Dark red / near-infrared organic electroluminescent material and application thereof

Abstract

The present invention is based on a novel receptor that is easy to synthesize, i.e., cyano-substituted dithiafulvalene fused benzothiadiazoles, for the construction of dark red / near infrared luminescent materials. The dark red / near-infrared luminescent material can be easily obtained in five steps by changing a donor and connected functional groups, and shows excellent luminous efficiency in both an aggregation state and a solid state. Based on the novel donor-acceptor system, various materials applied to organic electroluminescent devices can be designed, and the material has a good prospect in the aspect of being applied to high-performance non-doped OLED (Organic Light Emitting Diode) devices.

Description

Technical Field

[0001] The present invention belongs to the technical field of organic photoelectric materials, and in particular relates to a deep red / near infrared (DR / NIR) fluorescent material with aggregation-induced luminescence properties and an application thereof in preparing an organic electroluminescent device. Background Art

[0002] Highly efficient organic deep red / near-infrared (DR / NIR) (650-900 nm) fluorescent materials are of great significance due to their wide applications in flexible optoelectronics, night vision devices, and bio-imaging. The development of organic deep red / near-infrared (650-900 nm) fluorescent materials is a challenging task due to the limitation of the band gap law. In fact, with the decrease of the band gap (corresponding to the long emission wavelength), quenching processes such as vibrational coupling, twisted intramolecular charge transfer, and conical crossing are more likely to occur, which enhances the nonradiative decay channels and quenches the fluorescence.

[0003] The construction of donor-acceptor-donor (DAD) structure is the most commonly used strategy to produce DR / NIR luminescent materials. Due to the recombination of D and A orbitals, the band gap of DA compounds can be greatly narrowed. In the process of molecular design, there are abundant donor parts to choose from, such as aromatic amines, thiophene derivatives and fulvenes. However, the choice of acceptors with strong electron-withdrawing ability is still limited. Commonly used benzothiadiazole (BT), pyrido[2,1,3]thiadiazole and benzobis(thiadiazole) (BBT) either have weak electron-withdrawing ability or are difficult to prepare or purify, so the development of new acceptors is imminent.

[0004] Recently, cyano-substituted dithiofulvalene-fused benzothiadiazole (BSMCN) has been demonstrated to be a promising acceptor for constructing novel DA semiconductors for bioimaging and OLED applications. Since the acceptor contains both electron-rich sulfur and electron-withdrawing cyano and benzothiadiazole moieties, the sulfur-rich nature is beneficial to the charge transport of the semiconductor, while the fusion with electron-withdrawing group substitution can effectively suppress the quenching effect of sulfur atoms on fluorescence, thereby constructing efficient long-wavelength emitters. However, luminescent materials based on BSMCN have not been well developed and deserve further exploration.

[0005] DR / NIR OLEDs have great advantages in night vision devices, information security displays, and lighting devices. However, the performance of DR / NIR OLEDs lags far behind that of well-developed green and yellow electroluminescent devices. The 25% EQE limit in OLED devices can be broken by adopting the design principles of hybrid local and charge transfer (HLCT) and thermally activated delayed fluorescence (TADF). However, designing efficient HLCT- and TADF-characterized DR / NIR molecules remains a challenge, especially for those with high PLQY. In addition, most DR / NIR luminescent materials with DA structures are susceptible to aggregation-induced quenching (ACQ) effects due to the strong intermolecular π–π stacking generated by intermolecular DA interactions. Although doping organic emitters with host materials can solve the ACQ problem, precise control of doping concentration is required to reduce emission quenching and suppress the roll-off effect caused by exciton annihilation. In addition, doped films may also suffer from the disadvantages of high-cost large-scale production, performance degradation caused by phase separation upon heating, and technical complexity caused by the addition of dopants. Therefore, the development of luminescent materials suitable for non-doped devices is highly desirable. Summary of the invention

[0006] In view of the problems existing in the prior art, the purpose of the present invention is to provide a class of deep red / near infrared organic electroluminescent materials and their preparation methods and applications in the preparation of OLEDs, so as to solve the problems of the prior art such as the single type of organic electroluminescent materials, low solid-state luminescence efficiency and the need for doping.

