WO2014133062A1 - Organic el element, and lighting device and display device using same - Google Patents

Abstract

This organic EL element is provided with a light emitting layer between a pair of electrodes. The light emitting layer contains a host material and a fluorescent dopant material, and the content of the fluorescent dopant material in the light emitting layer is 49% or less of the total mass of the light emitting layer. The dopant material has a difference between the S₁ energy and the T₁ energy of 0.24 eV or less, and is composed of a cyanopyridine compound represented by general formula (I). In general formula (I), at least one of R₁-R₅ represents a cyano group, and at least one of R₁-R₅ represents a substituent that is not a hydrogen atom nor a cyano group.

Description

ORGANIC EL ELEMENT AND LIGHTING EQUIPMENT AND DISPLAY DEVICE USING THE SAME

The present invention relates to an organic electroluminescent device in which a light emitting layer has a host material and a predetermined fluorescent dopant material. Hereinafter, the organic electroluminescence element may be referred to as an “organic EL element”.

The organic EL element includes a light emitting layer between a pair of electrodes. The light emitting layer is usually composed of a host material and a dopant material. Although the host material itself has a low light emission capability, it is a material having a high film forming property, and is used by mixing other materials having a high light emission capability. The dopant material is a material having a high light emission capability. As the dopant material, a fluorescent material or a phosphorescent material is generally known.

In many cases, an organic EL element whose dopant material is a fluorescent material (hereinafter referred to as “fluorescent organic EL element”) emits fluorescence through the following steps (1) to (3).
(1) Recombination of holes and electrons occurs in the host material of the light emitting layer, and the host material changes from the ground state to the excited state. At this time, 25% of the host material that has reached the excited state is the singlet lowest excited state (hereinafter referred to as “S ₁ state”), and 75% is the triplet lowest excited state (hereinafter referred to as “T ₁ state”). become.
(2) After recombination, energy transfer occurs from the host material to the dopant material, and the dopant material transitions from the ground state to the excited state. At this time, in principle, the value of the host material follows the abundance ratio between the S ₁ state and the T ₁ state. That is, 25% of the dopant material that has reached the excited state is in the S ₁ state and 75% is in the T ₁ state.
(3) All of the dopant material in the T ₁ state and part of the dopant material in the S ₁ state are thermally deactivated. Then, the dopant material in the S ₁ state that has not been thermally deactivated emits fluorescence.

Since many fluorescent organic EL devices go through this process, the theoretical upper limit of the internal quantum efficiency of the fluorescent organic EL device was considered to be 25%. Therefore, particularly in application fields such as lighting fixtures and display devices, organic EL elements utilizing light emission from the T ₁ state, which occupies 75% of the excited dopant material, that is, phosphorescent organic EL elements are attracting attention. And host materials have been developed. For example, Patent Document 1 proposes a phosphorescent organic EL device having a low driving voltage and excellent external quantum efficiency by using a phosphorescent host material having a carbazole skeleton and a metal complex dopant material such as iridium or platinum.

However, as described in Patent Document 1, an organic EL element that emits phosphorescence with high efficiency needs to use a metal complex compound containing a noble metal such as iridium or platinum as a dopant material. The problem was the extremely high price. Therefore, there has been a demand for a technology that achieves an internal quantum efficiency exceeding 25%, which is the theoretical upper limit of a fluorescent organic EL element, while using an inexpensive fluorescent material.

As a technique for increasing the internal quantum efficiency of the fluorescent organic EL element to 25% or more, Patent Documents 2 to 4 and Non-Patent Documents 1 to 7 propose a technique of “using a thermally activated delayed fluorescent material”. The thermally activated delayed fluorescent material is a fluorescent dopant material characterized in that the difference between S ₁ energy and T ₁ energy is small. Since the energy difference between two states is small, the heat from the T ₁ state to the S ₁ state. A state transition caused by energy (hereinafter, a transition from the S ₁ state to the T ₁ state is referred to as “reciprocal crossing”). Here, the S ₁ and T ₁ energies are adiabatic transition energies between the S ₁ and T ₁ states and the singlet ground state (hereinafter referred to as “S ₀ state”), and are measured by a spectroscopic technique or the like. Is done. The S ₁ energy corresponds to the energy at the short wavelength side peak end of the fluorescence spectrum at 77K, and the T ₁ energy corresponds to the energy at the short wavelength side peak end of the phosphorescence spectrum at 77K. When inverse intersystem crossing due to thermal energy occurs, the proportion of the S ₁ state of the dopant material increases and the amount of emitted fluorescence also increases. Depending on the material used, an organic EL element that achieves an internal quantum efficiency of 25% or more can be realized. In addition, the fluorescence emitted after the inverse intersystem crossing due to thermal energy occurs is referred to as “thermally activated delayed fluorescence”.

