WO1999065961A1

WO1999065961A1 - Hole injector polymers

Info

Publication number: WO1999065961A1
Application number: PCT/FR1999/001282
Authority: WO
Inventors: Gilles Veriot; Marie Vergnolle
Original assignee: Thomson-Csf
Priority date: 1998-06-12
Filing date: 1999-06-01
Publication date: 1999-12-23
Also published as: FR2779729A1; FR2779729B1

Abstract

The invention relates to a new type of material that can be used for visual presentation in electroluminescent displays. The invention consists of straight-chain polymers containing active groups in terms of hole injection in an electroluminescent material. The above-mentioned active groups can be of a monopyrazoline or monoamine type.

Description

HOLE INJECTOR POLYMERS

The invention relates to side chain polymers capable of injecting holes in an electroluminescent material capable of being used in visualization.

The world of visualization is a constantly changing field, this to satisfy an increasingly demanding expectation. In particular, there is a growing demand for flat, light, inexpensive displays that consume little energy and generate a bright image visible from a wide angle of view.

Cathode ray tubes suffer from limitations such as their size, their weight, or the difficulty of obtaining by such technology curved screens of complex shape and of large dimension.

Liquid crystal displays require a relatively complex implementation (backlighting, alignment layer) and have a limited viewing angle. Plasma panels operate at high voltages which increase the cost of the control circuits and must be vacuum sealed.

In this context, organic electroluminescent materials offer a certain number of decisive advantages which would allow them in the more or less long term to take a significant market share of visualization systems. In particular :

- They can easily lead to flat and light displays since the device is assembled in the form of thin layers (<1 μm). - They allow access to large screens, possibly curved (when the substrate is flexible) and inexpensive by the use of wet-deposited polymers.

- They offer an excellent angle of view (Lambertian emission) and their implementation is simple (no alignment layer, no backlighting).

- They consume relatively little energy and operate at low control voltages (<10 V). - Lastly, they do not a priori require the development of a new technology since it is possible to reuse a large part of the stages in the production of liquid crystal flat screens which fall within the general field of large area electronics (deposits under vacuum of electrodes, film deposits by centrifugation, screen printing, transistor matrices ...).

Emission by electroluminescence results from the non-thermal deactivation of an exciton formed by the recombination within the material of an electron and a hole. The material is deposited by sublimation under vacuum or centrifugation between two electrodes of different nature, one of them being transparent in order to visualize the emission of light.

The application of a sufficient voltage across the terminals of the device allows the passage of current which is accompanied by light emission. The phenomena involved during the different stages of the emission process are the injection of charges, the transport of carriers, recombination and emission.

The charge injection stage is controlled by the redox properties of the anode and the cathode, which must be a good oxidant for injecting holes and a good reducer for injecting electrons, respectively (see Figure 1). More precisely, by assimilating the emitting layer to an organic semiconductor characterized by its valence band and its conduction band, the injection of holes will be optimal when the work of extraction of the anode will be energetically close to the top of the valence band , ie HOMO (“Highest Occupied Molecular Orbital”); similarly, the injection of electrons will be all the better as the work of extraction of the cathode is energetically close to the bottom of the conduction band, namely LUMO ("Lowest Unoccupied Molecular Orbital").

The organic electroluminescent materials known to date are characterized by a LUMO of relatively low energy and a HOMO of high energy. Consequently, the cathode must be a reducing metal of low extraction work (Ca, Mg, In, Sm, Al) and the anode an oxidant of high extraction work. The need for a transparent electrode is such that Indium oxide doped with Tin is generally chosen to make the anode. The transport of the charges in the material takes place by jumps and in the form of polarons. When the polarons relative to the electron and to the hole are at a distance such that the Coulomb attraction outweighs the other forces, there is a recombination of these two charges giving rise to an exciton. 25% of the excitons formed are in a state of singlet symmetry, 75% are in a state of triplet symmetry. These excitons migrate within the material before returning to the ground state; only the deactivation of the singlet exciton is radiative and leads to the emission of a photon, which limits the electroluminescence yield to 0.25 η (η being the photoluminescence yield of the material).

