JP3191374B2 - Organic electroluminescence device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescence device (organic EL device). Specifically, the present invention relates to an organic EL device using a conjugated copolymer as a light emitting material.

[0002]

2. Description of the Related Art An inorganic electroluminescent element (inorganic EL element) using an inorganic phosphor as a light emitting material is used in, for example, a planar light source as a backlight or a display device such as a flat panel display. Needed a high voltage AC. Recently, Tang et al. Manufactured an organic EL device having a two-layer structure in which an organic fluorescent dye was used as a light emitting layer, and an organic charge transporting compound used for an electrophotographic photoreceptor, etc. A high-efficiency, high-brightness organic EL device has been realized (Japanese Unexamined Patent Publication No.
194393). Compared to inorganic EL devices, organic EL devices have features that they can easily emit light of many colors in addition to low-voltage driving and high luminance. Attempts have been reported (Japanese Journal of Applied Physics (Jpn. J. Appl. Ph.
ys. 27, L269 (1988)], [Journal of Applied Physics (J. Ap)
pl. Phys. Vol. 65, p. 3610 (1989)
Year)〕. Heretofore, low-molecular weight organic fluorescent dyes have been generally used for the light-emitting layer, and high-molecular-weight light-emitting materials have been described in WO 9013148,
No.-126787, Applied Physics Letters (Appl. Phys. Lett.) Vol. 58,
It was only proposed on pages 1982 (1991).

[0003]

However, the organic EL devices using the polymer light emitting materials which have been reported so far have a high driving voltage and the brightness is not always sufficient. The polymer light-emitting material is thermally stable and can easily form a light-emitting layer having excellent uniformity by a coating method. Therefore, an organic EL device having a lower driving voltage and a higher luminance while utilizing these advantages. Is required.

An object of the present invention is to provide a low-voltage driven, high-brightness organic EL device using a polymer light-emitting material as a light-emitting layer.

[0005]

Means for Solving the Problems The present inventors have intensively studied low voltage driving and high luminance of an organic EL device using a polymer light emitting material as a light emitting layer. As a result, they have found that a low-voltage driven, high-brightness organic EL device can be realized by using a conjugated copolymer as a light-emitting layer as a high-molecular light-emitting material, leading to the present invention.

That is, the present invention relates to an organic electroluminescent device having at least a light emitting layer between a pair of anodes and cathodes, at least one of which is transparent or translucent, wherein the light emitting layer has the following formula (1)- Ar-CH = CH- (1) [wherein Ar is an aromatic group or a heterocyclic compound group forming a continuous carbon-carbon conjugate bond with a vinylene group], and is composed of at least two types of repeating units. Including a conjugated copolymer, the repeating unit constituting the conjugated copolymer has an energy at the light absorption end wavelength of each homopolymer of the repeating unit of 0 between the maximum and the minimum. An object of the present invention is to provide an organic electroluminescent element comprising a combination of elements having a difference of 0.05 eV or more.

Hereinafter, the organic EL device according to the present invention will be described in detail. The conjugated copolymer as a light emitting material used in the present invention has a repeating unit having at least two kinds of repeating units represented by the formula (1). Ar is represented by the following chemical formula 2.

[0008]

Embedded image (R _{1 to} R ₅₇ each independently represent hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkoxy group and an alkylthio group, an aryl group and an aryloxy group having 6 to 18 carbon atoms, and a heterocyclic compound group having 4 to 14 carbon atoms A group selected from the following.).

