JP2002237384A - Organic electroluminescent element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a red color emitting organic EL element that is superior in stability. SOLUTION: In the organic EL element having an organic compound layer 200 between the first and second electrodes 12, 14, the luminous layer 24 is formed using the following material. That is, when, as a guest material ( coloring matter), a quinoline derivative compound as shown by formula (1) and a compound having a structure, in which one or more of the substitutional groups X1-X7 of the formula (1) are substituted by formula (2) and out of it at least in one the substitutional group has the double bond number n of 2 or more, is used, a triphenylamine derivative having the condensation polycyclic aromatic group of more than naphthalene is used as a host material. As the portion of the above condensation polycyclic aromatic group out of the molecules of the host material suppresses generation of distortion in the plane structure of the double bond portion of the molecules of the guest material, the emission of original long wavelength (red) of the guest material is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an organic electroluminescent device (hereinafter, referred to as an organic EL device), and more particularly to a device having a long wavelength light emitting function of yellow to red.

[0002]

2. Description of the Related Art An organic EL device is formed on a transparent glass substrate.
A transparent first electrode (for example, ITO), an organic compound layer containing an organic compound having strong fluorescence, and a metal (for example, Mg) second electrode are sequentially laminated.

The organic compound layer has, for example, a three-layer structure in which a hole transport layer, a light emitting layer, and an electron transport layer are sequentially stacked, and emits light by applying an electric field to a pair of electrodes. That is,
When holes are injected from the first electrode and electrons are injected from the second electrode,
The injected holes and electrons move in the hole transport layer, the light emitting layer, and the electron transport layer of the organic compound layer, collide and recombine, and disappear. The energy generated by the recombination is used to generate an excited state in the light-emitting molecule, whereby the organic EL element emits fluorescence.

In such an organic EL device, an aluminum quinolinol complex (Alq ₃ ) is well known as a light emitting material having a quinoline ring. This compound is obtained by substituting a hydroxyl group on the quinoline ring to form a complex with aluminum, and emits green light.

Further, as a red light emitting material of the organic EL device, a phthalocyanine derivative as disclosed in JP-A-7-288184 and a porphyrin derivative as disclosed in JP-A-9-296166 are known. I have.

[0006]

A currently known luminescent material containing a quinoline ring represented by Alq ₃ is as follows:
In each case, the conjugated system in the molecule is short, and only a blue-green emission function is obtained. In order to realize a full-color organic EL device, it is necessary to obtain a compound that emits light with good characteristics for other yellow to red colors.

On the other hand, the above-mentioned phthalocyanine derivatives and porphyrin derivatives have a function of emitting red light, but are insufficient in both luminance and durability, and satisfy all the required performances in applications such as organic EL devices. Not.

Japanese Patent Application Laid-Open Nos. Hei 7-65958 and Hei 8-231951 disclose an organic electroluminescent device obtained by doping a triphenylamine derivative with a dye. It has been reported that the deterioration of the resin was reduced and the durability was improved.
However, the elements obtained in these configurations are:
It does not have a sufficiently long-wavelength light-emitting function and does not emit yellow to red light.

Further, Japanese Patent Application Laid-Open No. 2000-86595 discloses that the use of a triphenylamine derivative having a condensed polycyclic aromatic compound as a hole transporting material improves the heat resistance of the device. It has been reported that rubrene and coumarin were added as dyes to obtain yellow and green luminescence. However, even in this configuration, red light emission is not obtained.

An object of the present invention is to provide an organic EL device having excellent stability and light emission luminance characteristics and a long-wavelength light-emitting function.

[0011]

In order to achieve the above object, the present invention provides an organic electroluminescent device comprising the following chemical formula (i):

Embedded image Wherein n in the formula is an organic compound layer obtained by adding a dye having a structure of 2 or more to a triphenylamine derivative having a condensed polycyclic aromatic compound of naphthalene or more.

Another feature of the present invention is that an organic electroluminescent device has the following general formula (1):

Embedded image A quinoline derivative compound represented by the formula (1)
A dye in which one or more of the substituents X _{1 to} X _{7 in} the formula (2) is added to a triphenylamine derivative having a condensed polycyclic aromatic compound of naphthalene or more, That is.

In the present invention, as the quinoline derivative compound, a compound in which at least one of the substituents X _{1 to} X _{7 in} the formula (2) has a double bond number n of 2 or more can be employed. .

Another feature of the present invention is that, in the above-mentioned organic electroluminescent device, the device comprises at least an organic light-emitting layer between the first and second electrodes, and the organic light-emitting layer is doped with the dye. A triphenylamine derivative.

