Dithieno phenazine compound as well as preparation method and application thereof

Abstract

The invention discloses a dithieno phenazine compound as well as a preparation method and application thereof, and belongs to the technical field of organic small molecular luminescent materials. The whole molecule of the dithieno-phenazine compound provided by the invention shows a bipolar transmission characteristic, the dithieno-phenazine unit with an electricity absorption property enables the whole molecule to maintain a relatively good plane structure, relatively strong intramolecular charge transfer interaction can be formed between electron donor units and electron acceptor units, and obvious near-infrared light is emitted. Therefore, the material has great potential when being used as a luminescent material.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic small molecule luminescent materials, and particularly relates to a dithienophenazine compound, a preparation method thereof, and an application thereof. Background Art

[0002] In recent years, thermally activated delayed fluorescence (TADF) materials in the deep red - near infrared (DR - NIR) region have attracted strong research interest due to their great potential applications in fields such as bioimaging, phototherapy, anti - counterfeiting, microscopy, night vision devices, and organic light - emitting diodes (OLEDs). For OLEDs, an ideal TADF material needs to simultaneously satisfy that the singlet - triplet splitting energy (ΔE ST ) between the lowest singlet state (S1) and the lowest triplet state (T1) is small enough, a large horizontal dipole rate, and a high fluorescence quantum efficiency. Generally speaking, by increasing the twist angle between the electron - donor and electron - acceptor units, the spatial distributions of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) are separated to obtain a small ΔE ST , because this separation is beneficial for triplet excitons to be up - converted to singlet excitons through the reverse intersystem crossing (RISC) process. However, according to the Franck - Condon transition principle and Fermi's golden rule, the separated frontier molecular orbitals may lead to poor oscillator strength, low fluorescence quantum efficiency, and weak luminescence. In addition, according to the energy - band rule, constructing DR - NIR luminescent materials requires a narrow HOMO - LUMO bandgap, which may accelerate the non - radiative decay of the excited state and further deteriorate the fluorescence quantum efficiency. Recent research has shown that increasing the molecular planarity and reducing the twist angle between the donor and acceptor units can effectively enhance the oscillator strength. But this seems to be contradictory to a small ΔE ST . A small twist angle usually increases the exchange integral, so theoretically it leads to a larger ΔE ST . Therefore, developing DR - NIR - TADF materials with a small ΔE ST , high oscillator strength, and excellent fluorescence quantum efficiency is still full of challenges. Summary of the Invention

[0003] The purpose of the present invention is to provide a dithienophenazine compound, a preparation method thereof, and an application thereof. The dithienophenazine compound provided by the present invention has good solubility and film - forming property, strong electrophilicity, a relatively low LUMO energy level, and a relatively high electron mobility, and can emit obvious near - infrared light.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] One of the technical solutions of the present invention: Provide a dithienophenazine compound, the structural formula of which is shown in Formula I:

[0006]

[0007] In formula I, Ar1 to Ar4 are independently selected from H, an electron donor unit or an electron acceptor unit, and Ar1 to Ar4 are connected to the benzene ring structure or the thiophene structure through a single bond;

[0008] The electron donor unit is triphenylamine, diphenylamine, carbazole, indole or phenoxazine; the electron acceptor unit is cyano, azacycle, diphenyl sulfone, benzophenone or cyanobenzene.

[0009] The second technical solution of the present invention: Provide a preparation method of the above dithienophenazine compound, including the following steps:

[0010] Using halogenated benzodithiophene dione as a reaction raw material, an electron donor unit or an electron acceptor unit is connected to the benzodithiophene dione through a coupling reaction to obtain an intermediate; the intermediate is subjected to a ring-closure reaction with o-phenylenediamine, or o-phenylenediamine substituted with an electron donor unit or an electron acceptor unit, to prepare the dithienophenazine compound.

[0011] Preferably, the coupling reaction is carried out under alkaline conditions.

[0012] Preferably, the reaction temperature of the coupling reaction is 80-95 °C and the time is 15-30 h.