In order for a material to emit sufficient thermally activated delayed fluorescence at room temperature, the difference between the S ₁ energy and T ₁ energy of the material (hereinafter referred to as “S ₁ -T ₁ energy gap”) is sufficiently small. It is essential. The standard of this narrow S ₁ -T ₁ energy gap is about 0.24 eV. In fact, Non-Patent Document 1 reported a compound having an S ₁ -T ₁ energy gap of 0.24 eV, and thermal activity at 27 degrees Celsius. Type delayed fluorescence is observed.

According to the description in Non-Patent Document 2, the design guideline for a material having a narrow S ₁ -T ₁ energy gap is “an electron donating site by a π conjugated system and an electron withdrawing site by a π conjugated system are combined, and 2 The two π conjugate planes are twisted so that they do not line up in parallel. ” In fact, all thermally activated delayed fluorescent materials proposed in Non-Patent Documents 2 to 7 follow this guideline. Here, paying attention to the electron-donating site of each material, the carbazole derivative is used in the light-emitting materials described in Non-Patent Documents 2, 3, and 7, and the acridine derivative is used in the light-emitting material described in Non-Patent Document 3. The luminescent material described in 6 uses phenoxazine. When attention is paid to the electron-withdrawing site of each material, 1,3,5-triazine derivatives are described in Non-Patent Documents 3, 5, and 7 in the light-emitting materials described in Non-Patent Documents 2, 4, and 6. Cyanobenzene derivatives are used in these luminescent materials.

JP 2009-94486 A JP 2004-241374 A JP 2006-024830 A JP 2012-193352 A

The heat-activated delayed fluorescent material has an essential condition that the S ₁ -T ₁ energy gap is narrow, but there are few basic skeleton types of materials that satisfy this condition. For example, when focusing on electron-withdrawing sites in the molecule, material compounds containing 1,3,5-triazine derivatives and cyanobenzene derivatives have been reported as described above, but other types of electron-withdrawing sites have been reported. There have been few reports of thermally activated delayed fluorescent materials containing sex sites.

Thus, at present, there are few options for the thermally activated delayed fluorescent material, and many of the emission wavelengths are short, so the degree of freedom in controlling the characteristics of the organic EL element such as the emission wavelength is low. Therefore, an object of the present invention is to provide an organic EL element using a thermally activated delayed fluorescent material having a basic skeleton different from that of a conventional thermally activated delayed fluorescent material.

In view of the above problems, the inventor paid attention to cyanopyridine, which has never been seen before, as an electron-withdrawing site of the thermally activated delayed fluorescent material. Further, the present inventors have found that among compounds containing a cyanopyridine structure, there are compounds having a narrow S ₁ -T ₁ energy gap, which can be used as a thermally activated delayed fluorescent dopant material for an organic EL device. Furthermore, it has also been found that a compound containing cyanopyridine has a longer emission wavelength than a compound containing cyanobenzene as an electron withdrawing site.

That is, the present invention includes a light emitting layer between a pair of electrodes, and the fluorescent dopant material of the light emitting layer has a difference between S ₁ energy and T ₁ energy of 0.24 eV or less, and is represented by the following general formula (I). The present invention relates to an organic EL device which is a cyanopyridine compound.

R ₁ to R _{5 in} the general formula (I) are each independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, a silyl group, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 1 to 10 carbon atoms, An alkynyl group having 1 to 10 carbon atoms, a cycloalkyl group having 4 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 50 carbon atoms, a substituted or unsubstituted heteroaryl group having 6 to 50 elements, and the number of elements A substituted or unsubstituted heterocyclic group having 6 to 50 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkoxy group having 4 to 12 carbon atoms, an aryloxy group having 1 to 10 carbon atoms, and an alkylthio group having 1 to 10 carbon atoms A cycloalkylthio group having 4 to 12 carbon atoms, an arylthio group having 6 to 12 carbon atoms, an alkoxycarbonyl group having 1 to 10 carbon atoms, an aryloxycarbonyl group having 6 to 12 carbon atoms, a sulfamoyl having 1 to 10 carbon atoms Group, acyl group having 1 to 10 carbon atoms, acyloxy group having 1 to 10 carbon atoms, amide group having 1 to 10 carbon atoms, carbonyl group having 1 to 10 carbon atoms, ureido group having 1 to 10 carbon atoms, carbon number 1 It is one selected from the group consisting of ˜10 sulfinyl groups, alkylsulfonyl groups having 1 to 10 carbon atoms, arylsulfonyl groups having 6 to 12 carbon atoms, and amino groups having 1 to 10 carbon atoms. However, at least one of R ₁ to R ₅ is a cyano group, and at least one of R ₁ to R ₅ is a substituent that is neither a hydrogen atom nor a cyano group.

One or more of the substituents that are not hydrogen atoms or cyano groups of R ₁ to R ₅ are preferably electron-donating substituents, specifically, substituted or unsubstituted having 6 to 50 elements. The heteroaryl group is preferably.

