JP4904734B2 - Novel pyrazole derivative and organic EL device containing the same - Google Patents

Description

  The present invention relates to a novel pyrazole derivative and an organic EL device containing the same.

  In recent years, organic electroluminescence devices (organic EL devices) have been attracting attention as light emitting media with low power consumption and a small area occupied by devices in applications such as flat panel displays and lighting fixtures. Up to now, various electrode materials, charge transport materials, luminescent materials, etc. have been developed from many viewpoints such as reduction of drive voltage, longer life, and improvement of luminous efficiency for full-scale practical application of organic EL devices. Has been proposed.

  As a basic structure of a general organic EL element, for example, an anode made of a conductive metal oxide such as indium-tin oxide (ITO) is provided on a substrate that transmits visible light such as glass or plastic, and an anode is formed thereon. A hole transport layer that transports positive charges (holes), a light-emitting layer that recombines positive and negative charges to convert current to light, and an electron transport layer that transports negative charges (electrons) are sequentially stacked. A structure in which a cathode made of a metal such as aluminum, magnesium, calcium, cesium, silver, or an alloy in which these are mixed at an arbitrary ratio is provided.

Recently, from the viewpoint of greatly improving the light emission efficiency of organic EL devices, devices using phosphorescent materials containing iridium (III), platinum (II), etc. in the molecule as a light emitting material have attracted a great deal of attention. Especially for organic EL devices using the tris (2-phenylpyridine) iridium (III) complex (Ir (ppy) ₃ ), which is a green phosphorescent material, the efficiency of converting the current passed through the device into light (hereinafter, The internal quantum efficiency is almost 100% (Non-patent Document 1). Furthermore, the performance of devices using red phosphorescent materials has recently reached a practical level, and small displays using such devices have been marketed.

  On the other hand, for organic EL devices using blue phosphorescent materials, although the luminous efficiency is improving, the drive voltage is high, the stability of the various materials that make up the devices, and the drive life resulting from them. There are still many problems to be solved such as shortness.

  Generally, the light emitting layer in an organic EL device is 0.1 to 10% by weight by a co-evaporation method or a mixture solution coating method in a host material that plays a role of receiving positive and negative charges from a hole transport layer and an electron transport layer. It is made in the form of doping light emitting material of a degree.

  Here, in particular, when a phosphorescent material is used as the light emitting material, an energy difference between the ground state and the excited triplet state (hereinafter, triplet energy) of the host material and the light emitting material is extremely important. In the case of forming a light emitting material-doped light emitting layer, the triplet energy of the host material needs to be larger than the triplet energy of the light emitting material. Here, if the triplet energy of the luminescent material is larger than the triplet energy of the host material, the energy of the luminescent material excited by the current flows back to the host material, resulting in a significant decrease in luminous efficiency. Cause.

Actually, in the case of 4,4′-bis (9-carbazolyl) biphenyl (hereinafter referred to as CBP), which is generally used as a light emitting layer host of a phosphorescent material system, the aforementioned green phosphorescent material is used as the light emitting material. When (ppy) ₃ is used, the internal quantum efficiency is almost 100%. However, when FIrpic, which is a blue phosphorescent material, is used, the triplet energy of FIrpic is larger than the triplet energy of CBP as a host. For this reason, it is known that a reverse flow of energy from Firpic to CBP occurs, and as a result, the internal quantum efficiency of the device is significantly reduced (Non-Patent Documents 2 and 3).

In addition, a carbazole-based host material typified by CBP has a poor charge transport property, which causes a problem that the driving voltage of the device is increased.
M. Ikai et al., Appl. Phys. Lett., 79, 156 (2001) C. Adachi et al., Appl. Phys. Lett., 79, 2082 (2005) Y. Kawamura et al., Appl. Phys. Lett., 86, 071104 (2005)

  Accordingly, an object of the present invention is to provide a material having high triplet energy and excellent charge transportability as a light emitting layer host.

  As a result of intensive studies to solve the above problems, the present inventor can easily obtain a novel pyrazole derivative represented by the following general formula (1) from an inexpensive material, and the novel pyrazole derivative is extremely high. It has been found that it has triplet energy. In addition, when the pyrazole derivative is used as a light emitting layer host in the light emitting layer of an organic EL device, the doped light emitting material has a high absolute light emission quantum yield and excellent charge transportability, and as a result, sufficient even under low voltage driving. The present inventors have found that an organic EL device having a high luminance can be obtained, and have completed the present invention.

