KR100560776B1 - Hole transporting material AND THE ORGANIC LIGHTING DEVICE USING THE SAME - Google Patents

Abstract

The present invention provides a compound for hole transport containing thieno [3,2-b] thiophene represented by the following formula (1).

In addition, the present invention provides a material for hole transport, characterized by using thieno [3,2-b] thiophene represented by the following formula (1).

In addition, the present invention provides an organic electroluminescent display device comprising a compound for hole transport using a low molecular color compound for an electroluminescent device represented by the following formula (1).

When the hole transport layer is manufactured using thieno [3,2-b] thiophene provided in the present invention, an organic field display device having excellent thermal properties and luminous efficiency can be provided.

Formula 1

In the above formula, a is 1 to 20, and b is 1 to 20.

Organic EL, hole transport compound, light emitting device

Description

Hole transporting compound and organic electroluminescent device using same {Hole transporting material AND THE ORGANIC LIGHTING DEVICE USING THE SAME}

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the structure diagram of the organic electroluminescent element using the hole-transport compound containing thieno [3,2-b] thiophene of an Example.

Figure 2 is a graph showing the spectrum of 1H-NMR of 3-bromothiophene-2-carbaldehyde (bromothiophene-2-carbaldehyde) prepared in the embodiment of the present invention.

Figure 3 is a spectrum of 1H-NMR of ethylthieno [3,2-b] thiophene-2-carboxylate prepared in the Examples of the present invention A graph representing.

4 is a spectrum of 1H-NMR of thieno [3,2-B] thiophene-2-carboxylic acid prepared in Examples of the present invention. A graph representing.

FIG. 5 is a graph showing the spectrum of 1 H-NMR of thieno [3,2-B] thiophene prepared in Examples of the present invention. FIG.

FIG. 6 shows spectra of 1H-NMR and 13C-NMR of 2,5-dibromothieno [3,2-b] thiophene of the present invention. It is a graph.

7 is an FT-IR spectrum of thieno [3,2-b] thophene-2-carboxylic acid prepared in Examples of the present invention. It is a graph.

8 is a differential scanning calorific value (DCS) of 2,5-bromothieno [3,2-b] thiophene (2,5-dibromothiophene [3,2-b] thiophene) prepared in an embodiment of the present invention. Analysis graph.

[Industrial use]

The present invention relates to a hole transport compound for an electroluminescent device and an organic electroluminescent device (OELD) using the same, and more particularly, a hole that can improve the thermal properties and hole transport capacity of the organic electroluminescent device (EL Display) It relates to a compound for hole transport that can be applied to the transport layer and an organic electroluminescent device using the same.

[Prior art]

Recently, as the development of the information and communication industry is accelerated, higher performance is required in the field of display devices, which is one of the most important fields.

Such displays can be divided into luminescent and non-luminescent. Cathode ray tubes (CRTs), electroluminescent scene displays (ELDs), electroluminescent diodes (LEDs), and plasma display panels (PDPs) include have. Non-light emitting displays include liquid crystal displays (LCDs).

The light emitting and non-light emitting displays have basic performances such as operating voltage, power consumption, brightness, that is, brightness, contrast, response speed, lifetime, and display color. However, among these, liquid crystal displays, which are widely used to date, have problems in response speed, contrast, and visual dependence among the above basic performances. In this situation, the display using the light emitting diode has a fast response time and is self-luminous so that no back light is required, and the luminance is excellent, and it has various advantages, thus complementing the problems of the liquid crystal display. It is expected to take place as an element.

The light emitting diode is mainly difficult to apply to a large area electroluminescent device because an inorganic material having a crystalline form is used. In addition, in the case of an electroluminescent device using an inorganic material, a driving voltage is required to be 200 V or more, and a price is also disadvantageous. However, in 1987, Eastman Kodak reported that a material having a π-conjugated structure called alumina quinone was used as the electron transport layer to obtain a high luminance of about 1,000 at low voltages of 15 V or less.

Since then, more various research and development has been actively progressed for practical use.

The organic electroluminescent device (organic EL device) has a faster response speed than the light-receiving device using a liquid crystal that is currently in the limelight, and has a high luminance because it is a light emitting device, and an inorganic EL device that requires AC driving and high voltage. Unlike this, there is no such limit, and there is an advantage that a thin and wide display device can be realized.

