JP4493365B2 - Organic material for organic electroluminescent device and organic electroluminescent device - Google Patents

Description

  The present invention relates to an organic material for an organic electroluminescent element and an organic electroluminescent element using the same.

  Organic electroluminescent devices (organic EL devices) are easier to increase in area than inorganic electroluminescent devices, and can produce a desired color by selecting light-emitting materials and can be driven at a low voltage. Because of this, application research has been actively conducted in recent years. In an organic EL element, a layer made of an organic material such as a light emitting layer and a carrier transport layer is formed between a pair of electrodes.

  Conventionally, methods such as vacuum deposition have been used as a method for forming an organic material layer. However, if the organic material layer can be formed as a coating film by applying the solution, the device manufacturing process can be simplified. In order to form an organic material layer by such a coating film forming method, it is necessary to use a polymer having a film forming ability. By using a polymer having a light emitting property or a carrier transporting property, a light emitting layer or a carrier transport layer is used. Can be formed.

  However, since the polymer itself is a molecule that easily aggregates, when such a polymer material is used, there is a problem that the light emission property or carrier transport property of the unit introduced into the polymer molecule cannot be sufficiently exhibited. It was. For example, in the case of a polymer having a light emitting property, the light emission wavelength is shifted to a longer wavelength side than the light emission wavelength of the light emitting unit contained in the polymer, resulting in a problem that the color purity is lowered.

In Patent Document 1, in order to solve such a problem, it has been proposed to introduce a spacer segment into a polymer having a chromophore segment. As such a spacer segment, a structure such as a benzene ring or an aromatic condensed ring is shown.
JP-T 9-503239

  An object of the present invention is to provide an organic material for an organic electroluminescent device comprising a polymer material capable of lowering the driving voltage, increasing the luminous efficiency, and shortening the emission wavelength, and an organic material using the same. The object is to provide an electroluminescent device.

  The organic material for an organic electroluminescent device of the present invention is characterized by comprising a copolymer containing a conjugated unit having carrier transporting property or light emitting property and a bulky unit having a saturated cyclic compound structure in the main chain.

The present inventors have found that a unit having an aromatic ring structure as in Patent Document 1 is insufficient to suppress aggregation of polymers and obtain light emission of an original wavelength. That is, it was found that the aromatic ring structure disclosed in Patent Document 1 is a planar structure, and such a planar structure cannot sufficiently suppress aggregation of polymer molecules. The bulky unit in the present invention has a structure of a saturated cyclic compound, and is made of carbon having SP ³ hybrid orbitals, that is, carbon having a steric element bond. For this reason, it becomes three-dimensional and becomes a bulky structure as compared with a compound having an unsaturated planar carbon-carbon bond such as SP ² orbit and SP orbit. Moreover, it becomes more three-dimensional and bulky by having one or two or more cyclic structures. For this reason, aggregation of polymer molecules can be sufficiently suppressed, and the emission wavelength can be brought close to the original wavelength. That is, the emission wavelength can be shortened. In addition, the driving voltage can be lowered and the light emission efficiency can be increased.

  In Patent Document 1, since an aromatic structure is used as the spacer unit, the conjugated structure of the molecule becomes long, which causes a problem of increasing the wavelength. In the present invention, since the structure of the saturated cyclic compound is introduced as a bulky unit, the conjugated structure can be shortened, and the emission wavelength can also be shortened from this point.

  The conjugated unit in the present invention is not particularly limited as long as it has a carrier transporting property or a light emitting property, but a fluorene structure is particularly preferred. Examples of the fluorene structure include the following fluorene structures.

（ここで、Ｒは、炭素数１〜２０のアルキル基であり、Ｏ、Ｓ、Ｎ、Ｆ、Ｐ、Ｓｉ、またはアリール基が含まれていてもよいアルキル基である。）

(Here, R is an alkyl group having 1 to 20 carbon atoms, and may be an O, S, N, F, P, Si, or an alkyl group that may contain an aryl group.)

（ここで、Ａｒは、以下に示すアリール基である。）

(Here, Ar is an aryl group shown below.)