[0013] Preferably, the coupling reaction is carried out under the catalytic action of the catalyst tetrakis(triphenylphosphine)palladium (Pd(PPh3)4).

[0014] Preferably, the solvent for the coupling reaction is a mixed solution of tetrahydrofuran and water, toluene, ethanol or dioxane.

[0015] Preferably, the temperature of the ring-closure reaction is 110-130 °C and the time is 12-18 h.

[0016] Preferably, the solvent for the ring-closure reaction is acetic acid.

[0017] The third technical solution of the present invention: Provide an application of the above dithienophenazine compound in the preparation of thermally activated delayed fluorescence materials.

[0018] The fourth technical solution of the present invention: Provide an application of the above dithienophenazine compound in the preparation of organic light-emitting diodes.

[0019] The idea of the present invention to design the dithienophenazine compound as a DR-NIR material is:

[0020] To improve the fluorescence quantum efficiency of DR-NIR materials and suppress non-radiative processes, a rigid molecular structure is required. In this invention, a highly rigid molecular structure is constructed using a large planar polycyclic acceptor with strong electron-withdrawing ability and an electron donor unit.

[0021] Specifically, in the embodiment, the electron donor unit triphenylamine is first connected to obtain 2,7-bis(4-(diphenylamino)phenyl)benzo[2,1-b:3,4-b']dithiophene-4,5-dione, and then dehydration cyclization is carried out through reaction with 4,5-diaminophthalonitrile, so that the target compound has a rigid and strongly electron-withdrawing core - dithieno[3,2-a:2',3'-c]phenazine-9,10-dicarbonitrile, and the final product is 2,5-bis(4-(diphenylamino)phenyl)dithieno[3,2-a:2',3'-c]phenazine-9,10-dicarbonitrile (2TPA-SNCN), while achieving a lower ΔE ST and a large oscillator strength and high fluorescence quantum efficiency.

[0022] The beneficial technical effects of this invention are as follows:

[0023] The dithienophenazine compounds provided by this invention have a novel structure, are easy to purify, have good reproducibility in multiple syntheses, and are convenient for studying the relationship between structure-property-performance.

[0024] The dithienophenazine compounds provided by this invention have good solubility, film-forming property, and film morphology stability.

[0025] The dithienophenazine compounds provided by this invention have strong electrophilicity, low LUMO energy level, and high electron mobility.

[0026] The dithienophenazine compounds provided by this invention exhibit bipolar transport characteristics. The electron-withdrawing dithienophenazine unit makes the whole molecule maintain a good planar structure, and a relatively strong intramolecular charge transfer interaction can be formed between the electron donor and acceptor units, emitting obvious near-infrared light. Therefore, using such materials as luminescent materials has great potential. Description of the Drawings

[0027] Figure 1 It is the TGA spectrum of 2TPA-SNCN prepared in Example 1.

[0028] Figure 2 It is the DSC spectrum of 2TPA-SNCN prepared in Example 1.

[0029] Figure 3 It is the CV curve of 2TPA-SNCN prepared in Example 1.

[0030] Figure 4The UV-Vis-NIR absorption spectrum of 2TPA-SNCN prepared in Example 1 in toluene solution.

[0031] Figure 5 The UV-Vis-NIR absorption spectrum of 2TPA-SNCN prepared in Example 1 in the thin film state.

[0032] Figure 6 The fluorescence spectrum of 2TPA-SNCN prepared in Example 1 in toluene solution.

[0033] Figure 7 The fluorescence spectrum of 2TPA-SNCN prepared in Example 1 in the thin film state.

[0034] Figure 8 The current density-voltage (J-V) spectrum of OLEDs prepared with 2TPA-SNCN in Example 1 as the light-emitting material.

[0035] Figure 9 The external quantum efficiency-luminance (EQE-L) spectrum of OLEDs prepared with 2TPA-SNCN in Example 1 as the light-emitting material.