The substituted or unsubstituted heteroaryl group having 6 to 50 elements which is an electron donating substituent is, for example, a substituted or unsubstituted carbazolyl group having 21 to 50 elements. As a specific example of such a light emitting material, a compound represented by the following general formula (II) is preferable.

R ₆ and R _{7 in} the general formula (II) are each independently one selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group, and R ₆ and R ₇ May be the same or different. Especially, it is preferable that both of R ₆ and R ₇ are hydrogen atoms.

Another example of a substituted or unsubstituted heteroaryl group having 6 to 50 elements that is an electron donating substituent is a substituted indolyl group having 50 or less elements. Among the fluorescent dopant materials having such a substituent, a compound represented by the following general formula (III) is preferable.

R ₈ and R _{9 in} the general formula (III) are each independently one selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group. R ₉ is preferably a hydrogen atom or a methyl group, and R ₈ is preferably a hydrogen atom.

In the organic EL device of the present invention, the S ₁ energy of the fluorescent host material of the light emitting layer is higher than the S ₁ energy of the dopant material of the light emitting layer, and the difference between these two types of S ₁ energy is 1.5 eV or less. This is preferable because the luminous efficiency is further increased. The host material preferably has a hole mobility / electron mobility ratio in the range of 0.002 to 500. Examples of host materials that satisfy such conditions include carbazole compounds, arylsilane compounds, and phosphorus oxide compounds.

Furthermore, this invention relates to a lighting fixture and display apparatus provided with said organic EL element.

In the organic EL device of the present invention, a thermally activated delayed fluorescent material containing a cyanopyridine structure is used as a fluorescent dopant material, and therefore, the organic EL device can be an option for making the emission wavelength of the organic EL device longer. Further, in the fluorescent organic EL device using this fluorescent dopant material, the reverse intersystem crossing due to the thermal energy at room temperature occurs in the light emitting material, so that the ratio of the S ₁ state of the light emitting material is increased and high luminous efficiency is achieved. Show.

It is a schematic cross-sectional structure showing the structure of the organic EL element which concerns on embodiment of this invention. It is the fluorescence and phosphorescence spectrum of a compound (1).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing a configuration of an organic EL element according to an embodiment of the present invention. This element includes an anode 2 and a cathode 4 on a substrate 1 and a light emitting unit 3 between the pair of electrodes. The light emitting unit 3 has a plurality of layers, at least one of which is a light emitting layer. In addition, the organic EL element of this invention should just have a light emitting layer between a pair of electrodes, and is not limited to the structure shown in FIG.

The light emitting unit 3 of the organic EL element generally has a configuration in which a plurality of layers are laminated, and each layer is a thin film containing an organic compound, a polymer compound, an inorganic compound, and a transition metal complex. Among the layers constituting the light emitting unit 3, at least one layer is a light emitting layer formed of an amorphous film. For example, as shown in FIG. 1, the light emitting unit 3 includes a hole injection layer 31 and a hole transport layer 32 on the anode 2 side of the light emitting layer 33, and an electron transport layer on the cathode 4 side of the light emitting layer 33. A structure having 34 or an electron injection layer 35 can be employed.

[Configuration of light emitting layer]
The light emitting layer 33 is composed of a host material and a fluorescent dopant material. Here, the host material is a material having a high film forming property although its own light emitting ability is low. The fluorescent dopant material is a material having a high light emission capability. The content of the host material in the light emitting layer is 51% or more of the mass of the entire light emitting layer, and the content of the dopant material is 49% or less of the mass of the entire light emitting layer. Preferably, the content of the host material is 75% or more of the mass of the entire light emitting layer, and the content of the dopant material is 25% or less of the mass of the entire light emitting layer.

<Dopant material>
In the organic EL device of the present invention, as the fluorescent dopant material of the light emitting layer 33, a compound that causes reverse intersystem crossing from the T ₁ state to the S ₁ state at room temperature is used. Therefore, it is essential that the fluorescent dopant material has an S ₁ -T ₁ energy gap of 0.24 eV or less. In the organic EL device of the present invention, a cyanopyridine compound represented by the following general formula (I) having an S ₁ -T ₁ energy gap of 0.24 eV or less is used as the fluorescent dopant material of the light emitting layer. .

