TWI894149B - Organic electroluminescent element and display device - Google Patents

Abstract

The present invention relates to a composition for an organic electroluminescent device, comprising a compound represented by the following formula (1) in which a triazine ring is substituted at a specific position, a compound represented by the following formula (2) having a maximum emission wavelength shorter than that of the compound represented by the formula (1), and a solvent.

Description

Organic electroluminescent element and display device

The present invention relates to an organic electroluminescent element composition useful for forming a light-emitting layer of an organic electroluminescent element (hereinafter sometimes referred to as an "organic EL (Electro-Luminescence) element"). The present invention also relates to an organic electroluminescent element having a light-emitting layer formed using the organic electroluminescent element composition, a method for manufacturing the same, and a display device having the organic electroluminescent element.

Various electronic devices utilizing organic EL elements, such as organic EL lighting and displays, are becoming practical. Organic electroluminescent elements consume little power due to their low applied voltage and ability to emit light in all three primary colors. Therefore, they are beginning to be used not only in large monitors but also in small and medium-sized displays such as mobile phones and smartphones.

Organic electroluminescent (EL) devices are manufactured by stacking multiple layers, including light-emitting layers, charge injection layers, and charge transport layers. Currently, most EL devices are produced by vacuum evaporation of organic materials. However, this method is complex and has poor productivity. EL devices manufactured using vacuum evaporation are extremely difficult to scale up for use in lighting or display panels.

In recent years, wet film deposition (coating) has been studied as a process for efficiently manufacturing organic electroluminescent devices for use in large displays and lighting. Compared to vacuum evaporation, wet film deposition offers the advantage of easily forming stable layers, and therefore holds promise for mass production of displays and lighting devices, as well as for large displays.

To manufacture organic electroluminescent devices using wet film deposition, all materials used must be soluble in the organic solvent used as ink. Poor solubility of the materials used requires prolonged heating and other procedures, potentially leading to material degradation before use. Furthermore, if the solution cannot be maintained uniformly for extended periods, the material may precipitate from the solution, making film formation impossible using inkjet equipment. Materials used in wet film deposition require both rapid dissolution in the organic solvent and uniformity after dissolution without precipitation.

One advantage of wet film deposition over vacuum evaporation is the ability to use a wider variety of materials in a single layer. While vacuum evaporation makes it difficult to maintain a constant evaporation rate as the number of materials increases, wet film deposition allows for the creation of an ink with a constant composition ratio, even with a larger number of materials, as long as each material is dissolved in an organic solvent.

In recent years, attempts have been made to utilize this advantage by using two or more iridium complexes in inks to increase the luminescence efficiency or reduce the driving voltage of organic electroluminescent devices, thereby improving the performance of organic electroluminescent devices (for example, Patent Documents 1 and 2).

On the other hand, attention has been paid to the chemical structure of the material, and attempts have been made to use iridium complexes containing phenylpyridine substituted with a triazine ring at a specific position in the ligand as red light-emitting materials in white light-emitting devices (for example, Patent Documents 3 and 4).

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] International Publication No. 2015/192939

[Patent Document 2] International Publication No. 2016/015815

[Patent Document 3] International Publication No. 2017/154884

[Patent Document 4] Japanese Patent Publication No. 2018-83941

However, the prior art still fails to provide sufficient performance for organic electroluminescent devices for display applications. In particular, red devices require further reductions in driving voltage, improvements in luminous efficiency, and improvements in driving life.

This invention, in particular, enables the fabrication of organic electroluminescent devices using a wet film deposition method for red devices. The goal is to provide an organic electroluminescent device with lower driving voltage, higher luminous efficiency, and longer driving life than previous devices.

In order to flexibly utilize the advantages of wet film deposition, which allows for a wider variety of materials to be used in a single layer, the inventors conducted intensive research focused on this issue. As a result, they discovered that by preparing an iridium complex with a relatively short maximum emission wavelength as an auxiliary dopant, and using an iridium complex containing a phenylpyridine substituted with a triazine ring at a specific position in the ligand as the luminescent dopant in a red device, and dissolving the auxiliary dopant and luminescent dopant in a solvent to produce an organic electroluminescent device composition, the performance of the organic electroluminescent device was improved, leading to the completion of the present invention.

Furthermore, it was discovered that the performance of the organic electroluminescent device was further improved by using the iridium complex as a luminescent dopant at a larger composition ratio than that of the auxiliary dopant.

The composition for an organic electroluminescent device of the present invention contains an iridium complex with a shorter maximum emission wavelength than the primary luminescent dopant as a secondary dopant, and an iridium complex containing a phenylpyridine ligand substituted with a triazine ring at a specific position as the primary luminescent dopant. This enables the production of an organic electroluminescent device with a lower drive voltage, higher luminescence efficiency, and longer drive life than previously possible. Furthermore, the composition for an organic electroluminescent device of the present invention can appropriately suppress luminescence from the auxiliary dopant by making the composition ratio of the luminescent dopant greater than the composition ratio of the auxiliary dopant, thereby enabling the production of an organic electroluminescent device with a more vivid luminescent color.

That is, the gist of the present invention is as follows.

[1] A composition for an organic electroluminescent device, comprising a compound represented by the following formula (1), a compound represented by the following formula (2) having a maximum emission wavelength shorter than that of the compound represented by the formula (1), and a solvent.

[Chemistry 1]

[In the above formula, R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have a substituent; when there are multiple R ¹ and R ² , these groups may be the same or different; when there are multiple R ¹ , adjacent R ¹ may be bonded to form a ring; a is an integer from 0 to 4, and b is an integer from 0 to 3; R ³ and R ⁴ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms; these groups may further have substituents; when there are multiple R ³ and R ⁴ , they may be the same or different; L ¹ represents an organic ligand, and m is an integer from 1 to 3]

[In the above formula, R ⁵ is an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have substituents; in the presence of multiple R ⁵ , these may be the same or different; c is an integer from 0 to 4; Ring A is any one of a pyridine ring, a pyrazine ring, a pyrimidine ring, an imidazole ring, an oxazole ring, a thiazole ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, an azatriphenylene ring, a carboline ring, a benzothiazole ring, and a benzoxazole ring; Ring A may have a substituent, and the substituent is a fluorine atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 20 carbon atoms, a thiazole ring having 7 to 40 carbon atoms, or a thiazole ring having 1 to 20 carbon atoms. [a (hetero)aralkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms; in addition, adjacent substituents bonded to ring A may bond to each other to further form a ring; when there are multiple rings A, they may be the same or different; ^L2 represents an organic ligand, and n is an integer of 1 to 3]

[2] The composition for an organic electroluminescent device as described in [1], wherein the composition ratio of the compound represented by the formula (1) is greater than or equal to the composition ratio of the compound represented by the formula (2) in terms of mass fraction.

[3] The composition for an organic electroluminescent device as described in [1] or [2], wherein the compound represented by the formula (1) is a compound represented by the following formula (1-1).

[Chemistry 3]

[In the above formula, R ¹ , R ² , a, b, L ¹ , and m have the same meanings as R ¹ , R ² , a, b, L ¹ , and m in the above formula (1); R ⁶ and R ⁷ are independently an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have substituents; in the presence of multiple R ⁶ , R In the case of ⁷ , these may be the same or different; d and e are independently integers from 0 to 5.

[4] The composition for an organic electroluminescent device as described in [1] or [2], wherein the compound represented by the formula (1) is a compound represented by the following formula (1-2).

[In the above formula, R ² to R ⁴ , b, L ¹ , and m have the same meanings as R ² to R ⁴ , b, L ¹ , and m in formula (1); R ¹⁴ to R ¹⁶ are substituents. When there are multiple R ¹⁴ to R ¹⁶ groups, they may be the same or different; i is an integer from 0 to 4.]

[5] The composition for an organic electroluminescent device according to [3], wherein the compound represented by the formula (1-1) is a compound represented by the following formula (1-3).

[In the above formula, R ² , R ⁶ , R ⁷ , b, d, e, L ¹ , and m have the same meanings as R ² , R ⁶ , R ⁷ , b, d, e, L ¹ , and m in formula (1-1); R ¹⁴ to R ¹⁶ are substituents. If there are multiple R ¹⁴ to R ¹⁶ , they may be the same or different; i is an integer from 0 to 4.]

[6] The composition for an organic electroluminescent device according to any one of [1] to [5], wherein the compound represented by formula (2) is a compound represented by the following formula (2-1).

[In the above formula, Ring A, L ² , and n have the same meanings as Ring A, L ² , and n in Formula (2); R ⁸ is an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have substituents; when there are multiple R ^{8 s} , they may be the same or different; f is an integer from 0 to 5]

[7] The composition for an organic electroluminescent device according to any one of [1] to [6], wherein m in the formula (1) is less than 3, and ^L1 has at least one structure selected from the group consisting of the following formulas (3), (4), and (5).

[In formulas (3) to (5), R ⁹ and R ¹⁰ have the same meanings as R ¹ in formula (1). When multiple R ⁹ and R ¹⁰ are present, they may be the same or different; R ¹¹ to R ¹³ are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may be substituted with a fluorine atom, a phenyl group which may be substituted with an alkyl group having 1 to 20 carbon atoms, or a halogen atom; g is an integer from 0 to 4; h is an integer from 0 to 4; Ring B is a pyridine ring, a pyrimidine ring, an imidazole ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, an aza-tertiary phenyl ring, a carboline ring, a benzothiazole ring, or a benzoxazole ring; Ring B may further have a substituent.]

[8] The composition for an organic electroluminescent device according to any one of [1] to [7], wherein a in the formula (1) is 1, or a in the formula (1) is an integer greater than or equal to 2 and does not have a ring formed by mutually bonding adjacent ^R1s .

[9] A method for manufacturing an organic electroluminescent element, comprising the step of using the organic electroluminescent element composition described in any one of [1] to [8] to form a light-emitting layer by a wet film formation method.

[10] An organic electroluminescent device having a light-emitting layer formed using the composition for an organic electroluminescent device as described in any one of [1] to [8].

[11] A display device having the organic electroluminescent element described in [10].

According to the present invention, organic electroluminescent devices, particularly red devices, can be manufactured using a wet film deposition method, providing an organic electroluminescent device with lower driving voltage, higher luminous efficiency, and longer driving life than previously available devices.

1:Substrate

2: Anode

3: Hole injection layer

4: Hole transport layer

5: Luminescent layer

6: Hole blocking layer

7: Electron transmission layer

8: Electron injection layer

9: Cathode

10: Organic electroluminescent element

Figure 1 is a cross-sectional view schematically showing an example of the structure of an organic electroluminescent element of the present invention.

The following describes the embodiments of the present invention in detail. However, the present invention is not limited to the following embodiments and can be implemented in various modifications within the scope of its main purpose.

In this specification, the terms "(hetero)aralkyl," "(hetero)aryloxy," and "(hetero)aryl" represent an aralkyl group that may contain a hetero atom, an aryloxy group that may contain a hetero atom, and an aryl group that may contain a hetero atom, respectively. "May contain a hetero atom" means that one or more carbon atoms forming the aryl skeleton of the main skeleton of the aryl group, aralkyl group, or aryloxy group are substituted with a hetero atom. Examples of hetero atoms include nitrogen, oxygen, sulfur, phosphorus, and silicon atoms. Nitrogen atoms are preferred from the perspective of durability.

[Luminescent Dopants]

The composition for an organic electroluminescent device of this embodiment includes a compound represented by the following formula (1), which mainly functions as a luminescent dopant. The compound represented by formula (1) may contain only one type or multiple types. In addition, the compound serving as a luminescent dopant may contain a compound serving as a luminescent dopant other than the compound represented by formula (1). In this case, the total content of the compound represented by formula (1) relative to the total amount of the compound serving as a luminescent dopant is preferably set to 50% by mass or more, more preferably 100% by mass. That is, it is more preferable to use only the compound represented by formula (1).

In formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms. These groups may further have substituents. When there are multiple R ¹ and R ² groups, they may be the same or different. When there are multiple R ¹ groups, adjacent R ^{1 groups} may be bonded to each other to form a ring.

a is an integer between 0 and 4, and b is an integer between 0 and 3.

R ³ and R ⁴ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms. These groups may further have substituents. When there are multiple R ³ and R ⁴ groups, they may be the same or different.

^L1 represents an organic ligand, and m is an integer from 1 to 3.

From the perspective of durability, R ¹ to R ⁴ are each independently preferably an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms or a (hetero)aryl group having 3 to 20 carbon atoms. Further preferably, they are an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms or a (hetero)aryl group having 3 to 20 carbon atoms. Further preferably, they are an alkyl group having 1 to 20 carbon atoms, an aralkyl group having 7 to 40 carbon atoms or an aryl group having 6 to 20 carbon atoms.

The substituents that R ¹ to R ⁴ may further have are preferably substituents selected from the substituent group Z described below.

When a is 2 or more, two adjacent R ^{1 groups} may bond to each other to form a ring.

