Polymorphic organic eutectic material as well as preparation method and application thereof

Abstract

The invention discloses a polycrystalline organic eutectic material as well as a preparation method and application thereof, and belongs to the technical field of organic luminescent materials. According to the invention, a polycrystalline organic eutectic crystal 1-BrTC composed of an electron acceptor TCNB and an electron donor 1-BrDBT is synthesized. And carrying out self-assembly in different crystallization environments to obtain two polycrystalline crystals with obviously different emission colors, which are respectively named as g-eutectic and y-eutectic. Experimental results show that spin-orbit coupling is enhanced through multiple halogen bond effects in the g-eutectic, intersystem crossing and anti-intersystem crossing processes are remarkably accelerated, and thermal activation delayed fluorescence emission is enhanced. Besides thermally activated delayed fluorescence, singlet radiation attenuation and triplet non-radiative transition are inhibited by stronger hydrogen-bond interaction in the y eutectic, and room-temperature phosphorescence emission is realized. A new thought is provided for effective utilization of triplet excitons in the polycrystalline organic eutectic, and reasonable design of a novel luminescent material is facilitated.

Description

Technical Field

[0001] This invention relates to the field of organic light-emitting materials technology, specifically to a polycrystalline organic eutectic material, its preparation method, and its application. Background Technology

[0002] The excited-state dynamics of organic light-emitting materials are the core foundation determining their optical properties and their photonic applications in sensing, bioimaging, organic light-emitting diodes (OLEDs), and organic solid-state lasers. Unlike the optically bright singlet state, the long-lived triplet state typically exhibits an optically dark state, readily dissipating energy through non-radiative pathways. Therefore, understanding how to convert the dark triplet state into a bright state is crucial for developing light-emitting devices that efficiently utilize excitons, especially electroluminescent devices.

[0003] Thermally activated delayed fluorescence (TADF) and room-temperature phosphorescence (RTP) materials have been proven to be typical systems for efficiently utilizing triplet excitons. TADF originates from the triplet state (T... n The process involves a reverse intersystem crossing (RISC) from the S1 to the singlet state, followed by delayed fluorescence via a radiative transition of S1. The design strategy is primarily based on electron donor-acceptor (DA) compounds, utilizing the spatial separation of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) to reduce the energy level difference (ΔE) between S1 and T1. ST <0.3 eV), thereby promoting intersystem crossing (ISC) and RISC processes. RTP, on the other hand, is achieved through a rapid ISC transition to the triplet state, followed by a direct radiative transition from the T1 state to the ground state (S0). In recent years, researchers have developed strategies such as introducing heavy atoms, constructing intramolecular charge transfer (CT) states, host-guest doping, H-aggregation regulation, and constructing rigid molecular frameworks to stabilize the triplet state and obtain organic RTP materials with high photoluminescence quantum yield (PLQY) and long lifetimes.

[0004] Organic eutectics are novel substances with fixed stoichiometry and ordered packing structures formed by non-covalent intermolecular interactions between two or more different components. Their natural DA pair structure, intramolecular CT states, and halogen bonds provide a flexible and efficient platform for the manipulation of triplet excitons. In particular, polycrystalline organic eutectics constructed based on the same DA pair can achieve customized optical properties by controlling the molecular packing mode, exhibiting unique advantages. However, due to the difficulty in material screening, the challenging preparation process, and the unclear luminescence mechanism of polycrystalline organic eutectics, design strategies for their radiative decay kinetics are still rarely reported. Summary of the Invention

[0005] The present invention aims to provide a polycrystalline organic eutectic material, its preparation method and application, to solve the problems of unclear luminescence mechanism and difficulty in triplet exciton control in the prior art of polycrystalline systems, and to achieve effective control of TADF and RTP properties.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a polycrystalline organic eutectic material is provided, which is a monoclinic crystal system and is composed of electron acceptor 1,2,4,5-tetracyanobenzene and electron donor 1-bromodibenzothiophene.

[0007] Furthermore, when the molar ratio of electron donor 1-bromodibenzothiophene to electron acceptor 1,2,4,5-tetracyanobenzene is 1:2, the polycrystalline organic eutectic material is a g-eutectic and exhibits green light emission; when the molar ratio of electron donor 1-bromodibenzothiophene to electron acceptor 1,2,4,5-tetracyanobenzene is 2:1, the polycrystalline organic eutectic material is a γ-eutectic and exhibits yellow light emission.

[0008] This invention provides a method for preparing the above-mentioned polycrystalline organic eutectic material, which is synthesized by solution self-assembly. Specifically, it includes the following steps: mixing well prepared solutions of 1,2,4,5-tetracyanobenzene and electron donor 1-bromodibenzothiophene in a certain proportion and allowing them to stand; then slowly injecting the mixed solution into a poorly mixed solution of ethanol and H2O to form a suspension; finally, dropping the suspension onto a substrate and waiting for the solvent to evaporate to obtain the material.

[0009] Furthermore, the solvent for 1,2,4,5-tetracyanobenzene is acetonitrile; the solvent for 1-bromodibenzothiophene is tetrahydrofuran.

