JP7081924B2 - Luminescent material, luminescent thin film, organic electroluminescence element, display device and lighting device - Google Patents

Description

The present invention relates to a π-conjugated compound, an organic electroluminescence element material, a light emitting material, a light emitting thin film, an organic electroluminescence element, and a display device and a lighting device provided with the organic electroluminescence element. More specifically, the present invention relates to a π-conjugated compound having improved luminous efficiency.

An organic electroluminescence element (also referred to as an "organic electroluminescent element" or "organic EL element") using an organic material electroluminescence (hereinafter abbreviated as "EL") enables planar light emission. It is a technology that has already been put into practical use as a new electroluminescence system. Organic EL elements have recently been applied not only to electronic displays but also to lighting equipment, and their development is expected.

There are two light emission methods for organic EL elements: "phosphorus light emission" that emits light when returning from the triplet excited state to the ground state, and "fluorescent emission" that emits light when returning from the singlet excited state to the ground state. There is a street.
When an electric field is applied to an organic EL element, holes and electrons are injected from the anode and cathode, respectively, and recombine in the light emitting layer to generate excitons. At this time, since the singlet exciter and the triplet exciter are generated at a ratio of 25%: 75%, the phosphorescent emission using the triplet exciter has a theoretically higher internal quantum than the fluorescent emission. It is known that efficiency can be obtained.
However, in order to actually obtain high quantum efficiency in the phosphorescent emission method, it is necessary to use a complex using a rare metal such as iridium or platinum as the central metal, and in the future it is necessary to use the reserves of the rare metal and the metal itself. There is concern that price will be a major industrial issue.

On the other hand, various developments have been made to improve the luminous efficiency of the fluorescent light emitting type, and new movements have emerged in recent years.
For example, in Patent Document 1, a phenomenon in which singlet excitons are generated by collision of two triplet excitons (Triplet-Triplet Annihilation: hereinafter, abbreviated as “TTA” as appropriate. Further, Triplet-Triplet Fusion: “TTF”. A technique for efficiently causing TTA to improve the efficiency of the fluorescent element is disclosed. Although the luminous efficiency of the fluorescent light emitting material is improved to 2 to 3 times that of the conventional fluorescent light emitting material by this technology, the theoretical single term exciter generation efficiency in TTA is only about 40%, so that the phosphorescent light emission is still performed. It has a problem of high luminous efficiency.

Further, in recent years, a phenomenon utilizing a phenomenon in which reverse intersystem crossing (Reverse Intersystem Crossing: hereinafter abbreviated as "RISC" as appropriate) occurs from a triplet exciton to a singlet exciton ("heat-activated delayed fluorescence" ("" It is also reported that it can be used for fluorescent light emitting materials using "thermally excited delayed fluorescence" (hereinafter, abbreviated as "TADF" as appropriate) and organic EL elements (for example, for example). See Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2.). When the delayed fluorescence by this TADF mechanism is used, 100% internal quantum, which is theoretically equivalent to that of phosphorescent light emission, even in fluorescent light emission by electric field excitation. Efficiency is possible.

In order for the TADF phenomenon to occur, it is necessary to cause an inverse intersystem crossing from 75% triplet excitons to singlet excitons generated by electric field excitation at room temperature or the temperature of the light emitting layer in the light emitting element. Further, the singlet excitons generated by the intersystem crossing fluoresce in the same manner as the 25% singlet excitons generated by the direct excitation, so that 100% internal quantum efficiency is theoretically possible. In order for this inverse intersystem crossing to occur, the absolute value of the difference between the lowest excited singlet energy level (S ₁ ) and the lowest triplet excited energy level (T ₁ ) (hereinafter referred to as _ΔEST ) is extremely high. It is essential to be small.

Further, it is known that when a compound exhibiting TADF property is included in the light emitting layer as a third component (assist dopant) in the light emitting layer composed of a host compound and a light emitting compound, it is effective in exhibiting high luminous efficiency (non-). See Patent Document 3). By generating 25% singlet excitons and 75% triplet excitons on the assist dopant by field excitation, the triplet excitons generate singlet excitons with inverse intersystem crossing (RISC). be able to. The energy of the singlet exciter is transferred to the luminescent compound by fluorescence resonance energy transfer (hereinafter, abbreviated as "FRET" as appropriate), and the luminescent compound can emit light by the transferred energy. Will be. Therefore, it is theoretically possible to make the luminescent compound emit light by using 100% exciton energy, and high luminous efficiency is exhibited.

In order to minimize _ΔEST in an organic compound, it is desirable to localize the highest occupied molecular orbital (HOMO) and the lowest empty molecular orbital (LUMO) in the molecule without mixing them.

1 and 2 are schematic diagrams showing energy diagrams of a compound exhibiting the TADF phenomenon (TADF compound) and a general fluorescent light emitting compound. For example, in 2CzPN having the structure shown in FIG. 1, HOMO is localized in the carbazolyl groups at the 1st and 2nd positions on the benzene ring, and LUMO is localized in the cyano groups at the 4th and 5th positions. Therefore, HOMO and LUMO of 2CzPN can be separated, _ΔEST becomes extremely small, and the TADF phenomenon is exhibited. On the other hand, in 2CzXy (FIG. 2) in which the cyano groups at the 4- and 5-positions of 2CzPN are replaced with methyl groups, although the structures are similar, ΔE cannot be clearly separated from HOMO and LUMO as seen in 2CzPN. The _ST cannot be reduced, and the TADF phenomenon cannot be manifested.

In the prior art, in order to clearly separate HOMO and LUMO, a method using a strong electron-donating group or an electron-withdrawing group is known. However, the use of a strong electron donating group or electron attracting group forms a strong intramolecular charge transfer (CT) excited state, which causes the absorption spectrum and the emission spectrum to become longer wavelengths, resulting in an emission wavelength. There is a problem that it is difficult to control. On the contrary, if the electron donating property or the electron withdrawing property is weakened in order to control the emission wavelength, the expression of the TADF phenomenon is hindered. Therefore, a new method for expressing the TADF phenomenon while controlling the emission wavelength is desired.

International Publication No. 2010/134350 Japanese Unexamined Patent Publication No. 2013-116975

H. Uoyama, et al. , Nature, 2012, 492, 234-238 Q. Zhang et al. , Nature, Photonics, 2014,8,326-332 H. Nakanоtani, et al. , Nature Communication, 2014, 5, 4016-4022.

The present invention has been made in view of the above problems and situations, and a solution thereof is to provide a new π-conjugated compound capable of increasing luminous efficiency without lengthening the emission wavelength. Another object of the present invention is to provide an organic electroluminescence element material containing the π-conjugated compound, a luminescent thin film, and a display device and a lighting device provided with the organic electroluminescence element.

As a result of investigating the causes of the above problems in order to solve the above problems, the present inventor is characterized by containing a π-conjugated compound having a nitrogen-containing aromatic six-membered ring having an electron donating portion at the ortho position. We have arrived at the present invention by newly conceiving an organic electroluminescence element and finding that it is possible to improve the light emission efficiency.
That is, the above-mentioned problem according to the present invention is solved by the following means.

（一般式（１）中、
Ｄ^１及びＤ^２は、それぞれ独立に、電子供与性基で置換されたアリール基、置換されていてもよい電子供与性の複素環基、及び置換されていてもよいアミノ基からなる群より選ばれる電子供与性基Ｄを表し、
Ｍ^１～Ｍ^４は、それぞれ独立して、窒素原子又は－Ｃ－Ｚを表し、Ｍ^１～Ｍ^４のうちの少なくとも一つは窒素原子であり、Ｍ^１～Ｍ^４のいずれかが－Ｃ－Ｚの場合、Ｚはそれぞれ独立して水素原子、重水素原子、又は置換基を表す。）
［２］ 前記置換基は、前記電子供与性基Ｄ又はアルキル基であるか、又は
フッ素原子、シアノ基、フッ素原子で置換されたアルキル基、置換されていてもよいカルボニル基、置換されていてもよいスルホニル基、置換されていてもよいホスフィンオキサイド基、置換されていてもよいボリル基、電子吸引性基で置換されていてもよいアリール基、及び置換されていてもよい電子吸引性の複素環基からなる群より選ばれる電子吸引性基Ａである、［１］に記載のπ共役系化合物。
［３］ 前記π共役系化合物が、下記一般式（２）～（２６）のいずれかで表される、［１］又は［２］に記載のπ共役系化合物。

（一般式（２）～（２６）中、
Ｄ^１～Ｄ^６は、それぞれ独立して、前記電子供与性基Ｄを表し、
Ｚ^１～Ｚ^４は、それぞれ独立して、水素原子、重水素原子、アルキル基、又は前記電子吸引性基Ａを表す。）
［４］ 前記一般式（２）～（２６）において、Ｚ^１～Ｚ^４が電子吸引性基Ａである、［３］に記載のπ共役系化合物。
［５］ 前記π共役系化合物において、Ｄ^１＝Ｄ^２＝Ｄ^３＝Ｄ^４＝Ｄ^５＝Ｄ^６とＺ^１＝Ｚ^２＝Ｚ^３＝Ｚ^４のうち少なくとも一方を満たす、［３］又は［４］に記載のπ共役系化合物。
［６］ 前記π共役系化合物の最低励起一重項準位と最低励起三重項準位とのエネルギー差の絶対値（ΔＥ_ＳＴ）が０．５０ｅＶ以下である、［１］～［５］のいずれかに記載のπ共役系化合物。The first of the present invention relates to π-conjugated compounds.
[1] A π-conjugated compound having a structure represented by the following general formula (1).

(In general formula (1),
D ¹ and D ² are independently selected from the group consisting of an aryl group substituted with an electron donating group, an electron donating heterocyclic group optionally substituted, and an amino group optionally substituted. Represents the electron donating group D
M ¹ to M ⁴ independently represent a nitrogen atom or -CZ, at least one of M ¹ to M ⁴ is a nitrogen atom, and any of M ¹ to M ⁴ is -C. In the case of -Z, Z independently represents a hydrogen atom, a deuterium atom, or a substituent. )
[2] The substituent is the electron-donating group D or an alkyl group, or is substituted with a fluorine atom, a cyano group, an alkyl group substituted with a fluorine atom, a carbonyl group which may be substituted, or a substituent. A sulfonyl group which may be substituted, a phosphinoxide group which may be substituted, a boryl group which may be substituted, an aryl group which may be substituted with an electron-withdrawing group, and an electron-withdrawing complex which may be substituted. The π-conjugated compound according to [1], which is an electron-withdrawing group A selected from the group consisting of a ring group.
[3] The π-conjugated compound according to [1] or [2], wherein the π-conjugated compound is represented by any of the following general formulas (2) to (26).

(In general formulas (2) to (26),
D ¹ to D ⁶ independently represent the electron donating group D, respectively.
Z ¹ to Z ⁴ independently represent a hydrogen atom, a deuterium atom, an alkyl group, or the electron-withdrawing group A. )
[4] The π-conjugated compound according to [3], wherein Z ¹ to Z ⁴ are electron-withdrawing groups A in the general formulas (2) to (26).
[5] In the π-conjugated compound, at least one of D ¹ = D ² = D ³ = D ⁴ = D ⁵ = D ⁶ and Z ¹ = Z ² = Z ³ = Z ⁴ is satisfied, [3] or The π-conjugated compound according to [4].
[6] Any of [1] to [5], wherein the absolute value (ΔE _ST ) of the energy difference between the lowest excited singlet level and the lowest excited triplet level of the π-conjugated compound is 0.50 eV or less. The π-conjugated compound described in Kana.

The second aspect of the present invention relates to an organic electroluminescence device material, a light emitting material, a light emitting thin film, and an organic electroluminescence device using the π-conjugated compound of the present invention.
[7] An organic electroluminescence device material containing the π-conjugated compound according to any one of [1] to [6].
[8] A luminescent material containing the π-conjugated compound according to [1], wherein the π-conjugated compound radiates fluorescence.
[9] The light emitting material according to [8], wherein the π-conjugated compound emits delayed fluorescence.
[10] A luminescent thin film containing the π-conjugated compound according to any one of [1] to [6].
[11] The anode, the cathode, and a light emitting layer provided between the anode and the cathode are included.
An organic electroluminescence device in which at least one layer of the light emitting layer contains the π-conjugated compound according to any one of [1] to [6].
[12] The organic electroluminescence element according to [11], wherein the light emitting layer contains the π-conjugated compound and at least one of a fluorescent compound and a phosphorescent compound.
[13] The organic electroluminescence element according to [11], wherein the light emitting layer contains the π-conjugated compound, at least one of a fluorescent light emitting compound and a phosphorescent light emitting compound, and a host material.

The third aspect of the present invention relates to a display device and a lighting device using the organic electroluminescence element of the present invention.
[14] A display device having the organic electroluminescence device according to any one of [11] to [13].
[15] A lighting device having the organic electroluminescence element according to any one of [11] to [13].

By the above means of the present invention, it is possible to provide a new π-conjugated compound having improved luminous efficiency. Further, the π-conjugated compound provides an organic electroluminescence element material, a light emitting material, a light emitting thin film containing the organic electroluminescence element material, and a display device and a lighting device provided with the organic electroluminescence element. Can be done.

The mechanism of expression or mechanism of action of the effect of the present invention is inferred as follows.

In the method of the present application, it has been found that the luminous efficiency is improved in an organic electroluminescence device containing a π-conjugated compound having an electron donor at the ortho position of a nitrogen-containing aromatic six-membered ring. As its expression mechanism, the electron donating site bonded to the ortho position of the nitrogen-containing aromatic six-membered ring of the π-conjugated compound enhances the electron donating property of the molecule by the interaction in the through space, so that it has a strong CT property. It is speculated that it will be possible to form an excited state.

In the prior art, in order to enhance the electron donating property, a method of substituting with a strong electron donating group or expanding a π-conjugated system with a through bond by directly connecting a plurality of electron donating sites is known. There is. However, these conventional techniques have an adverse effect of increasing the emission wavelength. In the method of the present application, since the π-conjugated system is expanded by the through space, it is possible to suppress the lengthening of the emission wavelength. Being able to control the emission wavelength favors the development of organic electroluminescence devices.

The above-mentioned interaction of electron donating sites in the through space is not limited to two electron donating sites, and it is more effective to increase the number of electron donating sites. On the other hand, on the electron attracting portion side as well, if two or more electron attracting portions interact with each other in the through space, it is possible to enhance the electron attracting property of the molecule while suppressing the lengthening of the emission wavelength. It is effective in controlling the energy level of the frontier orbit of the molecule and improving the TADF property.

Schematic diagram showing energy diagrams of TADF compounds Schematic diagram showing energy diagrams of common fluorescent compounds Schematic diagram showing an energy diagram when a π-conjugated compound functions as an assist dopant. Schematic diagram showing an energy diagram when a π-conjugated compound functions as a host compound Schematic diagram showing an example of a display device composed of an organic EL element Schematic diagram of display device by active matrix method Schematic diagram showing a pixel circuit Schematic diagram of a display device using the passive matrix method Schematic diagram of lighting equipment Cross section of lighting equipment A graph showing the relationship between the time from the excitation light irradiation and the number of photons when the fluorescence attenuation measurement was performed on the vapor deposition film 4-1 using the π-conjugated compound of the present invention produced in the examples.

Hereinafter, the present invention, its constituent elements, and modes and embodiments for carrying out the present invention will be described in detail. In addition, in this application, "-" is used in the sense that the numerical values described before and after it are included as the lower limit value and the upper limit value.

1. 1. π-conjugated compound The π-conjugated compound of the present invention is a compound having a structure represented by the following general formula (1).

In the general formula (1), D ¹ and D ² existing at the ortho position are electron donating groups D.