Examples of compounds in which multiple R ^{1 groups} are present and adjacent R ¹ groups are bonded to form a ring include fluorene, naphthalene, dibenzothiophene, and dibenzofuran. From the perspective of stability, fluorene is particularly preferred.

From the perspective of increasing the wavelength of emitted light, it is preferred that adjacent R ¹ groups bond to each other to form a ring.

Furthermore, from the perspective of not increasing the wavelength of emitted light, it is preferred that adjacent R ^1s do not bond to each other and do not form a ring. In other words, it is preferred that a in formula (1) is 1, or a is 2 or greater and that there is no ring formed by adjacent R ^1s bonding to each other.

Regarding a, 0 is preferred for ease of production, and 1 or 2 is preferred for improved durability and solubility, and 1 is more preferred. Regarding b, 0 is preferred for ease of production, and 1 is preferred for improved solubility.

From the perspective of stabilizing the LUMO by accumulating a large number of highly electron-accepting structures containing triazine rings, m is preferably 2 or 3, and more preferably 3.

L ¹ is an organic ligand, not particularly limited, but preferably a monovalent, bidentate ligand, more preferably selected from the following chemical formulas. Furthermore, the dashed line in the chemical formula represents a coordination bond. When two organic ligands L ¹ are present, the organic ligands L ¹ may have different structures. Furthermore, when m is 3, L ¹ is absent.

When m in formula (1) is less than 3, ^L1 preferably has at least one structure selected from the group consisting of the following formulas (3), (4), and (5).

In formulas (3), (4), and (5), R ⁹ and R ¹⁰ have the same meanings as R ¹ in formula (1). Specifically, they are selected from the same group of substituents as those selected for R ¹ , and the preferred examples are also the same. Furthermore, they may have substituents. When there are multiple R ⁹ and R ¹⁰ , they may be the same or different.

R ¹¹ to R ¹³ are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may be substituted with a fluorine atom, a phenyl group which may be substituted with an alkyl group having 1 to 20 carbon atoms, or a halogen atom.

g is an integer between 0 and 4. h is an integer between 0 and 4.

Ring B is a pyridine ring, a pyrimidine ring, an imidazole ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, an azatriazole ring, a carboline ring, a benzothiazole ring, or a benzoxazole ring. Ring B may further have a substituent.

The substituents that R ⁹ , R ¹⁰ and Ring B may further have are preferably substituents selected from the substituent group Z described below.

More preferably, R ⁹ and R ¹⁰ are each independently an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 30 carbon atoms which may be substituted with an alkyl group having 1 to 20 carbon atoms. Here, the aryl group having 6 to 30 carbon atoms refers to a monocyclic ring, a bicyclic condensed ring, a tricyclic condensed ring, or a group formed by linking multiple monocyclic, bicyclic, or tricyclic condensed rings.

Regarding g and h, 0 is preferred for ease of production, while 1 or 2 is preferred for improved solubility, and 1 is even more preferred.

R ¹¹ to R ¹³ each independently represent a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may be substituted with a fluorine atom, a phenyl group which may be substituted with an alkyl group having 1 to 20 carbon atoms, or a halogen atom. More preferably, R ¹¹ and R ¹³ are methyl or t-butyl, and R ¹² is a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, or a phenyl group.

From the perspective of durability, Ring B is preferably a pyridine ring, a pyrimidine ring, or an imidazole ring, with a pyridine ring being more preferred. From the perspective of durability and improved solubility, the hydrogen atom on Ring B is preferably substituted with an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms.

In addition, from the perspective of ease of production, the hydrogen atom on ring B is preferably unsubstituted.

Furthermore, the hydrogen atoms on ring B are likely to generate excitons when used in an organic electroluminescent device. Therefore, from the perspective of improving luminescence efficiency, it is preferably substituted with a phenyl or naphthyl group that may have a substituent. The substituent that the phenyl or naphthyl group may have is preferably a substituent selected from the substituent group Z described below.

Ring B is more likely to generate excitons on the auxiliary dopant, so from the perspective of improving luminescence efficiency, quinoline rings, isoquinoline rings, quinazoline rings, quinoxaline rings, nitrogen-doped tert-benzene rings, and carboline rings are preferred. Among these, quinoline rings, isoquinoline rings, and quinazoline rings are more preferred from the perspective of durability and red luminescence.

More preferably, the substituent of Ring B is an alkyl group having 1 to 20 carbon atoms, or an aryl group having 6 to 20 carbon atoms which may be substituted with an alkyl group having 1 to 20 carbon atoms. Here, the aryl group having 6 to 20 carbon atoms refers to a monocyclic ring, a bicyclic condensed ring, a tricyclic condensed ring, or a group formed by linking multiple monocyclic, bicyclic, or tricyclic condensed rings.

The compound represented by formula (1) as the luminescent dopant contained in the composition for an organic electroluminescent device of this embodiment is preferably a phenyl group optionally having a substituent as R ³ and R ⁴ , namely, a compound represented by the following formula (1-1).

[In the above formula, R ¹ , R ² , a, b, L ¹ , and m have the same meanings as R ¹ , R ² , a, b, L ¹ , and m in formula (1); R ⁶ and R ⁷ are independently an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have substituents; in the presence of multiple R ⁶ , R In the case of ⁷ , these may be the same or different; d and e are independently integers from 0 to 5.

In terms of durability, R ⁶ and R ⁷ are more preferably an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms, further preferably an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms, and further preferably an alkyl group having 1 to 20 carbon atoms or an aralkyl group having 7 to 40 carbon atoms.

The substituent that R ⁶ and R ⁷ may further have is preferably a substituent selected from the substituent group Z described below.

Regarding d and e, 0 is preferred for ease of production, and 1 or 2 is preferred for improved durability and solubility, with 1 being more preferred. Regarding b, 0 is preferred for ease of production, and 1 is preferred for improved solubility.

The luminescent dopant represented by formula (1) contained in the composition for an organic electroluminescent device of this embodiment preferably has a structure in which a is 2 or greater and adjacent R ^1s are bonded to each other to form a fluorene ring. Among them, compounds represented by formula (1-2) are preferred.

[Chemistry 11]

[In the above formula, R ² to R ⁴ , b, L ¹ , and m have the same meanings as R ² to R ⁴ , b, L ¹ , and m in formula (1); R ¹⁴ to R ¹⁶ are substituents. When there are multiple R ¹⁴ to R ¹⁶ groups, they may be the same or different; i is an integer from 0 to 4.]

^R14 is a substituent for ^R1 when ^R1 is a phenyl group, and is preferably a substituent selected from the substituent group Z described below. More preferably, it is an alkyl group having 1 to 20 carbon atoms, or an aromatic alkyl group having 6 to 30 carbon atoms which may be substituted with an alkyl group having 1 to 20 carbon atoms. Here, the aromatic alkyl group having 6 to 30 carbon atoms refers to a monocyclic ring, a 2 to 4 condensed ring, or a group formed by linking multiple monocyclic or 2 to 4 condensed rings. Further preferably, it is an alkyl group having 1 to 20 carbon atoms, and even more preferably, it is an alkyl group having 1 to 8 carbon atoms.

^R15 and ^R16 are substituents for a portion of ^R1 or for ^R1 when ^R1 is a methyl group, and are preferably each independently an alkyl group having 1 to 20 carbon atoms, an aromatic alkyl group having 6 to 30 carbon atoms which may be substituted with an alkyl group having 1 to 20 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, or an aromatic alkyl group having 6 to 30 carbon atoms which may be substituted with an alkoxy group having 1 to 20 carbon atoms. Here, the aromatic alkyl group having 6 to 30 carbon atoms refers to a monocyclic ring, a 2- to 4-ring condensed ring, or a group formed by linking multiple monocyclic or 2- to 4-ring condensed rings. More preferably, it is an alkyl group having 1 to 20 carbon atoms or an aromatic hydrocarbon group having 6 or 12 carbon atoms which may be substituted by an alkyl group having 1 to 20 carbon atoms. Even more preferably, it is an alkyl group having 1 to 8 carbon atoms or an aromatic hydrocarbon group having 6 carbon atoms which may be substituted by an alkyl group having 1 to 8 carbon atoms. Here, the aromatic hydrocarbon structure having 6 carbon atoms is a benzene structure, and the aromatic hydrocarbon structure having 12 carbon atoms is a biphenyl structure.

Specific examples of preferred alkyl groups for R ¹⁴ to R ¹⁶ include methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, isopropyl, isobutyl, isopentyl, t-butyl, cyclohexyl, and 2-ethylhexyl.

Specific examples of preferable aromatic hydrocarbon groups in R ¹⁴ to R ¹⁶ include benzene ring, naphthalene ring, anthracene ring, phenanthrene ring, perylene ring, fused tetraphenyl ring, pyrene ring, benzopyrene ring, ring, triphenylene ring, fluoranthene ring, biphenyl, terphenyl, etc.

Specific examples of preferred alkoxy groups for R ¹⁵ and R ¹⁶ include methoxy, ethoxy, propoxy, isopropoxy, hexyloxy, cyclohexyloxy, and octadecyloxy.

The compound represented by formula (1-1) serving as a luminescent dopant contained in the composition for an organic electroluminescent device of this embodiment is preferably a compound represented by formula (1-3).

[In the above formula, R ² , R ⁶ , R ⁷ , b, d, e, L ¹ , and m have the same meanings as R ² , R ⁶ , R ⁷ , b, d, e, L ¹ , and m in formula (1-1); R ¹⁴ to R ¹⁶ are substituents. If there are multiple R ¹⁴ to R ¹⁶ , they may be the same or different; i is an integer from 0 to 4.]

The substituents represented by R ¹⁴ to R ¹⁶ have the same meanings as the substituents represented by R ¹⁴ to R ¹⁶ in formula (1-2), and the preferred ranges are also the same.

Preferred specific examples of the compound represented by formula (1) as a light-emitting dopant contained in the composition for an organic electroluminescent device of this embodiment other than the compounds shown in the examples are shown below, but the present invention is not limited to these.

[Chemistry 14]

[Chemistry 15]

[Auxiliary additives]

The composition for an organic electroluminescent device of this embodiment includes a compound represented by the following formula (2), which mainly functions as an auxiliary dopant. The maximum emission wavelength of the compound represented by formula (2) is shorter than that of the compound represented by formula (1) serving as the luminescent dopant. Therefore, when the auxiliary dopant represented by formula (2) becomes excited, energy shifts to the luminescent dopant represented by formula (1) having a lower excitation energy. Therefore, after the luminescent dopant becomes excited, luminescence of the self-luminescent dopant is observed.

The compound represented by formula (2) may be contained in one type or in multiple types. In addition, the compound serving as an auxiliary dopant may also contain a compound serving as an auxiliary dopant other than the compound represented by formula (2). However, in this case, the total content of the compound represented by formula (2) relative to the total amount of the compound serving as the auxiliary dopant is preferably set to 50% by mass or more, more preferably 100% by mass. In other words, it is more preferable to use only the compound represented by formula (2).

In addition, it is preferred that the composition ratio of the compound represented by formula (1) be greater than or equal to the composition ratio of the compound represented by formula (2) in terms of parts by mass. This can suppress direct luminescence from the auxiliary dopant represented by formula (2), and energy can be efficiently transferred from the auxiliary dopant represented by formula (2) to the luminescent dopant represented by formula (1). Therefore, luminescence from the luminescent dopant can be obtained with high efficiency.

[Chemistry 16]

In the formula, R ^<5> is an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms. These groups may further have substituents. When there are multiple R ^{<5> groups} , they may be the same or different.

c is an integer between 0 and 4.

Ring A is any one of a pyridine ring, a pyrazine ring, a pyrimidine ring, an imidazole ring, an oxazole ring, a thiazole ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, an nitrogen-doped tert-benzene ring, a carboline ring, a benzothiazole ring, and a benzoxazole ring.

Ring A may have a substituent.

The substituent is a fluorine atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms. Adjacent substituents bonded to Ring A may bond to each other to form a ring. When there are multiple Ring A groups, these substituents may be the same or different.

^L2 represents an organic ligand, and n is an integer from 1 to 3.

The substituent that R ⁵ may further have is preferably a substituent selected from the substituent group Z described below.

From the perspective of durability, R ^is more preferably an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms, and more preferably an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms. From the perspective of durability and solubility, R ^is preferably a phenyl group which may have a substituent and is bonded to the meta (m-) position of Ring A or the para (p-) position of the iridium. Specifically, a compound represented by the following formula (2-1) is preferred. The optional substituent is preferably a substituent selected from the substituent group Z described below.

[Chemistry 17]

[In the above formula, ring A, L ² , and n have the same meanings as ring A, L ² , and n in formula (2).

R ^<8> is an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms. These groups may further have substituents. When there are multiple R ^<8> groups, they may be the same or different.

f is an integer between 0 and 5.

The substituent that ^R8 may further have is preferably a substituent selected from the substituent group Z described below.