[0010] This invention provides an application of the above-mentioned polycrystalline organic eutectic material in the preparation of thermally activated delayed fluorescence materials.

[0011] This invention provides a thermally activated delayed fluorescence material, including the above-mentioned polycrystalline organic eutectic material.

[0012] This invention provides an application of the above-mentioned thermally activated delayed fluorescence material in the fabrication of optoelectronic devices.

[0013] This invention provides an application of the above-mentioned polycrystalline organic eutectic material in the preparation of room temperature phosphorescent materials.

[0014] The present invention provides a room temperature phosphorescent material, including the above-mentioned polycrystalline organic eutectic material.

[0015] The present invention also provides an application of the above-mentioned room temperature phosphorescent material in the fabrication of optoelectronic devices.

[0016] The present invention has the following beneficial effects: (1) By controlling the crystallization conditions, the present invention obtains two polymorphic crystals with different emission colors. Among them, the g-eutectic exhibits green light emission with a PLQY of 16.69% and a fluorescence lifetime of 1.34 μs; the y-eutectic exhibits yellow light emission with a PLQY of 28.35% and has double exponential lifetime characteristics (0.38 μs and 3.83 ms).

[0017] (2) Although g-eutectic and y-eutectic both belong to the monoclinic crystal system, their molecular packing modes and intermolecular interactions are significantly different: halogen bonds, heteroatom bonds, and CT interactions are stronger in g-eutectic, resulting in a larger oscillator strength in its S1 state ( f ) and transition dipole moment ( µ ), while T1 state µ Smaller; γ-eutectic is dominated by stronger hydrogen bonding, T1 state µ Relatively large.

[0018] (3) In g-eutectic, multiple intermolecular interactions synergistically enhance spin-orbit coupling (SOC), significantly accelerate ISC and RISC processes, improve singlet state radiation decay efficiency, and thus obtain TADF emission; In y-eutectic, strong hydrogen bonding effectively suppresses radiation decay of S1 state, while stabilizing T1 state and suppressing its nonradiative transition, thereby introducing additional RTP emission in addition to TADF emission.

[0019] (4) This invention constructs polycrystalline organic eutectics using the same DA system, achieving controllable switching between TADF and RTP properties, and revealing the intrinsic relationship between crystal stacking modes and excited-state dynamics. This invention provides a new design concept for the efficient utilization of triplet excitons in polycrystalline organic eutectic materials, and helps to promote the development and application of novel organic light-emitting materials. Attached Figure Description

[0020] Figure 1 The molecular structures of 1-BrDBT and TCNB, as well as fluorescence microscopy images and photoluminescence spectra of g-eutectic and γ-eutectic under 365 nm ultraviolet light; Figure 2 CIE chromaticity coordinates of the emission colors corresponding to g-eutectic and γ-eutectic; Figure 3 The diffuse reflectance absorption spectra of 1-BrDBT micro / nano crystals, TCNB micro / nano crystals, and binary g-eutectic and y-eutectic microrods at 298 K are shown. Figure 4 SEM images of g-eutectic and γ-eutectic microrods; Figure 5 XRD patterns of 1-BrDBT micro / nano crystals, TCNB micro / nano crystals, and binary g-eutectic and y-eutectic microrods; Figure 6 Elemental distribution analysis diagram for a single g-eutectic; Figure 7 Elemental distribution analysis diagram for a single y-eutectic; Figure 8 The temperature-dependent photoluminescence spectra and lifetimes of g-eutectic and γ-eutectic are shown. Figure 9 The temperature-varying spectra of g-eutectic and γ-eutectic in the range of 77 K to 298 K are shown. Figure 10 The steady-state and delayed spectra of the g-eutectic from 77 K to 298 K are shown. Figure 11 The steady-state and delayed spectra of the γ-eutectic from 77 K to 298 K are shown. Figure 12 The diagrams show the molecular packing structures of the g-eutectic along the a-plane, b-plane, and c-plane, respectively. Figure 13 The diagrams show the molecular packing structures of the y-eutectic along the a-plane, b-plane, and c-plane, respectively. Figure 14 TEM images and SAED images of g-eutectic and γ-eutectic; Figure 15 XRD patterns of g-eutectic and γ-eutectic; Figure 16 The predicted growth morphology and molecular packing pattern of g-eutectic and y-eutectic along the CT direction are shown in the diagram. Figure 17 The diagram shows the molecular packing patterns of g-eutectic and γ-eutectic. Figure 18 Theoretical calculation diagrams for the luminescence mechanisms of g-eutectic and γ-eutectic luminescence. Detailed Implementation

[0021] The examples given below are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified, conditions in the examples are performed under standard conditions or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0022] Example 1: Synthesis of polycrystalline organic eutectic (1-BrTC) microrods Based on a CT-guided self-assembly route, one-dimensional 1-BrTC microrods composed of 1,2,4,5-tetracyanobenzene (TCNB) and 1-bromodibenzothiophene (1-BrDBT) were synthesized. The specific preparation steps are as follows: 1) Preparation of g-eutectic mixed solution: 1-BrDBT was dissolved in tetrahydrofuran to prepare a donor solution with a concentration of 40 mmol / L; TCNB was dissolved in acetonitrile to prepare an acceptor solution with a concentration of 80 mmol / L. Equal volumes of the donor and acceptor solutions were mixed uniformly to make the molar ratio of 1-BrDBT to TCNB 1:2. The mixture was allowed to stand for 5-10 minutes to form a stable binary charge transfer complex.