That is, the present invention relates to the general formula (1):
Wherein, R ¹ to R ⁸ are the same or different and each represents a hydrogen atom, an alkyl group or an alkoxy group; ring A~E are the same or different and indicates a benzene ring or a pyridine ring; binding to ring E The bond between the pyrazole ring and ring E on the benzene ring is in the ortho position. ]
The organic EL device is characterized by having a light-emitting layer containing a pyrazole derivative represented by the formula: wherein the light-emitting layer contains a light-emitting material.
Here, before Symbol luminescent material is preferably a blue phosphorescent material.

  The novel pyrazole derivative of the present invention has extremely high triplet energy, and when this is used as a light emitting layer host in a light emitting layer, the doped light emitting material has a high absolute light emission quantum yield and further has a charge transport property. As a result, it is possible to obtain an organic EL element having sufficient light emission luminance even under low voltage driving.

Examples of the alkyl group represented by R ^{1 to} R ⁸ in the general formula (1) include linear or branched groups such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, and a tert-butyl group. Examples of the alkyl group include 1 to 6 carbon atoms in the chain, and examples of the alkoxy group include 1 to 6 alkoxy groups such as a methoxy group, an ethoxy group, an n-propoxy group, and an n-butoxy group.

R ^{1 to} R ⁸ are the same or different and preferably a hydrogen atom, and R ^{1 to} R ⁸ are preferably a hydrogen atom at the same time.

R ^{1 to} R ⁸ are preferably those in which R ¹ and R ⁵ , R ² and R ⁶ , R ³ and R ⁷ , and R ⁴ and R ⁸ are the same.

  The bond between the benzene ring and the benzene ring on the ring E in the general formula (1) may be o-, m-, or p-, and m- is particularly preferable.

  Further, the bond between the pyrazole ring and the ring E on the benzene ring bonded to the ring E may be o-, m- or p-, but o- or p- is preferable, and o- is more preferable.

  The pyrazole derivative of the present invention can be produced, for example, by the following method.

(Wherein R ^{1 to} R ⁸ and rings A to E are as defined above; X ¹ and X ² are the same or different and each represents a halogen atom; Y represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms) Is shown.)

  That is, the phenyl hydrazine (2) is reacted with the dibenzoylmethane derivative (3) to induce the pyrazole derivative (4). Subsequently, the pyrazole derivative (4) is reacted with alkyl lithium and trialkyl borate to form a boronic acid derivative (5), and then reacted with the halide (6) in the presence of a palladium catalyst and a base. The pyrazole derivative is obtained.

  The reaction of the compound (2) and the compound (3) is preferably performed in the presence of an acid such as acetic acid. The usage-amount of an acid is 2-10 mol normally with respect to 1 mol of phenylhydrazine (2), Preferably it is 2-5 mol.

  The reaction solvent used in the reaction is not particularly limited as long as it is inert to the reaction, but alcohol solvents such as 1-propanol and 2-propanol are preferable. The reaction is preferably performed in the range of room temperature to the boiling point of the solvent for about 5 to 20 hours.

  Examples of the alkyllithium used for the reaction of the pyrazole derivative (4) include alkyllithium having 1 to 6 carbon atoms such as ethyllithium, n-propyllithium, and n-butyllithium. From the viewpoint of handleability and reactivity, n-Butyl lithium is preferred. The usage-amount of alkyl lithium is 0.8-2 mol with respect to 1 mol of pyrazole derivatives (4), Preferably it is 1-1.5 mol.

  The reaction solvent used in the reaction is not particularly limited as long as it is inert to the reaction, but for example, ether solvents such as dimethoxyethane, diethyl ether, and tetrahydrofuran are preferable. The reaction is preferably performed at a temperature range of −80 ° C. to −30 ° C. for 15 minutes to 1 hour, and then at a temperature range of −20 ° C. to 0 ° C. for 30 minutes to 2 hours.

  Examples of the trialkyl borate used after the alkyllithium reaction include trimethyl borate and triethyl borate. The usage-amount of trialkyl borate is 1-3.5 mol normally with respect to 1 mol of pyrazole derivatives (4), Preferably it is 1.1-2.0 mol.

  The reaction solvent used for the reaction of the trialkyl borate is not particularly limited as long as it is inert to the reaction, but ether solvents such as dimethoxyethane, diethyl ether, and tetrahydrofuran are preferable. The reaction is preferably performed at a temperature range of -80 ° C to -30 ° C for 1 to 3 hours, and then at room temperature for about 2 to 16 hours.

  An acid such as acetic acid and hydrochloric acid is added to the reaction solution thus obtained, and the boronic acid derivative (5) is obtained by, for example, stirring reaction at room temperature for 15 to 45 minutes.