The lifetime of the device, which has been the most problematic, is more than 20,000 hours for a single color, and since the successful commercialization of organic EL displays (256 × 64 pixels, green) at pioneer in late 1996, full color has been achieved. color) The organic EL display has also reached the stage of commercialization by being announced by Pioneer, Idemitsu, and NEC, respectively.

However, the requirement of the phosphor used in the organic EL device must have a property of transporting electrons and holes, and high emission quantum efficiency must be high in order for good light emission to occur from the excited state.

However, since the phosphor is difficult to have all these functions, two or three layers of organic thin films are laminated and used. The fabrication of such a stacked device consists of fabrication of an organic electroluminescent device comprising a p-type thin film and a double layer of n-type thin film which simultaneously serves as an electron transport and light emitting layer. The monomolecular hole transfer mainly serving as a p-type thin film is performed. Vacuum depositing the material onto a high work function indium tin oxide (ITO) layer and vacuum depositing a monomolecular hole transport material on top of the high work function ITO layer to act as an electron transport and light emitting layer thereon A method of depositing a material serving as a light emitting layer has been used.

Carrier transporting materials, which form the basis of stacked organic electroluminescent devices, are currently being studied in various directions.

In general, various triphenylamine-based and diamine derivatives are used as the hole transport material, and various functional groups are introduced as adjacent substituents of the amine.

These are characterized by small ionization potential. The p-type thin film layer manufactured by vacuum deposition of the conventional monomolecular hole transport material has a vibration, crystallization and diffusion movement due to Joule heat generated when driving the device, so that the thickness of the thin film is changed or part or all of the thin film is destroyed. As a result, the lifetime of the device was shortened.

In order to improve this, it is to develop an organic material having a high glass transition temperature (Tg) in order to develop a derivative of a previously discovered phosphor and to develop a new pigment and to compensate for an existing disadvantage.

This method was achieved by introducing more phenyl groups with excellent thermal stability or by introducing a conjugated ring-based compound such as naphthalene.

Another research direction of carrier transport materials in organic electroluminescent devices is the development of polymeric materials. In order to reduce the crystallinity of a material which is one of the factors which lowers the performance of an organic electroluminescent element, the method of using a polymeric material as a carrier transport material is studied.

As an example of such a method, a method of doping a hole transport material at a molecular level in a polymer having high thermal stability was used, but there was a problem in that the film was not significantly improved due to its weak stability.

An object of the present invention is to provide a hole transport compound with improved thermal properties and hole transport capacity.                         

Another object of the present invention is to provide an organic electroluminescent device using the hole transport compound.

The present invention to achieve the above object,

It provides a compound for hole transport containing thieno [3, 2-b] thiophene represented by the following formula (1).

Formula 1

In the above formula, a is 1 to 20, and b is 1 to 20.

In addition, the present invention provides a material for hole transport, characterized in that using the thieno [3,2-b] thiophene represented by the formula (1).

In addition, the present invention provides an organic electroluminescent display device comprising a compound for transporting holes using a low molecular color compound for an electroluminescent device represented by the formula (1).

Hereinafter, the present invention will be described in detail.

The present invention relates to a general organic light emitting device (OLED) and provides a hole transport compound having improved thermal stability and hole transport ability that can be applied to a light emitting device that can be used in a flat panel display.

The compound contains thiophene in the molecular structure as shown in the following formula (1), it is excellent in hole mobility.

Formula 1

In the above formula, a is 1 to 20, b is 1 to 20, preferably a is 1 to 6 and b is 1 to 6.

A thiophene compound contains the sulfur atom which has a lone pair in a chemical structure, and is a structure which can improve the hole transport property by a double bond.

In the present invention, the number of thieno [3,2-b] thiophenes is gradually increased to help inject holes efficiently from ITO.

In addition, the present invention gradually increases the number of phenyl groups by introducing an organic material having a high glass transition temperature (Tg) in order to reduce the crystallization of the material deteriorating the characteristics of the organic electroluminescent device, as shown in the following formula (1).

In addition, the number of thiophene and phenyl group was gradually constructed to maximize the effect required above.

Thieno [3,2-b] thiophene of Formula 1 is prepared by the process represented by Schemes 1 to 4.

Scheme 1

Scheme 2

Scheme 3

Scheme 4

As in Scheme 1, 3-bromothiophene is reacted with lithium diisopropylamide (LDA) to form 3-bromothiophene-2-carbaaldehyde (3-bromothiphene-2- carbaldehyde). The reaction is carried out at low temperatures and preferably at -5 ° C to 5 ° C.

