JP2009040857A - Polythiophene and electroluminescent material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electroluminescent material excellent in luminescent characteristics. <P>SOLUTION: This polythiophene of which recurring unit is expressed by formula (1) [wherein, R<SP>1</SP>is an alkyl or formula (2) äwherein, R<SP>2</SP>is an alkyl; and (l) is an integer of 0 to 5}; (+) is a single bond; and the number of recurring units is a positive number of 10 to 100] is provided. By using the polythiophene as the electroluminescent material for an organic electroluminescent element, it is possible to prepare the electroluminescent material excellent in the luminescent characteristics. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a novel polythiophene and an electroluminescent material comprising the compound.

  An organic electroluminescence element (hereinafter referred to as “organic EL element”) is expected to be used as a solid light emitting type inexpensive large-area full-color display element, and is currently being actively developed. In general, an organic EL element is composed of a light emitting layer and a pair of counter electrodes sandwiching the layer. In light emission, when an electric field is applied between both electrodes, electrons are injected from the cathode and holes are injected from the anode. Furthermore, the electrons and holes are recombined in the light emitting layer, and energy is emitted as light when the energy level returns from the conduction band to the valence band.

  As a technique for realizing a low-voltage driven, high-efficiency, high-brightness organic EL device, Tang et al. Have used a hole-transporting layer made of a hole-transporting compound at the anode and an electron transport made of an electron-transporting light-emitting compound An element having a multilayer structure in which layers are stacked has been proposed. Among these, the hole transport layer facilitates the injection of holes from the anode, easily transports holes with a large hole drift mobility, and blocks electrons with a small electron drift mobility, And a function of increasing the recombination probability in the light emitting layer. However, when the charge injection efficiency into the light emitting layer is insufficient, a hole injection layer using a hole injection material is provided between the anode and the hole transport layer.

As such a hole injection material, various materials have been studied, and a thiophene-based material has also been studied. For example, an oligothiophene material composed of a thiophene hexamer (Non-Patent Document 1) has been studied, but is not yet at a sufficient level, and the maximum emission intensity of an EL element produced using α-6T (α-sexithiophene) is About 4 cd / m ² (applied voltage: 18 V).

Sung-Taek Lim et al., Synthetic Metals, 117, 229, 2001.

  An object of the present invention is to provide an electroluminescent material that gives excellent light emission characteristics, and in particular, a hole injection material.

  As a result of diligent studies to solve the above-mentioned problems, the present inventors have found that polythiophene having a specific structure has a hole injecting ability that provides high emission characteristics, and has provided the present invention. It was.

That is, the present invention
The repeating unit is represented by the following formula (1)

[Wherein R ¹ represents an alkyl group or the following formula (2)

{Wherein R ² is an alkyl group, and l is an integer of 0 to 5. }
+ Represents a single bond and is a positive number having 10 to 100 repeating units. ]
It is polythiophene shown by these.

  Further, the present invention provides the following formula (3)

[Wherein R ³ represents an alkyl group or the following formula (4)

{Wherein R ⁴ is an alkyl group, and m is an integer of 0 to 5. }
And n is a positive number from 5 to 50. ]
It is polybithiophene shown.

  Furthermore, another aspect of the present invention is an electroluminescent material comprising the polythiophene or polybithiophene.

  Since the polythiophene of the present invention operates at a high current density, particularly when used as a hole injection material, it is extremely useful as an electroluminescent material constituting an organic EL device.

The polythiophene of the present invention is represented by the formula (1). In Formula (1), R ¹ is an alkyl group or a group represented by Formula (2). The alkyl group may be linear or branched and has 1 to 8 carbon atoms. Examples of suitable groups as the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a 2-butyl group, an n-octyl group, and a 2-ethylhexyl group. Examples of the group represented by the formula (2), l is an integer of 0 to 5, ^{R 2} is equivalent to ^{R 1.}

  The number of repeating units of the polythiophene of the present invention is a positive number of 10 to 100, and is preferably a positive number of 10 to 80 from the viewpoint of film formability. Here, the number of repeating units is the number of repeating thiophene units in polythiophene and refers to a value obtained by dividing the weight average molecular weight of polythiophene by the unit molecular weight of thiophene.

