrole, pyrrolopyrrole, indole, isoindole, pyrroloisoindole, and carboline, as well as from thiophene, benzothiophene, dibenzothiophene, furan, benzofuran, dibenzofuran, carbazole, pyridine, pyrimidine, triazine, quinoline, isoquinoline, quinazoline, or quinoxaline. Preferred are groups formed from thiophene, benzothiophene, dibenzothiophene, furan, benzofuran, dibenzofuran, or carbazole, and more preferred are a dibenzothienyl group, a dibenzofuranyl group, or a carbazolyl group.

[0039] Ar １ , R １ ~R ５ Specific examples of the unsubstituted linking aromatic group include groups formed by removing one hydrogen from a group constituted by linking two or three aromatic groups described above as the specific examples of the unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms and the unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, such as a biphenyl group, a terphenyl group, a phenylcarbazole group, and a dibenzofuranylcarbazole group.

[0040] Next, the compound represented by the general formula (2) will be described. f represents the number of substitutions and is 0 to 3, preferably 0 to 2, g represents the number of substitutions and is 0 to 4, preferably 0 to 3, m represents the number of repetitions and is 2 or 3, preferably 2, and n represents the number of substitutions and is 1 or 2.

[0041] Ar ２represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two to three aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. Preferred are substituted or unsubstituted triarylsilyl groups having 18 to 36 carbon atoms, substituted or unsubstituted aromatic hydrocarbon groups having 6 to 11 carbon atoms, substituted or unsubstituted aromatic heterocyclic groups having 3 to 12 carbon atoms, or substituted or unsubstituted linked aromatic groups formed by linking two to three of these aromatic groups, and more preferred are substituted or unsubstituted triarylsilyl groups having 18 to 24 carbon atoms, substituted or unsubstituted aromatic hydrocarbon groups having 6 to 11 carbon atoms, or substituted or unsubstituted linked aromatic groups formed by linking two to three of these aromatic groups.

[0042] R ６ , R ７ each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking two to three aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. Preferred are substituted or unsubstituted triarylsilyl groups having 18 to 36 carbon atoms, substituted or unsubstituted aromatic hydrocarbon groups having 6 to 11 carbon atoms, substituted or unsubstituted aromatic heterocyclic groups having 3 to 12 carbon atoms, or substituted or unsubstituted linked aromatic groups formed by linking two to three of these aromatic groups, and more preferred are substituted or unsubstituted triarylsilyl groups having 18 to 24 carbon atoms, substituted or unsubstituted aromatic hydrocarbon groups having 6 to 11 carbon atoms, or substituted or unsubstituted linked aromatic groups formed by linking two to three of these aromatic groups.

[0043] However, Ar ２ , R ６ , and R ７ does not contain carbazole.

[0044] Ar ２ , R ６ ~R ７ is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, it may be any of a linear, branched, and cyclic aliphatic hydrocarbon groups, and specific examples thereof include linear saturated hydrocarbon groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, n-dodecyl, n-tetradecyl, and n-octadecyl groups, branched saturated hydrocarbon groups such as isopropyl, isobutyl, tert-butyl, neopentyl, 2-ethylhexyl, and 2-hexyloctyl groups, and saturated alicyclic hydrocarbon groups such as cyclopentyl, cyclohexyl, cyclooctyl, 4-butylcyclohexyl, and 4-dodecylcyclohexyl groups. Preferred are methyl, ethyl, n-propyl, n-butyl, tert-butyl, neopentyl, and cyclohexyl groups. More preferred are a methyl group, an ethyl group, a tert-butyl group, and a cyclohexyl group.

[0045] Ar ２ , R ６ ~R ７ Specific examples of when is an unsubstituted triarylsilyl group having 18 to 36 carbon atoms include triphenylsilyl, biphenyldiphenylsilyl, bisbiphenylphenylsilyl, and trisbiphenylsilyl. Triphenylsilyl, biphenyldiphenylsilyl, and bisbiphenylphenylsilyl are preferred, and triphenylsilyl and biphenyldiphenylsilyl are more preferred.

[0046] Ar ２ , R ６ ~R ７Specific examples of when is an unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms include groups formed by removing one hydrogen atom from benzene, naphthalene, acenaphthene, acenaphthylene, anthracene, chrysene, pyrene, phenanthrene, triphenylene, fluorene, benzo[a]anthracene, etc. Preferred examples include groups formed from benzene, naphthalene, anthracene, chrysene, pyrene, phenanthrene, triphenylene, or fluorene. More preferred examples include a phenyl group or a naphthyl group.

[0047] Ar ２ , R ６ ~R ７ Specific examples of when is an unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms include groups formed by removing one hydrogen atom from nitrogen-containing aromatic compounds having a pyrrole ring such as pyrrole, pyrrolopyrrole, indole, isoindole, pyrroloisoindole, and carboline, as well as from thiophene, benzothiophene, dibenzothiophene, furan, benzofuran, dibenzofuran, pyridine, pyrimidine, triazine, quinoline, isoquinoline, quinazoline, or quinoxaline. Preferred are groups formed from thiophene, benzothiophene, dibenzothiophene, furan, benzofuran, or dibenzofuran, and more preferred are a dibenzothienyl group or a dibenzofuranyl group.

[0048] Ar ２ , R ６ ~R ７ Specific examples of the unsubstituted linking aromatic group include those formed by linking 2 or 3 aromatic groups described above as specific examples of the unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms and the unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, ２ In the case of R ６ ~R ７ In the case of the formula: the group resulting from removing one hydrogen atom can be mentioned.

[0049] A part or all of the hydrogen atoms in the compound represented by the general formula (2) may be substituted with deuterium atoms. Preferably, 40% of the total hydrogen atoms contained in the compound represented by the general formula (2) are deuterated, and more preferably, 70% of the total hydrogen atoms are deuterated.

[0050] In this specification, the term "linked aromatic group" refers to a group in which aromatic rings of aromatic hydrocarbon groups or aromatic heterocyclic groups are linked by a single bond, and these may be linked in a linear or branched chain. The linked aromatic rings may be the same or different. When a group corresponds to a linked aromatic group, it is different from an aromatic hydrocarbon group having a substituent or an aromatic heterocyclic group having a substituent.