Among these, phenylene group and substituted phenyl
Len group, biphenylene group, substituted biphenylene group, naphthy
Len, substituted naphthylene, thienylene and substituted thi
Enylene groups are preferred. Here, the substituent is described.
And an alkyl group having 1 to 20 carbon atoms, for example,
Tyl, ethyl, propyl, butyl, pentyl
Group, hexyl group, heptyl group, octyl group, lauryl group
Such as methyl, pentyl, hexyl, hep
A tyl group is preferred. Or alkoxy having 1 to 20 carbon atoms
As the group, a methoxy group, an ethoxy group, a propoxy group,
Butoxy, pentyloxy, hexyloxy, f
Butyl, lauryloxy, etc.
Si, ethoxy, pentyloxy, hexyloxy
And a heptyloxy group are preferred. An alkylthio group
Are methylthio, ethylthio, propylthio,
Butylthio, pentylthio, hexylthio, hept
Such as tylthio, octylthio, laurylthio, etc.
Methylthio, ethylthio, pentylthio,
Xylthio and heptylthio are preferred. Aryl group
Represents a phenyl group, 4-C₁~ C₁₂Alkoxyfe
Nyl group, 4-C₁~ C ₁₂Alkylphenyl group, 1-naph
Examples thereof include a tyl group and a 2-naphthyl group. Arlio
Examples of the xyl group include a phenoxy group. Heterocyclization
As the compound group, 2-thienyl group, 2-pyrrolyl group, 2-
Examples include a furyl group, a 2-, 3- or 4-pyridyl group, and the like.
Is done.

From these recurring units, at least two types of recurring units having a difference of 0.05 eV or more in energy between the maximum and minimum wavelengths at the light absorption edge in the case of a homopolymer are selected. By the combination, a light-emitting material that gives an organic EL element with high light-emitting intensity can be obtained. In order to obtain a conjugated copolymer having good film-forming properties such as solubility in a solvent, Ar in at least one of the repeating units is an alkyl group having 4 to 20 carbon atoms, an alkoxy group or an alkylthio group, and 6 to 6 carbon atoms. It is preferably an aromatic group or a heterocyclic compound group having one or more aryl groups or aryloxy groups of 18 or a heterocyclic compound group having 4 to 14 carbon atoms as a substituent. The number of repeating units constituting one copolymer need not be two, but may be three or more.

The copolymerization ratio is such that the number of at least one kind of repeating unit constituting the copolymer is 5 to 95% in the copolymer.
%, More preferably in the range of 10 to 90%. In addition, as the conjugated copolymer used for the light emitting material, there are a random copolymer, a block copolymer, an alternating copolymer, and the like, all of which are suitably used, but having substantially regularity in the chain. The conjugated alternating copolymer represented by the following formula (3) is preferable because the structure control during synthesis is relatively easy and the solubility is excellent.

[0012]

Embedded image [In the formula, Ar ₁ and Ar ₂ are groups selected from Ar in the formula (1), and at least one of Ar ₁ and Ar ₂ has an alkyl group, an alkoxy group or an alkylthio group having 4 to 20 carbon atoms, and has 6 carbon atoms. An aromatic group or a heterocyclic compound group having at least one aryl group or aryloxy group of 1 to 18 or a heterocyclic compound group having 4 to 14 carbon atoms;
l and m are integers of 1 or more, n is an integer of 1 or more, and (l + m) × n is an integer of 3 or more, 0.1 <l / m <1
0. Here, Ar ₁ or Ar ₂ may be selected so as to satisfy the condition that the energy difference of the light absorption end wavelength of the homopolymer composed of the respective repeating units is different by 0.05 eV or more. As a preferred alternating copolymer as a light emitting material, l and m are 1, and examples thereof include copolymers having a repeating structure represented by the following chemical formulas 4, 5, and 6.

[0013]

Embedded image

[0014]

Embedded image and

[0015]

Embedded image (In the above structural formula, the substituents R _{58 to} R ₇₁ are each independently an alkyl group, an alkoxy group or an alkylthio group having 4 to 20 carbon atoms, an aryl group or an aryloxy group having 6 to 18 carbon atoms, or The same combination of repeating units as those described above is preferable also in a random copolymer, a block copolymer and the like.

In these, the substituents R _{58 to} R ₇₁ are a pentyl group, a hexyl group, a heptyl group, a pentyloxy group, a hexyloxy group, a heptyloxy group, a pentylthio group,
Those which are a hexylthio group or a heptylthio group are particularly preferred.

The degree of polymerization of the conjugated copolymer used in the present invention is not particularly limited and varies depending on the structure of the repeating unit. However, from the viewpoint of film-forming properties, it is generally 3 to 10,000, preferably 5 to 3000. Preferably it is 10-2000. In the conjugated copolymer having regularity in the chain represented by Chemical Formula 3, n represents the number of repeating units of the copolymer, and the preferred range depends on the number of repeating units and the values of l and m. Is different. When l + m is 2, n is preferably 5 or more because it has good film-forming properties, while 1 + m is 1
In the case of 0 or more, n is preferably 1 or more because it has a good film-forming property.

