KR100537502B1 - Blue Electroluminescent Polymer And Organo-electroluminescent Device Manufactured By Using The Same - Google Patents

Abstract

The present invention relates to a blue electroluminescent polymer and an organic electroluminescent device using the same, and more particularly, to a blue electroluminescent polymer represented by the following Chemical Formula 1, by applying the blue electroluminescent polymer of the present invention to a light emitting layer, An efficient organic electroluminescent device can be provided:

[Formula 1]

Where

Ar is an aromatic group having 6 to 26 carbon atoms or a heteroaromatic group having 4 to 14 heteroatoms included in an aromatic ring. The aromatic group or heteroaromatic group has an alkyl group having 1 to 12 carbon atoms. One or more alkoxy or amine groups may be substituted;

R and R 'are each independently a hydrogen atom or a linear, branched or cyclic alkyl group or alkoxy group having 1 to 12 carbon atoms, or an aromatic group having 6 to 14 carbon atoms, and the aromatic group includes an alkyl group having 1 to 12 carbon atoms, One or more alkoxy groups or amine groups may be substituted;

n is a real number from 0.01 to 0.99.

Description

Blue electroluminescent polymer and organic electroluminescent device using the same {Blue Electroluminescent Polymer And Organo-electroluminescent Device Manufactured By Using The Same}

The present invention relates to a blue electroluminescent polymer and an organic electroluminescent device using the same, and more particularly, to a high intensity, high efficiency blue electroluminescent polymer comprising a pyrazoline unit in a main chain of a polyarylene polymer, and using the same. The present invention relates to an organic electroluminescent device.

Electroluminescent devices using organic materials are light weighted, thinner and easier to implement in various colors, and have high brightness at high switching speed and low driving voltage after the multi-layered device separated by Kodak's CW Tang. Many studies have been conducted over the last decade because of its advantages. As a result, the device can be implemented for a short period of time, such as balanced charge injection of the device through the introduction of a multilayer thin film structure, color control and quantum efficiency through doping, and development of new electrode materials using alloys. Significant growth has been made in performance.

Organic electroluminescent displays can be classified into devices using low molecular materials and devices using high molecular materials in terms of material properties and manufacturing processes. When manufacturing a device using a low molecular material, a thin film is formed through vacuum deposition, and the light emitting material can be easily purified and purified, and color pixels can be easily implemented, but for practical applications, the improvement of quantum efficiency and the crystallization of the thin film are practical. There are still problems to be solved, such as prevention and improved color purity. Electroluminescent displays using small molecules have been studied in Japan and the United States, and Idemitsu-Kosan Co., Ltd., Japan, in 1997, used 10-inch full-color organic electroluminescence in a color scheme using a color changing medium. The display was unveiled for the first time, and soon followed by Pioneer, Japan, to introduce a 5-inch full-color organic electroluminescent display with a manual drive. Recently, Pioneer and Motorola have agreed to mass-produce mobile phones employing organic electroluminescent displays as terminals, suggesting the possibility of commercialization of low molecular electroluminescent displays in the near future.

On the other hand, studies on electroluminescent devices using polymers reported that light was emitted when the electric power was applied to the π-conjugated polymer poly (1,4-phenylenevinylene) (PPV) by the Cambridge Group in 1990. Since then, active research has been conducted. π-conjugated polymers have chemical structures with alternating single bonds (or σ-bonds) and double bonds (or π-bonds), and have π-electrons that can move relatively freely along the bond chain without localization have. Due to this semiconducting nature, π-conjugated polymers can easily obtain light in the entire visible region corresponding to the HOMO-LUMO band-gap through molecular design when they are applied to the light emitting layer of the electroluminescent device. Since the thin film can be simply formed by coating or printing, the device manufacturing process is simple, inexpensive, and has a high glass transition temperature, thereby providing a thin film having excellent mechanical properties. Thus, in the long run, it is expected to be more competitive commercially than the low molecular electroluminescent display.

However, in the case of a blue electroluminescent device using a polymer, problems such as color purity reduction, high driving voltage, and low efficiency are becoming a problem, and studies are currently being actively conducted to overcome these problems. For example, fluorene-containing polymers may be copolymerized (see US Patent No. 6,169,163; and Synthetic Metal, Vol. 106, pp. 115-119, 1999) and blended (Applied Physics Letter, Vol. 76, No. 14, p. 1810, 2000) Although methods for improving electroluminescent properties have been proposed, the degree of improvement is still insufficient.