Regarding f, 0 is preferred for ease of production, while 1 or 2 is preferred for durability and improved solubility, and 1 is more preferred.

In terms of durability, Ring A is preferably a pyridine ring, a pyrimidine ring, or an imidazole ring, and more preferably a pyridine ring.

From the perspective of durability and improved solubility, the hydrogen atoms on Ring A are preferably substituted with an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms. Furthermore, from the perspective of ease of production, the hydrogen atoms on Ring A are preferably unsubstituted. The hydrogen atoms on Ring A facilitate exciton generation when used in an organic electroluminescent device, so from the perspective of improved luminescence efficiency, they are preferably substituted with a phenyl or naphthyl group, which may have a substituent.

As Ring A, quinoline, isoquinoline, quinazoline, quinoxaline, nitrogen-doped tert-benzene, and carboline rings are preferred because they facilitate exciton generation on the auxiliary dopant and enhance luminescence efficiency. Among these, quinoline, isoquinoline, and quinazoline rings are particularly preferred because of their durability.

^L2 is an organic ligand, and is not particularly limited, but is preferably a monovalent bidentate ligand. More preferred examples are the same as those listed as preferred examples for ^L1 . Furthermore, when two organic ligands ^L2 are present, the organic ligands ^L2 may have different structures. Furthermore, when n is 3, ^L2 is absent.

Preferred specific examples of the compound represented by formula (2) as an auxiliary dopant contained in the composition for an organic electroluminescent device of this embodiment other than the compounds shown in the examples are shown below, but the present invention is not limited to these.

[Chemistry 18]

[Substituent Group Z]

As a substituent, an alkyl group, an aralkyl group, a heteroaralkyl group, an alkoxy group, an aryloxy group, a heteroaryloxy group, an alkylsilyl group, an arylsilyl group, an alkylcarbonyl group, an arylcarbonyl group, an alkylamino group, an arylamino group, an aryl group, or a heteroaryl group can be used.

Preferred are alkyl groups having 1 to 20 carbon atoms, aralkyl groups having 7 to 40 carbon atoms, heteroaralkyl groups having 7 to 40 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, aryloxy groups having 6 to 20 carbon atoms, heteroaryloxy groups having 3 to 20 carbon atoms, alkylsilanyl groups having 1 to 20 carbon atoms, arylsilanyl groups having 6 to 20 carbon atoms, alkylcarbonyl groups having 2 to 20 carbon atoms, arylcarbonyl groups having 7 to 20 carbon atoms, alkylamino groups having 1 to 20 carbon atoms, arylamino groups having 6 to 20 carbon atoms, aryl groups having 6 to 30 carbon atoms, or heteroaryl groups having 3 to 30 carbon atoms. More specifically, they are the substituents listed in [Specific Examples of Substituents] below.

Furthermore, it is preferably an alkyl group having 1 to 20 carbon atoms, an aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, an aryloxy group having 6 to 20 carbon atoms, or an aryl group having 6 to 30 carbon atoms.

[Specific examples of substituents]

Specific examples of the substituents in the above-mentioned compound structures and the substituents in the above-mentioned substituent group Z are described below.

The alkyl group having 1 to 20 carbon atoms may be any of linear, branched, or cyclic. More specifically, it includes methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-octyl, isopropyl, isobutyl, isopentyl, t-butyl, and cyclohexyl. Preferred are linear alkyl groups having 1 to 8 carbon atoms, such as methyl, ethyl, n-butyl, n-hexyl, and n-octyl.

The (hetero)aralkyl group having 7 to 40 carbon atoms refers to a group in which a portion of the hydrogen atoms constituting a linear, branched, or cyclic alkyl group are substituted with an aryl or heteroaryl group. More specifically, examples include 2-phenyl-1-ethyl, cumyl, 5-phenyl-1-pentyl, 6-phenyl-1-hexyl, 7-phenyl-1-heptyl, and tetrahydronaphthyl. Preferred among these are 5-phenyl-1-pentyl, 6-phenyl-1-hexyl, and 7-phenyl-1-heptyl.

Specific examples of the alkoxy group having 1 to 20 carbon atoms include methoxy, ethoxy, propoxy, isopropoxy, hexyloxy, cyclohexyloxy, and octadecyloxy. Of these, hexyloxy is preferred.

Specific examples of the (hetero)aryloxy group having 3 to 20 carbon atoms include phenoxy and 4-methylphenyloxy. Among them, phenoxy is preferred.

Specific examples of the alkylsilyl group having 1 to 20 carbon atoms include trimethylsilyl, triethylsilyl, triisopropylsilyl, dimethylphenyl, t-butyldimethylsilyl, and t-butyldiphenylsilyl. Among them, triisopropyl, t-butyldimethylsilyl, and t-butyldiphenylsilyl are preferred.

Specific examples of the arylsilyl group having 6 to 20 carbon atoms include diphenylpyridylsilyl and triphenylsilyl. Among them, triphenylsilyl is preferred.

Specific examples of the alkylcarbonyl group having 2 to 20 carbon atoms include acetyl, propionyl, trimethylacetyl, hexyl, decyl, and cyclohexylcarbonyl. Of these, acetyl and trimethylacetyl are preferred.

Specific examples of the arylcarbonyl group having 7 to 20 carbon atoms include benzoyl, naphthyl, and benzoimido. Among them, benzoyl is preferred.

Specific examples of the alkylamino group having 1 to 20 carbon atoms include methylamino, dimethylamino, diethylamino, ethylmethylamino, dihexylamino, dioctylamino, and dicyclohexylamino. Among them, dimethylamino and dicyclohexylamino are preferred.

Specific examples of the arylamino group having 6 to 20 carbon atoms include phenylamino, diphenylamino, di(4-tolyl)amino, and di(2,6-dimethylphenyl)amino. Among them, diphenylamino and di(4-tolyl)amino are preferred.

The (hetero)aryl group having 3 to 30 carbon atoms refers to an aromatic alkyl group having one free valence, an aromatic heterocyclic group, a linked aromatic alkyl group formed by linking multiple aromatic alkyl groups, a linked aromatic heterocyclic group formed by linking multiple aromatic heterocyclic groups, or a group formed by arbitrarily linking at least one aromatic alkyl group or aromatic heterocyclic group.

As specific examples, there are benzene rings, naphthalene rings, anthracene rings, phenanthrene rings, perylene rings, fused tetraphenyl rings, pyrene rings, benzopyrene rings, ring, tris-benzene ring, anthracene ring, furan ring, benzofuran ring, dibenzofuran ring, thiophene ring, benzothiophene ring, dibenzothiophene ring, pyrrole ring, pyrazole ring, imidazole ring, oxadiazole ring, indole ring, carbazole ring, pyrroloimidazole ring, pyrrolopyrazole ring, pyrrolopyrrole ring, thienopyrrole ring, thienothiophene ring, furanopyrrole ring, furanofuran ring , thienofuran ring, benzoisoxazole ring, benzoisothiazole ring, benzimidazole ring, pyridine ring, pyrazine ring, oxazine ring, pyrimidine ring, triazine ring, quinoline ring, isoquinoline ring, cinnoline ring, quinoxaline ring, perimidine ring, quinazoline ring, quinazolinone ring, azulene ring, etc. Examples of linked aromatic hydrocarbon groups formed by linking multiple aromatic hydrocarbons include biphenyl and terphenyl.

Among (hetero)aryl groups, from the perspective of durability, preferred are benzene rings, naphthalene rings, dibenzofuran rings, dibenzothiophene rings, carbazole rings, pyridine rings, pyrimidine rings, and triazine rings, each having one free valence. More preferred are aryl groups having 6 to 18 carbon atoms, such as benzene rings, naphthalene rings, or phenanthrene rings, which may be substituted with an alkyl group having 1 to 8 carbon atoms, or pyridine rings, which may be substituted with an alkyl group having 1 to 4 carbon atoms. Further preferred are aryl groups having 6 to 18 carbon atoms, such as benzene rings, naphthalene rings, or phenanthrene rings, which may be substituted with an alkyl group having 1 to 8 carbon atoms.

When a group in a compound has multiple substituents, combinations of these substituents may include, but are not limited to, combinations of aryl and alkyl groups, combinations of aryl and aralkyl groups, or combinations of aryl and alkyl or aralkyl groups. Examples of combinations of aryl and aralkyl groups include combinations of benzene, biphenyl, or terphenyl with 5-phenyl-1-pentyl or 6-phenyl-1-hexyl groups.

[Maximum luminous wavelength]

The following describes the method for measuring the maximum emission wavelength of the compound in this embodiment.

The maximum emission wavelength of a compound can be determined from the photoluminescence spectrum of a solution of the material dissolved in an organic solvent or from the photoluminescence spectrum of a thin film of the material alone.

For solution photoluminescence, the phosphorescence spectrum of a solution containing the compound dissolved at a concentration of 1×10 ^-4 mol/L or less in 2-methyltetrahydrofuran was measured at room temperature using a spectrophotometer (Hamamatsu Photonics C9920-02 Organic EL Quantum Yield Measurement Device). The wavelength at which the obtained phosphorescence intensity reaches its maximum value was defined as the maximum emission wavelength.

In the case of thin film photoluminescence, the material is vacuum evaporated or solution coated to form a thin film, and the photoluminescence is measured using the aforementioned spectrophotometer. The wavelength showing the maximum intensity of the obtained luminescence spectrum is defined as the maximum luminescence wavelength.

The maximum emission wavelengths of the compounds used as luminescent dopants and the compounds used as auxiliary dopants must be calculated using the same method for comparison.

The compound represented by formula (2) as an auxiliary dopant contained in the composition for an organic electroluminescent element of this embodiment has a shorter maximum emission wavelength than the compound represented by formula (1) as a luminescent dopant.

The maximum emission wavelength of the compound used as a luminescent dopant is preferably 580 nm or longer, more preferably 590 nm or longer, and even more preferably 600 nm or longer. Furthermore, it is preferably 700 nm or shorter, and even more preferably 680 nm or shorter. By keeping the maximum emission wavelength within this range, the material tends to exhibit a preferred color, making it a red luminescent material suitable for use in organic electroluminescent devices.

It is preferable to separate the maximum emission wavelength of the auxiliary dopant compound from the maximum emission wavelength of the luminescent dopant compound by at least 10 nm, as this allows for efficient energy exchange.

The compound represented by formula (1) is preferably contained in an amount equal to or greater than that of the compound represented by formula (2). That is, the composition ratio of the compound represented by formula (1) based on mass parts conversion is preferably equal to or greater than the composition ratio of the compound represented by formula (2). The compound represented by formula (1) is preferably contained in an amount 1 to 3 times the amount of the compound represented by formula (2) based on mass parts conversion. In terms of the luminous efficiency and life extension of the device, it is particularly preferably contained in an amount 1 to 2 times. In terms of obtaining brighter luminescence, it is further preferably contained in an amount of 2 times or more, and in terms of reducing the driving voltage of the device, it is further preferably contained in an amount of less than 2 times. This allows energy from the auxiliary dopant to be more efficiently transferred to the luminescent dopant, resulting in higher luminous efficiency and potentially extending the life of the device.

[Synthesis Method of Iridium Complex Compound]

The auxiliary dopant contained in the composition for the organic electroluminescent device of this embodiment and the compound represented by formula (2) and the compound represented by formula (1) serving as the luminescent dopant are all iridium complex compounds. The synthesis method of the iridium complex compound is shown below.

The ligand of the iridium complex compound can be synthesized by combining known methods. The ligand can be synthesized by a known reaction such as Suzuki-Miyaura coupling reaction of arylboronic acids with halogenated heteroaryls, or Friedlaender cyclization reaction of 2-formyl or acylanilines or acyl-aminopyridines located in adjacent positions (Chem. Rev. 2009, 109, 2652 or Organic Reactions, 1982, 28(2), 37-201).

Iridium complex compounds can be synthesized by combining the ligands obtained above with iridium chloride n-hydrate and other raw materials using known methods. This is described below.

As a method for synthesizing an iridium complex compound, for ease of understanding, the following method is used: a method of crosslinking an iridium binuclear complex represented by the following formula [A] via chlorine using a phenylpyridine ligand as an example (M.G.Colombo, T.C.Brunold, T.Riedener, H.U.Gudel, Inorganic Chemistry (Inorg.Chem.) 1994, 33, 545-550); a method of further crosslinking a binuclear complex represented by the following formula [B] via chlorine; The target product can be obtained by exchanging with acetylacetone and converting it into a mononuclear complex (S.Lamansky, P.Djurovich, D.Murphy, F.Abdel-Razzaq, R.Kwong, I.Tsyba, M.Borz, B.Mui, R.Bau, M.Thompson, Inorganic Chemistry (Inorg.Chem.), 2001, 40, 1704-1711), etc., but is not limited to these methods.

For example, the typical reaction conditions represented by the following formula [A] are as follows. In this specification, Et in the chemical formula refers to an ethyl group, and Tf refers to a trifluoromethylsulfonyl group.

