CN112898282A

CN112898282A - D-pi-A type AIE-TADF near-infrared luminescent material and preparation method and application thereof

Info

Publication number: CN112898282A
Application number: CN202110095376.5A
Authority: CN
Inventors: 朱卫国; 孙俊兰; 吴秀刚; 王亚飞; 张斌; 朱梦冰; 刘煜; 谭华
Original assignee: Changzhou University
Current assignee: Changzhou University
Priority date: 2021-01-25
Filing date: 2021-01-25
Publication date: 2021-06-04
Anticipated expiration: 2041-01-25
Also published as: CN112898282B

Abstract

The invention belongs to the technical field of luminescence and display, and particularly relates to a D-pi-A type AIE-TADF near infrared luminescent material, and a preparation method and application thereof. The near-infrared luminescent material takes phenyl dicyano quinoxaline with strong electron absorption as an acceptor (A) unit, and triarylamine [ diphenyl thiophene amine, di (4-methoxyphenyl) thiophene amine and di (4-fluorophenyl) thiophene amine ] with strong electron donor as a donor (D) unit. The near-infrared luminescent material has high thermal stability, excellent carrier transmission performance and photoluminescence performance, and fluorescence quantum efficiency of 27 percent, and has wide application in the fields of organic electroluminescent displays, biological imaging and the like.

Description

D-pi-A type AIE-TADF near-infrared luminescent material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of luminescence and display illumination, and particularly relates to a D-pi-A type AIE-TADF near infrared luminescent material, a preparation method thereof and application thereof in a near infrared organic electroluminescent device.

Background

Aggregation Induced Emission (AIE) is an effective method to suppress concentration quenching to obtain high-efficiency solid-state luminescence. Since the first report of the AIE phenomenon by the tenben faith team in 2001, AIE molecules have attracted researchers' attention due to the characteristic of high-efficiency light emission of their solid thin films, and have been widely used in Organic Light Emitting Diodes (OLEDs). The AIE fluorescent materials reported so far mainly include cyanobenzoate, tetraphenylstyrene, orthocarborane derivatives, and the like. They are applied to undoped OLEDs to realize full color display. However, the AIE fluorescent material can only utilize 25% singlet state (S)₁) The excitons emit light, and the quantum efficiency of the material light emission is low. Making full use of singlet state (S)₁) And triplet excitons (T)₁) The development direction of the organic light-emitting material field is to emit light and promote the improvement of the luminous efficiency of the material.

In 2012, the Adachi team designed and obtained a small singlet-triplet energy split (Δ E)_ST) The pure organic small molecule realizes the utilization of singlet state and triplet state excitons and high-efficiency electroluminescence through effective reverse intersystem crossing (RISC), and the material is named as a Thermal Activity Delayed Fluorescence (TADF) material. Through diligent efforts of researchers, organic TADF materials have achieved efficient full color emissive displays. However, near infrared organic TADF materials are less reported.

Organic Near Infrared (NIR) luminescent materials have received much attention from researchers due to their potential applications in the fields of imaging, communications, night vision, sensing, medical treatment, and energy. At present, the developed organic near-infrared luminescent materials are mainly organic fluorescent materials and transition metal complex phosphorescent materials. However, the organic fluorescent material has low luminous efficiency, the transition metal complex phosphorescent material has high cost, and the environment pollution problem of heavy metal exists.

Due to the limitation of the energy gap law, the light emitting efficiency of the organic near-infrared light emitting material generally decreases as the light emitting wavelength increases. In order to reduce the energy gap, the organic near-infrared light-emitting material inevitably needs to introduce a large-plane conjugated system, which has strong luminescence in a solution state, but is easy to generate an aggregation-quenching (ACQ) phenomenon in a thin film state, which results in that the organic near-infrared light-emitting material is difficult to obtain high-efficiency luminescence.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention designs a class of organic near-infrared luminescent materials with AIE and TADF characteristics, and realizes the high-efficiency luminescence of the AIE-TADF near-infrared luminescent material and the application thereof in an organic electroluminescent diode by utilizing the synergistic advantages of the AIE and the TADF in luminescence.