One object of the present invention is to provide a new high efficiency blue electroluminescent polymer with improved luminescence properties.

Another object of the present invention is to provide an organic electroluminescent device in which the blue electroluminescent polymer is introduced into a light emitting layer.

That is, one aspect of the present invention relates to a blue electroluminescent polymer represented by Formula 1 below:

[Formula 1]

Where

Ar is an aromatic group having 6 to 26 carbon atoms or a heteroaromatic group having 4 to 14 heteroatoms included in an aromatic ring. The aromatic group or heteroaromatic group has an alkyl group having 1 to 12 carbon atoms. One or more alkoxy or amine groups may be substituted;

R and R 'are each independently a hydrogen atom or a linear, branched or cyclic alkyl group or alkoxy group having 1 to 12 carbon atoms, or an aromatic group having 6 to 14 carbon atoms, and the aromatic group includes an alkyl group having 1 to 12 carbon atoms, One or more alkoxy groups or amine groups may be substituted;

n is a real number from 0.01 to 0.99.

Another aspect of the present invention relates to an organic electroluminescent device in which the blue electroluminescent polymer is introduced into a light emitting layer.

The present invention will be described in more detail below.

The present invention provides a blue electroluminescent polymer represented by Chemical Formula 1, wherein a pyrazoline unit is introduced into a polyarylene main chain.

Where

Ar is an aromatic group having 6 to 26 carbon atoms or a heteroaromatic group having 4 to 14 heteroatoms included in an aromatic ring. The aromatic group or heteroaromatic group has an alkyl group having 1 to 12 carbon atoms. One or more alkoxy or amine groups may be substituted;

R and R 'are each independently a hydrogen atom or a linear, branched or cyclic alkyl group or alkoxy group having 1 to 12 carbon atoms, or an aromatic group having 6 to 14 carbon atoms, and the aromatic group includes an alkyl group having 1 to 12 carbon atoms, One or more alkoxy groups or amine groups may be substituted;

n is a real number from 0.01 to 0.99.

In the present invention, the blue electroluminescent property of the polymer can be improved by introducing a pyrazoline unit having both easy hole mobility and blue light emitting property into the polyarylene backbone.

The arylene (Ar) unit constituting the main chain of the blue light emitting polymer of the present invention preferably has one of the structures illustrated in the following Chemical Formulas 2 or 3, and more preferably has an alkylfluorene structure.

In the above formula, R ₁ and R ₂ are each an alkyl group having 1 to 12 carbon atoms, an alkoxy group or an amine group.

In the above formula, R ₁ and R ₂ are each an alkyl group having 1 to 12 carbon atoms, an alkoxy group or an amine group.

It is preferable that the weight average molecular weight (Mw) of the blue electroluminescent polymer of this invention is about 10,000-200,000, and molecular weight distribution (MWD) is about 1.5-5. Molecular weight of the light emitting polymer acts as an important factor for the thin film formation characteristics and the lifetime of the device, especially if the molecular weight is too small, it causes the crystallization and the like during device fabrication and driving.

The organic electroluminescent device of the present invention is produced by forming a light emitting layer using the blue electroluminescent polymer. Such organic electroluminescent devices are commonly known as anode / light emitting layer / cathode, anode / buffer layer / light emitting layer / cathode, anode / hole transporting layer / light emitting layer / cathode, anode / buffer layer / hole transporting layer / light emitting layer / cathode, anode / buffer layer / hole It may be formed of a structure such as a transport layer / light emitting layer / electron transport layer / cathode, anode / buffer layer / hole transport layer / light emitting layer / hole blocking layer / cathode, but is not limited thereto.

At this time, the material of the buffer layer may be used a material commonly used, preferably copper phthalocyanine, polythiophene, polyaniline, polyacetylene, polyacetylene, polypyrrole, Polyphenylene vinylene, or derivatives thereof may be used, but is not limited thereto.

As the material of the hole transport layer, a material commonly used may be used. Preferably, polytriphenylamine may be used, but is not limited thereto.

As the material of the electron transport layer, a material commonly used may be used. Preferably, polyoxadiazole may be used, but is not limited thereto.

A material commonly used as the material of the hole blocking layer may be used, and preferably, LiF or MgF ₂ may be used, but is not limited thereto.

Fabrication of the organic electroluminescent device of the present invention does not require a special device or method, it can be produced according to the manufacturing method of the organic electroluminescent device using a conventional polymer.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the following Examples are for the purpose of explanation and are not intended to limit the present invention.

