JPH09104732A - Blue light emitting polymer and light emitting diode using the same - Google Patents

Abstract

(57) Abstract: A blue light emitting polymer and a light emitting diode using the same are provided. A conjugated polymer containing phenylene having a silicon-containing side chain in its main chain not only emits blue light, but also has excellent solubility in organic solvents and forms a polymer thin film with little scratches. Is easy. Therefore, the blue light emitting diode in which the positive electrode layer and the negative electrode layer are formed on both surfaces of the conjugated polymer layer has excellent luminous efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blue light emitting polymer and a light emitting diode using the same, and more specifically, it is capable of emitting blue light for a long time and is excellent in light emitting efficiency. And a light emitting diode employing the same.

[0002]

2. Description of the Related Art Conjugated polymers
Has electrical, non-linear optical and luminescent properties. In addition, since polymers are excellent in processability and low in cost as compared with metals and semiconductors, active research is being conducted on applications of conjugated polymers in the electric / electronic industry field.

However, most of the presently developed conjugated polymers have poor solubility, and if the length of the spacer group consisting of the alkyl group in the main chain is increased in order to increase the solubility, mechanical properties increase. There is a problem that various properties are impaired, and there is a limit to application. Therefore, electrical conductivity,
Active researches have been conducted on conductive polymers having not only nonlinear optical response characteristics and light emission characteristics but also excellent processability.

On the other hand, the current liquid crystal display element (LCD) is
It is widely used because of its low power consumption and light weight, but it is difficult to increase its size and color. Due to such a limitation of the liquid crystal display element, a light-emitting diode (hereinafter, LED)
There is an increasing interest in display devices that employ the.

Since the display device using the light emitting diode has far superior response and contrast as compared with the light receiving type liquid crystal display device, it can replace the liquid crystal display device which is a cathode ray tube and a flat panel type display device. Is foreseen.

Most of the light emitting diodes currently used are made of an inorganic crystal, but it is difficult to reduce the power consumption, colorize and upsize the light emitting diode made of such an inorganic material, and the driving voltage is high. There is a limit that it is difficult to obtain light in the green and blue regions.

[0007] Therefore, in order to overcome the limitation of inorganic crystals, research on organic polymer materials as materials for light emitting diodes has been concentrated. The results of research on polymer-based light emitting diodes were first published in 1990 by the Cambridge group in the United Kingdom (US Pat. No. 5,247,190). The polymer material used as the light emitting layer is poly (1,4-phenylenevinylene) having a conjugated double bond and has a structure represented by the following formula (I).

[0008]

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The poly (1,4-phenylene vinylene)
Is a conjugated polymer in which phenyl groups and double bonds are alternately linked, emits green light at a wavelength of 540 nm, and is 0.01% when aluminum and ITO (Indium Tin Oxide) are used for the cathode and the anode, respectively. The luminous efficiency was shown as%.

Thereafter, the Cambridge Group and the Heega Group (US Santa Barbara) conducted a study on poly (1,4-phenylene vinylene) (PPV) and its derivatives (WO 9216023),
It was reported that the emission efficiency was improved to about 4% through the development of various electrodes and new emission layers (Nature 1993, 365,
628). However, since PPV and its derivative have a complete conjugated double bond, there is a disadvantage that light having a wavelength region below green cannot be obtained.

As a result, research on the development of blue-emitting polymers has been concentrated, and it was announced that polyparaphenylene (PPP) emits blue light at 459 nm or less (Synth. Met. 1992, 51 383), and polyalkyl. It was announced that Floren exhibited a blue color at 470 nm (Jpn.
J. Appl. Phys. 1991, 30 ,, L1941). However,
PPP and alkylfluorene are difficult to synthesize, and the quality and processability of the film deteriorate, resulting in a very short emission life.

Meanwhile, a blue light emitting polymer (II) having a certain conjugated double bond unit made of phenylene vinylene was developed by the Karasz group of Massachusetts State Institute of Technology (MIT) in the United States.