  Examples of the halide (6) include dichlorobenzene, dibromobenzene, dichloropyridine, dibromopyridine and the like. The amount of the halide (6) used is usually 0.5 to 1.2 mol, preferably 0.8 to 1.0 mol, with respect to 1 mol of each of the boronic acid derivatives (5) and (5 ′). . Here, the boronic acid derivative (5 ') can be obtained by the same method as the boronic acid derivative (5), and the boronic acid derivative (5') may be the same as the boronic acid derivative (5).

  Palladium catalysts include tetrakis (triphenylphosphine) palladium, dichlorobis (triphenylphosphine) palladium, dichloro [bis (diphenylphosphino) ethane] palladium, dichloro [bis (diphenylphosphino) butane] palladium, dichloro [bis (diphenyl). Phosphino) ferrocene] palladium and the like, among which tetrakis (triphenylphosphine) palladium is preferable. The usage-amount of a palladium catalyst is 0.005-0.5 mol normally with respect to 1 mol of boronic acid derivatives (5), Preferably it is 0.01-0.15 mol.

  Examples of the base include alkali metal carbonates such as potassium carbonate, sodium carbonate, lithium carbonate and cesium carbonate; alkali metal hydrogen carbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate compound; sodium hydroxide, potassium hydroxide and lithium hydroxide And alkali metal hydroxides such as cesium hydroxide. The usage-amount of a base is 2-10 mol normally with respect to 1 mol of boronic acid derivatives (5), Preferably it is 2-5 mol.

  The reaction solvent used for the reaction between the boronic acid derivative and the halide (6) is not particularly limited as long as it is inert to the reaction. For example, benzene-based solvents such as benzene and toluene; dimethoxyethane, diethyl ether, tetrahydrofuran Ether solvents such as n-hexane, n-heptane, n-octane and the like, and ether solvents are preferred. The reaction is preferably performed in the range of room temperature to the boiling point of the solvent for about 6 to 15 hours. Note that the boronic acid derivatives may be used in combination of two types having different structures.

  Further, as shown below, the pyrazole derivative (1) of the present invention can also be produced by performing the same method as described above except that the halide (2 ′) is used instead of the phenylhydrazine (2). it can.

(Wherein R ^{1 to} R ⁸ and rings A to E are as defined above; X ^{1 to} X ³ are the same or different and each represents a halogen atom; Y represents a hydrogen atom or an alkyl group having 1 to 6 carbon atoms) Is shown.)

  Examples of the alkyl lithium used for the reaction of the pyrazole derivative (4 ′) include alkyl lithium having 1 to 6 carbon atoms such as ethyl lithium, n-propyl lithium, and n-butyl lithium, but from the viewpoint of handling and reactivity. N-Butyllithium is preferred. The amount of alkyl lithium used is 0.8 to 2 mol, preferably 1 to 1.5 mol, per 1 mol of pyrazole derivative (4 ').

  The reaction solvent used in the reaction is not particularly limited as long as it is inert to the reaction, but for example, ether solvents such as dimethoxyethane, diethyl ether, and tetrahydrofuran are preferable. The reaction is preferably carried out in the temperature range of −80 ° C. to −30 ° C. for 30 minutes to 3 hours.

  Examples of the trialkyl borate used after the alkyllithium reaction include trimethyl borate and triethyl borate. The amount of the trialkyl borate to be used is usually 1 to 3.5 mol, preferably 1.1 to 2.0 mol, per 1 mol of the pyrazole derivative (4 ').

  The reaction solvent used for the reaction of the trialkyl borate is not particularly limited as long as it is inert to the reaction, but ether solvents such as dimethoxyethane, diethyl ether, and tetrahydrofuran are preferable. The reaction is preferably performed at a temperature range of -80 ° C to -30 ° C for 1 to 3 hours, and then at room temperature for about 2 to 16 hours. An acid such as acetic acid or hydrochloric acid is added to the reaction solution thus obtained, and the boronic acid derivative (5 ″) is obtained by, for example, stirring at room temperature for 15 to 45 minutes. The boronic acid derivative (5 ′ ″) can also be produced by the same method.

  Although the reaction mixture containing the pyrazole derivative (1) of the present invention can be obtained by the above method, the present mixture can be obtained by appropriately combining general operations such as filtration, neutralization, extraction, concentration, recrystallization, and chromatography. The pyrazole derivative (1) of the invention can be isolated as crystals.