[0051] In the general formulas (1) to (3), Ar １ ~Ar ２ , R １ ~R ７ When Ar is an aromatic hydrocarbon group, an aromatic heterocyclic group, or a linking aromatic group, it may have a substituent, and the substituent is preferably deuterium, a triarylsilyl group having 18 to 36 carbon atoms, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a diarylamino group having 12 to 44 carbon atoms. When the substituent is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, it may be linear, branched, or cyclic. The number of substituents is 0 to 5, preferably 0 to 2. When the aromatic hydrocarbon group or aromatic heterocyclic group has a substituent, the number of carbon atoms in the substituent is not included in the calculation of the carbon number. However, it is preferable that the total number of carbon atoms, including the carbon atoms in the substituent, satisfies the above range. In addition, Ar １ ~Ar ２ , R １ ~R ７ When is a triarylsilyl group, the aryl group may have a substituent, and the substituent is preferably a deuterium atom, a methyl group, or a tert-butyl group.

[0052] Specific examples of the substituent include a methyl group, an ethyl group, a propyl group, an i-propyl group, a butyl group, a t-butyl group, a pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, a diphenylamino group, a naphthylphenylamino group, a dinaphthylamino group, a dianthranylamino group, a diphenanthrenylamino group, a dipyrenylamino group, and a triphenylsilyl group. Preferred examples include a methyl group, an ethyl group, a propyl group, a butyl group, a pentyl group, a hexyl group, a heptyl group, an octyl group, a diphenylamino group, a naphthylphenylamino group, a dinaphthylamino group, and a triphenylsilyl group.

[0053] Specific examples of the compound represented by the general formula (1) are shown below, but the compound is not limited to these exemplary compounds.

[0054] Specific examples of the compound represented by the general formula (2) are shown below, but the compound is not limited to these exemplary compounds.

[0055] The mixed host material for organic electroluminescent elements, which contains a first compound represented by the general formula (1) and a second compound represented by the general formula (2), preferably satisfies the following conditions (i) and (ii), and more preferably further satisfies the following condition (iii): (i) the excited singlet energy S1 of both the first compound represented by the general formula (1) and the second compound represented by the general formula (2) is 3.2 eV or more; (ii) when the concentration of the first compound represented by the general formula (1) is A% by mass and the concentration of the second compound represented by the general formula (2) is B% by mass, the difference between the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for organic electroluminescent elements, which contains A in a concentration of 5% by mass or more and B in a concentration of 95% by mass or less, and the maximum emission wavelength of the fluorescent emission spectrum of a mixture, which contains A in a concentration of less than 5% by mass and B in a concentration of more than 95% by mass, is 40 nm or more; and (iii) the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for organic electroluminescent elements is 455 nm or less. Here, the host material in the emitting layer plays the role of (a) efficiently transferring excitation energy generated in the host material to the emitting material, and conversely, (b) suppressing reverse energy transfer from the emitting material to the host material, and (c) suppressing the transfer of excitation energy of the emitting material to other emitting materials or materials in the surrounding layers, thereby promoting efficient light emission from the emitting material. In other words, a host material for an organic EL device is required to have the properties described above in (a) to (c). The relationship between these properties required of a host material and the above conditions (i) to (iii) is explained below.

[0056] First, the above condition (i) relates to the above characteristic (b) required of the host material, namely, suppression of reverse energy transfer from the light-emitting material to the host material. In order to suppress reverse energy transfer from the light-emitting material to the host material, the S1 of the host material must be sufficiently high relative to that of the light-emitting material. In particular, among light-emitting materials, light-emitting materials that emit blue light with a high S1 have an S1 of 2.8 to 3.0 eV. Therefore, it is preferable that the excited singlet energy S1 of both the first compound represented by the general formula (1) and the second compound represented by the general formula (2) is 3.2 eV or higher. It is more preferable that it is 3.3 eV or higher.

[0057] The method for measuring the excited singlet energy S1 and the excited triplet energy T1 is as follows. First, a quartz substrate was vacuum-deposited at a vacuum level of 10 －４ A sample compound is evaporated under conditions of 0.1 Pa or less to form an evaporated film with a thickness of 100 nm. S1 is calculated by measuring the emission spectrum of this evaporated film, drawing a tangent to the rising edge on the short wavelength side of the emission spectrum, and substituting the wavelength value λedge [nm] at the intersection of this tangent and the horizontal axis into the following equation (4): S1 [eV] = 1239.85 / λedge (4)

[0058] On the other hand, T1 is calculated by measuring the phosphorescence spectrum of the vapor-deposited film, drawing a tangent to the rising edge on the short wavelength side of this phosphorescence spectrum, and substituting the wavelength value λedge [nm] at the intersection of this tangent and the horizontal axis into the following formula (5): T1 [eV] = 1239.85 / λedge (5), where ΔEST represents the absolute value of the difference between S1 and T1 calculated above.