When a film is formed from a solution by using these organic solvent-soluble conjugated copolymers, it is only necessary to remove the solvent by drying after coating the solution.
The same method can be applied to the case where a charge transport material described later is mixed, which is very advantageous in production.

When a conjugated copolymer is used as a light-emitting material, the light-emitting site in the copolymer is not necessarily clear.
It is considered that the presence of the portion of the repeating unit having a small (band gap) contributes to light emission, and the difference of the absorption edge wavelength energy (band gap) of the homopolymer composed of each repeating unit is 0.05 eV. Conjugated copolymers having the above are preferred. This difference is 0.
If it is less than 05 eV, excitons are diffused by thermal energy even at about room temperature, and it is considered that the luminous efficiency does not always increase. In particular, when Ar ₁ and Ar ₂ each have a different skeleton group such as a phenylene group and a heterocyclic compound group, the difference in band gap can be increased.

A typical copolymer comprising a repeating unit represented by the above formula (3) is an arylene vinylene-based copolymer, and the synthesis method is not particularly limited. JP-A-1-792
The copolymer can be obtained using a method similar to that described in JP-A No. 17-No. That is, for example, two or more corresponding bis (methyl halide) compounds, more specifically, for example, 2,5-diheptyloxy-p-
A dehydrohalogenation method in which xylylene dibromide and p-xylylene dibromide are copolymerized in a xylene / tertiary butyl alcohol mixed solvent using tertiary butoxy potassium. In this case, it is usually a random copolymer, but if an oligomer is used, a block copolymer can also be obtained.

The corresponding bis (methyl halide)
Compounds, more specifically, for example, 2,5-diheptyl
Oxy-p-xylylenedibromide is converted to N, N-dimethyl
Reacts with triphenylphosphine in formamide solvent
To synthesize the phosphonium salt,
Compound, more specifically, for example, terephthalaldehyde
For example, in ethyl alcohol, lithium ethoxide
Wittig reaction for polymerization using
You. In this case, an alternating copolymer is obtained. Ar ₁Group
Or Ar_TwoGroup) and Ar_Two
Group (or Ar ₁Group) having a dialdehyde compound
To obtain an alternating copolymer (l = m = 1 in Chemical Formula 3).
Is obtained). Of course, Ar₁And Ar_TwoIs the same group
is not. In addition, phosphonium salts or dialdehydes
Either or both of the compounds are two or more compounds
If it is a mixture, all these copolymers are obtained.
In addition, the corresponding sulfonium salt is added in the presence of an alkali.
Polymerized and then treated with sulfonium salt
Examples thereof include a salt decomposition method. In addition, these conjugated systems
When the copolymer is used as a light emitting material of an organic EL device,
Since the purity affects the emission characteristics,
Purification such as purification and separation by chromatography
Is desirable.

In the structure of the EL device of the present invention, the light emitting material comprising the conjugated copolymer is used in a light emitting layer provided between a pair of anodes and cathodes, at least one of which is transparent or translucent. If so, there is no particular limitation, and a known structure is adopted. For example, a pair of electrodes are formed on both surfaces of a light-emitting layer formed of the copolymer or a light-emitting layer formed of a mixture of the copolymer and a charge transport material (which is a general term of an electron transport material and a hole transport material). And a structure in which an electron transporting layer containing an electron transporting material between a light emitting layer and a cathode and / or a hole transporting layer containing a hole transporting material between a light emitting layer and an anode are further laminated. . Further, the present invention includes a single light emitting layer and a charge transporting layer and a combination of a plurality of layers. Further, a light emitting material other than the conjugated copolymer described below, for example, may be mixed and used in the light emitting layer. Further, a layer in which the conjugated copolymer and / or the charge transporting material is dispersed in a polymer compound can be used.