[0013]

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It has been announced that the polymer represented by the above formula (II) is dissolved in an organic solvent and has excellent processability and film quality (Macromolecules 1993).
, 26 , 1188). However, when such a polymer is used as a light emitting material, there is a problem that the spacer group added to increase the solubility is large and the excellent mechanical properties of PPV are impaired.

Japanese Unexamined Patent Publication (Kokai) No. 5-320635 discloses the synthesis of blue-green and blue light-emitting polymers represented by the following formula (III).

[0016]

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In the polymer substance represented by the above formula (III), the most main part is an Ar ₂ unit, and this Ar ₂ unit has a form in which an alkoxy group is symmetrically replaced by phenylene. However, the alkoxy group is a strong electron donating group.
Since it is a g group), it has a function of shifting the absorption wavelength of the polymer to the long wavelength side and shifting the wavelength of emitted light to the long wavelength side. Therefore, the emission wavelength of the polymer in which the alkoxy group is replaced is 520 to 530 nm,
It comes to be located in the blue-green region where the green color is deep.

On the other hand, when the Ar ₂ unit is phenyl, naphthalene, biphenyl or the like having no substituent, the emission wavelength shifts to the shorter wavelength side, but the solubility of the polymer is not good.

On the other hand, when the number of spacer groups is increased in order to increase the solubility, the thermal stability of the film is poor and the life is shortened, so that there is a problem that its application is difficult. Therefore, there is an increasing need for a blue light emitting polymer substance having a high solubility in an organic solvent.

On the other hand, although a general light emitting diode is schematically shown in FIG. 1, a positive electrode 2 is generally formed on a substrate 1 by a method such as thermal evaporation, and a thin film type polymer is formed thereon. It is manufactured by the process of forming the negative electrode 4 after forming the film 3. In this case, in the formation of the polymer film, it is common to dissolve the polymer substance or the polymer precursor in a solvent and then spin-coat it. However, if the solubility of the polymer or polymer precursor is not good, not only is it difficult to form a polymer film, but also the luminous efficiency of the formed polymer is not good.

FIG. 2 schematically shows a process of electroluminescence when an electric field is applied to the light emitting diode as shown in FIG. As can be seen from FIG. 2, when an electric field is applied through each electrode of FIG. 1, polaron (polaron, p ⁻ , p ⁺ ) charged negatively and positively is generated due to the structural relaxation action of the polymer chain. Immediately forms polaron-exciton, and then within a very short time, it emits light by recombining a single polaron-exciton.

However, if there is a flaw in the polymer, the flaw becomes the center of recombination that does not emit light. Such scratches are generated in the process of processing when a polymer having a poor solubility is used, and a light emitting diode manufactured by using a polymer having a poor solubility has a problem that the luminous efficiency is also poor.

[0023]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above problems and provide a blue light emitting polymer which can emit light in the blue region for a long time and is excellent in processability. It is in.

Another object of the present invention is to provide a blue light emitting diode which can emit light in the blue region for a long time and is excellent in thermal stability.

[0025]

In order to achieve the above-mentioned object, the present invention is characterized by having the following general formula (IV) and having a weight average molecular weight of 5,000 to 30,000 and high blue emission. It provides a molecule.

[0026]

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In the above general formula (IV), X is one selected from the group consisting of the following formulas (V) and (VI), and Y is the following general formulas (VII) and (VIII). Z is one selected from the group consisting of the following formulas (V) and (IX), and n is 1 to 2
0 and m are 5 to 100.

[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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However, the above general formulas (VII) and (VIII
), R ₁ , R ₂ and R ₃ are each C _{1 to} C ₈
It is an alkyl group.

Particularly, n in the general formula (IV) is 2 to 5, and R ₁ , R ₂ and R _{3 in the} general formulas (VII) and (VIII) are each a C ₁ -C ₄ alkyl group. What is desirable is.

In order to achieve the above other object, the present invention provides a light emitting diode including a positive electrode layer, a negative electrode layer and a polymer layer formed between the two electrode layers, wherein the polymer is The present invention provides a blue light emitting diode characterized by comprising a conjugated polymer represented by the above general formula (IV) as a layer and having a weight average molecular weight of 5,000 to 30,000.