[0036] Figure 10 The electroluminescence (EL) spectrum of OLEDs prepared with 2TPA-SNCN in Example 1 as the light-emitting material. Detailed implementation manners

[0037] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention. It should be understood that the terms described in the present invention are only for describing specific implementation manners and are not used to limit the present invention.

[0038] In addition, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0039] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention.

[0040] As used herein, terms such as "comprising", "including", "having", "containing", etc. are all open-ended terms, meaning including but not limited to.

[0041] Example 1

[0042] Preparation of 2,5-bis(4-(diphenylamino)phenyl)dithieno[3,2-a:2',3'-c]phenazine-9,10-dicarbonitrile:

[0043] (1) Under a nitrogen atmosphere, 2,7-dibromobenzo[1,2-b:4,5-b']dithiophene-4,5-dione (2.00 g, 5.29 mmol), 4-(diphenylamino)phenylboronic acid (4.58 g, 15.87 mmol), a mixed solution of 240 mL of THF and H2O (volume ratio 6:1), K2CO3 (7.31 g, 52.90 mmol) and Pd(PPh3)4 (0.73 g, 0.63 mmol) were added to a 500 mL three-necked flask. The mixture was heated to 95 °C and stirred for 24 h. After cooling to room temperature, the reaction solution was poured into 300 mL of water and extracted with dichloromethane (DCM). The organic phase was separated, and the aqueous phase was extracted with DCM three times. The organic phases were combined and then washed with saturated brine three times. Dried over anhydrous magnesium sulfate, filtered by suction, and the solvent in the obtained filtrate was removed under reduced pressure; separated by silica gel column (petroleum ether (PE):DCM = 8:1, volume ratio) to obtain 2,7-bis(4-(diphenylamino)phenyl)benzo[2,1-b:3,4-b']dithiophene-4,5-dione (3.21 g, 4.5 mmol) as a gray-green powder solid with a yield of 85%. 1 H NMR (400 MHz, CDCl3), δ (ppm): 7.53 (s, 2H), 7.41 (d, J = 8.6 Hz, 4H), 7.30 (t, J = 7.8 Hz, 8H), 7.16 - 7.03 (m, 16H).. Calcd C 46 H 30 N2O2S2 706.8726, ESI-TOF-MS (m / z): 707.1785 (M + )。

[0044] The reaction process of step (1) is as follows:

[0045]

[0046] (2) Under a nitrogen atmosphere, 2,7-bis(4-(diphenylamino)phenyl)benzo[2,1-b:3,4-b']dithiophene-4,5-dione (1.00 g, 1.41 mmol), 4,5-diaminophthalonitrile (0.25 g, 1.55 mmol), and 100 mL of glacial acetic acid were added to a 250 mL three-necked flask. The reaction was refluxed for 16 hours under an oil bath condition at 120 °C. After cooling to room temperature, the reaction was quenched with 200 mL of deionized water. The mixture was extracted with DCM, and the organic phase was separated. The aqueous phase was extracted with DCM three times, and the organic phases were combined. The combined organic phase was washed with saturated brine three times. It was dried over anhydrous magnesium sulfate, filtered by suction, and the obtained filtrate was concentrated under reduced pressure to remove the solvent. Column chromatography on silica gel (PE:DCM = 2:1, v / v) gave 2,5-bis(4-(diphenylamino)phenyl)dithieno[3,2-a:2',3'-c]phenazine-9,10-dicarbonitrile (2TPA-SNCN) (600 mg, 0.72 mmol) as a gray-green powder solid, with a yield of 51%. 1 H NMR (400 MHz, CDCl3), δ (ppm): 8.67 (s, 2H), 8.24 (s, 2H), 7.57 (d, J = 8.2 Hz, 4H), 7.31 (t, J = 7.6 Hz, 8H), 7.18 (d, J = 7.8 Hz, 8H), 7.11 (d, J = 6.5 Hz, 8H). 13 C NMR (400 MHz, CDCl3) δ (ppm): 148.66, 147.07, 144.58, 141.35, 140.87, 137.40, 136.57, 134.48, 129.52, 126.96, 126.04, 125.24, 123.84, 122.49, 118.51, 118.29, 115.31, 112.53.. Calcd C 54 H 32 N6S2828.2130, ESI-TOF-MS (m / z): 829.2108 (M + )。

[0047] The reaction process of step (2) is as follows:

[0048]

[0049] The physical properties of 2TPA-SNCN prepared in Example 1 were analyzed:

[0050] I. Thermal analysis

[0051] Figure 1 Figure shows the TGA spectrum of 2TPA-SNCN prepared in Example 1.