As the charge transporting material to be used together with the conjugated copolymer used in the present invention, that is, an electron transporting material or a hole transporting material, known materials can be used. Is a pyrazoline derivative,
Arylamine derivatives, stilbene derivatives, triphenyldiamine derivatives, and the like include electron transport materials such as oxadiazole derivatives, anthraquinodimethane and its derivatives, benzoquinone and its derivatives, naphthoquinone and its derivatives, anthraquinone and its derivatives, and tetracyanoanthra. Examples include quinodimethane and its derivatives, fluorenone derivatives, diphenyldicyanoethylene and its derivatives, and diphenoquinone derivatives.

Specifically, JP-A-63-70257,
JP-A-63-175860, JP-A-2-135359
And the same as those described in JP-A-2-135361, JP-A-2-209988, JP-A-3-37992, and JP-A-3-152184. Examples of the hole transport material include triphenyldiamine derivatives, As the electron transporting material, oxadiazole derivatives, benzoquinone and its derivatives, and anthraquinone and its derivatives are preferable. In particular, as the hole transporting material, N, N'-diphenyl-N,
N'-bis (3-methylphenyl) -1,1'-biphenyl-4,4'-diamine;
(4-biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole, benzoquinone,
Anthraquinone is preferred. Among them, one or both of the electron transporting compound and the hole transporting compound may be used simultaneously. These may be used alone or as a mixture of two or more. The amount of the charge transporting material varies depending on the kind of the compound used and the like. Therefore, the amount may be appropriately determined in consideration of a sufficient range in which the film-forming property and the light-emitting characteristics are not impaired.

The known light-emitting material which can be used together with the conjugated copolymer used as the light-emitting material in the present invention is not particularly limited. , Coumarin-based, cyanine-based dyes, metal complexes of 8-hydroxyquinoline and its derivatives, aromatic amines, tetraphenylcyclopentadiene and its derivatives, tetraphenylbutadiene and its derivatives, and the like. Specifically, for example, JP-A-57-51781, 59-194
Known ones, such as those described in JP-A-393, can be used.

Next, a typical method for manufacturing the organic EL device of the present invention will be described. A pair of electrodes consisting of an anode and a cathode, as a transparent or translucent electrode, glass,
A transparent or translucent electrode formed on a transparent substrate such as a transparent plastic is used. As the material of the anode, a conductive metal oxide film, a translucent metal thin film, or the like is used. Specifically, indium tin oxide (ITO), tin oxide (NESA), Au, Pt, A
g, Cu, etc. are used. As a manufacturing method, a vacuum evaporation method, a sputtering method, a plating method, or the like is used.

Next, a luminescent layer containing the conjugated copolymer or a luminescent material containing the conjugated copolymer and a charge transport material is formed on the anode as a luminescent material. Examples of the forming method include a coating method such as a spin coating method, a casting method, a dipping method, a bar coating method, a roll coating method, or a vacuum evaporation method using a solution or a mixed solution of these materials. The spin coating method,
It is particularly preferable to form a film by a coating method such as a casting method, a dipping method, a bar coating method, and a roll coating method.

The thickness of the light emitting layer is 5 to 10 μm, preferably 10 to 1 μm. In order to increase the current density and the luminous efficiency, the range of 100 to 5000 ° is preferable. When a thin film is formed by a coating method, the solvent is removed, and thus, under a reduced pressure or an inert atmosphere, 30 to 30 minutes.
The heat treatment is desirably performed at a temperature of 200 ° C, preferably 60 to 100 ° C.

In the case of laminating a light emitting layer and a charge transporting layer (which is a general term of a hole transporting layer and an electron transporting layer), which is another embodiment, before forming the light emitting layer by the above-described film forming method. A hole transport layer is formed on the anode, and / or an electron transport layer is formed thereon after providing the light emitting layer.

The method for forming the charge transport layer is not particularly limited, but is a vacuum deposition method from a powder state, or a spin coating method after dissolving in a solution, a casting method, a dipping method, a bar coating method, a roll coating method. Or a coating method such as spin coating, casting, dipping, bar coating, roll coating, etc. after mixing and dispersing a polymer compound and a charge transport material in a solution state or a molten state. Can be used. The polymer compound to be mixed is not particularly limited, but preferably does not extremely inhibit charge transport,
In addition, those that do not have strong absorption for visible light are preferably used.