（ここで、Ｃ_nＨ_2n+1は、炭素数１〜２０のアルキル基であり、Ｏ、Ｓ、Ｎ、Ｆ、Ｐ、Ｓｉ、またはアリール基が含まれていてもよいアルキル基である。）

(Here, C _n H _{2n + 1} is an alkyl group having 1 to 20 carbon atoms, and may be an alkyl group which may contain O, S, N, F, P, Si, or an aryl group. )

（ここで、Ｅは、アルキル基、アリール基、フェニルアミン基、オキサジアゾール基、またはチオフェン基であり、アルキル基は、上記のような炭素数１〜２０のアルキル基Ｒであり、アリール基は、上記のようなＡｒである。）
上記において、アリール基の炭素数を１〜２０としているのは、炭素数が１より小さいとポリマーが溶剤に溶解しにくくなるからであり、炭素数が２０を超えるとポリマーのキャリア輸送性または発光性が低下するからである。

(Here, E is an alkyl group, an aryl group, a phenylamine group, an oxadiazole group, or a thiophene group. The alkyl group is an alkyl group R having 1 to 20 carbon atoms as described above, and an aryl group. Is Ar as described above.)
In the above, the reason why the aryl group has 1 to 20 carbon atoms is that if the carbon number is smaller than 1, the polymer is difficult to dissolve in the solvent, and if the carbon number exceeds 20, the carrier transportability or light emission of the polymer. This is because the sex is lowered.

  The bulky unit in the present invention is not particularly limited as long as it is a saturated cyclic compound structure, and examples thereof include a cyclohexane or adamantane structure. Adamantane has three rings that are three-dimensionally constructed, and is particularly highly bulky.

  The weight average molecular weight (Mw) of the polymer in the present invention is preferably in the range of 500 to 10,000,000, more preferably 1,000 to 5,000,000, and particularly preferably 5,000 to 5,000. 2,000,000. If the molecular weight is too low, polymer properties such as film-forming ability are lost, and if the molecular weight is too high, it is difficult to dissolve in a solvent.

  The amount of the bulky unit contained in the polymer of the present invention is preferably about 5 to 30 mol%. When there is too little content of a bulky unit, the effect in this invention may not fully be acquired. In addition, when the content of the bulky unit is too large, the amount of the conjugate unit having a carrier transport property or a light emission property is relatively reduced, and these characteristics may be deteriorated.

  The organic EL device of the present invention is characterized by containing the organic material of the present invention in a carrier transport layer or a light emitting layer.

  The copolymer of the present invention can be synthesized by various methods. For example, the copolymer synthesized in Examples 1 to 3 described later can be produced by the following reaction.

  ADVANTAGE OF THE INVENTION According to this invention, while being able to make the drive voltage of an organic EL element low, luminous efficiency can be raised, and the light emission wavelength can be shortened.

  EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited to a following example, It can change and implement suitably.

Example 1
<Preparation of poly [(9,9-dioctylfluorene-2,7-diyl) -co- (cyclohexane-1,2-diyl)] [Polymer 1] (PF8-Cy (10%))>

攪拌機、ラバーセプター、並びに真空及び窒素マニホールドの注入口を備えた反応容器に、１，２−ジブロモシクロヘキサン（２４．２ｍｇ、０．１ｍｍｏｌ）、２，７−ジブロモ−９，９−ジオクチルフルオレン（２１９ｍｇ、０．４ｍｍｏｌ）、９，９−ジオクチルフルオレン−２，７−ビス（４，４，５，５−テトラメチル−１，３，２−ジオキサボロラン（３２１ｍｇ、０．５ｍｍｏｌ）、鈴木カップリング触媒、トルエン５ｍｌ、及び塩基性水溶液８ｍｌを添加した。反応容器内を排気し、窒素で３回パージした後、９０℃に加熱した。窒素雰囲気下で、反応溶液を約３時間９０℃に保持した。次に、フェニルホウ酸６１ｍｇを添加し、反応容器を窒素雰囲気下で９０℃にさらに２時間保持した。その後、約０．１２ｍｌのブロモベンゼンを添加し、反応溶液を窒素雰囲気下で９０℃に２時間保持した。

