JP6326251B2 - Luminescent material and organic EL device using the same - Google Patents

Description

  The present invention relates to a light emitting material having high luminous efficiency and an organic electroluminescence (EL) device using the same.

  The organic EL element includes at least one light emitting layer between a pair of electrodes including an anode and a cathode. When a voltage is applied to the organic EL element, holes from the anode and electrons from the cathode are injected into the light emitting layer. The injected holes and electrons are recombined in the light emitting layer.

In the case where the light-emitting layer contains a host material and a dopant material, recombination of holes and electrons mainly occurs in the host material, and the host material transitions from the ground state (S ₀ state) to the excited state. At this time, according to the spin statistics law, 25% of the host material that has reached the excited state becomes the singlet lowest excited state (S ₁ state) and 75% becomes the triplet lowest excited state (T ₁ state). Subsequently, energy transfer from the host material in the excited state to the dopant material occurs, and the dopant material makes a state transition from the ground state to the excited state. At this time, in principle, the value of the host material follows the abundance ratio between the S ₁ state and the T ₁ state. That is, 25% of the dopant material that has reached the excited state is in the S ₁ state and 75% is in the T ₁ state.

The fluorescent material emits fluorescence during the transition from the S ₁ state to the S ₀ state. Therefore, in principle, a fluorescent material, can contribute only 25% in the S ₁ state into luminescence. On the other hand, phosphorescence is light emission at the transition from the T ₁ state to the S ₀ state. When intersystem crossing from the S ₁ state to the T ₁ state is performed efficiently in the phosphorescent dopant material, in principle, the internal quantum yield can be increased to 100%. For this reason, phosphorescent organic EL light emitting devices have been actively developed, and new dopant materials and host materials have been found.

In the light emitting layer of the phosphorescent organic EL element, an iridium complex, a platinum complex, or the like is used as the phosphorescent dopant material of the light emitting layer. The host material needs to have a larger T ₁ -S ₀ energy gap than the dopant material, and carbazole derivatives such as 4,4′-dicarbazole biphenyl (CBP) are widely used.

On the other hand, CBP and CDBP, since T ₁ is large, poor ability to receive holes or electrons, there is a problem of the driving voltage of the organic EL element becomes high. In view of such a problem, Patent Document 1 proposes to use, as a phosphorescent host material, a bipolar compound in which a carbazolyl group as an electron withdrawing site and a heteroarylene group as an electron transporting site are bonded. It is disclosed that this phosphorescent organic EL device is excellent in external quantum yield at a low driving voltage. Patent Document 2 proposes to use a bipolar compound in which a carbazolyl group and a cyano-substituted arylene group or a cyano-substituted heteroarylene group are bonded as a phosphorescent host material.

  As described above, an organic EL element using phosphorescence can realize high luminous efficiency. However, as described in Patent Documents 1 and 2, most of dopant materials that emit phosphorescence with high efficiency are metal complex compounds containing noble metals such as iridium and platinum, and the material cost is extremely high. That is a problem.

In recent years, organic EL elements using thermally activated delayed fluorescence have been developed and attracted attention as a technology for achieving an internal quantum yield exceeding 25%, which is the theoretical upper limit of fluorescent organic EL elements, while using inexpensive fluorescent materials. ing. Since the thermally activated delayed fluorescent material has a small difference ΔE _ST between S ₁ energy and T ₁ energy, a state transition from the T ₁ state to the S ₁ state (reverse intersystem crossing) occurs due to the thermal energy. When reverse intersystem crossing due to thermal energy occurs, fluorescence is emitted from the T ₁ state via the S ₁ state, so that an internal quantum yield of more than 25% can be achieved. It is also possible to increase to%.

  For example, Non-Patent Document 1 and Patent Document 3 show that a specific cyanobenzene derivative in which an electron-donating carbazolyl group is bonded to an electron-withdrawing dicyanobenzene is useful as a thermally activated delayed fluorescent material. ing. In Non-Patent Document 2, an organic EL device using 1,2,3,5-tetrakis (9-carbazolyl) -4,6-dicyanobenzene (4CzIPN) as a thermally activated delayed fluorescent material is electrically excited. It is reported that it is essentially stable below and has a durable life comparable to conventional phosphorescent organic EL devices.

JP 2010-241801 A JP 2009-094486 A WO2013 / 154064 International Publication Pamphlet

Nature, 492, 234 (2012) Scientific Reports, 3, 2127 (2013)

Thermally activated thermally activated delayed fluorescent materials are attracting attention as organic EL materials with high efficiency and long durability life. As described above, heat activated delayed fluorescent material is required to be Delta] E _ST is small. In general, a compound having a small ΔE _ST tends to have a small emission quantum yield. In Non-Patent Document 1, by steric hindrance of the dicyanobenzene and the electron donating carbazolyl group electron withdrawing, to both the π-conjugated system is present non-parallel, the low Delta] E _ST and high quantum yield It is described that it is compatible.

  However, the types of thermally activated delayed fluorescent materials with high quantum yield that satisfy such characteristics are limited, and the usefulness of only some compounds has been confirmed. In addition, no clear relationship has yet been found between the skeleton structure of electron-withdrawing sites and electron-donating sites, the types of substituents, and luminescent properties. Luminous efficiency and luminescence are based on chemical structures. It is difficult to predict the wavelength. In view of such a current situation, an object of the present invention is to provide a material useful as a light-emitting material of an organic EL element, particularly a thermally activated delayed fluorescent material, and an organic EL element using the material.

As a result of studies by the present inventors, it has been found that a compound in which a cyanopyridine as an electron withdrawing site and a heteroaryl group as an electron donating site are bonded is useful as a thermally activated delayed fluorescent material. It was. Further study results, by having an electron-attracting substituent on the aromatic heterocyclic ring of the heteroaryl group is an electron donating moiety, decreasing the electron density of the electron-donating site, maintain low Delta] E _ST However, the present inventors have found that the emission quantum yield can be improved, and have reached the present invention.

The present invention relates to a light emitting material comprising a compound represented by the following general formula (I).

  In the above general formula (I), m and n are each independently an integer of 1 to 3, and m + n is 2 to 4. A is a substituted heteroaryl group having an electron donating property, and at least one of the substituents on the aromatic heterocyclic ring is an electron withdrawing group. When m is 2 or more, each A may be the same or different.

  The light emitting material of the present invention is preferably a light emitting material that emits delayed fluorescence, and can be used for a light emitting layer of an organic EL element.

  In the general formula (I), at least one substituent A is preferably bonded to a carbon atom adjacent to the carbon atom to which the CN group of the pyridine ring is bonded. In the compound represented by the general formula (I), a CN group is preferably bonded to the 4-position carbon atom of the pyridine ring.

In the compound represented by the above general formula (I), the ¹ H-NMR chemical shift of the hydrogen atom bonded to the pyridine ring is preferably shifted in a low magnetic field. Specifically, the compound represented by the above general formula (I) and the compound in which all of the electron withdrawing groups on the aromatic heterocyclic ring of the substituent A in the above general formula (I) are substituted with hydrogen atoms And the chemical shift of the ¹ H-NMR of the hydrogen atom bonded to the former pyridine ring is 0.02 ppm or more lower than the chemical shift of the ¹ H-NMR of the hydrogen atom bonded to the latter pyridine ring. The magnetic field is preferably shifted.

In the general formula (I), at least one of the electron withdrawing groups on the aromatic heterocyclic ring of the substituent A is an electron withdrawing group having a Hammet substituent constant σ _p of 0.1 or more. Is preferred. As the electron withdrawing group, a cyano group, a perfluoroalkyl group, and a heteroaryl group are preferable, and among them, a cyano group, a 2-pyridyl group, a 3-pyridyl group, and a 4-pyridyl group are preferable.