  In the polythiophene of the present invention, as long as the number of repeating units satisfies the above range, thiophenes may be regularly bonded in the same direction, or thiophenes may be bonded in alternate directions. The polythiophene of the present invention may have thiophene bonded in an irregular direction. That is, in the polythiophene of the present invention, if the repeating unit is the thiophene of the formula (1) and the number of repeating units is in the above range, the bonding direction of thiophene is not specified.

  The method for producing the polythiophene of the present invention is not particularly limited, and any synthesis method may be used. Examples thereof include a method of treating thiophene with an oxidizing agent such as iron chloride.

  The polythiophene of the present invention thus obtained can be isolated and purified by performing treatments such as silica gel column purification, recrystallization and reprecipitation.

The polybithiophene of the present invention is represented by the above formula (3). In Formula (3), R ³ is an alkyl group or a group represented by Formula (4). The alkyl group may be linear or branched and has 1 to 8 carbon atoms. Examples of suitable groups as the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a 2-butyl group, an n-octyl group, and a 2-ethylhexyl group. Examples of the group represented by the formula (4), m is an integer of 0 to 5, ^{R 4} is equivalent to ^{R 2.}

  The degree of polymerization (n) of the polybithiophene of the present invention is a positive number of 5 to 50, and is preferably a positive number of 10 to 50 from the viewpoint of film formability. Here, the degree of polymerization (n) is the number of repeating bithiophene units in polybithiophene and refers to a value obtained by dividing the weight average molecular weight of polybithiophene by the bithiophene unit molecular weight.

  The production method of the polybithiophene of the present invention is not particularly limited, and any synthesis method may be used. For example, the following methods can be mentioned.

  That is, 3-alkoxythiophene is treated with a lithiating agent such as n-butyllithium or lithiated diisopropylamide to obtain 2-lithio-3-alkoxythiophene, followed by a coupling agent such as cupric chloride. 3,3′-dialkoxy-2,2′-bithiophene can be obtained. Furthermore, the poly3thiophene of this invention can be obtained by processing the obtained 3,3'- dialkoxy-2,2'-bithiophene with an oxidizing agent.

  The polybithiophene of the present invention thus obtained can be isolated and purified by performing treatments such as silica gel column purification, recrystallization and reprecipitation.

The polythiophene and polythiophene of the present invention (hereinafter sometimes referred to as the polymer of the present invention) generally exist as a colorless or pale yellow solid under normal temperature and normal pressure, and the structure thereof is a proton nuclear magnetic resonance spectrum ( ¹ H-NMR). It can be confirmed by an analytical method such as molecular weight measurement (gel permeation chromatography) or elemental analysis.

  The polythiophene and polybithiophene of the present invention (hereinafter referred to as the polymer of the present invention) have a feature of exhibiting hole injection characteristics superior to oligothiophene, and are preferably used as electroluminescent materials, particularly hole injection materials. In addition, an organic EL element can be produced using a hole injection material (electroluminescence material) made of the polymer of the present invention. Among the polymers of the present invention, polybithiophene exhibits superior properties compared to polythiophene. The reason is not clear, but it is assumed that polybithiophene is easier to increase the molecular weight.

  For the structure of the organic EL device using the hole injection material made of the polymer of the present invention, a hole injection layer containing the hole injection material of the present invention between a pair of electrodes at least one of which is transparent or translucent, There is no particular limitation as long as a hole transporting layer containing a hole transporting material, a light emitting layer or a layer in which a light emitting layer and a charge transporting layer are combined is formed, and a known structure can be adopted. For example, a hole injection layer containing the hole injection material of the present invention is provided on the anode, followed by a hole transport layer containing a hole transporting material, a light emitting layer thereon, and an electron transporter thereon. The thing which laminated | stacked the electron carrying layer can be mentioned. Further, the light emitting layer and the charge transport layer may be a single layer, or a plurality of layers may be combined.

