JP2007230867A - Fluorene group-containing carbazole derivative - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a compound that has excellent properties as a host compound, high stability in a thin film state and is useful for an organic EL element having high efficiency and high durability. <P>SOLUTION: The fluorene group-containing carbazole derivative is represented by general formula (1) (Cz is a substituted or nonsubstituted carbazole group; Ar is a substituted or nonsubstituted aromatic hydrocarbon group, a substituted or nonsubstituted aromatic heterocyclic group or a substituted or nonsubstituted condensed polycyclic aromatic group; A is a substituted or nonsubstituted fluorene group; n is an integer of 1-4). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an organic electroluminescence (EL) element which is a self-luminous element suitable for various display devices, and more particularly to an organic EL element using a carbazole derivative containing a fluorene group.

  Since organic EL elements are self-luminous elements, they have been actively researched because they are brighter and more visible than liquid crystal elements and can be clearly displayed.

In 1987, Eastman Kodak's C.I. W. Tang et al. Have made a practical organic EL device using an organic material by developing a laminated structure device in which various roles are assigned to each material. They laminate a phosphor capable of transporting electrons and an organic substance capable of transporting holes, and inject both charges into the phosphor layer to emit light. High luminance of 1000 cd / m 2 or more can be obtained (for example, see Patent Document 1 and Patent Document 2).

JP-A-8-48656 Japanese Patent No. 3194657

  In recent years, as an attempt to increase the luminous efficiency of an element, an element that generates phosphorescence using a phosphorescent material, that is, uses light emission from a triplet excited state has been developed. This is because according to the theory of the excited state, when phosphorescence is used, the efficiency about three times that of conventional fluorescence becomes possible, and a remarkable increase in luminous efficiency is expected.

The phosphor can be used alone as a light emitting layer. However, the phosphorescent emitter is supported by doping a charge transporting compound generally called a host compound in order to cause concentration quenching. As this host compound, 4,4′-di (N-carbazolyl) biphenyl (hereinafter abbreviated as CBP) represented by the formula [Chemical Formula 1] has been widely used (for example, see Non-Patent Document 1). .

Appl. Phys. Let. , 75.4 (1999)

  However, it has been pointed out that CBP has poor stability in a thin film state, such as a glass transition temperature is not observed by DSC analysis because of strong crystallization. Therefore, satisfactory element characteristics have not been obtained in a scene where heat resistance is required, such as high luminance emission of an organic EL element.

In order to improve the device characteristics of an organic EL device, an organic compound having excellent properties as a host compound and high stability in a thin film state is required.

An object of the present invention is to provide a highly efficient and highly durable organic EL device using a compound having excellent characteristics as a host compound and high stability in a thin film state. Another object of the present invention is to provide an organic compound having excellent characteristics as a material for an EL element. The physical properties of such an organic compound are as follows: (1) the thin film state is stable, (2) it has appropriate HOMO and LUMO levels, and (3) excitation of higher energy than the phosphorescent emitter. It can be mentioned that it has a triplet level.

Therefore, in order to achieve the above object, the present inventors have chemically synthesized various carbazole derivatives, prototyped an organic EL element, and conducted intensive evaluation of the characteristics of the element, thereby completing the present invention. It came.

  That is, the present invention is a carbazole derivative containing a fluorene group represented by the general formula (1).

[Wherein, Cz represents a substituted or unsubstituted carbazole group, Ar represents a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, Represents a group, A represents a substituted or unsubstituted fluorene group, and n represents an integer of 1 to 4. ]

  Moreover, this invention is a carbazole derivative containing the fluorene group represented by General formula (1) for organic electroluminescent elements.

  Specific examples of the aromatic hydrocarbon group, aromatic heterocyclic group, and condensed polycyclic aromatic group that are the group Ar in the general formula (1) include the following groups. Phenyl group, biphenylyl group, tert-phenylyl group, tetrakisphenyl group, styryl group, naphthyl group, anthryl group, acenaphthenyl group, fluorenyl group, phenanthryl group, indenyl group, pyrenyl group, pyridyl group, pyrimidyl group, furanyl group, pyronyl group Thiophenyl group, quinolyl group, benzofuranyl group, benzothiophenyl group, indolyl group, carbazolyl group, benzoxazolyl group, quinoxalyl group, benzoimidazolyl group, pyrazolyl group, dibenzofuranyl group, dibenzothiophenyl group.

Specific examples of the substituent for the ring of these groups Ar include the following. Fluorine atom, chlorine atom, cyano group, hydroxyl group, nitro group, alkyl group, alkoxy group, amino group, substituted amino group, trifluoromethyl group, phenyl group, tolyl group, naphthyl group, aralkyl group.

  The substitution position of the group A in the carbazole derivative containing the fluorene group represented by the general formula (1) is preferably the 9th position of the fluorene group. A preferred representative example of a carbazole derivative containing a fluorene group represented by the general formula (1) is shown as [Chemical Formula 3].

In order to increase the durability of the organic EL element, it is said that a compound having good thin film stability is preferably used. The thin film stability is higher for compounds having higher amorphous properties, and the glass transition point (Tg) is used as an index of amorphous properties (for example, see Non-Patent Document 4).

“M & BE Study Group” Vol. 11 No. 1 Pages 32-41 Publication year: 2000 Published by Japan Society of Applied Physics

  The higher the glass transition point (Tg), the better. However, the carbazole derivative containing a fluorene group of the present invention has a glass transition point exceeding 150 ° C. and is extremely amorphous.

  Furthermore, the carbazole derivative containing a fluorene group of the present invention has an energy level suitable as a host compound. From this, it is clear that an organic EL element with high luminous efficiency can be realized.

The carbazole derivative containing a fluorene group of the present invention is useful as a host compound or a hole transport material of a light emitting layer of an organic EL device. By using the compound of the present invention, the emission efficiency of a conventional organic EL device can be improved. Durability could be greatly improved.

The carbazole derivative containing a fluorene group of the present invention is a novel compound. These compounds can be synthesized by condensing arylamine and aryl halide by the Ullmann reaction.

These compounds can be purified by column chromatography purification, recrystallization with a solvent, or crystallization.

The structure of the compound was identified by NMR and elemental analysis of carbon and hydrogen. As a physical property value, a glass transition point (Tg) serving as an index of stability in a thin film state was measured. The glass transition point was measured with a differential scanning calorimeter manufactured by Mac Science using powder.

The work function was measured using an atmospheric photoelectron spectrometer AC2 manufactured by Riken Keiki Co., Ltd. after a 100 nm thin film was formed on the ITO substrate. The work function is an index of hole blocking ability.

  Similarly, a 100 nm thin film is prepared on a quartz substrate, an absorption spectrum is prepared using a UV3150 model made by Shimadzu Corporation, and an electron affinity is determined using the band gap obtained from the long wave end. did.

As the structure of the organic EL device suitable for the compound of the present invention, an anode, a hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a cathode are sequentially formed on the substrate. In addition, there may be mentioned, in order, on the substrate, an anode, a hole transport layer, a light-emitting layer, an electron transport layer, a cathode, etc., and an organic layer may be omitted. it can.

As an anode of the organic EL element, an electrode material having a large work function such as ITO or gold is used. As the hole injection layer, besides copper phthalocyanine, a starburst type triphenylamine derivative or the like or a coating type material can be used. As the hole transport layer, in addition to the compound of the present invention, N, N′-diphenyl-N, N′-di (m-tolyl) -benzidine (TPD) and N, N′-diphenyl-N, which are benzidine derivatives, N′-di (α-naphthyl) -benzidine (NPD), various triphenylamine tetramers, and the like can be used.

The light emitting layer is produced by doping the host compound of the present invention with a phosphor generally called a dopant or a phosphorescent light emitter. Examples of the dopant include phosphors such as quinacridone, coumarin 6, and rubrene, green phosphorescent emitters such as iridium complex of phenylpyridine (Ir (PPy) 3), blue phosphorescent emitters such as FIrpic and FIr6, Btp2Ir (acac ) And the like.

As the hole blocking layer, a compound having a low HOMO energy level such as bathocuproine (BCP) or aluminum (III) bis (2-methyl-8-quinolinato) 4-phenylphenolate (BAlq) is used.

As the electron transporting layer, oxadiazole derivatives, triazole derivatives, and quinoline aluminum complexes ALq and BAlq are used. Examples of the electron injection layer of the present invention include lithium fluoride, which can be omitted in the preferred selection of the electron transport layer and the cathode. As the cathode, an electrode material having a low work function such as aluminum or an alloy of magnesium and silver can be used.

  Embodiments of the present invention will be specifically described below with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

Synthesis of 9,9-bis (4-carbazolyl-phenyl) -fluorene (hereinafter abbreviated as CDPF) Under a nitrogen atmosphere, 8.9 g of 9,9-bis (4-iodophenyl) -fluorene, 5.5 g of carbazole, 4.8 g of potassium carbonate, 0.5 g of copper powder and 8 ml of diphenyl ether were charged and reacted at 240 ° C. for 4 hours. After completion of the reaction, 300 ml of toluene was added, stirred for 1 hour and filtered hot, and the filtrate was concentrated to dryness to obtain a crude product. The dried crude product was purified by column chromatography to obtain 3.7 g (yield 38%) of the desired product.

  The structure of the obtained white powder was identified using NMR. 1H-NMR measurement results are shown in FIG.

The following 32 signals of hydrogen were detected by 1H-NMR, and the structure of the target product was identified as the structure of [Chemical Formula 3].
δ (ppm) = 8.121 (d, 4H), 7.872 (d, 2H), 7.602 (d, 2H), 7.543-7.493 (m, 8HH), 7.470-7 .406 (m, 4HH), 7.434 (d, 4H), 7.383 (t, 4H), 7.263 (t, 4H)

Synthesis of 9,9-bis (4-carbazolyl-3-methyl-phenyl) -fluorene (hereinafter abbreviated as CDMPF) 9,9-bis (4-iodo-3-methyl-phenyl) under nitrogen atmosphere -Fluorene 4.6g, carbazole 2.8g, potassium carbonate 2.5g, copper powder 0.2g, n-dodecane 4ml was prepared, and it reacted at 220 degreeC for 6 hours. After completion of the reaction, 200 ml of toluene was added, stirred for 1 hour and filtered hot, and the filtrate was concentrated to dryness to obtain a crude product. The dried crude product was purified by column chromatography to obtain 1.7 g (yield 38%) of the desired product.

  The structure of the obtained white powder was identified using NMR. The results of 1H-NMR measurement are shown in FIG. 2 and the results of 13C-NMR measurement are shown in FIG.

Hereinafter, 36 hydrogen signals were detected by 1H-NMR, and the structure of the target product was identified.
δ (ppm) = 8.130 (d, 4H), 7.868 (d, 2H), 7.625 (d, 2H), 7.443 (t, 2H), 7.389 (d, 4H), 7.362 (t, 2H), 7.344 (t, 4H), 7.285 (t, 4H), 7.233 (s, 2H), 7.060 (d, 4HH), 1.883 (s) , 6H)

  By 19 C-NMR, 19 aromatic carbons (150.538, 146.145, 140.945, 140.147, 136.946, 134.603, 130.963, 128.957, 127.896, 127. 806, 127.197, 126.325125.707, 122.894, 120.351, 120.187, 119.442, 109.422) and one aliphatic carbon (65.218 ppm).

Furthermore, the chemical structure was identified by elemental analysis. The analysis results were as follows.
Theoretical value (carbon 90.5%) (hydrogen 5.4%) (nitrogen 4.1%)
Actual value (carbon 90.2%) (hydrogen 5.5%) (nitrogen 4.0%)
The above 1H-NMR and 13C-NMR measurement results and elemental analysis results were combined and identified as the target compound of C51H36N2.

For the compound CDPF of the formula [Chemical Formula 3], the compound CDMPF of [Example 2] and the CBP of the formula [Chemical Formula 1] for comparison, the glass transition point was measured by a differential scanning calorimeter DSC (manufactured by Mac Science). . The obtained glass transition point is shown below. From these results, it is clear that the compound of the present invention has a high glass transition point.
[Chemical Formula 3] Compound of the Present Invention CDPF Glass transition point: 185 ° C.
Compound of the present invention of [Example 2] CDMPF Glass transition point: 164 ° C.
[Chemical Formula 1] CBP glass transition point: not observed

For the compound CDPF of the formula [Chemical Formula 3] and the compound CDMPF of the [Example 2] and the CBP of the formula [Chemical Formula 1] for comparison, a thin film of 100 nm was formed on the ITO substrate, and the photoelectron spectrometer in the atmosphere The work function was measured using AC2 (manufactured by Riken Keiki). The measurement results are shown below.
[Chemical Formula 3] Compound of the Present Invention CDPF Work Function: 5.99 eV
Compound of the present invention of [Example 2] CDMPF Work function: 6.03 eV
[Chemical Formula 1] CBP work function: 6.00 eV

From the above results, it can be seen that the compound of the present invention has an energy level suitable as a host compound.

For the compound CDPF of [Chemical Formula 3] and the compound CDMPF of [Example 2], and CBP of [Chemical Formula 1] for comparison, a 100 nm thin film was prepared on a quartz substrate, and an ultraviolet-visible absorption spectrometer The absorption spectrum was measured using UV3150 (manufactured by Shimadzu Corporation), and the band gap value was calculated from the short wave end of the absorption spectrum. The band gap values are shown below.
[Chemical Formula 3] Compound of the present invention CDPF Gap value: 3.50 eV
Compound of the present invention of [Example 2] CDMPF Gap value: 3.55 eV
[Chemical Formula 1] CBP gap value: 3.44 eV

  From the above results, it can be said that the compound used in the organic EL device of the present invention has a remarkably wide gap value compared to CBP, and is suitable as a dopant host compound.

As shown in FIG. 4, the organic EL element has a hole transport layer 3, a light emitting layer 4, a hole blocking layer / electron transport on a glass substrate 1 on which an ITO electrode is previously formed as a transparent anode 2. The layer 5, the electron injection layer 6, and the cathode (aluminum electrode) 7 were formed by vapor deposition.
The glass substrate 1 on which ITO with a film thickness of 150 nm was formed was washed with an organic solvent, and then the surface was washed with UV-ozone treatment. This was attached in a vacuum vapor deposition machine and depressurized to 0.001 Pa or less. Subsequently, as the hole transport layer 3, TPD was formed to a thickness of about 30 nm at a deposition rate of 0.6 Å / s.

Next, the compound of Synthesis Example 1 as a host material is deposited at a deposition rate of 2 Å / s and FIrpic as a dopant at a deposition rate of 0.1 Å / s as a light-emitting layer 4 by a binary simultaneous deposition method. The light emitting layer 4 containing about 40% by weight was formed to about 40 nm. On the light emitting layer 5, BAlq was formed as a hole blocking layer / electron transport layer 5 at a deposition rate of 0.6 Å / s to about 30 nm. The vapor deposition so far was continuously performed without breaking the vacuum.

A cathode vapor deposition mask was inserted, and lithium fluoride was deposited on the hole blocking / electron transport layer 5 at a deposition rate of 0.1 Å / s to about 0.5 nm to form the electron injection layer 6. Finally, 200 nm of aluminum was deposited to form the cathode 7.

When a current density of 300 mA / cm 2 was applied to the produced organic EL element, a stable blue light emission with a high luminance of 30500 cd / m 2 was obtained. The luminous efficiency at this luminance was as high as 10.3 cd / A.

Since the carbazole derivative containing a fluorene group of the present invention has high amorphous properties and a stable thin film state, it is excellent as a compound for an organic EL device. By producing an organic EL device using the compound of the present invention, the light emission efficiency can be remarkably improved. For example, it can be applied to household appliances and lighting applications.

It is a 1H-NMR chart of CDPF. It is a 1H-NMR chart of CDMPF. It is a 13C-NMR chart of CDMPF. 10 is a diagram showing an EL element configuration of Example 6. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Transparent anode 3 Hole transport layer 4 Light emitting layer 5 Hole blocking and electron transport layer 6 Electron injection layer
7 Cathode

Claims (2)

A carbazole derivative containing a fluorene group represented by the general formula (1).

[Wherein, Cz represents a substituted or unsubstituted carbazole group, Ar represents a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, Represents a group, A represents a substituted or unsubstituted fluorene group, and n represents an integer of 1 to 4. ] The carbazole derivative containing the fluorene group represented by General formula (1) for organic electroluminescent elements.

[Wherein, Cz represents a substituted or unsubstituted carbazole group, Ar represents a substituted or unsubstituted aromatic hydrocarbon group, a substituted or unsubstituted aromatic heterocyclic group, a substituted or unsubstituted condensed polycyclic aromatic group, Represents a group, A represents a substituted or unsubstituted fluorene group, and n represents an integer of 1 to 4. ]

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