In order to achieve the above other object, the present invention provides a blue light emitting diode characterized in that the positive electrode is one selected from the group consisting of gold, platinum and ITO. To do.

Further, in order to achieve the above other object, the present invention provides a blue light emitting diode characterized in that the negative electrode is one selected from the group consisting of aluminum, magnesium and calcium. To do. Furthermore, in order to achieve the above other object, the present invention provides a blue light emitting diode characterized in that at least one of the positive electrode layer and the negative electrode layer is transparent. It is a thing.

In the present invention, in the blue light-emitting polymer (or the conjugated polymer used in the polymer layer of the blue light emitting diode) represented by the above general formula (IV) and having a weight average molecular weight of 5,000 to 30,000. , Phenylene replaced by a group containing silicon is contained in the main chain. That is, since silicon has an electric property similar to that of a hydrogen atom that gives or pulls an electron, it can emit blue light having a wavelength much shorter than that of a conventional alkoxy-substituted polymer. In addition, unlike a polymer having no substituent, it has an excellent solubility in an organic solvent such as chloroform, dichloromethane, tetrahydrofuran, and cyclohexanone, so that it is easy to form a polymer thin film having uniform scratches. Also, since the spacer group has a short length and good solubility, the mechanical strength and thermal stability similar to PPV can be maintained.

[0039]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to a method of manufacturing a blue light emitting polymer and a light emitting diode using the same.

Monomer Synthesis (1) 2,5-bis (trialkylsilyl) -1,4
-Synthesis of xylene bis (triphenylphosphonium bromide) (X) As shown in the following formula, 2,5-bis (trialkylsilyl) -1,4-bis (bromomethyl) benzene and triphenylphosphine are reacted with DMF. After that, it is precipitated with diethyl ether. Subsequently, the precipitate is filtered and dried in vacuum to obtain white 2,5-bis (trialkylsilyl) -1,4-xylene bis (triphenylphosphonium bromide) (X).

[0041]

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(2) 2-trialkylsilyl-1,4
-Synthesis of xylene bis (triphenylphosphonium bromide) (XI) 2-trialkylsilyl-1,4- as shown in the formula below.
Bis (bromomethyl) benzene and triphenylphosphine are reacted with DMF and then precipitated with diethyl ether. Then, the precipitate is filtered and dried in vacuum to obtain a white product represented by the following formula (XI).

[0043]

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(3) Synthesis of 1,3-bis (4-formyl-phenoxy) alkane An alkane (dibromoalkane) in which 4-hydroxybenzaldehyde and both ends are replaced by one bromine is represented by the following formula. ) Is reacted with a solution of potassium carbonate in DMF and then cooled to precipitate. Then, the precipitate is filtered and dried in a vacuum, and the precipitate is recrystallized from ethanol to obtain a white product represented by the following formula (XII).

[0045]

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(4) 1,3-bis (4-formyl-
Synthesis of 2,6-dimethoxyphenoxy) alkane As shown in the following formula, 4-hydroxybenzaldehyde and alkane (dibromoalkane) in which both ends are replaced by one bromine are dissolved in potassium carbonate in DM.
After reacting with the F solution, the solution is cooled to precipitate. Then
The precipitate is filtered and dried under vacuum, and the precipitate is recrystallized from ethanol to obtain a white product represented by the following formula (XIII).

[0047]

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Synthesis of Polymer (1) Synthesis of P-1 After completely dissolving the same equivalent amounts of the (X) and (XII) monomers in ethanol and chloroform as shown in the following formula, a slight excess amount is obtained. Add sodium ethoxylate and react at room temperature. Then, the reaction product is extracted with chloroform and then precipitated in methanol to obtain a final polymer represented by P-1.

[0049]

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(2) Synthesis of P-2 When the same equivalents of (XI) and (XII) monomers are used and a process such as the above process (1) is performed, a final polymer represented by P-2 is obtained. can get.

[0051]

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(3) Synthesis of P-3 When the steps (1) and (2) are carried out using the same equivalent amounts of the (X) and (XII) monomers, the final polymer represented by P-3 is obtained. can get.