R ₁ to R _{5 in} the general formula (I) are each independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, a silyl group, an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 1 to 10 carbon atoms, An alkynyl group having 1 to 10 carbon atoms, a cycloalkyl group having 4 to 12 carbon atoms, a substituted or unsubstituted aryl group having 6 to 50 carbon atoms, a substituted or unsubstituted heteroaryl group having 6 to 50 elements, and the number of elements A substituted or unsubstituted heterocyclic group having 6 to 50 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkoxy group having 4 to 12 carbon atoms, an aryloxy group having 1 to 10 carbon atoms, and an alkylthio group having 1 to 10 carbon atoms A cycloalkylthio group having 4 to 12 carbon atoms, an arylthio group having 6 to 12 carbon atoms, an alkoxycarbonyl group having 1 to 10 carbon atoms, an aryloxycarbonyl group having 6 to 12 carbon atoms, a sulfamoyl having 1 to 10 carbon atoms Group, acyl group having 1 to 10 carbon atoms, acyloxy group having 1 to 10 carbon atoms, amide group having 1 to 10 carbon atoms, carbonyl group having 1 to 10 carbon atoms, ureido group having 1 to 10 carbon atoms, carbon number 1 It is one selected from the group consisting of ˜10 sulfinyl groups, alkylsulfonyl groups having 1 to 10 carbon atoms, arylsulfonyl groups having 6 to 12 carbon atoms, and amino groups having 1 to 10 carbon atoms. However, at least one of R ₁ to R ₅ is a cyano group, and at least one of R ₁ to R ₅ is a substituent that is neither a hydrogen atom nor a cyano group.

In order to make the S ₁ -T ₁ energy gap 0.24 eV or less, it is preferable that the molecule includes an electron donating site in addition to having a cyanopyridine structure as an electron withdrawing site. Therefore, it is preferable that one or more of the substituents that are neither a hydrogen atom nor a cyano group of R ₁ to R ₅ is a substituted or unsubstituted heteroaryl group having 6 to 50 elements. Further, in order to enhance the electron donating property of the substituent, one or more of the substituted or unsubstituted heteroaryl group having 6 to 50 elements is a substituted or unsubstituted carbazolyl group having 21 to 50 elements. Preferably there is.

Further, in order to reduce the S ₁ -T ₁ energy gap, it is preferable to bond the cyanopyridine structure, which is an electron withdrawing site, in the molecule and the carbazolyl group, which is an electron donating site, while twisting. Examples of such a light emitting material include compounds represented by the following general formula (II).

R ₆ and R _{7 in} the general formula (II) are each independently one selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group. In the compound represented by the general formula (II), the carbazolyl group and the cyanopyridine are twisted and bonded by steric repulsion between the substituted or unsubstituted carbazolyl group and the cyano group of cyanopyridine.

The fluorescent dopant material in the present invention, among the compounds represented by the general formula (II), R ₆ and R _7, the compound are each independently a hydrogen atom or a methyl group is preferable, and R ₆ and R ₇ The following compound (1) in which both are hydrogen atoms is preferred.

Even when the substituted or unsubstituted heteroaryl group having 6 to 50 elements is a substituted or unsubstituted indolyl group having 15 to 50 elements, the electron donating property is enhanced, so that the S ₁ -T ₁ energy gap Can be reduced. In order to set the S ₁ -T ₁ energy gap to 0.24 eV or less, it is preferable that cyanopyridine, which is an electron withdrawing site, and an indolyl group, which is an electron donating site, are bonded while twisting. Therefore, the indolyl group, as represented by the following formula (A), is preferably an element number 50 following substitutions indolyl group having a substituent R ₁₀ at the 2-position.

In the substituent (A), R ₈ and R ₉ are each independently one type selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group; ₁₀ is one selected from the group consisting of a halogen atom, a cyano group, a methyl group, a methoxy group and a phenyl group. Among them, R ₁₀ is preferably a methyl group. In addition, in order to twist the bond between the cyanopyridine and the indolyl group so that both π-conjugated systems exist in a non-coplanar plane, the substitution in which the cyano group and the substituent (A) are bonded to the adjacent carbon atom It is preferably a group.

Examples of the light emitting material having such a substituent and satisfying the condition that the S ₁ -T ₁ energy gap is 0.24 eV or less include a compound represented by the following general formula (III).

R ₈ and R _{9 in} the general formula (III) are the same as described above. In the compound represented by the general formula (III), the 2-methylindolyl group and the cyanopyridine are twisted and bonded by steric repulsion between the substituted or unsubstituted 2-methylindolyl group and the cyano group of cyanopyridine.

As the fluorescent dopant material, among the compounds represented by the above general formula (III), the following compound (2) or (3) wherein R ₈ is a hydrogen atom and R ₉ is a methyl group or a hydrogen atom is preferable.

<Host material>
In addition to the fluorescent dopant material described above, a host material is used for the light emitting layer. As the host material, a compound that exhibits good film formability and ensures good dispersibility of the fluorescent dopant material is preferably used. The host material desirably has both hole transport performance and electron transport performance. In other words, the host material preferably has a small difference between the hole transport property and the electron transport property. Specifically, the ratio of hole mobility to electron mobility, which is an index of transport performance, is higher. When the degree is divided by the lower degree of mobility, it is preferably 500 or less, that is, the ratio of hole mobility / electron mobility is preferably in the range of 0.002 to 500.

The energy transfer to S ₁ state of the fluorescent dopant material from the viewpoint of actively causing the S ₁ state of the host material, S ₁ energy of the host material is preferably higher than S ₁ energy of the fluorescent dopant material. More desirably, the difference between these two types of S ₁ energy is smaller than 1.5 eV. The difference between the S ₁ energy of S ₁ energy and the fluorescent dopant material of the host material, more preferably at most 1.0 eV, more preferably not more than 0.5 eV.