Energy efficiency is directly linked to the ability of the electrodes to inject an equal number of holes and electrons into the material. In fact, when majority carriers circulate in the material, they pass through the device without recombining, thus creating a Joule effect, a rise in temperature of the material which contributes to its degradation. One way to solve this problem is to insert intermediate layers between the emitter and the electrodes, the function of which is to facilitate the injection of electrons and to block the passage of holes (see Figure 2) or to facilitate the injection of holes and block the passage of electrons (see Figure 3).

Electroluminescent displays are most often built on a substrate covered with ITO by deposition:

- either of the emitting material alone;

- either a hole injecting layer and then an emitting layer;

- either of an emitting layer then of an electron injecting layer;

- either of a hole injecting layer then of an emitting layer then of an electron injecting layer. In the case of the centrifugation of polymers, it is necessary to take special precautions, since the coating solvent of the emitting layer must not dissolve the bottom layer injecting holes. In this case, it is necessary to make this hole-injecting layer insoluble. The sublimation of small molecules offers the advantage of not imposing any constraint on the stacking of the different layers of materials. The invention falls within this context and proposes a new family of materials, particularly suitable for injecting holes inside emitting layers formed from small electroluminescent molecules.

In general, these are polymers comprising active groups in terms of hole injection, of simplified structure compared to that of the prior art and in particular that described by the applicant in published patent application 2757 525.

Indeed, according to the prior art, the tendency was to transpose the structures of small molecules known for their properties as hole injectors, directly on polymer chains. The invention proposes structures of simplified chemistry and in particular of the monopyrazoline or monoamine type, while retaining properties equivalent to those obtained with the molecules of the known art.

More specifically, the subject of the invention is a polymer with side chains, suitable for injecting holes in electroluminescent materials, characterized in that it comprises a molar percentage x of side chains comprising a group of type: * 2 - (2-hydroxyphenyl) benzoxazole

or * 2 - (2-hydroxyphenyl benzothiazole)

or * salicylideneamine

with R aryl group derived from benzene, naphthalene, anthracene, phenanthrene, fluorene or triphenylene

or

with Ar: phenyl or biphenyl aryl group

or

OR

According to a variant of the invention, the side chains are attached to a main chain of the polystyrene type. According to another variant of the invention, the side chains are attached to a main chain of polyacrylate type or of polymethacrylate type.

The invention also relates to an electroluminescent device comprising a layer of electroluminescent material and a layer of hole injector material comprising a polymer with side chains according to the invention.

The invention finally relates to a method for manufacturing an electroluminescent device comprising the following steps: - The deposition by centrifugation of a polymer with side chains according to the invention on a substrate covered with a transparent electrode, to obtain a hole injector film;

- the deposition by sublimation of small molecules of electroluminescent material on the surface of the hole injector film;

- The production of a counter electrode on the surface of the previously formed layer of electroluminescent material.

The invention will be better understood and other advantages will appear on reading the description which follows given without limitation and thanks to the appended figures among which:

- Figure 1 illustrates the energy levels of the highest occupied molecular orbital (HOMO) and the lowest vacant molecular orbital (LUMO) of an electroluminescent material as well as the work of extraction of the anode and the cathode;

- Figure 2 illustrates the energy levels corresponding to a two-layer system consisting of a hole injector film (HTL) and an electroluminescent film;

- Figure 3 illustrates the energy levels corresponding to a bilayer system formed by an electroluminescent film and an electron injector film;

- Figure 4 illustrates an example of a reaction scheme for obtaining a polymer according to the invention with a main chain of styrene type; - Figure 5 illustrates an example of a reaction scheme for obtaining a polymer according to the invention with a main chain of polyacrylate or polymethacrylate type;

FIG. 6 illustrates a structure of an electroluminescent device using a polymer according to the invention for injecting holes in a layer of electroluminescent material;

- Figure 7 illustrates the reaction scheme for the synthesis of an amino salycylidene type hole injector group;