In the first stage, a chlorinated iridium dinuclear complex is synthesized by reacting two equivalents of the first ligand with one equivalent of iridium chloride n-hydrate. A mixture of 2-ethoxyethanol and water is typically used as the solvent, but no solvent or other solvents can also be used. The ligand can be used in excess, or additives such as bases can be used to promote the reaction. Other crosslinking anionic ligands, such as bromine, can also be used in place of chlorine.

The reaction temperature is not particularly limited, but is generally preferably above 0°C, more preferably above 50°C. Furthermore, it is preferably below 250°C, more preferably below 150°C. By keeping the reaction temperature within this temperature range, only the target reaction proceeds without the production of byproducts or decomposition reactions, tending to achieve high selectivity.

In the second stage, a halogen ion scavenger, such as silver triflate, is added to allow the second ligand to come into contact, yielding the target complex. Ethoxyethanol or diglyme are typically used as the solvent, but depending on the type of ligand, no solvent, other solvents, or a mixture of multiple solvents may be used. The reaction sometimes proceeds even without the addition of a halogen ion scavenger, so it is not always necessary. However, its addition is beneficial to increase reaction yield and selectively synthesize the facial isomer with a higher quantum yield. The reaction temperature is not particularly limited and is typically conducted in the range of 0°C to 250°C.

Typical reaction conditions represented by the following formula [B] are described.

The first-stage binuclear complex can be synthesized in the same manner as formula [A].

The second stage involves reacting the dinuclear complex with one or more equivalents of a 1,3-diketone compound, such as acetylacetone, and one or more equivalents of an alkaline compound, such as sodium carbonate, that can extract the active hydrogen of the 1,3-diketone compound, to convert it into a mononuclear complex coordinated by a 1,3-diketone ligand. Typically, a solvent such as ethoxyethanol or dichloromethane is used, which can dissolve the dinuclear complex as a starting material. However, if the ligand is in liquid form, the reaction can also be carried out without a solvent. The reaction temperature is not particularly limited and is typically carried out in the range of 0°C to 200°C.

In the third stage, at least one equivalent of the second ligand is reacted. The type and amount of solvent are not particularly limited, and no solvent is required if the second ligand is liquid at the reaction temperature. The reaction temperature is also not particularly limited, but due to its slightly limited reactivity, the reaction is typically conducted at higher temperatures, between 100°C and 300°C. Therefore, a high-boiling-point solvent, such as glycerol, is preferably used.

After the final reaction, purification is performed to remove unreacted starting materials, reaction by-products, and the solvent. Conventional purification procedures in organic synthetic chemistry can be applied, but as described in the aforementioned non-patent document, purification is primarily performed by parallel-phase silica gel column chromatography. The developing solvent can be hexane, heptane, dichloromethane, chloroform, ethyl acetate, toluene, methyl ethyl ketone, or methanol, either singly or in mixtures. Purification can also be repeated multiple times with varying conditions. Other chromatographic techniques, such as reversed-phase silica gel chromatography, size exclusion chromatography, paper chromatography, or purification procedures such as fractional washing, reprecipitation, recrystallization, suspension washing of the powder, and pressure-reduced drying, can be employed as needed.

[solvent, composition ratio]

The composition for an organic electroluminescent device of this embodiment contains a solvent.

The composition for an organic electroluminescent device is generally used to form a layer or film by a wet film formation method, and is particularly preferably used to form the light-emitting layer of an organic electroluminescent device.

The content of the luminescent dopant in the composition for an organic electroluminescent device is usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 20% by mass or less, preferably 10% by mass or less. By setting the content of the luminescent dopant within this range, when the composition is used in an organic electroluminescent device, the excitation energy is less likely to migrate to adjacent layers, such as a hole transport layer or a hole blocking layer, and the excitation energy is less likely to extinguish due to the interaction between excitons, thereby improving the luminescence efficiency. The content of the luminescent dopant is the total content of the compound represented by formula (1).

The content of the auxiliary dopant in the composition for an organic electroluminescent device is generally 0.005% by mass or more, preferably 0.05% by mass or more, and generally 10% by mass or less, preferably 5% by mass or less. By setting the content of the auxiliary dopant within this range, when the composition is used in an organic electroluminescent device, holes or electrons can be efficiently injected from adjacent layers, such as a hole transport layer or a hole blocking layer, into the light-emitting layer, thereby reducing the driving voltage. The content of the auxiliary dopant refers to the total content of the compound represented by formula (2).

The composition for an organic electroluminescent element may contain only one compound serving as an auxiliary dopant represented by formula (2), or may contain two or more compounds in combination. However, when two or more compounds are contained, the maximum emission wavelength of all the compounds serving as auxiliary dopant is shorter than the maximum emission wavelength of the compound serving as a luminescent dopant represented by formula (1). In addition, when two or more compounds serving as luminescent dopant represented by formula (1) are contained, the maximum emission wavelength of all the compounds serving as auxiliary dopant is shorter than the maximum emission wavelength of all the compounds serving as luminescent dopant.

In the composition for an organic electroluminescent device, the composition ratio (mass %) of the compound represented by formula (1) serving as a luminescent dopant is preferably the same as or greater than the composition ratio (mass %) of the compound represented by formula (2) serving as an auxiliary dopant. By increasing the composition ratio of the compound serving as a luminescent dopant, the width of the luminescent spectrum becomes narrower when the organic electroluminescent device is manufactured, resulting in brighter luminescence, making it suitable for use in display devices. Furthermore, when two or more compounds serving as auxiliary dopants are included, the total composition ratio (mass %) of the compound serving as the light-emitting dopant is preferably greater than the total composition ratio (mass %) of all compounds serving as auxiliary dopants.

The compound serving as the luminescent dopant preferably has a mass ratio of 1 to 3 times that of the compound serving as the auxiliary dopant, calculated on a mass basis. This allows energy from the auxiliary dopant to be more efficiently transferred to the luminescent dopant, thereby achieving higher luminescence efficiency. A mass ratio of 1 to 2 times is particularly preferred. To achieve brighter luminescence, the composition ratio (mass %) of the compound serving as the luminescent dopant is more preferably at least twice that of the compound serving as the auxiliary dopant. On the other hand, in order to reduce the drive voltage of the device, the composition ratio (mass %) of the compound serving as the light-emitting dopant is preferably less than twice the composition ratio (mass %) of the compound serving as the auxiliary dopant.

The solvent contained in the composition for an organic electroluminescent device is a volatile liquid component used to form a layer containing an auxiliary dopant and a luminescent dopant by wet film formation.

The solvent is not particularly limited as long as it can well dissolve the compound serving as the auxiliary dopant and the compound serving as the luminescent dopant as a solute. Preferably, it can dissolve the charge transport compound described below.

Preferable solvents include, for example, alkanes such as n-decane, cyclohexane, ethylcyclohexane, decahydronaphthalene, and dicyclohexane; aromatic hydrocarbons such as toluene, xylene, mesitylene, phenylcyclohexane, and tetrahydronaphthalene; halogenated aromatic hydrocarbons such as chlorobenzene, dichlorobenzene, and trichlorobenzene; 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenethyl ether, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, 2,4-dimethylbenzene; Aromatic ethers such as phenyl ether and diphenyl ether; aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate; aliphatic ketones such as cyclohexanone, cyclooctanone, and fenchone; aliphatic alcohols such as cyclohexanol and cyclooctanol; aliphatic ketones such as methyl ethyl ketone and dibutyl ketone; aliphatic alcohols such as butanol and hexanol; aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA). Alkanes or aromatic hydrocarbons are more preferred, and phenylcyclohexane is particularly preferred due to its excellent viscosity and boiling point in wet film-forming processes.

These solvents may be used alone or in any combination and ratio.

The boiling point of the solvent is generally 80°C or higher, preferably 100°C or higher, more preferably 150°C or higher, and particularly preferably 200°C or higher. This range prevents a decrease in film stability caused by evaporation of the solvent from the composition for an electroluminescent device during wet film formation. Furthermore, the boiling point is generally 270°C or lower, preferably 250°C or lower, and more preferably 240°C or lower.

The content of the solvent is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, and particularly preferably 80 parts by mass or more, relative to 100 parts by mass of the composition for an organic electroluminescent device. It is also preferably 99.95 parts by mass or less, more preferably 99.9 parts by mass or less, and particularly preferably 99.8 parts by mass or less.

The thickness of the luminescent layer of an organic electroluminescent device formed from the composition for an organic electroluminescent device is generally approximately 3 nm to 200 nm. By setting the solvent content above the lower limit, the viscosity of the composition can be prevented from becoming excessively high, which could impair film-forming workability. On the other hand, by setting the content below the upper limit, the film obtained by removing the solvent after film formation can be of a certain thickness, resulting in excellent film-forming properties.

[Charge transport compounds]

The organic electroluminescent device composition of this embodiment preferably further contains a charge transport compound.

As the charge transport compound, those previously used as materials for organic electroluminescent devices can be used. For example, triarylamine, biscarbazole, triaryltriazine, triarylpyrimidine and their derivatives, naphthalene, perylene, pyrene, anthracene, substituted with arylamine or carbazole groups, , condensed aromatic ring compounds such as tetraphenyl, phenanthrene, coronene, fluoranthene, triphenylene, fluorene, and acetylnaphthofluoranthracene.

Furthermore, the charge transport compound may be a polymer. Examples of polymeric charge transport compounds include polyfluorene-based materials such as poly(9,9-dioctylfluorene-2,7-diyl), poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(4-tert-butylphenyl))diphenylamine)], and poly[(9,9-dioctylfluorene-2,7-diyl)-co-(1,4-benzo-2{2,1'-3}-triazole)], and polystyrene-based materials such as poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-styrene].

These charge transport compounds may be used alone or in any combination and ratio.

[Organic electroluminescent device]

The organic electroluminescent device of this embodiment includes a layer formed using the above-mentioned organic electroluminescent device composition, preferably by a wet film formation method.

The organic electroluminescent device preferably comprises at least an anode, a cathode, and at least one organic layer between the anode and cathode on a substrate, with at least one of the organic layers being formed using the organic electroluminescent device composition of this embodiment. The layer is more preferably formed by a wet film formation method. Furthermore, the organic layer includes a luminescent layer, and more preferably, the luminescent layer is formed using the organic electroluminescent device composition of this embodiment.

In this specification, the term "wet film-forming method" refers to a method that uses a wet film-forming method, such as spin coating, dip coating, die coating, rod coating, doctor blade coating, roll coating, spray coating, capillary coating, inkjet printing, nozzle printing, screen printing, gravure printing, or flexographic printing, as a film-forming method, i.e., a coating method, and then dries the film formed by these methods.

Figure 1 is a schematic cross-sectional view of an example structure preferred for an organic electroluminescent device 10 of the present invention. In Figure 1 , reference numeral 1 represents a substrate, reference numeral 2 represents an anode, reference numeral 3 represents a hole injection layer, reference numeral 4 represents a hole transport layer, reference numeral 5 represents a light-emitting layer, reference numeral 6 represents a hole blocking layer, reference numeral 7 represents an electron transport layer, reference numeral 8 represents an electron injection layer, and reference numeral 9 represents a cathode.

The materials used in these structures can be known materials and are not particularly limited. Representative materials and production methods for each layer are described below as examples. When citing publications or papers, the relevant content may be appropriately adapted and used within the scope of common knowledge of those skilled in the art.

<Substrate 1>

Substrate 1 serves as a support for the organic electroluminescent element and is typically made of a quartz or glass plate, metal plate, metal foil, or synthetic resin or plastic film or sheet. Preferred among these are glass plates or films of transparent synthetic resins such as polyester, polymethacrylate, polycarbonate, and polyester. To minimize degradation of the organic electroluminescent element due to external gases, substrate 1 is preferably made of a material with high gas barrier properties. In particular, when using a synthetic resin substrate, which generally has low gas barrier properties, it is preferable to provide a dense silicon oxide film or the like on at least one surface of substrate 1 to enhance the gas barrier properties.

<Anode 2>

Anode 2 is responsible for injecting holes into the layers adjacent to the light-emitting layer. Anode 2 typically includes metals such as aluminum, gold, silver, nickel, palladium, and platinum; metal oxides such as indium and/or tin oxides; metal halides such as copper iodide; and conductive polymers such as carbon black, poly(3-methylthiophene), polypyrrole, and polyaniline.

The anode 2 is typically formed using dry methods such as sputtering and vacuum evaporation. When using metal microparticles such as silver, copper iodide, carbon black, conductive metal oxide microparticles, or conductive polymer powders, the anode 2 can be formed by dispersing the metal in a suitable binder resin solution and coating the solution on the substrate 1. In the case of conductive polymers, the anode 2 can also be formed by directly forming a thin film on the substrate by electrolytic polymerization or by coating the substrate with the conductive polymer (Applied Physics Letters, Vol. 60, p. 2711, 1992).

Anode 2 typically has a single-layer structure, but a laminated structure may also be used. If anode 2 has a laminated structure, different conductive materials may be laminated on the first anode layer.