[0059] Next, the condition (ii) relates to the above-mentioned characteristic (a) required of the host material, that is, efficient transfer of excitation energy generated in the host material to the light-emitting material. As described above, efficient transfer of excitation energy generated in the host material to the light-emitting material in the light-emitting layer can promote efficient light emission from the light-emitting material. At this time, since the transfer of excitation energy from the S1 of the host material is caused by Förster energy transfer, the greater the overlap between the wavelength ranges of the emission spectrum of the host material and the absorption spectrum of the light-emitting material, the higher the energy transfer efficiency. In other words, from the perspective of energy transfer from the host material to the light-emitting material, it is preferable that the S1 energy of the host material and the S1 energy of the light-emitting material are at approximately the same level. On the other hand, as described in the above condition (i), in order to prevent reverse energy transfer from the light-emitting material to the host material, the S1 of the host material needs to be higher to a certain extent than that of the light-emitting material. In other words, to efficiently transfer excitation energy generated in the host material to the light-emitting material, it is preferable that the S1 energy of the host material and the S1 energy of the light-emitting material are approximately equal. However, conversely, to suppress reverse energy transfer from the light-emitting material to the host material, the S1 energy of the host material must be higher than that of the light-emitting material to a certain extent. These contradictory conditions are required for the host material. To satisfy these contradictory conditions, it is preferable to use an exciplex formed by a mixed host material consisting of two or more organic compounds. An exciplex forms an excited state with two molecules, resulting in a more stable (lower) excitation energy than the excitation energies of the individual molecules. On the other hand, since an exciplex disappears upon energy transfer, it cannot receive energy from the light-emitting material (reverse energy transfer does not occur). Therefore, by using a mixed host material that forms an exciplex while satisfying condition (i) (S1 energy somewhat higher than that of the light-emitting material), it is possible to achieve a level of S1 energy approximately equal to that of the light-emitting material. This allows for the host material to (a) efficiently transfer excitation energy generated in the host material to the light-emitting material and (b) suppress reverse energy transfer from the light-emitting material to the host material, as required.The combination of host materials and their mixing ratios are important factors in forming this exciplex. In the present invention, it has been discovered that a mixed host material containing 5% by mass or more of a first compound represented by general formula (1) and 95% by mass or less of a second compound represented by general formula (2) satisfies condition (i) (the S1 energy is somewhat higher than that of the light-emitting material), and when used as a mixed host material, the above exciplex is formed between the first compound and the second compound, stabilizing (lowering) the excitation energy and shifting the emission spectrum of the exciplex to a longer wavelength, thereby enabling the emission spectrum to have a wavelength range comparable to that of the absorption spectrum of the light-emitting material. Note that if the mixing ratio of the mixed host material does not satisfy the above (a mixture containing less than 5% by mass of the first compound and more than 95% by mass of the second compound), the exciplex is not formed, and the excitation energy is not stabilized, i.e., the emission spectrum does not shift to a longer wavelength. Specifically, from the results of Example 3 and Comparative Example 1 of the present invention, it was found that by setting the mixing ratio of the mixed host material for organic electroluminescent elements to 5% by mass or more of the first compound and 95% by mass or less of the second compound, the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material is extended by 40 nm or more compared to an organic mixed host material that does not satisfy this ratio (a mixture containing less than 5% by mass of the first compound and more than 95% by mass of the second compound), thereby enabling the emission spectrum to be in a wavelength range similar to that of the absorption spectrum of the light-emitting material. Based on the above, when the concentration of the first compound represented by the general formula (1) is A% by mass and the concentration of the second compound represented by the general formula (2) is B% by mass, the difference between the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for organic electroluminescent elements of the present invention, which contains A at a concentration of 5% by mass or more and B at a concentration of 95% by mass or less, and the maximum emission wavelength of the fluorescent emission spectrum of the mixture, which contains A at a concentration of less than 5% by mass and B at a concentration of more than 95% by mass, is preferably 40 nm or more, more preferably 50 nm or more.

[0060] Regarding condition (iii), it is preferable that the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for an organic electroluminescent device that satisfies condition (ii) be 455 nm or less. This is because the absorption spectrum of the light-emitting material that emits blue light has a maximum absorption peak at 455 nm or less, which further promotes energy transfer from the mixed host to the light-emitting material, and is expected to improve light-emitting efficiency. It is preferable to satisfy at least two of conditions (i) to (iii), and it is even better to satisfy all three. This is because satisfying multiple conditions simultaneously can synergistically promote light emission from the light-emitting material more than satisfying each condition alone.

[0061] When a thermally activated delayed fluorescent dopant is used as the luminescent dopant material, the thermally activated delayed fluorescent dopant is not particularly limited, and examples thereof include those containing boron atoms, metal complexes such as tin complexes and copper complexes, cyanobenzene derivatives and carbazole derivatives described in Nature 2012,492,234, phenazine derivatives, oxadiazole derivatives, triazole derivatives, sulfone derivatives, phenoxazine derivatives, and acridine derivatives described in Nature Photonics 2014,8,326, and polycyclic aromatic compounds described in WO2015 / 102118, etc. Among these, the thermally activated delayed fluorescent material is preferably a thermally activated delayed fluorescent material containing a boron atom.

[0062] The boron-containing polycyclic aromatic compound used as a light-emitting dopant in the organic EL device of the present invention preferably has a ΔEST, which is the difference between the excited singlet energy (S1) and the excited triplet energy (T1), of 0.20 eV or less, more preferably 0.15 eV or less, and even more preferably 0.10 eV or less. In this case, ΔEST (|S1-T1|) is a value calculated by measuring the emission spectrum for S1 and the phosphorescence spectrum for T1, and can be measured in the same manner as described above.

[0063] Next, the structure of the organic EL element of the present invention will be described with reference to the drawings, but the structure of the organic EL element of the present invention is not limited to this.

[0064] FIG. 1 is a cross-sectional view showing an example of the structure of a typical organic EL device used in the present invention, where 1 represents a substrate, 2 represents an anode, 3 represents a hole injection layer, 4 represents a hole transport layer, 5 represents an emitting layer, 6 represents an electron transport layer, and 7 represents a cathode. The organic EL device of the present invention may have an exciton blocking layer adjacent to the emitting layer, or an electron blocking layer between the emitting layer and the hole injection layer. The exciton blocking layer can be inserted on either the anode side or the cathode side of the emitting layer, or both simultaneously. The organic EL device of the present invention has an anode, an emitting layer, and a cathode as essential layers, but may also have a hole injection transport layer and an electron injection transport layer in addition to the essential layers, and may further have a hole blocking layer between the emitting layer and the electron injection transport layer. Note that the hole injection transport layer refers to either the hole injection layer or the hole transport layer, or both, and the electron injection transport layer refers to either the electron injection layer or the electron transport layer, or both.

[0065] It is also possible to have a structure opposite to that shown in FIG. 1 , that is, to stack the cathode 7, electron transport layer 6, light-emitting layer 5, hole transport layer 4, hole injection layer 3, and anode 2 on the substrate 1 in this order, and in this case too, layers can be added or omitted as necessary.

[0066] The organic EL device of the present invention is preferably supported on a substrate. There are no particular limitations on the substrate, and any substrate conventionally used in organic EL devices, such as glass, transparent plastic, or quartz, can be used.