- Figure 8 illustrates a first example of a reaction scheme for the synthesis of a precursor of an amino salicylidene type injector group; - Figure 9 illustrates a second example of a reaction scheme for the synthesis of a precursor of an amino salicydene type injector group;

- Figure 10 illustrates the reaction scheme for the synthesis of a pyrazoline type hole injector group;

- Figure 11 illustrates the reaction scheme for the synthesis of a first example of polymerization according to the invention;

- Figure 12 illustrates the reaction scheme for the synthesis of a second example of polymer according to the invention. According to a first variant of the invention, the main chain of the polymers with side chains can be of the polystyrene type.

FIG. 4 illustrates an example of synthesis making it possible to develop such a polymer. More precisely, we can proceed to the condensation of the hole injector pattern and referenced

on 4-chloromethylstyrene in the presence of sodium methanolate in dimethylformamide followed by polymerization initiated with azobisisobutyronitrile of the monomer obtained in the presence of an amount of styrene varying from 0 to 50 mol% in dimethylformamide. According to a second variant of the invention, the main chain of the polymers with side chains can be of the polyacrylate or polymethacrylate type.

FIG. 5 illustrates an example of synthesis making it possible to develop such polymers. It is thus possible to condense a hole injector pattern referenced ÇGp— OH on acryloyl or methacryloyl chloride in the presence of

EtβN in 1, 3 dimethyl.3,4,5,6 tetrahydro-2 (1 H) pyrimidone followed by a polymerization initiated with azobisisobutyronitrile of the monomer obtained in the presence of an amount of methyl acrylate or methacrylate methyl ranging from 0 to 50 mol% in dimethylformamide.

In general, the polymers according to the invention have excellent solubility in conventional organic solvents and can therefore easily be dissolved to be deposited by centrifugation on a substrate, in order to produce an electroluminescent device. The structure of such a device can be that illustrated in FIG. 6 in which the hole-injecting polymer 3 is deposited by centrifugation on a glass substrate 1 covered with a conductive layer of retium-doped indium oxide (ITO) 2. The emitting element is an electroluminescent material of low molecular mass that can be deposited by sublimation under vacuum 4. Depending on the emission color, it can be: - to emit in the green: tris (aluminum 8-hydroxyquilolinate) )

to emit into the blue a zinc complex derived from bis (2- sal icyl idèneamino) hexane

to emit into the orange bis (2-naphthylidene-8-hydroxyquinolinate) of zinc

The final evaporation of a calcium electrode 5 takes place under vacuum.

We will describe below examples of synthesis of hole injector groups, precursors of hole injector groups as well as two examples of side chain polymers according to the invention. Example 1

Synthesis of salycilldene aminomethylnaphthalene, illustrated in Figure 7

To a solution of 2 g (12.34 mmol) of naphthalene-2-aminomethyl in 80 ml of methanol, 1.35 ml (12.67 mmol) of salicylic aldehyde is added. The mixture is stirred for 15 minutes at room temperature. The precipitate is drained on a frit under vacuum, washed with methanol and then left in air. 2 g of an analytically pure yellow solid are obtained. Yield: 62%

Example 2:

Synthesis of 9-aminomethylphenathrene illustrated in FIG. 8

To a solution cooled to -78 ° C. containing 0.5 g (2.5 mmomol) of 9-cyanophenanthrene dissolved in 75 ml of tetrahydrofuran, 16 ml (16 mmol) of a molar solution of diborane in tetrahydrofuran are added. The mixture is slowly brought up to room temperature, stirred overnight and then treated with 50 ml of a 2M solution of hydrochloric acid. the tetrahydrofuran is then evaporated, the residue is redissolved in 50 ml of dichloromethane and acidified with 2 ml of concentrated hydrochloric acid. The precipitate obtained is drained on a frit under vacuum, taken up in 50 ml of dichloromethane and treated with 50 ml of a 2M sodium hydroxide solution. The organic phase is separated, washed twice with 50 ml of distilled water, dried over magnesium sulfate, filtered and then concentrated in a rotary evaporator. 0.5 g of an analytically pure solid is obtained. Yield: 73% Melting point: 109 ° C Example 3

Synthesis of aminomethylthphenylene, illustrated in Figure 9

Aminomethyltήphenylene is obtained in 5 steps from triphenylene.

