CN111662448A

CN111662448A - Bipolar green light-based organic electroluminescent material and preparation method thereof

Info

Publication number: CN111662448A
Application number: CN202010544059.2A
Authority: CN
Inventors: 万志豪
Original assignee: Individual
Current assignee: Individual
Priority date: 2020-06-15
Filing date: 2020-06-15
Publication date: 2020-09-15

Abstract

The invention belongs to the technical field of photoelectric display devices, and particularly relates to a bipolar green light organic electroluminescent material and a preparation method thereof. The invention provides a bipolar green light organic electroluminescent material, the structural formula of which is shown as the formula (I). The invention also provides a preparation method of the bipolar green light organic electroluminescent material, which comprises the step of carrying out Suzuki coupling reaction on 3, 10-dibromo-14- (3- (5-phenyl-1, 3, 4-oxadiazole-2-yl) phenyl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrole, 2- (3, 10-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborane-2-yl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrole-5-phenyl-1, 3, 4-oxadiazole and a compound shown in a formula (II) to prepare a polymer shown in a formula (I) and the preparation method thereof, the technical problem that the carrier transmission efficiency of the existing green light organic electroluminescent material is low is solved.

Description

Bipolar green light-based organic electroluminescent material and preparation method thereof

Technical Field

The invention belongs to the technical field of photoelectric display devices, and particularly relates to a bipolar green light organic electroluminescent material and a preparation method thereof.

Background

The organic electroluminescence phenomenon is discovered accidentally in 1936 by the G.Destriuu research group during the experiment. The initial report was that the m.pope group observed blue emission phenomena on both sides of 10-20m single crystal anthracene using a high dc voltage (below 400V). The large-scale development of international organic electroluminescent materials and devices was in 1987, and an organometallic complex (Alq) was designed by Kodak in the United states₃) The research on the heat trend of organic light emitting diodes by scientists is raised as a sandwich film electroluminescent device of a light emitting layer. Compared with the current mainstream LCD (liquid crystal display), OLEDs have self-luminescence, luminescence brightness and high luminescence efficiencyRate, fast response speed and the like. By using multiple organic material sources, a display screen with adjustable illumination colors can be realized more easily. The viewing angle range is larger. The choice of the light-emitting material has a very important influence on the performance in the preparation and optimization of OLED devices. The green light device in the three primary colors of blue and green has the highest efficiency, but the stability and the carrier transmission efficiency are relatively low, mainly because the green light has high energy, high requirements on organic matters and narrow wavelength, and the luminous color is not easy to adjust. Therefore, the low carrier transport efficiency of the existing green organic electroluminescent material becomes a technical problem to be solved urgently by the technical personnel in the field.

Disclosure of Invention

The invention provides a bipolar green light organic electroluminescent material and a preparation method thereof, and solves the technical problem of low carrier transmission efficiency of the existing green light organic electroluminescent material.

The invention provides a bipolar green light organic electroluminescent material, which has a structural formula shown as a formula (I):

wherein n is 2-1000.

The invention also provides a preparation method of the bipolar green organic electroluminescent material, which comprises the step of carrying out Suzuki coupling reaction on 3, 10-dibromo-14- (3- (5-phenyl-1, 3, 4-oxadiazole-2-yl) phenyl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrole, 2- (3, 10-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborane-2-yl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrole-5-phenyl-1, 3, 4-oxadiazole and a compound shown in a formula (II) to prepare the polymer shown in the formula (I)

Preferably, the temperature of the Suzuki coupling reaction is 85 ℃.

Preferably, the time of the Suzuki coupling reaction is 24-42 h.

Preferably, the time of the Suzuki coupling reaction is 42 h.

Preferably, the compound represented by the formula (II) is prepared by the following steps:

step 1: stirring 2-aminobenzaldehyde and 50mL of acetone in an ice bath for 30min, then dropwise adding 6% sodium hydroxide solution (120mL) into the system, removing the ice bath after dropwise adding, and stirring at normal temperature for 12h to obtain the compound shown in the formula (III)

Step 2: carrying out substitution reaction on 4, 7-dibromo-2, 1, 3-benzothiadiazole and a compound shown as a formula (III) to prepare a compound shown as a formula (IV)

And step 3: and (3) carrying out bromination reaction on the compound shown in the formula (IV) to obtain the compound shown in the formula (II).