[0052] Figure 2DSC spectrum of 2TPA-SNCN prepared in Example 1.

[0053] It can be seen from Figure 1 that the thermal decomposition temperature (T d ) of 2TPA-SNCN is 556 °C, showing good thermal stability, indicating that the dithienopyrazine unit structure is stable and the chemical bonds between the triphenylamine and cyano units are strong. It can be seen from Figure 2 that 2TPA-SNCN shows a relatively distinct glass transition, and the glass transition temperature (T g ) is 133 °C, indicating that the material has excellent thin-film morphological stability.

[0054] II. Electrochemical property analysis

[0055] Figure 3 CV curve of 2TPA-SNCN prepared in Example 1 (corrected with ferrocene as the internal standard).

[0056] Other electrochemical properties are shown in Table 1.

[0057] Table 1

[0058] Material <![CDATA[E OX (V)]]> <![CDATA[E red (V)]]> <![CDATA[E HOMO (eV)]]> <![CDATA[E LUMO (eV)]]> 2TPA - SNCN 0.41 -1.31 -4.81 -3.09

[0059] In Table 2, E HOMO = -e(oxidation potential + 4.40) V; E LUMO = -e(reduction potential + 4.40) V.

[0060] The data in Table 2 show that for 2TPA-SNCN prepared in Example 1, E HOMO is -4.81 eV, and E LUMO is -3.09 eV, and the energy levels are relatively well-matched with the surrounding charge transport layers, which is conducive to the injection and migration of charge carriers.

[0061] III. Optical property analysis

[0062] Figure 4 UV-Vis-NIR absorption spectrum of 2TPA-SNCN prepared in Example 1 in toluene solution, Figure 5 UV-Vis-NIR absorption spectrum of 2TPA-SNCN prepared in Example 1 in thin-film state, Figure 6 Fluorescence spectrum of 2TPA-SNCN prepared in Example 1 in toluene solution, Figure 7 Fluorescence spectrum of 2TPA-SNCN prepared in Example 1 in thin-film state.

[0063] From Figure 4It can be seen that in the toluene solution, the maximum absorption peak of 2TPA-SNCN is at 388 nm, which is caused by the π-π* transition of the molecular skeleton. There is a broad absorption band between 500 and 750 nm, which is due to the intramolecular charge transfer between triphenylamine and dithienopyrazine.

[0064] From Figure 5 It can be seen that, compared with that in the toluene solution, the absorption spectrum of 2TPA-SNCN in the thin film state shows a red shift. The highest peak redshifts to 402 nm, the full width at half maximum of the main peak becomes wider, and the absorption edge in the long wavelength direction extends from 750 nm to 800 nm. In the thin film state, due to the good planarity of the molecule and easy aggregation, the red shift of absorption is caused.

[0065] From Figure 6 It can be seen that, compared with the absorption spectrum, the fluorescence spectrum of 2TPA-SNCN prepared in Example 1 shows a very obvious Stokes red shift. In the toluene solution, the fluorescence emission peak is at 937 nm.

[0066] And from Figure 7 It can be seen that, compared with that in the toluene solution, the fluorescence spectrum of 2TPA-SNCN in the thin film state shows a certain red shift, the emission peak is at 968 nm, with a red shift of 31 nm, indicating that these materials show a certain aggregation ability in the thin film state.