The thickness of the anode 2 can be determined based on the desired transparency and material. In particular, when high transparency is required, a thickness that allows visible light transmittance to be 60% or greater, and more preferably 80% or greater, is preferred. The thickness of the anode 2 is typically 5 nm or greater, preferably 10 nm or greater, and typically 1000 nm or less, preferably 500 nm or less.

If transparency is not required, the thickness of the anode 2 can be set to any desired thickness based on the required strength, etc. In this case, the anode 2 can also be the same thickness as the substrate 1.

After forming the anode 2, if subsequent layers are to be deposited on its surface, it is preferable to perform a treatment such as ultraviolet light + ozone, oxygen plasma, or argon plasma before film formation to remove impurities on the anode and adjust its ionization potential to improve hole injection properties.

<Hole injection layer 3>

The layer responsible for transporting holes from the anode 2 side to the light-emitting layer 5 side is generally referred to as a hole injection transport layer or a hole transport layer. If there are two or more layers responsible for transporting holes from the anode 2 side to the light-emitting layer 5 side, the layer closer to the anode 2 side is sometimes referred to as the hole injection layer 3.

The following description of the hole injection layer 3 will refer to the hole injection transport layer or the hole transport layer when there is only one layer responsible for transporting holes. Specifically, the hole transport layer 4, described later, is distinct from the hole transport layer when there is only one layer responsible for transporting holes. It is the name of the layer closest to the light-emitting layer 5 when there are two or more layers, and is an arbitrary layer.

To enhance the function of transporting holes from the anode 2 to the light-emitting layer 5, it is preferable to use a hole injection layer 3. When using a hole injection layer 3, the hole injection layer 3 is typically formed on the anode 2.

The thickness of the hole injection layer 3 is usually at least 1 nm, preferably at least 5 nm, and usually at most 1000 nm, preferably at most 500 nm.

The hole injection layer 3 can be formed by vacuum evaporation or wet deposition. Wet deposition is preferred for superior film-forming properties.

The hole injection layer 3 preferably contains a hole-transporting compound, more preferably a hole-transporting compound and an electron-accepting compound. Furthermore, the hole injection layer 3 preferably contains a cationic radical compound, and particularly preferably contains a cationic radical compound and a hole-transporting compound.

(Hole-transporting compound)

The hole injection layer-forming composition generally contains a hole-transporting compound that will serve as the hole injection layer 3.

In the case of wet film deposition, a solvent is typically also included. The composition for forming the hole injection layer preferably has high hole transport properties and can efficiently transport injected holes. Therefore, it is preferred that the composition has a high hole mobility and is less likely to generate impurities that can trap holes during manufacturing or use. Furthermore, it is preferred that the composition has excellent stability, a low ionization potential, and high transparency to visible light. In particular, when the hole injection layer 3 is in contact with the light-emitting layer 5, that is, when the layer responsible for transporting holes from the anode 2 to the light-emitting layer 5 is a portion of the hole injection layer 3, it is preferred that the layer not quench the light emitted from the light-emitting layer 5 or that the layer not form an exciplex with the light-emitting layer 5 without reducing the light-emitting efficiency.

From the perspective of hindering charge injection from the anode 2 to the hole injection layer 3, the hole-transporting compound preferably has an ionization potential of 4.5 eV to 6.0 eV. Examples of hole-transporting compounds include aromatic amine compounds, phthalocyanine compounds, porphyrin compounds, oligothiophene compounds, polythiophene compounds, benzylphenyl compounds, compounds formed by linking tertiary amines with fluorenyl groups, hydrazone compounds, silazane compounds, and quinacridone compounds.

Among the exemplified compounds, aromatic amine compounds are preferred in terms of amorphousness and visible light transmittance, and aromatic tertiary amine compounds are particularly preferred. Aromatic tertiary amine compounds also include compounds having an aromatic tertiary amine structure and a group derived from an aromatic tertiary amine.

The type of aromatic tertiary amine compound is not particularly limited. From the perspective of achieving uniform luminescence due to its surface smoothing effect, it is preferred to use a polymer compound (a polymeric compound having linked repeating units) with a weight-average molecular weight of 1,000 to 1,000,000. Preferred examples of aromatic tertiary amine polymer compounds include polymer compounds having repeating units represented by the following formula (I).

In formula (I), ^Ar1 and ^Ar2 each independently represent a monovalent aromatic group that may have a substituent or a monovalent heteroaromatic group that may have a substituent. ^Ar3 to ^Ar5 each independently represent a divalent aromatic group that may have a substituent or a divalent heteroaromatic group that may have a substituent. Q represents a linking group selected from the following linking group group. In addition, two groups of ^Ar1 to ^Ar5 bonded to the same nitrogen atom may bond to each other to form a ring.

The linking base is shown below.

(In the above formulae, Ar ⁶ to Ar ¹⁶ each independently represent an aromatic group which may have a substituent or a heteroaromatic group which may have a substituent; ^Ra and ^Rb each independently represent a hydrogen atom or an arbitrary substituent)

The aromatic and heteroaromatic groups represented by Ar ¹ to Ar ¹⁶ are preferably groups derived from a benzene ring, a naphthalene ring, a phenanthrene ring, a thiophene ring, or a pyridine ring, and more preferably groups derived from a benzene ring or a naphthalene ring, in view of solubility, heat resistance, and hole injection transport properties of the polymer compound.

Specific examples of aromatic tertiary amine polymer compounds having repeating units represented by formula (I) include compounds described in International Publication No. 2005/089024.

(Electron-accepting compound)

The conductivity of the hole injection layer 3 can be increased by oxidation of the hole transport compound, so it is preferred that the hole injection layer 3 contain an electron accepting compound.

The electron-accepting compound is preferably a compound having an oxidizing ability and the ability to accept a single electron from the hole-transporting compound. Specifically, a compound having an electron affinity of 4 eV or greater is more preferred, and a compound having an electron affinity of 5 eV or greater is even more preferred.

Examples of such electron-accepting compounds include one or more compounds selected from the group consisting of triarylboron compounds, metal halides, Lewis acids, organic acids, onium salts, salts of arylamines and metal halides, and salts of arylamines and Lewis acids. Specifically, they include: organically substituted onium salts such as 4-isopropyl-4'-methyldiphenyliodonium tetrakis(pentafluorophenyl)borate and triphenylphosphine tetrafluoroborate (International Publication No. 2005/089024); high-valence inorganic compounds such as iron(III) chloride (Japanese Patent Publication No. 11-251067) and ammonium peroxodisulfate; cyano compounds such as tetracyanoethylene; aromatic boron compounds such as tris(pentafluorophenyl)borane (Japanese Patent Publication No. 2003-31365); fullerene derivatives, and iodine.

(Cationic free radical compound)

The cationic radical compound is preferably an ionic compound comprising a cationic radical, a chemical species that has removed one electron from a hole-transporting compound, and a counter anion. When the cationic radical originates from a hole-transporting polymer compound, the cationic radical has a structure in which one electron has been removed from a repeating unit of the polymer compound.

As a cation radical, in terms of amorphous properties, visible light transmittance, heat resistance, and solubility, a chemical species obtained by removing one electron from the compound described above as a hole-transporting compound is preferred.

Cationic radical compounds can be generated by mixing the hole-transporting compound and the electron-accepting compound. By mixing the hole-transporting compound and the electron-accepting compound, electrons migrate from the hole-transporting compound to the electron-accepting compound, generating a cationic radical compound containing cationic radicals of the hole-transporting compound and counter anions.

Cationic radical compounds derived from polymers, such as poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonic acid) (PEDOT/PSS) (Advanced Materials, 2000, Vol. 12, p. 481) or emeraldine hydrochloride (J. Phys. Chem., 1990, Vol. 94, p. 7716), can also be generated by oxidative polymerization (dehydrogenation polymerization).

The oxidative polymerization mentioned here involves chemically or electrochemically oxidizing monomers in an acidic solution using peroxodisulfate or the like. In this oxidative polymerization (dehydrogenation), the monomers are oxidized to form polymers, and cationic radicals are generated, which remove one electron from the repeating unit of the polymer, using anions from the acidic solution as counterions.

(Formation of hole injection layer 3 using wet film deposition)

When forming the hole injection layer 3 by a wet film formation method, the material to become the hole injection layer 3 is typically mixed with a soluble solvent (hole injection layer solvent) to prepare a film-forming composition (hole injection layer forming composition). This hole injection layer forming composition is then formed by a wet film formation method onto a layer corresponding to the lower layer of the hole injection layer 3, typically the anode 2, and dried. Drying of the formed film can be performed in the same manner as the drying method used to form the light-emitting layer 5 by a wet film formation method.

The concentration of the hole-transporting compound in the hole-injection layer-forming composition is arbitrary unless the effects of the present invention are significantly impaired. A low concentration is preferred for uniformity of film thickness, while a high concentration is preferred for minimizing defects in the hole-injection layer 3. The concentration of the hole-transporting compound in the hole-injection layer-forming composition is preferably 0.01% by mass or greater, more preferably 0.1% by mass or greater, and particularly preferably 0.5% by mass or greater. Furthermore, it is preferably 70% by mass or less, more preferably 60% by mass or less, and particularly preferably 50% by mass or less.

Examples of solvents include ether solvents, ester solvents, aromatic hydrocarbon solvents, and amide solvents.

Examples of ether solvents include aliphatic ethers such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA), and aromatic ethers such as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenethyl ether, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, and 2,4-dimethylanisole.

Examples of ester solvents include aromatic esters such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate.

Examples of aromatic hydrocarbon solvents include toluene, xylene, cyclohexylbenzene, 3-isopropylbiphenyl, 1,2,3,4-tetramethylbenzene, 1,4-diisopropylbenzene, and methylnaphthalene.

Examples of amide-based solvents include N,N-dimethylformamide and N,N-dimethylacetamide.

In addition to these, dimethyl sulfoxide and the like can also be used.

The hole injection layer 3 is typically formed using a wet film deposition method by preparing a hole injection layer-forming composition, applying it to a layer corresponding to the lower layer of the hole injection layer 3, typically the anode 2, and drying it. The hole injection layer 3 is typically dried after film formation by heating or reduced pressure drying.

(Formation of hole injection layer 3 using vacuum evaporation)

When the hole injection layer 3 is formed by vacuum evaporation, the constituent materials of the hole injection layer 3, i.e., one or more of the aforementioned hole transporting compounds, electron accepting compounds, etc., are usually placed in a crucible placed in a vacuum container. At this time, when two or more materials are used, they are usually placed in different crucibles respectively. Thereafter, after the vacuum container is evacuated to about 10 ^-4 Pa by a vacuum pump, the crucible is heated, and the material in the crucible is evaporated while controlling the evaporation amount. When two or more materials are used, each crucible is usually heated, and the evaporation amount is independently controlled while being evaporated. Through the above operation, the hole injection layer 3 is formed on the anode 2 on the substrate placed facing the crucible. When two or more materials are used, they may be placed in a crucible as a mixture and heated to evaporate to form the hole injection layer 3 .

The degree of vacuum during evaporation is not particularly limited unless it significantly impairs the effects of the present invention, but is typically 0.1× ^10-6 Torr (0.13× ^10-4 Pa) or higher and 9.0× ^10-6 Torr (12.0× ^10-4 Pa) or lower. The evaporation rate is not particularly limited unless it significantly impairs the effects of the present invention, but is typically 0.1 Å/s or higher and 5.0 Å/s or lower. The film formation temperature during evaporation is not particularly limited unless it significantly impairs the effects of the present invention, but is preferably 10°C or higher and 50°C or lower.

<Hole transport layer 4>

The hole transport layer 4 is a layer responsible for transporting holes from the anode 2 to the light-emitting layer 5. While the hole transport layer 4 is not essential for the organic electroluminescent device of this embodiment, its presence is preferred to enhance the function of transporting holes from the anode 2 to the light-emitting layer 5. When the hole transport layer 4 is provided, it is typically formed between the anode 2 and the light-emitting layer 5. If a hole injection layer 3 is present, it is formed between the hole injection layer 3 and the light-emitting layer 5.

The thickness of the hole transport layer 4 is usually 5 nm or more, preferably 10 nm or more, and usually 300 nm or less, preferably 100 nm or less.

The hole transport layer 4 can be formed by vacuum evaporation or wet deposition. Wet deposition is preferred for superior film-forming properties.

The hole transport layer 4 generally contains a hole transport compound forming the hole transport layer 4. Examples of hole transport compounds contained in the hole transport layer 4 include aromatic diamines containing two or more tertiary amines and two or more condensed aromatic rings substituted with nitrogen atoms, as exemplified by 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (Japanese Patent Publication No. 5-234681), aromatic amine compounds having a starburst structure, such as 4,4',4"-tris(1-naphthylphenylamino)triphenylamine (J. Lumin., Vol. 72-74, p. 985, 1997), and aromatic amine compounds containing tetramers of triphenylamine (Chemical Communications, 1997). Chem. Commun., p. 2175, 1996), spirocyclic compounds such as 2,2',7,7'-tetrakis-(diphenylamino)-9,9'-spirobifluorene (Synth. Metals, vol. 91, p. 209, 1997), and carbazole derivatives such as 4,4'-N,N'-dicarbazolebiphenyl. Also preferably used are polyvinylcarbazole, polyvinyltriphenylamine (Japanese Patent Publication No. 7-53953), and polyarylene ether sulfone containing tetraphenylbenzidine (Polym. Adv. Tech., vol. 7, p. 33, 1996).