Examples of the host material are not particularly limited as long as the above-described desirable elements are taken into consideration, and examples thereof include carbazole compounds, arylsilane compounds, and phosphorus oxide compounds. An example of a carbazole compound is N, N′-dicarbazolyl-4-4′-biphenyl (referred to as “CBP”), and an example of an arylsilane compound is p-bis (triphenylsilyl) benzene (“ UGH2 ”), but examples of phosphorus oxide compounds include 4,4′-bis (diphenylphosphoryl) -1,1′-biphenyl (referred to as“ PO1 ”).

Among the above host materials, CBP has a hole mobility of 1.0 × 10 ⁻³ to 2.0 × 10 ⁻³ cm ² / Vs and an electron mobility of 2.9 × 10 ⁻⁴ to 6.9 ×. 10 ⁻⁴ cm ² / Vs (Current Applied Physics, 5, 305 (2005)), and the ratio of hole mobility / electron mobility is about 1.4 to 6.9. It is preferably used as a host material having both hole transportability and electron transportability.

CBP has also been reported to have an S ₁ energy measured in dichloromethane at room temperature of 3.48 eV (New Journal of Chemistry, 32, 1379 (2008)). As will be shown later in Examples, the compound (1), which is a fluorescent dopant material, has an S ₁ energy of 2.99 eV in 2-methyltetrahydrofuran at 77K. S ₁ energy and the S ₁ energy of the above CBP, albeit difference in measurement conditions, even when the measurement conditions identical, S ₁ energy of CBP compounds of the compounds in the examples herein (1) ( It is higher than the S ₁ energy of 1), and the difference between the S ₁ energies of both is 1.5 eV or less. That is, it can be said that CBP is a preferable compound as a host material of an organic EL device using the compound (1) as a thermally activated delayed fluorescent dopant material.

[Configuration of organic EL element other than light emitting layer]
In the organic EL device of the present invention, the configuration and composition of each element other than the light emitting layer are not particularly limited. There is no restriction | limiting in particular about the board | substrate 1 used for formation of an organic EL element, For example, it selects from a transparent substrate like glass, a silicon substrate, a flexible film substrate, etc. suitably, and is used. In the case of a bottom emission type organic EL device that extracts light from the substrate side, the substrate 1 preferably has a transmittance in the visible light region of 80% or more, and 95% or more, from the viewpoint of reducing loss of emitted light. More preferably.

The anode 2 provided on the substrate 1 is not particularly limited. For example, indium tin oxide (ITO), indium zinc oxide (IZO), SnO ₂ , ZnO and the like can be mentioned. Among them, ITO or IZO having high transparency can be preferably used from the viewpoint of extraction efficiency of light generated from the light emitting layer and ease of patterning. Further, the anode may be doped with one or more dopants such as aluminum, gallium, silicon, boron, and niobium, if necessary.

From the viewpoint of transparency, the anode 2 preferably has a transmittance in the visible light region of 70% or more, more preferably 80% or more, and particularly preferably 90% or more.
The method for forming the anode 2 on the substrate 1 is not particularly limited, and can be formed by, for example, a sputtering method or a thermal CVD method.

As long as the light emitting unit 3 includes the light emitting layer 33, the stacked structure is not particularly limited. There are no particular restrictions on the method of forming each layer constituting the light emitting unit 3, and the layers can be formed by a vacuum deposition method, a spin coating method, or the like.

The light emitting unit 3 preferably has a hole transport layer 32. The substance contained in the hole transport layer is preferably a compound that easily undergoes radical cationization. For example, arylamine compounds, imidazole compounds, oxadiazole compounds, oxazole compounds, triazole compounds, chalcone compounds, styrylanthracene compounds Stilbene compounds, tetraarylethene compounds, triarylamine compounds, triarylethene compounds, triarylmethane compounds, phthalocyanine compounds, fluorenone compounds, hydrazine compounds, carbazole compounds, N-vinylcarbazole compounds Compound, pyrazoline compound, pyrazolone compound, phenylanthracene compound, phenylenediamine compound, polyarylalkane compound, polysilane compound, polyphenylene vinyle One or more compounds selected from the system compounds are contemplated. In particular, arylamine compounds have many hole mobility in addition to being easily radical cationized and are suitable as a hole transport layer.

Among the hole transport layers containing an arylamine compound, a hole transport layer containing a triarylamine derivative is particularly preferred, and 4,4′-bis [N- (2-naphthyl) -N is more preferred. -Phenyl-amino] biphenyl (referred to as “α-NPD” or “NPB”).

The light emitting unit 3 also preferably has an electron transport layer 34. The substance contained in the electron transport layer is preferably a compound that easily undergoes radical anionization. For example, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (referred to as “BCP”), tris [(8 -Hydroxyquinolinato)] Aluminum (III) (referred to as “Alq ₃ ”) and its derivatives. Among these, Alq ₃ is preferably used from the viewpoint of versatility.