  Next, an organic EL device using the pyrazole derivative (1) of the present invention will be described. A typical organic EL device of the present invention has a structure similar to that of the organic EL device described in JP-A-2004-339070, specifically, a transparent substrate, an anode made of a conductive material, and hole transport. A layer, a light emitting layer, an electron transport layer, and a cathode are sequentially laminated, and the light emitting layer contains the pyrazole derivative of the present invention as a light emitting layer host.

  As the transparent substrate, glass, transparent plastic or the like may be used. As the anode, ITO, which is a conductive material laminated to a thickness of about 110 nm, can be used. As the cathode, a semitransparent alloy having a small work function obtained by forming a film with a thickness of about 110 nm by co-evaporation of magnesium and silver, for example, MgAg / Ag may be used.

  The organic layer such as the light emitting layer and the electron transport layer of the organic EL device of the present invention may further contain various compounds conventionally used in the field. A light emitting material can be added to the light emitting layer, and a phosphorescent material is preferable as the light emitting material. Examples of phosphorescent materials include green phosphorescent materials, red phosphorescent materials, and blue phosphorescent materials, with blue phosphorescent materials being preferred and FIrpic being more preferred. When FIrpic is added to the light emitting layer, the amount of FIrpic added to the quinoline derivative (1) of the present invention is preferably 0.1 to 20%, more preferably 3 to 15% by weight.

  EXAMPLES Next, although an Example is given and this invention is demonstrated concretely, these do not limit the scope of the present invention.

Example 1
Synthesis of 2,6-bis (2- (3,5-diphenylpyrazol-1-yl) phenyl) pyridine (hereinafter BPP)
Into a 500 mL eggplant-shaped flask, 23.0 g (213 mmol) of phenylhydrazine and 52.5 g (234 mmol) of dibenzoylmethane were added, and 230 mL of 2-propanol and 4.5 mL of acetic acid were added to the flask. Reflux for hours. After cooling the reaction solution to room temperature, the precipitated white crystals were filtered and dried to obtain 61.0 g (206 mmol, yield 96.8%) of white crystals of 1,3,5-triphenylpyrazole (TPPz).
11.9 g (40 mmol) of this TPPz was dispensed into a 300 mL eggplant-shaped flask and dissolved by adding 120 mL of tetrahydrofuran. The reaction solution was cooled to −60 ° C. or lower with a dry ice-acetone bath. Thereafter, 40 mL of 1.6 M n-butyllithium / hexane solution was added dropwise while keeping the internal temperature at −40 ° C. or lower. After completion of the dropwise addition, stirring was continued for 1 hour while maintaining the internal temperature at −10 to 0 ° C., and then the internal temperature was again cooled to −60 ° C. or lower using a dry ice-acetone bath. To this reaction solution, 6.5 g (62.7 mmol) of trimethyl borate was dropped while maintaining the internal temperature at −40 ° C. or lower. After completion of the dropping, stirring was continued for 2 hours at an internal temperature of −40 ° C. or lower, and then stirring was continued overnight while gradually warming to room temperature. To this reaction solution, 60 mL of 1 M hydrochloric acid aqueous solution was added and stirred for 30 minutes. Stirring was stopped, the separated aqueous layer was discarded, and the resulting organic layer was concentrated under reduced pressure to obtain a light red amorphous boronic acid intermediate (1- (2- (dihydroxyboryl) phenyl) -3,5-diphenylpyrazole ) 12.6 g was obtained. This boronic acid intermediate contained a small amount of impurities, but was used in the next reaction as it was.
4.2 g of the boronic acid intermediate was taken in a 100 mL eggplant-shaped flask, and 670 mg (4.5 mmol) 2,6-dichloropyridine, 230 mg (0.4 mmol) tetrakis (triphenylphosphine) palladium ( 0), 4.8 g (35 mmol) of potassium carbonate, 20 mL of tetrahydrofuran and 10 mL of ion-exchanged water were added, and the mixture was refluxed for 8 hours under a nitrogen atmosphere. After cooling the reaction solution to room temperature, the separated aqueous layer was discarded, and the solvent was distilled off by concentration under reduced pressure to obtain 5 g of a yellow oil. This oil was purified by silica gel column chromatography (hexane: ethyl acetate = 3: 1) and sublimation purification to give 2.1 g of the title compound (BPP) as white crystals. The structure of BPP was identified by ¹ H and ¹³ C-NMR and mass spectrometry.

