Organic electroluminescent elements and their design methods, methods for improving multi-resonance light-emitting materials, multi-resonance light-emitting materials and compounds

Abstract

To provide an organic electroluminescent element with high stability and suppressed roll-off, using a combination of delayed fluorescence material and multi-resonance type luminescent material in the light-emitting layer. [Solution] The organic electroluminescent element of the present invention is characterized in that the light-emitting layer includes at least a delayed fluorescence material and a multi-resonance type light-emitting material, a substituent is introduced into the multi-resonance type condensed ring skeleton constituting the multi-resonance type light-emitting material, and the difference in HOMO energy levels between the multi-resonance type light-emitting material and the delayed fluorescence material is 0.4 eV or less.

Description

[Technical Field]

[0001] This invention relates to an organic electroluminescent element containing a delayed fluorescence material and a multi-resonance luminescent material in its light-emitting layer, and to a method for designing the same. Furthermore, this invention also relates to a multi-resonance luminescent material and a method for improving the same, and to compounds useful as multi-resonance luminescent materials. [Background technology]

[0002] Research is actively underway to improve the luminescence efficiency of organic electroluminescent devices (OLEDs). In particular, various methods are being employed to improve luminescence efficiency and color purity by developing new material compositions for the light-emitting layer of organic electroluminescent devices. For example, Patent Document 1 proposes an organic electroluminescent element having a light-emitting layer containing a host material, a delayed fluorescence material, and a multi-resonance light-emitting material. Here, the delayed fluorescence material is an organic compound with a small difference between the excited singlet energy and the excited triplet energy, and has the function of converting the excited triplet state to the excited singlet state and supplying the excited singlet energy to the multi-resonance light-emitting material. The multi-resonance light-emitting material is a condensed polycyclic compound whose molecules are designed so that the HOMO and LUMO are localized on different carbon atoms due to the multi-resonance effect of boron and nitrogen, and exhibits high color purity because it does not involve molecular stretching vibrations during radiative deactivation from the excited singlet S1 to the ground singlet S0. In an organic electroluminescent element using a combination of these materials, the energy of the excited triplet state, which would normally be deactivated without radiation in ordinary organic compounds, is effectively utilized for the emission of light by the multi-resonance light-emitting material, resulting in high luminescence efficiency and high color purity. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] Adv. Mater. 2016, 28(14), 2777-2781 [Non-Patent Document 2] Adv. Mater. 2022, 34(32), 2201778 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, conventional organic electroluminescent devices combining delayed fluorescence materials and multi-resonance luminescent materials have suffered from poor stability and a tendency to roll off. This is presumed to be a unique problem caused by the combination of delayed fluorescence materials and multi-resonance luminescent materials, but the cause has not been sufficiently analyzed, and an appropriate solution has not yet been found. Under these circumstances, the inventors diligently pursued research with the aim of providing an organic electroluminescent element that achieves high stability and suppresses roll-off by using a combination of delayed fluorescence material and multi-resonance type light-emitting material. [Means for solving the problem]

[0005] As a result of diligent research to solve the above problems, the inventors have found that in conventional organic electroluminescent devices combining a delayed fluorescence material and a multi-resonance type light-emitting material, the HOMO level of the multi-resonance type light-emitting material is much higher (shallower) than the HOMO level of the delayed fluorescence material, causing hole traps in the multi-resonance type light-emitting material. This reduces the efficiency and operational stability of the device and causes roll-off. The present invention is proposed based on these findings and has the following specific configuration.

[0006] [1] An organic electroluminescent element characterized in that the light-emitting layer comprises at least a delayed fluorescence material and a multi-resonance type light-emitting material, wherein a substituent with a σm of 0.2 or more is introduced into the multi-resonance type condensed ring skeleton constituting the multi-resonance type light-emitting material, and the difference in HOMO energy levels between the multi-resonance type light-emitting material and the delayed fluorescence material is 0.4 eV or less. [2] The organic electroluminescent element according to [1], wherein the substituent is bonded to an atom with a large electron density distribution of the HOMO. [3] The organic electroluminescent element according to [1], wherein the substituent is bonded to an atom in which both the electron density distribution of the HOMO and the electron density distribution of the LUMO are large. [4] The organic electroluminescent element according to any one of [1] to [3], wherein the energy level of the HOMO of the multi-resonance type light-emitting material is -5.6 eV or less. [5] The organic electroluminescent element according to any one of [1] to [4], wherein the energy level of the HOMO of the delayed fluorescence material is -5.9 eV or less. [6] The organic electroluminescent element according to any one of [1] to [5], wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the meta position of the boron atom. [7] The organic electroluminescent element according to any one of [1] to [5], wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the para position of the boron atom. [8] The organic electroluminescent element according to any one of [1] to [7], wherein the substituent is a fluorine atom, a cyano group, a trifluoromethyl group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group. [9] A method for designing an organic electroluminescent element comprising a host material, a delayed fluorescence material, and a multi-resonance type light-emitting material in a light-emitting layer, characterized in that a structure is determined by selecting substituents present in the multi-resonance type light-emitting material such that the difference in HOMO energy levels between the multi-resonance type light-emitting material and the delayed fluorescence material is 0.4 eV or less, and an organic electroluminescent element comprising the multi-resonance type light-emitting material having that structure, the host material, and the delayed fluorescence material is designed.

[10] The substituent is a substituent bonded to an atom with a large electron density distribution of the HOMO, the method for designing an organic electroluminescent device according to [9].

[11] The substituent is bonded to an atom in which both the electron density distribution of the HOMO and the electron density distribution of the LUMO are large, the method for designing an organic electroluminescent device according to [9].

[12] A method for designing an organic electroluminescent element according to any one of [9] to

[11] , wherein the energy level of the HOMO of the structure to be determined is -5.6 eV or less.

[13] A method for designing an organic electroluminescent device according to any one of [9] to

[12] , wherein the energy level of the HOMO of the delayed fluorescence material is -5.9 eV or less.

[14] A method for designing an organic electroluminescent element according to any one of [9] to

[13] , wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the meta position of the boron atom.

[15] A method for designing an organic electroluminescent element according to any one of [9] to

[13] , wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the para position of the boron atom.

[16] A method for designing an organic electroluminescent element according to any one of [9] to

[15] , wherein the distance between the bonding atom of the substituent and the atom furthest from that bonding atom is 7 angstroms or less.

[17] A method for designing an organic electroluminescent element according to any one of [8] to

[16] , wherein the substituent is a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group.

[18] An organic electroluminescent element manufactured using the design method described in any one of the items [9] to

[17] .

[19] A method for improving a multi-resonance luminescent material used in an organic electroluminescent element comprising a host material, a delayed fluorescence material, and a multi-resonance luminescent material in a light-emitting layer, characterized in that a multi-resonance luminescent material having a structure in which the difference between the energy level of the HOMO of the delayed fluorescence material and the energy level of the HOMO of the delayed fluorescence material is 0.4 eV or less is found by performing at least one step of calculating the difference between the structure and the energy level of the HOMO of the delayed fluorescence material, assuming a structure in which hydrogen atoms or groups present in the multi-resonance luminescent material before improvement are substituted.

[20] The improved method according to

[19] , wherein the hydrogen atom or group is a hydrogen atom or group bonded to an atom with a large electron density distribution of the HOMO.

[21] The improved method according to

[19] , wherein the hydrogen atom or group is bonded to an atom in which both the electron density distribution of the HOMO and the electron density distribution of the LUMO are large.

[22] Find a multi-resonance luminescent material in which the HOMO energy level is -5.6 eV or less, or an improved method as described in any one of

[19] to

[21] .

[23] A method for improving an organic electroluminescent element according to any one of

[19] to

[22] , wherein the energy level of the HOMO of the delayed fluorescence material is -5.9 eV or less.

[24] A method for improving an organic electroluminescent element according to any one of

[19] to

[23] , wherein the previously improved multi-resonance type light-emitting material contains a benzene ring bonded to a boron atom, and the hydrogen atom is a hydrogen atom of the benzene ring located at the meta position of the boron atom.

[25] A method for improving an organic electroluminescent element according to any one of

[19] to

[23] , wherein the previously improved multi-resonance type light-emitting material contains a benzene ring bonded to a boron atom, and the hydrogen atom is a hydrogen atom of the benzene ring located in the para position of the boron atom.

[26] The improvement method according to any one of

[19] to

[25] , wherein the substituent that substitutes a hydrogen atom or group present in the pre-improvement multi-resonance luminescent material is a substituent in which the distance between the bonding atom and the atom furthest from the bonding atom is 7 angstroms or less.

[27] The improved method according to any one of

[19] to

[26] , wherein the substituent is a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group.

[28] An improvement method according to any one of

[19] to

[27] , which improves a multi-resonance type light-emitting material while suppressing the variation in the full width at half maximum of the element to within a range of plus or minus 5 nm.

[29] The improvement method according to any one of

[19] to

[28] , which improves a multi-resonance type light-emitting material while suppressing the variation in the maximum emission wavelength of the element to within a range of plus or minus 15 nm.

[30] The improved method according to any one of

[19] to

[29] , wherein the maximum emission wavelength of the element is 490 nm or less.

[31] The improvement method according to any one of

[19] to

[30] , which improves a multi-resonance type light-emitting material while keeping the variation in the light emission quantum yield of the element within a range of plus or minus 10%.

[32] An improved method according to any one of

[19] to

[31] for suppressing Hole trapping by a multi-resonance type light-emitting material in the element. A program for implementing any one of the improvement methods described in

[33]

[19] to

[32] . A multi-resonance type light-emitting material manufactured using the improved method described in any one of the items

[34]

[19] to

[32] .

[35] Compounds represented by the following general formula (1). General formula (1) [ka] [In general formula (1), R 1 ~R 15 Each of these independently represents a hydrogen atom, a deuterium atom, or a substituent. 1 ~R 4 At least one of and R 11 ~R 14 At least one of them is independently a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group. 1and Ar 2 each independently represents a substituted or unsubstituted aryl group or a substituted or unsubstituted heteroaryl group.

[36] R 2 and R 3 one of which is a cyano group, and a compound as described in

[35] in which one of R 12 and R 13 is a cyano group.

Advantages of the Invention

[0007] According to the present invention, roll-off of an organic electroluminescence device including a delayed fluorescence material and a multi-resonance type luminescent material in a light-emitting layer can be suppressed, and stability can be improved.

Brief Description of the Drawings

[0008] [Figure 1] Graph showing the electron density-driving voltage characteristics of device E1 formed with a mixed film of compound 1:HDT-1:mCBP, device E2 formed with a mixed film of compound 2:HDT-1:mCBP, comparative device E1 formed with a mixed film of comparative compound 1:HDT-1:mCBP, comparative device E2 formed with a mixed film of HDT-1:mCBP, and comparative device E3 formed with a single film of mCBP. [Figure 2] Graph showing the hole density-driving voltage characteristics of device H1 formed with a mixed film of compound 1:HDT-1:mCBP, device H2 formed with a mixed film of compound 2:HDT-1:mCBP, comparative device H1 formed with a mixed film of comparative compound 1:HDT-1:mCBP, comparative device H2 formed with a mixed film of HDT-1:mCBP, and comparative device E4 formed with a single film of mCBP. [Figure 3] Emission spectra of EL device 1 formed with a light-emitting layer of compound 1:HDT-1:mCBP, EL device 2 formed with a light-emitting layer of compound 2:HDT-1:mCBP, and comparative EL device 1 formed with a light-emitting layer of comparative compound 1:HDT-1:mCBP. [Figure 4] Graph showing the current density-driving voltage-luminance characteristics of EL device 1, EL device 2, and comparative compound 1. [Figure 5]This graph shows the external quantum efficiency (EQE)-luminance characteristics of EL element 1, EL element 2, and comparative compound 1. [Figure 6] This graph shows the change in brightness over time when EL element 1, EL element 2, and comparative compound 1 are continuously driven. [Figure 7] This graph shows the change in emission intensity over time when excitation light is continuously irradiated onto EL element 1, EL element 2, comparative EL element 1, and PL element 1, PL element 2, and comparative PL element 1, each having the same light-emitting layer. [Figure 8] This graph shows the time evolution of EL intensity when a reverse bias voltage is applied after pulsed EL excitation (pulse width: 100 μs) is performed on EL element 1, EL element 2, and comparison EL element 1. [Figure 9] These are the transient decay curves of the electroluminescent (EL) intensity of EL element 1, which has an emissive layer of compound 1:HDT-1:mCBP, and comparative EL element 2, which also has an emissive layer of compound 1:mCBP. [Figure 10] These are the transient decay curves of the electroluminescent (EL) intensity of EL element 2, which has an emissive layer of compound 2:HDT-1:mCBP, and comparative EL element 3, which has an emissive layer of compound 1:mCBP. [Figure 11] These are the transient decay curves of the electroluminescent (EL) intensity of EL element 1, which has an emissive layer of comparative compound 1:HDT-1:mCBP, and comparative EL element 4, which also has an emissive layer of comparative compound 1:mCBP. [Modes for carrying out the invention]

[0009] The contents of the present invention will be described in detail below. The description of the constituent elements described below may be based on representative embodiments and specific examples of the present invention, but the present invention is not limited to such embodiments and specific examples. In this specification, numerical ranges represented by "~" mean a range that includes the numbers written before and after "~" as the lower limit and upper limit. Also, some or all of the hydrogen atoms present in the molecule of the compound used in the present invention are deuterium atoms ( 2It can be substituted with H (deuterium D). In the chemical structural formulas herein, hydrogen atoms are represented as H or omitted, and methyl groups are represented as CH3 or omitted. For example, when the representation of an atom bonded to a carbon atom in the ring skeleton of a benzene ring is omitted, it is assumed that H is bonded to the carbon atom in the ring skeleton where the representation is omitted. In this specification, the term "substituent" means an atom or group of atoms other than hydrogen atoms and deuterium atoms. On the other hand, the term "substituted or unsubstituted" means that the hydrogen atom may be substituted with a deuterium atom or a substituent.