M ¹ to M ⁴ independently represent a nitrogen atom or —CZ, and at least one of M ¹ to M ⁴ is a nitrogen atom. The compound of the present invention must have at least one nitrogen atom in the aromatic six-membered ring, but the number of nitrogen atoms is not particularly limited and is any one of 1 to 4.

When any of M ¹ to M ⁴ is -C-Z, Z is a hydrogen atom, a deuterium atom, or a substituent, preferably an electron donating group D, an alkyl group, or an electron attracting group A. ..

(Electron donating group D)
The electron donating group D represented by Z in D ¹ and D ² or —CZ is an “aryl group substituted with an electron donating group” or a “heterocyclic electron donating group optionally substituted”. It is a "ring group" or a "optionally substituted amino group".

As the "aryl group" of the "aryl group substituted with the electron donating group" represented by D, an aryl group having 6 to 24 carbon atoms is preferable. Specifically, benzene ring, inden ring, naphthalene ring, azulene ring, fluoranthene ring, phenanthrene ring, anthracene ring, acenaphtylene ring, biphenylene ring, naphthalene ring, pyrene ring, pentalene ring, acetylene ring, heptalene ring, triphenylene. Examples thereof include a ring, an as-indacene ring, a chrysene ring, an s-indacene ring, a pryaden ring, a phenalene ring, a fluoranthene ring, a perylene ring, an acephenanthrene ring, a biphenyl ring, a terphenyl ring, and a tetraphenyl ring. More preferably, benzene ring, naphthalene ring, fluorene ring, phenanthrene ring, anthracene ring, biphenylene ring, chrysene ring, pyrene ring, triphenylene ring, chrysene ring, fluoranthene ring, perylene ring, biphenyl ring and terphenyl ring can be mentioned.

As the "electron-donating heterocyclic group" of the "optionally substituted electron-donating heterocyclic group" represented by D, a heterocycle having 4 to 24 carbon atoms is preferable. Examples of such heterocycles include pyrrole ring, indole ring, carbazole ring, azacarbazole ring, diazacarbazole ring, indroindole ring, 9,10-dihydroacridin ring, 5,10-dihydrophenazacillin ring. 10,11-dihydrodibenzoazepine ring, phenoxazine ring, phenothiazine ring, dibenzothiophene ring, benzofurylindole ring, benzothienoindole ring, indolocarbazole ring, benzofurylcarbazole ring, benzothienocarbazole ring, benzothiophenobenzothiophene Examples include a ring, a benzocarbazole ring, a dibenzocarbazole ring, and the like. More preferably, a carbazole ring, an indole indole ring, a 9,10-dihydroacridine ring, a phenoxazine ring, a phenothiazine ring, a dibenzothiophene ring, a benzofurylindole ring, and a benzocarbazole ring can be mentioned. The above electron donating heterocycles may be combined by connecting two or more identical or different rings.

The "electron donating group" of the "aryl group substituted with an electron donating group" represented by D includes an alkyl group, an alkoxy group, an amino group which may be substituted, and an electron donating which may be substituted. Examples include sex complex rings. Preferred examples thereof include an alkyl group and a heterocyclic group of an electron donating group which may be substituted.

The "alkyl group" of the "electron donating group" of the "aryl group substituted with the electron donating group" represented by D may be linear, branched or cyclic, and may have, for example, 1 to 1 carbon atoms. Examples of the 20 linear, branched or cyclic alkyl groups include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, s-butyl group, t-butyl group, and the like. n-pentyl group, neopentyl group, n-hexyl group, cyclohexyl group, 2-ethylhexyl group, n-heptyl group, n-octyl group, 2-hexyloctyl group, n-nonyl group, n-decyl group, n-undecyl Examples thereof include a group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-pentadecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-nonadecyl group and an n-icosyl group. Preferred examples include a methyl group, an ethyl group, an isopropyl group, a t-butyl group, a cyclohexyl group, a 2-ethylhexyl group and a 2-hexyloctyl group.

The "arco-shiki group" of the "electron-donating group" of the "aryl group substituted with the electron-donating group" represented by D may be linear, branched, or cyclic, and may have, for example, 1 to 1 carbon atoms. Examples thereof include 20 linear, branched or cyclic alkyl groups, specifically methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, isobutoxy group, t-butoxy group, n. -Pentyloxy group, neopentyloxy group, n-hexyloxy group, cyclohexyloxy group, n-heptyloxy group, n-octyloxy group, 2-ethylhexyloxy group, nonyloxy group, decyloxy group, 3,7-dimethyloctyl Oxy group, n-undecyloxy group, n-dodecyloxy group, n-tridecyloxy group, n-tetradecyloxy group, 2-n-hexyl-n-octyloxy group, n-pentadecyloxy group, n -Hexadecyloxy group, n-heptadecyloxy group, n-octadecyloxy group, n-nonadecyloxy group, n-icosyloxy group, methoxy group, ethoxy group, isopropoxy group, t-butoxy group, cyclohexyloxy group. , 2-Ethylhexyloxy group, 2-hexyloctyloxy group are preferable.

The substituent of the "optionally substituted amino group" of the "electron-donating group" of the "aryl group substituted with the electron-donating group" represented by D is substituted with an alkyl group or an alkyl group. An aryl ring may be used, and examples of the alkyl group and the aryl group are the same as those described above, and the same ones are preferable.

The substituent of the "optionally substituted electron-donating heterocyclic group" represented by D may be an alkyl group, an alkoxy group, an aryl ring optionally substituted with an alkyl group, or a substituent may be substituted. Examples thereof include an amino group, and specific examples thereof include the same ones as described above, and the same ones are preferable.

Examples of the "optionally substituted electron-donating heterocyclic group" of the "electron-donating group" of the "electron-donating aryl group substituted with the electron-donating group" represented by D include the same as described above. And similar ones are preferred.

Examples of the substituent of the “optionally substituted amino group” represented by D include the same groups as described above, and the same group is preferable.

Examples of the "alkyl group" represented by Z in -CZ include the same groups as described above, and the same group is preferable.

(Electronic withdrawing group A)
The electron-withdrawing group A represented by Z in -CZ is a "fluorine atom", a "cyano group", an "alkyl group substituted with a fluorine atom", a "optionally substituted carbonyl group", and a "substituted carbonyl group". Substitutable sulfonyl group, "optionally substituted phosphinoxide group", "optionally substituted boryl group", "optionally optionally substituted aryl group (preferably an electron-withdrawing group) It may be an aryl group which may be substituted) ”or an electron-withdrawing heterocyclic group which may be substituted.

Examples of the "alkyl group" of the "alkyl group substituted with a fluorine atom" represented by A include the same as described above, and the same one is preferable.

Examples of the "aryl group" of the "optionally substituted aryl group" represented by A include the same as described above, and the same one is preferable.

As the "heterocyclic group" of the "optionally substituted electron-withdrawing heterocyclic group" represented by A, a heterocyclic group having 3 to 24 carbon atoms is preferable. Examples of such heterocyclic groups include dibenzothiophene oxide ring, dibenzothiophene dioxide ring, pyridine ring, pyridazine ring, pyrimidine ring, pyrazine ring, triazine ring, quinoline ring, isoquinoline ring, quinazoline ring, cinnoline ring, quinoxaline. Examples thereof include a ring, a phthalazine ring, a pteridine ring, a phenanthridine ring, a phenanthrolin ring, a dibenzofuran ring, a azadibenzofuran ring, a diazadibenzofuran ring, a dibenzosilol ring, a dibenzobolol ring, and a dibenzophosphor oxide ring. More preferably, a pyridine ring, a pyrimidine ring, a pyrazine ring, a triazine ring, a quinoline ring, an isoquinoline ring, a quinazoline ring, a quinoxaline ring, a phenanthridine ring, a phenanthroline ring, a dibenzofuran ring, or a dibenzofuran oxide ring can be mentioned. The above heterocyclic groups may be combined by connecting two or more rings that are the same or different.

Examples of the substituent of the "optionally substituted electron-withdrawing heterocyclic group" represented by A include a deuterium atom, a fluorine atom, a cyano group, an alkyl group optionally substituted with a fluorine atom, and a fluorine atom. Examples thereof include an aryl ring optionally substituted with an alkyl group and an aryl ring optionally substituted with a fluorine atom. Specific examples of the alkyl group and the aryl ring include the same as above, and the same ones are preferable.

As the substituent of the "aryl group optionally substituted with an electron-withdrawing group" represented by A, a heavy hydrogen atom, a fluorine atom, a cyano group, an alkyl group optionally substituted with a fluorine atom, and a substituent are substituted. Examples include a carbonyl group which may be substituted, a sulfonyl group which may be substituted, a phosphinoxide group which may be substituted, a boryl group which may be substituted, and an electron-withdrawing heterocyclic group which may be substituted. Be done.

Among them, the substituent that the aryl group can have is preferably an electron-withdrawing group, which is a fluorine atom, a cyano group, an alkyl group substituted with a fluorine atom, a carbonyl group which may be substituted, or a substituted group. A sulfonyl group which may be substituted, a phosphinoxide group which may be substituted, a boryl group which may be substituted, and an electron-withdrawing heterocyclic group which may be substituted are preferable, and the group is substituted with a fluorine atom, a cyano group, or a fluorine atom. A substituted alkyl group or an optionally substituted electron-withdrawing heterocyclic group is more preferred.

Of "optionally substituted carbonyl group", "optionally substituted sulfonyl group", "optionally substituted phosphine oxide group", "optionally substituted boryl group" represented by A Examples of the substituent include a heavy hydrogen atom, a fluorine atom, a cyano group, an alkyl group which may be substituted with a fluorine atom, an aryl ring which may be substituted, and an electron-withdrawing heterocycle which may be substituted. Be done. Specific examples include the same as above, and the same is preferable.

The π-conjugated compound of the present invention is preferably represented by any of the following general formulas (2) to (26).

In the general formulas (2) to (26), D ¹ to D ⁶ independently represent the electron donating group D, respectively. Examples of the electron donating group D include the same groups as D ¹ to D ² in the general formula (1), and the same group is preferable.

In the general formulas (2) to (26), Z ¹ to Z ⁴ independently represent a hydrogen atom, a deuterium atom, an alkyl group, or the electron-withdrawing group A. The electron-withdrawing group A is an electron-withdrawing group A that can be used as Z in the general formula (1), that is, a fluorine atom, a cyano group, an alkyl group substituted with a fluorine atom, a carbonyl group that may be substituted, and the like. A sulfonyl group which may be substituted, a phosphinoxide group which may be substituted, a boryl group which may be substituted, an aryl ring which may be substituted with an electron-withdrawing group, or an electron which may be substituted. It is an attractive heterocyclic group.

In the general formulas (2) to (26), "alkyl group" represented by Z ¹ to Z ⁴ , "alkyl group substituted with a fluorine atom", "may be substituted carbonyl group", "substituted". Examples of the "sulfonyl group which may be substituted", the "phosphinoxide group which may be substituted", and the "boryl group which may be substituted" include the same groups as described above, and the same ones are preferable.

In the general formulas (2) to (26), examples of the "aryl group" of the "aryl group optionally substituted with an electron-withdrawing group" represented by Z ¹ to Z ⁴ include the same as described above. And similar ones are preferred.

In the general formulas (2) to (26), the "electron-withdrawing heterocyclic group" of the "optionally substituted electron ^- withdrawing heterocyclic group" represented by ^Z1 to Z4 is as described above. Similar ones are mentioned, and similar ones are preferable.

In the general formulas (2) to (26), the substituents of the "optionally substituted electron-withdrawing heterocyclic group" represented by Z ¹ to Z ⁴ include a deuterium atom, a fluorine atom and a cyano group. Examples thereof include an alkyl group optionally substituted with a fluorine atom, an aryl ring optionally substituted with an alkyl group optionally substituted with a fluorine atom, and an aryl ring optionally substituted with a fluorine atom. Specifically, the same as above can be mentioned, and the same thing is preferable.

In the general formulas (2) to (26), the "electron-withdrawing group" of the "aryl group optionally substituted with an electron-withdrawing group" represented by Z ¹ to Z ⁴ includes a fluorine atom and a cyano group. , An alkyl group substituted with a fluorine atom, a optionally substituted carbonyl group, an optionally substituted sulfonyl group, an optionally substituted phosphinoxide group, an optionally substituted boryl group, substituted. It represents an electron-withdrawing heterocycle which may be optionally, preferably a fluorine atom, a cyano group, an alkyl group substituted with a fluorine atom, or an electron-withdrawing heterocycle which may be substituted.

In the general formulas (2) to (26), the "aryl group optionally substituted with an electron-withdrawing group" represented by Z ¹ to Z ⁴ is substituted with a "fluorine atom" of the "electron-withdrawing group". "Alkyl group", "optionally substituted carbonyl group", "optionally substituted sulfonyl group", "optionally substituted phosphine oxide group", "optionally substituted boryl group", "optionally substituted boryl group" Examples of the "optionally substituted electron-withdrawing heterocyclic group" include the same groups as described above, and the same group is preferable.

In the π-conjugated compound having the structure represented by the general formulas (2) to (26), D ¹ = D ² = D ³ = D ⁴ = D ⁵ = D ⁶ and Z ¹ = Z ² = Z ³ = Z. It is preferable to satisfy at least one of ⁴ . Not only is it easy to synthesize, but it is also easy to obtain good luminous efficiency.

In the π-conjugated compound having the structure represented by the general formula (1), the absolute value ( _ΔEST ) of the energy difference between the lowest excited singlet level and the lowest excited triplet level of the π-conjugated compound is It is preferably 0.50 eV or less, and is preferably contained in the organic electroluminescence element, the element material, or the luminescent thin film.

Hereinafter, preferred specific examples of the π-conjugated compound according to the present invention will be given, but these compounds may further have a substituent or may have a structural isomer or the like, and are limited to this description. Not done.

By using these compounds, as described above, it is possible to enhance the electron donating property while suppressing the lengthening of the emission wavelength. Of these compounds, materials having an absolute value of _ΔEST of 0.50 eV or less may exhibit TADF properties. Here, showing delayed fluorescence means that there are two or more types of components having different decay rates of the emitted fluorescence when the fluorescence attenuation measurement is performed. In addition, although the decay time of a component having a slow decay is generally sub-microsecond or more, the decay time is not limited because the decay time differs depending on the material. Fluorescence attenuation measurement can generally be performed as follows. A solution or thin film of a π-conjugated compound (luminescent compound) or a co-deposited film of the π-conjugated compound and the second component is irradiated with excitation light under a nitrogen atmosphere, and the number of photons at a certain emission wavelength is measured. At this time, when there are two or more types of components having different decay rates of the emitted fluorescence, the π-conjugated compound exhibits delayed fluorescence.

Furthermore, since these compounds have bipolarity and can cope with various energy levels, they can be used not only as a light emitting host but also as a compound suitable for hole transport and electron transport. Therefore, the use is not limited to the light emitting layer, and may be used for the hole injection layer, the hole transport layer, the electron blocking layer, the hole blocking layer, the electron transport layer, the electron injection layer, the intermediate layer and the like. ..

<Synthesis method>
The above-mentioned π-conjugated compound is described in, for example, International Publication No. 2010/117355, Organic Letters, 2002, 4, 1783-1785. It can be synthesized by referring to the method described in 1 or the method described in the references described in these documents.

2. 2. Organic electroluminescence element material The π-conjugated compound having the structure represented by the general formula (1) can be used as an organic electroluminescence (EL) element material containing the π-conjugated compound. Specifically, it is possible to use a π-conjugated compound having a structure represented by the general formula (1) as an organic electroluminescence device material in applications such as a luminescent material, a host material, and an assist dopant. It is preferable from the viewpoint of sex.

Next, the light emitting method and the light emitting material of the organic EL related to the technical idea of the present invention will be described.