¹ H-NMR (400 MHz, CDCl ₃ ) δ ppm: 6.310 (2H, d), 6.587-6.610 (6H, m), 6.950 (4H, t), 7.035-7.120 (5H, m), 7.306-7.371 ( 4H, m), 7.436 (4H, t), 7.503 (2H, t), 7.701 (2H, d), 7.913 (4H, d)
¹³ C-NMR (100 MHz, CDCl ₃ ) δ ppm: 103.791, 120.770, 125.648, 127.572, 127.638, 127.746, 127.788, 127.837, 128.501, 128.683, 129.198, 129.281, 131.130, 132.897, 135.419, 136.995, 137.492, 145.770, 151.634, 154.654
DIMS (EI) m / z: 667

Example 2 (Measurement of absorption spectrum, fluorescence and low-temperature phosphorescence spectrum of BPP thin film)
The pyrazole derivative (BPP) of the present invention was deposited on a quartz substrate (for absorption spectrum measurement) and a silicon substrate (for fluorescence and low-temperature phosphorescence spectrum measurement) to a thickness of 1000 mm, respectively, and the absorption spectrum and fluorescence spectrum at room temperature, The phosphorescence spectrum at low temperature (5 K) was measured (FIGS. 1-3). BPP has a very high triplet energy because it has a first emission peak in the vicinity of a wavelength of 450 nm, particularly in the low-temperature phosphorescence spectrum (FIG. 3).

Example 3 (Measurement of absolute emission quantum yield of FIrpic using BPP as a host material)
FIrpic and the pyrazole derivative (BPP) of the present invention were co-evaporated on a quartz substrate at a weight ratio of 1: 9, and the film thickness was 1000 mm. This substrate is introduced into an integrating sphere, irradiated with ultraviolet light with a wavelength of 280 nm, and the ratio of the number of photons emitted by the emission from FIrpic to the number of photons absorbed by BPP (hereinafter referred to as absolute emission quantum yield). ) Was measured. As a result of the measurement, the absolute luminescence quantum yield value obtained was almost 100%. This suggests that the energy transfer occurring between the host and the luminescent material is attributed only to the inflow from BPP to FIrpic, and there is no backflow of energy from FIrpic to BPP. Therefore, it was predicted that a blue phosphorescent device having very high luminous efficiency can be constructed by using the BPP of the present invention as a light emitting layer host of an organic EL device.

Example 4 (Organic EL device containing BPP as light emitting layer host)
On a glass substrate on which indium-tin oxide (ITO) was sputtered to a thickness of 1100 mm, 400 nm of NPD was vacuum deposited as a hole injection layer, and then mCP was vacuum deposited to a thickness of 100 mm as a hole transport layer. On top of that, FIrpic and the pyrazole derivative (BPP) of the present invention were co-evaporated as a light emitting layer at a weight ratio of 1: 9, and the film thickness was 200 mm. Further, 400 BP of BPhen was deposited as an electron transport layer. In this state, it was confirmed that the deposited organic thin film was uniform amorphous. On this organic thin film, 1000 wt% of a 10 wt% silver-magnesium alloy was co-deposited, and then silver was evaporated to a thickness of 100 mm. The light emission characteristics of the organic EL device obtained by the above operation are shown in FIGS.
When the voltage of 3.2 V or more is applied to the organic EL element, a current flows, and exhibits excellent charge transport properties and luminous efficiency from applied voltage-current density characteristics (FIG. 4) and current density-external quantum efficiency characteristics (FIG. 5). It was confirmed. The organic EL device shows a blue emission spectrum derived from FIrpic that shows a peak at a wavelength of about 450 to 500 nm, but no other emission (e.g., emission caused by exciplex formation or emission from BPP) is observed. (FIG. 6). Note that the maximum value of the external quantum efficiency of this device was 9%, and it was possible to obtain high luminance with low voltage driving.

It is a figure which shows the absorption spectrum of a BPP thin film. It is a figure which shows the fluorescence spectrum of a BPP thin film. It is a figure which shows the phosphorescence spectrum of a BPP thin film. It is a figure which shows the applied voltage-current density characteristic of the organic EL element which contains BPP as a light emitting layer host. It is a figure which shows the current density-external quantum efficiency characteristic of the organic EL element which contains BPP as a light emitting layer host. It is a figure which shows the emission spectrum of the organic electroluminescent element containing BPP as a light emitting layer host.

Claims (2)

General formula (1):
Wherein, R ¹ to R ⁸ are the same or different and each represents a hydrogen atom, an alkyl group or an alkoxy group; ring A~E are the same or different and indicates a benzene ring or a pyridine ring; binding to ring E The bond between the pyrazole ring and ring E on the benzene ring is in the ortho position. ]
A light emitting layer containing a pyrazole derivative represented by:
An organic EL device, wherein the light emitting layer contains a light emitting material . The luminescent material, characterized in that it is a blue phosphorescent material, according to claim 1 Symbol placement of the organic EL element.