(Formation of the hole transport layer 4 using a wet film deposition method)

When the hole transport layer 4 is formed by a wet film formation method, it is usually formed using a hole transport layer forming composition instead of a hole injection layer forming composition, similar to the case of forming the hole injection layer 3 by a wet film formation method.

When the hole transport layer 4 is formed using a wet film deposition method, the hole transport layer-forming composition generally further contains a solvent. The solvent used in the hole transport layer-forming composition can be the same solvent used in the hole injection layer-forming composition.

The concentration of the hole-transporting compound in the hole-transporting layer-forming composition can be set to the same range as the concentration of the hole-transporting compound in the hole-injection layer-forming composition.

The hole transport layer 4 can be formed using a wet film formation method in the same manner as the hole injection layer 3 described above.

(Formation of the hole transport layer 4 using vacuum evaporation)

When forming the hole transport layer 4 by vacuum evaporation, similar to the wet deposition method for forming the hole injection layer 3, the hole transport layer 4 can be formed using the material of the hole injection layer 3 instead of the material of the hole transport layer 4. The film formation conditions, such as the degree of vacuum, evaporation rate, and temperature during evaporation, can be the same as those used for vacuum evaporation of the hole injection layer 3.

<Luminous Layer 5>

The light-emitting layer 5 is a layer that emits light when an electric field is applied between a pair of electrodes. This is caused by the recombination of holes injected from the anode 2 and electrons injected from the cathode 9, which are excited and excited.

The light-emitting layer 5 is formed between the anode 2 and the cathode 9. If the hole injection layer 3 is present on the anode 2, the light-emitting layer 5 is formed between the hole injection layer 3 and the cathode 9. If the hole transport layer 4 is present on the anode 2, the light-emitting layer 5 is formed between the hole injection layer 3 and the cathode 9.

The thickness of the light-emitting layer 5 is arbitrary as long as it does not significantly impair the effects of the present invention. However, a thicker thickness is preferred to minimize film defects, while a thinner thickness is preferred to facilitate achieving a low drive voltage. The thickness of the light-emitting layer 5 is preferably 3 nm or greater, more preferably 5 nm or greater, and is generally preferably 200 nm or less, more preferably 100 nm or less.

The light-emitting layer 5 is preferably formed using the organic electroluminescent device composition of this embodiment, and more preferably formed by a wet coating method.

In addition to the luminescent layer formed by wet coating using the organic electroluminescent device composition of this embodiment, the organic electroluminescent device may also include other luminescent materials and charge-transporting materials. These other luminescent materials and charge-transporting materials are described in detail below.

(Luminescent material)

The luminescent material is not particularly limited as long as it emits light at the desired wavelength and does not impair the effects of the present invention. Known luminescent materials can be used. The luminescent material can be either fluorescent or phosphorescent, but preferably has good luminescence efficiency. From the perspective of internal quantum efficiency, phosphorescent materials are preferred.

Examples of fluorescent materials include the following.

Examples of the fluorescent material providing blue luminescence (blue fluorescent material) include naphthalene, perylene, pyrene, anthracene, coumarin, , p-bis(2-phenylvinyl)benzene and their derivatives, etc.

Examples of fluorescent materials that provide green luminescence (green fluorescent materials) include quinacridone derivatives, coumarin derivatives, and aluminum complexes such as Al(C ₉ H ₆ NO) ₃ .

Examples of fluorescent materials that provide yellow luminescence (yellow fluorescent materials) include rubrene and perimidone derivatives.

Examples of fluorescent materials that provide red luminescence (red fluorescent materials) include DCM (4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran) compounds, benzopyran derivatives, rose bengal derivatives, benzothiadone derivatives, and nitrogen-doped benzothiadone.

Examples of phosphorescent materials include organometallic complexes containing metals selected from Groups 7 to 11 of the Long Periodic Table (hereinafter, "the Periodic Table" refers to the Long Periodic Table unless otherwise specified). Preferred examples of metals selected from Groups 7 to 11 of the Periodic Table include ruthenium, rhodium, palladium, silver, chrysene, nimium, iridium, platinum, and gold.

Preferred ligands for organometallic complexes are (hetero)arylpyridine ligands, (hetero)arylpyrazole ligands, and other ligands formed by linking a (hetero)aryl group with pyridine, pyrazole, phenanthroline, or the like. Phenylpyridine ligands and phenylpyrazole ligands are particularly preferred. Here, "(hetero)aryl" refers to at least one of an aryl group and a heteroaryl group.

Preferred phosphorescent materials include, specifically, phenylpyridine complexes such as tris(2-phenylpyridine)iridium, tris(2-phenylpyridine)ruthenium, tris(2-phenylpyridine)palladium, bis(2-phenylpyridine)platinum, tris(2-phenylpyridine)barium, and tris(2-phenylpyridine)rhelium, and porphyrin complexes such as octaethylplatinum porphyrin, octaphenylplatinum porphyrin, octaethylpalladium porphyrin, and octaphenylpalladium porphyrin.

Examples of polymer-based luminescent materials include polyfluorene-based materials such as poly(9,9-dioctylfluorene-2,7-diyl), poly[(9,9-dioctylfluorene-2,7-diyl)-co-(4,4'-(N-(4-tert-butylphenyl))diphenylamine)], and poly[(9,9-dioctylfluorene-2,7-diyl)-co-(1,4-benzo-2{2,1'-3}-triazole)], and polystyrene-based materials such as poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-styrene].

(Charge conductive material)

The charge-transporting material is a material that transports positive charges (holes) or negative charges (electrons). There are no particular limitations on the material, and any known material can be used, as long as it does not impair the effects of the present invention.

The charge transport material can be a compound previously used in the light-emitting layer 5 of an organic electroluminescent device, and is particularly preferably a compound used as the main material of the light-emitting layer 5.

Specific examples of charge transport materials include aromatic amine compounds, phthalocyanine compounds, porphyrin compounds, oligothiophene compounds, polythiophene compounds, benzylphenyl compounds, compounds formed by linking a tertiary amine with a fluorenyl group, hydrazone compounds, silazane compounds, silaneamine compounds, phosphamide compounds, and quinacridone compounds, as exemplified as the hole transport compounds for the hole injection layer 3. Furthermore, electron transport compounds such as anthracene compounds, pyrene compounds, carbazole compounds, pyridine compounds, phenanthroline compounds, oxadiazole compounds, and silole compounds can also be cited.

As charge transport materials, aromatic diamines containing two or more tertiary amines and two or more condensed aromatic rings substituted with nitrogen atoms, such as 4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (Japanese Patent Publication No. 5-234681), aromatic amine compounds with starburst structures, such as 4,4',4"-tris(1-naphthylphenylamino)triphenylamine (Acta Luminosaci (J. Lumin.), vol. 72-74, p. 985, 1997), aromatic amine compounds containing tetramers of triphenylamine (Chem. Commun., p. 2175, 1996), fluorene compounds such as 2,2',7,7'-tetrakis-(diphenylamino)-9,9'-spirobifluorene (Synth. Metals, vol. 91, p. 1 Examples of hole-transporting compounds for the hole-transporting layer 4 include carbazole compounds such as 1997, 4,4'-N,N'-dicarbazolebiphenyl, and the like. Other examples include oxadiazole compounds such as 2-(4-biphenylyl)-5-(p-tert-butylphenyl)-1,3,4-oxadiazole (tBu-PBD) and 2,5-bis(1-naphthyl)-1,3,4-oxadiazole (BND); 2,5-bis( Silole compounds such as 6'-(2',2"-bipyridyl)-1,1-dimethyl-3,4-diphenylsilole (PyPySPyPy); phenanthroline compounds such as 4,7-diphenyl-1,10-phenanthroline (bathophenanthroline, BPhen) and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (bathocuproin, BCP).

(Formation of the light-emitting layer 5 using a wet film deposition method)

The organic electroluminescent device preferably has a light-emitting layer formed by a wet film-forming method using the organic electroluminescent device composition of this embodiment.

The light-emitting layer 5 may include other light-emitting layers besides the one formed using the organic electroluminescent device composition of this embodiment. These light-emitting layers can be formed by vacuum evaporation or wet film deposition, but wet film deposition is preferred for superior film-forming properties.

When the light-emitting layer 5 is formed by a wet film formation method, a light-emitting layer-forming composition prepared by mixing the material forming the light-emitting layer 5 with a soluble solvent (light-emitting layer solvent) is generally used in place of the hole-injection layer-forming composition, similar to the case of forming the hole-injection layer 3 by a wet film formation method.

Examples of solvents include ether solvents, ester solvents, aromatic hydrocarbon solvents, and amide solvents listed for the formation of the hole injection layer 3, as well as alkane solvents, halogenated aromatic hydrocarbon solvents, aliphatic alcohol solvents, alicyclic alcohol solvents, aliphatic ketone solvents, and alicyclic ketone solvents. The solvents used are also exemplified as solvents for the iridium complex compound-containing composition of this embodiment. Specific examples of solvents are listed below, but are not limited to these as long as the effects of the present invention are not impaired.

For example, the following can be cited: aliphatic ether solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, and propylene glycol-1-monomethyl ether acetate (PGMEA); aromatic ether solvents such as 1,2-dimethoxybenzene, 1,3-dimethoxybenzene, anisole, phenethyl ether, 2-methoxytoluene, 3-methoxytoluene, 4-methoxytoluene, 2,3-dimethylanisole, 2,4-dimethylanisole, and diphenyl ether; aromatic ester solvents such as phenyl acetate, phenyl propionate, methyl benzoate, ethyl benzoate, propyl benzoate, and n-butyl benzoate; toluene, xylene, mesitylene, cyclohexylbenzene, tetrahydronaphthalene, 3-isobutylene, and the like. Aromatic hydrocarbon solvents such as propylbiphenyl, 1,2,3,4-tetramethylbenzene, 1,4-diisopropylbenzene, and methylnaphthalene; amide solvents such as N,N-dimethylformamide and N,N-dimethylacetamide; alkane solvents such as n-decane, cyclohexane, ethylcyclohexane, decahydronaphthalene, and bicyclohexane; halogenated aromatic hydrocarbon solvents such as chlorobenzene, dichlorobenzene, and trichlorobenzene; aliphatic alcohol solvents such as butanol and hexanol; aliphatic alcohol solvents such as cyclohexanol and cyclooctanol; aliphatic ketone solvents such as methyl ethyl ketone and dibutyl ketone; aliphatic ketone solvents such as cyclohexanone, cyclooctanone, and fenchone, etc. Among these, alkane-based solvents and aromatic hydrocarbon-based solvents are particularly preferred.

To achieve a more uniform film, it is best to evaporate the solvent from the liquid film at an appropriate rate immediately after formation. Therefore, as mentioned above, the boiling point of the solvent used is typically 80°C or higher, preferably 100°C or higher, and more preferably 120°C or higher, and typically 270°C or lower, preferably 250°C or lower, and more preferably 230°C or lower.

The amount of solvent used is arbitrary as long as it does not significantly impair the effects of the present invention. However, a higher total content in the composition for forming the light-emitting layer, i.e., the composition containing the iridium complex compound, is preferred for ease of film formation due to its low viscosity, while a lower total content is preferred for ease of thick film formation. As described above, the content of the solvent in the composition containing the iridium complex compound is preferably 1% by mass or greater, more preferably 10% by mass or greater, and particularly preferably 50% by mass or greater, and preferably 99.99% by mass or less, more preferably 99.9% by mass or less, and particularly preferably 99% by mass or less.

Solvent removal after wet film formation can be achieved by heating or reducing pressure. For heating, a clean oven or hot plate is preferred for evenly applying heat to the entire film.

The heating temperature in the heating step is arbitrary, provided it does not significantly impair the effects of the present invention. However, a higher temperature is preferred to shorten the drying time, while a lower temperature is preferred to minimize damage to the material. The upper limit of the heating temperature is generally 250°C or lower, preferably 200°C or lower, and more preferably 150°C or lower. The lower limit of the heating temperature is generally 30°C or higher, preferably 50°C or higher, and more preferably 80°C or higher. By setting the heating temperature below the upper limit, the heat resistance of the charge transport material or phosphorescent material used is lower than that of the conventionally used materials, thereby suppressing decomposition or crystallization. By setting the heating temperature above the lower limit, prolonged solvent removal can be avoided. The heating time in the heating step can be appropriately determined based on the boiling point or vapor pressure of the solvent in the composition for forming the light-emitting layer, the heat resistance of the material, and the heating conditions.