  The known illuminant that can be used together with the hole injection material comprising the polymer of the present invention is not particularly limited. For example, naphthalene derivative, anthracene or derivative thereof, perylene or derivative thereof, polymethine, xanthene, coumarin, cyanine And the like, a metal complex of 8-hydroxyquinoline or a derivative thereof, an aromatic amine, tetraphenylcyclopentadiene or a derivative thereof, or tetraphenylbutadiene or a derivative thereof can be used. Specifically, for example, known ones such as those described in JP-A-57-51781 and JP-A-59-194393 can be used.

  Examples of known charge transporters that can be used together with the above-described hole injection material comprising the polymer of the present invention include pyrazoline derivatives, arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, polyvinylcarbazole. Examples of the electron transporter include oxadiazole derivatives, anthraquinodimethane or derivatives thereof, tetracyanoanthraquinodimethane or derivatives thereof, fluorenone derivatives, diphenoquinone derivatives, or 8-hydroxyquinoline or derivatives thereof. The metal complex of these can be mentioned.

  Specific examples of these compounds include JP-A-63-70257, JP-A-63-175860, JP-A-2-135359, JP-A-2-135361, JP-A-2-209998, and JP-A-3-37992. No. 3-152184 and the like.

  Among the above-described charge transporters, the hole transporter is preferably a triphenyldiamine derivative or polyvinylcarbazole derivative, and the electron transporter is preferably an oxadiazole derivative or a metal complex of 8-hydroxyquinoline or a derivative thereof. As the pore transporter, 4,4′-bis (N (3-methylphenyl) -N-phenylamino) biphenyl and polyvinylcarbazole derivatives are used, and as the electron transporter, 2- (4-t-butylphenyl) -1 is used. 3,4-oxadiazol, benzoquinone, anthraquinone and tris (8-quinolinol) aluminum are preferred.

  Among these, one or both of a hole transporter and an electron transporter can be used simultaneously. These materials may be used alone or in combination of two or more.

  Next, a typical method for producing an organic EL element using a hole injection material made of the polymer of the present invention will be described. First, an anode is formed on a transparent substrate such as glass or transparent plastic using a transparent or translucent metal oxide or metal thin film. As the material, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, a film (NESA etc.) made of conductive glass made of indium tin oxide (ITO), tin oxide or the like, Au, Pt, Ag, Cu or the like is used. As a manufacturing method, a vacuum deposition method, a sputtering method, a plating method, or the like is used.

  Next, a hole injection layer containing a hole injection material made of the polymer of the present invention is formed on the anode. Forming methods include vacuum deposition application method or melt solution of these materials, spin coating method using solution or mixed solution, casting method, dipping method, bar code method, roll coating method, gravure coating method, flexographic printing method, spraying A film can be formed by a coating method such as a coating method or an inkjet printing method.

  The thickness of the hole injection layer is preferably 1 nm to 1 μm, more preferably 2 to 500 nm. In order to increase the current density and increase the light emission efficiency, the range of 5 to 200 nm is preferable. In addition, when it thins by the apply | coating method, in order to remove a solvent preferably, it is heat-dried under the pressure of pressure reduction or an inert atmosphere, Preferably it is 30-300 degreeC, More preferably, it is 60-260 degreeC. desirable.

  Subsequently, a hole transport layer containing a hole transport material is formed. As a formation method, a method similar to that of the hole injection layer can be used.

  The film thickness of the hole transport layer is preferably 1 nm to 1 μm, more preferably 2 to 500 nm. In order to increase the current density and increase the light emission efficiency, the range of 5 to 200 nm is preferable. In addition, when it thins by the apply | coating method, Preferably it is 30-300 degreeC under reduced pressure or an inert atmosphere, and preferably 100-260 degreeC by the point which removes a solvent and raises a hole injection characteristic. It is desirable to heat and dry at a temperature.