[0010] <Organic electroluminescent element> The organic electroluminescent element of the present invention is characterized in that the light-emitting layer includes at least a delayed fluorescence material and a multi-resonance type light-emitting material, the multi-resonance type condensed ring skeleton constituting the multi-resonance type light-emitting material has substituents with a σm of 0.2 or more introduced into it, and the difference in HOMO (Highest Occupied Molecular Orbital) energy levels between the multi-resonance type light-emitting material and the delayed fluorescence material is 0.4 eV or less. In this invention, a "delayed fluorescence material" is a material that exhibits both short-lived fluorescence and long-lived fluorescence (delayed fluorescence) at 20°C. Fluorescence that is not delayed fluorescence typically has a luminescence lifetime on the order of nanoseconds. Furthermore, luminescent organic compounds other than organometallic complexes are typically either fluorescent materials or delayed fluorescence materials. Examples of delayed fluorescence materials include the difference between the excitation singlet energy and the excitation triplet energy ΔE ST A small luminescent organic compound can be used. STLuminescent organic compounds with low energy emission levels emit fluorescence (immediate fluorescence) through radiative deactivation from the directly generated excited singlet state, and are also prone to reverse intersystem crossing from the excited triplet state to the excited singlet state. As a result, they can emit fluorescence that is delayed compared to immediate fluorescence (delayed fluorescence) through radiative deactivation from the excited singlet state. However, in the organic electroluminescent element of the present invention, the excited singlet energy generated by the delayed fluorescence material is transferred to a multi-resonance type light-emitting material and used for the emission of light by the multi-resonance type light-emitting material. Therefore, it is not necessary for the delayed fluorescence material to emit fluorescence or delayed fluorescence in the light-emitting layer.

[0011] In this specification, "multi-resonance luminescent material" refers to a luminescent material made of an organic compound having a multi-resonance fused ring skeleton. In particular, the "multi-resonance luminescent material" used in the present invention is one in which substituents are introduced into the multi-resonance fused ring skeleton. Here, "multi-resonance fused ring skeleton" refers to a fused ring skeleton having a conjugated π-electron system and two or more complex atoms with different numbers of valence electrons than carbon atoms as constituent atoms of the ring skeleton, where each of these complex atoms resonates, and the entire structure resonates in multiple ways. For details of the multi-resonance fused ring skeleton, please refer to the description in the "Multi-Resonance Luminescent Material" section below. Due to the multi-resonance effect, the HOMO and LUMO of the multi-resonance luminescent material are localized on different carbon atoms, so when radiative deactivation occurs from excited singlet S1 to ground singlet S0, there is almost no stretching vibration of the molecule, and it exhibits luminescence with high color purity. While some multi-resonance luminescent materials exhibit delayed fluorescence, in this invention, multi-resonance luminescent materials exhibiting delayed fluorescence are also classified as "multi-resonance luminescent materials."

[0012] The multi-resonance luminescent material used in the organic electroluminescent element of the present invention has a multi-resonance fused ring skeleton into which substituents with a σm of 0.2 or more are introduced. The σm of the substituents introduced into the multi-resonance fused ring skeleton is, for example, 0.3 or more, for example, 0.4 or more, for example, 0.5 or more. σm as used herein refers to Hammett's σm. σm was proposed by L.P. Hammett and quantifies the effect of substituents on the reaction rate or equilibrium of metasubstituted benzene derivatives. Specifically, the following formula holds between substituents and the reaction rate constant or equilibrium constant in metasubstituted benzene derivatives: log(k / k0) = ρσm or log(K / K0) = ρσm This is a constant (σm) specific to the substituent in the above equation. In the above equation, k0 is the rate constant of the unsubstituted benzene derivative, k is the rate constant of the substituted benzene derivative, K0 is the equilibrium constant of the unsubstituted benzene derivative, K is the equilibrium constant of the substituted benzene derivative, and ρ is the reaction constant determined by the type and conditions of the reaction. For an explanation of "Hammett's σm" in this invention and the numerical values ​​of each substituent, refer to the description of σm values ​​in Hansch, C. et. al., Chem. Rev., 91, 165-195 (1991).

[0013] Preferred examples of substituents with a σm of 0.2 or greater include halogen atoms, cyano groups, haloalkyl groups (e.g., 1 to 10 carbon atoms), and nitrogen-containing teloaryl groups bonded to carbon atoms (e.g., 5 to 30 carbon atoms). In particular, fluorine atoms, cyano groups, trifluoromethyl groups, pyridyl groups, pyrimidyl groups, pyrazinyl groups, pyridadinyl groups, and triazyl groups are preferred. The number of substituents introduced into the multiple resonance fused ring skeleton may be one or two or more. When there are two or more substituents, they may be identical or different from each other. Furthermore, the positions of substituents introduced into the multiple resonance fused ring skeleton (atoms to which substituents are bonded among the constituent atoms of the multiple resonance fused ring skeleton) are preferably those atoms with a large electron density distribution for the HOMO, and more preferably those atoms with large electron density distributions for both the HOMO and LUMO. The electron density distributions for the HOMO and LUMO can be determined by calculation. For the calculation method, please refer to the description in the "Design Method for Organic Electroluminescent Devices" section.

[0014] The organic electroluminescent element of the present invention is characterized in that the multi-resonance luminescent material has a multi-resonance fused ring skeleton into which substituents with a σm of 0.2 or more are introduced, and the difference in HOMO energy levels between the multi-resonance luminescent material and the delayed fluorescence material is 0.4 eV or less. As a result, the organic electroluminescent element of the present invention exhibits high efficiency and high operational stability. This is presumed to be due to the following reasons. In the following explanation, the HOMO energy level is referred to as the "HOMO level," and the difference in HOMO energy levels between the multi-resonance luminescent material and the delayed fluorescence material ([HOMO level of the multi-resonance luminescent material] - [HOMO level of the delayed fluorescence material]) is referred to as "ΔE HOMO It is written as "". First, let's assume that the ΔE of multiple resonance luminescent materials and delayed fluorescence materials HOMO If the voltage is greater than 0.4 eV, the HOMO level of the multi-resonance luminescent material is much higher (shallower) than that of the delayed fluorescence material. As a result, holes injected into the luminescent layer can easily enter the HOMO level of the multi-resonance luminescent material rather than the HOMO level of the delayed fluorescence material and become trapped there. Consequently, hole transport is hindered, the current density-voltage characteristics deteriorate, and efficiency decreases. Furthermore, when holes trapped in the multi-resonance luminescent material recombine with electrons, singlet and triplet excitons are generated. Of these, the longer-lived triplet excitons accumulate, causing roll-off and reducing operational stability. In contrast, the ΔE of multiple resonance luminescent materials and delayed fluorescence materials HOMOWhen the voltage is 0.4 eV or less, the HOMO levels of the multi-resonance luminescent material and the delayed fluorescence material are close together. As a result, holes injected into the luminescent layer easily enter the HOMO level of the delayed fluorescence material, suppressing hole trapping in the multi-resonance luminescent material. Consequently, hole transport and current density-voltage characteristics are improved, resulting in high efficiency. Here, holes that enter the HOMO level of the delayed fluorescence material recombine with electrons in the LUMO level to generate singlet and triplet excitons. The energy of these singlet excitons, along with the energy of singlet excitons generated by reverse intersystem crossing from the triplet excitons, are used for luminescence in the multi-resonance luminescent material. On the other hand, in the multi-resonance luminescent material, exciton generation is also suppressed due to the suppression of hole trapping, and roll-off caused by triplet accumulation is also suppressed. This enables high luminescence efficiency and high operational stability. HOMO Organic electroluminescent elements with a voltage of 0.4 eV or less can be provided by using a multi-resonance luminescent material in which substituents with a σm of 0.2 or more are introduced into a multi-resonance fused ring skeleton. In the following, the delayed fluorescence material, the multi-resonance type luminescent material, and other materials that can be used in the light-emitting layer of the present invention will be described in detail.

[0015] [Delayed fluorescence materials] The delayed fluorescence material used in the present invention has the function of assisting the emission of light from a multi-resonance type light-emitting material by transferring the energy of the excited singlet state directly generated by current excitation and the energy of the excited singlet state generated by reverse intersystem crossing from the excited triplet state to the multi-resonance type light-emitting material. When used in the organic electroluminescent element of the present invention, it is not essential that the delayed fluorescence originating from the delayed fluorescence material is emitted. The emission from the delayed fluorescence material is preferably less than 10% of the emission from the organic electroluminescent element of the present invention, and may be, for example, less than 1%, less than 0.1%, less than 0.01%, or below the detection limit.

[0016] The delayed fluorescence material used in this invention is the difference ΔE between the lowest excitation singlet energy and the lowest excitation triplet energy at 77K. STIt is preferable that the voltage is 0.3 eV or less, more preferably 0.25 eV or less, more preferably 0.2 eV or less, more preferably 0.15 eV or less, even more preferably 0.1 eV or less, even more preferably 0.07 eV or less, even more preferably 0.05 eV or less, even more preferably 0.03 eV or less, and particularly preferably 0.01 eV or less. ΔE ST If the thermal energy absorption is small, the reverse intersystem crossover from the excited singlet state to the excited triplet state is more likely, allowing it to function as a thermally activated delayed fluorescence material. Thermally activated delayed fluorescence materials absorb the heat emitted by the device and relatively easily reverse intersystem crossover from the excited triplet state to the excited singlet state, and can efficiently supply that excited singlet energy to the multi-resonance luminescent material.

[0017] Examples of delayed fluorescence materials that can be used in the present invention include compounds having a structure in which an acceptor group and a donor group are bonded to an aromatic ring (for example, a benzene ring or a pyridine ring). For an explanation of acceptor groups and donor groups, please refer to the description of acceptor groups and donor groups as substituents for multi-resonance luminescent materials below. Examples of acceptor groups include cyano groups and nitrogen-containing heteroaryl groups bonded to the aromatic ring at a carbon atom. Examples of nitrogen-containing heteroaryl groups include pyridyl groups, pyrimidyl groups, pyrazinyl groups, pyridadinyl groups, and triazyl groups. Examples of donor groups include substituted or unsubstituted amino groups and heterofused ring groups having a structure in which two aryl groups of a diarylamino group are linked to each other. An example of a donor group is the group represented by the following general formula (3). The number of acceptor and donor groups bonded to the aromatic ring is not particularly limited, but it is preferable that there be 1 to 2 acceptor groups and 1 to 5 donor groups. In addition to the acceptor and donor groups exemplified above, substituted or unsubstituted alkyl groups and substituted or unsubstituted aryl groups may also be bonded to the aromatic ring.

[0018] Examples of delayed fluorescence materials that can be used in the present invention include compounds represented by the following general formula (2). General formula (2) [ka]

[0019] In general formula (2), R 21 ~R 25 0 to 1 of these represent a cyano group, R 21 ~R 25 The first 1 to 5 of these represent the group represented by the following general formula (3), R 21 ~R 25 The remainder represents a hydrogen atom or a substituent (however, the substituent referred to here is a cyano group, not the group represented by general formula (3) below). General formula (3) [ka]

[0020] In general formula (3), L 2 represents a single bond or a divalent linking group, R 33 and R 34 Each of the symbols represents an independent hydrogen atom or substituent, and * represents a bond position. L 2 The divalent linking group represented by is preferably a substituted or unsubstituted arylene group, or a substituted or unsubstituted heteroarylene group, more preferably a substituted or unsubstituted arylene group, and even more preferably a substituted or unsubstituted 1,4-phenylene group (with a substituent such as an alkyl group having 1 to 3 carbon atoms). R 33 and R 34Possible substituents include substituted or unsubstituted alkyl groups (e.g., 1-40 carbon atoms), substituted or unsubstituted alkenyl groups (e.g., 1-40 carbon atoms), substituted or unsubstituted aryl groups (e.g., 6-30 carbon atoms), or substituted or unsubstituted heteroaryl groups (e.g., 5-30 carbon atoms). Substituents for alkyl groups, alkenyl groups, aryl groups, and heteroaryl groups include hydroxyl groups, halogen atoms (e.g., fluorine, chlorine, bromine, iodine atoms), alkyl groups (e.g., 1-40 carbon atoms), alkoxy groups (e.g., 1-40 carbon atoms), alkylthio groups (e.g., 1-40 carbon atoms), aryl groups (e.g., 6-30 carbon atoms), aryloxy groups (e.g., 6-30 carbon atoms), arylthio groups (e.g., 6-30 carbon atoms), heteroaryl groups (e.g., 5-30 carbon atoms in the ring skeleton), heteroaryloxy groups (e.g., 5-30 carbon atoms in the ring skeleton), and heteroarylthio groups. Examples of groups include one or more groups selected from the group consisting of oxy groups (e.g., 5-30 atoms in the ring skeleton), acyl groups (e.g., 1-40 carbon atoms), alkenyl groups (e.g., 1-40 carbon atoms), alkynyl groups (e.g., 1-40 carbon atoms), alkoxycarbonyl groups (e.g., 1-40 carbon atoms), aryloxycarbonyl groups (e.g., 1-40 carbon atoms), heteroaryloxycarbonyl groups (e.g., 1-40 carbon atoms), silyl groups (e.g., trialkylsilyl groups with 1-40 carbon atoms), nitro groups, and cyano groups (hereinafter, these groups will be referred to as "substituent group B groups"). R 33 and R 34 These may be linked to each other by single bonds or linking groups to form a cyclic structure. In particular, R 33 and R 34 If the group is an aryl group, it is preferable that they are bonded to each other via single bonds or linking groups to form a cyclic structure. The linking groups referred to here are -O-, -S-, and -N(R 35 )-,-C(R 36 )(R 37 We can list -, -C(=O)-, -O-, -S-, -N(R 35 )-,-C(R 36 )(R 37 )- is preferred, -O-, -S-, -N(R35 )- is more preferable. R 35 ~R 37 Each of these independently represents a hydrogen atom or a substituent. The substituent can be selected from substituent group A above or from substituent group B below, and preferably is one group or a combination of two or more groups selected from the group consisting of alkyl groups having 1 to 10 carbon atoms and aryl groups having 6 to 14 carbon atoms.