To a reaction vessel equipped with a stirrer, rubber ceptor, and vacuum and nitrogen manifold inlets, was added 1,2-dibromocyclohexane (24.2 mg, 0.1 mmol), 2,7-dibromo-9,9-dioctylfluorene (219 mg). , 0.4 mmol), 9,9-dioctylfluorene-2,7-bis (4,4,5,5-tetramethyl-1,3,2-dioxaborolane (321 mg, 0.5 mmol), Suzuki coupling catalyst, Toluene (5 ml) and basic aqueous solution (8 ml) were added, the reaction vessel was evacuated, purged with nitrogen three times, and heated to 90 ° C. The reaction solution was maintained at 90 ° C. for about 3 hours under a nitrogen atmosphere. Next, 61 mg of phenylboric acid was added and the reaction vessel was held under a nitrogen atmosphere for an additional 2 hours at 90 ° C. Thereafter, about 0.12 ml of bromo It was added benzene, and the reaction solution was held for 2 hours at 90 ° C. under a nitrogen atmosphere.

Next, in order to precipitate the polymer, the reaction mixture was poured into 300 ml of methanol and washed three times with methanol. After drying under vacuum, the polymer was dissolved in about 10 ml of toluene, and column separation was performed using toluene as an eluent. After removing a part of the solvent with a rotary evaporator, the polymer solution was added to 300 ml of methanol to precipitate, and then washed with methanol three times. Drying under vacuum gave a pale yellow fibrous product. The yield was about 84%. The number average molecular weight (Mn) was 3.4 × 10 ⁴ , the weight average molecular weight (Mw) was 8.4 × 10 ⁴ , and Mw / Mn was 2.47.

(Example 2)
<Preparation of poly [(9,9-dioctylfluorene-2,7-diyl) -co- (cyclohexane-1,2-diyl)] [Polymer 2] (PF8-Cy (20%))>
Implementation was carried out except that the amount of 1,2-dibromocyclohexane used was 48.4 mg (0.2 mmol) and the amount of 2,7-dibromo-9,9-dioctylfluorene was 164.4 mg (0.3 mmol). Synthesized as in Example 1. A pale yellow powdery product was obtained. The yield was about 67%. The number average molecular weight (Mn) was 2.3 × 10 ⁴ , the weight average molecular weight (Mw) was 6.4 × 10 ⁴ , and Mw / Mn was 2.78.

(Example 3)
<Preparation of poly [(9,9-dioctylfluorene-2,7-diyl) -co- (cyclohexane-1,2-diyl)] [Polymer 3] (PF8-Cy (30%))>
Example 1 except that the amount of 1,2-dibromocyclohexane used was 72.6 mg (0.3 mmol) and the amount of 2,7-dibromo-9,9-dioctylfluorene was 110 mg (0.2 mmol). Was synthesized in the same manner as above. A pale yellow powdery product was obtained. The yield was about 44%. The number average molecular weight (Mn) was 1.3 × 10 ⁴ , the weight average molecular weight (Mw) was 4.4 × 10 ⁴ , and Mw / Mn was 3.38.

Example 4
<Preparation of poly [(9,9-dioctylfluorene-2,7-diyl) -co- (adamantane-1,3-diyl)] [polymer 4] (PF8-Adm (5%))>

１，２−ジブロモシクロヘキサンに代えて、１，３−ジブロモアダマンタンを１４．７ｍｇ（０．０５ｍｍｏｌ）用い、２，７−ジブロモ−９，９−ジオクチルフルオレンを２４６．６ｍｇ（０．４５ｍｍｏｌ）用いる以外は、実施例１と同様にして合成した。緑色の微細な繊維状生成物を得た。収率は約８７％であった。数平均分子量（Ｍｎ）は３．６×１０⁴であり、重量平均分子量（Ｍｗ）は８．４×１０⁴であり、Ｍｗ／Ｍｎは２．３３であった。

14.7 mg (0.05 mmol) of 1,3-dibromoadamantane is used in place of 1,2-dibromocyclohexane, and 246.6 mg (0.45 mmol) of 2,7-dibromo-9,9-dioctylfluorene is used. Was synthesized in the same manner as in Example 1. A green fine fibrous product was obtained. The yield was about 87%. The number average molecular weight (Mn) was 3.6 × 10 ⁴ , the weight average molecular weight (Mw) was 8.4 × 10 ⁴ , and Mw / Mn was 2.33.