  There are no particular limitations on the method for forming a film of a known light emitter or charge transporter, but a vacuum deposition method from a powder state, or a spin coating method after being dissolved in a solution, a casting method, a dipping method, a barcode method, a roll coating method A coating method such as a method can be used.

  The light emitting layer or the charge transport layer needs to have a thickness that does not generate pinholes at least. However, if the thickness is too large, the resistance of the device increases and a high driving voltage is required, which is not preferable. Therefore, the thickness of each layer is independently preferably 1 nm to 1 μm, more preferably 2 nm to 500 nm, and particularly preferably 5 nm to 200 nm.

  Next, a cathode is provided. This electrode becomes an electron injection cathode. The material is not particularly limited, but a material having a small ionization energy is preferable. For example, Al, In, Mg, Ca, Li, Mg—Ag alloy, In—Ag alloy, Mg—In alloy, Mg—Al alloy, Mg—Li alloy, Al—Li alloy, Al—Ca alloy, graphite thin film, etc. Is used. As a method for producing the cathode, a vacuum deposition method, a sputtering method, or the like is used.

  The material can also be used as a charge transport material, a single-layer electroluminescent material, and a potential-sensitive switching element.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

Example 1
3,3′-Dihexyloxy-2,2′-bithiophene was synthesized as follows. 28.6 ml of diethyl ether and 1.54 g (11.9 mmol) of diisopropylamine were placed in a 50 ml two-necked flask equipped with a reflux condenser, a 20 ml dropping funnel and a magnetic stirrer. At 0 ° C., 7.58 ml (11.9 mmol) of n-butyllithium in hexane (1.57M) was added dropwise, and the mixture was returned to room temperature and stirred for 1 hour to prepare lithium diisopropylamide (LDA). In a 200 ml three-necked flask equipped with a reflux condenser, a 50 ml dropping funnel, and a magnetic stirrer, 38.2 ml of diethyl ether and 2.0 g (10.9 mmol) of 3-hexyloxythiophene were placed. The LDA prepared previously was transferred to a 50 ml dropping funnel with a cannula, and the mixture was added dropwise and refluxed for 1 hour. This was cooled to −78 ° C., 1.60 g (11.9 mmol) of copper (II) chloride was added, and the mixture was slowly returned to room temperature and stirred overnight. After removing the salt by suction filtration, the solvent was distilled off by a rotary evaporator. The residue is purified by silica gel column chromatography using hexane: chloroform (9: 1) as a developing solvent, whereby the raw material 3-hexyloxythiophene is 0.58 g (recovery rate 29%), and white needle-like crystals are reduced to 0. Obtained in a yield of .74 g (37% yield). The white needle crystal was confirmed to be 3,3′-dihexyloxy-2,2′-bithiophene which is the target product from the following analysis results.
¹ H-NMR (400 MHz, δ in CDCl ₃ ) 0.90 (6H, t, J = 6.7 Hz, CH ₃ ), 1.35 (8H, m, CH ₂ CH ₂ ), 1.52 (4H, q, CH ₂ ), 1.84 (4H, q, CH ₂ ), 4.08 (4H, t, J = 6.3 Hz, OCH ₂ ), 6.83 (2H, d, J = 5.5 Hz, thiophene ring), 7.06 (2H, d, J = 5.5 Hz, thiophene ring); ¹³ C-NMR (100 MHz, δ in CDCl ₃ ) 14.05, 22.59, 25.73, 29.65, 31.56 (CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ ), 71.97 (OCH ₂ ), 114.09, 116.03, 121.59, 151.92 (thiophene ring); MS m / z 366 ( M ⁺ _{; Anal.Calcd for (C 20 H 30} O 2): C 65.53: H 8.25, Found: C 65.53: H 8.15.