3-bromothiophene-2-carbaaldehyde prepared in a mixture of N, N-dimethylformamide, potassium carbonate, and ethyl 2-sulfanylacetate The reaction was carried out as in Scheme 2 to prepare ethyl thieno [3,2-b] thiophene-2-carboxylate.

The reaction proceeds for about 60 hours to 84 hours at room temperature.

The prepared thieno [3,2-b] thiophene-2-carboxylate is mixed with an organic solvent such as tetrahydrofuran (THF) and an aqueous solution of lithium hydroxide, and the same as in Scheme 4 above. The reaction produces thieno [3,2-b] thiophene-2-carboxylic acid, which is then added to quinoline and copper powder. Put together to prepare a thieno [3,2-b] thiophene in the same manner as in Scheme 4.

Scheme 5

Scheme 6

Meanwhile, thieno [3,2-b] thiophene prepared as described above is reacted with N-bromosuccinimide in a mixed organic solvent as in Schemes 5 and 6 to 2,5-bromine. Motieno [3,2-b] thiophene (2,5-bromothieno [3,2-b] thiophene) was prepared, and the 2,5-bromothieno [3,2-b] thiophene was prepared. 4,4-dibromobiphenyl), tris (dibenzylideneacetone) dipalladium, and 1,1'-bis in a solvent such as dried toluene Diphenylphosphino) ferrocene (1,1'-Bis (diphneylphosphino) ferrocene) is put together and dissolved and stirred. Sodium-t-butoxide and N- (2-naphthylphenylamine) (N- (2-naphthyl phenyl amine)) were added to the mixed solution at a high temperature, preferably 80 to Stir in the range of 95 ° C.

Thus, 1-bromo-4- (2-naphthylphenylamine) biphenyl (1-bromo-4- (2-naphtylphenylamine) biphenyl) was prepared, and then dried in tetrahydrofuran (THF) as shown in Scheme 6. Into a solvent such as) to prepare a Grignard reagent (grinard reagent). Meanwhile, [1,3-bis (diphenylphosphino) propane] nickel (II) chloride ([1,3-bis (diphenylphosphino) propane] nickel (II) chloride; Ni (dppp) Cl ₂ ) and 2,5 Add dibromothieno [3,2-b] thiophene (2,5-dibromothieno [2,3-b] thiophene) and stir at room temperature. The mixed solution and the Grignard reagent prepared above were slowly reacted to reflux to increase the number of thieno [3,2-b] thiophenes.

The number of thieno [3,2-b] thiophenes is preferably 1 to 20, more preferably 1 to 6.

Step number of the thiophene and the phenyl group is gradually built to introduce an organic material having a high glass transition temperature (Tg) to gradually increase the number of phenyl groups by the method represented by the following schemes 7, 8 and 9 Proceed.

Schemes 7, 8, and 9 are continuously progressed in the same manner by reacting N-formylpiperidine with thieno [3,2-b] thiophene as in Scheme 6 above.

Scheme 7

Scheme 8

Scheme 9

The phenyl group is continuously introduced into thieno [3,2-b] thiophene and this thieno [3,2-b] thiophene in the same manner as above to prepare a compound for hole transport according to the present invention.

1-20 are preferable and, as for the number of the said phenyl groups, 1-6 are more preferable.

As such, the glass transition temperature of the prepared hole transporting compound is 140 to 160 ° C., and the glass transition temperature is higher than that of conventional materials.

As described above, the hole transporting material and the organic electroluminescent device manufactured using the hole transporting compound prepared in the present invention are excellent in thermal characteristics and luminous efficiency.

Hereinafter, a preferred embodiment of the present invention. However, the following examples are only presented to aid the understanding of the present invention, and the present invention is not limited to the following examples.

Example

Reagents Used

N-butyllithium, lithium hydroxide, quinoline, copper, n-bromosuccinimide, tris (dibenzylideneacetone) used in the present invention Dipalladium (tris (dibenzylideneacetone) dipalladium), sodium-t-butoxide, 1,1'-bis (diphenylphosphino) ferrosine (1,1-Bis (diphenylphosphino) ferrocene) , 3-bromothiophene was used by Aldrich Co., Ltd., diisopropylamine, magnesium, N- (2-naphthylphenylamine) (N- (2-naphtylphenylamine) Lancaster was used.

In addition, ethyl 2-sulfanylacetate, 4,4-dibromo-biphenyl (4,4-dibromo-biphenyl) was used by TCI, [1,3-bis (di Phenylphosphino) propane] nickel (II) chloride ([1,3-bis (diphenylphosphino) propane] nickel (II) chloride) and N-formylpiperidine are manufactured by Acros. Used.

N, N-Dimethyl formamide (DMF) was refluxed with a drying agent and refluxed, and the solvents used in the examples of the present invention including toluene, tetrahydrofuran, and the like are described in the literature. It was used after purification by the method shown in. Methylene chloride, hydrochloric acid, acetone, ammonium chloride, magnesium sulphate, and the like were used by Duksan Chemical.

Confirmation of the structure of the compound prepared in the present invention

The compound prepared in the present invention was confirmed by 1H-NMR, 13C-NMR, and FT-IR structure. 1 H-NMR was recorded using a Bruker AM-200, 300 spectrometer, and all chemical mobility was reported in ppm relative to the internal standard tetramethyl silane. IR spectra were measured on KBr pellets using a Perkin-Elmer Spectrometer. Thermogravimetric analysis and differential scanning calorimetry were measured using a Dupont 990 thermal analyzer equipped with 951 TGA and 910S DSC modules, respectively.

Monomer synthesis

Method for preparing 3-bromothiophene-2-carbaldehyde (3-Bromothiophene-2-carbaldehyde)

98 ml (245.3 mmol) of 2.5 M butyllithium (2.5 M) and 40 g (245.3 mmol) of diisopropylamine were added to 450 ml of THF at a temperature of 0 ° C. and stirred for 30 minutes. 27.763 g (245.3 mmol) of N-formylpiperidine was added, followed by stirring for about 4 hours to confirm the reaction by TLC. The solution was poured into an excess of 20% aqueous ammonium chloride solution, extracted with ether, and the ether was removed with a rotary evaporator. Vacuum distillation yielded a light yellow liquid. Yield was 76%.

1 H-NMR: δ H 7.11 (1H, d, H-4), 7.69 (1H, d, H-5), 9.92 (1H, s, CHO) (FIG. 2).

Process for preparing ethyl thieno [3,2-b] thiophene-2-carboxylate

220 ml of 3-bromothiophene-2-carbaaldehyde with N, N-dimethylamide, 21.939 g (158.74 mmol) of potassium carbonate, ethyl 2-sulfanylacetate 14.271 To a mixture of g (118.76 mmol) was stirred for 72 hours at room temperature. The reaction solution was poured into water and extracted with dichloromethane to remove the remaining water with magnesium sulfate (MgSO ⁴ ). Dichloromethane was removed with a rotary distiller and a violet liquid was obtained by vacuum distillation. Yield 84%.

1 H-NMR: δ H 1.37 (3H, t, Me), 4.34 (2H, q, CH ² ), 7.24 (1H, d, H-6), 7.55 (1H, d, H-5), 7.97 (1H, s, H-3) (FIG. 3).

Process for preparing thieno [3,2-b] thiophene-2-carboxylic acid

Add 100 ml of THF, 10 ml of 1.0 M aqueous lithium hydroxide solution, 10 g (47.108 mmol) of ethylthieno [3,2-b] thiophene-2-carboxylate, and reflux for 4 hours. The reaction was confirmed by TLC. The precipitate was slowly settled in 200 ml of hydrochloric acid and washed several times with water. After washing, the mixture was dried under a reduced pressure to obtain thieno [3,2-b] thiophene-2-carboxylic acid, and the melting point was 221 to 222 ° C. Yield 93%.

1 H-NMR: δ H 7.50 (1 H, d, H-6), 7.91 (1 H, d, H-5), 8.09 (1 H, s, H-3) (FIG. 4).

Process for preparing thieno [3,2-b] thiophene

17.494 g (94.994 mmol) of thieno [3,2-b] thiophene-2-carboxylic acid and 3.018 g (47.496 mmol) of copper powder were added to 140 mL of quinoline and refluxed at a temperature of 240 ° C. After confirming that the carbon dioxide gas comes out during the reaction to confirm the degree of reaction, after about 2 hours it was cooled to room temperature. Ether was added and washed several times with 1.0 M hydrochloric acid to remove quinoline. The ether was removed with a rotary distiller, and then purified by column chromatography using petroleum ether as a developing solvent. Melting point was 55 to 56 ℃. Yield 72%.