Some of the compounds having a molecular structure in which a double bond structure is long and connected as shown in the above formula (i) can exhibit a long-wavelength light emitting function. For example, in the quinoline derivative represented by the above chemical formula (1), 2
Compounds in which a substituent of the chemical formula (2) containing a heavy bond is introduced, in particular, a quinoline derivative having a plurality of the substituents of the formula (2) and having two or more double bonds n are conjugated as a whole molecule. Since the system has a long and connected structure, the energy difference between the excited state and the specified state of the compound is small, so that a yellow-red emission function can be obtained. In addition, a quinoline derivative of the formula (1) having a plurality of substituents of the formula (2) or a structure of the formula (i) has excellent planar structure stability. Has high stability, and the durability of the element can be improved.

However, as a result of the inventors' further research,
Even when such a compound having an excellent yellow to red light emitting function is used by adding this compound as a dye (guest material) to another host material in an application such as an organic electroluminescent device, the compound emits light. It was found that the wavelength shifted to the shorter wavelength side. In addition, the cause is that even in the above-described compound having a stable planar structure, depending on the host material when doped, the planar structure of the dye may be twisted, and the molecular structure is twisted. It is considered that the conjugated system is interrupted at that point, and the emission color of the dye is shortened in wavelength.

However, when the host material contains a condensed polycyclic aromatic compound of naphthalene or more as in the present invention, the site plays a role of a splint next to a divinyl structure or the like, thereby suppressing the structure from being twisted. . For this reason, it is possible to prevent the conjugated system from being divided by the twisting of the molecule, and it is possible to obtain a long-wavelength luminescent color that is inherent in the dye. Therefore, by adopting such a configuration, it is possible to realize a stable and long-life organic EL element capable of emitting yellow to red light, particularly red light. In addition, the emission color tone can be adjusted by the amount of the dye added, the host material, and the like, so that the color purity can be improved.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter, referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 shows an organic E according to an embodiment of the present invention.
3 shows a schematic sectional configuration of an L element. The organic EL device according to the present embodiment is configured such that a first electrode 12, an organic compound layer 200, and a second electrode 14 are sequentially stacked on a transparent substrate 10.

As the transparent substrate 10, a glass substrate, a transparent ceramics substrate, a diamond substrate or the like can be used. As the first electrode 12, a transparent electrode having high light transmittance and conductivity is used. For example, ITO (In
For example, a thin film material such as dium tin oxide, SnO ₂ , In ₂ O ₃ , or polyaniline can be used.

The organic compound layer 200 is a portion that emits light when an electric field is applied, such as a single-layer structure of a light-emitting layer, a two-layer structure of a hole transport layer and a light-emitting layer, a hole transport layer, a light-emitting layer, and an electron transport layer. And a three-layer structure. The organic compound layer 200 may be composed of a single layer or a multilayer. The thickness of the organic compound layer 200 is, for example, several tens to several hundreds of nm. In the present embodiment, the hole transport layer 22, the light emitting layer 24,
A layered structure of the electron transport layer 26 is adopted.

As the second electrode 14 formed on the organic compound layer 200, for example, Mg, Ag, Mg-Ag
Metal electrodes such as alloys, Al-Li alloys, and LiF / Al are used.

In the organic EL device of this embodiment, the light emitting layer 24 of the organic compound layer 200 is formed by doping a predetermined amount of a guest material into a host material.

As the guest material, the following chemical formula (i)

Embedded image As described above, a dye having a structure in which two or more double bonds are bonded in a molecule to cause twisting is used. Note that, in equation (i),
Ar is, for example, an aromatic ring (aryl group) and a partially substituted body thereof, an aromatic ring partially provided with an aliphatic ring, and a substituted body containing a hetero atom such as N, O, or S other than carbon in these rings. And so on.

Specifically, this dye is represented by the following formula (1)

Embedded image Wherein at least two or more of X _{1 to} X ₇ in the formula (1) are represented by the chemical formula (2), and the number n of at least one double bond in the quinoline derivative is 2
A structure comprising the above substituents is provided. As described above, since two or more substituents having the structure of the chemical formula (2) are introduced as substituents of the quinoline ring of the chemical formula (1), the conjugated system is long as a whole molecule, and the energy difference between the excited state and the ground state is reduced. to shrink. Therefore, by using this compound as a doping material in a host material in a light-emitting layer of an organic EL device, for example, a longer wavelength yellow to red light having a longer wavelength as compared with a known Alq ₃ (green light emission) having a quinoline ring is used. Shows the light emitting function.