<Light emission method of organic EL>
There are two types of light emission methods for organic EL: "phosphorus light emission" that emits light when returning from the triplet excited state to the ground state, and "fluorescent emission" that emits light when returning from the singlet excited state to the ground state. be.

When excited by an electric field such as an organic EL, triplet excitators are generated with a 75% probability and singlet excitors are generated with a 25% probability, so phosphorescence emission is more efficient than fluorescence emission. It is an excellent method to realize low power consumption.

On the other hand, even in fluorescence emission, the triplet-triplet exciter, which is normally generated with a 75% probability and whose energy of the exciter is normally only heat due to non-radiation deactivation, is present at a high density. A method using a TTA (Triplet-Triplet Annihilation, or Triplet-Triplet Fusion: abbreviated as "TTF") mechanism that generates one singlet exciter from two triplet excitors to improve light emission efficiency is available. It has been found.

Furthermore, in recent years, by reducing the energy gap between the single-term excited state and the triple-term excited state by the discovery of Adachi et al., Triple with a low energy level due to Joule heat during emission and / or the environmental temperature at which the emitting element is placed A phenomenon in which inverse crossing occurs from the term-excited state to the single-term excited state, and as a result, fluorescence emission close to 100% is possible (also referred to as thermal-excited delayed fluorescence or thermal-excited delayed fluorescence: "TADF"). Fluorescent substances that make this possible have been found (see, for example, Non-Patent Document 1 and the like).

<Phosphorescent compound>
As mentioned above, phosphorus light emission is theoretically three times more advantageous than fluorescence emission in terms of emission efficiency, but energy deactivation (= phosphorus light emission) from the triplet excited state to the singlet ground state is prohibited. Since it is a transition and the intersystem crossing from the singlet excited state to the triplet excited state is also a forbidden transition, its velocity constant is usually small. That is, since the transition is unlikely to occur, the exciton lifetime becomes long from milliseconds to seconds, and it is difficult to obtain desired light emission.

However, when a complex using a heavy metal such as iridium or platinum emits light, the rate constant of the forbidden transition increases by 3 orders of magnitude or more due to the heavy atom effect of the central metal, and 100 depending on the selection of the ligand. It is also possible to obtain a phosphorus photon yield of%.

However, in order to obtain such ideal light emission, it is necessary to use precious metals such as iridium, palladium, and platinum, which are rare metals, so-called white metals. The price of metal itself becomes a big problem in industry.

<Fluorescent luminescent compound>
The general fluorescent compound does not need to be a heavy metal complex like a phosphorus light emitting compound, and is a so-called organic compound composed of a combination of general elements such as carbon, oxygen, nitrogen and hydrogen. In addition, other non-metal elements such as phosphorus, sulfur, and silicon can be used, and compounds of typical metals such as aluminum and zinc can also be used, so that the variety can be said to be almost infinite.

However, since only 25% of excitons can be applied to light emission with a conventional fluorescent compound as described above, high-efficiency light emission such as phosphorescent light emission cannot be expected.

<Delayed fluorescent compound>
[Excited triplet-triplet annihilation (TTA) delayed fluorescent compound]
An emission method using delayed fluorescence has emerged to solve the problems of fluorescent compounds. The TTA method originating from the collision between triplet excitons can be described by the following general formula. That is, there is an advantage that a part of triplet excitons, in which the energy of excitons is conventionally converted only into heat by non-radiation deactivation, can cross the singlet excitons that can contribute to light emission. Even in an actual organic EL element, it is possible to obtain an external extraction quantum efficiency that is about twice that of a conventional fluorescent light emitting element.
General formula: T ^* + T ^* → S ^* + S
(In the equation, T ^* represents a triplet exciton, S ^* represents a singlet exciton, and S represents a ground state molecule.)

However, as can be seen from the above equation, since only one singlet exciton that can be used for light emission is generated from two triplet excitons, it is not possible in principle to obtain 100% internal quantum efficiency by this method.

[Thermal Activated Delayed Fluorescence (TADF) Compound]
The TADF method, which is another high-efficiency fluorescent emission, is a method that can solve the problems of TTA.

Fluorescent compounds have the advantage of being able to design an infinite number of molecules as described above. That is, among the molecularly designed compounds, there are compounds in which the energy level differences between the triplet excited state and the singlet excited state are extremely close to each other.

Although such a compound does not have a heavy atom in the molecule, an intersystem crossing from a triplet excited state to a singlet excited state, which cannot normally occur due to a small _ΔEST , occurs. Furthermore, since the rate constant of deactivation (= fluorescence emission) from the singlet excited state to the ground state is extremely large, the triplet excitator itself is thermally deactivated to the ground state (non-radiative deactivation). It is more rhythmically advantageous to return to the ground state while fluorescing via the singlet excited state. Therefore, TADF can theoretically emit 100% fluorescent light.

<Molecular design concept for _ΔEST >
The molecular design for reducing the above _ΔEST will be described.
In principle, in order to reduce _ΔEST , it is most effective to reduce the spatial overlap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in the molecule. It is a target.

It is generally known that HOMO is distributed in an electron-donating site and LUMO is distributed in an electron-withdrawing site in the electron orbit of a molecule. By introducing an electron-donating and electron-withdrawing skeleton into the molecule, HOMO is generally distributed. It is possible to move away from the position where LUMO and LUMO exist.

For example, in "Organic Optoelectronics Reaching the Practical Use Stage" Applied Physics Vol. 82, No. 6, 2013, electron-withdrawing skeletons such as cyano groups and triazines and electron donations such as carbazole and diphenylamino groups are provided. LUMO and HOMO are localized by introducing a sexual skeleton.

It is also effective to reduce the change in molecular structure between the ground state and triplet excited state of the compound. As a method for reducing the structural change, for example, it is effective to make the compound rigid. Rigidity described here means that there are few sites that can move freely in the molecule, such as suppressing free rotation in the bond between rings in the molecule and introducing a fused ring with a large π-conjugated surface. means. In particular, it is possible to reduce the structural change in the excited state by making the portion involved in light emission rigid.

<General problems with TADF compounds>
TADF compounds have various problems in terms of their light emitting mechanism and molecular structure. The following describes some of the problems that TADF compounds generally have.

In TADF compounds, it is necessary to separate the sites where HOMO and LUMO are present as much as possible in order to reduce _ΔEST . Therefore, the electronic state of the molecule is a donor / acceptor type in which the HOMO site and LUMO site are separated. It becomes a state close to intramolecular CT (intramolecular charge transfer state).

When a plurality of such molecules are present, stabilization is achieved when the donor portion of one molecule and the acceptor portion of the other molecule are brought close to each other. Such a stabilized state can be formed not only between two molecules but also between a plurality of molecules such as between three molecules or five molecules, and as a result, various stabilized states having a wide distribution can be obtained. It will be present and the shapes of the absorption and emission spectra will be broad. In addition, even when a multimolecular aggregate of more than two molecules is not formed, various existence states can be taken depending on the difference in the direction and angle of interaction between the two molecules, so that the absorption spectrum and the absorption spectrum are basically the same. The shape of the emission spectrum is broad.

Broadening the emission spectrum poses two major problems. One is the problem that the color purity of the emitted color becomes low. It does not pose a big problem when applied to lighting applications, but when used for electronic displays, the color reproduction range becomes smaller and the color reproducibility of pure colors becomes lower, so it is actually applied as a product. Will be difficult.

Another problem is that the rising wavelength on the short wavelength side of the emission spectrum (referred to as the "fluorescence 0-0 band") is shortened, that is, the S1 is increased (the energy level of the lowest excited _single term energy level is increased). It is to do.

Naturally, when the wavelength of the fluorescence 0-0 band is shortened, the wavelength of the phosphorescent 0-0 band derived from T ₁ , which has a lower energy than that of S ₁ , is also shortened (the T ₁ level rises). Therefore, the compound used for the host compound needs to have a high S ₁ level and a high T ₁ level in order to prevent reverse energy transfer from the dopant.

This is a very big problem. A host compound basically composed of an organic compound takes a state of a plurality of active and unstable chemical species such as a cation radical state, an anion radical state and an excited state in an organic EL element, and these chemical species are intramolecular. By expanding the π-conjugated system of, it can exist relatively stably.

However, in order to impart a high S ₁ level and a high T ₁ level to a molecule, it is necessary to reduce or cut off the π-conjugated system in the molecule, which makes it difficult to achieve both stability and stability. As a result, the life of the light emitting element is shortened.

In addition, in TADF compounds that do not contain heavy metals, the transition from the triplet excited state to the ground state is a forbidden transition, so the existence time (exciton lifetime) in the triplet excited state is from several hundred μs to millimeters. Very long, on the order of seconds. Therefore, even if the T1 energy level of the host compound is higher _than that of the fluorescent light-emitting compound, the triple-term excited state of the fluorescent light-emitting compound is changed to the host compound due to the length of its existence time. The probability of reverse energy transfer increases. As a result, the reverse intersystem crossing from the triplet excited state to the singlet excited state of the originally intended TADF compound does not sufficiently occur, and the unfavorable reverse energy transfer to the host compound becomes the mainstream, resulting in sufficient emission efficiency. Will occur.

In order to solve the above problems, it is necessary to sharpen the emission spectrum shape of the TADF compound and reduce the difference between the emission maximum wavelength and the rising wavelength of the emission spectrum. This can be basically achieved by reducing the change in the molecular structure of the singlet-excited state and the triplet-excited state.

Further, in order to suppress the reverse energy transfer to the host compound, it is effective to shorten the existence time (exciton lifetime) of the triplet excited state of the TADF compound. To achieve this, we need to take measures such as reducing the change in the molecular structure between the ground state and the triplet excited state and introducing substituents and elements suitable for unwinding the forbidden transition. Can be solved.

Hereinafter, various measuring methods for the π-conjugated compound according to the present invention will be described.

[Electron density distribution]
In the π-conjugated compound according to the present invention, it is preferable that HOMO and LUMO are substantially separated in the molecule from the viewpoint of reducing _ΔEST . The distribution state of these HOMO and LUMO can be obtained from the electron density distribution when the structure is optimized obtained by the molecular orbital calculation.

For the structural optimization and the calculation of the electron density distribution by the molecular orbital calculation of the π-conjugated compound in the present invention, software for molecular orbital calculation using B3LYP as a general function and 6-31G (d) as a base function is used as a calculation method. It can be calculated by using it, and the software is not particularly limited, and it can be calculated in the same manner by using any of them.

In the present invention, Gaussian 09 (Revision C.01, MJ Frisch, et al, Gaussian, Inc., 2010.) manufactured by Gaussian Co., Ltd. in the United States was used as the software for calculating the molecular orbital.

Further, "HOMO and LUMO are substantially separated" means that the central parts of the HOMO orbital distribution and the LUMO orbital distribution calculated by the above molecular calculation are separated, and more preferably, the HOMO orbital distribution and the LUMO orbital are separated. It means that the distributions of are almost non-overlapping.

Regarding the separated state of HOMO and LUMO, the structure optimization calculation using B3LYP as the above-mentioned general function and 6-31G (d) as the base function is further performed by the time-dependent density functional theory (Time-Dependent DFT). Excited state calculation is performed to obtain the energy levels of S ₁ and T ₁ (E (S ₁ ) and E (T ₁ ), respectively), and ΔE _ST = | E (S ₁ ) -E (T ₁ ) | It is also possible to calculate. The smaller the calculated _ΔEST , the more separated HOMO and LUMO are. In the present invention, the _ΔEST calculated by using the same calculation method as described above is 0.50 eV or less, preferably 0.30 eV or less, and more preferably 0.10 eV or less.

[Lowest excited singlet energy level S ₁ ]
The lowest excited singlet energy level S1 of the π _- conjugated compound in the present invention is defined in the same invention as in the usual method. That is, a compound to be measured is vapor-deposited on a quartz substrate to prepare a sample, and the absorption spectrum (vertical axis: absorbance, horizontal axis: wavelength) of this sample is measured at room temperature (300 K). A tangent line is drawn with respect to the rising edge of the absorption spectrum on the long wavelength side, and the calculation is performed from a predetermined conversion formula based on the wavelength value at the intersection of the tangent line and the horizontal axis.

However, if the molecule itself of the π-conjugated compound used in the present invention has a relatively high cohesiveness, an error due to cohesion may occur in the measurement of the thin film. Considering that the π-conjugated compound in the present invention has a relatively small Stokes shift and that the structural changes between the excited state and the ground state are small, the lowest excited _single -term energy level S1 in the present invention is set to room temperature (25 ° C.). ), The peak value of the maximum emission wavelength in the solution state of the π-conjugated compound was used as an approximate value.

Here, as the solvent used, a solvent that does not affect the aggregated state of the π-conjugated compound, that is, a solvent that is less affected by the solvent effect, for example, a non-polar solvent such as cyclohexane or toluene can be used.

[Lowest excited triplet energy level T ₁ ]
The lowest excited triplet energy level (T ₁ ) of the π-conjugated compound used in the present invention was calculated from the photoluminescence (PL) characteristics of the solution or thin film. For example, as a calculation method for a thin film, a dispersion of a dilute π-conjugated compound is made into a thin film, and then the transient PL characteristics are measured using a streak camera to separate the fluorescent component and the phosphorescent component. The lowest excited triple-term energy level can be obtained from the lowest excited single-term energy level with the absolute value of the energy difference as _ΔEST .

In the measurement and evaluation, the absolute PL quantum yield measuring device C9920-02 (manufactured by Hamamatsu Photonics Co., Ltd.) was used for the measurement of the absolute PL quantum yield. The emission lifetime was measured using a streak camera C4334 (manufactured by Hamamatsu Photonics Co., Ltd.) while exciting the sample with a laser beam.

3. 3. Organic EL Element The organic EL element of the present invention is an organic electroluminescence element having at least a light emitting layer between an anode and a cathode, and at least one of the light emitting layers has a structure represented by the general formula (1). It is characterized by containing a π-conjugated compound having.

Typical element configurations in the organic EL device of the present invention include, but are not limited to, the following configurations.
(1) anode / light emitting layer / cathode (2) anode / light emitting layer / electron transport layer / cathode (3) anode / hole transport layer / light emitting layer / cathode (4) anode / hole transport layer / light emitting layer / electron Transport layer / cathode (5) Anodic / hole transport layer / light emitting layer / electron transport layer / electron injection layer / cathode (6) anode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / cathode (6) 7) Anodic / hole injection layer / hole transport layer / (electron blocking layer /) light emitting layer / (hole blocking layer /) electron transport layer / electron injection layer / cathode Among the above, the configuration of (7) is preferable. Used, but not limited to.

The light emitting layer used in the present invention is composed of a single layer or a plurality of layers, and when there are a plurality of light emitting layers, a non-light emitting intermediate layer may be provided between the light emitting layers.

If necessary, a hole blocking layer (also referred to as a hole barrier layer) or an electron injection layer (also referred to as a cathode buffer layer) may be provided between the light emitting layer and the anode, and the light emitting layer and the anode may be provided. An electron blocking layer (also referred to as an electron barrier layer) or a hole injection layer (also referred to as an anode buffer layer) may be provided between them.

The electron transport layer used in the present invention is a layer having a function of transporting electrons, and in a broad sense, an electron injection layer and a hole blocking layer are also included in the electron transport layer. Further, it may be composed of a plurality of layers.

The hole transport layer used in the present invention is a layer having a function of transporting holes, and in a broad sense, a hole injection layer and an electron blocking layer are also included in the hole transport layer. Further, it may be composed of a plurality of layers.

In the above typical device configuration, the layer excluding the anode and the cathode is also referred to as an "organic layer".

(Tandem structure)
Further, the organic EL element of the present invention may be an element having a so-called tandem structure in which a plurality of light emitting units including at least one light emitting layer are laminated.