1 H-NMR: δ H 7.25 (2H, d, H-3 / 6), 7.37 (2H, d, H-2 / 5) (FIG. 5).

Method for preparing 2,5-dibromothieno [3,2-b] thiophene (2,5-dibromothieno [3,2-b] thiophene)

Acetic acid and dichloromethane were mixed 3: 7 and 7.422 g (52.957 mmol) of thieno [3,2-b] thiophene was dissolved in a solvent, and 18.852 g (105.913 mmol) of N-bromosuccinimide Was added and stirred for 24 hours at room temperature. The reaction solution was poured into water and extracted with dichloromethane to remove the remaining water with magnesium sulfate (MgSO ₄ ). Dichloromethane was removed with a rotary distiller to yield an off white solid. Yield was 78%.

1 H-NMR: δ H 7.49 (2H, s, H-3 / 6) (FIG. 6).

Method for preparing 1-bromo-4- (2-naphthylphenylamine) biphenyl (1-bromo-4- (2-naphthylphenylamine) biphenyl)

10 g (32.051 mmol) of 4,4-dibromo-biphenyl in 30 ml of toluene dried in a nitrogen stream environment, tris (dibenzylideneacetone) dipalladium (0) (Tris (dibenzylideneacetone) dipalladium (0)) 0.294 g (0.321 mmol) and 1,1'-bis (diphenylphosphino) ferrocene (1,1 bis (diphenylphosphino) ferrocene) dissolved in 0.267 g (0.482 mmol) After stirring for 15 minutes. 1.540 g (16.026 mmol) of sodium-t-butoxide and 2.811 g (12.821 mmol) of N- (2-naphtylphneylamine) were added to the solution. Stir 16 hours at a temperature of 90 ° C. When this solution was poured into water, precipitates were formed. A yellow solid was obtained by column chromatography using hexane as a developing solvent with the obtained solid. Yield 68%.

Method for producing a hole transporting material containing thieno [3,2-b] thiophene

5.439 g (12.076 mmol) of 1-bromo-4- (2-naphthylphenylamine) biphenyl and 0.331 g (13.613 mmol) of magnesium were added to 45 ml of dried THF to form a grinding reagent. Another flask contains 0.095 g (0.176) of [1,3-bis (diphenylphosphino) propane] nickel (II) chloride (1,3-bis (diphenylphosphino) propane] nickel (II) chloride; Ni (dppp) Cl ₂ ) mmol) and 1.328 g (5.489 mmol) of 2,5-dibromothieno [3,2-b] thiophene were added and stirred at room temperature for about 2 hours. The prepared Grignard reagent was slowly added to another flask using a cannula and refluxed for 48 hours. 0.2 M HCl aqueous solution was poured into the reaction solution, followed by extraction with dichloromethane to remove water remaining with magnesium sulfate. Dichloromethane was removed with a rotary distiller and purified by column chromatography. It was about 150 degreeC when the glass transition temperature of this compound was measured.

Fabrication of Electroluminescent Devices

FIG. 1 shows the structure of an electroluminescent device using an ITO 1 as a positive electrode, and a buffer layer 2 for compensating the surface of the ITO and assisting the injection and flow of holes. The material used as the buffer (alpha) is a low molecular material alpha-CuPc.

The manufacturing method of the electroluminescent element is as follows.

The ITO (1) substrate was washed with acetone, isopropyl alcohol (IPA) and pure water under a nitrogen atmosphere. Subsequently, the substrates were placed in a vacuum deposition chamber, and then all organic and metal depositions were performed at high vacuum of 2 × 10 ⁻⁶ torr or lower to form a thin film having a thickness ranging from 20 nm to 100 nm.

On this buffer layer, a material for hole hydrogen (3) containing thieno [3,2-b] thiophene prepared in an embodiment of the present invention was deposited to a thickness of 350 kPa, on which Alq3 and dopant coumarin 6 were deposited. The mixture of (4) was co-deposited at 400 kPa. Then, an Alq3 (5) was deposited on the electroluminescent layer, followed by vacuum deposition of LiF (6) (0.5 nm) and an aluminum metal (> 100 nm) (7) for the cathode to assist electron injection. Was prepared.

Investigation of characteristics of electroluminescent device

The compound prepared in Example 1 was applied to the hole transport layer (400 kPa) to apply an electric field to measure I-V characteristics of the light emitting diode (ITO / CuPc / hole transport compound / Alq3 / Al). The measured diode I-V characteristics showed that the maximum efficiency was 15 cd / A, which is about 20% higher than the conventional 12 cd / A.

Comparative example

An electroluminescent device having the same structure as in Example was manufactured using NPB as a compound used in the conventional hole transport layer, and the light emitting diode characteristics were measured. The luminous efficiency was 12 cd / A.

In the present invention, the number of phenyl groups was gradually increased to develop an organic material having a high glass transition temperature (Tg) in order to reduce the crystallization of the material deteriorating the characteristics of the organic electroluminescent device, and help to effectively inject holes from the ITO The number of thieno [3,2-b] thiophenes with excellent hole mobility was gradually increased. The organic material of the present invention was thermally stable and was able to improve hole transportability by introducing a thiophene structure in the hole transport material. In addition, the number of thiophene and phenyl groups can be built in steps to maximize the effect required above. In addition, the thermal stability is improved by structural control, and thus the life of the organic EL device may be increased.

Claims (8)

A compound for hole transport containing thieno [3,2-b] thiophene represented by the following Chemical Formula 1: Formula 1

In the above formula, a is 1 to 20, and b is 1 to 20. The method of claim 1, The hole transport compound is a hole transport compound having a glass transition temperature of 140 to 160 ℃. a) reacting 3-bromothiophene with lithium diisopropylamide to prepare 3-bromothiophene-2-carbaaldehyde; b) adding 3-bromothiophene-2-carbaaldehyde to a mixture of N, N-dimethylformamide, potassium carbonate, and ethyl 2-sulfanylacetate. Preparing thieno [3,2-b] thiophene-2-carboxylate (ethyl thieno [3,2-b] thiophene-2-carboxylate); c) converting thieno [3,2-b] thiophene-2-carboxylate of b) to an acid and then adding copper powder to quinoline to prepare thieno [3,2-b] thiophene; Doing; d) reacting thieno [3,2-b] thiophene of c) with N-bromosuccinimde in a mixed organic solvent to give 2,5-bromothieno [3,2-b ] Preparing thiophene; e) 2,5-bromothieno [3,2-b] thiophene of d) in 4,4-dibromobiphenyl, tris (dibenzyl) in a dried solvent Tridene (dibenzylideneacetone) dipalladium) and 1,1'-bis (diphenylphosphino) ferrosine (1,1'-bis (diphenylphosphino) ferrocene) are added together to prepare a mixed solution. T-butoxide (sodium-t-butoxide) and N- (2-naphtylphenylamine) (N- (2-naphtylphenyl amine)) was added and stirred at high temperature to 1-bromo-4- (2-naphthyl Phenylamine) (1-bromo-4- (2-naphtylphenylamine)); f) 1-bromo-4- (2-naphthylphenylamine) prepared in e) was prepared by [1,3-bis (diphenylphosphino) propane] nickel (II) chloride ([1,3-bis (diphenylphosphino) propane] nickel (II) chloride) and 2,5-dibromothienothiophene prepared in d) were added and stirred at room temperature to increase the number of thieno [3,2-b] thiophenes. step; g) repeating step f) to bring the number of thieno [3,2-b] thiophenes to 3 to 20; h) introducing thieno [3,2-b] thiophene and N-formylpiperidine prepared in f) above; And i) repeating step h) continuously so that the number of phenyl groups is from 2 to 20 Method for producing a hole-transporting compound containing thieno [3,2-b] thiophene represented by the following Chemical Formula 1, comprising: Formula 1

Wherein a is 1 to 20 and b is 1 to 20. The method of claim 4, wherein In Formula 1, a is 1 to 6, b is 1 to 6 method for producing a hole transport compound. The method of claim 4, wherein The reaction time of step b) is a method for producing a compound for hole transport is 60 to 84 hours. The method of claim 4, wherein Method for producing a hole transport compound is a reaction temperature of step e) is 80 to 95 ℃. A material for hole transport, comprising thieno [3,2-b] thiophene represented by the formula (1) of claim 1. An organic electroluminescent device using a hole transporting compound containing thieno [3,2-b] thiophene represented by the formula (1).

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