For example, poly (N-vinylcarbazole), polyaniline and its derivatives, polythiophene and its derivatives, poly (p-phenylenevinylene) and its derivatives, poly (2,5-thienylenevinylene) and its derivatives, polycarbonate, Examples thereof include polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, and polysiloxane. It is preferable to use a coating method in that the film can be easily formed.

The thickness of the charge transport layer is required to be at least such that pinholes do not occur. However, if the thickness is too large, the resistance of the device increases and a high drive voltage is required, which is not preferable. Therefore, the thickness of the charge transport layer is 5Å to 1
0 μm, preferably 10 ° to 1 μm, more preferably 50 to 2000 °.

Next, an electrode is provided on the light emitting layer or the electron transport layer. 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, M
A g-Ag alloy, an In-Ag alloy, a Mg-In alloy, a graphite thin film, or the like is used. As a method for manufacturing the cathode, a vacuum evaporation method, a sputtering method, or the like is used.

[0034]

In the present invention, the conjugated copolymer is excellent as a luminescent material because it has a relatively high melting point and decomposition temperature, is thermally stable, and has excellent uniformity easily by a coating method. Can be formed, so that an element with low driving voltage and high luminance can be manufactured.

[0035]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited to these examples.

Example 1 <Synthesis of Copolymer> A phosphonium salt was synthesized by reacting 2,5-diheptyloxy-p-xylylenedibromide with triphenylphosphine in an N, N-dimethylformamide solvent. 14.8 g of this phosphonium salt and 2.0 g of terephthalaldehyde were added to ethyl alcohol 10
0 g was dissolved. Separately, 0.24 g of lithium was reacted with 70 g of ethyl alcohol to obtain lithium ethoxide. This lithium ethoxide was added dropwise to a solution of phosphonium salt and terephthalaldehyde in ethyl alcohol, and polymerized by a Wittig reaction at room temperature. The precipitate was separated by filtration, washed with ethyl alcohol, and dried to obtain 3.0 g of an alternating copolymer of 2,5-diheptyloxy-p-phenylenevinylene and p-phenylenevinylene.

<Preparation of Element>
On a glass substrate with a 200 mm thick ITO film,
5-diheptyloxy-p-phenylenevinylene and p-
Using a 0.65 wt% chloroform solution of an alternate copolymer of phenylene vinylene, spin coating was performed at 3100 °.
With a thickness of Next, this was dried at 60 ° C. for 1 hour under reduced pressure, and then indium was applied thereon as a cathode.
An organic EL device was prepared by vapor deposition at 00 °. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 26.7 V was applied to this element, the current density was 49.2.
A current of mA / cm ² flowed, and yellow-green EL emission with a luminance of 144 cd / m ² was observed. Brightness was proportional to current density. Also, the voltage required to achieve a luminance of ²⁰ cd / m ² was 24.6 V. The band gap determined from the absorption edge wavelength of the UV absorption spectrum of the homopolymer composed of each of the above repeating units produced by a known method,
Poly (2,5-diheptyloxy-p-phenylenevinylene) was 2.12 eV, poly (p-phenylenevinylene) was 2.42 eV, and the difference was 0.30 eV.

Example 2 The alternating copolymer used in Example 1 was used as an electron transporting material.
Organic EL was prepared in the same manner as in Example 1 except that a light-emitting layer was provided by mixing 5% by weight of-(4-biphenylyl) -5- (4-t-butylphenyl) -1,3,4-oxadiazole.
A device was created. The thickness of the light emitting layer was 1370 °.
When a voltage of 16.7 V was applied to this device, a current having a current density of 253.9 mA / cm ² flowed and a luminance of 237 cd
/ M ² yellow-green EL emission was observed. Brightness was proportional to current density. Further, the voltage for achieving a luminance of ²⁰ cd / m ² was 15.4 V.

Comparative Example 1 <Synthesis of poly (2,5-diheptyloxy-p-phenylenevinylene)> According to the method described in Example 5 of JP-A-1-79217, 2,5-diheptyloxy- p
-Xylylenedibromide was polycondensed with potassium t-butoxy to obtain poly (2,5-diheptyloxy-p-phenylenevinylene) (HO-PPV).