The invention constructs a D-pi-A type AIE-TADF near infrared luminescent material by using a dicyanoquinoxaline structure with strong electron absorption as an electron acceptor (A) unit, a triarylamine structure with strong electron donor (diphenylthiophenamine, bismethoxyphenylthiophenamine and F-substituted diphenylthiophenamine) as an electron donor (D) unit and phenyl as a pi bridge unit.

The D-pi-A type AIE-TADF near infrared luminescent material provided by the invention has a structure shown in a formula 1:

wherein: x is a hydrogen atom, a fluorine atom or a methoxy unit.

Preferred AIE-TADF near-infrared phosphors are those wherein X is a hydrogen atom or a methoxy group and the molecular structural formula is DPA-ThPh-QCN (formula 2) or (OMe)₂DPA-ThPh-QCN (formula 3).

The preparation method of the AIE-TADF near infrared luminescent material comprises the following steps:

dissolving 1 molar equivalent of 2, 3-cyano-6- (4-bromophenyl) quinoxaline in toluene, adding 2-4 molar equivalents of diarylamine thiophene tributyltin compound and 0.01-0.10 molar equivalent of palladium catalyst in an inert gas environment, stirring, raising the temperature to 80-120 ℃, reacting for 5-24 hours, carrying out reduced pressure distillation to remove toluene, extracting residues with dichloromethane, washing extract liquor, drying with anhydrous magnesium sulfate, filtering, concentrating filtrate, and carrying out column chromatography separation to obtain a product.

The invention also provides application of the AIE-TADF near-infrared luminescent material, which is used as a luminescent material dopant to prepare a luminescent layer of a near-infrared OLEDs device.

The structure of the near-infrared OLEDs is as follows: ITO/PEDOT PSS (35nm)/TAPC (40nm)/TCTA (5nm)/AIE-TADF NIR-initiator (20nm)/TmPyPB (50nm)/CsF (1.2nm)/Al (120 nm).

The hole transport layer is TCTA, the electron transport layer is TmPyPB, the cathode layer is composed of metal aluminum and CsF, and the light emitting layer is the preferred AIE-TADF near-infrared light emitting material DPA-ThPh-QCN coating.

In a preferred application method, the AIE-TADF near-infrared luminescent material DPA-ThPh-QCN is used for preparing a luminescent layer of a near-infrared OLEDs device, and the near-infrared OLEDs device with the external quantum efficiency of 0.59 percent is obtained.

Compared with the prior art, the invention has the beneficial effects that:

(1) the AIE-TADF near-infrared luminescent material has simple molecular structure and low preparation cost.

(2) The AIE-TADF near-infrared luminescent material has high photoluminescence quantum efficiency which exceeds the theoretical quantum efficiency of the near-infrared luminescent material and reaches 27 percent. The donor unit and the acceptor unit in the molecule are connected by a benzene ring pi bridge, so that the spatial overlap between the HOMO of the donor unit and the LUMO of the acceptor unit is reduced to the maximum extent, and smaller S is obtained₁-T₁Energy splitting (Δ E)_ST) To promote reverse inter-system jump (RISC) and realize slave T₁To S₁The rapid transition of the state reduces the non-radiative transition of the molecule and improves the luminous efficiency of the material.

(3) The AIE-TADF near-infrared organic luminescent material can be used as a luminescent layer material, is applied to near-infrared OLEDs (organic light emitting diodes), and realizes the near-infrared luminescence of the OLEDs.

(4) The AIE-TADF near-infrared organic light-emitting micromolecule material has high thermal stability and excellent carrier transmission performance.