[0021] The group represented by general formula (3) is preferably the group represented by general formula (4) below. General formula (4) [ka]

[0022] In general formula (4), L 11 L represents a single bond or a divalent linking group. 11 For an explanation and preferred range, see L above. 2 You can refer to the explanation and preferred range. In general formula (4), R 41 ~R 48 Each of these independently represents a hydrogen atom or a substituent. 41 and R 42 , R 42 and R 43 , R 43 and R 44 , R 44 and R 45 , R 45 and R 46 , R 46 and R 47 , R 47 and R 48These rings may bond to each other to form a cyclic structure. The cyclic structure formed by the bonding may be an aromatic ring or an antilipid ring, and may contain heteroatoms. Furthermore, the cyclic structure may be a fused ring of two or more rings. The heteroatoms here are preferably selected from the group consisting of nitrogen atoms, oxygen atoms, and sulfur atoms. Examples of the cyclic structures formed include benzene rings, naphthalene rings, pyridine rings, pyridazine rings, pyrimidine rings, pyrazine rings, pyrrole rings, imidazole rings, pyrazole rings, imidazoline rings, oxazole rings, isoxazole rings, thiazole rings, isothiazole rings, cyclohexadiene rings, cyclohexene rings, cyclopentaene rings, cycloheptatriene rings, cycloheptadiene rings, cycloheptaene rings, furan rings, thiophene rings, naphthyridine rings, quinoxaline rings, and quinoline rings. For example, a ring formed by the fusion of multiple rings, such as a benzofuran ring, a benzothiophene ring, a phenanthrene ring, or a triphenylene ring, may also be formed. The number of rings included in the group represented by general formula (4) may be selected from the range of 3 to 5, or from the range of 5 to 7. R 41 ~R 48 Possible substituents include the groups of substituent group B listed below, preferably unsubstituted alkyl groups having 1 to 10 carbon atoms, or aryl groups having 6 to 10 carbon atoms that may be substituted with unsubstituted alkyl groups having 1 to 10 carbon atoms. In a preferred embodiment of the present invention, R 41 ~R 110 R is a hydrogen atom or an unsubstituted alkyl group having 1 to 10 carbon atoms. In a preferred embodiment of the present invention, R 41 ~R 110 R is a hydrogen atom or an unsubstituted aryl group having 6 to 10 carbon atoms. In a preferred embodiment of the present invention, R 41 ~R 110 It is all hydrogen atoms.

[0023] The following are preferred compounds that can be used as delayed fluorescence materials. In the structural formulas of the following example compounds, t-Bu represents a tert-butyl group. [ka] JPEG2026076041000006.jpg221170 JPEG2026076041000007.jpg214170 JPEG2026076041000008.jpg228170 JPEG2026076041000009.jpg223170 JPEG2026076041000010.jpg216170 JPEG2026076041000011.jpg226170 JPEG2026076041000012.jpg244170JPEG2026076041000013.jpg225170JPEG202 6076041000014.jpg255170JPEG2026076041000015.jpg254170JPEG20260760410 00016.jpg219170JPEG2026076041000017.jpg209170JPEG2026076041000018.j pg206170JPEG2026076041000019.jpg214170JPEG2026076041000020.jpg101170

[0024] In addition to the materials mentioned above, other known delayed fluorescence materials can be used in appropriate combinations. Furthermore, even unknown delayed fluorescence materials can be used. As delayed fluorescence materials, paragraphs 0008-0048 and 0095-0133 of Publication No. WO2013 / 154064, paragraphs 0007-0047 and 0073-0085 of Publication No. WO2013 / 011954, paragraphs 0007-0033 and 0059-0066 of Publication No. WO2013 / 011955, and paragraphs 0008-007 of Publication No. WO2013 / 081088 Paragraphs 1 and 0118~0133, paragraphs 0009~0046 and 0093~0134 of Japanese Patent Publication No. 2013-256490, paragraphs 0008~0020 and 0038~0040 of Japanese Patent Publication No. 2013-116975, paragraphs 0007~0032 and 0079~0084 of WO2013 / 133359, paragraph 0008~ Paragraphs 0054 and 0101-0121, paragraphs 0007-0041 and 0060-0069 of JP 2014-9352, paragraphs 0008-0048 and 0067-0076 of JP 2014-9224, paragraphs 0013-0025 of JP 2017-119663, paragraphs 0013-0026 of JP 2017-119664, JP 2017- Examples include compounds included in the general formulas described in paragraphs 0012-0025 of Japanese Patent Publication No. 222623, paragraphs 0010-0050 of Japanese Patent Application Publication No. 2017-226838, paragraphs 0012-0043 of Japanese Patent Application Publication No. 2018-100411, and paragraphs 0016-0044 of Japanese Patent Application Publication No. WO2018 / 047853, particularly exemplary compounds that emit delayed fluorescence.Also, Japanese Patent Publication No. 2013-253121, WO2013 / 133359, WO2014 / 034535, WO2014 / 115743, WO2014 / 122895, WO2014 / 126200, WO2014 / 136758, WO2014 / 133121, WO2014 / 136860, WO2014 / 196585, WO2014 / 189122, WO2014 / 168101, WO2015 / 00858 0 publication, WO2014 / 203840 publication, WO2015 / 002213 publication, WO2015 / 016200 publication, WO2015 / 019725 publication, Publications WO2015 / 072470, WO2015 / 108049, WO2015 / 080182, WO2015 / 072537, WO2015 / 080183, JP 2015-129240, WO2015 / 129714, WO2015 / 129715, WO2015 / 133 Light-emitting materials that emit delayed fluorescence, as described in Publication No. 501, WO2015 / 136880, WO2015 / 137244, WO2015 / 137202, WO2015 / 137136, WO2015 / 146541, and WO2015 / 159541, can also be used. The above publications mentioned in this paragraph are incorporated herein by reference as part of this specification.

[0025] It is preferable that the delayed fluorescence material does not contain metal atoms. For example, a compound consisting of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, and sulfur atoms can be selected.

[0026] [Multi-resonance type light-emitting materials] The multi-resonance luminescent material used in the present invention has a multi-resonance fused ring skeleton into which substituents are introduced, and the difference in HOMO energy levels (ΔE) between the multi-resonance luminescent material and the delayed fluorescence material is significant. HOMO) is less than or equal to 0.4 eV. ΔE HOMO By keeping the ΔE below 0.4 eV, it is possible to suppress the trapping of holes injected into the light-emitting layer by the multi-resonance light-emitting material. HOMO ΔE is preferably 0.3 eV or less, more preferably 0.2 eV or less, and even more preferably 0.15 eV or less. HOMO The lower limit may be, for example, 0 eV, for example, 0.05 eV, or for example, 0.10 eV. Furthermore, the HOMO level of the multi-resonance luminescent material is preferably -5.6 eV or lower, but may also be -5.8 eV or lower.

[0027] Furthermore, it is preferable that the multiple resonance luminescent material has a lower excitation singlet energy than the delayed fluorescence material. This allows the excitation singlet energy from the delayed fluorescence material to be efficiently transferred to the multiple resonance luminescent material and utilized for emission in the multiple resonance luminescent material. In a preferred embodiment of the present invention, the maximum component of light emission from the element is light emission from a multi-resonance light-emitting material. The fact that the maximum component of light emission from the element is light emission from a multi-resonance light-emitting material can be confirmed by the fact that, in the emission spectrum of the organic electroluminescent element, the area of ​​the emission peak originating from the multi-resonance light-emitting material is greater than 50% of the total emission peak area.

[0028] The multiple resonance fused ring skeleton constituting the multiple resonance luminescent material has a conjugated π-electron system and two or more complex atoms with different numbers of valence electrons than carbon atoms as constituent atoms of the ring skeleton, and these complex atoms resonate with each other, resulting in a fused ring skeleton that resonates in multiple ways as a whole. The two or more complex atoms included in the multiple resonance fused ring skeleton may be of the same type or different types. Examples of complex atoms include boron, nitrogen, oxygen, sulfur, silicon, and phosphorus atoms. The multiple resonance fused polycyclic structure preferably contains two or more complex atoms selected from the group consisting of boron, nitrogen, oxygen, and sulfur atoms, and more preferably contains two or more complex atoms selected from the group consisting of boron, nitrogen, and oxygen atoms.

[0029] The substituent introduced into the multiple resonance fused ring skeleton may be a donor group or an acceptor group, but an acceptor group is preferred. By introducing an acceptor group into the multiple resonance fused ring skeleton, the HOMO level of the multiple resonance luminescent material is lowered, and hole trapping in the multiple resonance luminescent material can be effectively suppressed. Furthermore, when introducing a donor group (for example, a diphenylamino group or a carbazole-9-yl group) into the multiple resonance fused ring skeleton, it is preferable to further introduce an acceptor group to that donor group. This weakens the electron-donating ability of the substituent and lowers the HOMO level. Hereinafter, "acceptor group" refers to a group with a positive Hammett σm value, and "donor group" refers to a group with a negative Hammett σm value. The σm of the substituent introduced into the multiple resonance fused ring skeleton is preferably 0.12 or higher, more preferably 0.20 or higher, for example 0.30 or higher, for example 0.40 or higher, for example 0.50 or higher. Preferred examples of substituents include halogen atoms, cyano groups, haloalkyl groups (e.g., 1 to 10 carbon atoms), alkoxy groups (e.g., 1 to 10 carbon atoms), and nitrogen-containing teloaryl groups bonded to carbon atoms (e.g., 5 to 30 carbon atoms). In particular, fluorine atoms, cyano groups, trifluoromethyl groups, methoxy groups, pyridyl groups, pyrimidyl groups, pyrazinyl groups, pyridadinyl groups, and triazyl groups are preferred. The number of substituents introduced into the multiple resonance fused ring skeleton may be one or two or more. When there are two or more substituents, they may be identical or different from each other. Furthermore, the positions where substituents are introduced into the multiple resonance fused ring skeleton, in other words, the atoms to which the substituents are bonded among the constituent atoms of the multiple resonance fused ring skeleton, are preferably atoms with a large electron density distribution in the HOMO, and more preferably atoms with large electron density distributions in both the HOMO and LUMO. The electron density distributions of the HOMO and LUMO can be determined by calculation. For the calculation method, please refer to the description in the "Design Method for Organic Electroluminescent Devices" section.

[0030] In a preferred embodiment of the present invention, the multi-resonance fused ring skeleton constituting the multi-resonance luminescent material includes a benzene ring bonded to a boron atom, with substituents bonded to this benzene ring. The substituents are preferably acceptor groups. For preferred ranges and specific examples of acceptor groups, refer to the description of "acceptor groups" above. The bonding position of the substituent on the benzene ring may be the ortho, meta, or para position of the boron atom, but the meta or para position is preferred. By having the substituent bonded to the benzene ring at the meta or ortho position of the boron atom, the HOMO level can be significantly altered compared to the unsubstituted material, and the HOMO level of the multi-resonance luminescent material can be precisely adjusted. Here, the boron atom may, for example, form a complex six-membered ring together with a nitrogen atom, and a fused ring may be formed by the condensation of the benzene ring bonded to the boron atom to this complex six-membered ring.

[0031] In one preferred embodiment of the present invention, the multi-resonance type light-emitting material comprises a compound having a structure represented by the following general formula (1a).

[0032] General formula (1a) [ka]

[0033] In general formula (1a), R 1a ~R 6a Each of these independently represents a hydrogen atom, a deuterium atom, or a substituent, and R 1a ~R 4a At least one of them is a substituent, R 2a and R 3a It is preferable that one of them is a substituent. 1a ~R 4a Preferably, at least one substituent represented is an acceptor group. For preferred ranges and specific examples of acceptor groups, refer to the description of "acceptor groups" above. R 1aand R 2a R 2a and R 3a R 3a and R 4a R 4a and R 5a R 6a and R 1a may be bonded to each other to form a cyclic structure. For the description of the cyclic structure, refer to the description of the cyclic structure formed by bonding R 41 and R 42 etc. to each other in the above general formula (4). A 1a represents a ring structure containing a benzene ring condensed to a hetero 6-membered ring containing a boron atom and a nitrogen atom. The ring structure (ring skeleton) in A 1a may be composed only of a benzene ring condensed to a hetero 6-membered ring, or may be a condensed ring in which another ring is condensed to this benzene ring. Another ring condensed to the benzene ring preferably contains a hetero 6-membered ring containing a boron atom and a nitrogen atom, more preferably has a structure in which a benzene ring is condensed to a hetero 6-membered ring containing a boron atom and a nitrogen atom, and further preferably has a substituent (preferably an acceptor group) bonded to this benzene ring. For the preferable range and specific examples of the acceptor group, refer to the description of the above "acceptor group". The ring structure represented by A 1a constitutes a part of a multi-resonance type condensed ring skeleton, and at least one of the hydrogen atoms bonded to the ring skeleton constituent atoms may be substituted with a deuterium atom or a substituent, and the substituents, the substituent and R 5a the substituent and R 5b may be bonded to each other to form a cyclic structure, and the cyclic structures may be condensed to form a condensed ring.