Preparation Example 1 Synthesis of Pyrazoline Monomer

1 schematically shows a synthesis scheme of a pyrazoline monomer according to Preparation Example 1. This will be described in more detail below.

1) Preparation of Compound (1)

After dissolving 10 g (51.5 mmol) of 1,1 '-(4,6-dihydroxy-1,3-phenylene) bisethanone in 300 ml of acetone, 17.8 g (128.7 mmol) of K ₂ CO ₃ and adogen (adogen) 2 ml were added. 23 g (118.5 mmol) of bromooctane was added to the solution and refluxed for 2 days with stirring. After the reaction was completed, K ₂ CO ₃ was removed by extraction with a water: CHCl ₃ = 2: 1 solution. The extracted organic layer was dried over MgSO ₄ and concentrated, and passed through a silica gel column using hexane as a developing solution. The eluate passed through was distilled under reduced pressure to remove unreacted bromooctane to give 20.5 g (yield: 95%) of product. The structure of the resulting compound was confirmed by ¹ H-NMR:

¹ H-NMR (300 MHz, CDCl ₃ ): δ 0.87 (t, 6H), δ 1.2 (broad, 16H), δ 1.4 (m, 4H),

                       δ1.9 (m, 4H), δ2.5 (s, 6H), δ4.3 (t, 4H),

                       δ6.44 (s, 1H), δ8.32 (s, 1H)

2) Preparation of Compound (2)

Compound (1) 20 g (47.8 mmol) and 18.5 g (100 mmol) of 4-bromobenzaldehyde were dissolved in 400 ml of ethanol, and then a solution of 26.8 g (477 mmol) of KOH was dissolved in 40 ml of distilled water was slowly added and stirred at room temperature for 24 hours or more. I was. After stirring was complete, 100 ml of HCl: water = 1: 5 solution was added to form a precipitate. The precipitate formed was washed several times with distilled water and finally washed with methanol and dried to give 28.7 g (80%) of the product. The structure of the resulting compound was confirmed by ¹ H-NMR:

¹ H-NMR (300 MHz, CDCl ₃ ): δ 0.87 (triplet s, 6H), δ 1.2 (broad, 16H),

                       δ1.4 (m, 4H), δ1.9 (m, 4H), δ4.3 (t, 4H),

                       δ6.47 (s, 1H), δ 7.48-7.6 (m, 12H), δ8.25 (s, 1H)

3) Preparation of Compound (3)

After dissolving 10 g (13.2 mmol) of compound (2) and 4.5 g (39.8 mmol) of phenylhydrazine in 300 ml of ethanol, 1 ml of acetic acid was added and refluxed for 12 hours. After the reaction was completed, 100 ml of distilled water was added to the solution to form a precipitate. The precipitate formed was washed several times with distilled water and finally washed with methanol and dried to yield 8.7 g (35%) of product. The structure of the resulting compound was confirmed by ¹ H-NMR:

¹ H-NMR (300 MHz, CDCl ₃ ): δ 0.87 (triplet s, 6H), δ 1.2 (broad, 16H),

                       δ1.4 (m, 4H), δ1.9 (m, 4H), δ4.3 (t, 4H),

                       δ6.47 (s, 1H), δ 7.48-7.6 (m, 12H), δ8.25 (s, 1H)

Preparation Example 2 Synthesis of 9,9′-Dioctyl-2,7-Dibromofluorene

25 g (77 mmol) of 2,7-dibromofluorene and 36 g (185 mmol) of octyl bromide were dissolved in 100 ml of toluene, and 1.25 g (3.85 mmol) of TBAB (tetrabutyl ammonium bromide) were added. To the solution was added a solution of 31 g (770 mmol) of NaOH in 50 ml of water, followed by reflux for 2 days. After the reaction was completed, the mixture was extracted with a water: CHCl ₃ = 2: 1 solution, and then the extracted organic layer was dried with MgSO ₄ and concentrated to pass through a silica gel column using n-nucleic acid as a developing solution. The eluate passed through was distilled under reduced pressure to remove unreacted octyl bromide to give 40 g (yield: 95%) of the product. The structure of the resulting compound was confirmed by ¹ H-NMR.