[0053]

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(4) Synthesis of P-4 By using the same equivalent amount of (XI) and (XIII) monomers, the final polymer represented by P-4 is obtained through the process such as the above process (1). can get.

[0055]

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[0056] manufacturing a light emitting diode in the form of a MIS (metal-semiconductor-metal) structure as shown in FIG. 1 by using the polymer produced by the production present invention of a light emitting diode. In this case, the positive electrode of the light emitting diode is made of gold, platinum, I having a high work function.
Desirably, the negative electrode is made of TO or the like, and the negative electrode is made of aluminum, magnesium, calcium, or the like having a relatively low work function.

In this case, at least one of the positive electrode and the negative electrode should be transparent in order to easily transmit the emitted light.

[0058]

EXAMPLES The present invention will be described in detail below with reference to Examples and Comparative Examples, but the present invention is not necessarily limited thereto.

Monomer Synthesis 1) Synthesis of 2,5-bis (trimethylsilyl) -1,4-xylenebis (triphenylphosphonium bromide) 7.4 g of 2,5-bis (trimethylsilyl) -1,4
-Bis (bromomethyl) benzene and 4.3 g of triphenylphosphine were reacted under 30 ml of DMF for 24 hours. The reacted solution was precipitated with diethyl ether to obtain a white precipitate. The precipitate was filtered and dried under vacuum to obtain the final product represented by the following formula (X-1) (yield 89%).

Melting point: 299 to 300 ° C. ¹ H-NMR (DMSO-d ₆ ): δ 7.94 to 7.
55 (m, 30H), 7.05 (s, 2H), 5.01
(D, 4H), -0.31 (s, 18H) Elemental analysis: Calculated value (C 64.35%, H 5.79).
%), Measured value (C 63.01%, H 6.04%)

[0061]

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2) Synthesis of 2-trimethylsilyl-1,4-xylenebis (triphenylphosphonium bromide) 3.0 g of 2-trimethylsilyl-1,4-bis (bromomethyl) benzene and 5.2 g of triphenylphosphine (30 ml) It was made to react with DMF for 24 hours. The reacted solution was precipitated with diethyl ether to obtain a white precipitate. The precipitate was filtered and dried under vacuum to obtain the compound of formula (XI
A white final product represented by -1) was obtained (yield 80
%).

Melting point: 233-235 ° C. ¹ H-NMR (DMSO-d ₆ ): δ 7.91-7.
49 (m, 30H), 7.25 (s, 1H), 6.78
(D, 1H), 6.65 (d, 1H), 5.80 (d,
2H), 5.01 (d, 2H), -0.15 (s, 9
H) Elemental analysis: Calculated value (C 65.56%, H 5.36)
%), Measured value (C 61.85%, H 5.33%)

[0064]

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3) Synthesis of 1,3-bis (4-formyl-phenoxy) propane 10.0 g of 1,3-dibromopropane was reacted with 100 ml of DMF in 6.2 g of potassium carbonate solution under reflux for 24 hours. It was The reaction mixture was poured into cold distilled water to precipitate, then filtered and vacuum dried. The obtained compound was put into ethanol and recrystallized to obtain the following formula (XII-1).
A white product represented by was obtained (yield 76%).

Melting point: 129 to 130 ° C. ¹ H-NMR (200 MHz, CDCl ₃ ) δ 9.
80 (s, 2H), 7.91 (s, 2H), 7.79
(D, 4H), 6.83 (d, 4H), 4.22 (t,
4H), 2.30 (q, 2H) ¹³ C-NMR (CDCl ₃ ) δ 190.7, 16
3.7, 131.9, 130.0, 114.6, 64.
4, 28.8 Elemental analysis: Calculated value (C 71.82%, H 5.67)
%), Measured value (C 70.43%, H 5.60%)

[0067]

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4) 1,5-bis (4-formyl-2,
Synthesis of 6-dimethoxyphenoxy) pentane 10.0 g of 4-hydroxybenzaldehyde and 6.3
g of 1,5-dibromopentane was reacted with 100 ml of DMF with 6.2 g of potassium carbonate solution under reflux for 24 hours. The reaction was poured into cold distilled water to precipitate, then filtered and vacuum dried. The obtained compound was recrystallized from ethanol to obtain a white product represented by the following formula (XIII-1) (yield 60%).