The material used for the cathode 4 is not particularly limited. For example, a metal having a small work function, an alloy thereof, a metal oxide, or the like is used. Examples of the metal having a small work function include Li for an alkali metal and Mg and Ca for an alkaline earth metal. In addition, a single metal made of rare earth metal or an alloy such as Al, In, or Ag may be used. Further, as disclosed in Japanese Patent Application Laid-Open No. 2001-102175 and the like, a metal complex compound containing at least one selected from the group consisting of alkaline earth metal ions and alkali metal ions is used as the organic layer in contact with the cathode. It can also be used. In this case, it is preferable to use a metal capable of reducing metal ions in the complex compound to a metal in a vacuum, such as Al, Zr, Ti, Si, or an alloy containing these metals, as the cathode.

¡Organic EL elements should be kept to a minimum in use environment. Therefore, it is preferable that a part or the whole of the element is sealed with a sealing glass or a metal cap in an inert gas atmosphere, or is covered with a protective layer made of an ultraviolet curable resin or the like.

In the organic EL device of the present invention, since the dopant material of the light emitting layer causes an inverse intersystem crossing due to thermal energy at room temperature, the ratio of the S ₁ state in the fluorescent dopant material is high and high internal quantum efficiency is exhibited. When reverse intersystem crossing due to thermal energy occurs at room temperature, the internal quantum efficiency at room temperature is expected to be 25% or more. Therefore, the organic EL device of the present invention preferably has an internal quantum efficiency of 25% or more at any temperature from 0 ° C. to 100 ° C. Also, when reverse intersystem crossing due to thermal energy occurs, the probability of occurrence of reverse intersystem crossing from the S ₁ state to the T ₁ state increases as the temperature increases. Therefore, it is preferable that the organic EL device of the present invention has an increase in luminous efficiency as the temperature rises in a temperature range from 0 ° C. to 100 ° C.

The organic EL element of the present invention is an energy-saving light source with low power consumption and can be effectively applied to a display device, a lighting device, and the like.

<Synthesis of Compound (1)>
Under a nitrogen atmosphere, 3,5-dibromopyridine-4-carbonitrile (1.006 g, 3.8 mmol), carbazole (1.912 g, 11.5 mmol), copper iodide (0.1174 g, 0.6 mmol), 18 -Crown-6 (0.158 g, 0.6 mmol), potassium carbonate (1.212 g, 8.8 mmol), 1,3-dimethyl-3,4,5,6-tetrahydro-2 (1H) -pyrimidinone (3 ml) ) Was heated at 170 ^° C. for 5 hours. After cooling to room temperature, it was washed with dichloromethane and purified by silica gel chromatography (scheme 1). This procedure yielded 0.470 g of yellow solid compound (1) (1.1 mmol, 29% yield).

The obtained crystal was confirmed to be compound (1) by ¹ H-NMR. The measurement results were as follows. ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.10 (s, 2H), 8.20 (s, 2H), 8.18 (s, 2H), 7.55-7.52 (m, 4H), 7.43-7.37 (m, 8H).

<S ₁ -T ₁ energy gap and emission wavelength of compound (1) evaluated from fluorescence and phosphorescence spectra>
Compound (1) was dispersed in 2-methyltetrahydrofuran, cooled to 77 K using liquid nitrogen, and then measured for fluorescence and phosphorescence spectra using a spectrofluorometer (Hitachi F-7000). The solid line in FIG. 2 is a fluorescence spectrum obtained from 320 nm incident light, and the broken line is a phosphorescence spectrum obtained from 320 nm incident light. These spectra are standardized so that the maximum value of the emission intensity is 1.0.

The peak ends on the short wavelength side of the fluorescence and phosphorescence spectra are defined as S ₁ energy and T ₁ energy, respectively. When these values were read from FIG. 2, they were 415 nm (2.99 eV; position of (a) in FIG. 2) and 430 nm (2.88 eV; position of (b) in FIG. 2), respectively.

That is, it can be seen that compound (1) is a thermally activated delayed fluorescent material that causes reverse intersystem crossing from the T ₁ state to the S ₁ state at room temperature.

The position of the peak top of the fluorescence spectrum at 77 K of compound (1) was defined as the experimental value of the emission wavelength. The emission wavelength of the compound (1) was 467 nm (position (C) in FIG. 2).

<Quantum chemical calculation of S ₁ -T ₁ energy gap>
The S ₁ -T ₁ energy gap of the compound (1) was evaluated from the quantum chemical calculation according to the following procedures 1 to 4. The quantum chemical calculation was performed using 6-31G (d) basis functions for all atoms. As a program for executing the calculation, Gaussian 09 (Revision C.01) manufactured by Gaussian was used.