[0007] The technical solution adopted by the present invention to solve the technical problem is to provide a deep red / near infrared organic electroluminescent material, the structural formula of the deep red / near infrared organic electroluminescent material is as follows:

[0008]

[0009] Wherein, R1 appears symmetrically and is taken from one of the following structures,

[0010]

[0011] In the deep red / near infrared organic electroluminescent material provided by the present invention, the structural formula of the deep red / near infrared organic electroluminescent material is as follows:

[0012]

[0013] In the deep red / near infrared organic electroluminescent material provided by the present invention, the structural formula of the deep red / near infrared organic electroluminescent material is as follows:

[0014]

[0015] In the deep red / near infrared organic electroluminescent material provided by the present invention, the structural formula of the deep red / near infrared organic electroluminescent material is as follows:

[0016]

[0017] The present invention also provides a use of the deep red / near infrared organic electroluminescent material as described above in the preparation of a non-doped organic electroluminescent device.

[0018] The present invention also provides an organic electroluminescent device, comprising a light-emitting layer, wherein the light-emitting layer comprises the deep red / near infrared organic electroluminescent material as described above.

[0019] In the organic electroluminescent device provided by the present invention, the organic electroluminescent device is selected from one of an organic light emitting diode, a light emitting electrochemical cell and a light emitting transistor.

[0020] The implementation of the present invention can achieve the following beneficial effects:

[0021] The present invention is based on a novel and easily synthesized acceptor, namely, cyano-substituted dithiofulvalene-fused benzothiadiazole (BSMCN), for constructing deep red / near-infrared luminescent materials. By changing the donor and the attached functional groups, deep red / near-infrared luminescent materials (650-1300nm) can be easily obtained within five steps, showing excellent luminescence efficiency in both the aggregated state and the solid state. Based on this novel donor-acceptor system, a variety of materials for organic light-emitting diodes (OLEDs) can be designed. Specifically, using BSMCN as an acceptor and triphenylamine derivatives as donors, three BSMCN-based molecules, named 2TB, 2MTB and 2MOTB, were designed and efficiently synthesized. All three molecules exhibit typical AIE properties, with emission maximum coverage ranging from 691nm to 749nm and high PLQY in the solid state. In particular, DBTM exhibits a high PLQY of 33.4% at a wavelength of 691nm. Based on the superior luminescence properties of these luminescent materials, we further prepared their non-doped electroluminescent (EL) devices. Among them, the EL device based on 2TB exhibited a fairly high EQE of 4.9% at a wavelength of 670nm, and 2MTB also exhibited a high EQE of 3.6% at a wavelength of 690nm. These results show that DR / NIR fluorescent materials based on BSMCN are very promising for high-performance non-doped OLED devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention provides a molecular structure of a deep red / near infrared organic electroluminescent material.

[0023] Figure 2This is the synthetic route for 2TB, 2MTB, and 2MOTB.

[0024] Figure 3 2TB in CDCl3 at 298K 1 H NMR spectrum.

[0025] Figure 4 2TB in CDCl3 at 298K 13 C NMR spectrum.

[0026] Figure 5 2MTB in CDCl3 at 298K 1 H NMR spectrum.

[0027] Figure 6 2MTB in CDCl3 at 298K 13 C NMR spectrum.

[0028] Figure 7 2MOTB in CDCl3 at 298K 1 H NMR spectrum.

[0029] Figure 8 2MOTB in CDCl3 at 298K 13 C NMR spectrum.

[0030] Fig. 9 This is a 2TB high-resolution mass spectrum.

[0031] Fig.10 This is the high-resolution mass spectrum of 2MTB.

[0032] Fig.11 This is the high-resolution mass spectrum of 2MOTB.

[0033] Fig.12 UV / VIS absorption spectra of 2TB, 2MTB, and 2MOTB in THF solutions (solution concentration c = 10 μM).

[0034] Fig.13 Normalized PL fluorescence spectra of 2TB, 2MTB, and 2MOTB spin-coated on thin films (solution concentration c = 10 μM, excitation wavelength λex = 480 nm).