In the general formula (I), at least one substituent A is preferably a substituted carbazolyl group. The substituted carbazolyl group is represented by A1 below. In A1 below, R ^{1 to} R ⁸ are each independently a hydrogen atom or an arbitrary substituent, and at least one of R ^{1 to} R ⁸ is an electron withdrawing group.

In the substituted carbazolyl group A1, the 3-position substituent R ³ is preferably an electron-attracting group. The 6-position substituent R ⁶ of the carbazole ring is preferably a hydrogen atom or an electron-attracting group, and the 1-position, 2-position, 4-position, 5-position, 7-position and 8-position substituent R ¹ , R ² , R ⁴ , R ⁵ , R ⁷ and R ⁸ are all preferably hydrogen atoms.

上記一般式（II）において、Ｒ^９〜Ｒ^２４はそれぞれ独立に、水素原子または任意の置換基であり、Ｒ^９〜Ｒ^１６の少なくとも１つ、およびＲ^１７〜Ｒ^２４の少なくとも１つは、電子求引性基である。 The luminescent material of the present invention is a compound having a cyano group at the 4-position of the pyridine ring and the above substituted carbazolyl group A1 at the 3-position and 5-position in the general formula (I), that is, the following general formula (II) ) Ru compounds der represented by.

In the general formula (II), R ^{9 to} R ²⁴ are each independently a hydrogen atom or an arbitrary substituent, and at least one of R ^{9 to} R ¹⁶ and at least one of R ^{17 to} R ²⁴ are It is an electron withdrawing group.

The compound represented by the general formula (II) preferably has a ¹ H-NMR chemical shift of 9.12 ppm or more of hydrogen atoms bonded to the pyridine ring (2- and 6-position hydrogen atoms).

  Furthermore, this invention relates to the organic EL element using the said luminescent material. The organic EL device of the present invention includes a light emitting layer containing the above light emitting material between a pair of electrodes. The light emitting layer includes a dopant material and a host material, and the dopant material is preferably the above light emitting material.

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

  The light emitting material of the present invention has a high internal quantum yield and excellent light emission efficiency. In particular, when the light-emitting material of the present invention is used for the light-emitting layer of an organic EL element, the emission efficiency can be dramatically increased by the emission of delayed fluorescence.

It is a schematic cross-sectional structure showing the structure of the organic EL element which concerns on embodiment of this invention. It is an emission spectrum in the toluene solution of compounds 1-6. (A) is a time-resolved spectrum of fluorescence of Compound 1. (B) is a fluorescence time-resolved spectrum of Compound 4. (A) is a fluorescence time-resolved spectrum of a co-deposited film using Compound 1 as a dopant. (B) is a fluorescence time-resolved spectrum of a co-deposited film using Compound 4 as a dopant.

[Luminescent material]
First, the light emitting material of the present invention will be described. The luminescent material of the present invention comprises a compound represented by the following general formula (I).

  In the above general formula (I), m and n are each independently an integer of 1 to 3, and m + n is 2 to 4. In the general formula (I), the substituent A is a substituted heteroaryl group having an electron donating property, and at least one of the substituents on the aromatic heterocyclic ring is an electron withdrawing group. When m is 2 or more, each A may be the same or different.

  The substituted heteroaryl group having electron donating means a heteroaryl group having at least one substituent on the electron donating aromatic heterocycle. The compound represented by the general formula (I) is a compound in which an electron-withdrawing cyanopyridine moiety and an electron-donating substituted heteroaryl moiety are bonded, that is, a bipolar compound.

  The aromatic heterocyclic ring of the substituent A has an electron donating property and preferably has 5 to 30 ring-forming atoms. From the viewpoint of enhancing the electron donating property by the heteroaryl group and causing the π-conjugated system of the pyridine ring and the π-conjugated system of the aromatic heterocyclic ring of the substituent A to exist non-parallel due to steric hindrance, the aromatic heterocycle is condensed. A ring is preferred. The aromatic heterocycle is preferably a nitrogen-containing condensed polycycle.

  Specific examples of the electron-donating aromatic heterocycle include condensed bicyclic rings such as indole, isoindole, thienoindole, indazole, purine, quinoline, isoquinoline; carbazole, acridine, β-carboline, acridone, perimidine, phenazine, Nanthridine, phenothiazine, phenoxazine, 1,7-phenanthroline, 1,8-phenanthroline, 1,9-phenanthroline, 1,10-phenanthroline, 2,7-phenanthroline, 2,8-phenanthroline, 2,9-phenanthroline, Examples include condensed tricycles such as 3,7-phenanthroline and 3,8-phenanthroline; condensed tetracycles such as kindin and quinindrin; condensed pentacycles such as aclindrin and the like.

  Among the above-mentioned electron-donating aromatic heterocycles, the aromatic heterocycle of the substituent A is preferably a carbazole ring, an indole ring, a thienoindole ring, an indoline ring, an acridine ring, or a phenoxazine ring, and more preferably a carbazole ring. preferable. In the compound represented by the general formula (I), a hetero atom (for example, nitrogen) of the substituent A is preferably bonded to a carbon atom of the pyridine ring. That is, the luminescent material of the present invention is preferably composed of a compound in which the substituent A is a substituted carbazolyl group represented by the following A1 in the above general formula (I).

In A1, R ^{1 to} R ⁸ are each independently a hydrogen atom or an arbitrary substituent, and at least one of R ^{1 to} R ⁸ is an electron withdrawing group.

To reduce the S ₁ energy and the T ₁ energy difference Delta] E _ST of the general formula (I) compound represented by the, HOMO is localized to electron-donating site, the LUMO to the electron-withdrawing site Localization is preferred. In order to cause such localization, the molecular structure preferably has symmetry. In the above general formula (I), the following structural formulas can be exemplified as combinations of positions of substituents having a symmetrical molecular structure. In the following structural formulas (123) and (124), a plurality of A may be the same or different from each other. However, in order to improve symmetry, it is preferable that both are the same.

In the general formula (I), in order to enhance the electron withdrawing property of cyanopyridine, it is preferable that a CN group is bonded to the 4-position carbon of the pyridine ring. Further, at least one substituent A is preferably bonded to a carbon atom adjacent to the carbon atom to which the CN group is bonded. When the substituent A and the CN group are bonded to adjacent carbon atoms, the bond is twisted due to steric hindrance between the aromatic heterocycle of the substituent A and the cyano group. The π-conjugated system of the aromatic heterocyclic ring exists in the same plane as the π-conjugated system of the pyridine ring. Therefore, the energy difference Delta] E _ST of smaller singlet lowest excitation state (S ₁ state) and the lowest triplet excited state (T ₁ state), reverse intersystem crossing due to thermal energy is likely to occur.

  Examples of the compound satisfying the combination of these substituents include compounds represented by the following structural formulas. In the following structural formulae, the plurality of A may be the same or different.

  Moreover, it is preferable that the compound represented by the said general formula (I) has two or more substituents A. Among the above exemplary structures, the structural formula (123) satisfies all of the above-described conditions and is particularly preferable as the structure of the light emitting material of the present invention.

  As described above, the substituent A has at least one electron-donating substituent on the aromatic heterocyclic ring. The electron-withdrawing substituent is a substituent that lowers the electron density of the π-conjugated system of the aromatic heterocyclic ring, and may be either aliphatic or aromatic.