Procedure 1: Using the density functional theory using the M06-2X functional (hereinafter referred to as “M06-2X method”), the molecular structure that gives the lowest energy within the range of the S ₀ state is calculated. the energy was defined as _{e 0.}
Procedure 2: Calculate the molecular structure that gives the lowest energy within the range of the S ₁ state using time-dependent density functional theory using the M06-2X functional (hereinafter referred to as “TD-M06-2X method”). The difference between the lowest energy e ₁ and the energy e ₀ obtained in the above procedure 1 was defined as E ₁ .
Procedure 3: Using the TD-M06-2X method, calculate the molecular structure having the lowest energy within the range of the T ₁ state, and calculate the difference between the lowest energy e ₂ and the energy e ₀ obtained in the above procedure 1 as E _It was defined as ₂ .
Procedure 4: The difference between E ₁ and E ₂ was defined as “calculated value of S ₁ -T ₁ energy gap”.

<Quantum chemical calculation of emission wavelength>
TD-M06-2X functional is used to calculate the molecular structure that has the lowest energy within the range of the S ₁ state, and corresponds to the energy of the difference between the lowest energy e ₃ and the energy e ₁ obtained in step 2 above. The wavelength was defined as “calculated value of emission wavelength”.

<Quantum chemical calculation of emission wavelength of comparative compound (1C)>
With respect to the following comparative compound (1C) in which the cyanopyridine portion of the compound (1) was changed to cyanobenzene, the emission wavelength was determined by quantum chemical calculation in the same manner as the compound (1).

Table 1 shows experimental values and calculated values of the S ₁ -T ₁ energy gap and emission wavelength of compound (1), and calculated values of emission wavelength of comparative compound (1C).

As shown in Table 1, the experimental value of the S ₁ -T ₁ energy gap of the compound (1) was 0.11 eV, and it was experimentally determined to be smaller than 0.24 eV. From this result, it can be seen that the compound (1) causes an inverse intersystem crossing from the T ₁ state to the S ₁ state at room temperature, that is, a thermally activated delayed fluorescent material.

The calculated value of the emission wavelength of the compound (1) was longer than the calculated value of the emission wavelength of the comparative compound (1C) in which the cyanopyridine moiety was changed to cyanobenzene. In the above-mentioned Non-Patent Document 7, the experimental value of the emission wavelength of 1,2,3,5-tetrakis (carbazolo-9-ryl) -4,6-dicyanobenzene (4CzIPN) is 507 nm. It has been reported that the calculated value of the emission wavelength of 4CzIPN determined by the same quantum chemistry calculation as described above is 429 nm, and the calculated value tends to be shorter than the experimental value. The experimental value of the emission wavelength of the compound (1) is shorter than the experimental value of the emission wavelength of 4CzIPN, and the calculated value of the emission wavelength of the compound (1) is the experimental value of the emission wavelength of 4CzIPN. Shorter wavelength.

In the above quantum chemistry calculation, the calculated emission wavelength of compound (1) is longer than the experimental value of the emission wavelength in 2-methyltetrahydrofuran at 77K. Taken together, the calculated emission wavelength does not accurately represent the absolute value of the experimentally measured emission wavelength, but is useful for relative evaluation of the emission wavelength of a specific compound. You can say that.

Therefore, from the result that the calculated value of the emission wavelength of the compound (1) is longer than the calculated value of the emission wavelength of the comparative compound (1C), the thermally activated delayed fluorescent material containing cyanopyridine is cyanobenzene. It can be seen that the emission wavelength is longer than that of the light-emitting material contained.

<Quantum chemical calculation of compound (2) (3) and comparative compound (2C) (3C)>
For the following compounds (2) and (3), the S ₁ -T ₁ energy gap was determined by quantum chemical calculation in the same procedure as described above. In addition, for each of the compound (2) and the compound (3), and the comparative compound (2C) and the comparative compound (3C) in which the cyanopyridine site of these compounds is changed to cyanobenzene, The emission wavelength was determined by calculation. The calculation results are shown in Table 2.

As shown in Table 2, the calculated value of the S ₁ -T ₁ energy gap of the compounds (2) and (3) is smaller than that of the compound (1). Therefore, the experimental value of the S ₁ -T ₁ energy gap of the compounds (2) and (3) is predicted to be smaller than the experimental value of 0.11 eV of the S ₁ -T ₁ energy gap of the compound (1). Therefore, like the compound (1), the compounds (2) and (3) are considered to cause reverse intersystem crossing from the T ₁ state to the S ₁ state at room temperature. That is, the compounds (2) and (3) are considered to be thermally activated delayed fluorescent materials.

In addition, the calculated emission wavelength of the compounds (2) and (3) is longer than the calculated emission wavelength of the comparative compounds (2C) and (3C) in which the cyanopyridine moiety is changed to the cyanobenzene moiety. The same tendency as in the case of comparison between the compound (1) and the comparative compound (1C) was exhibited. Also from this calculation result, it can be seen that the thermally activated delayed fluorescent material containing cyanopyridine has a longer emission wavelength than the light emitting material containing cyanobenzene.