[0034] In a preferred embodiment of the present invention, the multi-resonance type light-emitting material is composed of a compound having a structure represented by the following general formula (1b). General formula (1b)

Chemical formula

[0035] In general formula (1b), R 1a ~R 6a and R 9a ~R 16a Each of these independently represents a hydrogen atom, a deuterium atom, or a substituent, and R 1a ~R 4a At least one of and R 11a ~R 14a At least one of them is a substituent, R 2a and R 3a One of the two, R 12a and R 13a It is preferable that one of them is a substituent. 1a ~R 4a At least one of and R 11a ~R 14a Preferably, at least one substituent represented is an acceptor group. For preferred ranges and specific examples of acceptor groups, refer to the description of "acceptor groups" above. R 1a and R 2a , R 2a and R 3a , R 3a and R 4a , R 4a and R 5a , R 5a and R 16a , R 16a and R 10a , R 10a and R 11a , R 11a and R 12a , R 12a and R 13a , R 13a and R 14a , R 14a and R 9a , R 9a and R 15a , R 15a and R 6a , R 6a and R 1a These elements may be bonded to each other to form a cyclic structure, and these cyclic structures may be fused to each other to form a fused ring. For an explanation of the cyclic structure, see R in the general formula (4) above. 41 and R 42You can refer to descriptions of annular structures formed by the combination of these elements.

[0036] In one preferred embodiment of the present invention, the multi-resonance type light-emitting material comprises a compound represented by the following general formula (1). General formula (1) [ka]

[0037] In general formula (1), R 1 ~R 15 Each of these independently represents a hydrogen atom, a deuterium atom, or a substituent. 1 ~R 4 At least one of and R 11 ~R 14 At least one of these groups is independently a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group. Hereinafter, substituents selected from the fluorine atom, cyano group, trifluoromethyl group, methoxy group, pyridyl group, pyrimidyl group, pyrazinyl group, pyridadinyl group, and triazyl group will be collectively referred to as "specific acceptor groups." R 1 ~R 4 Of these, there may be one or more specific acceptor groups. 11 ~R 14 Of these, there may be one or more specific acceptor groups. 1 ~R 4 When two or more of them are specific acceptor groups, and R 11 ~R 14 When two or more of these are specific acceptor groups, these specific acceptor groups may be the same or different from each other. 1 ~R 15Of these, those other than the specific acceptor group may be hydrogen atoms, deuterium atoms, or substituents. The substituents may be selected from substituent group A, substituent group B, substituent group C, substituent group D, or substituent group E, for example. In one preferred embodiment of the present invention, R of general formula (1) 1 ~R 4 One of them and R 11 ~R 14 One of them is a specific acceptor group, and the remaining R 1 ~R 15 R is a hydrogen atom or a deuterium atom. In a preferred embodiment of the present invention, R of general formula (1) 2 and R 3 One of the two, R 12 and R 13 One of them is a specific acceptor group. In a more preferred embodiment of the present invention, R of general formula (1) 2 and R 3 One of the two and R 12 and R 13 One of them is a cyano group. In a more preferred embodiment of the present invention, R of general formula (1) 2 and R 3 One of the two, R 12 and R 13 One of them is a cyano group, and the remaining R 1 ~R 15 It is a hydrogen atom or a deuterium atom. Ar 1 and Ar 2 Each of these independently represents a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group. For explanations of substituted or unsubstituted aryl groups and substituted or unsubstituted heteroaryl groups, please refer to the "Definition of Chemical Structure" below.

[0038] The compound represented by general formula (1) is a novel compound. The compound represented by general formula (1) can be synthesized by combining known reactions. For details of the synthesis method, please refer to the synthesis examples described later.

[0039] Specific examples of compounds represented by general formula (1) are given below. However, the compounds that can be used as multi-resonance type light-emitting materials in the present invention should not be interpreted as being limited by these specific examples.

[0040] [ka]

[0041] Examples of multi-resonance luminescent materials that can be used in the present invention include compounds in which an acceptor group is introduced at the meta or para position of the boron atom to a benzene ring fused to a heterosix-membered ring of the following structure, and compounds in which an acceptor group is introduced to a substituent (amino group or diphenylamino group) substituted at the meta or para position of the boron atom to a benzene ring fused to a heterosix-membered ring of the following structure.

[0042] [ka]

[0043] Specific examples of compounds in which an acceptor group has been introduced into the above structure are given below. [ka]

[0044] As a multi-resonance type light-emitting material that can be used in the present invention, compounds in which acceptor groups are introduced into the indolocarbazole skeleton described below can also be mentioned.

[0045] [ka]

[0046] <Host Materials> The light-emitting layer of the organic electroluminescent element of the present invention may consist only of a delayed fluorescence material and a multi-resonance light-emitting material, or it may contain other materials in addition to the delayed fluorescence material and the multi-resonance light-emitting material. An example of such other material is a host material. The host material can be an organic compound with an excitation singlet energy level higher than that of the delayed fluorescence material and the multiple resonance luminescent material. This allows for efficient transfer of the excitation singlet energy generated in the host material to the delayed fluorescence material and the multiple resonance luminescent material, and also allows for the confinement of the excitation singlet energy within the molecules of the multiple resonance luminescent material, enabling efficient emission from the multiple resonance luminescent material. Furthermore, it is preferable that the host material has a lower HOMO level than the delayed fluorescence material, and more preferably, a lower HOMO level than the delayed fluorescence material and a higher LUMO level. This allows for efficient transfer of holes in the HOMO level of the host material to the HOMO level of the delayed fluorescence material. Additionally, because the LUMO level of the host material is higher than that of the delayed fluorescence material, electrons in the LUMO level of the host material can be efficiently transferred to the LUMO level of the delayed fluorescence material. The host material is preferably an organic compound that has hole transport ability and electron transport ability, prevents the emission from becoming longer wavelengths, and has a high glass transition temperature. In a preferred embodiment of the present invention, the host material is selected from compounds that do not emit delayed fluorescence. The emission from the host material is preferably less than 1% of the emission from the organic light-emitting element of the present invention, more preferably less than 0.1%, and may be, for example, less than 0.01% or below the detection limit. The host material preferably does not contain metal atoms. For example, a compound consisting of atoms selected from the group consisting of carbon atoms, hydrogen atoms, nitrogen atoms, oxygen atoms, and sulfur atoms can be selected as the host material. The following are some preferred compounds that can be used as host materials.

[0047] [ka] JPEG2026076041000029.jpg206170JPEG2026076041000030.jpg168170

[0048] [Proportion of each material constituting the luminescent layer] The concentration of the multi-resonance type light-emitting material in the light-emitting layer can be 0.1% or more by weight, 1% or more by weight, 30% or less by weight, 20% or less by weight, or 10% or less by weight, relative to the total amount of materials constituting the light-emitting layer. When the light-emitting layer contains a host material, it is preferable that the concentration of the host material is higher than the concentration of the delayed fluorescence material, and the concentration of the delayed fluorescence material is higher than the concentration of the multi-resonance light-emitting material, that is, that the relationship "concentration of multi-resonance light-emitting material < concentration of delayed fluorescence material < concentration of host material" is satisfied. Furthermore, it is preferable that the concentration of the delayed fluorescence material in the light-emitting layer be less than 50% by weight of the total amount of the host material, delayed fluorescence material, and multi-resonance light-emitting material, for example, less than 40% by weight, less than 30% by weight, less than 20% by weight, or less than 10% by weight. Furthermore, it is preferable that the concentration of the delayed fluorescence material be 0.1% by weight or more, for example, more than 1% by weight or more than 3% by weight.

[0049] Definition of chemical structure In this specification, "alkyl group" may be linear, branched, or cyclic. Furthermore, two or more of the linear, cyclic, and branched portions may be mixed. The number of carbon atoms in an alkyl group can be, for example, 1 or more, 2 or more, or 4 or more. Also, the number of carbon atoms can be 30 or less, 20 or less, 10 or less, 6 or less, or 4 or less. Specific examples of alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, tert-butyl group, n-pentyl group, isopentyl group, n-hexyl group, isohexyl group, 2-ethylhexyl group, n-heptyl group, isoheptyl group, n-octyl group, isooctyl group, n-nonyl group, isononyl group, n-decanyl group, isodecanyl group, cyclopentyl group, cyclohexyl group, and cycloheptyl group. In this specification, the "alkoxy group" may be linear, branched, or cyclic. Furthermore, two or more of the linear, cyclic, and branched portions may be mixed. The number of carbon atoms in the alkoxy group can be, for example, 1 or more, 2 or more, or 4 or more. Alternatively, the number of carbon atoms can be 30 or less, 20 or less, 10 or less, 6 or less, or 4 or less. Specific examples of alkoxy groups include those having an alkyl group bonded to oxygen, as listed above as a specific example of an "alkyl group." For example, alkoxy groups having a structure in which a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, or tert-butyl group bonded to oxygen are, respectively, methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, and tert-butoxy group. In this specification, the "aryl group" may consist of a monocyclic aromatic ring, a fused ring formed by the fusion of two or more aromatic rings, or a linked ring formed by the linkage of two or more aromatic rings. When two or more aromatic rings are linked, they may be linked in a linear chain or in a branched chain. The number of carbon atoms in the aromatic ring constituting the aryl group is preferably 6 to 22, more preferably 6 to 18, even more preferably 6 to 14, and even more preferably 6 to 10. Specific examples of aryl groups include the phenyl group, the naphthalenyl group, and the biphenyl group. In this specification, a "heteroaryl group" may consist of a monocycle or a fused ring formed by the fusion of one or more heterocycles with an aromatic ring or a heterocycle. The heterocycle constituting the heteroaryl group preferably has 3 to 40 carbon atoms, more preferably 5 to 22, even more preferably 5 to 18, even more preferably 5 to 14, and particularly preferably 5 to 10 carbon atoms. Examples of heteroatoms constituting the heterocycle include nitrogen atoms, oxygen atoms, and sulfur atoms. Specific examples of heterocycles include pyridine rings, pyridazine rings, pyrimidine rings, triazole rings, and benzotriazole rings.

[0050] In this specification, "substituent group A" refers to a hydroxyl group, halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom), alkyl group (e.g., C1-40), alkoxy group (e.g., C1-40), alkylthio group (e.g., C1-40), aryl group (e.g., C6-30), aryloxy group (e.g., C6-30), arylthio group (e.g., C6-30), heteroaryl group (e.g., C5-30), heteroaryloxy group (e.g., C5-30), and This refers to one or more groups selected from the group consisting of teloarylthio groups (e.g., 5-30 ring skeleton atoms), acyl groups (e.g., 1-40 carbon atoms), alkenyl groups (e.g., 1-40 carbon atoms), alkynyl groups (e.g., 1-40 carbon atoms), alkoxycarbonyl groups (e.g., 1-40 carbon atoms), aryloxycarbonyl groups (e.g., 1-40 carbon atoms), heteroaryloxycarbonyl groups (e.g., 1-40 carbon atoms), silyl groups (e.g., trialkylsilyl groups with 1-40 carbon atoms), and nitro groups. In this specification, "substituent group B" means one or more groups selected from the group consisting of alkyl groups (e.g., 1 to 40 carbon atoms), alkoxy groups (e.g., 1 to 40 carbon atoms), aryl groups (e.g., 6 to 30 carbon atoms), aryloxy groups (e.g., 6 to 30 carbon atoms), heteroaryl groups (e.g., 5 to 30 atoms in the ring skeleton), heteroaryloxy groups (e.g., 5 to 30 atoms in the ring skeleton), and diarylaminoamino groups (e.g., 0 to 20 carbon atoms). In this specification, "substituent group C" means one or more groups selected from the group consisting of alkyl groups (e.g., 1 to 20 carbon atoms), aryl groups (e.g., 6 to 22 carbon atoms), heteroaryl groups (e.g., 5 to 20 atoms in the ring skeleton), and diarylamino groups (e.g., 12 to 20 carbon atoms). In this specification, "substituent group D" means one or more groups selected from the group consisting of alkyl groups (e.g., 1 to 20 carbon atoms), aryl groups (e.g., 6 to 22 carbon atoms), and heteroaryl groups (e.g., 5 to 20 atoms in the ring skeleton). In this specification, "substituent group E" means one group or a combination of two or more groups selected from the group consisting of alkyl groups (e.g., C1 to C20) and aryl groups (e.g., C6 to C22). In this specification, "substituent group A" refers to a hydroxyl group, halogen atom (e.g., fluorine atom, chlorine atom, bromine atom, iodine atom), alkyl group (e.g., C1-40), alkoxy group (e.g., C1-40), alkylthio group (e.g., C1-40), aryl group (e.g., C6-30), aryloxy group (e.g., C6-30), arylthio group (e.g., C6-30), heteroaryl group (e.g., C5-30), heteroaryloxy group (e.g., C5-30), and This refers to one or more groups selected from the group consisting of teloarylthio groups (e.g., 5-30 ring skeleton atoms), acyl groups (e.g., 1-40 carbon atoms), alkenyl groups (e.g., 1-40 carbon atoms), alkynyl groups (e.g., 1-40 carbon atoms), alkoxycarbonyl groups (e.g., 1-40 carbon atoms), aryloxycarbonyl groups (e.g., 1-40 carbon atoms), heteroaryloxycarbonyl groups (e.g., 1-40 carbon atoms), silyl groups (e.g., trialkylsilyl groups with 1-40 carbon atoms), and nitro groups. In this specification, when a substituent is described as "substituent" or "substituted or unsubstituted," it may be selected from, for example, substituent group A, substituent group B, substituent group C, substituent group D, or substituent group E.

[0051] Method for measuring the HOMO and LUMO levels of compounds In this invention, the energy levels of the HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) are determined by atmospheric photoelectron spectroscopy. Measurements using atmospheric photoelectron spectroscopy can be performed, for example, using the AC-3 manufactured by RIKEN Keiki Co., Ltd.

