Spirochiral boron-nitrogen-based CPMR-TADF luminescent materials and their applications

Abstract

This invention belongs to the field of organic light-emitting materials, specifically providing a spirochiral boron-nitrogen-based CPMR-TADF light-emitting material and its application. This type of material has significant advantages over existing fluorescent light-emitting materials: the spirochiral boron-nitrogen-based light-emitting material of this invention (1) has a frontier orbital distribution in which chiral motifs actively participate in the molecule; (2) has a narrow spectral emission characteristic and high color purity; (3) has high exciton utilization, reaching 100%; (4) OLED devices prepared with it as the light-emitting active layer have narrow half-width and high color purity light emission, without the need for color purity improvement technologies such as filters or optical microcavities; (5) OLED devices prepared with it as the light-emitting active layer are not affected by light reflection, and the light utilization rate can reach 100%.

Description

Technical Field

[0001] This invention belongs to the field of organic light-emitting materials, and specifically relates to a helical boron-nitrogen CPMR-TADF light-emitting material, which has helical chirality and narrow half-peak emission; when applied to organic electroluminescent devices, it can achieve high color purity and circularly polarized emission. Background Technology

[0002] With the development of third-generation luminescent materials—thermally activated delayed fluorescence (TADF) materials—TCDF materials with circularly polarized emission (CPL) characteristics and MR-TADF materials with multiple resonance characteristics have become cutting-edge research hotspots in the field of luminescent materials due to their distinctive features and advantages. Among them, organic light-emitting diodes (CP-OLEDs) based on CP-TADF materials are considered the most promising luminescent devices for achieving 100% light utilization and low power consumption; organic light-emitting diodes (MR-OLEDs) based on MR-TADF materials have color purity comparable to gallium nitride-based LEDs and cadmium-based quantum dots, and are considered the most promising luminescent devices with narrow full width at half maximum (FWHM) and high color purity.

[0003] Currently reported CP-OLEDs devices have large field-to-light (FWHM) and low luminous asymmetry factor (|g|), while MR-OLEDs devices suffer from low light utilization due to light reflection, hindering their high-quality development and application. Developing novel organic light-emitting materials and their organic light-emitting diodes (OLEDs) with high efficiency, high light utilization, high color purity, low power consumption, and low cost has become a new growth point in the display and lighting field. Summary of the Invention

[0004] The present invention aims to develop helical boron-nitrogen-based CPMR-TADF materials as organic light-emitting materials with characteristics of circularly polarized emission, high color purity, and high exciton utilization.

[0005] Tracing back to the root cause, the problems with CP-TADF materials stem from the "chiral perturbation strategy" involving carbon chirality or axial chirality. Therefore, developing luminescent materials with helical chirality that combine the excellent properties of both CP-TADF and MR-TADF materials (referred to as CPMR-TADF materials) is not only the best choice to break through the design dilemma of CP-TADF materials and meet the development needs of novel organic light-emitting materials, but also a refinement and sublimation of the chiral functionalization of MR-TADF molecules.

[0006] These helical CPMR-TADF materials can, on the one hand, actively participate in the reconstruction of the frontier molecular orbital electron cloud through helical chirality, thereby increasing the luminescence asymmetry factor (|g|) and thus improving light utilization; on the other hand, they can achieve efficient exciton utilization and reduce the free wave size (FWHM) through short-range charge transfer within the molecule, enabling the HOMO / LUMO electron cloud to shuttle and delocalize throughout the molecule, thus improving luminescence efficiency and color purity. Therefore, these helical CPMR-TADF materials possess strong competitive advantages and represent a promising new type of organic light-emitting material.

[0007] The chemical structure of the spirochetal chiral boron-nitrogen-based CPMR-TADF luminescent material provided by this invention is shown in Formula 1.

[0008]

[0009] for O, S, Se;

[0010] Using chalcogen elements O, S, and Se is beneficial for effectively reducing the EST between the lowest singlet and lowest triplet states by utilizing the lone pair electrons of chalcogen elements and the heavy atom effect of S and Se.

[0011] It has a ring-expansion effect, which helps to enhance the helical chirality of molecules;

[0012] for

[0013] To regulate the solubility of molecules; the asymmetric donors on both sides of the boron atom are beneficial for the chiral resolution of molecules.

[0014] Another object of this invention is to provide applications of chiral boron-nitrogen-based CPMR-TADF materials, which are used in the field of light emission and formed into organic light-emitting layers for use in electroluminescent devices. Specifically, they are used in organic light-emitting diodes (OLEDs).

[0015] The beneficial effects of this invention are as follows:

[0016] Compared with existing technologies, the beneficial effects of this invention are as follows: the helical chiral boron-nitrogen-based CPMR-TADF luminescent material of this invention has a stable structure, high luminous efficiency, circularly polarized emission, and a small full width at half maximum (FWHM). This invention differs from chiral perturbation strategy-based CP-TADF molecules, which are more likely to achieve a high luminous asymmetry factor g value; CP-TADF materials with narrow FWHM and high color purity are rare. This design strategy inherits the excellent characteristics of MR-TADF, but also endows this type of material with the novel characteristic of helical circularly polarized emission. Attached image description:

[0017] Figure 1 This is a schematic diagram of the single-crystal diffraction structure of compound 3 in Example 1 of the present invention.

[0018] Figure 2 This is a graph showing the results of the chiral column separation of compound 3 in Example 1 of the present invention.

[0019] Figure 3 A schematic diagram of the single-crystal diffraction structure of compound 5 in Example 1 of this invention.

[0020] Figure 4 This is a graph showing the results of the chiral column separation of compound 5 in Example 1 of the present invention.

[0021] Figure 5 Compound 3 in Example 1 of this invention in toluene solution (10 -5 (a) UV-Vis absorption, (b) circular dichroism absorption-circularly polarized emission, and (c) emission asymmetry factor in mol / L.

[0022] Figure 6 The following are the (a) UV-Vis absorption, (b) circular dichroism absorption-circular polarization emission, and (c) emission asymmetry factor of compound 3 in mCPCN thin film (1wt%, 30nm) in Example 1 of this invention.

[0023] Figure 7 Compound 5 in Example 1 of this invention in toluene solution (10 -5 (a) UV-Vis absorption, (b) circular dichroism absorption-circularly polarized emission, and (c) emission asymmetry factor in mol / L.

[0024] Figure 8 The following are the (a) UV-Vis absorption, (b) circular dichroism absorption-circular polarization emission, and (c) emission asymmetry factor of compound 5 in mCPCN thin film (1wt%, 30nm) in Example 1 of this invention.

[0025] Figure 9 The electroluminescence performance of (+)-compound 3 (black) and (-)-compound 3 (gray) in device 1 and device 2 in Example 1 of this invention is as follows: Electroluminescence performance in device 1 and device 2: (a) External quantum efficiency-current density curve, with the inset showing the electroluminescence spectrum. (b) Electroluminescent circularly polarized emission. (c) Electroluminescence asymmetry factor.

[0026] Figure 10The electroluminescence performance of (+)-compound 5 (black) and (-)-compound 5 (gray) in devices 3 and 4 in Example 1 of this invention is shown in the figures: (a) External quantum efficiency-current density curves, with the inset showing the electroluminescence spectra; (b) Electroluminescence circularly polarized emission; and (c) Electroluminescence asymmetry factor. Detailed Implementation

[0027] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments and accompanying drawings, further clarifies the invention. Those skilled in the art should understand that the specific details described below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0028] In this invention, the preparation methods are all conventional unless otherwise specified. The raw materials used are all available from publicly available commercial sources unless otherwise specified.

[0029] Example 1

[0030] In formula (1) provided by the present invention, when For H, For S, for When the compound is of formula 3, its synthetic route is as follows:

[0031]

[0032] Synthesis of Compound 1:

[0033] 2,3-Dichlorobromobenzene (5.43 g, 24.04 mmol), phenothiazine (4.78 g, 23.98 mmol), Pd2(dba)3 (549 mg, 0.30 mmol), t Bu3PHBF4 (175mg, 0.60mmol) and t BuONa (2.87 g, 29.9 mmol) was added to 20 mL of toluene, and the reaction was carried out at 100 °C for 12 hours under a nitrogen atmosphere. After cooling, the reaction solution was diluted with ethyl acetate and washed with water. The organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated. The residue was subjected to silica gel column chromatography (petroleum ether: dichloromethane = 4:1) to give 5.91 g of a white solid, yield 71.5%. MS (EI): m / z 343.1 [M] + Elemental analysis, theoretical: C, 62.80; H, 3.22; N, 4.07; actual: C, 62.77; H, 3.26; N, 4.082.

[0034] Synthesis of compound 2:

[0035] Compound 1 (3.44 g, 0.01 mol), 9,10-dihydro-9,9-dimethylacridine (2.30 g, 0.011 mmol), Pd2(dba)3 (92 mg, 0.10 mmol), t Bu3PHBF4 (29 mg, 0.10 mmol) and t BuONa (289 mg, 3.00 mmol) was added to 20 mL of toluene, and the reaction was carried out at 100 °C for 12 hours under a nitrogen atmosphere. After cooling, the reaction solution was diluted with ethyl acetate and washed with water. The organic phase was dried over anhydrous sodium sulfate, filtered, and concentrated. The residue was subjected to silica gel column chromatography (petroleum ether: dichloromethane = 4:1) to give 2.62 g of a white solid, yield 50.6%. MS (EI): m / z 516.1 [M] + Elemental analysis, theoretical: C, 76.65; H, 4.87; N, 5.42; practical: C, 76.67; H, 4.85; N, 5.43.

[0036] Synthesis of compound 3:

[0037] Compound 2 (1.03 g, 0.002 mol) was dissolved in 20 mL of tert-butylbenzene. Tert-butyllithium (1.3 mol / L, 3.1 mL) was slowly added dropwise under a nitrogen atmosphere at -30 °C. After the addition was complete, the reaction apparatus was transferred to an oil bath and reacted at 60 °C for 2 hours. The mixture was then cooled to 0 °C, and boron tribromide (1.00 g, 4.00 mmol) was slowly added. The mixture was stirred at room temperature for 1 hour, and then diisopropylamine (517 mg, 4.00 mmol) was added. The reaction was refluxed for 12 hours, cooled, and the tert-butylbenzene was removed under reduced pressure. The mixture was extracted with dichloromethane, dried over anhydrous sodium sulfate, filtered, concentrated, and subjected to silica gel column chromatography (petroleum ether: dichloromethane = 5:1) to give 300 mg of a yellow solid, with a yield of 30.6%. MS (EI): m / z 490.1 [M] + Elemental analysis: Theoretical: C, 80.82; H, 4.73; N, 5.71; Actual: C, 80.87; H, 4.65; N, 5.73. Compound 3 slowly grew into single crystals in a mixed solvent of dichloromethane and methanol, and its structure was confirmed by XRD single-crystal diffraction (e.g., Figure 1 Racemic compounds were resolved by chiral column chromatography (CHIRALPAK IG(IG00CE-UC011)) to prepare (+)-compound 3 and (-)-compound 3, the separation results of which are shown below. Figure 2 .

[0038] Example 2

[0039] In formula (1) provided by the present invention, when For H, For S, for When the compound is of formula 5, its synthetic route is as follows:

[0040]

[0041] Synthesis of compound 4:

[0042] 9,10-dihydro-9,9-diphenylacridine was used instead of 9,10-dihydro-9,9-dimethylacridine, and the procedure was the same as the synthesis of compound 2 in Example 1. The yield of compound 4 was 56.9%. MS (EI): m / z 640.2 [M] + Elemental analysis, theoretical: C, 80.54; H, 4.56; N, 4.37; practical: C, 80.55; H, 4.55; N, 4.39.

[0043] Synthesis of compound 5:

[0044] Using compound 4 as the reaction substrate, the procedure was the same as the synthesis of compound 3 in Example 1. The yield of compound 5 was 35.7%. MS (EI): m / z 614.2 [M] + Elemental analysis: Theoretical: C, 84.04; H, 4.43; N, 4.56; Actual: C, 84.06; H, 4.44; N, 4.57.

[0045] Compound 5 slowly grew into single crystals in a mixed solvent of dichloromethane and methanol, and its structure was confirmed by XRD single-crystal diffraction (e.g. Figure 3 Racemic compounds were resolved by chiral column chromatography (CHIRALPAK IG(IG00CE-UC011)) to prepare (+)-compound 5 and (-)-compound 5, as shown in the figure. Figure 4 .

[0046] Other novel CPMR-TADF compounds involved in this invention can be synthesized using methods similar to those shown in the above embodiments. All target molecules are molecularly rigid, reducing molecular vibrations and suppressing inter-ring rotation, thus yielding emission peaks with high color purity; the obtained target products all exhibit helical chirality and circularly polarized luminescence. This invention also provides the ultraviolet-visible absorption spectra and photoluminescence spectra of the novel CPMR-TADF compounds involved, using compound 3 as an example to illustrate its photophysical properties.

[0047] Example 3

[0048] Compound 3 was dissolved in toluene to prepare a 10 -5 Solution M was tested for its UV-Vis absorption spectrum. Figure 5 The photophysical properties of (+)-compound 3 and (-)-compound 3 in toluene solution. Figure 5 Compound 3 exhibits two absorption peaks in both solution and solid, located at a short wavelength of 375 nm and a long wavelength of 467 nm, respectively. The short-wavelength absorption peak is attributed to the π-π* and n-π* transition absorptions of the molecule, while the long-wavelength absorption peak is attributed to the charge transfer (ICT) interaction between the donor and acceptor units within the molecule. Comparison of fluorescence emission and ultraviolet absorption spectra reveals that both exhibit a small Stokes shift (30 nm). In this type of split absolute configuration, peak 1 shows positive values ​​in circular dichroism absorption and circularly polarized emission, corresponding to (+)-compound 3; peak 2 shows negative values ​​in both circular dichroism absorption and circularly polarized emission, corresponding to (-)-compound 3. Both (+)-compound 3 and (-)-compound 3 show positive values ​​in toluene solution (1×10⁻⁶). -5 The luminescence asymmetry factor |g in M,298K) PL |≈(1.0-2.0)×10 -3 Doping (+)-compound 3 and (-)-compound 3 into 9-[3-(9H-carbazole-9-yl)phenyl]-9H-carbazole-3-carboxynitrile (mCPCN) also yielded photophysical properties similar to those in toluene. It should be noted that in the UV-Vis absorption, since compound 3 doping accounts for only 1 wt%, the long-wavelength absorption peaks attributable to intramolecular charge transfer (ICT) from donor to acceptor units appear lower due to normalization. Figure 6 .

[0049] Example 5

[0050] Compound 5 was dissolved in toluene to prepare a 10-fold dilution. -5 Solution M was tested for its UV-Vis absorption spectrum. Figure 7 The photophysical properties of (+)-compound 5 and (-)-compound 5 in toluene solution. Figure 7 Compound 5 exhibits two absorption peaks in both solution and solid, located at a short wavelength of 375 nm and a long wavelength of 467 nm, respectively. The short-wavelength absorption peak is attributed to the π-π* and n-π* transition absorptions of the molecule, while the long-wavelength absorption peak is attributed to the charge transfer (ICT) interaction between the donor and acceptor units within the molecule. Comparison of the fluorescence emission and ultraviolet absorption spectra reveals that both exhibit a small Stokes shift (33 nm). The absolute configuration after separation shows that peak 1 is positive in both circular dichroism absorption and circularly polarized emission, corresponding to (+)-compound 5; peak 2 is negative in both circular dichroism absorption and circularly polarized emission, corresponding to (-)-compound 5; and (+)-compound 3 and (-)-compound 3 show similar absorption peaks in toluene solution (1×10⁻⁶). -5 The luminescence asymmetry factor |g in M,298K) PL |≈(1.0-2.0)×10 -3 .

[0051] Doping mCPCN with (+)- and (-)- compounds also yielded photophysical properties similar to those in toluene. It should be noted that in the UV-Vis absorption, since compound 3 doping accounts for only 1 wt%, the long-wavelength absorption peaks attributable to intramolecular charge transfer (ICT) from donor to acceptor units appear lower after normalization. Figure 8 .

[0052] Example 6

[0053] The highest occupied molecular orbital (HOMO) level and the lowest unoccupied molecular orbital (LUMO) level of compounds 3 and 5 were measured by cyclic voltammetry, as shown in Table 1. Their energy levels are all between the corresponding energy levels of mCPCN (-2.6 eV / -6.2 eV), indicating that mCPCN is suitable as their host material.

[0054] Table 1 Energy levels of compounds

[0055]

[0056] a E 1 / 2 ox E 1 / 2 red It is the redox potential. b HOMO l Reference Fc / Fc + The redox potential (0.49 Vo) HOMO=-[E 1 / 2 ox -0.49+4.8]; c LUMO = -[E GP -HOMO]. d The optical band gap is determined by the ultraviolet absorption edge.

[0057] Example 7

[0058] Electroluminescent devices were fabricated using compounds (+) / (-)-3 and (+) / (-)-5 with absolute configurations as emitting layer materials. The fabrication process was illustrated using compound 3 as the undoped emitting layer material. The device structure was as follows: ITO / PEDOT:PSS (35nm) / PVK (20nm) / mCPCN: compounds 3 and 5 with absolute configurations (1wt%, 30nm) / DPEPO (9nm) / TmPyPB (50nm) / LiF (0.5nm) / Al (120nm). (Depending on the different device numbers for the light-emitting layer: device 1: [mCPCN: (+)-compound 3: (1 wt%, 30 nm)]; device 2: [mCPCN: (-)-compound 3: (1 wt%, 30 nm)]; device 3: [mCPCN: (+)-compound 5: (1 wt%, 30 nm)]; device 4: [mCPCN: (-)-compound 5: (1 wt%, 30 nm)];) The fabrication process of the devices is as follows: 35 nm of poly(dioxyethylthiophene) / poly(p-phenylene sulfonate) (PEDOT-PSS, Bayer Batron) is spin-coated onto the treated ITO glass. P4083 was used as the hole injection layer; then 20 nm of poly(9-vinylcarbazole) (PVK) was spin-coated as the hole transport layer; 30 nm of 9-[3-(9H-carbazole-9-yl)phenyl]-9H-carb-3-carbazole nitrile (mCPCN) and compounds 3 and 5 with absolute configurations were spin-coated as the light-emitting layer; then, 9 nm of DPEPO was vacuum-deposited on the light-emitting layer as the electron blocking layer, 50 nm of TmPyPB as the electron transport layer, 1.2 nm of LiF as the cathode buffer layer, and 120 nm of Al as the cathode. The light-emitting area of ​​the device was 0.16 cm². 2 .

[0059] The thicknesses of the hole injection layer and hole transport layer were measured using a surface profilometer (Tencor, ALFA-Step500). The thicknesses and deposition rates of the electron transport layers TmPyPB, CsF, and Al were measured using a thickness / velocity meter (Sycon STM-100 thickness / velocity meter). The deposition rates of the TmPyPB, CsF, and Al layers were 1–2 nm / s. All operations were performed in a nitrogen glove box.

[0060] The performance of devices 1 and 2, which use mCPCN:(+) / (-)-compound 3 as the light-emitting layer, was as follows: their start-up voltage (Von) was 4.4V / 4.4V, and their maximum luminance (Lmax) was 3334 cd / m². -2 / 3037 cd m -2 Maximum current efficiency (CEmax) 66.30 cd A -1 / 55.05cd A -1 Maximum power efficiency (PEmax) 38.58 lm W -1 / 35.16lm w -1 The maximum external quantum efficiency (EQEmax) is 20.57% / 18.98. See below for other performance metrics. Figure 9 See Table 2.

[0061] For specific new performance details of devices 3 and 4 using mCPCN:(+) / (-)-compound 5 as the light-emitting layer, see [link to device description]. Figure 10 Compared with Table 2

[0062] Table 2. Device performance of OLEDs based on (+) / (-)-compound 3 and (+) / (-)-compound 5

[0063]

[0064] a device 1: [mCPCN: (+)-compound 3: (1 wt%, 30 nm)]; device 2: [mCPCN: (-)-compound 3: (1 wt%, 30 nm)]; device 3: [mCPCN: (+)-compound 5: (1 wt%, 30 nm)]; device 4: [mCPCN: (-)-compound 5: (1 wt%, 30 nm)]; b V on :1cd m -2 The starting voltage is as follows; c L max Maximum brightness; d CE max Maximum current efficiency; e PEmax: Maximum power efficiency; f EQEmax: Maximum external quantum efficiency; g Electroluminescence spectral peaks; h Half-peak width; i g EL Electroluminescence asymmetry factor; j Color coordinates.

[0065] Although the invention has been described in conjunction with preferred embodiments, the invention is not limited to the above embodiments, and it should be understood that the appended claims summarize the scope of the invention. Guided by the inventive concept, those skilled in the art should recognize that any modifications made to the various embodiments of the invention will be covered by the spirit and scope of the claims.

Claims

1. A chiral boron-nitrogen-based CPMR-TADF light-emitting material for an organic light-emitting diode, characterized in that, The light emitting material has the following helical chirality, (+)- or (-) , (+)- or (-) .

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