¹ H-NMR (300 MHz, CDCl ₃ ): δ 0.65 (broad s, 4H), δ0.87 (m, 6H), δ1.21 (m, 20H),

                        δ 1.93 (m, 4H), δ 7.48 (m, 4H), δ 7.54 (m, 2H)

Example 1 Synthesis of Poly (dioctylfluorene-co-pyrazoline) (95: 5)

The inside of the flask was evacuated several times to completely remove moisture by refluxing with nitrogen, and then bis 1,5-cyclooctadiene nickel (Bis (1,5-cyclooctadiene) nickel (0); 830 mg (3.0 mmol) and bipyridal 463 mg (3.0 mmol) were added into a glove box, and the inside of the flask was evacuated and nitrogen refluxed several times. Subsequently, 10 ml of anhydrous DMF, 320 mg (1,5-Cyclooctadiene (hereinafter COD)) 320 mg (3.0 mmol) and 10 ml of anhydrous toluene were added under a nitrogen stream. After stirring for 30 minutes at 80 ° C., 81 mg (0.086 mmol) of Compound (3) obtained from Preparation Example 1 and 9,9′-dioctyl-2,7-dibromofluorene obtained from Preparation Example 2 900 mg (1.64 mmol) was added diluted in 10 ml of toluene. Next, 10 ml of toluene was added while washing all the substances on the base wall, followed by stirring at 80 ° C. for 4 days. After 4 days, 1 ml of bromopentafluorobenzene was added and stirred at 80 ° C. for about a day. After stirring was complete, the temperature was lowered to 60 ° C., and then poured into a HCl: acetone: methanol = 1: 1: 2 solution to form a paste. The precipitate was dissolved in chloroform, and then precipitated again in methanol, followed by soxhlet to give 540 mg of poly (dioctylfluorene-co-pyrazoline) (95: 5) (yield: 50%). Obtained, the molecular weight (Mw) was 48000 and the dispersion degree (MWD) was 1.9.

Example 2: Synthesis of Poly (dioctylfluorene-co-pyrazoline) (99: 1)

The inside of the Schlenk flask was evacuated several times to remove water completely by nitrogen reflux, and then 880 mg (3.2 mmol) of Ni (COD) and 500 mg (3.2 mmol) of bipyridal were placed in a glove box. Afterwards, the flask was evacuated and nitrogen refluxed several times. Subsequently, 10 ml of anhydrous DMF, 346 mg (3.2 mmol) of COD and 10 ml of anhydrous toluene were added under a nitrogen stream. After stirring for 30 minutes at 80 ° C., 17 mg (0.018 mmol) of Compound (3) obtained from Preparation Example 1 and 9,9′-dioctyl-2,7-dibromofluorene obtained from Preparation Example 2 1.0 g (1.82 mmol) was added diluted to 10 ml of toluene. Next, 10 ml of toluene was added while washing all the substances on the base wall, followed by stirring at 80 ° C. for 4 days. After 4 days, 1 ml of bromopentafluorobenzene was added and stirred at 80 ° C. for about a day. After stirring was completed, the temperature was lowered to 60 ° C., and then poured into a solution of HCl: acetone: methanol = 1: 1: 2 to form a precipitate. The precipitate was dissolved in chloroform, and then precipitated again in methanol, followed by soxhlet to give 540 mg of poly (dioctylfluorene-co-pyrazoline) (99: 1) (yield: 50%). Obtained, the molecular weight (Mw) was 65000, and the degree of dispersion (MWD) was 2.1.

Comparative Example 1: Synthesis of Poly (9,9'-dioctyl-2,7-fluorene)

The inside of the flask was evacuated several times, and nitrogen was refluxed to completely remove moisture. Then, 880 mg (3.2 mmol) of Ni (COD) and 500 mg (3.2 mmol) of bipyridal were placed in a glove box. After the addition, the flask was evacuated and nitrogen refluxed several times. Subsequently, 10 ml of anhydrous DMF, 346 mg (3.2 mmol) of COD and 10 ml of anhydrous toluene were added under a nitrogen stream. After stirring at 80 ° C. for 30 minutes, 1.03 g (1.28 mmol) of 9,9′-dioctyl-2,7-dibromofluorene obtained from Preparation Example 2 was added to dilution in 10 ml of toluene. Next, 10 ml of toluene was added while washing all the substances on the base wall, followed by stirring at 80 ° C. for 4 days. After 4 days, 1 ml of bromopentafluorobenzene was added and stirred at 80 ° C. for about a day. After stirring was completed, the temperature was lowered to 60 ° C., and then poured into a HCl: acetone: methanol = 1: 1: 2 solution, followed by stirring for at least 12 hours to form a precipitate. The precipitate was collected by a gravity filter, dissolved in a small amount of chloroform, and then reprecipitated in methanol. The precipitate was recovered through a gravity filter, and then subjected to soxhlet using methanol and chloroform in sequence to give 450 mg of poly (9,9'-dioctyl-2,7-fluorene) as a final product (yield: 60 %) Was obtained, molecular weight (Mw) was 72000, dispersion degree (MWD) was 2.0.