As a typical element configuration of the tandem structure, for example, the following configuration can be mentioned.
Anode / 1st light emitting unit / intermediate layer / 2nd light emitting unit / intermediate layer / 3rd light emitting unit / cathode

Here, the first light emitting unit, the second light emitting unit, and the third light emitting unit may all be the same or different. Further, the two light emitting units may be the same, and the remaining one may be different.

A plurality of light emitting units may be directly laminated or laminated via an intermediate layer, and the intermediate layer is generally an intermediate electrode, an intermediate conductive layer, a charge generation layer, an electron extraction layer, a connection layer, or an intermediate layer. A known material structure can be used as long as it is also called an insulating layer and has a function of supplying electrons to the adjacent layer on the anode side and holes to the adjacent layer on the cathode side.

Examples of the material used for the intermediate layer include ITO (inorganic tin oxide), IZO (indium / zinc oxide), ZnO ₂ , TiN, ZrN, HfN, TiOx, VOx, CuI, InN, GaN, and CuAlO ₂ . Conductive inorganic compound layers such as CuGaO ₂ , SrCu ₂ O ₂ , LaB ₆ , RuO ₂ , Al, two-layer films such as Au / Bi ₂ O ₃ , SnO ₂ / Ag / SnO ₂ , ZnO / Ag / ZnO. , Bi ₂ O ₃ / Au / Bi ₂ O ₃ , TIO ₂ / TIN / TIO ₂ , Multilayer film such as _{TIO 2} / ZrN / TIO ₂ , Fullerenes such as C60, Conductive organic material layer such as oligothiophene, Examples thereof include conductive organic compound layers such as metallic phthalocyanines, metal-free phthalocyanines, metal porphyrins, and metal-free porphyrins, but the present invention is not limited thereto.

Preferred configurations in the light emitting unit include, for example, configurations in which the anode and the cathode are removed from the configurations (1) to (7) mentioned in the above typical element configurations, and the present invention includes these. Not limited.

Specific examples of the tandem organic EL element include, for example, US Pat. No. 6,337,492, US Pat. No. 7,420,203, US Pat. No. 7,473,923, US Pat. No. 6,872,472, US Pat. No. 6,107,734, US Pat. No. 6,337,492, International. Publication No. 2005/009087, JP-A-2006-228712, JP-A-2006-24791, JP-A-2006-49393, JP-A-2006-49394, JP-A-2006-49396, JP-A-2011 -96679, Japanese Patent Application Laid-Open No. 2005-340187, Japanese Patent No. 4711424, Japanese Patent No. 3496681, Japanese Patent No. 3884564, Japanese Patent No. 4213169, Japanese Patent Application Laid-Open No. 2010-192719, Japanese Patent Application Laid-Open No. 2009-07629, Japanese Patent Publication No. The element configurations and constituent materials described in JP-A-2007-07844, JP-A-2007-059848, JP-A-2003-272860, JP-A-2003-045676, International Publication No. 2005/094130, etc. are listed. However, the present invention is not limited thereto.

Hereinafter, each layer constituting the organic EL element of the present invention will be described.

(Light emitting layer)
The light emitting layer used in the present invention is a layer that provides a place where electrons and holes injected from an electrode or an adjacent layer are recombined and emit light via excitons, and the light emitting portion is a light emitting layer. It may be in the layer or at the interface between the light emitting layer and the adjacent layer. The structure of the light emitting layer used in the present invention is not particularly limited as long as it satisfies the requirements specified in the present invention.

The total thickness of the light emitting layer is not particularly limited, but the homogeneity of the film to be formed, the prevention of applying an unnecessary high voltage at the time of light emission, and the improvement of the stability of the light emission color with respect to the drive current are improved. From the viewpoint, it is preferably adjusted to the range of 2 nm to 5 μm, more preferably to the range of 2 to 500 nm, and further preferably to the range of 5 to 200 nm.

Further, the layer thickness of each light emitting layer used in the present invention is preferably adjusted in the range of 2 nm to 1 μm, more preferably in the range of 2 to 200 nm, and further preferably in the range of 3 to 150 nm. It will be adjusted.

The light emitting layer used in the present invention may be one layer or may be composed of a plurality of layers. When the π-conjugated compound of the present application is used for the light emitting layer, it may be used alone or mixed with a host material, a fluorescent light emitting material, a phosphorescent light emitting material and the like described later. At least one layer of the light emitting layer may contain a light emitting dopant (a light emitting compound, a light emitting dopant, also simply referred to as a dopant), and further contain a host compound (a matrix material, a light emitting host compound, also simply referred to as a host). preferable. It is preferable that at least one layer of the light emitting layer of the π-conjugated compound of the present application contains the π-conjugated compound of the present application and the host compound because the luminous efficiency is improved. It is preferable that at least one layer of the light emitting layer contains the π-conjugated compound of the present application and at least one of the fluorescent light emitting compound and the phosphorescent light emitting compound because the luminous efficiency is improved. It is preferable that at least one layer of the light emitting layer contains at least one of the π-conjugated compound of the present application, a fluorescent light emitting compound and a phosphorescent light emitting compound, and a host compound because the luminous efficiency is improved.

(1) Light-emitting dopant As the light-emitting dopant, a fluorescent light-emitting dopant (also referred to as a fluorescent light-emitting compound or a fluorescent dopant) and a phosphorescent light-emitting dopant (also referred to as a phosphorescent light-emitting compound or a phosphorescent dopant) are preferably used. Be done. In the present invention, the light emitting layer contains the π-conjugated compound according to the present invention as a fluorescent light emitting compound or an assist dopant in the range of 0.1 to 50% by mass, and particularly in the range of 1 to 30% by mass. It is preferable to contain it within.

In the present invention, it is preferable that the light emitting layer contains the luminescent compound in the range of 0.1 to 50% by mass, and particularly preferably in the range of 1 to 30% by mass.

The concentration of the luminescent compound in the light emitting layer can be arbitrarily determined based on the specific luminescent compound used and the requirements of the device, and at a uniform concentration with respect to the layer thickness direction of the light emitting layer. It may be contained or may have an arbitrary concentration distribution.

Further, the luminescent compound used in the present invention may be used in combination of a plurality of types, and may be used in combination of fluorescent compounds having different structures or in combination of a fluorescent compound and a phosphorescent compound. You may. This makes it possible to obtain an arbitrary emission color.

The π-conjugated compound, the luminescent compound, and the host compound according to the present invention, wherein the absolute value ( _ΔEST ) of the difference between the lowest excited singlet energy level and the lowest excited triplet energy level is 0.50 eV or less. When contained in the light emitting layer, the π-conjugated compound according to the present invention acts as an assist dopant. On the other hand, when the light emitting layer contains the π-conjugated compound and the luminescent compound according to the present invention and does not contain the host compound, the π-conjugated compound according to the present invention acts as the host compound. When the light emitting layer contains only the π-conjugated compound according to the present invention, the π-conjugated compound according to the present invention acts as a host compound and a luminescent compound.

The mechanism by which the effect is exhibited is the same in all cases, and the triplet excitons generated on the π-conjugated compound according to the present invention are converted into singlet excitons by an intersystem crossing (RISC). It is in.

As a result, theoretically all exciton energies generated on the π-conjugated compound according to the present invention can be transferred to the luminescent compound by fluorescence resonance energy transfer (FRET), and high luminous efficiency can be achieved.

Therefore, when the light emitting layer contains the three components of the π-conjugated compound, the luminescent compound, and the host compound according to the present invention, the energy levels of S ₁ and T ₁ of the π-conjugated compound are the S of the host compound. It is preferably lower than the energy levels of ₁ and T ₁ and higher than the energy levels of the luminescent compounds S ₁ and T ₁ .

Similarly, when the light emitting layer contains two components of the π-conjugated compound and the luminescent compound according to the present invention, the energy levels of S ₁ and T ₁ of the π-conjugated compound are S ₁ of the luminescent compound. It is preferable that the energy level is higher _than the energy level of T1.

3 and 4 show schematic views of the case where the π-conjugated compound of the present invention acts as an assist dopant and a host compound, respectively. 3 and 4 are examples, and the process of generating triplet excitons generated on the π-conjugated compound according to the present invention is not limited to electric field excitation, and energy transfer within the light emitting layer or from the interface of the peripheral layer. And electron transfer are also included.

Further, in FIGS. 3 and 4, a fluorescent light emitting compound is used as the light emitting material, but the present invention is not limited to this, and a phosphorescent light emitting compound may be used, and the fluorescent light emitting compound and the phosphorescent light emitting compound may be used. Both sex compounds may be used.

When the π-conjugated compound according to the present invention is used as an assist dopant, the light emitting layer contains a host compound having a mass ratio of 100% or more with respect to the π-conjugated compound, and is a fluorescent compound and / or a phosphorescent compound. Is preferably contained in the range of a mass ratio of 0.1 to 50% with respect to the π-conjugated compound.

When the π-conjugated compound according to the present invention is used as the host compound, the light emitting layer contains a fluorescent compound and / or a phosphorescent compound within a mass ratio of 0.1 to 50% with respect to the π-conjugated compound. It is preferable to contain in.

When the π-conjugated compound according to the present invention is used as an assist dopant or a host compound, it is preferable that the emission spectrum of the π-conjugated compound according to the present invention and the absorption spectrum of the luminescent compound overlap.

The emission colors of the organic EL element of the present invention and the compound used in the present invention are shown in FIG. 3.16 on page 108 of the "New Color Science Handbook" (edited by the Japan Color Society, Tokyo University Press, 1985). It is determined by the color when the result measured by the brightness meter CS-1000 (manufactured by Konica Minolta Co., Ltd.) is applied to the CIE chromaticity coordinates.

In the present invention, it is also preferable that the light emitting layer of one layer or a plurality of layers contains a plurality of light emitting dopants having different light emitting colors and exhibits white light emission.

The combination of light emitting dopants showing white color is not particularly limited, and examples thereof include a combination of blue and orange, and a combination of blue and green and red.

The white color in the organic EL element of the present invention means that the chromaticity in the CIE 1931 color system at 1000 cd / m ² is x = 0.39 ± 0.09 when the 2 degree viewing angle front luminance is measured by the above method. , Y = 0.38 ± 0.08, preferably within the region.

(1) -1 Fluorescent light emitting dopant As the fluorescent light emitting dopant (fluorescent dopant), the π-conjugated compound of the present invention may be used, or a known fluorescent dopant or delayed fluorescence used for the light emitting layer of the organic EL element. It may be appropriately selected from sex dopants and used.

Specific examples of known fluorescent dopants that can be used in the present invention include, for example, anthracene derivatives, pyrene derivatives, chrysene derivatives, fluorentene derivatives, perylene derivatives, fluorene derivatives, arylacetylene derivatives, styrylarylene derivatives, styrylamine derivatives, and arylamine derivatives. , Boron complex, coumarin derivative, pyran derivative, cyanine derivative, croconium derivative, squalium derivative, oxobenzanthracene derivative, fluorescein derivative, rhodamine derivative, pyrylium derivative, perylene derivative, polythiophene derivative, rare earth complex compound and the like. Further, in recent years, light emitting dopants using delayed fluorescence have also been developed, and these may be used. Specific examples of the light emitting dopant using delayed fluorescence include the compounds described in International Publication No. 2011/156793, Japanese Patent Laid-Open No. 2011-213643, Japanese Patent Application Laid-Open No. 2010-93181, Japanese Patent No. 5366106, and the like. However, the present invention is not limited to these.

(1) -2 Phosphorescent light emitting dopant The phosphorescent light emitting dopant used in the present invention will be described.
The phosphorescent dopant used in the present invention is a compound in which light emission from an excited triple term is observed, specifically, a compound that emits phosphorescent light at room temperature (25 ° C.), and has a phosphorescent quantum yield. Is defined as a compound of 0.01 or more at 25 ° C., but a preferable phosphorescence quantum yield is 0.1 or more.

The phosphorus photon yield can be measured by the method described on page 398 (1992 edition, Maruzen) of Spectroscopy II of the 4th Edition Experimental Chemistry Course 7. Although the phosphorus photon yield in a solution can be measured using various solvents, the phosphorus photon dopant used in the present invention achieves the above-mentioned phosphorus photon yield (0.01 or more) in any of any solvents. Just do it.

The phosphorescent dopant can be appropriately selected and used from known ones used for the light emitting layer of the organic EL element. Specific examples of known phosphorescent dopants that can be used in the present invention include compounds described in the following documents.

Nature 395, 151 (1998), Appl. Phys. Let. 78, 1622 (2001), Adv. Mater. 19,739 (2007), Chem. Mater. 17, 3532 (2005), Adv. Mater. 17, 1059 (2005), International Publication No. 2009/100991, International Publication No. 2008/101842, International Publication No. 2003/040257, US Patent Application Publication No. 2006/835469, US Patent Application Publication No. 2006 / 0202194, US Patent Application Publication No. 2007/0087321, US Patent Application Publication No. 2005/0244673, Inorg. Chem. 40,1704 (2001), Chem. Mater. 16, 2480 (2004), Adv. Mater. 16, 2003 (2004), Angew. Chem. lnt. Ed. 2006, 45, 7800, Appl. Phys. Let. 86,153505 (2005), Chem. Let. 34,592 (2005), Chem. Commun. 2906 (2005), Inorg. Chem. 42,1248 (2003), International Publication No. 2009/050290, International Publication No. 2002/015645, International Publication No. 2009/000673, US Patent Application Publication No. 2002/0034656, US Patent No. 7332232, USA Patent Application Publication No. 2009/01087737, US Patent Application Publication No. 2009/00397776, US Patent No. 6921915, US Patent No. 6688266, US Patent Application Publication No. 2007/0190359, US Patent Application Publication No. 2006/0008670, US Patent Application Publication No. 2009/0165846, US Patent Application Publication No. 2008/0015355, US Patent No. 7250226, US Patent No. 7396598, US Patent Application Publication No. 2006/0263635, US Patent Application Publication No. 2003/0138657, US Patent Application Publication No. 2003/0152802, US Patent No. 70090928, Angew. Chem. lnt. Ed. 47, 1 (2008), Chem. Mater. 18, 5119 (2006), Inorg. Chem. 46,4308 (2007), Organometallics 23,3745 (2004), Apple. Phys. Let. 74,1361 (1999), International Publication No. 2002/002714, International Publication No. 2006/009024, International Publication No. 2006/056418, International Publication No. 2005/019373, International Publication No. 2005/123873, International Publication No. 2005/123873, International Publication No. 2007/004380, International Publication No. 2006/082742, US Patent Application Publication No. 2006/0251923, US Patent Application Publication No. 2005/02060441, US Patent No. 73935999. , US Patent No. 7534505, US Patent No. 7445855, US Patent Application Publication No. 2007/0190359, US Patent Application Publication No. 2008/0297033, US Patent No. 7338722, US Patent Application Publication No. 2002 / 0134984, US Patent No. 7279704, US Patent Application Publication No. 2006/098120, US Patent Application Publication No. 2006/103874, International Publication No. 2005/07638380, International Publication No. 2010/032663 , International Publication No. 2008140115, International Publication No. 2007/052431, International Publication No. 2011/134013, International Publication No. 2011/157339, International Publication No. 2010/086089, International Publication No. 2009/113646, International Publication No. 2012/20327, International Publication No. 2011/051404, International Publication No. 2011/004639, International Publication No. 2011/073149, US Patent Application Publication No. 2012/228583, US Patent Application Publication No. 2012/212126 Japanese Patent Application Laid-Open No. 2012-069737, Japanese Patent Application Laid-Open No. 2011-181303, Japanese Patent Application Laid-Open No. 2009-1140886, Japanese Patent Application Laid-Open No. 2003-81988, Japanese Patent Application Laid-Open No. 2002-302671 and Japanese Patent Application Laid-Open No. 2002-363552 And so on.