(Example 5)
<Preparation of poly [(9,9-dioctylfluorene-2,7-diyl) -co- (adamantane-1,3-diyl)] [Polymer 5] (PF8-Adm (10%))>
Example 4 except that the amount of 1,3-dibromoadamantane was 29.4 mg (0.10 mmol) and the amount of 2,7-dibromo-9,9-dioctylfluorene was 219.2 mg (0.40 mmol). Was synthesized in the same manner as above. A gray powdery product was obtained. The yield was about 80%. The number average molecular weight (Mn) was 1.6 × 10 ⁴ , the weight average molecular weight (Mw) was 4.4 × 10 ⁴ , and Mw / Mn was 2.75.

(Comparative Example 1)
<Preparation of poly (9,9-dioctylfluorene-2,7-diyl) [polymer 6] (PF8)>

攪拌機、ラバーセプター、並びに真空及び窒素マニホールドの注入口を備えた反応容器に、２，７−ジブロモ−９，９−ジオクチルフルオレン（２７４ｍｇ、０．５ｍｍｏｌ）、９，９−ジオクチルフルオレン−２，７−ビス（４，４，５，５−テトラメチル−１，３，２−ジオキサボロラン（３２１ｍｇ、０．５ｍｍｏｌ）、鈴木カップリング触媒、トルエン５ｍｌ、及び塩基性水溶液８ｍｌを添加した。反応容器内を排気し、窒素で３回パージした後、９０℃に加熱した。窒素雰囲気下で、反応溶液を約３時間９０℃に保持した。次に、フェニルホウ酸６１ｍｇを添加し、反応容器を窒素雰囲気下で９０℃にさらに２時間保持した。その後、約０．１２ｍｌのブロモベンゼンを添加し、反応溶液を窒素雰囲気下で９０℃に２時間保持した。

To a reaction vessel equipped with a stirrer, rubber ceptor, and vacuum and nitrogen manifold inlets, 2,7-dibromo-9,9-dioctylfluorene (274 mg, 0.5 mmol), 9,9-dioctylfluorene-2,7 -Bis (4,4,5,5-tetramethyl-1,3,2-dioxaborolane (321 mg, 0.5 mmol), Suzuki coupling catalyst, 5 ml of toluene, and 8 ml of basic aqueous solution were added. After evacuating and purging with nitrogen three times, it was heated to 90 ° C. Under a nitrogen atmosphere, the reaction solution was held for about 3 hours at 90 ° C. Next, 61 mg of phenylboric acid was added and the reaction vessel was placed under a nitrogen atmosphere. Held at 90 ° C. for a further 2 hours, after which about 0.12 ml of bromobenzene was added and the reaction solution was held at 90 ° C. for 2 hours under nitrogen atmosphere.

Next, in order to precipitate the polymer, the reaction mixture was poured into 300 ml of methanol and washed three times with methanol. After drying under vacuum, the polymer was dissolved in about 10 ml of toluene, and column separation was performed using toluene as an eluent. After removing a part of the solvent with a rotary evaporator, the polymer solution was added to 300 ml of methanol to precipitate, and then washed with methanol three times. Drying under vacuum gave a light gray fibrous product. The yield was about 86%. The number average molecular weight (Mn) was 1.4 × 10 ⁵ , the weight average molecular weight (Mw) was 4.4 × 10 ⁵ , and Mw / Mn was 3.23.

(Measurement of fluorescence spectrum)
The fluorescence spectrum was measured about the polymers 1-6. The measurement results are shown in FIGS.

  As can be seen from FIG. 1, the polymers 1 to 3 into which the structure of cyclohexane is introduced as the bulky unit have a shorter emission wavelength than the polymer 6 having no bulky unit. Moreover, it turns out that the light emission wavelength shifts to a shorter wavelength as the content of the bulky unit increases.