<Preparation of device> HO-PPV was used instead of the alternating copolymer of 2,5-diheptyloxy-p-phenylenevinylene and p-phenylenevinylene, and a mixed solvent of chloroform and toluene (weight ratio) 3/2)
An organic EL device was prepared in the same manner as in Example 1 except that the above was used. The thickness of the light emitting layer was 980 °. When a voltage of 33.3 V was applied to this element, the current density was 617.0.
A current of mA / cm ² flowed, but only orange EL emission with a luminance of 26 cd / m ² was observed. Brightness was proportional to current density. Further, the voltage for obtaining a luminance of ²⁰ cd / m ² was 32.9 V.

[0041] In Comparative Example 2 <poly (p- phenylenevinylene) Synthesis of Intermediate> JP-2-32121 Patent described in Example 2 of the method of the publication, poly (p- phenylenevinylene) (PPV) of Intermediate Cl ^-
A methanol solution of the salt was obtained.

<Preparation of device> 0.22w of PPV intermediate
A film is formed by spin coating using a t% methanol solution, and then heat-treated at 200 ° C. under reduced pressure for 2 hours to form PP.
A V thin film was formed to form a light emitting layer. The thickness of this layer is 150
It was 0 °. On top of that, as a cathode, aluminum
An organic EL device was prepared by vapor deposition at 000 °. The degree of vacuum at the time of vapor deposition was 3 × 10 ⁻⁶ Torr or less. When a voltage of 28.0 V was applied to this device, the current density was 18.1 V
Although a current of mA / cm ² flowed, the luminance was 0.92 cd / m ^2.
Only yellow-green EL emission was observed. The brightness was almost proportional to the current density. Further, when the voltage was increased, the luminance could not be increased to 20 cd / m ² due to dielectric breakdown.

[0043]

As described above, the organic EL device using the conjugated copolymer of the present invention as a light emitting material can be driven at a lower voltage and has improved luminance as compared with a conventional device. It can be used as a device such as a planar light source as a backlight or a flat panel display.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-244630 (JP, A) International Publication 90/13148 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C09K 11/06 CA (STN) REGISTRY (STN)

Claims (4)

(57) [Claims] 1. An organic electroluminescent device having at least one light-emitting layer between an electrode comprising a pair of anodes and cathodes, at least one of which is transparent or translucent, wherein the light-emitting layer has the following formula (1) -Ar-CH = CH- (1) [where Ar is an aromatic group or a heterocyclic compound group forming a continuous carbon-carbon conjugate bond with a vinylene group] Including a polymer, the repeating unit constituting the conjugated copolymer, the energy of the light absorption edge wavelength of each homopolymer of the repeating unit is 0.05 eV or more between the maximum and minimum. An organic electroluminescent element comprising a combination of elements having a difference of 2. An alkyl group having 4 or more carbon atoms, an alkoxy group and an alkylthio group, and an aryl group having 6 or more carbon atoms, wherein at least one of the repeating units represented by the formula (1) is
And an aromatic or heterocyclic compound group forming a carbon-carbon conjugated bond having at least one substituent selected from an aryloxy group and a heterocyclic compound group having 4 or more carbon atoms. The organic electroluminescent device according to claim 1, wherein 3. The conjugated copolymer is represented by the following formula 1, Wherein Ar ₁ and Ar ₂ are an aromatic group or a heterocyclic compound group forming a continuous carbon-carbon conjugate bond with a vinylene group,
And at least one of Ar ₁ and Ar ₂ is at least one selected from an alkyl group having 4 or more carbon atoms, an alkoxy group and an alkylthio group, an aryl group and an aryloxy group having 6 or more carbon atoms, and a heterocyclic compound group having 4 or more carbon atoms. An aromatic group or a heterocyclic compound group having at least one kind of a substituent, l and m are integers of 1 or more, and n is 1
(L + m) × n is an integer of 3 or more;
1 <l / m <10. The organic electroluminescence device according to claim 1, wherein the organic electroluminescence device is a copolymer represented by the following formula: 4. The conjugated copolymer is represented by the formula 1
The organic electroluminescence device according to claim 3, wherein the organic electroluminescence device is an alternating copolymer of = 1.