Synthesis of triphenylene-2-carboxaldehyde

To a solution cooled to 0 ° C. containing 1 g (4.38 mmol) of triphenylene and 3.3 g (17.4 mmol) of titanium chloride freshly distilled in 75 ml of dry dichloromethane, 5 g are added dropwise (43.4 mmol) bis (chloromethyl) ether. The mixture is stirred at room temperature for 6 hours and then hydrolyzed slowly with 100 ml of a 2M solution of hydrochloric acid. The organic phase is recovered, washed with 2 times 100 ml of the 2M hydrochloric acid solution, washed in fractions of 100 ml of distilled water until neutral, dried over magnesium sulfate and then concentrated on a rotary evaporator, the crude product is recrystallized hot from a dichloromethane / hexane mixture. We obtain

0.88 g of an analytically pure brown / orange solid. Yield: 78% Melting point: 148 ° C

Synthesis of 2- (hydroxymethyl) triphenylene To a solution of 0.5 g (1.95 mmol) of triphenylene-2-carboxaldehyde in 75 ml of dry tetrahydrofuran cooled to 0 ° C., 3 ml (3 mmol) of a molar solution of borane-tetrahydrofuran complex. The solution is stirred for 2 hours at room temperature and then hydrolyzed with 75 ml of a molar solution of soda. The organic phase is recovered, washed in fractions of 50 ml of distilled water until neutral, dried over magnesium sulfate and then concentrated to the rotary evaporator. The crude product is triturated in dichloromethane. 0.47 g of an analytically pure solid is obtained after spinning on a frit. Yield: 93% Melting point: 152 ° C

Synthesis of 2- (bromomethyl) triphenylene

To a solution of 0.5 g (1.94 mmol) of 2- (hydroxymethyl) triphenylene in 75 ml of toluene, 0.79 g (2.9 mmol) of a molar solution of phosphorus tribromide is added. The solution is stirred for 2 hours at 50 ° C. and then neutralized with 75 ml of a molar solution of soda. The organic phase is recovered, washed in fractions of

50 ml of distilled water until neutral, dried over magnesium sulfate and then concentrated on a rotary evaporator. We obtain after spinning on frit,

0.59 g of an analytically pure white solid. Yield: 94% Melting point: 137 ° C

Synthesis of 2- (phta / imidomethy /) triphenylene

To a solution of 0.5 g (1.56 mmol) of 2- (bromomethyl) triphenylene in 25 ml of dimethylformamide, 0.32 g (1.72 mmol) of potassium phthalimide is added. The solution is stirred overnight at 40 ° C. and then concentrated on a rotary evaporator. The residue is dissolved in 50 ml of dichloromethane washed with 3 times 50 ml of a 0.1 M sodium hydroxide solution, washed in portions of 50 ml of distilled water until neutral, dried over magnesium sulfate and then concentrated to 1%. 'Rotary evaporator. 0.6 g of an analytically pure white solid is obtained.

Yield: 100% Melting point: 213 ° C

Synthesis of 2- (aminomethyl) t phenylene

To a solution containing 0.5 g (1.29 mmol) of 2- (phthalimidomethyl) triphenylene in 50 ml of ethanol, 0.32 g (6.46 mmol) of hydrazine monohydrate is added. The solution is brought to reflux for 2 hours, treated with 0.5 ml of concentrated hydrochloric acid, again brought to reflux for 2 hours then concentrated on a rotary evaporator. The residue is taken up in 50 ml of dichloromethane and 50 ml of distilled water. The organic phase is recovered, washed with 2 times 50 ml of distilled water and then again acidified with 1 ml of concentrated hydrochloric acid. The yellow solid obtained is taken up in 50 ml of dichloromethane and then basified in 50 ml of a molar solution of soda. The organic phase is then separated, washed in fractions of 50 ml of distilled water until neutral, dried over magnesium sulfate and then concentrated on a rotary evaporator. 0.35 g of an analytically pure oil is obtained. Efficiency: 94%

Example 4 illustrated in FIG. 10 Synthesis of 1,3-diphenyl-5- (4-hydroxyphenyl) -2-pyrazoline

1,3-diphenyl-5- (4-hydroxyphenyl) -2-pyrazoline is prepared in 3 steps from 4-hydroxybenzaldehyde.

Synthesis of 4-Cbutyldiphenylsilyloxy) benzaldehyde

To a solution containing 5 g (40.9 mmol) of 4-hydroxybenzaldehyde dissolved in 45 ml of dimethylformamide, 5 g (73.4 mmol) of imidazole and 14 g (50.9 mmol) of butylchlorodiphenylsilane are added. the mixture is stirred for 72 hours at room temperature and then treated with 150 ml of a 5% aqueous sodium hydrogencarbonate solution. The reaction products are extracted with 3 times 100 ml of hexane. The 3 combined organic phases are washed with 3 times 25 ml of deionized water, dried over sodium sufate and then concentrated in a rotary evaporator. A viscous oil is obtained which is taken up in 20 ml of a 1: 1 methanol / dichloromethane mixture. The solution is then concentrated until precipitation begins and then placed in the refrigerator for a few hours, the precipitate formed is drained on a frit under vacuum and then air dried. 11 g of an analytically pure powder are obtained. Yield: 74.5%

Synthesis of 4-hydroxyphenyl-phenyl chalcone

To a solution of 5 g (13.9 mmol) of 4- (butyldiphenylsilyloxyjbenzaldehyde in 50 ml of ethanol at 95 ^c , 1.62 ml (13.9 mmol) of acetophenone previously distilled on calcium chloride are added and 720 mg (13.3 mmol) of sodium methylate The mixture is stirred for 4 days at room temperature and then treated for 2 days with 50 ml of a molar solution of hydrochloric acid. The precipitate is drained on a vacuum frit, recrystallized hot from toluene and then left to air dry. 1.2 g of analytically pure product are obtained. Yield: 50%

Synthesis of 1,3-diphenyf-5- (4-hydroxyphenyl) -2-pyrazoline

To a suspension of 1 g (2.15 mmol) of 4-hydroxyphenyl-phenyl chalcone in 30 ml of acetic acid, 3 ml of phenylhydrazine are added.

The mixture is brought to reflux under argon for 24 hours. gradually, the starting ketone dissolves with red coloration of the solution then a yellow solid precipitates. The precipitate is drained on a frit under vacuum, washed thoroughly and then digested hot in 95 ° ethanol and then left to dry in air. 1.25 g of an anally pure solid are obtained. Efficiency: 90%

Example 5

Synthesis of poly (4- (2- (2benzothiazoyl)) phenyloxy-methyl) styrene) illustrated in Figure 11

The polymer is obtained in two stages from 2- (hydroxyphenyl) -benzothiazole and 4-chloromethylstyrene.

Synthesis of 4- (2- (2-benzothiazoyl)) phenyloxomethyl) styrene

To a solution of 1 g (4.40 mmol) of 2- (2-hydroxyphenyl) benzothiazole in 10 ml of distilled dimethylformamide, 0.72 g (12.44 mmol) of sodium methylate is added. The mixture is stirred for half an hour at room temperature then 0.55 ml (4.58 mmol) of distilled chloromethyl styrene and heated to 70 ^β C for 24 hours. After returning to room temperature, the mixture is thrown into 20 ml deionized water then triturated until a whitish solid is obtained. This crude product, drained on a frit under vacuum, is purified by chromatography on a silica column, eluting with a dichloromethane-petroleum ether mixture 50:50. The fractions containing the pure product are combined and concentrated on a rotary evaporator, an oil is obtained which crystallizes after trituration in petroleum ether. After drying on a vacuum frit and drying in air until constant weight 1 g of pure product is obtained. Yield: 69%

Synthesis of the polymer

1 g of (1.46 mmol) of

4- (2- (2-benzothiazoyl)) phenyloxomethyl) styrene, 5 ml of distilled dimethylformamide and 4.8 mg (29.3 mmol) of AIBN. The solution is degassed three times under vacuum, then the vial is sealed under vacuum and the mixture is brought to 60 ° C. for 24 ° C.

After returning to ambient temperature, the ampoule is opened and the polymer is precipitated three times in methanol. 1 g of pure product is obtained. Yield: 100% Glass transition: 119 ° C

A two-layer light-emitting diode was produced using the polymer described above as the hole injector and the aluminum tris (8-hydroxyquinolinate) as the emitter.

Example 6.

Synthesis of poly (methacryloyloxybenzylidenenaphthylmethylamine) illustrated in Figure 12

Poly (methacryloyloxybenzylidenenaphthylmethylamine) is prepared in 2 steps from methacyloyole chloride and 2-hydroxybezylidenenaphthylmethylamine.

Synthesis of methacryloyloxybenzylidènenaphtylméthylamine

5 g (19.13 mmol) of 4-hydroxybenzylidenenaphthylmethylamine are dissolved in 100 ml of DMPU brought to 100 ° C. 6.5 ml (46.6 mmol) of triethylamine are added and then 4 ml (40.9 mmol) of distilled methacryloyl chloride are added dropwise. After returning to ambient temperature, the mixture is stirred for 18 hours at ambient temperature, the hydrochloride of triethylamine gradually precipitates. The mixture is then thrown into

200 ml of distilled water. The precipitate is drained on a vacuum frit, washed with

200 ml of distilled water then 300 ml of hexane and allowed to air dry. The crude product is purified by chromatography on silica, eluting with a 1: 1 dichloromethane / hexane mixture. The fractions containing the pure product are combined and then concentrated on a rotary evaporator. 3 g of an analytically pure solid are obtained. Yield: 47%

Synthesis of poly (methacryloyloxybenzylidenenaphthylmethylamine)

1 g (3.03 mmol) of methacryloyloxybenzilidene-naphthylmethylamine, 5 ml of distilled dimethylformamide and 5 mg (30.3 μg) of AIBN are introduced into a pre-sealed vial. The solution degassed three times under vacuum then the ampoule is sealed under vacuum. It is brought to 60 ° C for 24 hours. After returning to ambient temperature, the ampoule is opened and the polymer is precipitated three times in methanol. 0.9 g of pure product is obtained. Efficiency: 90%

Claims

1. Polymer with side chains, suitable for injecting holes into electroluminescent materials, characterized in that it comprises a molar percentage x of side chains comprising a group of the type: * 2 - (2-hydroxyphenyl)benzoxazole

or * 2 - (2-hydroxyphenyl benzothiazole)

or * salicylideneamine

Or

with Ar: aryl group of phenyl or biphenyl type

OR

2. Side chain polymer according to claim 1, characterized in that the side chains are attached to a main chain of polystyrene type.

3. Side chain polymer according to claim 1, characterized in that the side chains are attached to a main chain of polyacrylate or polymethacrylate type.

4. Polymer with side chains according to one of claims 1 to 3, characterized in that the molar percentage x is between 0.5 and

1.

5. Electroluminescent device comprising a layer of hole injector material and a layer of electroluminescent material characterized in that the hole injector material comprises a side chain polymer according to one of claims 1 to 4.

6. Electroluminescent device according to claim 5, characterized in that the electroluminescent material is of the type:

7. Electroluminescent device according to claim 5, characterized in that the electroluminescent material is of the type

8. Electroluminescent device according to claim 5, characterized in that the electroluminescent material is of the type:

9. Method for manufacturing an electroluminescent device according to one of claims 5 to 8, characterized in that it comprises the following steps: - deposition by centrifugation of a polymer with side chains according to one of claims 1 at 4, on a substrate covered with a transparent electrode to obtain a hole injector film;

- producing a counter electrode on the surface of the previously formed layer of electroluminescent material.