Among them, preferred phosphorescent dopants include organometallic complexes having Ir as the central metal. More preferably, a complex containing at least one coordination mode of a metal-carbon bond, a metal-nitrogen bond, a metal-oxygen bond, and a metal-sulfur bond is preferable.

(2) Host compound The host compound used in the present invention is a compound mainly responsible for charge injection and transport in the light emitting layer, and its own light emission is not substantially observed in the organic EL element.

Among the compounds contained in the light emitting layer, the host compound preferably has a mass ratio of 20% or more in the layer.

The host compound may be used alone or in combination of two or more. By using a plurality of types of host compounds, it is possible to adjust the charge transfer, and it is possible to improve the efficiency of the organic electroluminescence device.

Hereinafter, the host compound preferably used in the present invention will be described.

As the host compound, the π-conjugated compound used in the present invention may be used as described above, but there is no particular limitation. From the viewpoint of reverse energy transfer, those having an excitation energy larger than the excitation singlet energy of the dopant are preferable, and those having an excitation triplet energy larger than the excitation triplet energy of the dopant are more preferable.

The host compound is responsible for carrier transport and exciton generation in the light emitting layer. Therefore, it can exist stably in all active species in the cation radical state, the angstrom state, and the excited state, does not cause chemical changes such as decomposition and addition reaction, and further, the host molecule is generated in the layer over time of energization. It is preferable not to move at the angstrom level.

Further, especially when the light emitting dopant used in combination exhibits TADF emission, the existence time of the triple-term excited state of the _TADF compound is long, so that the T1 energy level of the host compound itself is high, and the host compounds are associated with each other. Molecules that do not reduce the T ₁ of the host compound, such as not forming a low T ₁ state in the state of being in the state, the TADF compound and the host compound not forming an exciplex, and the host compound not forming an electromer by an electric field. Appropriate design of the structure is required.

In order to meet these requirements, the host compound itself must have high electron hopping mobility, high hole hopping mobility, and small structural changes in the triplet excited state. Is. As a representative of the host compound satisfying such a requirement, those having _a high T1 energy level such as a carbazole skeleton, an azacarbazole skeleton, a dibenzofuran skeleton, a dibenzothiophene skeleton or a azadibenzofuran skeleton are preferably mentioned.

Further, the host compound has a hole transporting ability or an electron transporting ability, prevents the wavelength of light emission from being lengthened, and further stabilizes the organic electroluminescence element against heat generation during high temperature drive or element drive. It is preferable to have a high glass transition temperature (Tg) from the viewpoint of operation. Tg is preferably 90 ° C. or higher, and more preferably 120 ° C. or higher.

Here, the glass transition point (Tg) is a value obtained by a method based on JIS K 7121-2012 using DSC (Differential Scanning Colorimetry).

Further, as the host compound used in the present invention, it is also preferable to use the π-conjugated compound according to the present invention as described above. Since the π-conjugated compound according to the present invention has a high T ₁ , it can be suitably used for a light emitting material having a short emission wavelength (that is, a high energy level of T ₁ and S ₁ ). Is.

When a known host compound is used for the organic EL device of the present invention, specific examples thereof include the compounds described in the following documents, but the present invention is not limited thereto.

Japanese Patent Laid-Open Nos. 2001-257076, 2002-308855, 2001-313179, 2002-319491, 2001-357977, 2002-334786, 2002-8860, 2002-334787, 2002-15871, 2002-334788, 2002-43056, 2002-334789, 2002-75445, 2002-338579, 2002. 2002-105445, 2002-343568, 2002-141173, 2002-352957, 2002-203683, 2002-363227, 2002-231453, 2003. -3165, 2002-234888, 2003-27048, 2002-255934, 2002-260861, 2002-280183, 2002-299060, 2002- 302516, 2002-305083, 2002-305084, 2002-308837, US Patent Application Publication No. 2003/01755553, US Patent Application Publication No. 2006/0280965, USA Publication No. 2005/0112407, Publication No. 2009/0017330, U.S. Patent Application Publication No. 2009/0030202, U.S. Patent Application Publication No. 2005/0238919, International Publication No. 2001/039234, International Publication No. 2009/021126, International Publication No. 2008/056746, International Publication No. 2004/093207, International Publication No. 2005/089025, International Publication No. 2007/0637996, International Publication No. 2007 / 063754, International Publication No. 2004/107822, International Publication No. 2005/030900, International Publication No. 2006/114966, International Publication No. 2009/0860228, International Publication No. 2009/003898, International Publication No. 2012/0293947 , JP-A-2008-074939, JP-A-2007-254297, European Patent No. 2034538, International Publication No. 2011/055933, International Publication No. 2012/035853, JP-A-2015-38941, etc. a To. Examples thereof include compounds H-1 to H-230 described in paragraphs 0255 to 0293 of JP-A-2015-38941, and the following compounds H-231 to H-234.

(Electron transport layer)
In the present invention, the electron transport layer may be made of a material having a function of transporting electrons and may have a function of transmitting electrons injected from the cathode to the light emitting layer.

The total thickness of the electron transport layer according to the present invention is not particularly limited, but is usually in the range of 2 nm to 5 μm, more preferably 2 to 500 nm, and further preferably 5 to 200 nm.

Further, in the organic EL element, when the light generated in the light emitting layer is taken out from the electrode, the light taken out directly from the light emitting layer and the light taken out after being reflected by the electrode located opposite to the electrode from which the light is taken out interfere with each other. It is known to wake up. When light is reflected by the cathode, this interference effect can be efficiently utilized by appropriately adjusting the total thickness of the electron transport layer between several nm and several μm.

On the other hand, if the layer thickness of the electron transport layer is increased, the voltage tends to increase. Therefore, especially when the layer thickness is thick, the electron mobility of the electron transport layer is preferably ^10-5 cm ² / Vs or more. ..

The material used for the electron transport layer (hereinafter referred to as electron transport material) may have any of electron injection property, electron transport property, and hole barrier property, and is arbitrary from conventionally known compounds. Can be selected and used.

For example, nitrogen-containing aromatic heterocyclic derivatives (carbazole derivatives, azacarbazole derivatives (one or more of the carbon atoms constituting the carbazole ring substituted with nitrogen atoms), pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, pyridazine derivatives, Triazine derivative, quinoline derivative, quinoxalin derivative, phenanthroline derivative, azatriphenylene derivative, oxazole derivative, thiazole derivative, oxadiazole derivative, thiadiazol derivative, triazole derivative, benzimidazole derivative, benzoxazole derivative, benzthiazole derivative, etc.), dibenzofuran derivative, Examples thereof include dibenzothiophene derivatives, silol derivatives, aromatic hydrocarbon ring derivatives (naphthalene derivatives, anthracene derivatives, triphenylene derivatives, etc.).

Further, metal complexes having a quinolinol skeleton or a dibenzoquinolinol skeleton as ligands, for example, tris (8-quinolinol) aluminum (Alq), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-). Dibromo-8-quinolinol) aluminum, tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), etc., and their metal complexes. A metal complex in which the central metal is replaced with In, Mg, Cu, Ca, Sn, Ga or Pb can also be used as an electron transport material.

In addition, metal-free or metal phthalocyanines, or those whose terminals are substituted with an alkyl group, a sulfonic acid group, or the like can also be preferably used as an electron transport material. Further, the distyrylpyrazine derivative exemplified as the material of the light emitting layer can also be used as an electron transport material, and an inorganic semiconductor such as n-type-Si or n-type-SiC is used like the hole injection layer and the hole transport layer. Can also be used as an electron transport material.

Further, it is also possible to use a polymer material in which these materials are introduced into a polymer chain or these materials are used as a polymer main chain.

In the electron transport layer according to the present invention, the electron transport layer may be doped with a doping material as a guest material to form an electron transport layer having a high n property (electron rich). Examples of the doping material include n-type dopants such as metal compounds and metal compounds such as metal halides. Specific examples of the electron transport layer having such a structure include, for example, JP-A-4-297076, JP-A-10-270172, JP-A-2000-196140, JP-A-2001-102175, J. Am. Apple. Phys. , 95, 5773 (2004) and the like.

Specific examples of known and preferable electron transporting materials used in the organic EL device of the present invention include, but are not limited to, the compounds described in the following documents.

US Patent No. 6528187, US Patent No. 7230107, US Patent Application Publication No. 2005/0025993, US Patent Application Publication No. 2004/0036077, US Patent Application Publication No. 2009/0115316, US Patent Publication No. 2009/0101870, US Patent Application Publication No. 2009/0179554, International Publication No. 2003/060956, International Publication No. 2008/32085, Appl. Phys. Let. 75, 4 (1999), Appl. Phys. Let. 79,449 (2001), Appl. Phys. Let. 81, 162 (2002), Appl. Phys. Let. 81, 162 (2002), Appl. Phys. Let. 79,156 (2001), US Pat. No. 7,964,293, US Patent Application Publication No. 2009/030202, International Publication No. 2004/080975, International Publication No. 2004/063159, International Publication No. 2005/08537, International. Publication No. 2006/067931, International Publication No. 2007/086552, International Publication No. 2008/114690, International Publication No. 2009/069422, International Publication No. 2009/066779, International Publication No. 2009/054253, International Publication No. 2011/086935, International Publication No. 2010/150593, International Publication No. 2010/047707, European Patent No. 2311826, JP-A-2010-251675, JP-A-2009-209133, JP-A-2009-124114 No., JP-A-2008-277810, JP-A-2006-156445, JP-A-2005-340122, JP-A-2003-45662, JP-A-2003-31367, JP-A-2003-282270. , International Publication No. 2012/115034, etc.

More preferred known electron transport materials in the present invention include aromatic heterocyclic compounds containing at least one nitrogen atom and compounds containing a phosphorus atom, such as pyridine derivatives, pyrimidine derivatives, pyrazine derivatives, triazine derivatives and dibenzofurans. Examples thereof include derivatives, dibenzothiophene derivatives, azadibenzofuran derivatives, azadibenzothiophene derivatives, carbazole derivatives, azacarbazole derivatives, benzimidazole derivatives, arylphosphine oxide derivatives and the like.

The electron transport material may be used alone or in combination of two or more.

(Hole blocking layer)
The hole blocking layer is a layer having the function of an electron transporting layer in a broad sense, and is preferably made of a material having a function of transporting electrons and a small ability to transport holes, and holes while transporting electrons. It is possible to improve the recombination probability of electrons and holes by blocking the above.

Further, the structure of the electron transport layer described above can be used as the hole blocking layer according to the present invention, if necessary.

The hole blocking layer provided in the organic EL device of the present invention is preferably provided adjacent to the cathode side of the light emitting layer.

The layer thickness of the hole blocking layer according to the present invention is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.

As the material used for the hole blocking layer, the material used for the electron transport layer described above is preferably used, and the material used as the host compound described above is also preferably used for the hole blocking layer.

(Electron injection layer)
The electron injection layer (also referred to as “cathode buffer layer”) according to the present invention is a layer provided between the cathode and the light emitting layer in order to reduce the driving voltage and improve the light emitting brightness, and is referred to as “organic EL element and its light emitting layer”. It is described in detail in Volume 2, Chapter 2, "Electrode Materials" (pages 123-166) of "Forefront of Industrialization (Published by NTS, November 30, 1998)".

In the present invention, the electron injection layer may be provided as needed and may be present between the cathode and the light emitting layer or between the cathode and the electron transport layer as described above.

The electron injection layer is preferably a very thin film, and the layer thickness is preferably in the range of 0.1 to 5 nm, although it depends on the material. Further, it may be a non-uniform layer (film) in which the constituent material is intermittently present.

The details of the electron-injected layer are also described in JP-A-6-325871, JP-A-9-17574, JP-A-10-74586, etc., and specific examples of materials preferably used for the electron-injected layer are as follows. , Metals typified by strontium, aluminum, etc., alkali metal compounds typified by lithium fluoride, sodium fluoride, potassium fluoride, etc., alkaline earth metal compounds typified by magnesium fluoride, calcium fluoride, etc., oxidation Examples thereof include metal oxides typified by aluminum, metal complexes typified by 8-hydroxyquinolinate lithium (Liq), and the like. It is also possible to use the above-mentioned electron transport material.

Further, the material used for the above electron injection layer may be used alone or in combination of two or more.

(Hole transport layer)
In the present invention, the hole transport layer may be made of a material having a function of transporting holes and may have a function of transmitting holes injected from the anode to the light emitting layer.

The total thickness of the hole transport layer according to the present invention is not particularly limited, but is usually in the range of 5 nm to 5 μm, more preferably 2 to 500 nm, and further preferably 5 to 200 nm.

The material used for the hole transport layer (hereinafter referred to as a hole transport material) may have any of hole injection property, hole transport property, and electron barrier property, and is among conventionally known compounds. Any one can be selected and used from.

For example, porphyrin derivative, phthalocyanine derivative, oxazole derivative, oxadiazole derivative, triazole derivative, imidazole derivative, pyrazoline derivative, pyrazolone derivative, phenylenediamine derivative, hydrazone derivative, stilben derivative, polyarylalkane derivative, triarylamine derivative, carbazole derivative. , Indrocarbazole derivative, Isoindole derivative, Asen derivative such as anthracene and naphthalene, Fluolene derivative, Fluolenone derivative, Polyvinylcarbazole, Polymer material or oligomer in which aromatic amine is introduced into the main chain or side chain, Polysilane, Conductive Examples thereof include sex polymers or oligomers (eg, PEDOT / PSS, aniline-based copolymers, polyaniline, polythiophene, etc.).

Examples of the triarylamine derivative include a benzidine type represented by α-NPD (4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) and a starburst type represented by MTDATA. Examples thereof include compounds having fluorene or anthracene in the triarylamine linking core portion.

Further, hexaazatriphenylene derivatives as described in JP-A-2003-591432 and JP-A-2006-135145 can also be used as the hole transport material in the same manner.

Further, a hole transport layer having a high p property doped with impurities can also be used. Examples thereof include JP-A-4-297076, JP-A-2000-196140, and JP-A-2001-102175. Apple. Phys. , 95, 5773 (2004) and the like.

Further, Japanese Patent Application Laid-Open No. 11-251067, J. Mol. Hung et. al. So-called p-type hole transport materials and inorganic compounds such as p-type-Si and p-type-SiC, as described in the authored literature (Applied Physics Letters 80 (2002), p. 139), can also be used. Further, an orthometalated organometallic complex having Ir or Pt in the central metal as typified by Ir (ppy) 3 is also preferably used.

As the hole transport material, the above can be used, but a triarylamine derivative, a carbazole derivative, an indolocarbazole derivative, an azatriphenylene derivative, an organic metal complex, and an aromatic amine are introduced into the main chain or side chain. The polymer material or oligomer is preferably used.

Specific examples of the known and preferable hole transporting material used in the organic EL device of the present invention include the compounds described in the following documents in addition to the documents mentioned above, but the present invention is limited thereto. Not done.

For example, Appl. Phys. Let. 69,2160 (1996), J. Mol. Lumin. 72-74,985 (1997), Appl. Phys. Let. 78,673 (2001), Appl. Phys. Let. 90,183503 (2007), Appl. Phys. Let. 90,183503 (2007), Appl. Phys. Let. 51,913 (1987), Synth. Met. 87,171 (1997), Synth. Met. 91,209 (1997), Synth. Met. 111,421 (2000), SID Symposium Digital, 37,923 (2006), J. Mol. Mater. Chem. 3,319 (1993), Adv. Mater. 6,677 (1994), Chem. Mater. 15, 3148 (2003), US Patent Application Publication No. 2003/0162053, US Patent Application Publication No. 2002/0158242, US Patent Application Publication No. 2006/0240279, US Patent Application Publication No. 2008/ 022265, US Patent No. 5061569, International Publication No. 2007/002683, International Publication No. 2009/01809, EP650955, US Patent Application Publication No. 2008/01245772, US Patent Application Publication No. 2007/0278938 Japanese Patent Application Publication No. 2008/01061190, US Patent Application Publication No. 2008/0018221, International Publication No. 2012/115034, Japanese Patent Application Laid-Open No. 2003-591432, JP-A-2006-135145. , US Patent Application No. 13/585981, etc.

The hole transport material may be used alone or in combination of two or more.

(Electronic blocking layer)
The electron blocking layer is a layer having a function of a hole transporting layer in a broad sense, and is preferably made of a material having a function of transporting holes but having a small ability to transport electrons, while transporting holes. By blocking the electrons, the probability of recombination of electrons and holes can be improved.

Further, the structure of the hole transport layer described above can be used as an electron blocking layer according to the present invention, if necessary.

The electron blocking layer provided in the organic EL element of the present invention is preferably provided adjacent to the anode side of the light emitting layer.

The layer thickness of the electron blocking layer according to the present invention is preferably in the range of 3 to 100 nm, and more preferably in the range of 5 to 30 nm.

As the material used for the electron blocking layer, the material used for the hole transporting layer described above is preferably used, and the host compound described above is also preferably used for the electron blocking layer.

(Hole injection layer)
The hole injection layer (also referred to as “anode buffer layer”) according to the present invention is a layer provided between the anode and the light emitting layer in order to reduce the driving voltage and improve the emission brightness, and is referred to as an “organic EL element”. It is described in detail in Volume 2, Chapter 2, "Electrode Materials" (pages 123-166) of "The Forefront of Industrialization (Published by NTS, November 30, 1998)".

In the present invention, the hole injection layer may be provided as needed and may be present between the anode and the light emitting layer or between the anode and the hole transport layer as described above.

The details of the hole injection layer are described in JP-A-9-45479, 9-2660062, 8-288609, etc., and examples of the material used for the hole injection layer include. Examples thereof include materials used for the hole transport layer described above.

Among them, phthalocyanine derivatives typified by copper phthalocyanine, hexaazatriphenylene derivatives as described in JP-A-2003-591432 and JP-A-2006-135145, metal oxides typified by vanadium oxide, and amorphous carbon. , Conductive polymers such as polyaniline (emeraldine) and polythiophene, orthometallated complexes typified by tris (2-phenylpyridine) iridium complexes, triarylamine derivatives and the like are preferred.

The material used for the hole injection layer described above may be used alone or in combination of two or more.

(Additive)
The organic layer in the present invention described above may further contain other additives.
Examples of the additive include halogen elements such as bromine, iodine and chlorine, halogenated compounds, alkali metals and alkaline earth metals such as Pd, Ca and Na, compounds and complexes of transition metals, salts and the like.

The content of the additive can be arbitrarily determined, but is preferably 1000 ppm or less, more preferably 500 ppm or less, still more preferably 50 ppm or less, based on the total mass% of the contained layer. ..

However, it is not within this range depending on the purpose of improving the transportability of electrons and holes and the purpose of favoring the energy transfer of excitons.

(Method of forming organic layer)
A method for forming an organic layer (hole injection layer, hole transport layer, light emitting layer, hole blocking layer, electron transport layer, electron injection layer, intermediate layer, etc.) according to the present invention will be described.

The method for forming the organic layer according to the present invention is not particularly limited, and a conventionally known method for forming an organic layer, for example, a vacuum vapor deposition method, a wet method (also referred to as a wet process), or the like can be used.

Examples of the wet method include a spin coat method, a cast method, an inkjet method, a printing method, a die coat method, a blade coat method, a roll coat method, a spray coat method, a curtain coat method, and an LB method (Langmuir-Bloget method). From the viewpoint of easy obtaining a uniform thin film and high productivity, a method having high suitability for a roll-to-roll method such as a die coating method, a roll coating method, an inkjet method, and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the organic EL material used in the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene and xylene. Aromatic hydrocarbons such as mecitylene and cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin and dodecane, and organic solvents such as DMF and DMSO can be used.

Further, as the dispersion method, it can be dispersed by a dispersion method such as ultrasonic wave, high shear force dispersion or media dispersion.

Further, a different film forming method may be applied to each layer. When a thin-film deposition method is used for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally the boat heating temperature is 50 to 450 ° C, the vacuum degree is ^10-6 to ^10-2 Pa, and the vapor deposition rate is 0.01 to. It is desirable to appropriately select within the range of 50 nm / sec, substrate temperature -50 to 300 ° C., layer (film) thickness 0.1 nm to 5 μm, preferably 5 to 200 nm.

The formation of the organic layer according to the present invention is preferably carried out consistently from the hole injection layer to the cathode by one vacuuming, but it may be taken out in the middle and a different film forming method may be applied. In that case, it is preferable to carry out the work in a dry inert gas atmosphere.

(anode)
As the anode in the organic EL element, a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function (4 eV or more, preferably 4.5 eV or more) as an electrode material is preferably used. Specific examples of such an electrode material include metals such as Au and conductive transparent materials such as CuI, indium tin oxide (ITO), SnO ₂ , and ZnO. Further, a material such as IDIXO (In ₂ O ₃ -ZnO) that is amorphous and can produce a transparent conductive film may be used.

For the anode, a thin film may be formed by forming a thin film of these electrode materials by a method such as thin film deposition or sputtering, and a pattern of a desired shape may be formed by a photolithography method, or when pattern accuracy is not required so much (about 100 μm or more). The pattern may be formed through a mask having a desired shape during vapor deposition or sputtering of the electrode material.

Alternatively, when a coatable substance such as an organic conductive compound is used, a wet film forming method such as a printing method or a coating method can also be used. When light emission is taken out from this anode, it is desirable to increase the transmittance to more than 10%, and the sheet resistance as the anode is preferably several hundred Ω / □ or less.

The film thickness of the anode depends on the material, but is usually selected within the range of 10 nm to 1 μm, preferably 10 to 200 nm.

(cathode)
As the cathode, a metal having a small work function (4 eV or less) (referred to as an electron-injectable metal), an alloy, an electrically conductive compound, or a mixture thereof as an electrode material is used. Specific examples of such electrode materials include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al ₂ O). ₃ ) Examples include mixtures, indium, lithium / aluminum mixtures, aluminum, rare earth metals and the like. Among these, from the viewpoint of electron injectability and durability against oxidation and the like, a mixture of an electron injectable metal and a second metal which is a stable metal having a larger work function value than this, for example, a magnesium / silver mixture. A magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide (Al ₂ O ₃ ) mixture, a lithium / aluminum mixture, aluminum and the like are suitable.

The cathode can be produced by forming a thin film of these electrode materials by a method such as thin film deposition or sputtering. The sheet resistance of the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 5 μm, preferably 50 to 200 nm.

In order to transmit the emitted light, it is convenient if either the anode or the cathode of the organic EL element is transparent or translucent because the emission brightness is improved.

Further, a transparent or translucent cathode can be produced by producing the above metal on the cathode having a thickness of 1 to 20 nm and then producing the conductive transparent material mentioned in the description of the anode on the cathode. By applying the above, it is possible to manufacture an element in which both the anode and the cathode have transparency.

[Support board]
The type of support substrate (hereinafter, also referred to as substrate, substrate, etc.) that can be used for the organic EL element of the present invention is not particularly limited, and even if it is transparent, it is opaque. You may. When light is taken out from the support substrate side, the support substrate is preferably transparent. Examples of the transparent support substrate preferably used include glass, quartz, and a transparent resin film. A particularly preferable support substrate is a resin film capable of imparting flexibility to the organic EL element.

Examples of the resin film include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyethylene, polypropylene, cellophane, cellulose diacetate, cellulose triacetate (TAC), cellulose acetate butyrate, and cellulose acetate propionate. CAP), cellulose ester phthalates, cellulose esters such as cellulose nitrate or derivatives thereof, polyvinylidene chloride, polyvinyl alcohol, polyethylene vinyl alcohol, syndiotactic polystyrene, polycarbonate, norbornene resin, polymethylpentene, polyether ketone, polyimide , Polyether sulfone (PES), Polyphenylene sulfide, Polysulfones, Polyetherimide, Polyetherketoneimide, Polyamide, Fluororesin, Nylon, Polymethylmethacrylate, Acrylic or Polyallylates, Arton (trade name: JSR) or Appel Cycloolefin-based resins such as (trade name: manufactured by Mitsui Kagaku Co., Ltd.) can be mentioned.

A film of an inorganic substance, an organic substance, or a hybrid film thereof may be formed on the surface of the resin film, and the water vapor permeability (25 ± 0.5 ° C.) measured by a method according to JIS K 7129-1992. , Relative humidity (90 ± ² )% RH) is preferably 0.01 g / m 2.24 h or less, and moreover, oxygen permeability measured by a method according to JIS K 7126-1987. However, it is preferable that the film has a high barrier property of 1 × 10 ^-3 ml / ^m 2.24 h · atm or less and a water vapor permeability of 1 × 10 ^-5 g / ^m 2.24 h or less.

As the material for forming the barrier film, any material may be used as long as it has a function of suppressing infiltration of a material that causes deterioration of the element such as moisture and oxygen, and for example, silicon oxide, silicon dioxide, silicon nitride and the like can be used. Further, in order to improve the vulnerability of the film, it is more preferable to have a laminated structure of these inorganic layers and layers made of an organic material. The stacking order of the inorganic layer and the organic layer is not particularly limited, but it is preferable to stack the inorganic layer and the organic layer alternately a plurality of times.

The method for forming the barrier film is not particularly limited, and for example, a vacuum vapor deposition method, a sputtering method, a reactive sputtering method, a molecular beam epitaxy method, a cluster ion beam method, an ion plating method, a plasma polymerization method, and an atmospheric pressure plasma polymerization method. , Plasma CVD method, laser CVD method, thermal CVD method, coating method and the like can be used, but the atmospheric pressure plasma polymerization method as described in JP-A-2004-68143 is particularly preferable.

Examples of the opaque support substrate include metal plates such as aluminum and stainless steel, films and opaque resin substrates, and ceramic substrates.

The external extraction quantum efficiency of the light emission of the organic EL device of the present invention at room temperature (25 ° C.) is preferably 1% or more, more preferably 5% or more.

Here, the external extraction quantum efficiency (%) = the number of photons emitted to the outside of the organic EL element / the number of electrons passed through the organic EL element × 100.

Further, a hue improving filter such as a color filter may be used in combination, or a color conversion filter that converts the emission color from the organic EL element into multiple colors using a phosphor may be used in combination.

[Sealing]
Examples of the sealing means used for sealing the organic EL element of the present invention include a method of adhering a sealing member, an electrode, and a support substrate with an adhesive. The sealing member may be arranged so as to cover the display area of the organic EL element, and may have a concave plate shape or a flat plate shape. Further, transparency and electrical insulation are not particularly limited.

Specific examples thereof include a glass plate, a polymer plate / film, and a metal plate / film. Examples of the glass plate include soda-lime glass, barium / strontium-containing glass, lead glass, aluminosilicate glass, borosilicate glass, barium borosilicate glass, and quartz. Examples of the polymer plate include polycarbonate, acrylic, polyethylene terephthalate, polyether sulfide, polysulfone and the like. Examples of the metal plate include those made of one or more metals or alloys selected from the group consisting of stainless steel, iron, copper, aluminum, magnesium, nickel, zinc, chromium, titanium, molybdenum, silicon, germanium and tantalum.

In the present invention, a polymer film or a metal film can be preferably used because the organic EL element can be made into a thin film. Furthermore, the polymer film had an oxygen permeability of 1 × 10 ^-3 ml / ^m 2.24 h or less measured by a method according to JIS K 7126-1987, and was measured by a method according to JIS K 7129-1992. It is preferable that the water vapor transmission rate (25 ± 0.5 ° C., relative humidity 90 ± ² %) is 1 × 10 ^-3 g / m 2.24 h or less.

Sandblasting, chemical etching, etc. are used to process the sealing member into a concave shape.

Specific examples of the adhesive include acrylic acid-based oligomers, photocurable and heat-curable adhesives having a reactive vinyl group of methacrylic acid-based oligomers, and moisture-curable adhesives such as 2-cyanoacrylic acid ester. be able to. In addition, heat and chemical curing type (two-component mixing) such as epoxy type can be mentioned. Further, hot melt type polyamide, polyester and polyolefin can be mentioned. Further, a cation-curable type ultraviolet-curable epoxy resin adhesive can be mentioned.

Since the organic EL element may be deteriorated by heat treatment, it is preferable that the organic EL element can be adhesively cured from room temperature to 80 ° C. Further, the desiccant may be dispersed in the adhesive. A commercially available dispenser may be used to apply the adhesive to the sealed portion, or printing may be performed as in screen printing.

Further, it is also possible to preferably cover the electrode and the organic layer on the outside of the electrode on the side facing the support substrate by sandwiching the organic layer, and form a layer of an inorganic substance or an organic substance in contact with the support substrate to form a sealing film. .. In this case, the material for forming the film may be any material having a function of suppressing infiltration of a material that causes deterioration of the element such as moisture and oxygen, and for example, silicon oxide, silicon dioxide, silicon nitride or the like may be used. can.

Further, in order to improve the vulnerability of the film, it is preferable to have a laminated structure of these inorganic layers and layers made of an organic material. The method for forming these films is not particularly limited, and for example, vacuum deposition method, sputtering method, reactive sputtering method, molecular beam epitaxy method, cluster ion beam method, ion plating method, plasma polymerization method, atmospheric pressure plasma weight. Legal, plasma CVD method, laser CVD method, thermal CVD method, coating method and the like can be used.

In the gas phase and liquid phase, an inert gas such as nitrogen or argon or an inert liquid such as fluorinated hydrocarbon or silicon oil may be injected into the gap between the sealing member and the display region of the organic EL element. preferable. It is also possible to create a vacuum. Further, a hygroscopic compound can be enclosed inside.

Examples of the hygroscopic compound include metal oxides (eg, sodium oxide, potassium oxide, calcium oxide, barium oxide, magnesium oxide, aluminum oxide, etc.) and sulfates (eg, sodium sulfate, calcium sulfate, magnesium sulfate, cobalt sulfate, etc.). Etc.), metal halides (eg calcium chloride, magnesium chloride, cesium fluoride, tantalum fluoride, cerium bromide, magnesium bromide, barium iodide, magnesium iodide, etc.), perchlorates (eg, perchloric acid) Barium, magnesium perchlorate, etc.) and the like, and anhydrous salts are preferably used for sulfates, metal halides and perchlorates.

[Protective film, protective plate]
A protective film or a protective plate may be provided on the outside of the sealing film or the sealing film on the side facing the support substrate with the organic layer sandwiched in order to increase the mechanical strength of the element. In particular, when the sealing is performed by the sealing film, the mechanical strength thereof is not necessarily high, so it is preferable to provide such a protective film and a protective plate. As the material that can be used for this, a glass plate, a polymer plate / film, a metal plate / film, etc. similar to those used for the sealing can be used, but the polymer film is lightweight and thin. It is preferable to use.

[Light extraction improvement technology]
The organic EL element emits light inside a layer having a refractive index higher than that of air (within a refractive index of about 1.6 to 2.1), and about 15% to 20% of the light generated in the light emitting layer is emitted. It is generally said that only can be taken out. This is because light incident on the interface (intersection between the transparent substrate and air) at an angle θ equal to or higher than the critical angle causes total internal reflection and cannot be taken out to the outside of the element, and the transparent electrode or light emitting layer and the transparent substrate. This is because the light causes total internal reflection, the light is waveguideed through the transparent electrode or the light emitting layer, and as a result, the light escapes toward the side surface of the element.

As a method for improving the efficiency of light extraction, for example, a method of forming irregularities on the surface of a transparent substrate to prevent total reflection at the interface between the transparent substrate and the air (for example, US Pat. No. 4,774,435), the substrate. A method of improving efficiency by providing light-collecting property (for example, Japanese Patent Application Laid-Open No. 63-314795), a method of forming a reflective surface on a side surface of an element (for example, Japanese Patent Application Laid-Open No. 1-220394), a substrate. A method of forming an antireflection film by introducing a flat layer having an intermediate refractive index between the light emitter and the light emitter (for example, Japanese Patent Application Laid-Open No. 62-172691), which has a lower refractive index than the substrate between the substrate and the light emitter. A method of introducing a flat layer having a refractive index (for example, Japanese Patent Application Laid-Open No. 2001-202827), a method of forming a diffraction grating between layers (including, between the substrate and the outside world) of a substrate, a transparent electrode layer, or a light emitting layer (inclusive). Japanese Unexamined Patent Publication No. 11-283751) and the like.

In the present invention, these methods can be used in combination with the organic EL element of the present invention, but a method of introducing a flat layer having a lower refractive index than the substrate between the substrate and the light emitter, or the substrate, transparent. A method of forming a diffraction grating between layers (including between the substrate and the outside world) of any of the electrode layer and the light emitting layer can be preferably used.

In the present invention, by combining these means, it is possible to obtain an element having higher brightness or excellent durability.

When a medium with a low refractive index is formed between the transparent electrode and the transparent substrate with a thickness longer than the wavelength of light, the light emitted from the transparent electrode has a higher efficiency of being taken out to the outside as the refractive index of the medium is lower. Become.

Examples of the low refractive index layer include airgel, porous silica, magnesium fluoride, and a fluorine-based polymer. Since the refractive index of the transparent substrate is generally in the range of about 1.5 to 1.7, it is preferable that the low refractive index layer has a refractive index of about 1.5 or less. Further, it is preferably 1.35 or less.

Further, it is desirable that the thickness of the low refractive index medium is at least twice the wavelength in the medium. This is because the effect of the low refractive index layer diminishes when the thickness of the low refractive index medium becomes about the wavelength of light and the film thickness of the electromagnetic wave exuded by evanescent enters the substrate.

The method of introducing a diffraction grating into an interface that causes total internal reflection or in any of the media is characterized by a high effect of improving the light extraction efficiency. This method is generated from the light emitting layer by utilizing the property that the diffraction lattice can change the direction of light to a specific direction different from the diffraction by so-called Bragg diffraction such as first-order diffraction and second-order diffraction. Of the generated light, the light that cannot go out due to total reflection between the layers is diffracted by introducing a diffraction lattice into either layer or in the medium (inside the transparent substrate or transparent electrode). , Trying to get the light out.

It is desirable that the diffraction grating to be introduced has a two-dimensional periodic refractive index. This is because the light emitted by the light emitting layer is randomly generated in all directions, so in a general one-dimensional diffraction grating that has a periodic refractive index distribution only in one direction, only the light traveling in a specific direction is diffracted. The light extraction efficiency does not increase so much.

However, by making the refractive index distribution a two-dimensional distribution, the light traveling in all directions is diffracted, and the light extraction efficiency is improved.

The position where the diffraction grating is introduced may be one of the layers or in the medium (inside the transparent substrate or the transparent electrode), but it is desirable that the position is near the organic light emitting layer where light is generated. At this time, the period of the diffraction grating is preferably in the range of about 1/2 to 3 times the wavelength of the light in the medium. As for the arrangement of the diffraction grating, it is preferable that the arrangement is repeated two-dimensionally, such as a square lattice shape, a triangular lattice shape, and a honeycomb lattice shape.

[Condensing sheet]
The organic EL element of the present invention is frontal to a specific direction, for example, the light emitting surface of the element, by processing to provide a structure on a microlens array on the light extraction side of the support substrate (board) or by combining with a so-called condensing sheet. By condensing light in a direction, the brightness in a specific direction can be increased.

As an example of a microlens array, a quadrangular pyramid having a side of 30 μm and an apex angle of 90 degrees is arranged two-dimensionally on the light extraction side of the substrate. One side is preferably in the range of 10 to 100 μm. If it is smaller than this, the effect of diffraction is generated and it is colored, and if it is too large, the thickness becomes thick, which is not preferable.

As the condensing sheet, for example, a light-collecting sheet that has been put into practical use in an LED backlight of a liquid crystal display device can be used. As such a sheet, for example, a luminance increasing film (BEF) manufactured by Sumitomo 3M Ltd. can be used. The shape of the prism sheet may be, for example, a base material having a Δ-shaped stripe having an apex angle of 90 degrees and a pitch of 50 μm, or a shape having a rounded apex angle and a random change in pitch. It may have a shape like a stripe or another shape.

Further, a light diffusing plate / film may be used in combination with the light collecting sheet in order to control the light emission angle from the organic EL element. For example, a diffusion film (lighted up) manufactured by Kimoto Co., Ltd. can be used.

[Use]
The organic EL element of the present invention can be used as an electronic device, for example, a display device, a display, and various light emitting devices.

Examples of the light emitting device include lighting devices (household lighting, interior lighting), clocks and LCD backlights, signage advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processors, and light. Examples thereof include, but are not limited to, a light source of a sensor, but the light source can be effectively used as a backlight of a liquid crystal display device and a light source for lighting.

In the organic EL element of the present invention, if necessary, patterning may be performed by a metal mask, an inkjet printing method, or the like at the time of film formation. In the case of patterning, only the electrode may be patterned, the electrode and the light emitting layer may be patterned, or the entire element layer may be patterned. In the production of the element, a conventionally known method is used. Can be done.

4. Display device The display device provided with the organic EL element of the present invention may be monochromatic or multicolored, but here, a multicolor display device will be described.

In the case of a multi-color display device, a shadow mask is provided only when the light emitting layer is formed, and a film can be formed on one surface by a vapor deposition method, a casting method, a spin coating method, an inkjet method, a printing method, or the like.

When patterning only the light emitting layer, the method is not limited, but a vapor deposition method, an inkjet method, a spin coating method, and a printing method are preferable.

The configuration of the organic EL element provided in the display device is selected from the above-mentioned configuration examples of the organic EL element, if necessary.

Further, the method for manufacturing the organic EL device is as shown in the above-mentioned aspect of manufacturing the organic EL device of the present invention.

When a DC voltage is applied to the multicolor display device thus obtained, light emission can be observed by applying a voltage of about 2 to 40 V with the anode as the positive polarity and the cathode as the negative polarity. Further, even if a voltage is applied with the opposite polarity, no current flows and no light emission occurs. When an AC voltage is further applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The waveform of the alternating current to be applied may be arbitrary.

The multicolor display device can be used as a display device, a display or various light emitting sources. Full-color display is possible by using three types of organic EL elements of blue, red, and green emission in a display device or display.

Examples of the display device or display include televisions, personal computers, mobile devices, AV devices, teletext displays, information displays in automobiles, and the like. In particular, it may be used as a display device for reproducing a still image or a moving image, and the drive method when used as a display device for reproducing a moving image may be either a simple matrix (passive matrix) method or an active matrix method.

Light emitting devices include household lighting, interior lighting, backlights for clocks and liquid crystals, signboard advertisements, traffic lights, light sources for optical storage media, light sources for electrophotographic copying machines, light sources for optical communication processors, light sources for optical sensors, etc. However, the present invention is not limited thereto.

Hereinafter, an example of the display device having the organic EL element of the present invention will be described with reference to the drawings.

FIG. 5 is a schematic diagram showing an example of a display device composed of an organic EL element. It is a schematic diagram of a display such as a mobile phone which displays image information by light emission of an organic EL element.

The display 1 has a display unit A having a plurality of pixels, a control unit B that scans an image of the display unit A based on image information, a wiring unit C that electrically connects the display unit A and the control unit B, and the like.

The control unit B is electrically connected via the display unit A and the wiring unit C, sends a scanning signal and an image data signal to each of the plurality of pixels based on image information from the outside, and the scanning signal is used to send a pixel for each scanning line. Lights up sequentially according to the image data signal, scans the image, and displays the image information on the display unit A.

FIG. 6 is a schematic diagram of a display device using the active matrix method.

The display unit A has a wiring unit C including a plurality of scanning lines 5 and a data line 6 and a plurality of pixels 3 and the like on the substrate. The main members of the display unit A will be described below.

FIG. 6 shows a case where the light emitted from the pixel 3 is taken out in the direction of the white arrow (downward).

The scanning line 5 and the plurality of data lines 6 of the wiring portion are each made of a conductive material, and the scanning line 5 and the data line 6 are orthogonal to each other in a grid pattern and are connected to the pixel 3 at orthogonal positions (details are shown in the figure). Not).

When a scanning signal is applied from the scanning line 5, the pixel 3 receives an image data signal from the data line 6 and emits light according to the received image data.

Full-color display is possible by appropriately arranging pixels in the red region, pixels in the green region, and pixels in the blue region of the emission color on the same substrate.

Next, the light emitting process of the pixel will be described. FIG. 7 is a schematic diagram showing a pixel circuit.

The pixel includes an organic EL element 10, a switching transistor 11, a drive transistor 12, a capacitor 13, and the like. As the organic EL element 10 for a plurality of pixels, red, green, and blue light emitting organic EL elements are used, and by arranging them side by side on the same substrate, full-color display can be performed.

In FIG. 7, an image data signal is applied from the control unit B to the drain of the switching transistor 11 via the data line 6. Then, when a scanning signal is applied from the control unit B to the gate of the switching transistor 11 via the scanning line 5, the driving of the switching transistor 11 is turned on, and the image data signal applied to the drain is the capacitor 13 and the driving transistor 12. It is transmitted to the gate of.

By transmitting the image data signal, the capacitor 13 is charged according to the potential of the image data signal, and the drive transistor 12 is driven on. In the drive transistor 12, the drain is connected to the power supply line 7, the source is connected to the electrode of the organic EL element 10, and the power supply line 7 is connected to the organic EL element 10 according to the potential of the image data signal applied to the gate. Current is supplied.

When the scanning signal is transferred to the next scanning line 5 by the sequential scanning of the control unit B, the driving of the switching transistor 11 is turned off. However, even if the drive of the switching transistor 11 is turned off, the capacitor 13 holds the potential of the charged image data signal, so that the drive of the drive transistor 12 is kept on and the next scan signal is applied. The light emission of the organic EL element 10 continues until. When the next scanning signal is applied by the sequential scanning, the driving transistor 12 is driven according to the potential of the next image data signal synchronized with the scanning signal, and the organic EL element 10 emits light.

That is, for the light emission of the organic EL element 10, the switching transistor 11 and the drive transistor 12, which are active elements, are provided for the organic EL element 10 of each of the plurality of pixels, and the light emission of the organic EL element 10 of each of the plurality of pixels 3 is provided. It is carried out. Such a light emitting method is called an active matrix method.

Here, the light emission of the organic EL element 10 may be light emission of a plurality of gradations by a multi-valued image data signal having a plurality of gradation potentials, or may be on or off of a predetermined light emission amount by a binary image data signal. good. Further, the potential of the capacitor 13 may be continuously maintained until the next scanning signal is applied, or may be discharged immediately before the next scanning signal is applied.

In the present invention, the present invention is not limited to the active matrix method described above, and may be a passive matrix type light emission drive in which the organic EL element emits light in response to the data signal only when the scanning signal is scanned.

FIG. 8 is a schematic diagram of a display device using a passive matrix method. In FIG. 8, a plurality of scanning lines 5 and a plurality of image data lines 6 are provided in a grid pattern so as to face each other with the pixel 3 interposed therebetween.

When the scanning signal of the scanning line 5 is applied by the sequential scanning, the pixel 3 connected to the applied scanning line 5 emits light according to the image data signal.

In the passive matrix method, the pixel 3 does not have an active element, and the manufacturing cost can be reduced.

By using the organic EL element of the present invention, a display device having improved luminous efficiency was obtained.

5. Lighting device The organic EL element of the present invention can also be used in a lighting device.
The organic EL element of the present invention may be used as an organic EL element having a resonator structure. The purpose of using the organic EL element having such a resonator structure includes a light source of an optical storage medium, a light source of an electrophotographic copying machine, a light source of an optical communication processor, a light source of an optical sensor, and the like. Not limited. Further, it may be used for the above-mentioned applications by oscillating a laser.

Further, the organic EL element of the present invention may be used as a kind of lamp such as for lighting or an exposure light source, a projection device of a type for projecting an image, or a type for directly visually recognizing a still image or a moving image. It may be used as a display device (display).

When used as a display device for moving image reproduction, the drive method may be either a passive matrix method or an active matrix method. Alternatively, a full-color display device can be manufactured by using two or more kinds of organic EL elements of the present invention having different emission colors.

Further, the π-conjugated compound used in the present invention can be applied to a lighting device including an organic EL element that emits substantially white light. For example, when a plurality of light emitting materials are used, white light emission can be obtained by simultaneously emitting a plurality of light emitting colors and mixing the colors. The combination of a plurality of emission colors may include three emission maximum wavelengths of the three primary colors of red, green and blue, or two using the relationship of complementary colors such as blue and yellow and blue-green and orange. It may contain the maximum emission wavelength.

Further, in the method for forming the organic EL element of the present invention, a mask may be provided only when the light emitting layer, the hole transport layer, the electron transport layer, or the like is formed, and the mask may be applied separately. Since the other layers are common, patterning such as a mask is not required, and for example, an electrode film can be formed on one surface by a vapor deposition method, a casting method, a spin coating method, an inkjet method, a printing method, or the like, and productivity is also improved.

According to this method, unlike a white organic EL device in which light emitting elements of a plurality of colors are arranged in parallel in an array, the elements themselves emit white light.

[One aspect of the lighting device of the present invention]
An aspect of the lighting device of the present invention provided with the organic EL element of the present invention will be described.

The non-light emitting surface of the organic EL element of the present invention is covered with a glass case, a glass substrate having a thickness of 300 μm is used as a sealing substrate, and an epoxy-based photocurable adhesive (Lux manufactured by Toa Synthetic Co., Ltd.) is used as a sealing material around the glass substrate. Track LC0629B) is applied, which is placed on the cathode and brought into close contact with the transparent support substrate, irradiated with UV light from the glass substrate side, cured, sealed, and illuminated as shown in FIGS. 9 and 10. The device can be formed.

FIG. 9 shows a schematic view of the lighting device, and the organic EL element (organic EL element 101 in the lighting device) of the present invention is covered with a glass cover 102 (note that the sealing work with the glass cover is lighting. The organic EL element 101 in the apparatus was carried out in a glove box under a nitrogen atmosphere (under an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more) without contacting the atmosphere.)

10A and 10B show a cross-sectional view of a lighting device, 105 is a cathode, 106 is an organic layer, and 107 is a glass substrate with a transparent electrode. The glass cover 102 is filled with nitrogen gas 108, and a water catching agent 109 is provided.

By using the organic EL element of the present invention, a lighting device having improved luminous efficiency can be obtained.

6. Luminous thin film The luminescent thin film according to the present invention is characterized by containing the above-mentioned π-conjugated compound according to the present invention, and can be produced in the same manner as in the method for forming an organic layer.

The luminescent thin film and the luminescent thin film of the present invention can be produced in the same manner as in the method for forming the organic layer.

The method for forming the luminescent thin film of the present invention is not particularly limited, and conventionally known methods such as a vacuum vapor deposition method and a wet method (also referred to as a wet process) can be used.