Fabrication of Electroluminescent Devices and Evaluation of Electroluminescent Properties

Using the polymers synthesized in Examples 1 and 2 and Comparative Example 1, an electroluminescent device was manufactured as follows.

First, the transparent electrode substrate coated with indium-tin oxide (ITO) on the glass substrate was cleanly cleaned, and then ITO was patterned into a desired shape using a photoresist resin and an etchant, and then washed again. Bayer Batron P 4083 was coated on the conductive buffer layer to a thickness of about 500 ~ 1100Å, and then baked at 180 ° C. for about 1 hour. Next, the organic electroluminescent polymer solution prepared by dissolving in toluene was spin coated on the buffer layer, and after the baking process, the solvent was completely removed in a vacuum oven to form a polymer thin film. At this time, the polymer solution was used for spin coating after filtering with a 0.2 mm filter, the polymer thin film thickness was adjusted to fall in the range of about 50 to 100 nm by adjusting the concentration and spin speed of the polymer solution. Subsequently, a cathode was formed by sequentially depositing Ca and Al on the light emitting polymer thin film while maintaining a vacuum degree of 4 × 10 ⁻⁶ torr or less using a vacuum evaporator. During deposition, the film thickness and growth rate of the film were controlled by using a crystal sensor, the emission area was 4 mm ² , and the driving voltage was a forward bias voltage as a DC voltage. The schematic structure of the fabricated electroluminescent device is shown in FIG. 2.

The electroluminescence (EL) characteristics of the electroluminescent devices fabricated above were evaluated and the results are summarized in Table 1 below. The voltage-luminance relationship and the current density-efficiency relationship of each device were graphically illustrated in FIGS. 3 and 4. Shown.

Example 1 Example 2 Comparative Example 1 Maximum emission wavelength (emission color) 490 nm (blue) 490 nm (blue) 470 nm (blue) Brightness 1600 cd / m ² 3000 cd / m ² 1200 cd / m ² Efficiency 0.6 cd / A 1.0 cd / A 0.25 cd / A Drive voltage (100 cd / m ² ) 10 V 5.7 V 5.5 V

As described in detail above, by applying the blue electroluminescent polymer of the present invention to the light emitting layer, it is possible to provide an organic electroluminescent device having excellent brightness and efficiency.

1 is a schematic diagram showing the synthesis scheme of pyrazoline monomers used in the synthesis of the polymer of the present invention,

Figure 2 is a cross-sectional view schematically showing the structure of the electroluminescent device manufactured in Example and Comparative Example,

3 is a voltage-luminance graph measured using electroluminescent devices manufactured in Examples and Comparative Examples, and

4 is a current density-efficiency graph measured using electroluminescent devices fabricated in Examples and Comparative Examples.

Claims (5)

A blue electroluminescent polymer represented by Formula 1 below: [Formula 1] Where Ar is an aromatic group having 6 to 26 carbon atoms or a heteroaromatic group having 4 to 14 heteroatoms included in an aromatic ring. The aromatic group or heteroaromatic group has an alkyl group having 1 to 12 carbon atoms. One or more alkoxy or amine groups may be substituted; R and R 'are each independently a hydrogen atom or a linear, branched or cyclic alkyl group or alkoxy group having 1 to 12 carbon atoms, or an aromatic group having 6 to 14 carbon atoms, and the aromatic group includes an alkyl group having 1 to 12 carbon atoms, One or more alkoxy groups or amine groups may be substituted; n is a real number from 0.01 to 0.99. The blue electroluminescent polymer of claim 1, wherein the Ar unit of Formula 1 has one structure selected from the group consisting of the structures of Formulas 2 and 3. [Formula 2] [Formula 3] In the formulas (2) and (3), R ₁ and R ₂ are each independently an alkyl group having 1 to 12 carbon atoms, an alkoxy group or an amine group. 3. The blue electroluminescent polymer according to claim 2, wherein the Ar unit of Formula 1 is alkylfluorene. The blue electroluminescent polymer according to claim 1, wherein the polymer has a mass average molecular weight (Mw) of 10,000 to 200,000 and a molecular weight distribution (MWD) of 1.5 to 5. An organic electroluminescent device in which the blue electroluminescent polymer of claim 1 is introduced into a light emitting layer.