[0035] Fig.14a is the PL spectrum of 2TB in a water / THF mixed system, and fw is the volume ratio of water. Fig.14b The relative intensity of PL, αAIE, was plotted against fw. (αAIE=I / I0, where I0 is the luminescence intensity of 2TB in pure THF solution at 677 nm). c=10 μM, λex=480 nm.

[0036] Fig.15 It is a 2TB single crystal structure.

[0037] Fig.16 2MTB single crystal structure

[0038] Fig.17 Electroluminescence spectra of non-doped OLED devices prepared with organic electroluminescent materials obtained from 2TB, 2MTB and 2MOTB.

[0039] Fig.18 This is a curve of current density versus voltage for non-doped OLED devices prepared from organic electroluminescent materials obtained from 2TB, 2MTB and 2MOTB.

[0040] Fig.19 The power efficiency of non-doped OLED devices prepared with organic electroluminescent materials obtained from 2TB, 2MTB and 2MOTB varies with current density.

[0041] Fig. 20 This is a curve showing the change in brightness of non-doped OLED devices made from organic electroluminescent materials obtained from 2TB, 2MTB and 2MOTB as a function of current density.

[0042] Fig.21 This is a curve of the external quantum efficiency of non-doped OLED devices prepared with organic electroluminescent materials obtained from 2TB, 2MTB and 2MOTB as a function of current density. DETAILED DESCRIPTION

[0043] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific embodiments of the present invention are now described in detail with reference to the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments described in this specification, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] The existing acceptor skeletons of organic deep red / near infrared molecules, such as benzothiadiazole, pyridinethiadiazole and benzobisthiadiazole, etc., have the problems of difficult synthesis, complicated purification process and insufficient electron-withdrawing ability when used to construct deep red / near infrared molecules. Therefore, in the present invention, the dithiofulvalene structure commonly used in the semiconductor field is introduced into the benzothiadiazole system, so that the skeleton has electron-rich sulfur atoms and electron-deficient cyano and benzothiadiazole at the same time, which can suppress the quenching effect of sulfur atoms on fluorescence while having strong electron-withdrawing ability. Therefore, the new skeleton is very suitable for constructing fluorescent molecules with deep red / near infrared emission.

[0045] Existing doped organic light-emitting diode devices have significant disadvantages in device manufacturing and engineering cost. Therefore, the development of non-doped organic light-emitting materials is very valuable. In the manufacturing process of organic light-emitting diode devices, the doped ligand material will cause the aggregation-induced light quenching of the light-emitting material to a certain extent. Therefore, designing semiconductor materials with aggregation-induced light emission can solve the above problems, and such materials have great potential for application in non-doped devices.

[0046] Example 1 - Synthesis and Characterization of Representative Compounds

[0047] The synthetic routes of the molecules in question are as follows Figure 2 As shown. Generally, the first step is to symmetrically connect the donor part (TPA with different R groups) to the benzo[c][1,2,5]thiadiazole acceptor by Suzuki coupling. In the second step, the extended acceptor is obtained by nucleophilic substitution between the obtained structure and 2,2-dicyanoethylene-1,1-bis(thiolate) sodium, and the cyano-substituted dithiofulvalene fused benzothiadiazole. All new compounds are obtained 1 H NMR, 13 C NMR and high-resolution mass spectrometry characterization.

[0048] Example 2 - Synthesis of Intermediates M1-M3

[0049] 4,7-Dibromo-5,6-difluorobenzo[c][1,2,5]thiadiazole (1 eq.), (4-(diphenylamino)phenyl)boronic acid (2 eq.), Pd(PPh3)4 (0.1 eq.) and K2CO3 (3 eq.) were dissolved in dioxane / water (v / v=5 / 1). The reactants were heated to reflux overnight under N2 atmosphere. The reaction was quenched by adding water. The organic layer was separated and the solvent was removed by rotary evaporator. The residue was purified by recrystallization using dichloromethane / petroleum ether as solvent.