Drawings

FIG. 1 shows DPA-ThPh-QCN and (OMe) obtained in example 1 of the present invention₂A graph of the UV-VIS absorption spectrum and photoluminescence spectrum of DPA-ThPh-QCN in Tetrahydrofuran (THF) solution;

FIG. 2 shows a solution of DPA-ThPh-QCN in Tetrahydrofuran (THF) and THF/H prepared in example 1 of the present invention₂Photoluminescence spectra in O mixtures;

FIG. 3 shows a solution of DPA-ThPh-QCN in Tetrahydrofuran (THF) and THF/H prepared according to example 1 of the present invention₂A graph of light intensity versus water content in the O mixture;

FIG. 4 shows (OMe) obtained in example 1 of the present invention₂DPA-ThPh-QCN in Tetrahydrofuran (THF) and THF/H₂Photoluminescence spectra in O mixtures;

FIG. 5 shows (OMe) obtained in example 1 of the present invention₂DPA-ThPh-QCN in Tetrahydrofuran (THF) and THF/H₂A graph of light intensity versus water content in the O mixture;

FIG. 6 shows DPA-ThPh-QCN and (OMe) obtained in example 1 of the present invention₂A thermogram of Thermogravimetry (TGA) of DPA-ThPh-QCN;

FIG. 7 shows DPA-ThPh-QCN and (OMe) obtained in example 1 of the present invention₂Lifetime profile of DPA-ThPh-QCN in degassed films.

FIG. 8 is an electroluminescence spectrum (EL) of a DPA-ThPh-QCN doped device made in accordance with example 1 of the present invention;

FIG. 9 is a graph of current density-voltage-luminance (J-V-L) for a DPA-ThPh-QCN undoped device made in example 1 of the present invention;

FIG. 10 is a graph of the External Quantum Efficiency (EQE) of the DPA-ThPh-QCN undoped device made in example 1 of the present invention.

Detailed Description

The following specific examples are intended to further illustrate the invention, but these specific embodiments do not limit the scope of the invention in any way.

Example 1

The synthesis route of DPA-ThPh-QCN is as follows:

preparation of 6- (4-bromophenyl) quinoxaline-2, 3-dicarbonitrile (1)

Diaminomaleonitrile (20.0g,92.5mmol) and acetonitrile (350mL) are added into a 500mL double-mouth bottle, after stirring and dissolving, dichlorodicyanobenzoquinone (DDQ) (42.0g) is added, stirring and reacting are carried out for 30min at room temperature, filtering is carried out, and the filtrate is concentrated and dried to obtain a reddish brown solid which is directly used for the next step without further purification. The intermediate oxalimidodicyanide (22.0g,207mmol) and 4-bromoo-phenylenediamine (25.8g,118mmol) were mixed and added to trifluoroacetic acid (500mL) in portions, stirred at room temperature for 8h, poured into ice water, filtered and washed. Column chromatography (PE/EA 5/1) gave 12.0g (yield: 50.0%) of an off-white solid (compound 1).¹H NMR(400MHz,DMSO)δ8.69(d,J＝2.0Hz,1H),8.37(dd,J＝9.0,2.1Hz,1H),8.28(d,J＝9.0Hz,1H).MALDI-MS(m/z):calcd.257.95found.258.00.

Preparation of Compound 2

In a 250mL two-necked flask, compound 1(1.0g,3.9mmol), p-bromophenylboronic acid (1.0g,5.0mmol), palladium tetratriphenylphosphine (223mg, 0.2mmol), and 2M potassium carbonate solution (15mL) were sequentially added, dissolved in toluene, heated to 80 ℃ under nitrogen, and refluxed for 12 h. Cooling to room temperature, distilling under reduced pressure to remove toluene, and adding CH₂Cl₂(3X 20mL), and the extract was washed with water (3X 20mL) and dried over anhydrous magnesium sulfate. Column chromatography separation (PE/CH)₂

Cl

₂3/1) to give 998mg of a yellow-green solid (compound 2) (yield: 77.0%).¹H NMR(400MHz,CDCl₃)δ8.41(s,1H),8.33(s,2H),7.72(d,J＝8.5Hz,2H),7.66(d,J＝8.5Hz,2H).MALDI-MS(m/z):calcd.333.99found.334.00.

Preparation of Compound 3

In a 200mL single-neck flask, 2-bromothiophene (2.5g, 15.4mmol), diphenylamine (2.0g, 11.8mmol), palladium acetate (159mg, 0.708mmol), tri-tert-butylphosphine tetrafluoroborate (616mg, 2.12mmol), toluene (50mL) were added in this order, and the mixture was heated to 120 ℃ under nitrogen protection and refluxed for 12 h. Cooling to room temperature, distilling under reduced pressure to remove toluene, and adding CH₂Cl₂(3X 40mL), and the extract was washed with water (3X 40mL) and dried over anhydrous magnesium sulfate. Column chromatography (PE) gave 2g (yield: 67.3%) of a white solid (Compound 3).¹H NMR(400MHz,CDCl₃)δ7.24(d,J＝7.5Hz,4H),7.12(d,J＝7.7Hz,4H),7.01(dd,J＝10.4,4.3Hz,3H),6.88(dd,J＝5.6,3.7Hz,1H),6.72(dd,J＝3.6,1.1Hz,1H).

Preparation of Compound 4

Under the protection of nitrogen, compound 3(5.0g, 19.9mmol) was dissolved in anhydrous tetrahydrofuran (50mL), the reaction system was held at-78 deg.C, n-butyllithium (9.6mL, 23.9mmol) was slowly added dropwise with a syringe, tributyltin chloride (7.5mL, 25.9mmol) was added dropwise after 2h of reaction, reaction was carried out for 1h after completion of addition, the reaction system was warmed to room temperature, and stirred for 12 h. The reaction was quenched with 2mL of deionized water, then with CH₂Cl₂(3X 40mL), washed with deionized water and then anhydrous MgSO₄After drying and removal of the solvent under reduced pressure, Compound 4(7.0g) was obtained, which was used in the next step without further purification.

Preparation of Compound 5

In a 200mL single-neck flask, 2-bromothiophene (4.6g, 28.4mmol), 4, 4-dimethoxydiphenylamine (5.0g, 21.8mmol), palladium acetate (489mg, 2.18mmol), sodium tert-butoxide (8.4g, 87.2mmol), tri-tert-butylphosphine tetrafluoroborate (1.9g, 6.54mmol), toluene (50mL) were added in this order, and the mixture was heated to 120 ℃ under nitrogen protection and refluxed for 12 h. Cooling to room temperature, distilling under reduced pressure to remove toluene, and adding CH₂Cl₂(3X 40mL), and the extract was washed with water (3X 40mL) and dried over anhydrous magnesium sulfate. Column chromatography (PE) gave 5g (yield: 75%) of a white solid (Compound 5).¹H NMR(400MHz,CDCl3)δ7.06(d,J＝8.4Hz,4H),6.81(d,J＝8.8Hz,6H),6.53(s,1H),3.78(s,6H).

Preparation of Compound 6

Nitrogen protectionUnder the control, compound 5(5.0g, 16.1mmol) was dissolved in anhydrous tetrahydrofuran (50mL), the reaction system was held at-78 deg.C, n-butyllithium (8.0mL, 23.9mmol) was slowly added dropwise with a syringe, tributyltin chloride (6.1mL, 20.9mmol) was added dropwise after 2 hours of reaction, reaction was carried out for 1 hour after completion of the addition, the reaction system was warmed to room temperature, and stirred for 12 hours. The reaction was quenched with 2mL of deionized water, then with CH₂Cl₂(3X 40mL), washed with deionized water and then anhydrous MgSO₄Drying, and removing the solvent under reduced pressure to obtain the product, Compound 6(7.3g), which is used in the next step without purification.

Preparation of compound DPA-ThPh-QCN

In a 100mL two-necked flask, compound 4(2.02g, 3.73mmol), compound 2(500mg, 1.49mmol), bis (triphenylphosphine) palladium dichloride (63mg, 0.0894mmol), toluene (30mL) were added in this order, heated to 110 ℃ under nitrogen, and the reaction was stirred under reflux for 8 h. Cooling to room temperature, distilling under reduced pressure to remove toluene, and adding CH₂Cl₂(3X 40mL), and the extract was washed with water (3X 40mL) and dried over anhydrous magnesium sulfate. Column chromatography separation (PE/CH)₂

Cl

₂1/1) to give a dark red solid 200mg (yield: 23.0%).¹H NMR(500MHz,CDCl3)δ8.26(d,J＝4.3Hz,1H),8.21(s,1H),8.02(d,J＝8.9Hz,1H),7.98(d,J＝8.8Hz,1H),7.81(d,J＝8.8Hz,4H),7.38(t,J＝7.6Hz,4H),7.32(d,J＝8.1Hz,4H),7.21(t,J＝7.2Hz,2H),6.54(d,J＝4.4Hz,1H).

Compound (OMe)₂Preparation of DPA-ThPh-QCN

In a 100mL two-necked flask, compound 6(1.34g, 2.24mmol), compound 2(300mg, 0.895mmol), bis (triphenylphosphine) palladium dichloride (38mg, 0.0537mmol), toluene (10mL) were added in this order, heated to 110 ℃ under nitrogen, and the reaction was stirred under reflux for 8 h. Cooling to room temperature, distilling under reduced pressure to remove toluene, and adding CH₂Cl₂(3X 30mL), and the extract was washed with water (3X 30mL) and dried over anhydrous magnesium sulfate. Column chromatography separation (PE/CH)₂

Cl

₂1/1) to give a dark red solid 180mg (yield: 40.0%).¹H NMR(500MHz,CDCl3)δ8.26(d,J＝4.3Hz,1H),8.21(s,1H),8.02(d,J＝8.9Hz,1H),7.98(d,J＝8.8Hz,1H),7.81(d,J＝8.8Hz,4H),7.38(t,J＝7.6Hz,4H),7.32(d,J＝8.1Hz,4H),7.21(t,J＝7.2Hz,2H),6.54(d,J＝4.4Hz,1H),3.78(d,J＝8.1Hz,6H).

Example 2

DPA-ThPh-QCN and (OMe) of example 1₂AIE Performance test of DPA-ThPh-QCN:

the DPA-ThPh-QCN is prepared into 10^-5Tetrahydrofuran/water of M (THF/H)₂O) mixed solution, and photoluminescence properties of water contents of different ratios were measured at room temperature, respectively, as shown in fig. 2 and 3.

As can be seen from fig. 2: DPA-ThPh-QCN at f with excitation wavelength of 500nm_w(Water content)<Almost no luminescence in 70% THF/water solution, and increasing the water content when f_wAt 70%, a strong emission peak appears at 680 nm; when f is_wAt 90%, the emission intensity is maximal, the luminescence intensity increases by 14-fold, and the maximum emission peak is red-shifted by 10 nm. Water content (f)_w) And luminous intensity (I/I)₀) Water content (f)_w) The relationship with the maximum emission peak wavelength is shown in fig. 3.

Excitation wavelength of 500nm, (OMe)₂A similar phenomenon also occurs for DPA-ThPh-QCN, as shown in FIG. 4, at f_w<In a 70% solution of THF in water, the solution showed little luminescence. When f is_wAt 80%, a strong emission peak appears at 703 nm; continuing to increase the water content to f_wAt 90%, the luminescence intensity reached a maximum, increasing by a factor of 9, but the maximum emission peak was blue-shifted by 8 nm. This is mainly due to (OMe)₂The DPA-ThPh-QCN has larger molecular torsion, and the distorted structure of an aromatic ring causes the blue shift of the luminescence wavelength of the material in the process of aggregation. Its water content (f)_w) And luminous intensity (I/I)₀) Water content (f)_w) The relationship with the maximum emission peak wavelength is shown in fig. 5.

Example 3

DPA-ThPh-QCN and (OMe) of example 1₂TADF characterization test of DPA-ThPh-QCN:

DPA-ThPh-QCN and (OMe)₂The DPA-ThPh-QCN is made into a film which is uniformly adsorbed on the inner wall of the small test tube, sealed and discharged with oxygen for more than 30 minutes. It was measured at room temperature under nitrogen atmosphereTransient decay lifetime as shown in figure 7.

As can be seen in fig. 7: the transient decay life curve of the DPA-ThPh-QCN film in the nitrogen atmosphere presents obvious second-order exponential decay, and the data fitting result shows longer delay life: t is_d26 mus. Also, as shown in FIG. 7, (OMe)₂The transient decay life curve of the DPA-ThPh-QCN solid film presents obvious second-order exponential decay, and the data fitting result is as follows: t is_d19 mus. Microsecond-scale life represents a typical TADF characteristic.

Example 4

Based on the compounds DPA-ThPh-QCN and (OMe) in example 1₂Measurement of photoluminescence quantum efficiency (PLQY) of DPA-ThPh-QCN:

the test was performed in a transient fluorescence photometer equipped with an integrating sphere. The test method is as follows: the compounds DPA-ThPh-QCN and (OMe)₂DPA-ThPh-QCN is dissolved in toluene to prepare a solution with the absorbance of about 0.1. The fluorescence intensity of the pure toluene solvent and the toluene solution were measured sequentially. Luminescence quantum efficiency (PLQY) data was obtained by software operations.

DPA-ThPh-QCN PLQY＝26.8％

(OMe)₂DPA-ThPh-QCN PLQY＝23.1％

Example 5

Fabrication protocol and testing of electroluminescent properties of organic electroluminescent devices (OLEDs) based on the compound DPA-ThPh-QCN in example 1:

the structure of a near-infrared OLEDs device prepared from the material of example 1 is as follows: ITO/PEDOT PSS (35nm)/TAPC (40nm)/TCTA (5nm)/DPA-ThPh-QCN (20nm)/TmPyPB (50nm)/CsF (1nm)/Al (100 nm). Wherein, the electron transport layer is TmPyPB, and the luminescent layer is a DPA-ThPh-QCN near infrared luminescent material coating with AIE-TADF performance which is preferred by the invention; the cathode layer is composed of metallic aluminum and cesium fluoride (CsF).

Manufacturing procedure of the device: a hole injection layer of 40nm poly (ethylenedioxythiophene)/poly (styrenesulfonic acid) (PEDOT-PSS) (Bayer Batron P4083) and a light-emitting layer of 20nm thickness and an electron transport layer of 50nm were spin-coated on ITO glass treated with acetone, UV or the like, and thenA1 nm CsF layer and a 100nm aluminum (Al) layer were sequentially evaporated. The light emitting area of the device is 0.04cm²。

FIG. 8 is a graph of EL spectra and color coordinates of doped devices. As shown, the DPA-ThPh-QCN based device exhibited a maximum emission peak at 680nm with color coordinates (0.676, 0.310), which is a near-infrared emission.

Fig. 9 and 10 are a current-voltage-luminance curve and an external quantum efficiency curve of the device, respectively. As can be seen, the threshold voltage of the device is 4.4V. The device showed a maximum luminance of 296cd m^-2The maximum external quantum efficiency is 0.59%, and it is noted that the external quantum efficiency has no obvious roll-off of efficiency, indicating that the device performance is stable.

While the present invention has been described in connection with the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. In light of the present inventive concept, those skilled in the art will recognize that certain changes may be made in the embodiments of the invention to which the invention pertains without departing from the spirit and scope of the claims.

Claims

1. An AIE-TADF near infrared luminescent material is characterized in that the luminescent material has a structure shown in the following formula:

wherein: x is a hydrogen atom, a fluorine atom or a methoxy unit.

2. The preparation method of the AIE-TADF near infrared luminescent material according to claim 1, characterized in that the preparation method comprises the following steps:

3. The use of the AIE-TADF near-infrared luminescent material according to claim 1, wherein the AIE-TADF near-infrared luminescent material according to claim 1 is used as a luminescent material in the preparation of a luminescent layer of a near-infrared organic electroluminescent diode.