KR100244160B1 - Electroluminescence display type of a luminous polymer - Google Patents

Abstract

The light emitting polymer for EL display of the present invention is a poly (2,5-dialkylphenylene-alt-N-alkyl-3,6 combination of a dialkyl substituted phenylene and a carbazole type Carbazole vinylene) polymer is represented by the following structural formula (I).

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Wherein R ₁ , R ₂ and R ₃ are the same as or different from each other, are a long chain aliphatic alkyl group or a branched aliphatic alkyl group, the long chain aliphatic alkyl group is represented by-(CH ₂ ) _n CH ₃ (where n is 1-12), Branched chain aliphatic alkyl groups are represented by -CH ₂ CHCH ₃ (CH ₂ ) _n CH ₃ , where n is 1 to 12, and p is an integer of 5 to 100.

Description

Light emitting polymer for electroluminescence display and display using same

1 is a reaction scheme for preparing poly (2,5-dihexylphenylene-alt-N-ethyl-3,6-carbazole vinylene) (PDPCVz) luminescent polymer from dichlorobenzene according to an embodiment of the present invention. to be.

2 is the ¹ H-NMR spectrum of the composite of Example 1. FIG.

3 is the ¹ H-NMR spectrum of the composite of Example 2. FIG.

4 is the ¹ H-NMR spectrum of the composite of Example 3. FIG.

5 is the ¹ H-NMR spectrum of the composite of Example 4. FIG.

6 is a ¹ H-NMR spectrum of the light emitting polymer of Example 5. FIG.

7 is a sectional view showing a schematic shape of the light emitting polymer device.

8 is a UV-Visible spectrum of a film made of the light emitting polymer of Example 5.

9 is a PL-spectrum of a film made of the light emitting polymer of Example 5. FIG.

10 is an EL-spectrum of a film made of the light emitting polymer of Example 5. FIG.

11 is a voltage-current curve of an EL display of a film made of the light emitting polymer of Example 5. FIG.

12 is a voltage-current curve of an EL display made of MEH-PPV of the comparative example.

[Field of Invention]

The present invention relates to light emitting polymers for electroluminescence displays. More specifically, the present invention relates to poly (2,5-dialkylphenylene-alt-N-alkyl-3,6-carbazole combining a combination of a dialkyl substituted phenylene and a carbazole. Vinylene (PDPCVz) -based light emitting polymer.

Background of the Invention and Prior Art

In the modern information electronics industry, optoelectronic devices using light energy into electric energy or conversion of electric energy into light energy are very important. Such semiconductor optoelectronic devices can be broadly classified into electroluminescent devices, semiconductor laser devices, light receiving devices, and the like. A flat panel display is a light and thin element that solves the inconvenience of image realization by a conventional CRT method, and generically refers to a device having a CRT level or more. Early displays were mainly used as wall-mounted TVs, but in the 21st century's information and multimedia era, many applications such as computer monitors, notebook PCs, and PDA terminals have been developed. In recent years, most displays are light-receiving types, while self-emissive electroluminescence displays have a fast response and self-emissive type, which does not require backight, has excellent brightness, and wide viewing angle. There is a lot of research in progress. In the case of an EL device made of an inorganic material, a driving voltage is required to be AC 20V or more, and the manufacturing method of the device is made by vacuum deposition, which makes it difficult to enlarge the size and has a high cost. However, since 1987, when Eastmann Kodak published a device made of a pigment having a π-conjugated structure called alumina-quinone (Alq ₃ ), research on EL devices using organic materials has been active. The organic material has an advantage of easy synthesis of various types of materials due to the simple synthesis route, color tuning, and low mechanical strength and crystallization by heat. Replacement is in progress with devices. Due to the superposition of the π-electron wave functions in the polymer backbone, the energy level is separated into a conduction band and a valence band, and the band gap energy corresponding to the energy difference causes the polymer's semiconductor The nature is determined and full color can be realized. Such polymers are referred to as "π-conjugated polymers". A study on electroluminescence was reported by Keiichi Kaneto Group in 1974 to report that electroluminescence of poly (ethylene terephthalate) in high electric fields has not been actively studied since then. A light emitting device made of para-phenylenevinylene) (poly (p-phenylenvinylene): PPV) has been announced for the first time, and its application to electroluminescent displays using π-electron conjugated polymers has been concentrated. As a representative organic EL polymer, a π-electron conjugated polymer derivative called poly (p-phenylenvinylene) (PPV) is typically used.