Claims (16)

1. An organic EL element comprising a light emitting layer between a pair of electrodes,
   The light emitting layer has a host material and a fluorescent dopant material, and the content of the fluorescent dopant material in the light emitting layer is 49% or less of the mass of the entire light emitting layer,
   The fluorescent dopant material is an organic EL device in which a difference between S ₁ energy and T ₁ energy is 0.24 eV or less, and is a cyanopyridine compound represented by the following general formula (I).
   

   

   (R ₁ to R _{5 in} the general formula (I) are each independently a hydrogen atom, a halogen atom, a cyano group, a nitro group, a silyl group, an alkyl group having 1 to 10 carbon atoms, or an alkenyl group having 1 to 10 carbon atoms. , Alkynyl groups having 1 to 10 carbon atoms, cycloalkyl groups having 4 to 12 carbon atoms, substituted or unsubstituted aryl groups having 6 to 50 carbon atoms, substituted or unsubstituted heteroaryl groups having 6 to 50 carbon atoms, elements A substituted or unsubstituted heterocyclic group having 6 to 50 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, a cycloalkoxy group having 4 to 12 carbon atoms, an aryloxy group having 1 to 10 carbon atoms, and an alkylthio having 1 to 10 carbon atoms Group, cycloalkylthio group having 4 to 12 carbon atoms, arylthio group having 6 to 12 carbon atoms, alkoxycarbonyl group having 1 to 10 carbon atoms, aryloxycarbonyl group having 6 to 12 carbon atoms, sulfamo having 1 to 10 carbon atoms Group, acyl group having 1 to 10 carbon atoms, acyloxy group having 1 to 10 carbon atoms, amide group having 1 to 10 carbon atoms, carbonyl group having 1 to 10 carbon atoms, ureido group having 1 to 10 carbon atoms, carbon number 1 to 10 sulfinyl groups, an alkylsulfonyl group having 1 to 10 carbon atoms, an arylsulfonyl group having 6 to 12 carbon atoms, and an amino group having 1 to 10 carbon atoms, and R ₁ At least one of -R ₅ is a cyano group, and at least one of R ₁ -R ₅ is a substituent that is neither a hydrogen atom nor a cyano group.
2. 2. In the general formula (I), one or more of the substituents that are neither a hydrogen atom nor a cyano group in R ₁ to R ₅ are a substituted or unsubstituted heteroaryl group having 6 to 50 elements. The organic EL element as described in.
3. 3. The organic EL device according to claim 2, wherein the substituted or unsubstituted heteroaryl group having 6 to 50 elements is a substituted or unsubstituted carbazolyl group.
4. The organic EL device according to claim 3, wherein the cyanopyridine compound represented by the general formula (I) is a compound represented by the following general formula (II).
   

   

   (R ₆ and R _{7 in} formula (II) are each independently one selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group.)
5. The organic EL device according to claim 4, wherein in the general formula (II), R ₆ and R ₇ are both hydrogen atoms.
6. The organic EL device according to claim 2, wherein one or more of the substituted or unsubstituted heteroaryl groups having 6 to 24 elements are substituted indolyl groups having 50 or less elements represented by the following formula (A): .
   

   

   (In the above substituent (A), R ₈ and R ₉ are each independently one type selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group; R ₁₀ is one selected from the group consisting of a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group)
7. The organic EL device according to claim 6, wherein R ₁₀ is a methyl group, and the cyanopyridine compound represented by the general formula (I) is a compound represented by the following general formula (III).
   

   

   (R ₈ and R _{9 in} formula (III) are each independently one selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, a methyl group, a methoxy group, and a phenyl group.)
8. The organic EL device according to claim 7, wherein in the general formula (III), R ₉ is a hydrogen atom or a methyl group.
9. The organic EL device according to claim 8, wherein in the general formula (III), R ₈ is a hydrogen atom.
10. The S ₁ energy of the host material is higher than the S ₁ energy of the fluorescent dopant material, and the difference between the two types of S ₁ energy is 1.5 eV or less. The organic EL element as described in.
11. 11. The organic EL device according to claim 1, wherein the host material has a hole mobility to electron mobility ratio in the range of 0.002 to 500.
12. The organic EL device according to any one of claims 1 to 11, wherein the host material is at least one selected from the group consisting of a carbazole compound, an arylsilane compound, and a phosphorus oxide compound.
13. The organic EL device according to any one of claims 1 to 12, wherein the internal quantum efficiency at any temperature of 0 to 100 degrees Celsius is 25% or more.
14. The organic EL device according to any one of claims 1 to 13, wherein the light emission efficiency increases as the temperature rises in a temperature range of 0 to 100 degrees Celsius.
15. A lighting fixture comprising the organic EL element according to any one of claims 1 to 14.
16. A display device comprising the organic EL element according to any one of claims 1 to 14.
    
    

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