[0050] M1, yellow solid, yield 83.54%. 1 H NMR (500MHz, CDCl3) δppm 7.75 (d, J = 8.5Hz, 4H), 7.34 (t, J = 8.0, 8.0Hz, 8H), 7.26-7.20 (m, 12H), 7.12 (t, J = 7.5Hz, 4H).

[0051] M1, yellow solid, yield 76.85%. 1 H NMR (500MHz, CDCl3) δppm 7.71 (d, J = 8.5Hz, 4H), 7.19-7.11 (m, 20H), 2.37 (s, 12H).

[0052] M1, yellow solid, yield 84.42%. 1 H NMR (500MHz, CDCl3) δppm 7.69 (d, J = 8.5 Hz, 4H), 7.06 (d, J = 8.5 Hz, 8H), 7.19 (d, J = 9.0 Hz, 4H), 6.90 (d, J = 9.0 Hz, 8H), 3.84 (s, 12H).

[0053] Example 3-Synthesis of 2TB, 2MTB, 2MOTB

[0054] The intermediate products M1, M2 and M3 (1 equivalent), 2,2-dicyanoethylene-1,1-bis(thiolate) sodium (10 equivalents) and tetrabutylammonium bromide (32 mg, 2 equivalents) were dissolved in dry dimethylformamide. Under N2 atmosphere, the reaction was heated at 80 °C overnight in a pressure tube. The reaction was quenched by adding saturated ammonium chloride solution. The dark red solid was separated by filtration. The residue was purified by column chromatography (dichloromethane / petroleum ether) to obtain 2TB, 2MTB and 2MOTB.

[0055] 2TB, dark red solid, yield 81.48%. 1 H NMR (500MHz, CDCl3) δppm7.57-7.51(m,4H),7.38(m,8H),7.24-7.19(m,4H),7.30(m,4H),7.28(m,4H),7.17(t,J=7.5Hz,4H); 13 C NMR (125MHz, CDCl3, 298K) δ (ppm): 178.25, 153.35, 149.53, 146.79, 145.47, 136.84, 129.91, 129.66, 128.16, 127.11, 125.97, 124.38, 123.48, 120.94, 119.02, 118.88, 112.53. High resolution mass spectrum m / z calcd 760.1538; found 760.1530.

[0056] 2MTB, dark red solid, yield 52.5%. 1 H NMR (500MHz, CDCl3) δppm 7.49 (m, 4H), 7.23-7.08 (m, 20H), 2.38 (s, 12H); 13C NMR (125MHz, CDCl3, 298K) δ (ppm): 153.39, 149.86, 144.19, 136.74, 134.20, 130.28, 129.79, 128.17, 126.22, 126.14, 119.74, 112.58, 20.94. High resolution mass spectrum m / z calcd 816.2164; found 816.2167.

[0057] 2MOTB, dark red solid, yield 58.63%. 1 H NMR (500MHz, CDCl3) δppm 7.47 (d, J = 9.0 Hz, 4H), 7.24 (d, J = 9.0 Hz, 8H), 7.03 (d, J = 9.0 Hz, 4H), 6.94 (d, J = 9.0 Hz, 8H), 3.85 (s, 12H); 13 C NMR (125MHz, CDCl3, 298K) δ (ppm): 156.89, 153.44, 139.57, 136.66, 129.79, 128.18, 127.98, 125.35, 117.99, 115.03, 112.63, 55.52. High resolution mass spectrum m / z calcd 880.1960 found 880.1965.

[0058] Example 4 - Photophysical properties of 2TB, 2MTB, and 2MOTB

[0059] First, the photophysical properties of 2TB, 2MTB, and 2MOTB were studied. The tetrahydrofuran (THF) solutions of the three molecules all showed three UV-visible absorption peaks at around 330nm, 390nm, and 480nm, of which the first can be attributed to π-π* absorption, the second comes from the BSMCN part, and the last is the intramolecular charge transfer (ICT) absorption.