The invention has the following beneficial effects:

the LUMO energy level of the polymer prepared by the present invention is reduced from-2.35 eV to-2.86 eV, which is attributed to the increase of the SO electron withdrawing unit, SO that the electron injection and transport capability of the polymer is enhanced. And the HOMO energy level is increased from-5.74 eV to-5.57 eV, so that the polymer prepared by the invention has a bipolar property due to the electron donating group and the electron withdrawing group, and can promote the injection and the transmission of holes and electrons simultaneously.

In addition, the green light material prepared by the invention obtains the best device effect, the maximum lumen efficiency is 2.47cd/A, and the maximum brightness also reaches 4125cd/m². When the polymerization degree is high, the color coordinate is (0.26,0.65) from the color coordinate, and standard green light is emitted.

Drawings

FIG. 1 is a PL spectrum in a thin film state of polymers prepared in examples 10-13 of the present invention;

FIG. 2 is a cyclic voltammogram of green polymers prepared in examples 10-13 of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples, which are not intended to limit the present invention in any manner. Reagents, methods and apparatus used in the present invention are conventional in the art unless otherwise indicated.

Example 1

Adding 2-aminobenzaldehyde (4.8g, 40mmol) and 50mL of acetone into a 250mL round-bottom flask, stirring for 30min in ice bath, dropwise adding 6% sodium hydroxide solution (120mL) into the system, removing the ice bath after dropwise adding is finished, and stirring at normal temperature for 12 h; then transferring the system into a 1000mL beaker, adding a proper amount of ice water, adjusting the pH value of the system to 5.5 by using 8% diluted hydrochloric acid solution, precipitating a large amount of yellow solid, performing suction filtration, and recrystallizing with ethanol/water (2:1) to obtain the compound shown as the formula (III) (5.15, the yield is 80%) which has the chemical reaction equation:

example 2

To a 500mL flask were added 4, 7-dibromo-2, 1, 3-benzothiadiazole (2.95g, 10mmol), potassium carbonate (4g, 30mmol), and 80mL acetonitrile. Stirring and dissolving under argon, adding a compound (4.8g.30mmol) shown in the formula (III), stirring and refluxing at 85 ℃, and detecting the reaction progress by TLC; after completion of the reaction, the potassium carbonate was filtered off, the solvent was removed under reduced pressure, and the obtained crude product was purified by silica gel chromatography using petroleum/ethyl acetate 10/1 as an eluent. The product was then recrystallized from ethanol to give the compound represented by the formula (IV) (6.54g, yield 72%) whose chemical reaction equation is:

example 3

A250 ml single-neck reaction flask was charged with the compound represented by the formula (IV) (4.54g, 10mmol), followed by addition of chloroform solvent until the starting material was completely dissolved (100ml), and NBS powder (7.12g, 40mmol) was dissolved in 30ml of chloroform solution, which was then added dropwise to the reaction flask, and the reaction was carried out for 24 hours while keeping out of the shade. Extraction with DCM three times, washing once with water, collection of the organic phase, spin-drying of DCM, and purification by recrystallization with THF gave compound of formula (II) (11.3g, 92% yield) according to the equation:

example 4

Dissolving 2, 7-dibromocarbazole (6.5g,20mmol) in 50ml of N, N-Dimethylformamide (DMF), adding potassium hydroxide (2.7g,48mmol), stirring at room temperature for 30min, adding 2- (3-bromophenyl) -5-phenyl-1, 3, 4-oxadiazole (12.94g,43mmol), and after the dropwise addition, continuing to stir at 85 ℃ for 10 h. After the reaction, the reaction solution was poured into water, and a pale yellow solid was precipitated. The solid is filtered under reduced pressure, washed with distilled water for many times, and dried under reduced pressure to obtain 2- (3- (2, 7-dibromo 9H-carbazole-9-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (9.8g, yield 90%), and the chemical equation of the reaction is as follows:

example 5

Dissolving 2- (3- (2, 7-dibromo 9H-carbazol-9-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (10.9g,20mmol) in 150mL absolute tetrahydrofuran, stirring and dissolving at room temperature in an argon atmosphere, then placing a reaction bottle into a low-temperature reactor at-80 ℃, slowly dropwise adding n-butyl lithium (33mL,80mmol) into the reaction bottle, reacting the reaction liquid at low temperature for 2H, then rapidly adding 2-isopropyl-4, 4 ', 5, 5' -tetramethyl-1, 3, 2-dioxaborane (16.3mL,80mmol), and reacting at room temperature overnight. Stopping the reaction, pouring the reaction solution into water for quenching, concentrating the reaction solution, extracting with dichloromethane, purifying by column chromatography, taking 200-300 mesh silica gel as a stationary phase, and taking petroleum ether/dichloromethane (2:1) as an eluent to obtain 2- (3- (2, 7-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborane-2-yl) -9H-carbazole-9-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (8.31g, yield 65%) according to the chemical reaction equation:

example 6

2- (3- (2, 7-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl) -9H-carbazol-9-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (19.18g,30mmol), 1-bromo-2-methanesulfonamylbenzene (14.5g,66mmol), tetrabutylammonium bromide (0.84g,2.6mmol) and an aqueous solution of potassium carbonate (34.5g,250mmol) at a concentration of 2M were added to a 500ml three-necked round-bottomed flask, and 250ml of toluene were added to dissolve sufficiently, heated under argon atmosphere to reflux and stirred, and tetrakis (triphenylphosphine) palladium (1.5g,1.3mmol) was added when the temperature stabilized at 85 ℃ and reacted overnight. Stopping the reaction, cooling to room temperature, washing the reaction solution for 2-3 times with water, concentrating the reaction solution, purifying the reaction solution by a chromatographic column, wherein the silica gel is 200-300 meshes, and the eluent is petroleum ether/ethyl acetate (3:1), so as to obtain the product 2- (3- (2, 7-bis (2- (methylsulfinyl) phenyl) -9H-carbazol-9-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (15.9g, yield 80%). The chemical reaction equation is as follows:

example 7

2- (3- (2, 7-bis (2- (methylsulfinyl) phenyl) -9H-carbazol-9-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (6.63g,10mmol) was charged to a 50mL single-neck round-bottom flask, phosphorus pentoxide (151.7mg,1mmol) and 9mL trifluoromethanesulfonic acid were added and reacted for 10H under ice-bath conditions. Stopping the reaction, dripping the reaction liquid into ice water, stirring, carrying out suction filtration on the mixed liquid to obtain a yellow powdery solid, and airing. The filter residue is added into a 250mL three-neck round-bottom flask, 100mL pyridine is added, and the mixture is heated and refluxed for reaction for 6 hours in an argon atmosphere. The reaction was stopped and cooled to room temperature, the reaction was poured into ice water, hydrochloric acid was slowly added to neutralize excess pyridine, extraction was performed with dichloromethane, then the organic phase was concentrated and purified by column chromatography on silica gel 200-300 mesh, eluent was petroleum ether/dichloromethane (6:1), and recrystallization from ethanol was performed to obtain 2- (3- (14H-bis (dibenzothiophene) pyrrol-14-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (3.47g, 58% yield).

Example 8

2- (3- (14H-dibenzothiophen-14-yl) phenyl) -5-phenyl-1, 3, 4-oxadiazole (4.8g,8mmol) was dissolved in 100mL of a three-necked round-bottomed flask with methylene chloride, and m-chloroperoxybenzoic acid (7.2g,42mmol) was added thereto in ice bath (0 to 5 ℃ C.) and the mixture was stirred overnight with exclusion of light. Stopping the reaction, pouring the reaction solution into a cold saturated aqueous solution of sodium hydroxide, stirring, extracting with dichloromethane, washing with water for 3-4 times, purifying by column chromatography, silica gel 200-300 meshes, eluting with dichloromethane/tetrahydrofuran (10:1), and recrystallizing with ethanol after passing through the column to obtain 14- (3- (5-phenyl-1, 3, 4-oxadiazol-2-yl) phenyl-bis (S, S-dioxo-dibenzothiophene) pyrrole (4.4g, yield 83%) with the chemical reaction equation:

example 8

Dissolving 14- (3- (5-phenyl-1, 3, 4-oxadiazole-2-yl) phenyl-bis (S, S-dioxo-dibenzothiophene) pyrrole (0.66g,1mmol) in a mixed solution of 10mL of trifluoroacetic acid and 3mL of trichloromethane, stirring under ice bath condition until the reactant is completely dissolved, dissolving N-bromosuccinimide (0.89g,5mmol) in 10mL of trifluoroacetic acid and 3mL of sulfuric acid, slowly dropwise adding the solution into the reaction solution under dark condition, reacting for 2h under dark condition, pouring the reaction solution into water, extracting with dichloromethane, purifying by column chromatography, using 200-mesh 300-mesh silica gel as a stationary phase and petroleum ether/dichloromethane (1:7) as an eluent, recrystallizing with ethanol after the column chromatography to obtain 3, 10-dibromo-14- (3- (5-phenyl-1), 3, 4-oxadiazol-2-yl) phenyl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrolopyrrole (0.65g, 81% yield).

Example 9

3, 10-dibromo-14- (3- (5-phenyl-1, 3, 4-oxadiazol-2-yl) phenyl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrole (8.21g, 10mmol) was dissolved in 100mLN, N-dimethylacetamide under an argon atmosphere at room temperature with stirring, and then the reaction flask was placed in a-78 ℃ low-temperature reactor, N-butyllithium (33mL,80mmol) was slowly dropped into the reaction flask, and after the reaction solution was reacted at low temperature for 3 hours, 2-isopropyl-4, 4 ', 5, 5' -tetramethyl-1, 3, 2-dioxaborane (12.2mL,60mmol) was rapidly added, followed by overnight reaction at room temperature. The reaction was stopped and quenched by pouring the reaction into water, concentrating and extracting the reaction with dichloromethane, purifying by column chromatography using 300-mesh 400-mesh silica gel as the stationary phase and petroleum ether/dichloromethane (5:1) as the eluent to give 2- (3- (3, 10-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrolopyrrole-5-phenyl-1, 3, 4-oxadiazole (6.86g, 75% yield) having the chemical reaction equation:

example 10

3, 10-dibromo-14- (3- (5-phenyl-1, 3, 4-oxadiazol-2-yl) phenyl) -14H- -bis (S, S-dioxo-dibenzothiophene) pyrrolopyrrole (0.74g, 0.9mmol), 2- (3, 10-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborolan-2-yl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrolopyrrole-5-phenyl-1, 3, 4-oxadiazole (0.91g, 1mmol) and the compound represented by the formula (II) (0.06g, 0.1mmol) were dissolved in 10ml of refined toluene with stirring, and tetrakis (triphenylphosphine) palladium (0.11 g) was added to the reaction flask in one portion, 0.1mmol) and then processed with tinfoil paper in the dark, the reaction flask is sealed with a sealing film, and the temperature is slowly raised. When the temperature stabilized at 85 deg.C, the organic base (Et) was added in one portion with a syringe₄NOH, 15 wt/v%, 5 mL). After 10 minutes of aeration, the gas was turned off and the temperature was maintained for 24 hours. After the reaction, 1ml of bromobenzene end cap is added into the reaction system, and the reaction is carried out for 8 hours. After the reaction system is cooled to room temperature, the reaction solution is slowly dripped into 200ml of methanol solution for precipitation and filtration. Sequentially using methanol, acetone and n-hexane for dissolving the crude productThe solution is extracted by an extractor to be colorless. Silica gel with 200-mesh and 300-mesh is used as a stationary phase, and the ratio of petroleum ether: silica gel column chromatography with dichloromethane 5:1 as eluent, filtration and vacuum drying gave polymer P1(5.6g, 70% yield) according to the equation:

example 11

The difference between this example and example 10 is: the polymerization time in example 10 was 24 hours, and the polymerization time in this example was 30 hours, whereby Polymer P2(6.9g, yield 75%) was finally obtained.