(Formation of the light-emitting layer 5 using vacuum evaporation)

When the light-emitting layer 5 is formed by vacuum evaporation, the constituent materials of the light-emitting layer 5, i.e., one or more of the light-emitting materials, charge transport compounds, etc., are usually placed in a crucible placed in a vacuum container. At this time, when two or more materials are used, they are usually placed in different crucibles respectively. After that, after the vacuum container is evacuated to about ^10-4 Pa by a vacuum pump, the crucible is heated, and the material in the crucible is evaporated while controlling the evaporation amount. When two or more materials are used, each crucible is usually heated, and the evaporation amount is independently controlled while being evaporated. Through the above operation, the light-emitting layer 5 is formed on the hole injection layer 3 or the hole transport layer 4 placed facing the crucible. When two or more materials are used, they may be placed in a crucible as a mixture and heated to evaporate to form the light-emitting layer 5 .

The degree of vacuum during evaporation is not limited unless it significantly impairs the effects of the present invention, but is typically 0.1× ^10-6 Torr (0.13× ^10-4 Pa) or higher and 9.0× ^10-6 Torr (12.0× ^10-4 Pa) or lower. The evaporation rate is not limited unless it significantly impairs the effects of the present invention, but is typically 0.1 Å/s or higher and 5.0 Å/s or lower. The film formation temperature during evaporation is not limited unless it significantly impairs the effects of the present invention, but is preferably 10°C or higher and 50°C or lower.

<Hole blocking layer 6>

A hole blocking layer 6 may be provided between the light-emitting layer 5 and the electron injection layer 8 described later. The hole blocking layer 6 is a layer laminated on the light-emitting layer 5 so as to be in contact with the interface of the light-emitting layer 5 on the cathode 9 side.

The hole-blocking layer 6 blocks holes migrating from the anode 2 from reaching the cathode 9 and efficiently transports electrons injected from the cathode 9 toward the light-emitting layer 5. Required physical properties for the material constituting the hole-blocking layer 6 include high electron mobility and low hole mobility, a large energy gap (i.e., the difference between the HOMO and LUMO), and a high excited triplet energy level (T1).

Examples of materials for the hole blocking layer 6 that meet this condition include bis(2-methyl-8-hydroxyquinolinolato)(phenol)aluminum, bis(2-methyl-8-hydroxyquinolinolato)(triphenylsilanol)aluminum, Mixed ligand complexes such as silanolato)aluminum, metal complexes such as bis(2-methyl-8-hydroxyquinolinolato)aluminum-μ-oxo-bis-(2-methyl-8-hydroxyquinolinolato)aluminum dinuclear metal complexes, styryl compounds such as distyrylbiphenyl derivatives (Japanese Patent Publication No. 11-242996), triazole derivatives such as 3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (Japanese Patent Publication No. 7-41759), and phenanthroline derivatives such as bathocuproin (Japanese Patent Publication No. 10-79297). The compound described in International Publication No. 2005/022962 having at least one pyridine ring substituted at the 2, 4, or 6 positions is also preferred as the material for the hole blocking layer 6.

The method for forming the hole blocking layer 6 is not limited and can be formed in the same manner as the method for forming the light-emitting layer 5.

The thickness of the hole blocking layer 6 is arbitrary as long as it does not significantly impair the effects of the present invention. It is usually 0.3 nm or more, preferably 0.5 nm or more, and usually 100 nm or less, preferably 50 nm or less.

<Electronic Transmission Layer 7>

To further improve the current efficiency of the device, the electron transport layer 7 is provided between the light-emitting layer 5 or the hole blocking layer 6 and the electron injection layer 8.

The electron-transporting layer 7 is formed from a compound that can efficiently transport electrons injected from the cathode 9 toward the light-emitting layer 5 between electrodes subjected to an electric field. The electron-transporting compound used in the electron-transporting layer 7 must have high efficiency in electron injection from the cathode 9 or the electron-injecting layer 8, high electron mobility, and the ability to efficiently transport the injected electrons.

Examples of electron-transmitting compounds that meet this condition include metal complexes such as aluminum complexes of 8-hydroxyquinoline (Japanese Patent Publication No. 59-194393), metal complexes of 10-hydroxybenzo[h]quinoline, oxadiazole derivatives, distyrylbiphenyl derivatives, silole derivatives, 3-hydroxyflavonoid metal complexes, and 5-hydroxyflavonoid gold complexes. Metal complexes, benzoxazole metal complexes, benzothiazole metal complexes, tribenzimidazolylbenzene (U.S. Patent No. 5,645,948), quinoxaline compounds (Japanese Patent Publication No. 6-207169), phenanthroline derivatives (Japanese Patent Publication No. 5-331459), 2-tert-butyl-9,10-N,N'-dicyanoanthraquinone diimide, n-type hydrogenated amorphous silicon carbide, n-type zinc sulfide, n-type zinc selenide, etc.

The thickness of the electron transport layer 7 is usually 1 nm or more, preferably 5 nm or more, and usually 300 nm or less, preferably 100 nm or less.

The electron transport layer 7 is formed by laminating on the light-emitting layer 5 or the hole blocking layer 6 by wet film deposition or vacuum evaporation, similar to the light-emitting layer 5. Vacuum evaporation is usually used.

<Electron injection layer 8>

The electron injection layer 8 plays the following role: it efficiently injects electrons injected from the cathode 9 into the electron transport layer 7 or the light-emitting layer 5.

In order to efficiently inject electrons, it is preferable to use a metal with a low work function as the material forming the electron injection layer 8. For example, alkaline metals such as sodium or cesium, or alkaline earth metals such as barium or calcium, can be used.

The thickness of the electron injection layer 8 is preferably 0.1nm~5nm.

Inserting an extremely thin insulating film of approximately 0.1 nm to 5 nm thick, such as LiF, _MgF2 , _Li2O , or _{Cs2CO3 ,} at the interface between the cathode 9 and the electron transport layer 7 as the electron injection layer 8 is also an effective method for improving device efficiency (Applied Physics Letters, Vol. 70, p. 152, 1997; Japanese Patent Publication No. 10-74586; IEEE Transactions on Electron Devices, Vol. 44, p. 1245, 1997; Society for Information Display (SID) 04 Digest, 2004, p. 154).

Furthermore, organic electron transport materials, such as nitrogen-containing heterocyclic compounds like p-4,7-diphenyl-1,10-phenanthroline or metal complexes like aluminum complexes of 8-hydroxyquinoline, doped with alkali metals such as sodium, potassium, cesium, lithium, and cadmium (described in Japanese Patent Publication Nos. 10-270171, 2002-100478, and 2002-100482, are preferred because they achieve excellent film quality with both enhanced electron injection and transport properties. The film thickness in this case is typically 5 nm or greater, preferably 10 nm or greater, and typically 200 nm or less, preferably 100 nm or less.

The electron injection layer 8 is formed similarly to the light-emitting layer 5 by laminating on the light-emitting layer 5 or the hole blocking layer 6 or electron transport layer 7 thereon using a wet film deposition method or a vacuum evaporation method.

The details of the wet film formation method are the same as those of the light-emitting layer 5 described above.

<Yin Pole 9>

Cathode 9 injects electrons into electron injection layer 8 or layers on the side of light-emitting layer 5, such as light-emitting layer 5. The material used for anode 2 can be used for cathode 9. However, for efficient electron injection, a metal with a low work function is preferred. Examples include tin, magnesium, indium, calcium, aluminum, silver, and alloys thereof. Examples of materials for cathode 9 include low-work-function alloy electrodes such as magnesium-silver alloys, magnesium-indium alloys, and aluminum-lithium alloys.

In terms of device stability, it is preferable to laminate a metal layer with a high work function and stable relative to the atmosphere on cathode 9 to protect cathode 9, which is made of a metal with a low work function. Examples of the laminated metal include aluminum, silver, copper, nickel, chromium, gold, and platinum.

The cathode film thickness is usually the same as that of the anode 2.

<Other constituent layers>

The above description focuses on the layered device shown in Figure 1 . However, the organic electroluminescent device of this embodiment may include any layers other than those described above between the anode 2 and cathode 9 and the light-emitting layer 5, as long as their performance is not impaired. Furthermore, any layers other than the light-emitting layer 5 may be omitted.

For example, providing an electron blocking layer between the hole transport layer 4 and the light-emitting layer 5 is also effective for the same purpose as the hole blocking layer 6. The electron blocking layer has the following functions: by preventing electrons migrating from the light-emitting layer 5 from reaching the hole transport layer 4, the probability of recombination with holes within the light-emitting layer 5 is increased, thereby confining the generated excitons within the light-emitting layer 5; and by efficiently transporting holes injected from the hole transport layer 4 toward the light-emitting layer 5.

The properties required of an electron-blocking layer include high hole transport, a large energy gap (i.e., the difference between the HOMO and LUMO), and a high excited triplet energy level (T1).

When the light-emitting layer 5 is formed using a wet film deposition method, it is preferable to also form the electron blocking layer using a wet film deposition method because this facilitates device manufacturing.

Therefore, the electron blocking layer is preferably suitable for wet film formation. Examples of materials used in such an electron blocking layer include copolymers of dioctylfluorene and triphenylamine, such as F8-TFB (International Publication No. 2004/084260).

The structure can also be reversed from that shown in Figure 1 , where cathode 9, electron injection layer 8, electron transport layer 7, hole blocking layer 6, luminescent layer 5, hole transport layer 4, hole injection layer 3, and anode 2 are sequentially layered on substrate 1. Alternatively, the organic electroluminescent device of this embodiment can be placed between two substrates, at least one of which has high transparency.

A structure with multiple layers, similar to the one shown in Figure 1, can also be used, i.e., a structure with multiple light-emitting units. In this case, using a charge-generating layer, such as _V₂O₅ , instead of the interface layer between the layers, reduces the number of barriers between the layers, resulting in improved _luminous efficiency and drive voltage. For example, if the anode is indium tin oxide (ITO) and the cathode is Al, the interface layer refers to these two layers.

The present invention can be applied to any of the following types of organic electroluminescent devices: a single device, a device with an array-like structure, or a device with an anode and cathode arranged in an X-Y matrix.

[Display device]

The display device and lighting device of this embodiment include the organic electroluminescent element described above. There are no particular limitations on the form or structure of the display device; the organic electroluminescent element of this embodiment can be used and assembled according to conventional methods.

For example, the display device of this embodiment can be formed using the method described in "Organic EL Display" (Ohmsha, published on August 20, 2004, by Shizue Tokito, Chinaya Adachi, and Hideyuki Murata).

Implementation Examples

The following examples illustrate the present invention in more detail. The present invention is not limited to the following examples, and can be implemented with various modifications without departing from the spirit of the present invention.

[Example 1]

An organic electroluminescent device was fabricated using the following method.

A transparent conductive film of indium/tin oxide (ITO) deposited to a thickness of 50nm on a glass substrate (manufactured by Sanyong Vacuum Co., Ltd., sputter-deposited) was patterned into 2mm-wide stripes using conventional photolithography and hydrochloric acid etching to form the anode. The substrate, with the ITO pattern, was cleaned in this order: ultrasonic cleaning with a surfactant solution, washing with ultrapure water, ultrasonic cleaning with ultrapure water, and washing with ultrapure water. It was then dried with compressed air and finally cleaned with UV ozone.

A hole-injection layer-forming composition was prepared by dissolving 3.0 mass% of a hole-transporting polymer compound having a repeating structure represented by the following formula (P-1) and 0.6 mass% of an oxidizing agent represented by the following formula (HI-1) in ethyl benzoate.

The solution was spin-coated on the substrate in air and dried on a hot plate at 240°C for 30 minutes to form a uniform thin film with a thickness of 40 nm, which served as the hole injection layer.

[Chemistry 23]

Next, 100 parts by mass of a charge transporting polymer compound having a structure represented by the following formula (HT-1) was dissolved in cyclohexylbenzene to prepare a 3.0% by mass solution.

This solution was spin-coated on the substrate coated with the hole injection layer in a nitrogen glove box and dried on a hot plate at 230°C for 30 minutes to form a uniform 40 nm thick thin film, which served as the hole transport layer.

[Chemistry 24]

Next, 60 parts by mass of the compound represented by the following formula (H-1), 40 parts by mass of the compound represented by the following formula (H-2), 15 parts by mass of the compound represented by the following formula (D-1) serving as a red-luminescent dopant, and 15 parts by mass of the compound represented by the following formula (D-2) serving as an auxiliary dopant were weighed as materials for the luminescent layer and dissolved in cyclohexylbenzene to prepare a 7.8% by mass solution.

This solution was spin-coated on the substrate coated with the hole transport layer in a nitrogen glove box and dried on a hot plate at 120°C for 20 minutes to form a uniform thin film with a thickness of 80 nm, serving as the luminescent layer. The compound represented by formula (D-1) and the compound represented by formula (D-2) are dopants with maximum emission wavelengths of 613 nm and 555 nm, respectively.

Place the substrate with the luminescent layer in a vacuum evaporation device and evacuate the device to below 2×10 ^-4 Pa.

Next, the compound represented by the following formula (HB-1) and 8-hydroxyquinolinium were co-deposited on the light-emitting layer by vacuum evaporation at a rate of 1 Å/s in a film thickness ratio of 2:3, forming a 30 nm thick hole-blocking layer.

Next, a 2mm-wide striped shadow mask, used as a mask for cathode evaporation, was placed in close contact with the substrate, perpendicular to the ITO stripes on the anode, and placed in another vacuum evaporation apparatus. Aluminum was then heated using a molybdenum boat, and an 80nm-thick aluminum layer was formed at an evaporation rate of 1Å/s to 8.6Å/s, forming the cathode.

By performing the above operations, an organic electroluminescent device with a light-emitting area of 2 mm × 2 mm was obtained.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-1) was observed.

[Example 2]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the composition of the light-emitting layer was set to a mass ratio of (H-1):(H-2):(D-1):(D-3) = 60:40:15:15.

The structural formula of the compound represented by formula (D-3) is shown below. Furthermore, the compound represented by formula (D-3) is a dopant having a maximum emission wavelength of 560 nm.

[Example 3]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the composition of the light-emitting layer was adjusted to a mass ratio of the compounds represented by the respective formulas: (H-1): (H-2): (D-1): (D-4) = 60:40:15:15.

The structural formula of the compound represented by formula (D-4) is shown below. Furthermore, the compound represented by formula (D-4) is a dopant having a maximum emission wavelength of 558 nm.

[Comparative example 1]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the compound represented by formula (D-5) was used as a red-emitting dopant and the composition of the luminescent layer was set to a mass ratio of (H-1):(H-2):(D-5):(D-2) = 60:40:15:15.

The structural formula of the compound represented by formula (D-5) is shown below.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-5) was observed.

[Comparative example 2]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the compound represented by formula (D-5) was used as a red-emitting dopant and the composition of the luminescent layer was set to a mass ratio of (H-1):(H-2):(D-5):(D-3) = 60:40:15:15.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-5) was observed.

[Comparative example 3]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the compound represented by formula (D-5) was used as a red-emitting dopant and the composition of the luminescent layer was set to a mass ratio of (H-1):(H-2):(D-5):(D-4) = 60:40:15:15.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-5) was observed.

[Component Evaluation]

The resulting organic electroluminescent devices of Examples 1 to 3 and Comparative Examples 1 to 3 were measured for current luminous efficiency (cd/A) and external quantum efficiency (EQE) (%) when emitting at a luminance of 1000 cd/ ^m² . The ratio of the current luminous efficiency of Example n (n ranges from 1 to 3) to the current luminous efficiency of Comparative Example n (n ranges from 1 to 3) was calculated and reported in Table 1 as relative luminous efficiency. Furthermore, the values of ΔEQE = EQE (Example n) - EQE (Comparative Example n), obtained by subtracting the EQE of Comparative Example n (n ranges from 1 to 3) from the EQE of Example n (n ranges from 1 to 3), are also reported in Table 1 below.

As shown in Table 1, the organic electroluminescent device of this embodiment using the compound represented by formula (D-1) as a light-emitting dopant in the light-emitting layer material exhibits improved efficiency compared to the organic electroluminescent device using the compound represented by formula (D-5), regardless of the structure of the auxiliary dopant compound.

[Comparative example 4]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the compound represented by formula (D-2) was not used as an auxiliary dopant and the composition of the light-emitting layer was set to a mass ratio of (H-1):(H-2):(D-1) = 60:40:15 for the compounds represented by the respective formulae.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-1) was observed.

[Comparative example 5]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the compound represented by formula (D-5) was used as a red-emitting dopant, the compound represented by formula (D-2) was not used as an auxiliary dopant, and the composition of the luminescent layer was set to a mass ratio of (H-1):(H-2):(D-5) = 60:40:15 for the compounds represented by the respective formulae.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-5) was observed.

[Component Evaluation]

The external quantum efficiency (EQE) of the resulting organic electroluminescent devices of Example 1, Comparative Example 1, Comparative Example 4, and Comparative Example 5 was measured when emitting light at a luminance of 1000 cd/ ^m² . The magnitude of the change in EQE of the organic electroluminescent device containing the compound serving as an auxiliary dopant (Example 1 or Comparative Example 1) relative to the EQE of the organic electroluminescent device not containing the compound serving as an auxiliary dopant (Comparative Example 4 or Comparative Example 5) was defined as ΔEQE and is reported in Table 2 or Table 3 below.

As shown in Tables 2 and 3, the organic electroluminescent device (Example 1) using the compound represented by Formula (D-1) as a luminescent dopant for the luminescent layer material according to this embodiment shows a greater change in external quantum efficiency when a compound serving as an auxiliary dopant is added, compared to the organic electroluminescent device (Comparative Example 1) using the compound represented by Formula (D-5).

[Example 4]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the compound represented by formula (D-6) was used as a red-emitting dopant, and the composition of the luminescent layer was set to a mass ratio of (H-1):(H-2):(D-6):(D-2) = 60:40:15:15. The compound represented by formula (D-6) is a dopant with a maximum emission wavelength of 627 nm.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-6) was observed.

[Example 5]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the composition of the luminescent layer was set to a mass ratio of (H-1):(H-2):(D-6):(D-7) = 60:40:15:15. The compound represented by formula (D-7) is a dopant with a maximum emission wavelength of 605 nm.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-6) was observed.

[Comparative example 6]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the composition of the light-emitting layer was set to a mass ratio of (H-1): (H-2): (D-6) = 60:40:15 of the compounds represented by the respective formulae.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-6) was observed.

[Comparative Example 7]

An organic electroluminescent device was fabricated in the same manner as in Example 1, except that the composition of the luminescent layer was adjusted to a mass ratio of the compounds represented by the formulae: (H-1): (H-2): (D-5): (D-7) = 60:40:15:15.

When voltage was applied to the obtained organic electroluminescent device, red luminescence originating from the compound represented by formula (D-5) was observed.

[Component Evaluation]

The external quantum efficiency (EQE) of the organic electroluminescent devices obtained in Examples 4, 5, Comparative Examples 6, and 7 was measured when emitting light at a luminance of 1000 cd/ ^m². The difference from the EQE of Comparative Example 6 was recorded as ΔEQE. Furthermore, the organic electroluminescent devices were driven at a current density of 60 mA/ ^cm² , and the time required for the relative luminance to reach 80% (LT80) was measured. The relative lifetime was recorded, with the LT80 of Comparative Example 6 being set to 100. The results are shown in Table 4 below.

As shown in Table 4, the organic electroluminescent device of this embodiment using the compound represented by formula (D-6) as a luminescent dopant in combination with a compound serving as an auxiliary dopant in the luminescent layer exhibits high efficiency and a long driving life. Among them, the organic electroluminescent device using the compound represented by formula (D-7) as the auxiliary dopant exhibits even higher luminescent efficiency and a long driving life.

[Table 4]

While the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present invention. This application is based upon a Japanese patent application filed on May 20, 2019 (Japanese Patent Application No. 2019-094708), the contents of which are incorporated herein by reference.

1:Substrate

2: Anode

3: Hole injection layer

4: Hole transport layer

5: Luminescent layer

6: Hole blocking layer

7: Electron transmission layer

8: Electron injection layer

9: Cathode

10: Organic electroluminescent element

Claims (8)

An organic electroluminescent device comprising a compound represented by the following formula (1) and a compound represented by the following formula (2) having a maximum emission wavelength shorter than that of the compound represented by the formula (1), wherein the compound represented by the formula (1) is a red-emitting dopant, and the compound represented by the formula (2) is an auxiliary dopant, and the composition ratio of the compound represented by the formula (1) is greater than the composition ratio of the compound represented by the formula (2) in terms of parts by mass. The organic electroluminescent device has a light-emitting layer that emits red light from the red-emitting dopant. [In the formula (1), R ¹ and R ² are each independently an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have a substituent; when there are multiple R ¹ and R ² , these groups may be the same or different; when there are multiple R ¹ , adjacent R ¹ may be bonded to form a ring; a is an integer of 0 to 4, and b is an integer of 0 to 3; R ³ and R ⁴ are each independently a hydrogen atom, a fluorine atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms; these groups may further have substituents; when there are multiple R ³ and R ⁴ , they may be the same or different; L ¹ represents an organic ligand, and m is an integer from 1 to 3] [In the formula (2), R ⁵ is an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have a substituent; in the presence of multiple R ⁵ , these may be the same or different; c is an integer of 0 to 4; Ring A is any one of a pyridine ring, a pyrazine ring, a pyrimidine ring, an imidazole ring, an oxazole ring, a thiazole ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, an nitrogen-heteroaryl benzene ring, a carboline ring, a benzothiazole ring, and a benzoxazole ring; Ring A may have a substituent, and the substituent is a fluorine atom, a chlorine atom, a bromine atom, an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, a 1 to 20 carbon atoms, or a 2 to 30 carbon atoms. [the alkyl group] is an alkoxy group having 3 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilyl group having 1 to 20 carbon atoms, an arylsilyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 2 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 20 carbon atoms; in addition, adjacent substituents bonded to ring A may bond to each other to further form a ring; when there are multiple rings A, they may be the same or different; ^L2 represents an organic ligand, and n is an integer of 1 to 3]. The organic electroluminescent device according to claim 1, wherein the compound represented by formula (1) is a compound represented by the following formula (1-1); [In the formula (1-1), R ¹ , R ² , a, b, L ¹ , and m have the same meanings as R ¹ , R ² , a, b, L ¹ , and m in the formula (1); R ⁶ and R ⁷ are independently an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have substituents; in the presence of multiple R ⁶ , R ⁷ , these may be the same or different; d and e are independently integers from 0 to 5]. The organic electroluminescent device according to claim 1, wherein the compound represented by formula (1) is a compound represented by the following formula (1-2); [In formula (1-2), R ² to R ⁴ , b, L ¹ , and m have the same meanings as R ² to R ⁴ , b, L ¹ , and m in formula (1); R ¹⁴ to R ¹⁶ are substituents. When there are multiple R ¹⁴ to R ¹⁶ , they may be the same or different; i is an integer from 0 to 4]. The organic electroluminescent device according to claim 2, wherein the compound represented by formula (1-1) is a compound represented by the following formula (1-3); [In formula (1-3), R ² , R ⁶ , R ⁷ , b, d, e, L ¹ , and m have the same meanings as R ² , R ⁶ , R ⁷ , b, d, e, L ¹ , and m in formula (1-1); R ¹⁴ to R ¹⁶ are substituents. When there are multiple R ¹⁴ to R ¹⁶ , they may be the same or different; i is an integer from 0 to 4]. The organic electroluminescent device according to claim 1 or claim 2, wherein the compound represented by formula (2) is a compound represented by the following formula (2-1); [In the formula (2-1), ring A, L ² , and n have the same meanings as ring A, L ² , and n in the formula (2); R ⁸ is an alkyl group having 1 to 20 carbon atoms, a (hetero)aralkyl group having 7 to 40 carbon atoms, an alkoxy group having 1 to 20 carbon atoms, a (hetero)aryloxy group having 3 to 20 carbon atoms, an alkylsilanyl group having 1 to 20 carbon atoms, an arylsilanyl group having 6 to 20 carbon atoms, an alkylcarbonyl group having 2 to 20 carbon atoms, an arylcarbonyl group having 7 to 20 carbon atoms, an alkylamino group having 1 to 20 carbon atoms, an arylamino group having 6 to 20 carbon atoms, or a (hetero)aryl group having 3 to 30 carbon atoms; these groups may further have substituents; when there are multiple R ⁸ s, they may be the same or different; f is an integer from 0 to 5]. The organic electroluminescent device according to claim 1 or claim 2, wherein m in formula (1) is less than 3, and ^L1 has at least one structure selected from the group consisting of the following formulas (3), (4), and (5); [In formulae (3) to (5), R ⁹ and R ¹⁰ have the same meanings as R ¹ in formula (1). When multiple R ⁹ and R ¹⁰ are present, they may be the same or different; R ¹¹ to R ¹³ are each independently a hydrogen atom, an alkyl group having 1 to 20 carbon atoms which may be substituted with a fluorine atom, a phenyl group which may be substituted with an alkyl group having 1 to 20 carbon atoms, or a halogen atom; g is an integer from 0 to 4; h is an integer from 0 to 4; Ring B is a pyridine ring, a pyrimidine ring, an imidazole ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, an aza-tertiary phenyl ring, a carboline ring, a benzothiazole ring, or a benzoxazole ring; Ring B may further have a substituent]. The organic electroluminescent element according to claim 1 or claim 2, wherein a in the formula (1) is 1, or a in the formula (1) is an integer greater than 2 and does not have a ring formed by mutually bonding adjacent ^R1s . A display device comprising the organic electroluminescent element according to any one of claims 1 to 7.