[0060] We then studied the luminescence behavior of 2TB in a mixed solvent of THF and water to see if it has AIE properties. When water is added to the THF solution, the photoluminescence (PL) intensity decreases as the volume fraction of water increases (in the range of 0% to 50%). In this case, the TICT effect dominates the photophysical process and reduces the emission intensity. When the volume fraction exceeds 50%, the 2TB molecules begin to aggregate and reduce the polarity of the local microenvironment. Therefore, conformational restrictions play a dominant role, causing the PL intensity to change from weak to strong. Therefore, 2TB has typical AIE characteristics ( Fig.14a and Fig.14b )

[0061] Example 5-Single Crystal Structure of 2TB and 2MTB

[0062] In order to gain a deeper understanding of the photophysical properties of this type of material, we analyzed its crystal structure. 2TB and 2MTB were selected as representatives, and their crystal structures both exhibited a distorted molecular configuration, with comparable torsion angles between adjacent benzene rings of the acceptor and donor (47.09° and 65.27° for 2TB, and 44.19° and 38.99° for 2MTB), which is not only conducive to the red shift of the emission wavelength, but also effectively avoids emission quenching caused by π-π stacking. In addition, the stacking pattern of 2TB shows that the molecules in the 2TB crystal do not exhibit strong π-π stacking, but rather exhibit multiple intermolecular CH…π interactions, which is conducive to efficient solid-state emission. In contrast, 2MTB exhibits relatively tighter stacking, with an S…π distance of 3.6-3.7 angstroms between the intermolecular acceptor units. The relatively strong intermolecular interactions may have led to the lower PLQY of 2MTB. ( Fig.15 , Fig.16 )

[0063] Example 6-2TB, 2MTB, 2MOTB OLED device performance

[0064] Considering the excellent performance of 2TB, 2MTB, and 2MOTB, we applied them to non-doped OLED devices prepared by solution processing. OLEDs using targeted AIEgen as non-doped emission layers were prepared by solution processing using the configuration of ITO / m-PEDOT:PSS(70nm) / AIEgens(40nm) / DPEPO(10nm) / TmPyPyPB(50nm / Liq(1nm) / Al(100nm). Aluminum (Al) and indium tin oxide (ITO) were used as cathode and anode, respectively. Modified poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (m-PEDOT:PSS) and lithium quinolinate (Lq) were used as hole injection devices. injection layer and electron injection layer. Bis[2-(diphenylphosphino)phenyl]ether oxide (DPEPO) has the functions of electron transport layer and hole blocking layer. 1,3,5-Tri(3-pyridyl-3-phenyl)benzene (TmPyPB) serves as the electron transport layer. The EL device based on 2TB exhibits a fairly high EQE of 4.9% at a wavelength of 670nm, and 2MTB also exhibits a high EQE of 3.6% at a wavelength of 690nm. These results indicate that DR / NIR fluorescent materials based on BSMCN are very promising for application in high-performance non-doped OLED devices. ( Figure 17-21 ).

[0065] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific embodiments. The above-mentioned specific embodiments are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can make many modifications without departing from the scope of protection of the present invention and the claims, all of which belong to the scope of protection of the present invention.

Claims

1. A deep red / near infrared organic electroluminescent material, characterized in that: The structural formula of the deep red / near infrared organic electroluminescent material is as follows: Wherein, R1 appears symmetrically and is taken from one of the following structures, 2. The deep red / near infrared organic electroluminescent material according to claim 1, characterized in that: The structural formula of the deep red / near infrared organic electroluminescent material is as follows:

3. The deep red / near infrared organic electroluminescent material according to claim 1, characterized in that: The structural formula of the deep red / near infrared organic electroluminescent material is as follows:

4. The deep red / near infrared organic electroluminescent material according to claim 1, characterized in that: The structural formula of the deep red / near infrared organic electroluminescent material is as follows:

5. Use of the deep red / near infrared organic electroluminescent material according to any one of claims 1 to 4 in the preparation of a non-doped organic electroluminescent device.

6. An organic electroluminescent device, characterized in that: The invention comprises a light-emitting layer, wherein the light-emitting layer comprises the deep red / near infrared organic electroluminescent material according to any one of claims 1 to 4.

7. The organic electroluminescent device according to claim 6, characterized in that: The organic electroluminescent device is selected from one of an organic light emitting diode, a light emitting electrochemical cell and a light emitting transistor.

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