In the case of poly (p-phenylenevinylene) derivative, which is a material of a typical polymer electroluminescent device, it has a limitation in mass production due to low solubility, polymerization time, and polymerization yield in organic solvents. have.

The general PPV organic EL material has the following problems.

First, in the case of a polysulfonium precursor, which is a precursor of PPV, polymerization time and yield are very low and expensive.

Second, the sulfonium salt must be removed to make a complete PPV derivative, which is difficult to remove completely.

Third, when the thin film (600 Å) is formed, unreacted sulfonium salts are gradually removed, resulting in pinholes, and thus the uniformity of the film is not good.

Fourth, soluble PPV can be synthesized, but the synthesis and polymerization conditions are very demanding.

Therefore, the present inventors have led to the development of a stable light emitting polymer that eliminates the above-mentioned defects of the PPV-based organic electroluminescent polymer material, realizes blue color in the short UV wavelength, and has no reactivity at the interface with the electrode.

[Purpose of invention]

An object of the present invention is to provide a light emitting polymer for EL display which is superior in solubility to an organic solvent than a conventional PPV light emitting polymer.

Another object of the present invention is to provide a light emitting polymer having excellent interfacial properties with the electrode because there is no oxygen atom in the polymer backbone to cause oxidation reaction with the electrode.

It is still another object of the present invention to provide a light emitting display having a very low driving voltage than a conventional blue light emitting polymer and capable of driving a uniform blue light and having excellent electro-optic properties.

Still another object of the present invention is to provide a light emitting polymer having excellent light transmittance, environmental resistance, adhesion to a substrate, thin film formation ability, and electric field stability to be provided as an electronic material.

The above and other objects of the present invention can be achieved by the present invention described below.

[Summary of invention]

The light emitting polymer for EL display of the present invention is poly (2,5, -dialkylphenylene-alt-N-alkyl-3, in which a dialkyl substituted phenylene and a carbazole type are combined; 6-carbazole vinylene) polymer is represented by the following structural formula (I).

Wherein R ₁ , R ₂ and R ₃ are the same or different from each other and are a long chain aliphatic alkyl group or a branched aliphatic alkyl group, and the long chain aliphatic alkyl group is represented by-(CH ₂ ) nCH ₃ (where n is 1-12), and The chain aliphatic alkyl group is represented by -CH ₂ CHCH ₃ (CH ₂ ) nCH ₃ (where n is 1 to 12), and p is an integer of 5 to 100.

Hereinafter, the details of the present invention will be described below.

Detailed Description of the Invention

MEH-PPV, a typical conventional PPV-based light emitting polymer, has excellent solubility because alkoxide is substituted for a substituent, but has a disadvantage of absorbing UV light at a long wavelength because the electron density is very high. . Accordingly, the present invention aims to synthesize a stable light emitting polymer having a PPV skeleton, which is the most stable structure as a light emitting polymer, absorbed in the short wavelength of UV and controlling blue color by controlling substituents to realize blue color and having no reactivity at the interface with the electrode. have. Therefore, in order to reduce the reactivity at the interface with the electrode while maintaining the skeleton of the PPV, long carbon side chains were introduced into the carbazole which controls the mobility of the light emitting portion and the charge so as to increase the solubility without introducing oxygen atoms. Synthesis of blue monomers with new dialkyl substituents could be applied to Wittig polymerization, which has been studied in recent years, rather than conventional precursors, to obtain soluble and excellent electro-optic properties.

The light emitting polymer for EL display of the present invention is poly (2,5, -dialkylphenylene-alt-N-alkyl-3, in which a dialkyl substituted phenylene and a carbazole type are combined; 6-carbazole vinylene) polymer is represented by the following structural formula (I).

Wherein R ₁ , R ₂ and R ₃ are the same or different from each other and are a long chain aliphatic alkyl group or a branched aliphatic alkyl group, and the long chain aliphatic alkyl group is represented by-(CH ₂ ) nCH ₃ (where n is 1-12), and The chain aliphatic alkyl group is represented by -CH ₂ CHCH ₃ (CH ₂ ) nCH ₃ (where n is 1 to 12), and p is an integer of 5 to 100. In a preferred embodiment of the invention R ₁ and R ₂ are hexyl group, methylhexyl group or ethylhexyl group and R ₃ is ethyl group.