The electron-withdrawing substituent on the aromatic heterocyclic ring of the substituent A preferably has an action of reducing the electron density of the π-conjugated system of cyanopyridine to which the substituent A is bonded. Whether or not the substituent on the aromatic heterocyclic ring of the substituent A reduces the electron density of the π-conjugated system of cyanopyridine should be judged from the ¹ H-NMR chemical shift of the hydrogen atom bonded to the pyridine ring. Can do. Specifically, when the compound represented by the general formula (I) is compared with a compound in which all of the electron withdrawing groups on the aromatic heterocyclic ring of the substituent A of the compound are substituted with hydrogen atoms In addition, it is preferable that the ¹ H-NMR chemical shift of the hydrogen atom bonded to the pyridine ring is a low magnetic field shift (the chemical shift is large).

As an example, the case where the compound represented by the general formula (I) is the compound represented by the above exemplary structure (123) will be described, and the ¹ H-NMR chemical shift of the hydrogen atom bonded to the pyridine ring will be described. To do. The compound of the above exemplary structure (123) can be represented by the following general formula (II). In the following general formula (II), R ^{9 to} R ²⁴ are each independently a hydrogen atom or an arbitrary substituent, at least one of R ^{9 to} R ¹⁶ , and at least one of R ^{17 to} R ²⁴ are It is an electron withdrawing group.

The chemical shift of ¹ H-NMR of the hydrogen atom bonded to the 2nd and 6th carbon atoms of the pyridine ring of the compound represented by the general formula (II) is the same as that of the compound represented by the general formula (II). A compound in which all of R ^{9 to} R ²⁴ are hydrogen atoms, that is, hydrogen bonded to carbons at the 2-position and 6-position of the pyridine ring of 3,5-bis (9-carbazolyl) -4-cyanopyridine represented by It is preferable that the magnetic field shift is lower than the ¹ H-NMR chemical shift of the atoms.

In 3,5-bis (9-carbazolyl) -4-cyanopyridine, a peak (s, 2H) derived from hydrogen on the pyridine ring is observed at 9.10 ppm in ¹ H-NMR in CDCl ₃ (described later). Synthesis Example 5). In contrast, in the compound represented by the general formula (II), any one or more of R ^{9 to} R ¹⁶ and any one or more of R ^{17 to} R ²⁴ are electron withdrawing substituents. Therefore, it is preferable that the electron density of the π-conjugated system of cyanopyridine is reduced, and the ¹ H-NMR peak derived from hydrogen of cyanopyridine is observed on the lower magnetic field side than 9.10 ppm.

The chemical shift of ¹ H-NMR of the hydrogen atom bonded to the pyridine ring of the compound represented by the general formula (I) is such that all of the electron withdrawing groups on the aromatic heterocyclic ring of the substituent A of the compound are all. It is preferable that the magnetic field shift is 0.02 ppm or more lower than the ¹ H-NMR chemical shift of the hydrogen atom bonded to the pyridine ring of the compound substituted with a hydrogen atom, and the magnetic field shift is 0.04 ppm or more lower than the chemical shift. More preferably, a low magnetic field shift of 0.06 ppm or more is further preferable, and a low magnetic field shift of 0.07 ppm or more is particularly preferable.

Therefore, the chemical shift of ¹ H-NMR of the hydrogen atom bonded to the pyridine ring of the compound represented by the general formula (II) is preferably 9.12 ppm or more, more preferably 9.14 ppm or more, and 9.16 ppm or more. Is more preferable, and 9.17 ppm or more is particularly preferable.

The compound represented by the general formula (I), by having an electron-attracting substituent on the aromatic heterocyclic substituents A, S ₁ energy and the T ₁ energy difference Delta] E _ST is small, and The emission quantum yield tends to be high. Therefore, the compound represented by the general formula (I) has a high probability of occurrence of reverse intersystem crossing from the T ₁ state to the S ₁ state due to thermal energy, and is useful as a light emitting material that emits delayed fluorescence.

Here, in order to reduce the Delta] E _ST, it is necessary to limit the overlap of electron orbitals HOMO and LUMO, the HOMO electron donating sites, it is preferred to localize LUMO electron withdrawing site . Therefore, in the conventional molecular design of the thermally activated delayed fluorescent material, the direction of increasing the electron density of the electron donating site of the bipolar material and decreasing the electron density of the electron withdrawing site was fundamental. . Further, as described in Non-Patent Document 1 described above, it has been known that when a substituent is introduced into the electron donating portion of the bipolar material, the emission quantum yield tends to decrease. On the other hand, when the electron withdrawing site is cyanopyridine, the electron withdrawing moiety is substituted when the substituent A which is the electron donating site has an electron withdrawing substituent on the aromatic heterocyclic ring. It reduces the electron density of the cyano pyridine moiety is sex site, it is possible to achieve both low Delta] e _ST and high quantum yield.

The electron-withdrawing substituent preferably has a Hammet substituent constant σ _p greater than 0, more preferably 0.1 or more, still more preferably 0.3 or more, and 0.6 or more. Are particularly preferred. If the value of Hammet's substituent constant is positive, it indicates electron withdrawing property, and the larger the value, the stronger the electron withdrawing property. Hammet's substituent constants are described in detail in Hansch, C. et. Al., Chem. Rev., 91, 165-195. (1991).

Specific examples of the electron-withdrawing substituent include a cyano group, a phenyl group, a nitro group, an acyl group, a formyl group, an acyloxy group, an acylthio group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a halogen atom, and at least two. Alkyl group substituted with the above halogen atoms (preferably a perfluoroalkyl group substituted with two or more fluorine atoms, preferably having 1 to 6 carbon atoms, more preferably 1 to 3 carbon atoms, An alkoxy group substituted with at least two halogen atoms; an aryloxy group substituted with at least two halogen atoms; an alkyl substituted with at least two halogen atoms; An amino group; an alkylthio group substituted with at least two halogen atoms; ^{a (R a} is a hydrogen atom or an alkyl group, preferably an alkyl group having 1 to 20 carbon _{^{atoms); - CONR b 2 (R}} b are each independently a hydrogen atom, having 1 to 20 carbon atoms An alkyl group, an aryl group having 6 to 20 carbon atoms or a heteroaryl group having 6 to 20 carbon atoms, preferably a hydrogen atom); SO ₃ M (M is a hydrogen atom or an alkali metal); Groups containing a phosphine oxide structure such as a carbonyl group, diarylphosphono group, dialkylphosphinyl group, diarylphosphinyl group; sulfonyl group; alkylsulfonyl group; arylsulfonyl group; alkylsulfinyl group, arylsulfinyl group; acylthio group Sulfamoyl group; thiocyanate group; thiocarbonyl group; imino group; imino group substituted by N atom Carboxy group or a salt thereof; acylamino group; azo group; selenocyanate group; a heteroaryl group; sigma _p aryl group having greater than 0 (preferably sigma _p is greater than 0.3) electron-withdrawing group substituent Etc.

  Among the electron-withdrawing substituents, those selected from the group consisting of a cyano group, a perfluoroalkyl group (in particular, a trifluoromethyl group), and a heteroaryl group are preferable. The heteroaryl group preferably has a heterocyclic structure containing a nitrogen atom or a sulfur atom as a hetero atom. Specific examples of the electron withdrawing heteroaryl group include an oxadiazolyl group, a benzothiadiazolyl group, a tetrazolyl group, a thiazolyl group, an imidazolyl group, and a pyridyl group. In the heteroaryl group, either a carbon atom or a hetero atom may be bonded to an aromatic heterocycle, but from the viewpoint of enhancing electron withdrawing properties, it is preferable that a carbon atom is bonded to an aromatic heterocycle. . Among the heteroaryl groups, those selected from the group consisting of 2-pyridyl group, 3-pyridyl group, and 4-pyridyl group are particularly preferable.

  In particular, when the electron withdrawing group is a cyano group, the emission wavelength tends to be shortened. Therefore, a compound in which the electron withdrawing group on the substituent A in the general formula (I) is a cyano group is useful as a blue delayed fluorescent material.

  When the electron withdrawing group is a pyridyl group, particularly when it is a 4-pyridyl group, the emission quantum yield tends to be increased. Therefore, in the general formula (I), a compound in which the electron withdrawing group on the substituent A is a pyridyl group is useful as a delayed fluorescent material with high emission efficiency.

The position of the electron withdrawing group on the aromatic heterocyclic ring of the substituent A is not particularly limited. Preferably, the bonding position of the electron withdrawing group is determined so as to reduce the electron density of the π-conjugated system of cyanopyridine to which the substituent A is bonded, depending on the type of the aromatic heterocyclic ring of the substituent A. It is done. For example, when the aromatic heterocyclic ring of the substituent A is a carbazole ring, that is, when the substituent A is the A1, the electron withdrawing substituent is present at the 3-position and / or the 6-position. There is a tendency that the electron density of cyanopyridine, which is an electron withdrawing site, decreases. Therefore, in the substituent A1, R ³ is preferably an electron withdrawing group. R ⁶ is preferably an electron withdrawing group or a hydrogen atom.

  Of the substituents on the aromatic heterocyclic ring of the substituent A, those other than the electron withdrawing group are hydrogen atoms or arbitrary substituents. Examples of substituents other than electron-withdrawing groups include hydroxy groups, alkyl groups having 1 to 20 carbon atoms, alkoxy groups having 1 to 20 carbon atoms, alkylthio groups having 1 to 20 carbon atoms, and 1 to 20 carbon atoms. An alkyl-substituted amino group, an aryl group having 6 to 40 carbon atoms, a diarylamino group having 12 to 40 carbon atoms, a substituted or unsubstituted carbazolyl group having 12 to 40 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, and 2 carbon atoms -10 alkynyl group, C3-C20 trialkylsilyl group, C4-C20 trialkylsilylalkyl group, C5-C20 trialkylsilylalkenyl group, C5-C20 trialkylsilyl An alkynyl group etc. are mentioned.

It is preferable that the aromatic heterocyclic ring has no substituent other than the electron-withdrawing substituent (that is, has no electron-donating substituent). For example, in A1 above, among R ^{1 to} R ⁸ , other than the electron withdrawing group is preferably a hydrogen atom. That is, the substituents R ^{1 to} R ⁸ are preferably electron withdrawing groups or hydrogen atoms, and at least one of R ^{1 to} R ⁸ is preferably an electron withdrawing group. When these are put together, A 1 has R ³ as an electron withdrawing group, R ⁶ has a hydrogen atom or an electron withdrawing group, R ¹ , R ² , R ⁴ , R ⁵ , R ⁷ and R ^8. Are preferably hydrogen atoms.

  In particular, the substituent A1 preferably has one of the following structures. In the following (A21) and (A22), Py is a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, and a 4-pyridyl group is particularly preferable. In the following (A22), two Py may be the same or different but are preferably the same.

From the same viewpoint, also in the general formula (II), a hydrogen atom other than the electron-withdrawing group among R ^{9 to} R ²⁴ is preferable. R ¹¹ and R ¹⁹ are preferably electron withdrawing groups, and R ¹⁴ and R ²² are preferably hydrogen atoms or electron withdrawing groups. When these are put together, in the compound represented by the general formula (II), R ¹¹ and R ¹⁹ are electron withdrawing groups, R ¹⁴ and R ²² are hydrogen atoms or electron withdrawing groups, and R ⁹ , R ¹⁰ , R ¹² , R ¹³ , R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ , R ²⁰ , R ²¹ , R ²³ , R ²⁴ are all preferably hydrogen atoms.

  In particular, the compound represented by the general formula (II) is preferably any of the following compounds. In the following compounds (P1) and (P2), Py is a 2-pyridyl group, a 3-pyridyl group, or a 4-pyridyl group, and a 4-pyridyl group is particularly preferable. In the following (P2), two Py may be the same or different but are preferably the same.

[Organic EL device]
Next, the organic EL element will be described. The organic EL element includes an organic layer between a pair of electrodes including an anode and a cathode, and at least one of the organic layers is a light emitting layer. The light emitting material of the present invention is useful as a light emitting material for an organic EL device and can be effectively used as a material for a light emitting layer. The compound represented by the general formula (I) includes a delayed fluorescent material (delayed phosphor) that emits delayed fluorescence. An organic EL element using a delayed fluorescent material as a light emitting material emits delayed fluorescent light and has high luminous efficiency according to the principle described below.

<Principle of high luminous efficiency by delayed fluorescence>
In an organic EL device, when carriers (holes and electrons) are injected into a light emitting material from an anode and a cathode, the light emitting material is changed to an excited state by carrier recombination, and light is emitted when the exciton changes to a ground state. Is emitted. According to the spin statistics rule, 25% of excitons are in a singlet excited state (S ₁ ), and the remaining 75% are in a triplet excited state (T ₁ ). Therefore, in principle, the internal quantum yield is higher when phosphorescence, which is light emission from a triplet excited state, is used. However, since the triplet excited state has a long lifetime, energy deactivation is likely to occur due to saturation of the excited state and interaction with other excitons, and in general, the internal quantum yield of phosphorescence is often not high.

  On the other hand, in the delayed fluorescent material, a transition from the triplet excited state to the singlet excited state (reverse intersystem crossing) occurs due to triplet-triplet annihilation or absorption of thermal energy, and the singlet excited state changes to the ground state. Fluorescence is emitted during the transition. Thus, the fluorescence generated via the inverse intersystem crossing is delayed fluorescence. In particular, in the organic EL element, a “thermally activated delayed fluorescent material” that causes crossing of inverse terms by absorption of thermal energy is particularly useful.

  When a delayed fluorescent material is used for the organic EL element, excitons in the singlet excited state emit fluorescence as usual. On the other hand, excitons in the triplet excited state absorb thermal energy emitted from the device, and are excited into a singlet excited state (crossing between inverse terms) to emit fluorescence. Fluorescence generated via reverse intersystem crossing is light emission from singlet excitation, and thus light emission at the same wavelength as light emission from excitons excited directly from the ground state to the singlet excitation state. However, since the lifetime of the fluorescence (light emission lifetime) generated via the crossing between inverse terms is longer than that of normal fluorescence or phosphorescence, it is observed as fluorescence delayed from these. This can be defined as delayed fluorescence.

  By using such a thermally activated exciton transfer mechanism, it is possible to increase the ratio of singlet excited states, which normally generate only 25%, to 25% or more by absorbing thermal energy after carrier injection. It becomes. In particular, if a compound that emits strong fluorescence and delayed fluorescence even at a low temperature of less than 100 ° C., the reverse intersystem crossing from the triplet excited state to the singlet excited state is sufficiently generated by the heat of the device to emit delayed fluorescence. Therefore, the light emission efficiency can be dramatically improved.

<Configuration of organic EL element>
FIG. 1 is a schematic cross-sectional view illustrating a configuration of an organic EL element according to an embodiment. This element includes an anode 2 and a cathode 4 on a substrate 1 and an organic layer 3 between the pair of electrodes. The organic layer 3 has at least one light emitting layer. The organic layer 3 may be composed of only the light emitting layer, or may have one or more organic layers in addition to the light emitting layer.

  Examples of the organic layer other than the light emitting layer include a hole transport layer, a hole injection layer, an electron blocking layer, a hole blocking layer, an electron injection layer, an electron transport layer, and an exciton blocking layer. The hole transport layer may be a hole injection transport layer having a hole injection function, and the electron transport layer may be an electron injection transport layer having an electron injection function. In the form shown in FIG. 1, the organic layer 3 has a hole injection layer 31 and a hole transport layer 32 on the anode 2 side of the light emitting layer 33, and an electron transport layer 34 and an electron injection on the cathode 4 side of the light emitting layer 33. It has a layer 35. In addition, the organic EL element of this invention should just have a light emitting layer between a pair of electrodes, and is not limited to the structure shown in FIG. Below, each member and each layer of an organic EL element are demonstrated.

(substrate)
The organic EL element preferably has a pair of electrodes 2 and 4 and an organic layer 3 on the substrate 1. The material of the substrate is not particularly limited, and is appropriately selected from, for example, a transparent substrate such as glass, a silicon substrate, a flexible film substrate, and the like. In the case of a bottom emission type organic EL device that extracts light from the substrate side, the substrate preferably has a transmittance in the visible light region of 80% or more and 90% or more from the viewpoint of increasing light extraction efficiency. Further preferred.

(anode)
The material of the anode is not particularly limited, but metals, alloys, metal oxide electrically conductive compounds and mixtures thereof having a high work function (for example, 4 eV or more) are preferably used. Specific examples of the material of the anode include a metal thin film such as Au, and metal oxides such as indium / tin oxide (ITO), indium / zinc oxide (IZO), zinc oxide, and tin oxide. Among them, ITO or IZO, which is a highly transparent metal oxide, is preferably used from the viewpoint of improving the extraction efficiency of light generated from the light emitting layer and ease of patterning. In the metal oxide which comprises an anode, dopants, such as aluminum, gallium, silicon, boron, and niobium, may be contained as needed.

(cathode)
The material of the cathode is not particularly limited, but metals, alloys, metal oxides, electrically conductive compounds and mixtures thereof having a low work function (for example, 4 eV or less) are preferably used. Examples of the metal having a small work function include Li for an alkali metal and Mg and Ca for an alkaline earth metal. In addition, a simple metal made of rare earth metal or the like, or an alloy such as Al, In, or Ag with these metals can also be used. Further, as disclosed in JP-A-2001-102175 and the like, a metal complex compound containing at least one selected from the group consisting of alkaline earth metal ions and alkali metal ions is used as the organic layer in contact with the cathode. It can also be used. In this case, it is preferable to use a metal capable of reducing metal ions in the complex compound to a metal in a vacuum, such as Al, Zr, Ti, Si, or an alloy containing these metals, as the cathode.

  In order to extract light from the light emitting layer to the outside, either the anode or the cathode is preferably light transmissive, and specifically, the transmittance in the visible light region is preferably 70% or more. % Or more is more preferable, and it is further more preferable that it is 90% or more. In addition, by making both the anode and the cathode light transmissive, an organic EL element capable of extracting light from both the anode side and the cathode side can be produced.

(Light emitting layer)
The light emitting layer is a layer that emits light after excitons are generated by recombination of holes and electrons injected from the anode and the cathode, respectively. The organic EL device of the present invention contains one or more light-emitting materials composed of the compound represented by the general formula (I) in the light-emitting layer. The organic EL device of the present invention may be one in which the above light emitting material is used alone in the light emitting layer, but the light emitting layer contains a dopant material and a host material, and the above light emitting material is used as the dopant material. Is preferred. When the light-emitting layer includes a dopant material and a host material, singlet excitons and triplet excitons generated from the light-emitting material (dopant material) can be confined in the light-emitting material, and thus the light emission efficiency tends to be increased. There is.

  In the organic EL device of the present invention, light is emitted from the dopant material contained in the light emitting layer. This emission includes both fluorescence emission and delayed fluorescence emission. Note that part of the light emission may be light emission from the host material. When the light emitting layer contains a host material and a dopant material, the content of the dopant material in the light emitting layer is preferably 0.1 to 49% by weight, more preferably 0.5 to 40% by weight, and 1 to 30% by weight. Is more preferable. The content of the host material in the light emitting layer is preferably 51 to 99.9% by weight, more preferably 60 to 99.5% by weight, and even more preferably 70 to 99% by weight.

  The host material is preferably a compound that exhibits good film formability and ensures good dispersibility of the dopant material. In addition, the host material preferably has at least one of singlet excitation energy and triplet excitation energy higher than that of the dopant material. Since the excitation energy of the host material is higher than the excitation energy of the dopant material, singlet and triplet excitons generated by the dopant can be confined in the molecule of the dopant material, increasing the luminous efficiency. Can do.

  In order to increase the light emission efficiency, it is preferable that the energy transfer of the dopant material actively occurs from the singlet excitons of the host material. For this reason, the singlet excitation energy of the host material is preferably larger than the singlet excitation energy of the dopant material. In order to increase the intermolecular energy transition probability between the host material and the dopant material, the difference between the singlet excitation energies of both is preferably 1 eV or less, and more preferably 0.5 eV or less.

  The host material preferably has both hole transport performance and electron transport performance, and preferably has a small difference between the hole transport performance and the electron transport performance. Specifically, the ratio of hole mobility to electron mobility, which is an index of transport performance, is preferably in the range of 0.002 to 500.

  Specific examples of the host material include carbazole compounds, aryl silane compounds, phosphorus oxide compounds, oxadiazole compounds, quinolinol metal complexes, and the like. Examples of the carbazole compound include N, N′-dicarbazolyl-4,4′-biphenyl (CBP) and N, N-dicarbazolyl-3,5-benzene (mCP). An example of the arylsilane compound is p-bis (triphenylsilyl) benzene (UGH2). Examples of phosphorus oxide compounds include 4,4′-bis (diphenylphosphoryl) -1,1′-biphenyl (PO1) and bis (2- (diphenylphosphino) phenyl) ether oxide (DPEPO). Can be mentioned. As the host material, one kind of material may be used alone, or two or more kinds of materials may be used in combination.

(Hole transport layer and hole injection layer)
The organic layer 3 preferably has a hole injection layer 31 and a hole transport layer 32 on the anode 2 side of the light emitting layer 33. The hole transport material has either hole injection or transport or electron barrier properties, and may be either organic or inorganic.

  The hole transport material is preferably a compound that is easily radical cationized. For example, an arylamine compound, an imidazole compound, an oxadiazole compound, an oxazole compound, a triazole compound, a chalcone compound, a styrylanthracene compound, or a stilbene compound. Compound, tetraarylethene compound, triarylamine compound, triarylethene compound, triarylmethane compound, phthalocyanine compound, fluorenone compound, hydrazine compound, carbazole compound, N-vinylcarbazole compound, pyrazoline Compounds, pyrazolone compounds, phenylanthracene compounds, phenylenediamine compounds, polyarylalkane compounds, polysilane compounds, polyphenylene vinylene compounds, etc. It is below.

  In particular, an arylamine compound is suitable as a hole transport material because it has a high hole mobility in addition to being easily radical cationized. Among the hole transport materials containing an arylamine compound, a triarylamine derivative such as 4,4′-bis [N- (2-naphthyl) -N-phenyl-amino] biphenyl (α-NPD) is preferable.

(Electron transport layer and electron injection layer)
The organic layer 3 preferably has an electron injection layer 35 and an electron transport layer 34 on the cathode 4 side of the light emitting layer 33. The electron transport material has either electron injection or transport or hole barrier properties, and may be either organic or inorganic.

The electron transport material is preferably a compound that easily undergoes radical anion, for example, a nitro-substituted fluorene derivative, a diphenylquinone derivative, a thiopyran dioxide derivative, a carbodiimide, a fluorenylidenemethane derivative, an anthraquinodimethane and anthrone derivative, an oxadiazole derivative And thiadiazole derivatives, phenanthroline derivatives, quinoline derivatives, quinoxaline derivatives and the like. Specific examples of the electron transport material include 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), tris [(8-hydroxyquinolinato)] aluminum (III) (Alq ₃ ), and the like. Is mentioned. Among these, Alq ₃ is preferably used from the viewpoint of versatility.

(Blocking layer)
A blocking layer may be provided for the purpose of blocking diffusion of holes, electrons, or excitons existing in the light emitting layer to the outside of the light emitting layer. The electron blocking layer is disposed between the light emitting layer and the hole transport layer, and blocks electrons from passing through the light emitting layer and diffusing to the hole transport side layer side. The hole blocking layer is disposed between the light emitting layer and the electron transport layer, and prevents holes from passing through the light emitting layer and diffusing to the electron transport side layer side. For the hole blocking layer, the same material as that of the above-described electron transport layer can be used. For the electron blocking layer, the same material as the hole transport layer described above can be used.

  The exciton blocking layer is a layer for preventing excitons generated by recombination of holes and electrons in the light emitting layer from diffusing into the charge transport layer or the hole transport layer. By providing the exciton blocking layer, excitons can be efficiently confined in the light emitting layer, and the light emission efficiency of the device can be improved. The exciton blocking layer can be disposed on either the anode side or the cathode side of the light emitting layer, or may be disposed on both. As the blocking layer, a material in which at least one of singlet excitation energy and triplet excitation energy is higher than the singlet excitation energy and triplet excitation energy of the light-emitting dopant material is preferably used.

<Production of organic EL element>
The method for forming the electrodes and the organic layer is not particularly limited, and dry processes such as sputtering, CVD, and vacuum deposition, and wet processes such as spin coating and various printing methods are appropriately employed. The light emitting layer containing the host material and the dopant material can be formed, for example, by co-evaporating the host material and the dopant material. At this time, the host material and the dopant material may be mixed in advance.

  In addition to the light emitting layer, the organic EL device of the present invention may be one using a compound represented by the above general formula (I). When the compound represented by the general formula (1) is used in a layer other than the light emitting layer, the same compound may be used in the light emitting layer and the layer other than the light emitting layer, or different compounds may be used.

  In practical use, in order to minimize deterioration in the usage environment in practical use, a part or the whole of the element is sealed with a sealing glass or a metal cap under an inert gas atmosphere, or It is preferable to coat with a protective layer made of an ultraviolet curable resin or the like.

  The organic EL device of the present invention emits light by applying an electric field between an anode and a cathode. At this time, if light is emitted by singlet excitation energy, light having a wavelength corresponding to the energy level is confirmed as fluorescence emission and delayed fluorescence emission. In the case of light emission by triplet excitation energy, the wavelength corresponding to the energy level is confirmed as phosphorescence. Since normal fluorescence has a shorter fluorescence lifetime than delayed fluorescence, the emission lifetime can be distinguished from fluorescence and delayed fluorescence.

  As described above, in the organic EL element using the light emitting material of the present invention, it is preferable that the dopant material of the light emitting layer causes reverse intersystem crossing due to thermal energy. The exciton transitioned to the singlet excited state due to the crossing between inverse terms emits thermally activated delayed fluorescence. Therefore, the organic EL device of the present invention can exhibit a high internal quantum yield and can be an energy-saving light source with low power consumption.

  The organic EL element of the present invention can be effectively applied to lighting fixtures, display devices, and the like. Examples of the display device include a liquid crystal display device using an organic EL element as a lighting device (backlight), an organic EL display device using an organic EL element as a display panel, and the like. For details of the organic EL display device, refer to “Organic EL Display” by Shizushi Tokito, Chiba Yasada, Hideyuki Murata (Ohm), and the like.

  Hereinafter, the present invention will be described in more detail with reference to synthesis examples and evaluation results of the compounds obtained in the synthesis examples. However, the present invention is not limited to the following examples.

[Synthesis Example 1]
In Synthesis Example 1, Compound 1 was synthesized according to the following scheme.

  Under a nitrogen atmosphere, NMP (65 ml) solution containing 3-bromocarbazole (4.34 g, 17.6 mmol) and copper cyanide (3.16 g, 35.3 mmol) was subjected to 190 ° C. oil bath heating conditions. Stir. The reaction was followed by thin layer chromatography and after 4 hours cooled to room temperature. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to obtain 2.85 g (yield 84%) of 3-cyanocarbazole.

  Subsequently, 3,5-dibromopyridine-4-carbonitrile (0.51 g, 1.95 mmol), 3-cyanocarbazole (0.9 g, 4.68 mmol), cesium carbonate (1.83 g, 5.62 mmol), A DMF (20 ml) solution containing palladium acetate (11 mg, 1 mol%) and 1,1′-bis (diphenylphosphino) ferrocene (dppf) (39 mg, 1.5 mol%) was subjected to oil bath heating conditions at 100 ° C. The mixture was stirred for 7 hours and then cooled to room temperature. The reaction solution was poured into water and extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to give a mixture. The obtained mixture was purified by silica gel chromatography to obtain 0.53 g (yield 56%) of the target product as a yellow solid. The obtained compound was further purified by sublimation and used as a luminescent material.

The obtained compound was confirmed to be Compound 1 by ¹ H-NMR. The measurement results were as follows: ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.18 (s, 2H), 8.51 (d, 2H), 8.22 (dd, 2H), 7.80 (ddd, 2H), 7.64 to 7.61 (m, 2H), 7.54 to 7.50 (m, 2H), 7.40 to 7.35 (m, 4H).

[Synthesis Example 2]
In Synthesis Example 2, Compound 2 was synthesized according to the following scheme.

Under a nitrogen atmosphere, 3-bromocarbazole (20 g, 81.3 mmol), bis (pinacolato) diboron (B ₂ pin ₂ ) (23.7 g, 93.5 mmol), potassium acetate (24.7 g, 0.25 mol), and A 1,4-dioxane (350 ml) solution containing [1,1′-bis (diphenylphosphino) ferrocene] dichloropalladium (Pd (dppf) Cl ₂ ) (1.2 g, 1.63 mmol) was added to a 90 ° C. oil. Stirred under bath heating conditions. The reaction was followed by thin layer chromatography and cooled to room temperature after 18 hours. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, concentrated under reduced pressure, and used as it was in the next reaction.

The total amount of boronate ester of carbazole obtained above with 2-bromopyridine (7.11 g, 45 mmol), tetrakistriphenylphosphine palladium (Pd (PPh ₃ ) ₄ ) (0.94 g, 0.8 mmol), and 2M A mixed solvent of 2-propanol (60 ml) and toluene (60 ml) containing an aqueous potassium carbonate solution (75 ml) was heated to reflux in a nitrogen atmosphere. The reaction was followed by thin layer chromatography and cooled to room temperature after 10 hours. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, concentrated under reduced pressure, and purified by crystallization operation to obtain 6.92 g (yield 70% in 2 steps) of the desired product.

  Subsequently, 3,5-dibromopyridine-4-carbonitrile (1.88 g, 7.2 mmol), 3- (2-pyridyl) carbazole (3.51 g, 14.4 mmol), copper (1.09 g, 17. 2 mmol) and a solution of potassium carbonate (4 g, 28.7 mmol) in DMAc (40 ml) were stirred for 2 hours under oil bath heating conditions at 180 ° C., and then cooled to room temperature. The reaction solution was poured into water and extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to give a mixture. The resulting mixture was purified by silica gel chromatography to obtain 1.86 g (yield 44%) of the target product as a yellow solid. The obtained compound was further purified by sublimation and used as a luminescent material.

The obtained compound was confirmed to be Compound 2 by ¹ H-NMR. The measurement results were as follows: ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.17 (s, 2H), 8.86 (dd, 2H), 8.76 (d, 2H), 8.27 (d, 2H), 8.20 (ddd, 2H), 7.90 (dd, 2H), 7.81 (dd, 2H), 7.57 (ddd, 2H), 7.49-7 .40 (m, 6H), 7.27 (d, 2H).

[Synthesis Example 3]
In Synthesis Example 3, Compound 3 was synthesized according to the following scheme.

Under a nitrogen atmosphere, 3-bromocarbazole (20 g, 81.3 mmol), B ₂ Pin ₂ (23.7 g, 93.5 mmol), potassium acetate (24.7 g, 0.25 mol), Pd (dppf) Cl ₂ (1 .2, g (1.63 mmol) in 1,4-dioxane (350 ml) was stirred under 90 ° C. oil bath heating conditions. The reaction was followed by thin layer chromatography and cooled to room temperature after 18 hours. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, concentrated under reduced pressure and used as it was in the next reaction.

Boronate ester of carbazole obtained above (13.2 g, 45 mmol), 3-bromopyridine (7.82 g, 49.5 mmol), Pd (PPh ₃ ) ₄ (1.04 g, 0.9 mmol), and 2M A mixed solvent of 2-propanol (60 ml) and toluene (60 ml) containing an aqueous potassium carbonate solution (75 ml) was heated to reflux under a nitrogen atmosphere. The reaction was followed by thin layer chromatography and after 4 hours cooled to room temperature. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, concentrated under reduced pressure, and purified by crystallization to obtain 10.19 g (yield 93% in two steps) of the target product.

  Subsequently, 3,5-dibromopyridine-4-carbonitrile (2.28 g, 8.7 mmol), 3- (3-pyridyl) carbazole (4.83 g, 19.8 mmol), cesium carbonate (9.66 g, 30 mmol) ), Palladium acetate (135 mg, 0.6 mmol), and a DMF (100 ml) solution containing dppf (0.5 g, 0.9 mmol) were stirred for 30 hours under oil bath heating conditions at 100 ° C. and then cooled to room temperature. did. The reaction solution was poured into water and extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to give a mixture. The resulting mixture was purified by silica gel chromatography to obtain 0.57 g (yield 11%) of the target product as a yellow solid. The obtained compound was further purified by sublimation and used as a luminescent material.

The obtained compound was confirmed to be Compound 3 by ¹ H-NMR. The measurement results were as follows: ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.17 (s, 2H), 9.00 (d, 2H), 8.63 (d, 2H), 8.38 (d, 2H), 8.25 (d, 2H), 8.02 (dd, 2H), 7.76 (ddd, 2H), 7.58 (ddd, 2H), 7.50-7 .41 (m, 8H).

[Synthesis Example 4]
In Synthesis Example 4, Compound 4 was synthesized according to the following scheme.

Under a nitrogen atmosphere, 3-bromocarbazole (20 g, 81.3 mmol), B ₂ Pin ₂ (23.7 g, 93.5 mmol), potassium acetate (24.7 g, 0.25 mol), and Pd (dppf) Cl ₂ ( A 1,4-dioxane (350 ml) solution containing 1.2 g, 1.63 mmol) was stirred under an oil bath heating condition of 90 ° C. The reaction was followed by thin layer chromatography and cooled to room temperature after 18 hours. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, concentrated under reduced pressure and used as it was in the next reaction.

Boronate ester of carbazole obtained above (3.5 g, 11.9 mmol) and 4-bromopyridine hydrochloride (2.55 g, 13.1 mmol), Pd (PPh ₃ ) ₄ (0.58 g, 0.5 mmol) And a mixed solvent of 2-propanol (18 ml) and toluene (18 ml) containing 2M aqueous potassium carbonate solution (24 ml) was heated to reflux under a nitrogen atmosphere. The reaction was followed by thin layer chromatography and after 5 hours cooled to room temperature. The reaction solution was poured into water, and the target product was extracted with ethyl acetate. The organic layer was dried over magnesium sulfate, concentrated under reduced pressure, and purified by crystallization to obtain 2.07 g of the desired product (yield 71% in 2 steps).

  Subsequently, 3,5-dibromopyridine-4-carbonitrile (3.51 g, 13.4 mmol), 3- (4-pyridyl) carbazole (6.55 g, 26.8 mmol), copper (2.04 g, 32. 2 mmol) and potassium carbonate (7.4 g, 53.6 mmol) in DMAc (80 ml) solution was stirred for 6 hours under oil bath heating conditions at 180 ° C., and then cooled to room temperature. The reaction solution was poured into water and extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to give a mixture. The obtained mixture was purified by silica gel chromatography to obtain 1.55 g (yield 20%) of the target product as a yellow solid. The obtained compound was further purified by sublimation and used as a luminescent material.

The obtained compound was confirmed to be compound 4 by ¹ H-NMR. The measurement results were as follows: ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.18 (s, 2H), 8.72 (dd, 4H), 8.46 (s, 2H), 8.26 (d, 2H), 7.82 (ddd, 2H), 7.66 (dd, 4H), 7.59 (ddd, 2H), 7.48-7.40 (m, 6H).

[Synthesis Example 5]
In Synthesis Example 5, Compound 5 was synthesized according to the following scheme.

  Under a nitrogen atmosphere, 3,5-dibromopyridine-4-carbonitrile (2 g, 7.6 mmol), carbazole (2.81 g, 16.8 mmol), cesium carbonate (8.2 g, 25.2 mmol), palladium acetate (113 mg) , 0.5 mmol), and dppf (419 mg, 0.76 mmol) in DMF (60 ml) solution were stirred for 17 hours under oil bath heating conditions at 100 ° C. and then cooled to room temperature. The reaction solution was poured into water and extracted with dichloromethane. The dichloromethane layer was dried over magnesium sulfate and concentrated under reduced pressure to obtain a mixture. The obtained mixture was purified by silica gel chromatography to obtain 1.29 g (yield 39%) of the target product as a yellow solid. The obtained compound was further purified by sublimation and used as a luminescent material.

The obtained compound was confirmed to be Compound 5 by ¹ H-NMR. The measurement results were as follows: ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.10 (s, 2H), 8.20 (s, 2H), 8.18 (s, 2H), 7.55-7.52 (m, 4H), 7.43-7.37 (m, 8H).

[Synthesis Example 6]
In Synthesis Example 6, Compound 6 was synthesized according to the following scheme.

  To a mixed solution of ethyl acetate and toluene (2 ml each) containing 3-bromocarbazole (2.64 g, 10.6 mmol) and copper bromide (0.8 g, 5.6 mmol) in a nitrogen atmosphere, methanol of sodium methoxide was added. The solution (100 ml) was added and stirred under oil bath heating conditions at 80 ° C. The reaction was followed by thin layer chromatography. After 7 hours, the reaction solution was cooled to room temperature, and the reaction solution was poured into water. The target product was extracted with dichloromethane, dried over magnesium sulfate, and concentrated under reduced pressure to obtain 1.81 g (yield 85%) of 3-methoxycarbazole.

  Subsequently, 3,5-dibromopyridine-4-carbonitrile (3.29 g, 12.6 mmol), 3-methoxycarbazole (5.7 g, 28.9 mmol), cesium carbonate (14.1 g, 43.4 mmol), A DMF (120 ml) solution containing palladium acetate (195 mg, 0.87 mmol) and dppf (721 mg, 1.3 mmol) was stirred under oil bath heating conditions at 100 ° C. for 20 hours, and then cooled to room temperature. The reaction solution was poured into water and extracted with ethyl acetate. The organic layer was dried over magnesium sulfate and concentrated under reduced pressure to give a mixture. The obtained mixture was purified by silica gel chromatography to obtain 2.38 g (yield 38%) of the target product as a yellow solid. The obtained compound was further purified by sublimation and used as a luminescent material.

The obtained compound was confirmed to be compound 6 by ¹ H-NMR. The measurement results were as follows: ¹ H-NMR (400 MHz, CDCl ₃ ); δ = 9.06 (s, 2H), 8.13 (d, 2H), 7.63 (d, 2H), 7.51 (dd, 2H), 7.39-7.35 (m, 4H), 7.28 (d, 2H), 7.15 (dd, 2H) 3.97 (s, 6H).

[Example 1: Evaluation of emission characteristics in toluene solution]
In Example 1, a toluene solution of compounds 1 to 6 obtained in Synthesis Examples 1 to 6 was prepared, and nitrogen was bubbled for about 30 minutes, and then a fluorescence spectrum was measured at 300K. An emission spectrum of the compounds 1 to 6 in a toluene solution is shown in FIG. In FIG. 2, the emission intensity is normalized by the intensity value at the peak wavelength.

After bubbling nitrogen into the toluene solution of compounds 1 to 6 for about 30 minutes, the internal quantum yield was measured using an absolute PL quantum yield measuring apparatus (Quantaurus-QY manufactured by Hamamatsu Photonics). Moreover, the time-resolved spectrum of fluorescence in the toluene solution was measured using a small fluorescence lifetime measuring apparatus (Quantaurus-Tau manufactured by Hamamatsu Photonics). From the obtained time-resolved spectrum, a component having a short emission lifetime was determined to be fluorescence, and a component having a long emission lifetime was determined to be delayed fluorescence, and each emission lifetime (half-life of emission intensity) τ ₁ and τ ₂ was calculated. In all of the compounds 1 to 6, fluorescence having a lifetime τ ₁ in the ns order and delayed fluorescence having a lifetime τ ₂ in the μs order were observed.

The time-resolved spectra of the fluorescence of compound 1 and compound 4 are shown in FIGS. 3 (A) and 3 (B), respectively. Here, when oxygen is present in the environment, exciton quenching (energy transfer from the triplet excited state of the luminescent material to the oxygen molecule) occurs, and it is known that delayed fluorescence shortens the life ( For example, see Endo, A. et al., Appl. Phys. Lett., 98, 83302 (2011)). When the time-resolved spectrum was measured without bubbling nitrogen into the solution, the lifetime τ ₂ was shortened in all of the compounds 1 to 6 (see “no bubbling” in FIGS. 3A and 3B). Also from these results, it was confirmed that the compounds 1 to 6 are materials that emit delayed fluorescence.

Emission peak wavelength, internal quantum yield, lifetime of fluorescent component (τ ₁ ), and lifetime of delayed fluorescent component (τ ₂ ) in toluene solutions of compounds 1-6 are substituted at the 3-position of the carbazolyl group of each compound Table 1 shows the ¹ H-NMR chemical shifts of the groups and the hydrogen atoms at the 2-position and 6-position of the pyridine ring.

  As shown in Table 1, Compound 1 having a cyano group that is an electron-attracting substituent on the carbazole ring of the electron-donating moiety is higher than Compound 5 having no substituent on the carbazole ring. The emission peak wavelength is blue-shifted, suggesting that it is useful as a blue delayed fluorescent material. Moreover, it was suggested that the compounds 2-4 which have a pyridyl group on a carbazole ring have a higher internal quantum yield than the compound 5, and are useful as a delayed fluorescent material with high luminous efficiency. On the other hand, Compound 6 having an electron-donating methoxy group on the carbazole ring has a significantly red-shifted emission peak wavelength and a low internal quantum yield as compared with Compound 5.

[Example 3: Formation and evaluation of vacuum-deposited film containing host material]
A compound for measurement was prepared by forming a film on a quartz substrate by vacuum deposition at a weight ratio of dopant material: host material = 94: 6 using compounds 1 to 5 as a dopant material. As the host material, bis (2- (diphenylphosphino) phenyl) ether oxide (DPEPO) was used. However, only for compound 5, N, N-dicarbazolyl-3,5-benzene (mCP) was used as the host material. Using the above measurement sample, the fluorescence spectrum, internal quantum yield, and fluorescence lifetime were measured. In measuring the internal quantum yield, the measurement was performed in a nitrogen atmosphere while flowing nitrogen into the measuring apparatus. The measurement results are shown in Table 2. In addition, FIGS. 4A and 4B show fluorescence time-resolved spectra of samples using Compound 1 and Compound 4 as dopant materials, respectively.

  As shown in Table 2, all of the co-deposited films using compounds 1 to 4 having an electron-withdrawing substituent on the carbazole ring of the electron-donating moiety as a dopant have an internal quantum yield exceeding 70%. It was shown that it is useful as a light emitting material for organic EL devices.

  In particular, the co-deposited film using Compound 4 having a 4-pyridyl group as an electron-attracting substituent as a dopant showed an extremely high quantum yield of 99.0%. Further, the co-deposited film using Compound 1 having a cyano group as an electron-donating substituent as a dopant has a short emission wavelength of 459 nm and a high internal quantum yield of 76.4%. It can be seen that this is useful as a blue delayed fluorescent material with high luminous efficiency.

Claims (9)

Luminescent material comprising a compound represented by the following general formula (II) :

In the general formula (II), R ^{9 to} R ²⁴ are each independently a hydrogen atom or an arbitrary substituent, and at least one of R ^{9 to} R ¹⁶ and at least one of R ^{17 to} R ²⁴ are electrons. It is an attractive group. ^{1 H-NMR} chemical shift of the hydrogen atoms attached to the pyridine ring of the compound represented by the general formula (II) is not less than 9.12Ppm, luminescent material according to claim 1. R ¹¹ and R ¹⁹ are electron withdrawing groups, R ¹⁴ and R ²² are hydrogen atoms or electron withdrawing groups, and R ⁹ , R ¹⁰ , R ¹² , R ¹³ , R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ , R ²⁰ , R ²¹ , R ²³ and R ²⁴ are all luminescent materials according to claim 1 or 2 , wherein all are hydrogen atoms. The luminescent material according to claim 3 , wherein R ¹¹ and R ¹⁹ are cyano groups. The light emitting material according to claim 3 , wherein R ¹¹ and R ¹⁹ are heteroaryl groups selected from the group consisting of 2-pyridyl group, 3-pyridyl group, and 4-pyridyl group. A light emitting layer is provided between a pair of electrodes,
The organic electroluminescent element containing the luminescent material of any one of Claims 1-5 in the said light emitting layer. The organic EL device according to claim 6 , wherein the light emitting layer includes a dopant material and a host material, and the dopant material is the light emitting material. Lighting instrument comprising an organic EL element according to claim 6 or 7. Display device comprising an organic EL element according to claim 6 or 7.

Images