Subsequently, poly (3,3′-dihexyloxy-2,2′-bithiophene) was synthesized as follows. A 50 ml two-necked flask equipped with a 10 ml dropping funnel and a magnetic stirrer was charged with 0.534 g (3.29 mmol) of anhydrous iron (III) chloride and 3.2 ml of chloroform. To a 10 ml dropping funnel, 0.302 g (0.823 mmol) of 3,3′-dihexyloxy-2,2′-bithiophene and 2.0 ml of chloroform were added dropwise at 0 ° C. over 30 minutes, followed by stirring for 4 hours. To this reaction solution, 50 ml of a 50% hydrazine aqueous solution was poured, returned to room temperature, and stirred overnight to dedope the reaction mixture. This was filtered through Celite to remove insoluble matters such as salts, extracted with chloroform, and dried over anhydrous magnesium sulfate. By distilling off the solvent with a rotary evaporator and reprecipitating with chloroform-hexane, 0.110 g (condensation) of poly (3,3′-dihexyloxy-2,2′-bithiophene) having the following physical properties was obtained as a dark purple film. Rate 37%).
Molecular weight (GPC): weight average molecular weight (Mw) = 6200, number average molecular weight (Mn) = 4300; ¹ H-NMR (400 MHz, δ in CDCl ₃ ) 0.91-1.88 (11H, m, CH ₃ CH _{2 CH 2 CH 2 CH 2)} , 4.13 (2H, m, OCH 2), divided by 6.84-7.08 (1H, m, thiophene ring ), bithiophene unit molecular weight the weight average molecular weight (366) The value, that is, the degree of polymerization (n) was 16.9.

Example 2
<EL emission characteristics>
One drop of the poly (3,3′-dihexyloxy-2,2′-bithiophene) chloroform solution (1 g / 1 L) obtained in Example 1 on a edged ITO substrate using a spin coater at 3000 rpm. By dropping, a thin film having a thickness of about 10 nm was produced. The obtained film was heat-treated at 250 ° C. for 20 minutes under a nitrogen stream. On top of that, a polyvinylcarbazole chloroform solution (3.6 g / 1 L) was dropped on an edged ITO substrate using a spin coater at a rate of 3000 rpm to produce a thin film having a thickness of about 60 nm. Subsequently, an Alq3 thin film was vacuum-deposited at a reduced pressure of 1 × 10 ⁻⁵ Pa to produce a film thickness of 60 nm. Further, a Mg—Ag alloy thin film as a cathode was vacuum-deposited by an electron beam method at a reduced pressure of 2 × 10 ⁻⁵ Pa to produce a film thickness of 170 nm.

When voltage was applied to the device, current began to flow from about 6 V, and light emission was observed. The maximum light emission intensity of this device was about 12000 cd / m ² (applied voltage 12.5 V).

Example 3
Poly (3-hexyloxythiophene) was synthesized in the following manner. A 100 ml two-necked flask equipped with a magnetic stirrer was charged with 0.777 g (4.79 mmol) of anhydrous iron (III) chloride and 24 ml of chloroform, and 0.201 g (1.20 mmol) of 3-hexyloxythiophene was added at −45 ° C. And stirred for 72 hours. To this reaction solution, 50 ml of a 50% hydrazine aqueous solution was poured, returned to room temperature, and stirred overnight to dedope the reaction mixture. This was filtered through Celite to remove insoluble matters such as salts, extracted with chloroform, and dried over anhydrous magnesium sulfate. The solvent was distilled off with a rotary evaporator, and reprecipitation with chloroform-methanol gave 0.0720 g (yield 36%) of poly (3-hexyloxythiophene) as a slightly viscous dark purple solid. The analysis data of the obtained dark purple solid is shown below.
Molecular weight (GPC): weight average molecular weight (Mw) = 2600, number average molecular weight (Mn) = 2000; ¹ H-NMR (400 MHz, δ in CDCl ₃ ) 0.91-1.88 (11H, m, CH ₃ CH _{2 CH 2 CH 2 CH 2)} , 4.13 (2H, m, OCH 2), 6.84-7.04 (1H, m, thiophene ring); Anal. Calcd for (C ₂₀ H ₃₀ O ₂ ): C 65.89: H 7.74, Found: C 64.18: H 7.63, the value obtained by dividing the weight average molecular weight by the thiophene unit molecular weight (183), The number of repeating units was 14.2.