1 is a reaction scheme for preparing poly (2,5-dihexylphenylene-alt-N-ethyl-3,6-carbazole vinylene) (PDPCVz) light emitting polymer from dichlorobenzene according to an embodiment of the present invention. It is shown.

The light emitting polymer of the present invention shown in FIG. 1 has a structure in which a hexyl group is bonded to 2,5 positions of phenylene and an ethyl group is bonded to a nitrogen atom of carbazole. The description of each step of preparing poly (2,5-dihexyl phenylene-alt-N-ethyl-3,6-carbazole vinylene) luminescent polymer from dichlorobenzene in FIG. 1 is well described in the Examples. .

The light emitting polymer of the present invention is soluble in an organic solvent, in particular, dissolved in a solvent such as THF, chloroform or trichloroethylene at 2.0 to 0.5% by weight, and the thickness can be controlled by spin coating. A uniform film free from defects such as pin holes is formed, and a light emitting polymer thin film having excellent adhesion to a substrate is formed.

The invention will be further illustrated by the following examples, which are intended to illustrate the invention and are not intended to limit the protection scope of the invention.

EXAMPLE

Example 1 Preparation of 2,5-dihexylbenzene

Injecting nitrogen into a 250 ml three-necked flask, 10 ml of diethyl ether was removed at room temperature, and 15 g (0.625 mole) of magnesium was added thereto and stirred. Add 100 g (0.61 mole) of hexyl bromide to 50 ml of diethyl ether, add to the dropping funnel, and slowly add for 1 hour. The reaction is continued while stirring the reaction temperature at 45 ° C. for 3 hours. After the reacted Grignard reactant was placed in a dropping funnel, 42 g (0.29 mole) of 1,4-dichlorobenzene, 0.3 g of NiCl ₂ (dppp) and 80 ml of diethyl ether were slowly added to a 1 L three-neck flask and allowed to react at room temperature for 24 hours. 6 N HCl was slowly added to neutralize the solid reaction product, extracted with diethyl ether, dried over anhydrous MgSO ₄ , solvent removed, and vacuum distillation (122 ° C./0.1 mm Hg) separated the reaction. Structural analysis was confirmed by ¹ H-NMR (Figure 2).

Example 2 Preparation of 2,5-bis (chloromethyl) -1,4-dihexylbenzene

1,4-Dihexylbenzene (20 g, 0.081 mole) and chloromethyl methyl ether (18 g, 0.226 mole) are cooled to 10 ° C. 60% fuming sulfuric acid (11.2g) is slowly added dropwise at 0 ° C for 30 minutes. After completion of the dropwise addition, the reaction mixture is stirred at room temperature for 22 hours. After completion of the reaction, the reaction mixture is placed in 200 ml of cooling water, and a reaction precipitate is formed. After filtration and separation, the developing solvent is separated by hexane using a column. Structural analysis was confirmed by 1 H-NMR (Figure 3).

Example 3 Preparation of 1,6-bis (chloromethyl) -2,5-dihexylbenzene triphenylphosphonium salt

5 g of 2,5-bis (chloromethyl) -1,4-dihexylbenzene and 7.66 triphenylphosphine were added to 80 ml of DMF and reacted under reflux for 12 hours. After the reaction was cooled to room temperature, it was added to 1 L of ether, stirred for 1 hour, white solid was separated and dried. The reaction yield was about 45% and the structural analysis was confirmed by ¹ H-NMR (FIG. 4).

Example 4 Preparation of N-ethyl-3,6-diformyl-carbazole

After cooling 109 g of DMF to 0 ° C., 228 g of phosphorus oxychloride was slowly added dropwise. After slowly raising the reaction to room temperature, 30 g of N-ethylcarbazole and 75 ml of 1,2-dichloroethane were slowly added dropwise. Care must be taken to ensure that the reaction temperature is not too high. The reaction mixture was reacted at 90 ° C. for 20 hours, cooled to room temperature, poured into 1.5 L of ice water, extracted with chloroform, dried over anhydrous MgSO ₄ , and separated by column using hexane and ethyl acetate. The reaction yield was about 40% and the structural analysis was confirmed by ¹ H-NMR (FIG. 5).