In this embodiment, in particular, a red color is realized by using a triphenylamine derivative having a condensed polycyclic aromatic compound of naphthalene or more as described below as a host material, and doping the quinoline derivative into the derivative. are doing.

Here, the terminal group Q of the chemical formulas (i) and (2)
Is particularly preferably an aromatic group (aromatic hydrocarbon group or aromatic heterocyclic group). As an example, the following equation (3)

Embedded image A phenyl group as shown in the following can be adopted. In the formula (3), the substituent _XQ is not particularly limited. However, by employing an electron-donating substituent, the fluorescent quantum yield of the organic compound is improved, and an excellent luminescent material (the present invention) In the embodiment, a guest material) can be used. Examples of the electron donating substituent include an amino group, an alkoxy group, an alkylthio group, an alkyl group, and an amino group substituted with an alkyl group. In addition, adjacent substituents R _Q (X ₈ and X ₉ , X ₉ and X ₁₀ , X ₁₀ and X _{10 in} the above formula (3))
_And when X ₁₁ and X ₁₂ ) are bonded to each other to form an aromatic ring or an aliphatic ring, the electron-donating substituents listed above are introduced into the aromatic ring or the aliphatic ring. By adopting such a structure, the fluorescence quantum yield can be similarly improved.

In the chemical formula (1), the above chemical formula (2)
The remaining substituents of X _{1 to} X ₇ which are not substituted with are independent of each other, and may be a hydrogen atom or any substituent other than a hydrogen atom. For example, a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, an alkylthio group, an aryl group,
An arylthio group, an aryloxy group, an alkoxy group, an amino group, a cyano group, a nitro group, an ester group, a carboxyl group, a heterocyclic group, and derivatives thereof can be employed, and each substituent is further substituted with a substituent. May be.
In the groups other than the substituent represented by the above formula (2), X ₁ and X ₂ , X ₂ and X ₃ , X ₃ and X ₄ , X ₄ and X ₅ , X ₅
And any of X _6, X ₆ and X _7, are substituted may be a structure forming an aromatic ring or aliphatic ring bonded to each other, also aromatic ring or aliphatic ring with another substituent You may. The substituents that can be employed as the substituents on the aromatic ring or the aliphatic ring are the same as the characteristic groups listed above.
Further, the bonded aromatic ring or aliphatic ring may be not only a ring composed of carbon and hydrogen such as a benzene ring or a naphthalene ring but also a ring containing a hetero atom. Heteroatoms include nitrogen, oxygen, sulfur, silicon and the like.

The substituents R _n and R ′ _{n in the} chemical formula (2) can be any characteristic groups and are independent of each other. For example, a hydrogen atom, a hydroxyl group, a halogen atom, an alkyl group, an alkylthio group, an aryl Group, an arylthio group, an aryloxy group, an alkoxy group, an amino group, a cyano group, a nitro group, an ester group, a carboxyl group, a heterocyclic group, or a derivative thereof, for example, a part of which is further substituted with the substituents listed above. And other substituents. In the group where the number of n in the chemical formula (2) is 2 or more, a double bond substituent R _n ,
R ′ _n may be all the same, all different, or partially the same. Further, a structure in which R _n and R ′ _n are cyclized may be employed.

Examples of the compound having the characteristics described above include the following chemical formulas (4) to (8).

Embedded image And the like.

Next, the host material of the light emitting layer 24 will be described. In the present embodiment, as the host material, a compound which is a triphenylamine derivative and has a condensed polycyclic aromatic compound of naphthalene or more in a molecule is used. Although not particularly limited to the following compounds, for example, as a compound satisfying the above conditions

Embedded image And the like. Formula (9) is a triphenylamine dimer having a naphthalene ring (α-NPD),
Represents a triphenylamine tetramer having a naphthalene ring (α-NPTE). The compound (DBC1) of the formula (11) has a configuration in which four triphenylamines are each condensed with a phenyl group of another triphenylamine via an aromatic ring and an aliphatic ring.