[0067] Anode materials for organic EL devices are preferably metals, alloys, electrically conductive compounds, or mixtures thereof, each having a large work function (4 eV or more). Specific examples of such electrode materials include metals such as Au, CuI, indium tin oxide (ITO), and SnO. ２ ZnO and other conductive transparent materials. ２ O ３Alternatively, amorphous materials capable of forming a transparent conductive film, such as ZnO, may be used. The anode may be formed by forming a thin film of these electrode materials by methods such as vapor deposition or sputtering, followed by forming a pattern of the desired shape using photolithography. Alternatively, if pattern precision is not required (approximately 100 μm or more), a pattern may be formed using a mask of the desired shape during vapor deposition or sputtering of the electrode material. Alternatively, when a coatable material such as an organic conductive compound is used, wet film formation methods such as printing and coating can also be used. When light is extracted from this anode, it is desirable for the transmittance to be greater than 10%, and the sheet resistance of the anode as a whole to be several hundred Ω / □ or less. The film thickness, although depending on the material, is typically selected in the range of 10 to 1,000 nm, preferably 10 to 200 nm.

[0068] - Cathode - On the other hand, as the cathode material, a metal (called an electron injecting metal), an alloy, an electrically conductive compound, or a mixture thereof having a small work function (4 eV or less) is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, a magnesium / copper mixture, a magnesium / silver mixture, a magnesium / aluminum mixture, a magnesium / indium mixture, and aluminum / aluminum oxide (Al ２ O ３ Among these, in view of electron injection property and durability against oxidation, etc., mixtures of an electron injection metal and a second metal which is a metal having a larger and more stable work function than the electron injection metal, such as magnesium / silver mixtures, magnesium / aluminum mixtures, magnesium / indium mixtures, aluminum / aluminum oxide (Al ２ O ３) mixture, lithium / aluminum mixture, aluminum, etc. are suitable. The cathode can be produced by forming a thin film of these cathode materials by methods such as vapor deposition or sputtering. The cathode preferably has a sheet resistance of several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm. In order to transmit emitted light, it is advantageous if either the anode or cathode of the organic EL element is transparent or semitransparent, as this improves the luminance of the emitted light.

[0069] Furthermore, a transparent or semi-transparent cathode can be fabricated by forming the above metal in a thickness of 1 to 20 nm as the cathode and then forming the conductive transparent material described in the description of the anode thereon. This can be applied to fabricate an element in which both the anode and cathode are transparent.

[0070] -Light-emitting layer- The light-emitting layer is a layer that emits light after excitons are generated by the recombination of holes and electrons injected from the anode and cathode, respectively, and contains a light-emitting dopant and a host. The light-emitting dopant and host are preferably mixed in proportions of 0.10 to 10% of the light-emitting dopant and 99.9 to 90% of the host, more preferably 1.0 to 5.0% of the light-emitting dopant and 99 to 95% of the host, and even more preferably 1.0 to 3.0% of the light-emitting dopant and 99 to 97% of the host. In this specification, "%" refers to "mass %" unless otherwise specified.

[0071] As the host in the light-emitting layer, the compound of the present invention represented by the general formula (1) or the general formulas (1) and (2) can be used.

[0072] When the first compound of the present invention represented by the general formula (1) is used as a first host material, it is preferable to use a second compound represented by the general formula (2) as a second host. It is also preferable that the compound represented by the general formula (1) is an electron-transporting host, and the compound represented by the general formula (2) is a hole-transporting host. The mixing ratio of the first host and the second host is preferably 5 to 95% first host and 95 to 5% second host, more preferably 30 to 70% first host and 70 to 30% second host, and even more preferably 30 to 50% first host and 70 to 50% second host.

[0073] In the light-emitting layer, the host represented by the general formula (1) or (2) of the present invention may be used alone or in combination with two or more different compounds. Also, one or more known other hosts may be used in combination, but the amount used should be 50% or less, preferably 25% or less, of the total amount of the host material. The known other hosts that can be used are compounds that have hole-transporting ability and electron-transporting ability and a high glass transition temperature, and preferably have a T1 greater than that of the luminescent dopant. Specifically, the T1 of the host is preferably 0.010 eV or more higher, more preferably 0.030 eV or more higher, and even more preferably 0.10 eV or more higher than that of the luminescent dopant. A TADF-active compound may also be used as the host material, and this compound preferably has a ΔEST of 0.20 eV or less.

[0074] The above-mentioned other known hosts can be selected from many known patent documents, etc. Specific examples of the host include, but are not particularly limited to, indole derivatives, carbazole derivatives, indolocarbazole derivatives, triazole derivatives, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, phenylenediamine derivatives, arylamine derivatives, styrylanthracene derivatives, fluorenone derivatives, stilbene derivatives, triphenylene derivatives, carborane derivatives, porphyrin derivatives, phthalocyanine derivatives, metal complexes of 8-quinolinol derivatives, metal phthalocyanines, various metal complexes typified by metal complexes of benzoxazole and benzothiazole derivatives, poly(N-vinylcarbazole) derivatives, aniline copolymers, thiophene oligomers, polythiophene derivatives, polyphenylene derivatives, polyphenylenevinylene derivatives, and polyfluorene derivatives.

[0075] When multiple types of hosts are used, each host can be vapor-deposited from a different vapor deposition source, or multiple types of hosts can be simultaneously vapor-deposited from one vapor deposition source by premixing them before vapor deposition to form a premixed host material.

[0076] In preparing the organic electroluminescent device of the present invention, when the first compound represented by the general formula (1) of the present invention is used as a first host and the second compound represented by the general formula (2) is used as a second host, it is preferable to use them as a premixed host material for organic electroluminescent devices that is premixed before deposition in order to vapor-deposit them from a single vapor deposition source. In order to vapor-deposit them from a single vapor deposition source, in the premixed host material for organic electroluminescent devices, it is preferable that the difference in 50% weight loss temperature between the first compound represented by the general formula (1) and the second compound represented by the general formula (2) is 20°C or less, more preferably within 10°C.

[0077] The premixing method is preferably one that can mix as uniformly as possible, and examples thereof include pulverization and mixing, heating and melting under reduced pressure or in an inert gas atmosphere such as nitrogen, sublimation, etc. The premix may be in the form of a powder, stick, or granules.

[0078] In the premixed host material for organic electroluminescent devices, in which two hosts are premixed in advance, the difference in 50% weight loss temperatures between the two hosts is preferably within 20°C. Vaporizing and depositing this premix from a single evaporation source makes it possible to obtain a uniform deposited film. In this case, a luminescent dopant material required for forming the emitting layer or other hosts to be used as needed may be mixed into the premix. However, if there is a large difference in the temperatures at which the desired vapor pressure 8 is achieved, it is preferable to deposit them from separate evaporation sources.

[0079] When the compound of the present invention represented by general formula (1) is used as a host, the energy level of the highest occupied molecular orbital (HOMO) obtained by a structure optimization calculation using density functional theory calculation B3LYP / 6-31G(D) is preferably −4.7 eV or less, more preferably in the range of −5.9 eV to −4.7 eV.

[0080] The energy level of the lowest unoccupied molecular orbital (LUMO) obtained by the structural optimization calculation is preferably −2.5 eV or higher, more preferably in the range of −1.8 eV to −1.2 eV.

[0081] When the compound of the present invention represented by general formula (1) is used as a host, the difference (absolute value) between the HOMO energy level and the LUMO energy level is preferably in the range of 2.5 to 5.0 eV, more preferably in the range of 3.0 to 4.5 eV.

[0082] As the light-emitting dopant in the light-emitting layer, it is preferable to use a polycyclic aromatic compound material containing a boron atom.

[0083] The light-emitting layer may contain two or more light-emitting dopants, for example, a combination of two or more light-emitting dopants including a TADF dopant made of a polycyclic aromatic compound containing a boron atom and a phosphorescent dopant made of a platinum complex, or a combination of two or more light-emitting dopants made of other compounds.

[0084] TADF dopants made of polycyclic aromatic compounds can emit blue light with high efficiency by utilizing the TADF mechanism. However, because of their low resistance to holes and electrons, it has been difficult to ensure a practical device life when used in combination with conventional known host materials in organic EL devices.

[0085] When the light-emitting layer contains two or more types of luminescent dopants, the first dopant is a polycyclic aromatic compound containing a boron atom or a fluorescent dopant, the second dopant is a phosphorescent material, and the third dopant may be a known compound used in combination as a luminescent dopant. The contents of the first dopant and the second dopant are preferably 0.050 to 50% and 0.050 to 50%, respectively, based on the host material, and the total content of the first and second dopants does not exceed 50% based on the host material.

[0086] The other luminescent dopants are known in many patent documents, etc., and can be selected from them. Specific examples of the dopants include, but are not limited to, fused ring derivatives such as phenanthrene, anthracene, pyrene, tetracene, pentacene, perylene, naphthopyrene, dibenzopyrene, rubrene, and chrysene, benzoxazole derivatives, benzothiazole derivatives, benzimidazole derivatives, benzotriazole derivatives, oxazole derivatives, oxadiazole derivatives, thiazole derivatives, imidazole derivatives, thiadiazole derivatives, triazole derivatives, pyrazoline derivatives, stilbene derivatives, thiophene derivatives, tetraphenylbutadiene derivatives, cyclopentadiene derivatives, bisstyryl derivatives such as bisstyrylanthracene derivatives and distyrylbenzene derivatives, bisstyrylarylene derivatives, diazaindacene derivatives, furan derivatives, benzo ... Examples of the phosphorescent material include benzophenone derivatives, isobenzofuran derivatives, dibenzofuran derivatives, coumarin derivatives, dicyanomethylenepyran derivatives, dicyanomethylenethiopyran derivatives, polymethine derivatives, cyanine derivatives, oxobenzoanthracene derivatives, xanthene derivatives, rhodamine derivatives, fluorescein derivatives, pyrylium derivatives, carbostyril derivatives, acridine derivatives, oxazine derivatives, phenylene oxide derivatives, quinacridone derivatives, quinazoline derivatives, pyrrolopyridine derivatives, furopyridine derivatives, 1,2,5-thiadiazolopyrene derivatives, pyrromethene derivatives, perinone derivatives, pyrrolopyrrole derivatives, squarylium derivatives, violanthrone derivatives, phenazine derivatives, acridone derivatives, deazaflavin derivatives, fluorene derivatives, and benzofluorene derivatives. Furthermore, examples of the phosphorescent material include, but are not limited to, platinum materials.

[0087] The luminescent dopant and the first host or the second host can be deposited from different deposition sources, or can be premixed before deposition to form a premixture, so that the luminescent dopant and the first host or the second host can be simultaneously deposited from a single deposition source.

[0088] Injection layer: An injection layer is a layer provided between an electrode and an organic layer to reduce driving voltage and improve luminance, and includes a hole injection layer and an electron injection layer. An injection layer may be provided between the anode and the light-emitting layer or the hole transport layer, and between the cathode and the light-emitting layer or the electron transport layer. An injection layer can be provided as needed.

[0089] -Hole Blocking Layer- In a broad sense, a hole blocking layer functions as an electron transport layer and is made of a hole blocking material that has the ability to transport electrons but has a significantly low ability to transport holes. By transporting electrons while blocking holes, the probability of electron and hole recombination in the light-emitting layer can be improved. Known hole blocking materials can be used for the hole blocking layer. To bring out the properties of the light-emitting dopant, the material used as the first host can also be used as the material for the hole blocking layer. Multiple hole blocking materials may also be used in combination.

[0090] -Electron Blocking Layer- In a broad sense, the electron blocking layer functions as a hole transport layer, and by transporting holes while blocking electrons, it is possible to improve the probability of electrons and holes recombining in the light-emitting layer. Known electron blocking layer materials can be used as the material for the electron blocking layer. To bring out the properties of the light-emitting dopant, the material used as the second host can also be used as the material for the electron blocking layer. The thickness of the electron blocking layer is preferably 3 to 100 nm, and more preferably 5 to 30 nm.

[0091] -Exciton Blocking Layer- The exciton blocking layer is a layer that prevents excitons generated by the recombination of holes and electrons in the light-emitting layer from diffusing into the charge transport layer. Insertion of this layer makes it possible to efficiently confine excitons within the light-emitting layer, thereby improving the luminous efficiency of the device. In a device in which two or more light-emitting layers are adjacent to each other, the exciton blocking layer can be inserted between two adjacent light-emitting layers. Known exciton blocking layer materials can be used as the material for the exciton blocking layer.

[0092] Layers adjacent to the light-emitting layer include a hole-blocking layer, an electron-blocking layer, an exciton-blocking layer, etc., but if these layers are not provided, the adjacent layers are a hole-transporting layer, an electron-transporting layer, etc.

[0093] -Hole Transport Layer- The hole transport layer is made of a hole transport material having a function of transporting holes, and the hole transport layer may be provided as a single layer or as a plurality of layers.

[0094] The hole transport material has either hole injection or transport properties or electron barrier properties, and may be either organic or inorganic. Any conventionally known compound can be selected and used for the hole transport layer. Examples of such hole transport materials include porphyrin derivatives, arylamine derivatives, triazole derivatives, oxadiazole derivatives, imidazole derivatives, polyarylalkane derivatives, phenylenediamine derivatives, arylamine derivatives, amino-substituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline-based copolymers, and conductive polymer oligomers, particularly thiophene oligomers. Porphyrin derivatives, arylamine derivatives, and styrylamine derivatives are preferred, and arylamine derivatives are more preferred.

[0095] - Electron Transport Layer - The electron transport layer is made of a material having a function of transporting electrons, and the electron transport layer may be a single layer or multiple layers.

[0096] The electron transport material (which may also serve as a hole blocking material) may have the function of transporting electrons injected from the cathode to the light-emitting layer. The electron transport layer may be formed from any of conventionally known compounds, including polycyclic aromatic derivatives such as naphthalene, anthracene, and phenanthroline, tris(8-quinolinolato)aluminum(III) derivatives, phosphine oxide derivatives, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, carbodiimides, fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, bipyridine derivatives, quinoline derivatives, oxadiazole derivatives, benzimidazole derivatives, benzothiazole derivatives, and indolocarbazole derivatives. Furthermore, polymeric materials in which any of these materials are incorporated into a polymer chain or in which any of these materials form the polymer backbone may also be used.

[0097] When the organic EL element of the present invention is produced, the method for forming each layer is not particularly limited, and the layers may be produced by either a dry process or a wet process.

[0098] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples and can be implemented in various forms as long as they do not depart from the gist of the invention.

[0099] Synthesis Example 1 (Synthesis of intermediate Dibenzothiophene-1-ol) Under a nitrogen atmosphere, 1-bromodibenzothiophene (6.1 g, 61.1 mmol), tris(dibenzylideneacetone)dipalladium(0) (1.1 g, 1.2 mmol), 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl (tBuXPhos) (1.0 g, 2.4 mmol), and potassium hydroxide (7.0 g, 124.7 mmol) were suspended in 1,4-dioxane (100 mL) and distilled water (100 mL). The suspension was heated and stirred at 105 °C for 16 h. After cooling, the mixture was neutralized with dilute hydrochloric acid and extracted with methylene chloride. The organic layer was separated. The organic layer was dried over sodium sulfate, and the filtrate was concentrated under reduced pressure. Dibenzothiophene-1-ol was obtained as a colorless solid by silica gel column chromatography (hexane:ethyl acetate = 5:2, v / v → methylene chloride). (7.6 g, 38.0 mmol, 62%) 1 H NMR (400 MHz, CDCl3) δ 8.65 (dd, J = 6.1, 1.6 Hz, 1H), 7.84-7.82 (m, 1H), 7.46-7.43 (m, 3H), 7.29 (t, J = 7.9 Hz, 1H), 6.77 (d, J = 7.8 Hz, 1H), 5.46 (s, 1H)

[0100] Synthesis Example 2 (Synthesis of intermediate 1,1'-((2-bromo-1,3-phenylene)bis(oxy))dibenzo[b,d]thiophene) Under a nitrogen atmosphere, dibenzothiophene-1-ol (1.2 g, 6.1 mmol), cesium carbonate (2.0 g, 6.0 mmol), and 1-bromo-2,6-difluorobenzene (0.22 mL, 2.0 mmol) were suspended in DMAc (7 mL). This suspension was heated and stirred at 150 °C for 24 hours. After cooling, saturated brine was added to the reaction solution, which was then extracted with methylene chloride to separate the organic layer. The organic layer was dried over sodium sulfate, and the filtrate was concentrated under reduced pressure. The precipitated solid was washed with methanol and hexane to obtain 1,1'-((2-bromo-1,3-phenylene)bis(oxy))didibenzo[b,d]thiophene as a white solid. (1.0 g, 1.8 mmol, 90%) 1 H NMR (400 MHz, CDCl3 δ) 6.85 (d, J= 8.2 Hz, 2H), 6.92 (d, J = 7.9 Hz), 7.21 (t, J = 8.2 Hz, 1H), 7.42 (t, J = 7.9 Hz, 2H), 7.47-7.49 (m, 4H), 7.66 (d, J = 7.6 Hz, 2H), 7.87-7.89 (m, 2H), 8.66-8.68 (m, 2H) MALDI-MS 551.985 calcd for C 30 H 17 BrO2S2, found 551.976

[0101] Synthesis Example 3 (Synthesis of Compound 1-1) Under a nitrogen atmosphere, 1,1'-((2-bromo-1,3-phenylene)bis(oxy))didibenzo[b,d]thiophene (1.3 g, 2.3 mmol) synthesized in Synthesis Example 2 was suspended in tert-butylbenzene (40 mL). This suspension was placed in an ice bath, and n-BuLi (1.6 M hexane solution, 2.0 mL, 3.2 mmol) was added dropwise thereto and stirred at room temperature for 1 hour. Then, boron tribromide (0.35 mL, 3.8 mmol) was added at 0°C and stirred at 90°C for 1 hour. After cooling, an ice bath was placed therein, and N,N-diisopropylethylamine (0.80 mL, 4.7 mmol) was added thereto. The mixture was heated and stirred at 170°C for 18 hours. After cooling to room temperature, water and methanol were added, and the precipitated solid was collected by suction filtration. This solid was washed with hot chloroform to give compound 1-1, 15,19-dioxa-5,10-dithia-7b-boraindeno[1,2-a]indeno[1',2':5,6]naphtho[1,2,3-fg]anthracene, as a colorless solid (403.8 mg, 0.84 mmol, 35%). MALDI-MS 482.06 calcd for C 30 H 15 BO2S2, found 482.14

[0102] The compounds used in the examples and comparative examples are listed below.

[0103] Example 1 The 50% weight loss temperature (Ts) refers to the temperature at which a 50% weight loss occurs when the temperature is raised from room temperature to 550°C at a rate of 10°C per minute in a TG-DTA measurement under reduced pressure (1 Pa) of nitrogen gas flow. It is believed that vaporization by evaporation or sublimation occurs most actively around this temperature. Table 1 shows the Ts of compounds 1-1 and 2-134. It can be seen from Table 1 that the difference in the 50% weight loss temperature between the first compound 1-1 represented by general formula (1) and the second compound 2-134 represented by general formula (2) is 4°C, within 20°C.

[0104]

[0105] Example 2 For compound 1-1 represented by general formula (1) and compound 2-134 represented by general formula (2), structural optimization calculations were performed at the B3LYP / 6-31G* level using density half-function theory (DFT) with the molecular orbital program Gaussian 16, and the excited singlet energy S1 was calculated at the TD-B3LYP / 6-31G* level. The results are shown in Table 2. Table 2 shows that the S1 values ​​of the host materials, compound 1-1 and compound 2-134, are both 3.2 eV or higher. As such, because the host has a high S1 value, back energy transfer from the dopant to the host can be suppressed, and singlet excitons can be efficiently utilized for light emission, which is expected to result in high luminous efficiency.

[0106]

[0107] Example 3: A film was deposited on a quartz substrate by vacuum deposition at a vacuum of 4.0 × 10 －５ Compound 1-1 and compound 2-134 were co-deposited from different deposition sources at 100 Pa to form an organic thin film having a thickness of 100 nm. At this time, the co-deposition was carried out under deposition conditions such that the concentration of compound 1-1 was 50 mass % and the concentration of compound 2-134 was 50 mass %, thereby producing the organic thin film of Example 3.

[0108] Comparative Example 1 Compound 1-1 and Compound 2-134 were co-deposited from different deposition sources on a quartz substrate to form an organic thin film having a thickness of 100 nm in the same manner as in Example 3. The co-deposition was carried out under deposition conditions such that the concentration of Compound 1-1 was 1.5% by mass and the concentration of Compound 2-134 was 98.5% by mass, thereby producing the organic thin film according to Comparative Example 1.

[0109] The photoluminescence (PL: fluorescence emission) spectra of the thin films prepared in Example 3 and Comparative Example 1 were measured using a spectrofluorometer (FP-6500, manufactured by JASCO). In the obtained PL spectrum, the wavelength at which the emission intensity was maximum was defined as the maximum emission wavelength. The results are shown in Table 3.

[0110]

[0111] From Tables 2 and 3, it can be seen that the S1 of the first compound 1-1 represented by the general formula (1) and the second compound represented by the general formula (2) are both 3.2 eV or more, and the difference between the maximum emission wavelength of an organic thin film (Example 3) prepared by depositing a mixed host material for organic electroluminescent elements, in which the concentration of the first compound 1-1 represented by the general formula (1) is 5 mass % or more and the concentration of the second compound represented by the general formula (2) is 95 mass % or less, and the maximum emission wavelength of an organic thin film (Comparative Example 1) prepared by depositing a mixed host material for organic electroluminescent elements, in which the concentration of the first compound 1-1 is less than 5 mass % and the concentration of the second compound is more than 95 mass %, is 49 nm. It can be seen that in Example 3, the excitation energy is stabilized due to the formation of an exciplex between the first compound and the second compound, and the maximum wavelength of the fluorescence emission spectrum is elongated by 49 nm. In other words, as described above, the mixed host material for organic electroluminescent devices of the present invention is a material that is required as a host material for organic electroluminescent devices, (a) efficiently transferring excitation energy generated in the host material to the light-emitting material, and (b) suppressing reverse energy transfer from the light-emitting material to the host material (i.e., it can achieve both properties). Furthermore, Table 3 shows that the maximum emission wavelength of the organic thin film of Example 3 of the present invention is 455 nm or less, making it a host that is particularly advantageous for energy transfer to a blue-emitting dopant.

[0112] The compounds used in Examples 4 to 6 and Comparative Examples 2 and 3 are shown below.

[0113] Example 4 On a glass substrate on which an anode made of ITO with a film thickness of 70 nm was formed, each of the thin films shown below was deposited by vacuum deposition at a vacuum degree of 4.0 × 10 －５The layers were laminated at a pressure of 10 Pa. First, HAT-CN, as previously described, was formed on ITO as a hole injection layer to a thickness of 10 nm, and then HT-1 was formed as a hole transport layer to a thickness of 60 nm. Next, (2-134) was formed as an electron blocking layer to a thickness of 5 nm. Next, compound (1-1) was co-deposited as a first host, compound (2-134) as a second host, and BD-2 as a dopant from different evaporation sources to form an emitting layer having a thickness of 40 nm. At this time, the co-deposition was performed under evaporation conditions such that the concentration of BD-2 was 13% by mass and the mass ratio of the first host to the second host was 50:50. Next, ET-2 was formed as a hole blocking layer to a thickness of 5 nm. Next, ET-3 was formed as an electron transport layer to a thickness of 31 nm. Furthermore, lithium fluoride (LiF) was formed as an electron injection layer to a thickness of 1 nm on the electron transport layer. Finally, aluminum (Al) was formed as a cathode to a thickness of 70 nm on the electron injection layer, thereby completing the organic EL element according to Example 1.

[0114] Examples 5 and 6, Comparative Examples 2 and 3 Organic EL devices were prepared in the same manner as in Example 4, except that the first host and second host were the compounds shown in Table 4 in the mixing ratios.

[0115]

[0116] The evaluation results of the prepared organic EL devices are shown in Table 5. When an external power source was connected to the organic EL devices obtained in Examples and Comparative Examples and a DC voltage was applied, an emission spectrum with a maximum emission wavelength of 450 nm to 480 nm was observed in all the organic EL devices, and it was found that they emitted blue light. The voltage and external quantum yield in the table were measured at a driving current of 4.0 mA / cm. ２ The values ​​are those at 1000 kJ / s. The luminescent color was confirmed by the emission spectrum of the organic EL element. From the results of the Examples and Comparative Examples shown in Table 5, it can be seen that the organic EL element using the mixed material for organic electroluminescent element of the present invention as a host in the luminescent layer emits blue light and has highly efficient characteristics.