Example 5: Preparation of poly (2,5-dihexyl phenylene-alt-N-ethyl-3,6-carbazole vinylene) light emitting polymer

0.7 g of 1,6-bis (chloromethyl) -2,5-dihexylbenzene triphenylfonium salt as the monomer prepared in Example 3 and N-ethyl-3,6-diphore as the monomer prepared in Example 4 0.2 g of mill-carbazole are completely dissolved in 10 ml of chloroform solvent and 4 ml of EtOH. 2.15 mL (1 M) of potassium t-butoxide was added very slowly, and a precipitate slowly formed on the reaction vessel wall and allowed to proceed with polymerization for 6 hours. Then, 1 ml of 1N HCl is added to terminate the polymerization reaction, and the crude luminescent polymer in powder form is separated by adding to MeOH. The unreacted monomers and oligomers were removed again using a Soxhlet apparatus and precipitated again in MeOH to obtain pure light emitting polymers in a yield of about 60%. Structural analysis was confirmed by ¹ H-NMR (Figure 6).

Example 6 Manufacture of Polymer Light Emitting Display

A device in the form of a single layer was manufactured using the light emitting polymer of the present invention prepared in Example 5 (Fig. 7). In order to manufacture the polymer light emitting display, the glass substrate coated with the transparent electrode was cleaned in order of boiling MeOH, IPA, and acetone, and then the transparent electrode was patterned by a photolithographic method using a photoresist resin. Each light emitting polymer was dissolved in trichloroethane at 1.5% by weight, and impurities and dust were removed using a 0.2 μm filter, coated with a spin coator to a thickness of about 1000 to 1500Å, followed by baking to completely remove trace solvents. . And Al metal was vacuum deposited while maintaining the vacuum degree below 1x10 <^-5> Torr to form an electrode. The film thickness and the growth rate of the film during Al deposition were controlled using a film thickness monitor. The emission area is 2mm2 and the driving voltage is forward bias voltage.

Example 7 Electro-optical Characterization

The luminescent polymer prepared in Example 5 exhibited a maximum UV-absorption wavelength at 372 nm in the about UV-Vis spectrum of the film cast on ITO using trichloroethylene solvent (FIG. 8). The band gap of the light emitting polymer of the present invention is about 2.64 eV calculated from the band edge of the UV-spectrum.

When the excitation wavelength was the wavelength of the maximum absorption peak of each of the light emitting polymers, the fluorescence spectrum (photoluminescence spectrum) showed the maximum absorption at 490 nm (FIG. 9). PL intensity was found to be significantly superior to the existing blue light emitting polymer. 11 is a current-voltage curve in the forward bias, and the current starts to flow at about 8V, and the turn on voltage is about 10V and the light is gradually emitted.

Comparative Example

The following comparative examples compared the electro-optic properties with MEH-PPV. FIG. 10 shows the emission spectrum measured by fixing the voltage at 10V and emits light in the blue region.

12 is a current-voltage curve when MEH-PPV is used as the light emitting layer.

You can see the current flows slowly when the turn on voltage is about 7V. It can be seen that the resistance of the MEH-PPV light emitting layer is lower than that of the light emitting layer of Example 5.

Simple modifications and variations of the present invention can be readily used by those skilled in the art, and all such variations or modifications can be considered to be included within the scope of the present invention.

Claims (3)

A light emitting polymer for EL display, characterized by the following structural formula (I) combining a dialkyl substituted phenylene system and a carbazol e system:

Wherein R ₁ , R ₂ and R ₃ are the same as or different from each other, and are represented by-(CH ₂ ) nCH ₃ (where n is 1-12), a long-chain aliphatic alkyl group or -CH ₂ CHCH ₃ (CH ₂ ) nCH ₃ Is a branched chain aliphatic alkyl group wherein n is from 1 to 12, and p is an integer from 5 to 100 The light emitting polymer for EL display according to claim 1, wherein R ₁ and R ₂ are a hexyl group, a methylhexyl group or an ethylhexyl group, and R ₃ is an ethyl group. An EL display comprising the light emitting polymer of claim 1.

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