The quinoline derivative (divinylquinoline derivative) can be an excellent reddish luminescent dye. However, in relation to the host material, when the luminescent layer is doped to form a luminescent layer, the luminescent wavelength shifts to shorter wavelengths. May be observed. However, when a triphenylamine derivative containing a condensed polycyclic aromatic group not less than naphthalene as described above is used as a host material, a portion of the condensed polycyclic aromatic group having a stable planar structure is a divinyl group of a quinoline derivative, particularly n In the vicinity of the polyvinyl group of> 2, the twist of the planar structure is suppressed, that is, it serves as a splint. When the double bond portion of the quinoline derivative is twisted, the conjugate system in the molecule is broken, and light emission of a short wavelength is generated. In contrast, in the present embodiment, the triphenylamine derivative can prevent the quinoline derivative from being twisted, and does not impair the long-wavelength red light emission performance that the quinoline derivative can originally emit. Therefore, red light emission can be realized by using a triphenylamine derivative having a condensed polycyclic aromatic group equal to or greater than the above naphthalene as a host material of the light emitting layer 24 and using the above quinoline derivative as a doping material.

For the hole transporting layer, the electron transporting layer, etc., currently known electron transporting functional molecules and hole transporting functional molecules can be used. For example, examples of the hole transport function molecule include copper-phthalocyanine and triphenylamine tetramer (TPTE) having a hole transport function. Here, the triphenylamine derivative containing the condensed polycyclic compound of naphthalene or more also has excellent hole transporting property and further has higher heat resistance, so that not only the host material of the light emitting layer but also the positive It can also be used for a hole transport layer. As the electron transporting functional molecule, for example, Alq ₃ or the like can be used.

In the organic EL device having the above-described structure, the first electrode 12 is used as an anode and the second electrode 14 is used as a cathode.
The holes and electrons are recombined in and around the light emitting layer 24, and the quinoline derivative compound is excited,
Red fluorescence resulting from this compound is obtained.

[0035]

Next, an embodiment will be described.

(Preparation of Device) As a device according to the embodiment, 4
Types (Examples 1 to 4) were produced. The configuration of each element is the same as in FIG. 1 described above. As the substrate 10, a glass substrate on which ITO 12 was patterned was used. Substrate 1
After washing ultrasonic cleaning in the order of organic alkali cleaning agent Semico Clean 56 (Furuuchi Chemical), pure water, acetone and ethanol, remove UV to remove organic contaminants on the ITO surface.
After the ozone treatment, it was quickly set in a vapor deposition device. Next, after mounting a mask for an organic film in a vacuum, the hole transport layer 2 is formed as an organic compound layer 200 by heating the carbon crucible.
2. The light emitting layer 24 and the electron transport layer 26 were continuously formed. Specifically, the hole transport layer 22 has the above-mentioned chemical formulas (9) to (1).
40 nm of any of the triphenylamine derivatives of 1)
Formed. The light-emitting layer 24 has the above chemical formulas (9) to (11).
To the compound K represented by the chemical formula (4) or the compound L represented by the chemical formula (5)
Was added in an amount of 1% to form a film having a thickness of 20 nm. The electron transport layer 26 was formed using a quinolinol aluminum complex (Alq ₃ ) to a thickness of 60 nm.
Each deposition rate of the organic compound layer 200 is 2 to 6 nm / m
in.

Next, the mask was changed to a cathode electrode in a vacuum, LiF was 3 nm / min from a Ta boat, and Al was P
0.5 nm and 150 nm were formed at a deposition rate of 10 nm / min from a BN crucible, respectively. The film was formed at a degree of vacuum of 5 × 10 ⁻⁷ Torr (1 Torr @ 133 P)
a) The following was performed.

The emission spectra of the organic EL devices (Examples 1 to 4) produced by the above method were measured in a chamber sufficiently purged with nitrogen.

As a comparative example, the following formulas (12) and (13) were used instead of the host materials (compounds M, N, and O) of the devices of Examples 1 to 4 as the host material of the light emitting layer 24.

Embedded image And the same quinoline derivative compounds K and L as in Examples 1-3 and 4 were used as guest materials, and other triphenylamine dimers (compound P) and triphenylamine tetramers (compound Q) were used. Elements (Comparative Examples 1 to 3) were manufactured with the same configuration and manufacturing conditions as in Examples 1 to 4. As the material of the hole transport layer 22, the same compound P and compound Q as those of the light emitting layer host material were used.

(Results) Table 1 shows the obtained device characteristics.

[0041]

[Table 1] FIGS. 2 to 4 show device emission spectra when the compound K was used as the guest material (dye) and the host material was changed.

The peak wavelength of the device of Comparative Example 1 using TPD as the host material was 589 nm, while the peak wavelength of the device of Example 1 using α-NPD as the host material was 61 nm.
Emission at a wavelength as long as 8 nm is realized (see FIG. 2).