[0117]

[0118] An organic EL device using the host material of the present invention can be an organic EL device with high luminous efficiency. ​

[0119] 1 Substrate, 2 Anode, 3 Hole injection layer, 4 Hole transport layer, 5 Light-emitting layer, 6 Electron transport layer, 7 Cathode

Claims

1. A mixed host material for an organic electroluminescent device, comprising two or more organic compounds, characterized in that it contains a first compound represented by the following general formula (1) in a concentration of 5% by mass or more and 95% by mass or less: Here, ring A and ring E are each independently represented by the above general formula (1a) or (1b), and are fused to the adjacent ring at any position. １ , X ２ , Y １ , and Y ２ are each independently N-Ar １ , O, or S. Ar １ each independently represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. １ , or Y ２ is N-Ar １ and Ar １ is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, １ is the Ar １ may be condensed with an adjacent ring to form a ring. １ ~R ５ each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and aromatic heterocyclic groups. a and d represent the number of substitutions in the range of 0 to 4, b and c represent the number of substitutions in the range of 0 to 2, and e represents the number of substitutions in the range of 0 to 3. In addition, some or all of the hydrogen atoms in the compound represented by general formula (1) may be substituted with deuterium. B represents a boron atom.

2. The mixed host material for an organic electroluminescent device according to claim 1, wherein the mixed host material further contains a second compound represented by the following general formula (2): Here, f is the number of substitutions and represents 0 to 3, g is the number of substitutions and represents 0 to 4, m is the number of repetitions and represents 2 or 3, and n is the number of substitutions and represents 1 or 2. Ar ２ represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and aromatic heterocyclic groups. ６ , R ７ each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. ２ , R ６ , and R ７ In addition, some or all of the hydrogen atoms in the compound represented by the general formula (2) may be substituted with deuterium atoms.

3. The mixed host material for an organic electroluminescent device according to claim 1, wherein the first compound represented by the general formula (1) is represented by the following general formula (3): Here, X １ , X ２ , Y １ , Y ２ , R １ ~R ５ , a to e have the same meanings as in general formula (1). In addition, some or all of the hydrogen atoms in the compound represented by general formula (3) may be substituted with deuterium atoms.

4. Among the compounds represented by the general formula (1), X １ , X ２ , Y １ , and Y ２ 2. The mixed host material for an organic electroluminescent device according to claim 1, wherein at least two of the above compounds contain a compound represented by S.

5. The mixed host material for organic electroluminescent devices according to claim 2, characterized in that it satisfies the following conditions (i) and (ii): (i) the excited singlet energy S1 of the first compound represented by the general formula (1) and the second compound represented by the general formula (2) is both 3.2 eV or more, and (ii) when the concentration of the first compound represented by the general formula (1) is A% by mass and the concentration of the second compound represented by the general formula (2) is B% by mass, the difference between the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for organic electroluminescent devices containing A in a concentration of 5% by mass or more and B in a concentration of 95% by mass or less and the maximum emission wavelength of the fluorescent emission spectrum of a mixture containing A in a concentration of less than 5% by mass and B in a concentration of more than 95% by mass is 40 nm or more.

6. The mixed host material for organic electroluminescent devices according to claim 5, further satisfying the following condition (iii): (iii) the maximum emission wavelength of the fluorescent emission spectrum of the mixed host material for organic electroluminescent devices is 455 nm or less.

7. An organic electroluminescent device comprising one or more organic layers between opposing anode and cathode, wherein at least one of the organic layers contains the mixed host material for organic electroluminescent devices according to claim 1.

8. An organic electroluminescent device comprising one or more organic layers between opposing anode and cathode, wherein at least one organic layer contains the mixed host material for organic electroluminescent devices according to claim 2, which contains the compounds of general formula (1) and general formula (2).

9. The organic electroluminescent device according to claim 7, wherein the organic layer containing the mixed host material for the organic electroluminescent device is a light-emitting layer.

10. The organic electroluminescent device according to claim 9, further comprising a thermally activated delayed fluorescent material in the light-emitting layer.

11. The organic electroluminescent device according to claim 10, wherein the thermally activated delayed fluorescent emitting material is a thermally activated delayed fluorescent emitting material containing a boron atom, with the proviso that the thermally activated delayed fluorescent emitting material containing a boron atom is a compound different from the first compound represented by general formula (1).

12. The organic electroluminescent device according to claim 9, further comprising a phosphorescent material in the light-emitting layer.

13. The organic electroluminescent device according to claim 12, wherein the phosphorescent material is a phosphorescent material containing platinum atoms.

14. The organic electroluminescent device according to claim 9, wherein the organic layer containing the mixed host material for organic electroluminescent devices is an emitting layer, and the emitting layer further contains a thermally activated delayed fluorescent material containing a boron atom and a phosphorescent material containing a platinum atom, with the proviso that the thermally activated delayed fluorescent material containing a boron atom is a compound different from the first compound represented by general formula (1).

15. A premixed host material for an organic electroluminescent device, comprising a compound represented by the general formula (1) described in claim 1 and a compound represented by the general formula (2) described in claim 2.

16. The premixed host material for organic electroluminescent devices according to claim 15, characterized in that the difference in 50% weight loss temperature between the first compound represented by general formula (1) and the second compound represented by general formula (2) is 20°C or less.

17. A host material for an organic electroluminescent device represented by the following general formula (1): Here, ring A and ring E are each independently represented by the above general formula (1a) or (1b), and are fused to the adjacent ring at any position. １ , X ２ , Y １ , and Y ２ are each independently N-Ar １ , O, or S. Ar １ each independently represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and the aromatic heterocyclic groups. １ , or Y ２ is N-Ar １ and Ar １ is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, or a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, １ is the Ar １ may be condensed with an adjacent ring to form a ring. １ ~R ５ each independently represents deuterium, an aliphatic hydrocarbon group having 1 to 10 carbon atoms, a substituted or unsubstituted triarylsilyl group having 18 to 36 carbon atoms, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, a substituted or unsubstituted aromatic heterocyclic group having 3 to 20 carbon atoms, or a substituted or unsubstituted linked aromatic group formed by linking 2 to 3 aromatic groups selected from the aromatic hydrocarbon groups and aromatic heterocyclic groups. a and d represent the number of substitutions in the range of 0 to 4, b and c represent the number of substitutions in the range of 0 to 2, and e represents the number of substitutions in the range of 0 to 3. In addition, some or all of the hydrogen atoms in the compound represented by general formula (1) may be substituted with deuterium. B represents a boron atom.

18. A method for producing an organic electroluminescent device having one or more organic layers between opposing anode and cathode, at least one of which is an emitting layer, the method comprising depositing the premixed host material for organic electroluminescent devices according to claim 15 from a single deposition source.

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