[0067] Using 2TPA-SNCN in Example 1 as the light-emitting material to prepare organic deep red-near infrared light-emitting diodes (OLEDs), the following device structure is adopted:

[0068] ITO / TAPC(30 nm) / MCP(10 nm) / CBP:x wt% 2TPA-SNCN(20 nm) / B3PyMPM(70 nm) / LiF(1 nm) / Al(150 nm), where x is 5 or 15 or 30 or 100.

[0069] Figure 8 It is the current density-voltage (J-V) spectrum of OLEDs prepared using 2TPA-SNCN in Example 1 as the light-emitting material.

[0070] Figure 9 It is the external quantum efficiency-luminance (EQE-L) spectrum of OLEDs prepared using 2TPA-SNCN in Example 1 as the light-emitting material.

[0071] Figure 10 It is the electroluminescence (EL) spectrum of OLEDs prepared using 2TPA-SNCN in Example 1 as the light-emitting material.

[0072] From Figures 8 - 10As can be seen, when the small molecule material 2TPA-SNCN prepared in Example 1 is used as the luminescent material, different device performances are exhibited when doped at different concentrations in the host material CBP.

[0073] Figure 8 It shows that under the voltage drive of 0 - 10V, as the doping concentration gradually increases, the current density at the same voltage gradually increases.

[0074] Figure 9 It shows that the maximum EQE of the device doped with 30% reaches 4.93%. At a brightness of 100 cd / m 2 the EQE is 3.3%, while at a brightness of 1000 cd / m 2 the EQE of the undoped device is the highest, which is 2.9%. Generally speaking, because 2TPA-SNCN has strong electron-withdrawing properties, as the doping concentration increases, the electron transport ability in the device increases, and the carriers are relatively balanced.

[0075] Figure 10 It shows that as the doping concentration gradually increases, the EL emission peak gradually redshifts, at 601, 611, 620, and 624 nm respectively, and the emission range is 500 - 780 nm, showing the characteristics of red light to near-infrared light.

[0076] The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A dithienophenazine compound, characterized in that, The structural formula is as shown in Formula I: In Formula I, Ar1 to Ar4 are independently selected from H, an electron donor unit or an electron acceptor unit, and Ar1 to Ar4 are connected to the benzene ring structure or the thiophene structure by a single bond; The electron donor unit is triphenylamine, diphenylamine, carbazole, indole or phenoxazine; the electron acceptor unit is cyano, azacycle, diphenyl sulfone, benzophenone or benzonitrile.

2. A method for preparing the dithienopyrazine compound according to claim 1, characterized in that, It includes the following steps: Using halogenated benzodithiophene dione as a reaction raw material, an electron donor unit or an electron acceptor unit is attached to the benzodithiophene dione through a coupling reaction to obtain an intermediate; the intermediate undergoes a ring-closure reaction with o-phenylenediamine or o-phenylenediamine substituted with an electron donor unit or an electron acceptor unit to prepare the dithienophenazine compound.

3. The preparation method of the dithienophenazine compound according to claim 2, characterized in that, The coupling reaction is carried out under alkaline conditions.

4. The preparation method of the dithienophenazine compound according to claim 2, characterized in that The reaction temperature of the coupling reaction is 80 - 95 °C, and the time is 15 - 30 h.

5. The preparation method of the dithienopyrazine compound according to claim 2, characterized in that, The coupling reaction is carried out under the catalysis of the catalyst tetrakis(triphenylphosphine)palladium.

6. The preparation method of the dithienophenazine compound according to claim 2, characterized in that, The solvent for the coupling reaction is a mixed solution of tetrahydrofuran and water, toluene, ethanol or dioxane.

7. The preparation method of the dithienopyrazine compound according to claim 2, wherein The temperature of the ring-closure reaction is 110 - 130 °C, and the time is 12 - 18 h.

8. The preparation method of the dithienophenazine compound according to claim 2, characterized in that, The solvent for the ring-closure reaction is acetic acid.

9. Use of the dithienophenazine compound according to claim 1 in the preparation of a thermally activated delayed fluorescence material.

10. Use of the dithienophenazine compound according to claim 1 in the preparation of an organic light-emitting diode.

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