[0052] Method for measuring the excitation energy of compounds In the present invention, the lowest excitation singlet energy (E) of the compound S1 ) and the lowest excited triplet energy (E T1 ) is the value obtained by the following procedure: ΔE ST is E S1 -E T1 This value was obtained by calculation. (1) Lowest excitation singlet energy (E S1 ) A thin film or toluene solution of the compound to be measured (concentration 10%) -5 Prepare a sample (mol / L). Measure the fluorescence spectrum of this sample at room temperature (300K). The fluorescence spectrum has emission on the vertical axis and wavelength on the horizontal axis. Draw a tangent to the rising edge of the short-wave side of the emission spectrum, and determine the wavelength value λedge [nm] at the intersection of this tangent and the horizontal axis. Convert this wavelength value to an energy value using the following conversion formula: E S1 Let's assume that. Conversion formula: E S1 [eV]=1239.85 / λedge In the examples described below, the emission spectra were measured using an LED light source (Thorlabs, M300L4) as the excitation light source and a detector (Hamamatsu Photonics, PMA-12 multi-channel spectrometer C10027-01). (2) Lowest excited triplet energy (E T1 ) Lowest excitation singlet energy (E S1 The same sample used in the measurement is cooled to 77[K] with liquid nitrogen, and excitation light (300 nm) is irradiated onto the phosphorescence measurement sample. Phosphorescence is measured using a detector. The emission from 100 milliseconds after excitation light irradiation is taken as the phosphorescence spectrum. A tangent line is drawn to the rising edge of the short-wavelength side of this phosphorescence spectrum, and the wavelength value λedge[nm] at the intersection of this tangent line and the horizontal axis is determined. This wavelength value is converted to an energy value using the following conversion formula E T1 Let's assume that. Conversion formula: E T1 [eV]=1239.85 / λedge The tangent to the rise of the phosphorescence spectrum on the short-wavelength side is drawn as follows: When moving along the spectral curve from the short-wavelength side of the phosphorescence spectrum to the shortest wavelength maximum value of the spectrum, consider the tangent at each point on the curve toward the long-wavelength side. The slope of this tangent increases as the curve rises (i.e., as the vertical axis increases). The tangent drawn at the point where this slope value is maximum is taken as the tangent to the rise of the phosphorescence spectrum on the short-wavelength side. Furthermore, maxima with peak intensity less than 10% of the maximum peak intensity of the spectrum are not included in the shortest wavelength maxima mentioned above. Instead, the tangent line drawn at the point closest to the shortest wavelength maxima, where the slope value is at its maximum, is considered the tangent line to the rising edge of the phosphorescence spectrum on the short wavelength side.

[0053] [Layer structure of organic electroluminescent elements] An organic electroluminescent element has a structure comprising at least an anode, a cathode, and an organic layer formed between the anode and the cathode. The organic layer has at least an emissive layer. The emissive layer is an organic layer containing a multi-resonance emissive material and a delayed fluorescence material that satisfy predetermined conditions, and for a description thereof, please refer to the descriptions in the respective sections above. The organic layer may consist only of the emissive layer, or it may have one or more organic layers in addition to the emissive layer. Examples of such other organic layers include hole transport layers, hole injection layers, electron barrier layers, electron injection layers, electron transport layers, and exciton barrier layers. The hole transport layer may be a hole injection transport layer having a hole injection function, and the electron transport layer may be an electron injection transport layer having an electron injection function. The following describes each component of the organic electroluminescent element and each layer other than the light-emitting layer.

[0054] Base material: In some embodiments, the organic electroluminescent element of the present invention is held by a substrate, which is not particularly limited and may be any of the materials commonly used in organic electroluminescent elements, such as glass, transparent plastic, quartz, and silicon.

[0055] anode: In some embodiments, the anode of an organic electroluminescent apparatus is manufactured from a metal, alloy, conductive compound, or a combination thereof. In some embodiments, the metal, alloy, or conductive compound has a high work function (4 eV or more). In some embodiments, the metal is Au. In some embodiments, the conductive transparent material is selected from CuI, indium tin oxide (ITO), SnO2, and ZnO. In some embodiments, an amorphous material capable of forming a transparent conductive film, such as IDIXO (In2O3-ZnO), is used. In some embodiments, the anode is a thin film. In some embodiments, the thin film is manufactured by vapor deposition or sputtering. In some embodiments, the film is patterned by photolithography. In some embodiments, if the pattern does not need to be highly precise (e.g., about 100 μm or more), the pattern may be formed using a mask with a shape suitable for vapor deposition or sputtering onto the electrode material. In some embodiments, when a coating material such as an organic conductive compound can be applied, wet film formation methods such as printing or coating methods are used. In some embodiments, when synchrotron radiation passes through the anode, the anode has a transmittance of more than 10%, and the anode has a sheet resistance of several hundred ohms or less per unit area. In some embodiments, the thickness of the anode is 10 to 1,000 nm. In some embodiments, the thickness of the anode is 10 to 200 nm. In some embodiments, the thickness of the anode varies depending on the material used.

[0056] cathode: In some embodiments, the cathode is made of an electrode material such as a metal with a low work function (4 eV or less) (referred to as an electron-injection metal), an alloy, a conductive compound, or a combination thereof. In some embodiments, the electrode material is selected from sodium, sodium-potassium alloy, magnesium, lithium, magnesium-copper mixture, magnesium-silver mixture, magnesium-aluminum mixture, magnesium-indium mixture, aluminum-aluminum oxide (Al2O3) mixture, indium, lithium-aluminum mixture, and rare earth elements. In some embodiments, a mixture of the electron-injection metal and a second metal that is a stable metal having a higher work function than the electron-injection metal is used. In some embodiments, the mixture is selected from magnesium-silver mixture, magnesium-aluminum mixture, magnesium-indium mixture, aluminum-aluminum oxide (Al2O3) mixture, lithium-aluminum mixture, and aluminum. In some embodiments, the mixture improves electron-injection properties and resistance to oxidation. In some embodiments, the cathode is manufactured by forming the electrode material as a thin film by vapor deposition or sputtering. In some embodiments, the cathode has a sheet resistance of several hundred ohms or less per unit area. In some embodiments, the thickness of the cathode is 10 nm to 5 μm. In some embodiments, the thickness of the cathode is 50 to 200 nm. In some embodiments, either the anode or cathode of the organic electroluminescent element is transparent or translucent in order to transmit synchrotron radiation. In some embodiments, a transparent or translucent electroluminescent element enhances the light radiance. In some embodiments, a transparent or translucent cathode is formed by forming the cathode with respect to the conductive transparent material described above. In some embodiments, the element includes an anode and a cathode, both of which are transparent or translucent.

[0057] Injection layer: The injection layer is a layer between the electrode and the organic layer. In some embodiments, the injection layer reduces the driving voltage and enhances the light radiance. In some embodiments, the injection layer includes a hole injection layer and an electron injection layer. The injection layer can be located between the anode and the light-emitting layer or hole transport layer, and between the cathode and the light-emitting layer or electron transport layer. In some embodiments, an injection layer is present. In some embodiments, an injection layer is absent. The following are examples of preferred compounds that can be used as hole injection materials.

[0058] [ka]

[0059] Next, we will list some examples of preferred compounds that can be used as electron injection materials. [ka]

[0060] Barrier layer: A barrier layer is a layer that can prevent charges (electrons or holes) and / or excitons present in the light-emitting layer from diffusing to the outside of the light-emitting layer. In some embodiments, an electron barrier layer is located between the light-emitting layer and the hole transport layer, preventing electrons from passing through the light-emitting layer to the hole transport layer. In some embodiments, a hole barrier layer is located between the light-emitting layer and the electron transport layer, preventing holes from passing through the light-emitting layer to the electron transport layer. In some embodiments, a barrier layer prevents excitons from diffusing to the outside of the light-emitting layer. In some embodiments, the electron barrier layer and the hole barrier layer constitute an exciton barrier layer. As used herein, the terms “electron barrier layer” or “exciton barrier layer” include layers that have both the functions of an electron barrier layer and an exciton barrier layer.

[0061] Hole barrier layer: The hole barrier layer functions as an electron transport layer. In some embodiments, the hole barrier layer prevents holes from reaching the electron transport layer during electron transport. In some embodiments, the hole barrier layer increases the probability of electron-hole recombination in the light-emitting layer. The material used for the hole barrier layer may be the same material described above for the electron transport layer. The following are examples of preferred compounds that can be used in the hole barrier layer.

[0062] [ka]

[0063] Electron barrier layer: The electron barrier layer transports holes. In some embodiments, the electron barrier layer prevents electrons from reaching the hole transport layer during hole transport. In some embodiments, the electron barrier layer increases the probability of electron-hole recombination in the light-emitting layer. The material used for the electron barrier layer may be the same material described above for the hole transport layer. The following are specific examples of preferred compounds that can be used as electron barrier materials.

[0064] [ka] JPEG2026076041000035.jpg45170

[0065] Exciton barrier layer: The exciton barrier layer prevents excitons generated through the recombination of holes and electrons in the light-emitting layer from diffusing to the charge transport layer. In some embodiments, the exciton barrier layer enables effective confinement of excitons in the light-emitting layer. In some embodiments, the optical emission efficiency of the device is improved. In some embodiments, the exciton barrier layer may be adjacent to only one side of the light-emitting layer, either the anode side or the cathode side, or one exciton barrier layer may be adjacent to the anode side of the light-emitting layer and another exciton barrier layer may be adjacent to the cathode side of the light-emitting layer. In some embodiments, when the exciton barrier layer is on the anode side, it may be located between the hole transport layer and the light-emitting layer and adjacent to the light-emitting layer. In some embodiments, when the exciton barrier layer is on the cathode side, it may be located between the light-emitting layer and the cathode and adjacent to the light-emitting layer. In some embodiments, a hole injection layer, electron barrier layer, or similar layer is located between the anode and the exciton barrier layer adjacent to the light-emitting layer on the anode side. In some embodiments, a hole injection layer, electron barrier layer, hole barrier layer, or similar layer is located between the cathode and an exciton barrier layer adjacent to the cathode-side light-emitting layer. In some embodiments, the exciton barrier layer includes an excitation singlet energy and an excitation triplet energy, at least one of which is higher than the excitation singlet energy and excitation triplet energy of the light-emitting material, respectively.

[0066] Hole transport layer: The hole transport layer comprises a hole transport material. In some embodiments, the hole transport layer is a single layer. In some embodiments, the hole transport layer has multiple layers. In some embodiments, the hole transport material has one of the following properties: hole injection or transport properties and electron barrier properties. In some embodiments, the hole transport material is an organic material. In some embodiments, the hole transport material is an inorganic material. Examples of known hole transport materials that can be used in the present invention include, but are not limited to, triazole derivatives, oxadiazole derivatives, imidazole derivatives, carbazole derivatives, indrocarbazole derivatives, polyarylalkane derivatives, pyrazoline derivatives, pyrazolone derivatives, phenylenediamine derivatives, allylamine derivatives, aminosubstituted chalcone derivatives, oxazole derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline copolymers and conductive polymer oligomers (especially thiophene oligomers), or combinations thereof. In some embodiments, the hole transport material is selected from porphyrin compounds, aromatic tertiary amine compounds and styrylamine compounds. In some embodiments, the hole transport material is an aromatic tertiary amine compound. Specific examples of preferred compounds that can be used as hole transport materials are given below.

[0067] [ka]

[0068] Electron transport layer: The electron transport layer comprises an electron transport material. In some embodiments, the electron transport layer is a single layer. In some embodiments, the electron transport layer has multiple layers. In some embodiments, the electron transport material only needs to have the function of transporting electrons injected from the cathode to the light-emitting layer. In some embodiments, the electron transport material also functions as a hole barrier material. Examples of electron transport layers that can be used in the present invention include, but are not limited to, nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyrandioxide derivatives, carbodiimides, fluorenylidene methane derivatives, anthraquinodimethane, anthrone derivatives, oxadiazole derivatives, azole derivatives, azine derivatives or combinations thereof, or polymers thereof. In some embodiments, the electron transport material is a thiadiazole inducer or a quinoxaline derivative. In some embodiments, the electron transport material is a polymer material. Specific examples of preferred compounds that can be used as electron transport materials are listed below.

[0069] [ka]

[0070] Furthermore, examples of preferred compounds that can be added to each organic layer are given. For example, they can be added as stabilizing materials.

[0071] [ka]

[0072] While specific examples of preferred materials that can be used in organic electroluminescent elements have been provided, the materials that can be used in the present invention are not limited to the following exemplary compounds. Furthermore, even compounds exemplified as materials with specific functions can be repurposed as materials with other functions. <Design Method for Organic Electroluminescent Devices> Next, the design method for the organic electroluminescent element of the present invention will be described. The present invention relates to a method for designing an organic electroluminescent element comprising a host material, a delayed fluorescence material, and a multi-resonance type light-emitting material in a light-emitting layer. The method is characterized by selecting substituents present in the multi-resonance type light-emitting material to determine a structure in which the difference in HOMO energy levels between the multi-resonance type light-emitting material and the delayed fluorescence material is 0.4 eV or less, and then designing an organic electroluminescent element comprising the multi-resonance type light-emitting material, host material, and delayed fluorescence material having that structure. For a description of the host material, delayed fluorescence material, multi-resonance type light-emitting material, and layer configuration of the organic electroluminescent element used in this invention, please refer to the description in the "Organic Electroluminescent Element" section above.

[0073] In the design method of the present invention, first, a specific multi-resonance luminescent material and a specific delayed fluorescence material are selected. In the following description, the specific multi-resonance luminescent material and the specific delayed fluorescence material selected here may be referred to as the "specific multi-resonance luminescent material" and the "specific delayed fluorescence material," respectively. The specific delayed fluorescence material is preferably a delayed fluorescence material with a HOMO level of -5.9 eV or lower. Next, from among the substituents present in the specific multiple resonance luminescent material, the difference in energy levels of the HOMO of the multiple resonance luminescent material and the delayed fluorescence material (ΔE HOMOA substituent is selected to adjust the electron density distribution (LOMO). Preferably, the substituent selected is one that bonds to an atom with a large electron density distribution for the HOMO, and preferably one that bonds to an atom with large electron density distributions for both the HOMO and LUMO. By controlling such substituents, the HOMO level of a multi-resonance luminescent material can be precisely adjusted. The electron density distributions for the HOMO and LUMO can be determined, for example, at the PEB0 / 6-31G(d,p) level using density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. This calculation can be performed, for example, using Gaussian 16 program package 32. For example, if a particular multi-resonance luminescent material contains a benzene ring bonded to a boron atom, a substituent bonded to the benzene ring at the meta position of the boron atom or a substituent bonded to the benzene ring at the para position of the boron atom can be selected.

[0074] Next, the structure of the selected substituent is changed, and the ΔE of the modified multi-resonance luminescent material and the specific delayed fluorescence material is changed. HOMO Find ΔE HOMO The structure of a multi-resonance luminescent material is determined so that ΔE is 0.4 eV or less. HOMO The LUMO level can be determined and calculated by measuring the HOMO level of the multi-resonance luminescent material and the HOMO level of the delayed fluorescence material, or by calculations such as DFT calculations. The HOMO and LUMO levels can be measured using atmospheric photoelectron spectroscopy (such as the AC-3 manufactured by RIKEN Keiki Co., Ltd.). When changing the structure of the selected substituent, the substituent to be changed is preferably one in which the distance between the bonded atom of the substituent and the atom furthest from that bonded atom is 7 angstroms or less, and more preferably an acceptor group selected from a fluorine atom, cyano group, trifluoromethyl group, methoxy group, pyridyl group, pyrimidyl group, pyrazinyl group, pyridadinyl group, and triazyl group. This results in ΔE HOMO It can be easily adjusted to 0.4 eV or less. Also, the structure of the multi-resonance luminescent material to be determined is ΔE HOMOIt is preferable that the structure is such that the voltage is 0.4 eV or less, and the HOMO level of the multi-resonance luminescent material is -5.6 eV or less.

[0075] Next, an organic electroluminescent element is designed, comprising a multi-resonance luminescent material having the determined structure, a host material, and a specific delayed fluorescence material. For details on the configuration of the organic electroluminescent element, please refer to the description in the "Organic Electroluminescent Element" section. The organic electroluminescent element designed using the design method of the present invention has ΔE HOMO Because it is designed to have a voltage of 0.4 eV or less, hole trapping in multi-resonance luminescent materials is suppressed. As a result, roll-off is suppressed, enabling high efficiency and high operational stability.

[0076] <Method for improving multi-resonance luminescent materials> The multi-resonance type light-emitting material improved in this invention is a multi-resonance type light-emitting material used in an organic electroluminescent element that includes a host material, a delayed fluorescence material, and a multi-resonance type light-emitting material in its light-emitting layer. The present invention provides a method for improving a multi-resonance luminescent material, characterized by finding a multi-resonance luminescent material having a structure in which the energy level difference with that of the HOMO of a delayed fluorescence material is 0.4 eV or less, by performing at least one step of calculating the difference between the structure and the energy level difference with that of the HOMO of a delayed fluorescence material, assuming a structure in which hydrogen atoms or groups present in the multi-resonance luminescent material before improvement have been substituted. For a description of the host material, delayed fluorescence material, multi-resonance type light-emitting material, and layer configuration of the organic electroluminescent element used in this invention, please refer to the description in the "Organic Electroluminescent Element" section above.

[0077] In the improved method of the present invention, first, a multi-resonance luminescent material to be improved and a delayed fluorescence material to be combined with the improved multi-resonance luminescent material are selected. Hereinafter, the multi-resonance luminescent material to be improved will be referred to as the "target multi-resonance luminescent material," and the delayed fluorescence material to be combined with the improved multi-resonance luminescent material will be referred to as the "specific delayed fluorescence material." Furthermore, the assumed multi-resonance luminescent material, in which a hydrogen atom or group described later is assumed to be substituted with a substituent, may be referred to as the "virtual multi-resonance luminescent material." The specific delayed fluorescence material is preferably a delayed fluorescence material with a HOMO level of -5.9 eV or lower.

[0078] Next, from the structure of the pre-improvement multi-resonance luminescent material (target multi-resonance luminescent material), a hydrogen atom or group that is assumed to have been substituted with a substituent is selected. Preferably, the hydrogen atom or group selected here is bonded to an atom with a large electron density distribution in the HOMO, and more preferably, it is bonded to an atom with both a large electron density distribution in the HOMO and a large electron density distribution in the LUMO. By substituting such a hydrogen atom or group with a substituent, the HOMO level of the multi-resonance luminescent material can be precisely adjusted. For the calculation method of the electron density distribution in the HOMO and the electron density distribution in the LUMO, refer to the description in the "Design Method for Organic Electroluminescent Devices" section above. For example, if the target multi-resonance luminescent material contains a benzene ring bonded to a boron atom, a hydrogen atom or group bonded to the benzene ring at the meta position of the boron atom or a hydrogen atom or group bonded to the benzene ring at the para position of the boron atom can be selected. Here, the substituent assumed to replace the hydrogen atom or group is preferably a substituent in which the distance between the bonded atom and the atom furthest from that bonded atom is 7 angstroms or less, and more preferably an acceptor group selected from a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, and a triazyl group.

[0079] Next, the difference in HOMO levels (ΔE) between a multi-resonance luminescent material (virtual multi-resonance luminescent material) assumed to have hydrogen atoms or groups substituted with substituents and a specific delayed fluorescence material. HOMO The calculation method is not particularly limited, but DFT calculation is one example. In the present invention, the above series of steps (a step of assuming that selected hydrogen atoms or groups are substituted with substituents, and the ΔE of a virtual multiple resonance luminescent material and a specific delayed fluorescence material) is calculated. HOMO By performing the process of calculating ΔE at least once, HOMO We will find a multi-resonance luminescent material (improved multi-resonance luminescent material) having a structure in which ΔE is 0.4 eV or less. HOMO It is preferable to find a multi-resonance type light-emitting material having a structure such that the voltage is 0.4 eV or less and the HOMO level of the multi-resonance light-emitting material is -5.6 eV or less. By combining a multi-resonance type light-emitting material improved by the method of the present invention with a host material and a specific delayed fluorescence material to construct the light-emitting layer of an organic electroluminescent element, roll-off can be suppressed, and an organic electroluminescent element with excellent efficiency and operational stability can be realized.

[0080] Furthermore, the present invention can take the following forms. In other words, in one aspect of the present invention, the multi-resonance type light-emitting material is improved while keeping the variation in the full width at half maximum of the element's maximum emission within a range of plus or minus 5 nm. In one aspect of the present invention, the multi-resonance type light-emitting material is improved while keeping the variation in the element's maximum emission wavelength within a range of plus or minus 15 nm. In one aspect of the present invention, the maximum emission wavelength of the element is 490 nm or less. In one aspect of the present invention, the multi-resonance type light-emitting material is improved while keeping the variation in the element's emission quantum yield within a range of plus or minus 10%. In one aspect of the present invention, hole trapping by the multi-resonance type light-emitting material in the element is suppressed.

[0081] <Program> Next, the program of the present invention will be described. The program of the present invention is a program for implementing the method for improving the multi-resonance type light-emitting material according to the above invention. For details on the method for improving the multi-resonance type light-emitting material implemented by the program of the present invention, please refer to the description in the "Method for Improving the Multi-Resonance Type Light-Emitting Material" section above. The program of the present invention may be recorded on a recording medium in a computer-readable manner. The recording medium may be a magnetic recording medium, an optical recording medium, or a semiconductor memory. Specific examples include flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs (Read Only Memory), CD-Rs, DVD-ROMs, magnetic tapes, non-volatile memory cards, ROMs, EEPROMs, silicon disks, and the like. [Examples]

[0082] The features of the present invention will be further described in detail below with reference to synthesis examples and embodiments. The materials, processing content, processing procedures, etc. shown below can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. The device lifetime was measured with an initial brightness of 1000 cd / m². 2 Under constant current density driving conditions, measurements were performed using a luminance meter (Topcon SR-3AR). Transient EL characteristics were measured using a photomultiplier tube (PMT) module (Hamamatsu Photonics H10721-01) and a current amplifier (Femto DHPCA-100). Other element characteristics were evaluated using a source meter (Keysight B2911A) and a luminance meter (Konica Minolta CS-2000). In this embodiment, unless otherwise specified, thin films of each compound (single films and mixed films) were measured under a vacuum of 10°C. -5 The film was deposited using vacuum deposition as Pa.

[0083] (Synthesis Example 1) Synthesis of Compound 1 [ka]

[0084] 3,6-dimethyl-9H-carbazole (3.9 g, 20 mmol), 1,3-dibromo-5-fluorobenzene (5.6 g, 22 mmol), and cesium carbonate (7.2 g, 22 mmol) were dissolved in N,N-dimethylformamide (150 mL) under a nitrogen atmosphere and stirred at 150 °C for 24 hours. After the reaction mixture was cooled to room temperature, water (300 mL) was added and the mixture was filtered to recover a gray solid (crude product). This crude product was purified by silica gel column chromatography using a mixed solvent of petroleum ether:dichloromethane = 10:1 as the eluent, and dried under vacuum to obtain a white solid intermediate C1 (yield: 7.3 g, yield: 85%). 1 H NMR (400 MHz, CDCl3) δ 7.91-7.85 (m, 2H), 7.72 (t, J = 1.7 Hz, 1H), 7.68 (d, J = 1.7 Hz, 2H), 7.31 (d, J = 8.3 Hz, 2H), 7.23 (dd, J = 8.4, 1.7 Hz, 2H), 2.54 (s, 6H). 13 C NMR (101 MHz, CDCl3) δ 140.58, 138.65, 132.44, 130.07, 128.42, 127.43, 123.84, 123.65, 120.38, 109.21, 21.39. MS (MALDI-TOF): Calcd for C 20 H 15 Br2N: 429.16; Found: 428.35.

[0085] [ka]

[0086] The solution of intermediate C1 (4.3 g, 10 mmol), 2,4,6-trimethylaniline (3.0 g, 22 mmol), tris(dibenzylideneacetone)dipalladium(0) (549 mg, 0.6 mmol), 1,1'-bis(diphenylphosphino)ferrocene (665 mg, 1.2 mmol), and sodium tert-butoxide (2.2 g, 22 mmol) dissolved in toluene (80 mL) was degassed and heated at 100 °C for 24 hours. After cooling the reaction mixture, it was filtered through silica gel, and the filtrate was concentrated under vacuum to obtain the crude product. This crude product was purified by silica gel column chromatography using a mixed solvent of petroleum ether:dichloromethane = 4:1 as the eluent, and dried under vacuum to obtain the white solid intermediate C2 (yield: 4.8 g, yield: 90%). 1 H NMR (400 MHz, CDCl3) δ 7.85-7.79 (m, 2H), 7.30 (d, J = 8.3 Hz, 2H), 7.16 (dd, J = 8.4, 1.7 Hz, 2H), 6.89 (s, 4H), 5.95 (d, J = 2.0 Hz, 2H), 5.80 (t, J = 2.1 Hz, 1H), 5.07 (s, 2H), 2.51 (s, 6H), 2.25 (s, 18H). 13 C NMR (101 MHz, CDCl3) δ 149.02, 139.87, 139.31, 136.09, 135.59, 135.37, 129.20, 128.35, 126.73, 123.02, 119.87, 109.94, 101.94, 97.26, 21.37, 20.87, 18.33. MS (MALDI-TOF): Calcd for C 38 H 39 N3: 537.75; Found: 537.58.

[0087] [ka]

[0088] The solution, prepared by dissolving intermediate C2 (1.1 g, 2 mmol), 1-chloro-4-iodobenzene (1.0 mg, 4.4 mmol), palladium(II) acetate (45 mg, 0.2 mmol), tri-tert-butylphosphine (0.1 mL, 0.4 mmol), and sodium tert-butoxide (431 mg, 4.4 mmol) in toluene, was degassed and heated at 80°C for 12 hours. After cooling the reaction mixture to room temperature, it was filtered through silica gel, and the filtrate was concentrated under vacuum to obtain the crude product. This crude product was purified by silica gel column chromatography using a mixed solvent of petroleum ether:dichloromethane = 6:1 as the eluent, and dried under vacuum to obtain the white solid intermediate C3 (yield: 1.2 g, yield: 81%). 1 H NMR (400 MHz, CDCl3) δ 7.80 (q, J = 1.1 Hz, 2H), 7.13-7.08 (m, 8H), 6.94-6.90 (m, 4H), 6.88 (s, 4H), 6.75 (t, J = 2.1 Hz, 1H), 6.49 (d, J = 2.1 Hz, 2H), 2.51-2.48 (m, 6H), 2.28 (s, 6H), 2.01 (s, 12H). 13 C NMR (101 MHz, CDCl3) δ 147.60, 144.09, 139.70, 139.32, 138.70, 137.25, 137.06, 130.08, 129.04, 128.93, 126.91, 125.67, 123.29, 120.62, 120.05, 110.23, 109.48, 108.90, 21.33, 20.98, 18.34. MS (MALDI-TOF): Calcd for C 50 H 45 Cl2N3: 758.83; Found: 758.14.

[0089] [ka]

[0090] To a solution of intermediate C3 (1.1 g, 1.5 mmol) in o-dichlorobenzene (20 mL), boron tribromide (2.9 mL, 30 mmol) was added at 0°C under a nitrogen atmosphere, and the mixture was heated at 180°C for 24 hours. After the reaction mixture was cooled to room temperature, phosphate buffer (50 mL) was added. The aqueous phase was extracted with dichloromethane, and the organic phase was concentrated under vacuum to obtain the crude product. This crude product was recrystallized with high-temperature methanol and dried under vacuum to obtain the solid intermediate C4 (yield: 767 mg, yield: 66%). 1H NMR (400 MHz, CD2Cl2) δ 8.91 (d, J = 8.5 Hz, 2H), 8.78 (s, 2H), 8.30 (d, J = 1.1 Hz, 2H), 6.94 (dd, J = 8.4, 2.2 Hz, 2H), 6.74 (s, 4H), 13C NMR spectra could not be obtained due to the extremely poor solubility. MS (MALDI-TOF): Calcd for C50H39Cl2B2N3: 774.40; Found: 773.27.

[0091] [ka]

[0092] The intermediate C4 (774 mg, 1 mmol), potassium ferrocyanide (1.5 g, 4 mmol), bis(di-tert-butyl(4-dimethylaminophenyl)phosphine)dichloropalladium(II) (71 mg, 0.1 mmol), and sodium carbonate (170 mg, 1.6 mmol) were dissolved in N,N-dimethylacetamide (10 mL). The solution was degassed and heated at 140 °C for 24 hours. After cooling the reaction mixture to room temperature, it was extracted with dichloromethane, and the organic phase was concentrated under vacuum to obtain the crude product. This crude product was purified by silica gel columnography using a 1:1 mixture of petroleum ether and dichloromethane as the eluent, and dried under vacuum to obtain the solid form of the target compound 1 (yield: 280 mg, yield: 37%). 1 H NMR (400 MHz, CD2Cl2) δ 9.50 (d, J = 2.1 Hz, 2H), 8.89 (s, 2H), 8.41 (s, 2H), 7.72 (dd, J = 8.8, 2.0 Hz, 2H), 7.01 (s, 4H), 6.93 (d, J = 8.9 Hz, 2H), 5.47 (s, 1H), 2.90 (s, 6H), 2.46 (s, 6H), 1.72 (s, 12H). 13 C NMR spectra could not be obtained due to the extremely poor solubility. MS (MALDI-TOF): Calcd for C 52 H 39 B2N5: 755.54; Found: 775.47.

[0093] (Synthesis Example 2) Synthesis of Compound 2 [ka]

[0094] The solution, prepared by dissolving intermediate C2 (1.1 g, 2 mmol), 1-chloro-4-iodobenzene (1.0 mg, 4.4 mmol), palladium(II) acetate (45 mg, 0.2 mmol), tri-tert-butylphosphine (0.1 mL, 0.4 mmol), and sodium tert-butoxide (431 mg, 4.4 mmol) in toluene, was degassed and heated at 80°C for 12 hours. After cooling the reaction mixture to room temperature, it was filtered through silica gel, and the filtrate was concentrated under vacuum to obtain the crude product. This crude product was purified by silica gel column chromatography using a mixed solvent of petroleum ether:dichloromethane = 6:1 as the eluent, and dried under vacuum to obtain the white solid intermediate C5 (yield: 1.2 g, yield: 78%). 1 H NMR (400 MHz, CDCl3) δ 7.83-7.77 (m, 2H), 7.17-7.09 (m, 6H), 7.03 (t, J = 2.1 Hz, 2H), 6.89 (d, J = 2.0 Hz, 5H), 6.87-6.81 (m, 4H), 6.53 (d, J = 2.1 Hz, 2H), 2.50 (s, 6H), 2.28 (s, 6H), 2.02 (s, 12H). 13 C NMR (101 MHz, CDCl3) δ 147.30, 146.93, 139.79, 139.07, 138.59, 137.35, 137.04, 134.85, 130.16, 129.01, 126.97, 123.36, 120.91, 120.03, 119.02, 117.32, 111.05, 109.81, 109.58, 21.33, 21.00, 18.35. 50 H 45 Cl2N3: 758.83; Found: 758.22.

[0095] [ka]

[0096] To a solution of intermediate C5 (1.1 g, 1.5 mmol) in o-dichlorobenzene (20 mL), boron tribromide (2.9 mL, 30 mmol) was added under a nitrogen atmosphere at 0°C, and the mixture was heated at 180°C for 24 hours. After the reaction mixture was cooled to room temperature, phosphate buffer (50 mL) was added. The aqueous phase was extracted with dichloromethane, and the organic phase was concentrated under vacuum to obtain the crude product. This crude product was recrystallized with high-temperature methanol and dried under vacuum to obtain the solid intermediate C6 (yield 790 mg, yield 68%). 1 H NMR (400 MHz, CD2Cl2) δ 9.31 (d, J = 7.8 Hz, 2H), 8.91 (s, 2H), 8.40 (s, 2H), 7.62 (dd, J = 7.8, 1.4 Hz, 2H), 7.17 (d, J = 1.5 Hz, 2H), 7.03 (s, 4H), 5.40 (s, 1H), 2.88 (s, 6H), 2.48 (s, 6H), 1.72 (s, 12H). 13 C NMR spectra could not be obtained due to the extremely poor solubility. MS (MALDI-TOF): Calcd for C 50 H 39 Cl2B2N3: 774.40; Found: 773.28.

[0097] [ka]

[0098] The intermediate C6 (774 mg, 1 mmol), potassium ferrocyanide (1.5 g, 4 mmol), bis(di-tert-butyl(4-dimethylaminophenyl)phosphine)dichloropalladium(II) (71 mg, 0.1 mmol), and sodium carbonate (170 mg, 1.6 mmol) were dissolved in N,N-dimethylacetamide (10 mL). The solution was degassed and heated at 140 °C for 24 hours. After cooling the reaction mixture to room temperature, it was extracted with dichloromethane, and the organic phase was concentrated under vacuum to obtain the crude product. This crude product was purified by silica gel columnography using a 1:1 mixture of petroleum ether and dichloromethane as the eluent, and dried under vacuum to obtain the target compound 2 as a green solid (yield: 234 mg, yield: 31%). 1 H NMR (400 MHz, CD2Cl2) δ 9.30 (d, J = 7.9 Hz, 2H), 8.88 (s, 2H), 8.35 (s, 2H), 7.62 (dd, J = 7.8, 1.5 Hz, 2H), 7.17 (d, J = 1.4 Hz, 2H), 7.03 (s, 4H), 5.41 (s, 1H), 2.85 (s, 6H), 2.48 (s, 6H), 1.72 (s, 12H). 13 C NMR spectra could not be obtained due to the extremely poor solubility. MS (MALDI-TOF): Calcd for C 52 H 39 B2N5: 755.54; Found: 775.45.

[0099] (Comparative Synthesis Example 1) Synthesis of Comparative Compound 1 [ka]

[0100] A solution prepared by dissolving intermediate C2 (1.1 g, 2 mmol), iodobenzene (898 mg, 4.4 mmol), palladium(II) acetate (45 mg, 0.2 mmol), tri-tert-butylphosphine (0.1 mL, 0.4 mmol) and sodium tert-butoxide (431 mg, 4.4 mmol) in toluene (40 mL) was degassed and heated at 100 °C for 12 hours. After cooling this reaction mixture to room temperature, it was filtered through silica gel, and the filtrate was concentrated in vacuo to obtain a crude product. This crude product was purified by silica gel column chromatography using a mixed solvent of petroleum ether:dichloromethane = 6:1 as an eluent and dried under vacuum to obtain a white solid of intermediate C7 (yield: 1.3 g, yield: 92%). 1 H NMR (400 MHz, CDCl3) δ 7.82 - 7.78 (m, 2H), 7.19 - 7.10 (m, 8H), 7.02 (dd, J = 8.7, 1.1 Hz, 4H), 6.94 (t, J = 2.1 Hz, 1H), 6.89 - 6.82 (m, 6H), 6.45 (d, J = 2.1 Hz, 2H), 2.49 (s, 6H), 2.27 (s, 6H), 2.03 (s, 12H). 13 C NMR (101 MHz, CDCl3) δ 147.82, 145.55, 139.76, 139.46, 138.80, 137.27, 136.83, 129.94, 129.00, 128.72, 126.84, 123.20, 120.91, 119.94, 119.58, 109.98, 109.67, 109.01, 21.33, 20.99, 18.39. MS (MALDI-TOF): Calcd for C 50 H 47 N3: 689.95; Found: 689.86.

[0101]

Chemical formula

[0102] To a solution of intermediate C7 (1.0 g, 1.5 mmol) in o-dichlorobenzene (20 mL), boron tribromide (2.9 mL, 30 mmol) was added at 0 °C under a nitrogen atmosphere, and the mixture was heated at 180 °C for 24 hours. After cooling the reaction mixture to room temperature, phosphate buffer (50 mL) was added. The aqueous phase was extracted with dichloromethane, and the organic phase was concentrated in vacuo to obtain a crude product. The crude product was purified by silica gel column chromatography using a mixed solvent of petroleum ether:dichloromethane = 4:1 as an eluent and dried under vacuum to obtain a solid of the target comparative compound 1 (yield: 635 mg, yield: 60%). 1 H NMR (400 MHz, CD2Cl2) δ 9.22 (dd, J = 7.6, 1.7 Hz, 2H), 8.95 (s, 2H), 8.37 (dd, J = 1.5, 0.7 Hz, 2H), 7.51 (ddd, J = 8.6, 7.0, 1.7 Hz, 2H), 7.42-7.34 (m, 2H), 7.01-6.97 (m, 4H), 6.85 (dd, J = 8.6, 1.0 Hz, 2H), 5.34 (s, 1H), 2.88 (s, 6H), 2.45 (s, 6H), 1.72 (s, 12H). 13 C NMR spectra could not be obtained due to the extremely poor solubility. MS (MALDI-TOF): Calcd for C 50 H 41 B2N3: 705.52; Found: 705.35.

[0103] The measured values of the HOMO levels and LUMO levels of the synthesized compounds 1, 2 and comparative compound 1 are shown in Table 1 below. In this example, mCBP was used as the host material, HDT-1 was used as the delayed fluorescence material, and SF3-TRZ was used as the electron transport material. The HOMO levels and LUMO levels of these compounds are also shown in Table 1. Furthermore, the difference ΔE HOMO between the HOMO level of compounds 1, 2 and the comparative compound and the HOMO level of HDT-1 is shown in Table 1.

[0104] [ka]

[0105] [Table 1]

[0106] [Evaluation of electron transport capabilities] A first electrode made of indium tin oxide (ITO) with a thickness of 100 nm was formed on a glass substrate, and each thin film was deposited by vacuum deposition. First, Liq was formed to a thickness of 2 nm on the ITO, and then SF3-TRZ and Liq were co-deposited on it from different deposition sources to form a thin film with a thickness of 30 nm. At this time, the weight ratio of each compound in the thin film (SF3-TRZ:Liq) was 30:70. Next, SF3-TRZ was formed to a thickness of 10 nm, and then compound 1, HDT-1, and mCBP were co-deposited on it from different deposition sources to form a mixed film containing compound 1 with a thickness of 50 nm. At this time, the weight ratio of each compound in the mixed film (compound 1:HDT-1:mCBP) was 0.15:20:80. Subsequently, SF3-TRZ was formed to a thickness of 10 nm, and then SF3-TRZ and Liq were co-deposited on it in the same weight ratio as above to form a thin film with a thickness of 30 nm. Furthermore, by forming a Liq layer to a thickness of 2 nm and then depositing aluminum (Al) to a thickness of 100 nm on top of it to form a second electrode, we created an evaluation element E1. Furthermore, element E2 and comparative elements E1-E3 were fabricated using the same method by changing the materials of the mixed film as shown in Table 2 below, or by forming single films of the materials shown in Table 2 instead of the mixed film.

[0107] [Table 2]

[0108] Figure 1 shows the results of measuring the electron density-drive voltage characteristics for each fabricated element. As shown in Figure 1, the comparative element E2, which had a mixed film of HDT-1 and mCBP, showed a higher electron density than the comparative element E3, which had a single mCBP film. This indicates that HDT-1 exhibits electron transport and electron injection properties. Furthermore, elements E1 and E2, which had compound 1 or compound 2 added to the mixed film, showed even higher electron densities than comparative element E2, indicating that compound 1 and compound 2 also contribute to electron transport.

[0109] [Evaluation of hole transport] Each thin film was deposited by vacuum deposition on a glass substrate on which a first electrode made of indium tin oxide (ITO) with a thickness of 100 nm had been formed. First, HAT-CN was formed to a thickness of 10 nm on the ITO, and then NPD was formed on top of this to a thickness of 20 nm. Next, Tris-Pcz was formed to a thickness of 10 nm, and then mCBP was formed on top of that to a thickness of 5 nm. Then, compound 1, HDT-1, and mCBP were co-deposited from different deposition sources to form a mixed film containing compound 1 to a thickness of 50 nm. At this time, the weight ratio of each compound in the mixed film (compound 1:HDT-1:mCBP) was 0.15:20:80. On top of this mixed film, mCBP was formed to a thickness of 5 nm, and then Tris-Pcz was formed to a thickness of 10 nm. Furthermore, by forming HAT-CN to a thickness of 10 nm and then depositing aluminum (Al) to a thickness of 100 nm on top of it to form a second electrode, we created an evaluation element H1. Furthermore, evaluation element H2, comparative evaluation elements H1-H3 were fabricated using the same method by changing the materials of the mixed film as shown in Table 3, or by forming single films of the materials shown in Table 3 instead of the mixed film.

[0110] [Table 3]

[0111] Figure 2 shows the results of measuring the hole density-drive voltage characteristics for each evaluation element that was fabricated. As shown in Figure 2, no difference in hole density was observed between comparison element H2, which had a mixed film of HDT-1 and mCBP, and comparison element H3, which had a film of mCBP alone. From this, it was found that HDT-1 does not have a significant effect on hole injection or hole transport. On the other hand, ΔE HOMO When comparative compound 1 with a voltage of 0.66 eV was added, comparative element 1 showed a lower hole density than comparative element H2, and ΔE HOMO Elements H1 and H2, to which compound 1 or compound 2 with a ΔE of 0.40 eV or less was added, showed a hole density equivalent to that of comparative element H2. The lower hole density in comparative element 1 is thought to be due to the low HOMO level of comparative compound 1, which traps holes in its HOMO. From this, it can be concluded that in an emissive layer using a delayed fluorescence material and a multi-resonance emissive material, in order to suppress hole trapping and ensure hole transport, ΔE HOMO It was found that devices with a voltage of 0.40 eV or less must be used.

[0112] (Example 1) Fabrication of an organic electroluminescent device using compound 1 Each thin film is deposited onto a glass substrate with an anode made of indium tin oxide (ITO) with a thickness of 100 nm using a vacuum deposition method at a vacuum level of 10 -5 Lamination was carried out using Pa. First, HAT-CN was formed to a thickness of 10 nm on ITO, and then NPD was formed to a thickness of 20 nm on top of it. Next, Tris-PCz was formed to a thickness of 10 nm, and then mCBP was formed to a thickness of 5 nm on top of it. Then, compound 1, HDT-1, and mCBP were co-deposited from different deposition sources to form a 30 nm thick layer which served as the emissive layer. At this time, the weight ratio of each compound in the emissive layer (compound 1:HDT-1:mCBP) was 0.15:20:80. SF3-TRZ was formed to a thickness of 10 nm on top of this emissive layer. Next, Liq and SF3-TRZ were co-deposited from different deposition sources to form a 30 nm thick layer. At this time, the weight ratio in the layer (Liq:SF3-TRZ) was 30:70. Next, an organic electroluminescent element (EL element 1) was created by forming a Liq layer to a thickness of 2 nm and then depositing aluminum (Al) to a thickness of 100 nm to form a cathode.

[0113] (Example 2) Using Compound 2 instead of Compound 1, an organic electroluminescent device (EL device 2) was fabricated according to the same procedure as in Example 1.

[0114] (Comparative Example 1) Using Comparative Compound 1 instead of Compound 1, an organic electroluminescent device (Comparative EL device 1) was fabricated according to the same procedure as in Example 1.

[0115] (Comparative Examples 2 to 4) An organic electroluminescent device (Comparative EL devices 2 to 4) was fabricated using the same method as in Example 1, 2 or Comparative Example 1, except that the light-emitting layer was formed without using HDT-1.

[0116] The materials and weight ratios of the light-emitting layers formed in each example and each comparative example are shown in Table 4 below.

[0117]

Table 4

[0118] The EL spectra of the fabricated EL devices 1 and 2 and Comparative EL device 1 are shown in Figure 3, the current density-driving voltage-luminance characteristics are shown in Figure 4, the external quantum efficiency (EQE)-luminance characteristics are shown in Figure 5, and the change in luminance over time during continuous driving is shown in Figure 6. Also, for the photoluminescence devices fabricated by forming a light-emitting layer with the same composition as the light-emitting layers of EL devices 1, 2 and Comparative EL device 1 on a quartz substrate, the change in PL intensity over time during continuous irradiation with excitation light is shown in Figure 7. In Figure 7, PL device 1 is provided with the light-emitting layer of EL device 1, PL device 2 is provided with the light-emitting layer of EL device 2, and Comparative PL device 1 is provided with the light-emitting layer of Comparative EL device 1. As shown in Figure 3, the full width at half maximum of the emission peaks of EL elements 1, 2, and comparative EL element 1 were all 20 nm or less. This confirms that the use of multi-resonance type light-emitting materials improves the color purity of the EL elements. On the other hand, as shown in Figures 4-6, the current density-driving voltage-luminance characteristics, external quantum efficiency (EQE)-luminance characteristics, and stability were superior for EL elements 1 and 2 compared to comparative EL element 1. To analyze the reason for the inferior performance of comparative EL element 1, pulsed EL excitation (pulse width: 100 μs) was applied to EL elements 1, 2, and comparative EL element 1 to turn them off, and then a reverse bias voltage of -10 V was applied. Figure 8 shows the time change of the EL intensity during this process. As shown in Figure 8, when a reverse bias voltage was applied to EL elements 1 and 2 after the pulsed EL excitation was turned off, the EL intensity remained constant and decayed rapidly. In contrast, in comparative EL element 1, the EL intensity spiked up before decaying when a reverse bias voltage was applied. This is presumed to be due to the detrapping of trapped holes and subsequent carrier recombination, resulting in instantaneous light emission. From this, it was found that hole trapping occurs in the light-emitting layer of comparative EL element 1. Next, the EL intensity decay curves (transient decay curves) were measured for EL elements 1 and 2, comparative EL element 1, and comparative EL elements 2-4 (with HDT-1 removed) after EL excitation and subsequent switching off. The results are shown in Figures 9-11. Figure 9 shows the transient decay curve of EL intensity for EL element 1 and comparative EL element 2, Figure 10 shows the transient decay curve of EL intensity for EL element 2 and comparative EL element 3, and Figure 11 shows the transient decay curve of EL intensity for comparative EL element 1 and comparative EL element 4. Here, the system without HDT-1 (comparative EL elements 2-4) corresponds to a host-guest system consisting of mCBP (host material) and compound 1, 2 or comparative compound 1 (guest material). Since delayed fluorescence emission occurs in the luminescent guest material via exciton generation and reverse intersystem crossing, the transient decay curve of EL intensity is a gentle curve, reflecting this delayed fluorescence emission. On the other hand, in a system containing HDT-1, exciton generation and reverse intersystem crossing occur in HDT-1, and the excited singlet energy is transferred to the multi-resonance luminescent material, causing the multi-resonance luminescent material to emit light. Therefore, if this luminescence process proceeds smoothly (i.e., exciton generation occurs more favorably in HDT-1 than in the multi-resonance luminescent material), the EL intensity decay curve will be steeper than in a host-guest system. From the above points, looking at Figures 9-11, the transient decay curves of EL intensity for EL elements 1 and 2 are steeper than those of comparative EL elements 2 and 3 (excluding HDT-1), indicating that the light emission process proceeded smoothly. In contrast, the transient decay curve of comparative EL element 1 shown in Figure 11 overlaps with the decay curve of comparative EL element 4, and they exhibit almost identical curves. This indicates that, similar to comparative EL element 4, comparative EL element 1 generated excitons directly in comparative compound 1, resulting in delayed fluorescence emission. Considering these factors, in comparative EL element 1, ΔE HOMOIt is presumed that the large size of comparative compound 1 causes hole trapping, hindering hole transport, degrading the current density-driving voltage-brightness characteristics, and resulting in a lower external quantum efficiency (EQE). Furthermore, the observation of delayed fluorescence emission originating from comparative compound 1 suggests that the holes trapped in comparative compound 1 undergo carrier recombination to generate triplet excitons. The accumulation of these triplet excitons is presumed to cause roll-off during high-brightness driving and a decrease in operational stability (reduced durability for continuous driving). From the above, the reason why comparative EL element 1 has inferior element characteristics compared to EL elements 1 and 2 is ΔE HOMO It was shown that a large value is the cause of hole trapping. And ΔE HOMO It was found that by selecting a combination of delayed fluorescence material and multi-resonance luminescent material such that the voltage is 0.40 eV or less, roll-off can be suppressed, resulting in an organic EL device with improved efficiency and operational stability.

[0119] [ka] [Industrial applicability]

[0120] According to the present invention, the efficiency of an organic electroluminescent element containing a delayed fluorescence material and a multi-resonance type luminescent material in the light-emitting layer can be improved, and roll-off can be suppressed to improve operational stability. Therefore, according to the present invention, a highly practical organic electroluminescent element can be realized. For this reason, the present invention has high industrial applicability.

Claims

1. The light-emitting layer includes at least a delayed fluorescence material and a multi-resonance light-emitting material. An organic electroluminescent element characterized in that a substituent with a σm of 0.2 or more is introduced into the multiple resonance condensed ring skeleton constituting the multiple resonance light-emitting material, and the difference in HOMO energy levels between the multiple resonance light-emitting material and the delayed fluorescence material is 0.4 eV or less.

2. The organic electroluminescent element according to claim 1, wherein the substituent is a substituent bonded to an atom with a large electron density distribution of HOMO.

3. The organic electroluminescent element according to claim 1, wherein the substituent is bonded to an atom in which both the electron density distribution of HOMO and the electron density distribution of LUMO are large.

4. The organic electroluminescent element according to claim 1, wherein the HOMO energy level of the multi-resonance type light-emitting material is -5.6 eV or lower.

5. The organic electroluminescent element according to claim 1, wherein the energy level of the HOMO of the delayed fluorescence material is -5.9 eV or lower.

6. The organic electroluminescent element according to claim 1, wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the meta position of the boron atom.

7. The organic electroluminescent element according to claim 1, wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the para position of the boron atom.

8. The organic electroluminescent element according to any one of claims 1 to 6, wherein the substituent is a fluorine atom, a cyano group, a trifluoromethyl group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group.

9. A method for designing an organic electroluminescent element comprising a host material, a delayed fluorescence material, and a multi-resonance type light-emitting material in a light-emitting layer, A method for designing an organic electroluminescent element, characterized by selecting substituents present in a multi-resonance type light-emitting material to determine a structure in which the difference in HOMO energy levels between the multi-resonance type light-emitting material and the delayed fluorescence material is 0.4 eV or less, and designing an organic electroluminescent element comprising a multi-resonance type light-emitting material having that structure, the host material, and the delayed fluorescence material.

10. The method for designing an organic electroluminescent element according to claim 9, wherein the substituent is a substituent bonded to an atom with a large electron density distribution of HOMO.

11. The method for designing an organic electroluminescent element according to claim 9, wherein the substituent is a substituent bonded to an atom in which both the electron density distribution of the HOMO and the electron density distribution of the LUMO are large.

12. A method for designing an organic electroluminescent element according to claim 9, wherein the energy level of the HOMO of the structure to be determined is -5.6 eV or less.

13. The method for designing an organic electroluminescent element according to claim 9, wherein the energy level of the HOMO of the delayed fluorescence material is -5.9 eV or lower.

14. The method for designing an organic electroluminescent element according to claim 9, wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the meta position of the boron atom.

15. The method for designing an organic electroluminescent element according to claim 9, wherein the multi-resonance type light-emitting material includes a benzene ring bonded to a boron atom, and the substituent is bonded to the benzene ring at the para position of the boron atom.

16. The method for designing an organic electroluminescent element according to claim 9, wherein the distance between the bonding atom of the substituent and the atom furthest from that bonding atom is 7 angstroms or less.

17. The method for designing an organic electroluminescent element according to claim 16, wherein the substituent is a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group.

18. An organic electroluminescent element manufactured using the design method described in any one of claims 9 to 17.

19. A method for improving a multi-resonance luminescent material used in an organic electroluminescent element that includes a host material, a delayed fluorescence material, and a multi-resonance luminescent material in its light-emitting layer, A method characterized by finding a multi-resonance luminescent material having a structure in which the difference between the energy level of the HOMO of the delayed fluorescence material and the energy level of the delayed fluorescence material is 0.4 eV or less, by performing at least one step of calculating the difference between the structure and the energy level of the HOMO of the delayed fluorescence material, assuming a structure in which hydrogen atoms or groups present in the pre-improvement multi-resonance luminescent material are substituted.

20. The improved method according to claim 19, wherein the hydrogen atom or group is a hydrogen atom or group bonded to an atom with a large electron density distribution of HOMO.

21. The improved method according to claim 19, wherein the hydrogen atom or group is a hydrogen atom or group bonded to an atom in which both the electron density distribution of HOMO and the electron density distribution of LUMO are large.

22. The improved method according to claim 19, which involves finding a multi-resonance type light-emitting material in which the HOMO energy level is -5.6 eV or lower.

23. The method for improving an organic electroluminescent element according to claim 19, wherein the energy level of the HOMO of the delayed fluorescence material is -5.9 eV or lower.

24. The method for improving an organic electroluminescent element according to claim 19, wherein the previously improved multi-resonance type light-emitting material contains a benzene ring bonded to a boron atom, and the hydrogen atom is a hydrogen atom of the benzene ring located at the meta position of the boron atom.

25. The method for improving an organic electroluminescent element according to claim 19, wherein the previously improved multi-resonance type light-emitting material contains a benzene ring bonded to a boron atom, and the hydrogen atom is a hydrogen atom of the benzene ring located in the para position of the boron atom.

26. The improvement method according to claim 19, wherein the substituent that substitutes a hydrogen atom or group present in the pre-improvement multi-resonance type light-emitting material is a substituent in which the distance between the bonding atom and the atom furthest from that bonding atom is 7 angstroms or less.

27. The improved method according to claim 26, wherein the substituent is a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group.

28. The improvement method according to claim 19, which improves a multi-resonance type light-emitting material while suppressing the variation in the full width at half maximum of the element's maximum light emission to within a range of plus or minus 5 nm.

29. The improvement method according to claim 19, which improves a multi-resonance type light-emitting material while suppressing the variation in the maximum emission wavelength of the element to within a range of plus or minus 15 nm.

30. The improved method according to claim 19, wherein the maximum emission wavelength of the element is 490 nm or less.

31. The improvement method according to claim 19, which improves a multi-resonance type light-emitting material while keeping the variation in the light emission quantum yield of the element within a range of plus or minus 10%.

32. The improved method according to claim 19, which suppresses Hole trapping by a multi-resonance type light-emitting material in the element.

33. A program for carrying out the improved method described in any one of claims 19 to 32.

34. A multi-resonance type light-emitting material manufactured using the improved method described in any one of claims 19 to 32.

35. A compound represented by the following general formula (1). General formula (1) 【Chemistry 1】 [In general formula (1), R １ ~R １５ Each of these independently represents a hydrogen atom, a deuterium atom, or a substituent. １ ~R ４ At least one of and R １１ ~R １４ At least one of them is independently a fluorine atom, a cyano group, a trifluoromethyl group, a methoxy group, a pyridyl group, a pyrimidyl group, a pyrazinyl group, a pyridadinyl group, or a triazyl group. １ and Ar ２ Each of these independently represents a substituted or unsubstituted aryl group, or a substituted or unsubstituted heteroaryl group.

36. R ２ and R ３ where one of them is a cyano group, and R １２ and R １３ where one of them is a cyano group, the compound according to claim 35.

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