Example 2 except that poly (3-hexyloxythiophene) obtained by the above method was vacuum-deposited on the ITO anode substrate by 10 nm instead of poly (3,3′-dihexyloxy-2,2′-bithiophene). A device was prepared in the same manner as described above. When voltage was applied to the device, current began to flow from about 6 V, and light emission was observed. The maximum light emission intensity of this device was about 7000 cd / m ² (applied voltage 12.5 V).

Example 4
Poly (3-methoxyethoxyethoxythiophene) was synthesized in the following manner. A 50 ml two-necked flask equipped with a 10 ml dropping funnel and a magnetic stirrer was charged with 0.776 g (4.78 mmol) of anhydrous iron (III) chloride and 4.3 ml of chloroform. To a 10 ml dropping funnel, 0.242 g (1.20 mmol) of 3-methoxyethoxyethoxythiophene and 1.5 ml of chloroform were added dropwise at 0 ° C. over 30 minutes and then stirred for 12 hours. To this reaction solution, 50 ml of a 50% hydrazine aqueous solution was poured, returned to room temperature, and stirred overnight to dedope the reaction mixture. This was filtered through Celite to remove insoluble matters such as salts, extracted with chloroform, and dried over anhydrous magnesium sulfate. By distilling off the solvent with a rotary evaporator and reprecipitating with chloroform-hexane, 0.090 g (yield 38%) of poly (3-methoxyethoxyethoxythiophene) was obtained as a slightly viscous dark purple solid. Analytical data for a dark purple solid is shown below.
Molecular weight (GPC): weight average molecular weight (Mw) = 3200, number average molecular weight (Mn) = 2500; ¹ H-NMR (400 MHz, δ in CDCl ₃ ) 3.36-4.29 (11H, m, CH ₃ OCH _{2 CH 2 OCH 2 CH 2 O} ), 6.77-7.03 (1H, m, thiophene ring) Anal. Cald for (C ₂₀ H ₃₀ O ₂ ): C 53.98: H 6.04, Found: C, 53.42: H 5.88, a value obtained by dividing the weight average molecular weight by the thiophene unit molecular weight (202), The number of repeating units was 15.8.

Example except that poly (3-methoxyethoxyethoxythiophene) obtained by the above method was vacuum-deposited by 10 nm on the ITO anode substrate instead of poly (3,3′-dihexyloxy-2,2′-bithiophene) A device was prepared in the same manner as in 2. When voltage was applied to the device, current began to flow from about 6 V, and light emission was observed. The maximum light emission intensity of this device was about 7000 cd / m ² (applied voltage 12.5 V).

  The polymer of the present invention can be used as an electroluminescent material of an organic electroluminescent element (organic EL element) that is expected to be used as a large-area full-color display element, particularly as a hole injection material.

Claims (4)

The repeating unit is represented by the following formula (1)

[Wherein R ¹ represents an alkyl group or the following formula (2)

{Wherein R ² is an alkyl group, and l is an integer of 0 to 5. }
+ Represents a single bond and is a positive number having 10 to 100 repeating units. ]
Polythiophene represented by Following formula (3)

[Wherein R ³ represents an alkyl group or the following formula (4)

{Wherein R ⁴ is an alkyl group, and m is an integer of 0 to 5. }
And n is a positive number from 5 to 50. ]
Polybithiophene represented by An electroluminescent material comprising the polythiophene according to claim 1. An electroluminescent material comprising the polybithiophene according to claim 2.