Example 12

The difference between this example and example 10: the polymerization time in example 10 was 24 hours, and the polymerization time in this example was 36 hours, whereby Polymer P3(9.8g, yield 75%) was finally obtained.

Example 13

The difference between this example and example 10 is: the polymerization time in example 10 was 24 hours, and that in this example was 42 hours, to finally obtain polymer P4(12.8g, yield 76%)

In summary, FIG. 1 shows PL spectra of the polymers prepared in examples 10-13 of the present invention in thin film state, and it can be seen from FIG. 1 that the fluorescence emission peak appears significantly red-shifted when the polymerization time is increased, which indicates that the D-A effect inside the polymer is significantly increased and the charge transfer effect is enhanced with the increase of electron-donating groups in the SO unit and the thiazole unit, thereby red-shifting the spectra, and it can be seen from the graph that the emission peaks of the polymers P1-P4 are all between 500 and 570nm, and exhibit green emission.

FIG. 2 is a cyclic voltammogram of green polymers prepared in examples 10-13 of the present invention, wherein E_HOMO＝-e(E_ox+4.8) (eV) and E_LUMO＝-e(E_red+4.8) (eV). As can be seen from FIG. 2, the LUMO level of the polymers P1-P4 decreased from-2.35 eV to-2.86 eV with the increase of polymerization time, which is attributed to the increase of SO electron-withdrawing unit, SO that the electron injection and transport ability of the polymers was enhanced. And its HOMO energy level is from-5.74 eThe increase in V to-5.57 eV indicates that the electron donating groups (methyl and nitrogen atoms) on the thiazole units in the polymers of the invention can facilitate hole injection and transport. Therefore, the polymer prepared by the invention has an electron-donating group and an electron-withdrawing group, so that the polymer has a bipolar property, and can promote the injection and the transmission of holes and electrons at the same time.

Specific electroluminescent properties and electrochemical data of P1-P4 prepared in the embodiment of the invention are shown in Table 1:

TABLE 1 electroluminescent Property data of Polymer P1-P4 devices

As can be seen from Table 1, the polymers P1-P4 prepared by the invention have the best device effect of green materials along with the increase of polymerization degree, the maximum lumen efficiency is 2.47cd/A, and the maximum brightness also reaches 4125cd/m². From the color coordinate, when the polymerization degree is higher, the color coordinate (0.26,0.65) of the polymer emits standard green light, and other polymers with different proportions also emit green light, which indicates that the green photopolymer with higher purity is prepared by the embodiment of the invention.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims

1. A bipolar green light organic electroluminescent material is characterized in that the structural formula is shown as the formula (I):

wherein n is 2-1000.

2. A preparation method of a bipolar green organic electroluminescent material is characterized by comprising the steps of mixing 3, 10-dibromo-14- (3- (5-phenyl-1, 3, 4-oxadiazole-2-yl) phenyl) -14H-bis (S, S-dioxo-dibenzothiophene) pyrrole, 2- (3- (3, 10-bis (4,4,5, 5-tetramethyl-1, 3, 2-dioxaborane-2-yl) -14H-bis (S, the polymer shown in the formula (I) is prepared from S-dioxo-dibenzothiophene) pyrrole-5-phenyl-1, 3, 4-oxadiazole and the compound shown in the formula (II) through a Suzuki coupling reaction.

3. The method for preparing the bipolar green-light organic electroluminescent material according to claim 2, wherein the temperature of the Suzuki coupling reaction is 85 ℃.

4. The method for preparing the bipolar green organic electroluminescent material of claim 2, wherein the time of the Suzuki coupling reaction is 24-42 h.

5. The method for preparing the bipolar green organic electroluminescent material of claim 4, wherein the time of the Suzuki coupling reaction is 42 h.

6. The method of claim 2, wherein the compound of formula (II) is prepared by the following steps: