JP5866902B2 - Carbazole derivative and organic electroluminescence device using the same - Google Patents

Description

  The present invention relates to a carbazole derivative that is a thermally polymerizable host material and an organic electroluminescence device (hereinafter referred to as an organic EL device) using the carbazole derivative.

The formation method of each constituent layer such as an organic layer in the production of an organic electronic device such as an organic EL element is roughly classified into a vacuum deposition method and a coating method.
In the vacuum deposition method, since organic layers can be stacked, charge injection from the electrode to the light-emitting layer and confinement of charges and excitons are easy, and a highly efficient device can be manufactured. On the other hand, there are problems such as difficulty in uniform film formation over a large area, low material utilization efficiency, and high cost.

On the other hand, the coating method has an advantage that the area of the device can be increased and the cost can be reduced because the organic layer is formed from a solution. However, in the coating method, it is a problem that the lower layer is dissolved by the coating solvent when laminating.
For this reason, an insolubilization process after coating film formation is important for multi-layer lamination by a coating method, and materials that are polymerized or insolubilized by light or heat are drawing attention.

  As such a material, for example, as a photopolymerizable material, an oxetane derivative (Chemical Formula 1) (Patent Documents 1 and 2), a vinyl derivative (Chemical Formula 2) (Patent Document 3), a nitrene derivative (Chemical Formula 3) (non- Patent Document 1) and the like are known. Further, trifluorovinyl phenyl ether derivatives (Chemical Formula 4), vinyl benzyl ether derivatives (Chemical Formula 5) (Patent Document 4) and the like are known as thermally polymerizable materials.

International Publication No. 2005/083812 International Publication No. 2008/108430 International Publication No. 2010/001830 International Publication No. 2007/133633

Rui-Qi Png etal., Nature Materials 2010, 9, 152

  However, the polymerizable materials described in Patent Documents 1 to 4 have an arylamine which is excellent in hole transportability in the main skeleton but inferior in electron transportability. Or it was limited to the transport layer. According to this, it is possible to apply and laminate a light emitting layer on the upper layer of the polymerizable hole injection or transport layer, but when it is not a polymerizable light emitting layer, the upper electron transport layer is formed by vacuum deposition of a low molecular material. It was necessary to form by film formation or coating film formation of an alcohol soluble material.

  For this reason, in order to be able to select the material of the electron transport layer that is not limited to the type of solvent used in the coating film formation, a polymerizable material that can also be applied to the host material of the light emitting layer is required. Furthermore, a polymerizable host material that can simultaneously realize a bipolar charge transport property suitable for the light emitting layer and a high light emission quantum yield is desired.

  The present invention has been made in order to solve the above technical problem, and is not limited to the type of solvent used in coating film formation, and is capable of multistage lamination in which each layer is functionally separated. An object of the present invention is to provide a polymerizable material that can also be applied as a host material of a light emitting layer and an organic EL device using the same, in order to make it possible to apply an electron transport layer on the light emitting layer. Is.

According to the present invention, as a solution to the above technical problem, a host material comprising a carbazole derivative represented by the following chemical formula (1) or (2) is provided.

The host material is a polymer of a carbazole derivative represented by the chemical formula (2) or a mixture of a carbazole derivative represented by the chemical formula (1) and a carbazole derivative represented by the chemical formula (2). It is preferable that it is a thing.
The host material as described above is a thermal material can be suitably used as an organic EL material by coating the fabric deposition.

The organic EL device according to the present invention is an organic electroluminescent device comprising one or more organic layers including a light emitting layer between a pair of electrodes, wherein at least one of the organic layers contains the host material. It is characterized by.
By using the carbazole derivative according to the present invention, the layers constituting the organic EL element can be suitably stacked by coating.

In the organic EL device, at least one of the organic layers preferably contains a polymer of the carbazole derivative as a host material and a fluorescent or phosphorescent material as a guest material.
The carbazole derivative can also be suitably used as a host material in the light emitting layer.

  In the organic EL device, a polymer of the carbazole derivative represented by the chemical formula (2) or a mixture of the carbazole derivative represented by the chemical formula (1) and the carbazole derivative represented by the chemical formula (2). A coating film for the electron transport layer can also be suitably formed between the organic layer containing the polymer and the electrode.

The carbazole derivative according to the present invention is an excellent thermopolymerizable material that enables formation of a multi-stage laminated structure in which each layer is functionally separated without being limited to the type of solvent used in coating film formation. According to the carbazole derivative, in particular, an electron transport layer can be formed on the light emitting layer by coating, and can also function as a host material for the light emitting layer.
Therefore, the organic EL device according to the present invention using the carbazole derivative is expected to be effectively used as a large-area and low-cost display device or light source.

10 is a schematic cross-sectional view showing a layer configuration of an organic EL element according to Example 8. FIG. 10 is a schematic cross-sectional view showing a layer configuration of an organic EL element according to Example 9. FIG.

Hereinafter, the present invention will be described in more detail.
The carbazole derivative according to the present invention has a structure represented by the above chemical formula (1) or (2).
These compounds are compounds in which a vinylbenzyl ether group is introduced into 4,4′-bis (carbazol-9-yl) biphenyl (abbreviation: CBP) of a carbazole derivative, which is a general host material. ) Is one introduced (abbreviation: V-CBP), and chemical formula (2) is one introduced (abbreviation: DV-CBP).

  The vinyl benzyl ether group does not require a polymerization initiator that is likely to affect the optical and electrical properties of the organic semiconductor, and is thermally polymerized at a relatively low temperature. In the present invention, by introducing this vinyl benzyl ether group into CBP which is a general host material, V-CBP and DV-CBP which are novel carbazole derivatives having both functions of a polymerizable material and a host material. Is based on the synthesis of

Although the synthesis | combining method of V-CBP and DV-CBP is not specifically limited, An example of those synthetic routes is shown below.
First, CBP is obtained by the Ullmann reaction using 9H-carbazole and 4,4′-diiodobiphenyl as starting materials. An alcohol form is obtained by introducing a formyl group at the 3-position of the carbazole moiety by Vilsmeier-Hack reaction and reducing with sodium borohydride. Then, V-CBP and DV-CBP, which are target compounds, can be synthesized by coupling with 4-vinylbenzyl chloride by the Williamson ether method. In addition, each specific synthesis example is shown in the following Example.

Further, the organic EL device according to the present invention is the organic EL device comprising the V-CBP or DV-CBP polymer and one or more organic layers including a light emitting layer between a pair of electrodes. It is contained in at least one layer. Specifically, the structure of such an organic EL element is as follows: first electrode / light emitting layer / second electrode, first electrode / hole injection layer / light emitting layer / second electrode, first electrode / Examples of the structure include a hole injection layer / light emitting layer / electron transport layer / second electrode, a first electrode / hole injection layer / hole transport layer / light emitting layer / electron transport layer / second electrode, and the like.
Furthermore, a known laminated structure including a hole transport light emitting layer, an electron injection layer, an electron transport light emitting layer, and the like can also be used.

  The polymer of V-CBP or DV-CBP may be used in any organic layer in the laminated structure, and may be used by being dispersed together with a hole transport material, a light emitting material, or an electron transport material. It is also possible to dope a luminescent dye into the formed layer.

Since the polymer of V-CBP or DV-CBP can function as a host material when a fluorescent or phosphorescent material is used as a guest material, it can also be suitably applied to a light emitting layer.
In addition, when a polymer of DV-CBP or a polymer of a mixture of V-CBP and DV-CBP is used as a host material in the light-emitting layer, the light-emitting layer is also insolubilized. The layer can be formed by coating. In other words, a functionally separated electron transport layer coating film is laminated between an electrode and an organic layer containing a polymer of DV-CBP or a polymer of a mixture of V-CBP and DV-CBP. be able to.
Therefore, in the laminated structure of the organic EL element, all organic layers other than the metal layer such as electrodes can be formed by the coating film.

In the laminated structure of the organic EL element, film forming materials other than the carbazole derivative which is a polymerizable material according to the present invention are not particularly limited, and can be appropriately selected from known materials and used. Either a system or a polymer system may be used.
The film thickness of each of the layers is appropriately determined depending on the situation in consideration of adaptability between the layers and the required total layer thickness, but is usually preferably in the range of 5 nm to 5 μm.

  The film formation method for each of the layers may be any one of a deposition method, a coating method such as spin coating, and the like. However, as described above, the carbazole derivative according to the present invention is a coating that is advantageous for increasing the area and cost of the device. The coating method is more preferable because it can exhibit its superiority in film formation.

EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.
(Synthesis Example 1) Synthesis of V-CBP

9H-carbazole (18.0 g, 0.108 mol), 4,4′-diiodobiphenyl (20.0 g, 0.0492 mol), copper powder (8.6 g, 0.135 mol), potassium carbonate (54.4 g, 0.394 mol), 18-crown-6-ether (2.6 g, 9.8 mmol) and o-dichlorobenzene (125 mL) were heated and stirred at 175 ° C. for 20 hours in a nitrogen atmosphere. The mixture was allowed to cool to room temperature, dissolved in chloroform, and insolubles were filtered through celite. The filtrate was poured into water, the aqueous phase was extracted with chloroform, and the organic layer was washed with saturated brine and dried over magnesium sulfate. The solution was concentrated under reduced pressure, methanol was added, and the precipitated white solid was filtered to obtain the desired product (CBP). The yield was 22.8 g and the yield was 95%.
The product was identified by ¹ H-NMR, ¹³ C-NMR and elemental analysis (hereinafter the same).

  Next, CBP (10.0 g, 21.2 mmol) was dissolved in chlorobenzene (150 mL) and DMF (40.0 mL, 0.44 mol), and phosphoryl chloride (1.80 mL, 19.8 mmol) was added under a nitrogen atmosphere. ) Was added dropwise. The mixture was heated and stirred at 95 ° C. for 24 hours, and the reaction solution was poured into an ice block. The solution was neutralized with potassium carbonate, the aqueous phase was extracted with chloroform, the organic layer was washed with saturated brine, and dried over magnesium sulfate. The solution was concentrated under reduced pressure and then purified by silica gel column chromatography (DCM) to obtain the desired product (CBP-CHO) as a white solid. The yield was 4.78 g, and the yield was 44%.

THF (150 mL), EtOH (100 mL), NaBH ₄ (1.32 g, 35.1 mmol) were added to CBP-CHO (2.00 g, 3.90 mmol), and the mixture was stirred for 24 hours. Water was added to stop the reaction, and then the organic solvent was distilled off under reduced pressure. The product was washed with 0.1 M aqueous sodium hydroxide, water, and chloroform to obtain the desired product (CBP-CH ₂ OH) as a white solid. The yield was 1.97 g and the yield was 97%.

CBP—CH ₂ OH (1.00 g, 1.95 mmol) was dissolved in DMF (30 mL), and NaH (liquid paraffin dispersion, min. 55%, 0.14 g, 3.0 mmol) was added under nitrogen. Stir for hours. The reaction solution was cooled to 0 ° C., and 4-vinylbenzyl chloride (0.39 mL, 2.9 mmol) was added dropwise. After heating and stirring at 60 ° C. for 24 hours, water was added to stop the reaction. The aqueous phase was extracted with DCM, and the organic layer was washed with saturated brine and dried over magnesium sulfate. The solution was concentrated under reduced pressure and then purified by silica gel column chromatography (DCM: hexane = 3: 2) to obtain the desired product (V-CBP) as a white solid. The yield was 0.50 g and the yield was 40%.

(Synthesis Example 2) Synthesis of DV-CBP

  CBP (10.0 g, 21.2 mmol) was dissolved in chlorobenzene (150 mL) and DMF (40.0 mL, 0.44 mol), and phosphoryl chloride (47 mL, 0.52 mol) was added dropwise under a nitrogen atmosphere. The mixture was heated and stirred at 95 ° C. for 9 hours, and the reaction solution was poured into an ice block. The solution was neutralized with potassium carbonate, the aqueous phase was extracted with chloroform, and the organic layer was washed with saturated brine and dried over magnesium sulfate. The solution was concentrated under reduced pressure, and then purified by silica gel column chromatography (DCM: EtOAc = 1: 0 to 99: 1) to obtain the desired product (CBP-2CHO) as a white solid. The yield was 5.50 g and the yield was 48%.

THF (200 mL), EtOH (120 mL) and NaBH ₄ (1.69 g, 44.7 mmol) were added to CBP-2CHO (5.00 g, 9.26 mmol), and the mixture was stirred for 24 hours. Water was added to stop the reaction, and then the organic solvent was distilled off under reduced pressure. The product was washed with 0.1 M aqueous sodium hydroxide, water, and chloroform to obtain the desired product (CBP-2CH ₂ OH) as a white solid. The yield was 4.90 g and the yield was 97%.

CBP-2CH ₂ OH (1.00 g, 1.80 mmol) was dissolved in DMF (80 mL), and NaH (paraffin dispersion, min. 55%, 0.25 g, 5.4 mmol) was added under nitrogen for 3 hours. Stir. The reaction solution was cooled to 0 ° C., and 4-vinylbenzyl chloride (0.76 mL, 5.4 mmol) was added dropwise. After heating and stirring at 60 ° C. for 24 hours, water was added to stop the reaction. The aqueous phase was extracted with DCM, and the organic layer was washed with saturated brine and dried over magnesium sulfate. The solution was concentrated under reduced pressure and then purified by silica gel column chromatography (DCM: hexane = 3: 2) and preparative GPC (1,2-dichloroethane) to obtain the desired product (DV-CBP) as a white solid. . The yield was 0.45 g and the yield was 32%.

  Various characteristics of the V-CBP and DV-CBP synthesized as described above were evaluated in the following examples.

Example 1 Thermogravimetry (TGA)
TGA was measured using a calorimetric analyzer (SEIKO EXSTAR 6000 TG / DTA6200 unit) on an aluminum pan at a heating rate of 10 ° C./min.
The decomposition temperature of V-CBP and DV-CBP was estimated to be 375 ° C. from the temperature at the time of 5% weight decay.

(Example 2) Differential scanning calorimetry (DSC) measurement DSC was performed by sealing a sample in an aluminum pan using a differential scanning calorimeter (Perkin-Elmer Diamond DSCPyris), heating rate 10 ° C / mi cooling rate, 100 Measured at ° C / min.
In V-CBP, an endothermic peak derived from the glass transition at 72 ° C. and a broad exothermic peak due to the polymerization reaction were observed at 159 ° C.
In DV-CBP, an endothermic peak derived from melting at 177 ° C. and an exothermic peak due to a polymerization reaction were observed at 183 ° C.
In both V-CBP and DV-CBP, when the temperature was raised again after the temperature was lowered, no clear peak appeared, and it was confirmed that the polymerization was thermally stable.

(Example 3) Insolubility test of thermally polymerized thin film The insolubility test of V-CBP and DV-CBP thin film after polymerization was conducted. The polymer film was formed by spin coating on a quartz substrate under a nitrogen atmosphere in a glove box and then heating at 180 ° C. for 30 minutes. Each polymerized film is immersed in chloroform, o-dichlorobenzene, and THF for 30 minutes, and the change in absorbance is confirmed by UV-vis absorption spectrum measurement (Shimadzu Corporation UV-3150 UV-visible near-infrared spectrophotometer). did.

The polymer film of DV-CBP did not decrease the absorbance in the UV-vis absorption spectrum and had very high insolubility. V-CBP having only one polymerization group produces a linear polymer, whereas DV-CBP having two polymerization groups produces a three-dimensionally crosslinked polymer, which is considered to exhibit higher insolubility. . A polymer film in which V-CBP and DV-CBP were mixed at a weight ratio of 1: 1 also showed high insolubility.
As a result, it was shown that the DV-CBP or the mixture of V-CBP and DV-CBP formed by coating becomes a thermal polymerization film, so that an electron transport layer or the like can be formed thereon by coating.

(Example 4) Photoluminescence (PL) spectrum measurement Using a fluorescence spectrophotometer (Jobin-Yvon-Spex FluroMax-2), when the PL spectrum of a polymer film of V-CBP and DV-CBP was measured, 386 nm, Blue light emission having a maximum emission wavelength at 380 nm was observed.

(Example 5) Phosphorescence spectrum measurement The phosphorescence spectrum of the polymer film of DV-CBP at 5K was measured using a streak camera and a cryostat (manufactured by Hamamatsu Photonics).
The triplet energy of the polymer film of DV-CBP was estimated to be 2.60 eV from the light emitting end on the short wavelength side. DV-CBP was found to have triplet energy equivalent to CBP (2.60 eV).

(Example 6) the ionization potential (I _p) measured photoelectron yield spectroscopy, to measure the ionization potential of the polymer film of the DV-CBP (I _p). AC-3 (Riken Keiki) was used for measurement under the atmosphere, and PYS-202-Y (Sumitomo Heavy Industries, Ltd.) was used for measurement under the vacuum. Further, the optical energy gap was obtained from the absorption edge of the UV-vis absorption spectrum, and the electron affinity (E _a ) was estimated from the difference from the ionization potential.
The _Ip of the polymer film of DV-CBP was 6.10 eV under the atmosphere, 6.20 eV under vacuum, and E _a was 2.75 eV. On the other hand, CBP had I _p of 6.10 eV under the atmosphere, 5.91 eV under vacuum, and E _a of 2.66 eV. Thus, I _p and E _a of the polymer film of DV-CBP showed the same value as CBP which is the main skeleton, and it was confirmed that the thermal polymerization group did not affect the electronic state of CBP. .

Example 7 Luminescence Quantum Yield (PLQE) Measurement of Fluorescent Material Doped Film 8 wt% of blue fluorescent material 4,4′-bis [4- (diphenylamino) styryl] biphenyl (abbreviation: BDAVBi) was added to DV-CBP The PLQE of the thin film doped with the concentration was measured. A dope film of DV-CBP polymer was formed by heating at 180 ° C. for 30 minutes after spin coating on a quartz substrate in a nitrogen atmosphere in a glove box.
When DV-CBP was used for the host, PLQE was 0.75, indicating high efficiency equivalent to 0.78 for CBP. From this, it was recognized that excitons were efficiently transferred from the host to the fluorescent dopant, and that the thermal polymerization group did not work as a quencher. In addition, it is considered that DV-CBP is polymerized only by heat and does not use an initiator that may affect the optical properties of the light-emitting material, which is one cause of high PLQE.

  Hereinafter, examples in which DV-CBP is applied to an organic EL element will be described.

(Example 8) Coating type blue fluorescent organic EL element using DV-CBP An organic EL element having a layer structure as shown in FIG. 1 was prepared.
An aqueous dispersion of polyethylenedioxythiophene / polystyrenesulfonic acid (abbreviation: PEDOT: PSS) was spin-coated on a glass substrate (anode 1) with indium-tin oxide (abbreviation: ITO), and then at 120 ° C. for 10 minutes. Heating was performed to form a buffer layer 2 (40 nm).
Next, blue fluorescent material 4,4′-bis [4- (diphenylamino) styryl] biphenyl (abbreviation: BDAVBi) and DV-CBP are mixed at a weight ratio of 1:12 and dissolved in 1,2-dimethoxyethane. After spin coating on PEDOT: PSS, heating was performed at 180 ° C. for 30 minutes to form an insoluble light-emitting layer 3 (40 nm).
Further, 2,2 ′, 2 ″-(1,3,5-benzenetriyl) tris (1-phenyl-1H-benzimidazole) (abbreviation: TPBi) is dissolved in 1,2-dichloroethane, and insoluble luminescence is obtained. After spin coating on the layer, it was heated at 135 ° C. for 1 hour to form an electron transport layer 4 (50 nm).
Finally, LiF (1 nm) and an Al cathode 6 (80 nm) were deposited as the electron injection layer 5 by vacuum deposition.
The layer structure of the organic EL element produced in the above is as follows. Note that sp means spin coating (application), and vd means film formation by vacuum deposition (hereinafter the same).
ITO / PEDOT: PSS (40 nm, sp) / DV-CBP: 8 wt% BDAVBi (40 nm, sp) / TPBi (50 nm, sp) / LiF (1 nm, vd) / Al (80 nm, vd)

Further, when a polymer film in which V-CBP and DV-CBP are mixed at a weight ratio of 1: 1 is used as a host material, it exhibits high insolubility similarly to the above DV-CBP alone, and further electron transport is performed on the light emitting layer. The layer could be applied and deposited.
As described above, by using a material that is polymerized and insolubilized for the light emitting layer after the coating film formation, the coating film formation of the electron transport layer, which is limited to the alcohol-soluble material, is performed in the 1,2-dichloroethane used in this example. Even a highly soluble solvent such as

(Example 9) Coating type green phosphorescent organic EL element A PEDOT: PSS aqueous dispersion was spin-coated on a glass substrate with ITO (anode 1), heated at 120 ° C. for 10 minutes, and buffer layer 2 (20 nm). Was deposited. DV-TCTA (Chemical Formula 17) was dissolved in p-xylene, spin-coated on PEDOT: PSS, and then heated at 180 ° C. for 30 minutes to form an insoluble hole transport layer 7 (20 nm).
Next, tris [2- (4-toluyl) pyridine] iridium (III) (abbreviation: Ir (mppy) ₃ ) and DV-CBP were mixed at a weight ratio of 1:12 and dissolved in 1,2-dimethoxyethane. Then, after spin-coating on the insoluble hole transport layer 7, it was heated at 180 ° C. for 30 minutes to form an insoluble light-emitting layer 3 (40 nm).
Further, TPBi was dissolved in 1,2-dichloroethane, spin-coated on the insoluble light-emitting layer 3, and then heated at 135 ° C. for 1 hour to form an electron transport layer 4 (50 nm).
Finally, LiF (1 nm) and an Al cathode 6 (80 nm) were deposited as the electron injection layer 5 by vacuum deposition.

The layer structure of the organic EL element produced in the above is as follows.
ITO / PEDOT: PSS (20 nm, sp) / DV-TCTA (20 nm, sp) / DV-CBP: 8 wt% Ir (mppy) ₃ (20 nm, sp) / TPBi (50 nm, sp) / LiF (1 nm, vd) / Al (80 nm, vd)

DESCRIPTION OF SYMBOLS 1 Anode 2 Buffer layer 3 Light emitting layer 4 Electron transport layer 5 Electron injection layer 6 Cathode 7 Hole transport layer

Claims (5)

A host material comprising a carbazole derivative represented by the following chemical formula (1) or (2) .

Polymerization of a polymer of a carbazole derivative represented by the chemical formula (2) or a mixture of a carbazole derivative represented by the chemical formula (1) and a carbazole derivative represented by the chemical formula (2) as the host material. The host material according to claim 1, wherein the host material is a product . In an organic electroluminescence device comprising one or more organic layers including a light emitting layer between a pair of electrodes,
At least 1 layer of the said organic layer contains the host material of Claim 1 or 2, The organic electroluminescent element characterized by the above-mentioned. At least one layer of the organic layer, and the host material according to claim 1 or 2, organic electroluminescence according to claim 3, characterized by containing a fluorescent or phosphorescent material as a guest material element. The organic electroluminescence device according to claim 3 or 4 , wherein a coating film of an electron transport layer is formed between the organic layer and the electrode.

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