  As can be seen from FIG. 2, the polymers 4 and 5 into which the adamantane structure is introduced as the bulky unit also have a shorter emission wavelength than the polymer 6 having no bulky unit. Moreover, it turns out that the light emission wavelength shifts to a shorter wavelength as the content of the bulky unit increases.

(Measurement of UV absorption spectrum)
UV absorption spectra were measured for polymers 1 to 3 and polymer 6. The measurement results are shown in FIG.

  As is clear from the results shown in FIG. 3, in the polymers 1 to 3 into which the bulky unit was introduced, the maximum absorption wavelength of the UV absorption spectrum was shifted to the short wavelength side compared to the polymer 6 to which the bulky unit was not introduced. I understand that. It can also be seen that the shift amount increases as the content of the bulky unit increases. The peak wavelengths of UV absorption (light absorption spectrum) and fluorescence spectrum are summarized in Table 1.

(Example 6)
<Preparation of Light-Emitting Element 1 Using Polymer 4>
The ITO-glass substrate used for device fabrication was washed with ion exchange water, 2-propanol, and acetone, and then treated with ozone gas. Poly (ethylenedioxythiophene): poly (styrenesulfonate) (hereinafter referred to as PEDOT: PSS) (manufactured by Bavaria) was spin-coated on the ITO substrate. The thickness of the PEDOT: PSS thin film (PEDOT thin film) was controlled to about 200 mm. The PEDOT film was heated in air at about 200 ° C. for about 10 minutes, and then heated in vacuo at 80 ° C. for about 30 minutes. Next, a toluene solution of polymer 4 was applied to form a light emitting layer. The thickness of the light emitting layer was controlled to 1000 mm. Next, calcium and aluminum were deposited in a vacuum on the light emitting layer to form a cathode. This substrate was covered with a glass carrier in a glove box to obtain an element.

  PEDOT: PSS has the following structure.

(Example 7)
<Preparation of Light-Emitting Element 2 Using Polymer 5>
In Example 6, a device was produced in the same manner as in Example 6 except that polymer 5 was used instead of polymer 4.

(Comparative Example 2)
<Preparation of Light-Emitting Element 3 Using Polymer 6>
In Example 6, a device was produced in the same manner as in Example 6 except that polymer 6 was used instead of polymer 4.

(Evaluation of light emitting element)
About the light emitting elements 1-3, the drive voltage, the highest brightness | luminance, the highest luminous efficiency, and the CIE color coordinate were measured. The measurement results are shown in Table 2. In addition, Table 3 shows the chromaticity (at 100 cd / m ² ) of a light-emitting element using Polymer 1 to Polymer 6.

表２に示す結果から明らかなように、本発明に従う発光素子１及び２は、比較の発光素子３よりもより青色に近い発光を示している。また、本発明に従う発光素子１及び２は、発光素子３に比べ駆動電圧が低くなっており、発光効率が高くなっていることがわかる。また、ポリマー１〜３を用いた発光素子についても、より青色の濃い発光が得られることが明らかになった。

As is clear from the results shown in Table 2, the light-emitting elements 1 and 2 according to the present invention emit light closer to blue than the comparative light-emitting element 3. In addition, it can be seen that the light-emitting elements 1 and 2 according to the present invention have a lower driving voltage than the light-emitting element 3 and have higher luminous efficiency. In addition, it was revealed that light-emitting elements using polymers 1 to 3 can also emit deeper blue light.

The figure which shows the emission spectrum of the polymers 1-3. The figure which shows the emission spectrum of the polymers 4 and 5. FIG. The figure which shows the UV absorption spectrum of the polymers 1-3.

Claims (2)

An organic material for an organic electroluminescent device comprising a copolymer containing a conjugated unit having carrier transporting property or light emitting property and a bulky unit having a saturated cyclic compound structure in the main chain ,
The conjugated unit has a fluorene structure, the structure of the saturated cyclic compound of the bulky unit is a structure of cyclohexane or adamantane, and the bulky unit is based on the total number of the conjugated unit and the bulky unit constituting the copolymer. 5-30 mol% is contained, The organic material for organic electroluminescent elements characterized by the above-mentioned. An organic electroluminescent device comprising the organic material according to claim 1 in a carrier transport layer or a light emitting layer.

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