In the device of Example 2 using α-NPTE as the host material, light of 611 nm was obtained. This was because only the presence or absence of a naphthalene ring in the host material was the same as that of α-NPTE.
It can be seen that the wavelength is longer than that of Comparative Example 2 using TPTE different from PTE (see FIG. 3).

Further, in the device of Example 3 using DBC1 as the host material, the emission peak wavelength was 601 nm, which was also longer than that of the device of Comparative Example 1 using the host material TPD. 4).

In the case where the compound L was used as the guest material, the peak wavelength of the device of Comparative Example 3 using TPTE as the host material was 550 nm, but the example using α-NPD as the host material was used. The peak wavelength of the device No. 4 is 600 nm, and it can be seen that the wavelength is also long.

From the above results, when a divinylquinoline derivative compound such as Compound K or Compound L is used as a guest material, a triphenylamine derivative having a condensed polycyclic aromatic compound of naphthalene or more is used as a host material. This indicates that the emission color of the organic electroluminescent element has a longer wavelength.

The results of evaluating the durability of each element are as follows. The half life of the luminance when the current was injected from the electrodes 12 and 14 to the light emitting layer of the element so that the initial luminance of the element was 300 cd / m ² was 20 in Example 1.
00 hours, 3000 hours in Example 2, 3500 hours in Example 3, 600 hours in Example 4, 2500 hours in Comparative Example 1, and 750 in Comparative Example 2.
0 hour and 450 hours in Comparative Example 3. A good life was obtained in each of the elements, and it can be seen that, in particular, the elements of Examples 1 to 4 achieve the same or higher durability as the element of the comparative example.

[0048]

As described above, in the present invention, when a derivative such as quinoline having a substituent having a double bond is used as a guest material (dye) in an organic EL device, naphthalene or more is used as a host material. By using a triphenylamine derivative having a condensed polycyclic aromatic compound of the formula (1), the dye can exhibit its inherent red light emission function without loss. When the light-emitting layer is formed using the host material and the guest material, the durability of the light-emitting layer is improved. Therefore, a stable, long-life, long-wavelength organic EL element can be realized.

Further, since the color tone of the luminescent color can be changed by adjusting the doping amount of the guest material, the color purity of the red luminescent color can be improved, or the blue luminescent layer having a complementary color relationship with red can be obtained. In addition, when a white light-emitting organic EL element is manufactured, the color purity of white can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a schematic cross-sectional configuration of an organic EL device according to an embodiment and an example.

FIG. 2 is a diagram showing emission spectra of the organic EL devices of Example 1 and Comparative Example 1.

FIG. 3 is a diagram showing emission spectra of the organic EL devices of Example 2 and Comparative Example 2.

FIG. 4 is a diagram showing emission spectra of the organic EL devices of Example 3 and Comparative Example 1.

[Explanation of symbols]

Reference Signs List 10 glass substrate, 12 first electrode (anode), 14 second electrode (cathode), 22 hole transport layer, 24 light emitting layer, 26
Electron transport layer, 200 organic compound layer.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Masahiko Ishii 41-cho, Yokomichi, Nagakute-machi, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. (72) Inventor Hisato Takeuchi Institution, Nagakute-cho, Aichi-gun, Aichi No. 41, Toyota Chuo-Yokomichi, Toyota Chuo Research Institute, Inc. (72) Inventor Yasunori Taga 41, Nagakute-cho, Aichi-gun, Aichi-gun, Aichi Prefecture, Japan F-term in Toyota Central Research Institute, Inc. (reference) 3K007 AB02 AB04 AB11 EB00 FA00

Claims (4)

[Claims] 1. The chemical formula (i) below: And an organic electroluminescent device having an organic compound layer in which a dye having a structure in which n in the formula is 2 or more is added to a triphenylamine derivative having a condensed polycyclic aromatic compound of naphthalene or more. 2. The following general formula (1): A quinoline derivative compound represented by the formula (1):
A dye in which one or more of the substituents X _{1 to} X _{7 in} the formula (2) is added to a triphenylamine derivative having a condensed polycyclic aromatic compound of naphthalene or more, Organic electroluminescent device. 3. The organic electroluminescent device according to claim 2, wherein at least one of the substituents X _{1 to} X ₇ of the quinoline derivative compound has a double bond number n in the chemical formula (2).
Is 2 or more. 4. The organic electroluminescent device according to claim 1, wherein the device comprises at least an organic light emitting layer between the first and second electrodes, wherein the organic light emitting layer is An organic electroluminescent device comprising a triphenylamine derivative to which the dye is added.