¹ H-NMR (200 MHz, CDC
l ₃ ) δ 9.82 (s, 2H), 7.08 (s, 2)
H), 4.05 (t, 4H), 3.86 (s, 12)
H), 1.93 to 1.71 (m, 4H), 1.61
(M, 2H) Elemental analysis: Calculated value (C 71.82%, H 5.67)
%), Measured value (C 70.43%, H 5.60%)

[0070]

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Example 1 Polymer Synthesis 3.28 g of 2,5-bis (trimethylsilyl) -1,
4-Xylene bis (triphenylphosphonium bromide) (X-1) and 1.00 g of 1,3-bis (4-formyl-phenoxy) propane (XII-1) (same equivalent) in 20 ml of ethanol and chloroform solvent. After the solution was added and completely dissolved, 0.6 g of sodium ethoxylate was added thereto and reacted for 24 hours. After the reaction, the product was extracted with chloroform, water was removed and the product was precipitated in methanol to give poly [1,3-propanedioxy-1,4-phenylene-1,2-ethylene- (2,5-bis (trimethylsilyl)). -1,4-phenylene) -1,2-ethenylene-1,4-phenylene] (P-1-1) was synthesized.

P obtained above with polystyrene as the standard
The molecular weights for 1-1 were measured and shown in Table 1. The number average molecular weight was 2,100 and the weight average molecular weight was 7,200. Also, the polymer P-1-1 was excited using a 330 nm xenon lamp as a light source, and the photoluminescence (PL) spectrum emitted from the polymer was recorded and shown in Table 1. It fired. Here, a lock-in having a chopping frequency of 150 Hz.
Recordings were made using a Perkin Elma LS-50 fluorescence system with an amplifier.

Production of Light Emitting Diode 1.2 g of the obtained P-1-1 was dissolved in 12 ml of cyclohexanone and filtered with a microfilter to remove dust. Then, the ITO formed on the substrate
The layer was washed with an ultrasonic washer and then spin-coated with the solution on the ITO layer while rotating the substrate at a speed of 4000 rpm for 15 seconds to form a polymer layer having a thickness of 140 nm. Finally, a light emitting diode of the present invention was manufactured through a process of coating aluminum with a vacuum deposition method to form a rectangular electrode having a diameter of 5 mm.

The wavelength of light emitted from the aluminum electrode to the ITO electrode side was measured by applying a voltage of 25 V through each electrode of the manufactured light emitting diode.
The wavelength was 470 nm and was in the blue region. Here, the wavelength of light was measured using a double grating monochromator (Spex 270M) equipped with a photomultiplier tube (Hammatuz R955) as a detector.

Example 2 3.02 g of 2-trimethylsilyl-1,4-xylene bis (triphenylphosphonium bromide) (XI-
1) and 1.00 g of 1,3-bis (4-formyl-phenoxy) propane (XII-1) were used in the same manner as in Example 1 except that poly [1,3-propanediene was used. Oxy-1,4-phenylene-1,2-ethenylene- (2-trimethylsilyl-1,4-phenylene)-
1,2-Ethenylene-1,4-phenylene] (P-2-
1) was synthesized.

P-2 produced by the method as in Example 1
After measuring the molecular weight and PL spectrum for -1, a light emitting diode was fabricated and the EL wavelength was measured. Example 3 2.14 g of 2,5-bis (trimethylsilyl) -1,
4-Xylene bis (triphenylphosphonium bromide) (X-1) and 1.00 g of 1,5-bis (4-formyl-2,6-dimethoxyphenoxy) pentane (XII
By the same method as in Example 1 except that I-1) was used, poly [1,5-propanedioxy- (2,6
-Dimethoxy-1,4-phenylene) -1,2-ethenylene- (2,5-bis (trimethylsilyl-1,4-phenylene) -1,2-ethenylene- (3,5-dimethoxy-1,4-phenylene ] (P-3-1) was synthesized.

P-3 produced by the same method as in Example 1
After measuring the molecular weight and PL spectrum with respect to -1, a light emitting diode was manufactured and the EL wavelength was measured.

Example 4 2.00 g of 2-trimethylsilyl-1,4-xylene bis (triphenylphosphonium bromide) (XI-
1) and 1.00 g of 1,5-bis (4-formyl-2,
By the same method as in Example 1 except that 6-dimethoxyphenoxy) pentane (XIII-1) was used,
Poly [1,5-propanedioxy- (2,6-dimethoxy-1,4-phenylene) -1,2-ethenylene- (2
-Trimethylsilyl-1,4-phenylene) -1,2-
Ethenylene- (3,5-dimethoxy-1,4-phenylene] (P-4-1) was synthesized.

P-4 produced in the same manner as in Example 1
After measuring the molecular weight and PL spectrum for -1, a light emitting diode was fabricated and the EL wavelength was measured.

[0080]

[Table 1]

[0081]

As described above, the polymer manufactured according to the present invention not only emits blue light, but also has excellent solubility in an organic solvent, and a blue light emitting diode manufactured using this polymer emits high light.

[Brief description of the drawings]

FIG. 1 is a sectional view schematically showing a general light emitting diode.

FIG. 2 is a view schematically showing a process of emitting light when an electric field is applied to the light emitting diode of FIG.

[Explanation of symbols]

 1 ... Substrate, 2 ... Positive electrode, 3 ... Polymer substance, 4 ... Negative electrode.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication location H05B 33/14 H05B 33/14 (72) Inventor Yong Doi, Chungcheongnam-do, Korea Seongdong 371-1 Department of Chemistry, Korea Institute of Science and Technology (72) Inventor Hiroyuki Shen, Incheon Chungcheongnam-do, Republic of Korea No. 99, Yukaku-dong, Yuseong-gu, 132, Hanbuk Apartment 132, Incheon (72) City Bung Tang Book ▲ Hyun ▼ 87, Dong-dong Illustrated Maul Hanshin Apartment 115 115 號

Claims (7)

[Claims] 1. A blue light-emitting polymer represented by the following general formula (IV), having a weight average molecular weight of 5,000 to 30,000. Embedded image However, in the above general formula (IV), X is one selected from the group consisting of the following formulas (V) and (VI), and Y is a group consisting of the following general formulas (VII) and (VIII) Z is one selected from the group consisting of the following formulas (V) and (IX), n is 1 to 20, and m is 5 to 100. Embedded image Embedded image Embedded image Embedded image Embedded image However, in the general formulas (VII) and (VIII), R ₁ ,
R ₂ and R ₃ are each a C ₁ -C ₈ alkyl group. 2. A light emitting diode comprising a positive electrode layer, a negative electrode layer and a polymer layer formed between the two electrode layers, wherein the polymer layer has the following general formula (IV): Shown,
A blue light-emitting diode comprising a conjugated polymer having a weight average molecular weight of 5,000 to 30,000. Embedded image However, in the above general formula (IV), X is one selected from the group consisting of the following formulas (V) and (VI), and Y is a group consisting of the following general formulas (VII) and (VIII) Z is one selected from the group consisting of the following formulas (V) and (IX), n is 1 to 20, and m is 5 to 100. Embedded image Embedded image Embedded image Embedded image Embedded image However, in the general formulas (VII) and (VIII), R ₁ ,
R ₂ and R ₃ are each a C ₁ -C ₈ alkyl group. 3. The positive electrode is gold, platinum and ITO.
The blue light emitting diode according to claim 2, wherein the blue light emitting diode is one selected from the group consisting of: 4. The blue light emitting diode according to claim 2, wherein the negative electrode is one selected from the group consisting of aluminum, magnesium and calcium. 5. The blue light emitting diode according to claim 2, wherein n in the general formula (IV) is 2 to 5. 6. The blue light emission according to claim 2, wherein R ₁ , R ₂ and R _{3 in the} general formulas (VII) and (VIII) are each a C ₁ -C ₄ alkyl group. diode. 7. The blue light emitting diode according to claim 2, wherein at least one of the positive electrode layer and the negative electrode layer is transparent.