Examples of the wet method include a spin coat method, a cast method, an inkjet method, a printing method, a die coat method, a blade coat method, a roll coat method, a spray coat method, a curtain coat method, and an LB method (Langmuir-Bloget method). From the viewpoint of easy obtaining a uniform thin film and high productivity, a method having high suitability for a roll-to-roll method such as a die coating method, a roll coating method, an inkjet method, and a spray coating method is preferable.

Examples of the liquid medium for dissolving or dispersing the luminescent material used in the present invention include ketones such as methyl ethyl ketone and cyclohexanone, fatty acid esters such as ethyl acetate, halogenated hydrocarbons such as dichlorobenzene, toluene, xylene and mesitylene. , Aromatic hydrocarbons such as cyclohexylbenzene, aliphatic hydrocarbons such as cyclohexane, decalin and dodecane, and organic solvents such as DMF and DMSO can be used.

Further, as the dispersion method, it can be dispersed by a dispersion method such as ultrasonic wave, high shear force dispersion or media dispersion.

Further, a different film forming method may be applied to each layer. When a vapor deposition method is used for film formation, the vapor deposition conditions vary depending on the type of compound used, but generally the boat heating temperature is in the range of 50 to 450 ° C and the degree of vacuum is in the range of ^10-6 to ^10-2 Pa. Among them, the vapor deposition rate can be appropriately selected within the range of 0.01 to 50 nm / sec, the substrate temperature within the range of -50 to 300 ° C, the layer thickness within the range of 0.1 nm to 5 μm, and preferably within the range of 5 to 200 nm. desirable.
When the spin coating method is adopted for film formation, it is preferable to carry out the spin coater within the range of 100 to 1000 rpm and within the range of 10 to 120 seconds in a dry inert gas atmosphere.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited thereto. In addition, although the display of "%" is used in the examples, it represents "mass%" unless otherwise specified.

List of compounds used in this example.

1. 1. Synthesis of π-conjugated compounds (Compound T-1)
International Publication No. 2010/117355 and Organic Letters, 2002, 4, 1783-1785. Compound T-1 was synthesized in the same manner as described in 1. Specifically, compound T-1 is produced by reacting carbazole with 3,4,5,6-tetrafluoropyridazine under basic conditions in the same manner as described in International Publication No. 2010/113755. Got

In the same manner as described above, the compounds T-4, T-14, T-21, T-32, T-37, T-44, T-57, T-66, T-73, T-75, T-76. Was synthesized.

The _ΔEST of the obtained compound was calculated and obtained by the following method.

(Calculation of _ΔEST )
Using B3LYP as a functional and 6-31G (d) as a basis function, the structure optimization calculation was performed by the software for molecular orbital calculation. Gaussian09 (Revision C.01, MJ Frisch, et al, Gaussian, Inc., 2010.) manufactured by Gaussian Co., Ltd. in the United States was used as the software for calculating the molecular orbital. Furthermore, the excited state was calculated by the time-dependent density functional theory (Time-Dependent DFT). As a result, the energy levels E (S1) and E (T1) of each compound were obtained. The obtained values were applied to the following formula to calculate _ΔEST .
ΔE _ST = | E (S1) -E (T1) |

[Example 1]
2. 2. Fabrication of organic EL element (manufacture of organic EL element 1-1)
ITO (indium tin oxide) as an anode is formed on a glass substrate having a thickness of 50 mm × 50 mm and a thickness of 0.7 mm to a thickness of 150 nm, and after patterning, a transparent substrate to which the ITO transparent electrode is attached. Was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes, and then this transparent substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus.

Each of the crucibles for vapor deposition in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in the optimum amount for manufacturing the device. As the crucible for vapor deposition, a crucible made of molybdenum or tungsten made of a resistance heating material was used.

After depressurizing to a vacuum degree of 1 × 10 ^-4 Pa, the crucible for vapor deposition containing HI-1 (1,4,5,8,9,12-hexaazatriphenylenehexacarbonitrile) is energized and heated for vapor deposition. A hole injection transport layer having a layer thickness of 10 nm was formed by vapor deposition on an ITO transparent electrode at a speed of 0.1 nm / sec.

Next, α-NPD (4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) was deposited on the hole injection layer at a vapor deposition rate of 0.1 nm / sec, and the layer thickness was 40 nm. A hole transport layer was formed. The host compound mCP (1,3-bis (N-carbazolyl) benzene) and the comparative compound 1 were co-deposited at a vapor deposition rate of 0.1 nm / sec so as to be 94% and 6% by volume, respectively, and the layer thickness was 30 nm. Formed a light emitting layer.

Then, BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form an electron transport layer having a layer thickness of 30 nm.

Further, after forming lithium fluoride with a film thickness of 0.5 nm, aluminum 100 nm was vapor-deposited to form a cathode.

The non-light emitting surface side of the element was covered with a can-shaped glass case in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more, and an electrode take-out wiring was installed to manufacture an organic EL element 1-1.

(Manufacturing of organic EL elements 1-2 to 1-14)
Organic EL devices 1-2 to 1-14 were produced in the same manner as the organic EL device 1-1 except that the luminescent compound was changed from Comparative Compound 1 as shown in Table 1.

(Measurement of relative luminous efficiency)
The obtained organic EL element was made to emit light at room temperature (about 25 ° C.) under a constant current condition of 2.5 mA / cm ² . Then, the emission luminance of the organic EL element immediately after the start of emission was measured using a spectral radiance meter CS-2000 (manufactured by Konica Minolta).
The obtained emission luminance was applied to the following equation to obtain the relative emission luminance with respect to the emission luminance of the organic EL element 1-1.
Relative emission brightness (%) = (emission brightness of each organic EL element / emission brightness of organic EL element 1-1) × 100
The obtained measurement results are shown in Table 1.

It can be seen that the organic EL elements 1-3 to 1-14 containing the luminescent material of the present invention as the luminescent material exhibit higher emission luminance than the organic EL elements 1-1 and 1-2 containing the comparative compound. In particular, it can be seen that compounds having a _ΔEST of 0.50 eV or less show higher luminous efficiency.

[Example 2]
(Manufacturing of organic EL element 2-1)
A transparent support provided with this ITO transparent electrode after patterning on a substrate (NA45 manufactured by NH Technoglass Co., Ltd.) in which 100 nm of ITO (indium tin oxide) was formed on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode. The substrate was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes.

On this transparent support substrate, poly (3,4-ethylenedioxythiophene) -polystyrene sulfonate (PEDOT / PSS, Bayer, Baytron P Al 4083) diluted to 70% with pure water was used at 3000 rpm. After forming a thin film by a spin coating method under the condition of 30 seconds, it was dried at 200 ° C. for 1 hour to provide a hole injection layer having a layer thickness of 20 nm. This transparent support substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus, and each of the vapor deposition crucibles in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in an optimum amount for manufacturing an element. As the crucible for vapor deposition, a crucible made of molybdenum or tungsten made of a resistance heating material was used.

After depressurizing to a vacuum degree of 1 × 10 ^-4 Pa, α-NPD was deposited on the hole injection layer at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a layer thickness of 40 nm.
Next, CDBP as a host material and 2,5,8,11-tetra-t-butylperylene as a light emitting material were co-existed at a vapor deposition rate of 0.1 nm / sec so as to be 93% and 7% by volume, respectively. It was vapor-deposited to form a light emitting layer having a layer thickness of 30 nm.

Then, TPBi (1,3,5-tris (N-phenylbenzimidazol-2-yl)) was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form an electron transport layer having a layer thickness of 30 nm.

Further, after forming sodium fluoride with a film thickness of 1 nm, 100 nm of aluminum was vapor-deposited to form a cathode.

The non-light emitting surface side of the element was covered with a can-shaped glass case in an atmosphere of high-purity nitrogen gas having a purity of 99.999% or more, and an electrode take-out wiring was installed to manufacture an organic EL element 2-1.

(Manufacturing of organic EL element 2-2)
CDBP was used as the host compound, 2,5,8,11-tetra-t-butylperylene was used as the luminescent compound, and comparative compound 1 was used as the third component, and the ratios were 79%, 7%, and 14% by volume, respectively. The organic EL element 2-2 was produced in the same manner as in the production of the organic EL element 2-1 except that the light emitting layer was formed so as to be.

(Manufacturing of organic EL elements 2-3 to 2-8)
As shown in Table 2, organic EL elements 2-3 to 2-8 were produced in the same manner as the organic EL element 2-2 except that the third component was changed.

In the same manner as described above, the emission luminance of the organic EL element 2-1 was measured, and the relative emission luminance of each organic EL element with respect to the emission luminance of the organic EL element 2-1 was obtained. The obtained measurement results are shown in Table 2.

The organic EL devices 2-4 to 2-8 containing the luminescent material of the present invention as the third component include the organic EL device 2-1 not containing the third component and the organic EL devices 2-2 and 2 containing the comparative compound. It can be seen that the emission brightness is higher than -3. In particular, it can be seen that compounds having a _ΔEST of 0.50 eV or less show higher luminous efficiency.

[Example 3]
(Manufacturing of organic EL element 3-1)
ITO (indium tin oxide) as an anode is formed on a glass substrate having a thickness of 50 mm × 50 mm and a thickness of 0.7 mm to a thickness of 150 nm, and after patterning, a transparent substrate to which the ITO transparent electrode is attached. Was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes, and then this transparent substrate was fixed to a substrate holder of a commercially available vacuum vapor deposition apparatus.

Each of the resistance heating boats for vapor deposition in the vacuum vapor deposition apparatus was filled with the constituent materials of each layer in the optimum amount for manufacturing the device. The resistance heating boat was made of molybdenum or tungsten.

After depressurizing to a vacuum degree of 1 × 10 ^-4 Pa, the resistance heating boat containing HI-1 is energized and heated, and the film is vapor-deposited on an ITO transparent electrode at a vapor deposition rate of 0.1 nm / sec to a positive layer thickness of 15 nm. A hole injection layer was formed.

Next, α-NPD (4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl) was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form a hole transport layer having a layer thickness of 30 nm. did.

Next, a resistance heating boat containing Comparative Compound 1 as a host material and GD-1 as a light emitting material was energized and heated, and the hole transport layer was heated at a vapor deposition rate of 0.1 nm / sec and 0.010 nm / sec, respectively. To form a light emitting layer having a layer thickness of 40 nm.

Next, HB-1 was deposited at a vapor deposition rate of 0.1 nm / sec to form a first electron transport layer having a layer thickness of 5 nm.

Further, ET-1 was vapor-deposited on it at a vapor deposition rate of 0.1 nm / sec to form a second electron transport layer having a layer thickness of 45 nm.

Then, after vapor-filming lithium fluoride to a thickness of 0.5 nm, aluminum 100 nm was vapor-deposited to form a cathode, thereby producing an organic EL element 3-1.

(Manufacturing of organic EL elements 3-2 to 3-7)
Organic EL elements 3-2 to 3-7 were produced in the same manner as the organic EL element 3-1 except that the host material was changed as shown in Table 3.

In the same manner as described above, the emission luminance of the organic EL element 3-1 was measured, and the relative emission luminance of each organic EL element with respect to the emission luminance of the organic EL element 3-1 was obtained. The obtained measurement results are shown in Table 3.

It can be seen that the organic EL elements 3-3-3-7 containing the luminescent material of the present invention as the host material exhibit higher emission luminance than the organic EL elements 3-1 and 3-2 containing the comparative compound. In particular, it can be seen that compounds having a _ΔEST of 0.50 eV or less show higher luminous efficiency.

[Example 4]
(Preparation of thin-film deposition film 4-1)
A 50 mm × 50 mm, 0.7 mm thick quartz substrate was ultrasonically washed with isopropyl alcohol, dried with dry nitrogen gas, and UV ozone washed for 5 minutes, and then this transparent substrate was used as a substrate holder for a commercially available vacuum vapor deposition apparatus. Fixed to.
The crucible for vapor deposition in the vacuum vapor deposition apparatus was filled with the π-conjugated compound T-1. As the crucible for vapor deposition, a crucible made of molybdenum for resistance heating was used.
After depressurizing to a vacuum degree of 1 × 10 ^-4 Pa, the π-conjugated compound T-1 was vapor-deposited at a vapor deposition rate of 0.1 nm / sec to form a thin-film deposition film 4-1 having a layer thickness of 40 nm.

(Measurement of Delayed Fluorescence of Vapor Deposition Film 4-1)
Under a nitrogen atmosphere, the vapor deposition film 4-1 was irradiated with excitation light of 355 nm, and fluorescence attenuation was measured at the maximum emission wavelength.
FIG. 11 shows a graph showing the relationship between time and the number of photons for the thin-film deposition film 4-1.

As shown in FIG. 11, in the π-shared compound (T-1) of the present invention, two or more components having different fluorescence attenuation rates were confirmed, and delayed fluorescence radiation was confirmed.

This application claims priority based on Japanese Patent Application No. 2015-095812 filed on May 8, 2015. The scope of claims, the specification and the contents described in the drawings of the application are all incorporated in the specification of the present application.

According to the present invention, it is possible to provide a π-conjugated compound capable of increasing luminous efficiency without lengthening the emission wavelength.

1 Display 3 pixels 5 Scan line 6 Data line 7 Power supply line 10 Organic EL element 11 Switching transistor 12 Drive transistor 13 Condenser 101 Organic EL element in lighting device 102 Glass cover 105 Cathode 106 Organic layer 107 Glass substrate with transparent electrode 108 Nitrogen gas 109 Water trapping agent A Display unit B Control unit C Wiring unit

Claims (10)

It has a structure represented by any of the following general formulas (7), (9), (10), (12), (16), (20), and (25), and has the lowest excited singlet level and the lowest. A light emitting material containing a π-conjugated compound having an absolute value ( _ΔEST ) of energy difference from the excited triplet level of 0.50 eV or less, and the π-conjugated compound radiating fluorescence.

(In the general formulas (7), (9), (10), (12), (16), (20), (25),
D ¹ to D ⁶ each independently represent an electron donating group D selected from the group consisting of electron donating heterocyclic groups.
The electron-donating heterocyclic group is a carbazole ring, an indoleindole ring, a phenoxazine ring, or a benzofurylindole ring .
Z ¹ to Z ⁴ independently represent a hydrogen atom, a deuterium atom, or an electron-withdrawing group A selected from the group consisting of a fluorine atom, a cyano group, and an aryl group .
The aryl group is a benzene ring, an indene ring, a naphthalene ring, a biphenyl ring, or a terphenyl ring. ) The light emitting material according to claim 1, wherein in the π-conjugated compound, Z ¹ to Z ⁴ are the electron-withdrawing groups A. In claim 1 or 2, the π-conjugated compound satisfies at least one of D ¹ = D ² = D ³ = D ⁴ = D ⁵ = D ⁶ and Z ¹ = Z ² = Z ³ = Z ⁴ . The luminescent material described. The following compounds T-1, T-21, wherein the π-conjugated compound has a structure represented by any of the general formulas (9), (10), (12), (16), and (25). The light emitting material according to claim 1, which is T-32, T-37, T-44, T-73, or T-76.

Any of claims 1 to 4, wherein the absolute value (ΔE _ST ) of the energy difference between the lowest excited singlet level and the lowest excited triplet level of the π-conjugated compound is 0.17 eV or more and 0.40 eV or less. The luminescent material according to item 1. The light emitting material according to any one of claims 1 to 5, wherein the π-conjugated compound emits delayed fluorescence. A luminescent thin film comprising the luminescent material according to any one of claims 1 to 6. It comprises an anode, a cathode, and a light emitting layer provided between the anode and the cathode.
An organic electroluminescence device in which at least one layer of the light emitting layer contains the light emitting material according to any one of claims 1 to 6. A display device having the organic electroluminescence device according to claim 8. A lighting device having the organic electroluminescence element according to claim 8.

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