[0023] 2) Preparation of γ-eutectic mixed solution: 1-BrDBT was dissolved in tetrahydrofuran to prepare a donor solution with a concentration of 80 mmol / L; TCNB was dissolved in acetonitrile to prepare an acceptor solution with a concentration of 40 mmol / L. Equal volumes of the donor and acceptor solutions were mixed uniformly to make the molar ratio of 1-BrDBT to TCNB 2:1. The mixture was allowed to stand for 5-10 minutes to form a stable binary charge transfer complex.

[0024] 3) Inducing micro / nano crystal growth: Take 1 mL of each of the mixed solutions obtained in step 1) and step 2) and slowly inject them into 5 mL of a poorly mixed solvent of ethanol and water (the volume ratio of ethanol to water is 1:1) to induce the formation of g-eutectic and γ-eutectic, and obtain the corresponding eutectic suspension.

[0025] 4) Preparation of micron rod-shaped micro / nano crystal samples: The above suspensions were dropped onto a quartz substrate. After the solvent evaporated naturally, one-dimensional micron rod-shaped CT eutectic was obtained, which were denoted as g-eutectic and y-eutectic, respectively.

[0026] Example 2: Synthesis of a large polycrystalline eutectic 1-BrTC single crystal To obtain large-size single crystals suitable for single-crystal X-ray diffraction analysis, g-eutectic and γ-eutectic were cultured separately using a slow solvent evaporation method. The specific preparation steps are as follows: 1) Cultivation of g-eutectic large single crystals: The g-eutectic mixed solution (1-BrDBT and TCNB molar ratio 1:2, with concentrations increased to saturation of 120 mmol / L and 240 mmol / L respectively) prepared according to step 1) of Example 1 was allowed to stand at room temperature for 10 minutes to allow the binary charge transfer complex to fully form. 5 mL of this mixed solution was placed in a sample vial, the vial opening was sealed with sealing film, and three small holes were pricked with a needle tip. The vial was placed in a constant temperature (25°C) vibration-free environment to allow the solvent (tetrahydrofuran and acetonitrile) to slowly evaporate. After approximately 7 days, green blocky crystals precipitated at the bottom of the vial, which were the g-eutectic large single crystals.

[0027] 2) Cultivation of γ-eutectic large single crystals: The γ-eutectic mixed solution (1-BrDBT and TCNB molar ratio 2:1, with concentrations increased to saturation of 240 mmol / L and 120 mmol / L respectively) prepared according to step 2) of Example 1 was allowed to stand at room temperature for 10 minutes. 5 mL of this mixed solution was placed in a sample vial, sealed with a sealing film and punctured, and placed in a constant temperature and vibration-free environment at 25°C to allow the solvent to evaporate slowly. After approximately 7 days, yellow blocky crystals precipitated at the bottom of the vial, which are the γ-eutectic large single crystals.

[0028] The obtained single crystals were removed from the mother liquor and allowed to air dry at room temperature. Single-crystal X-ray diffraction data were then collected and the structure was analyzed to obtain the single-crystal CIF file. The crystal structure and morphology were simulated using Mercury, Diamond, and Materials Studio software.

[0029] Example 3: Sample Characterization 1) Structural characterization: The microstructure of the samples was observed using a field emission scanning electron microscope (SEM, model Apreo S LoVac) at an accelerating voltage of 5 kV; high-resolution imaging and selected area electron diffraction (SAED) analysis were performed using a transmission electron microscope (TEM, model JEOL-2100) at an accelerating voltage of 200 kV; and the crystal structure of the samples spin-coated on the quartz substrate was characterized using an X-ray diffractometer (XRD, model D / max 2400, CuKα radiation, λ=1.54050 Å) in the range of 2θ=3°~40°.

[0030] 2) Optical performance characterization: The photoluminescence spectra of the samples were measured using a UV-Vis spectrophotometer (HATCHI U3600H) and a fluorescence spectrophotometer (HATCHI F4600), respectively. Fluorescence microscopy images were acquired using a fluorescence microscope (Olympus FV1000-IX81) with an enhanced charge-coupled device (CCD, Diagnostic Instrument, Inc.). Steady-state photoluminescence spectra, temperature-dependent spectra, PLQY (φ), and fluorescence lifetime (τ) of the samples were measured using a steady-state transient fluorescence spectrometer (Edinburgh FLS1000). All test samples were deposited on the surface of a coverslip.

[0031] 3) Theoretical Calculations: Based on single-crystal structure data, density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were performed on the g-eutectic and y-eutectic structures using the ωB97-XD / def2-TZVP method in the Gaussian16 package. The ω parameter of the long-range corrected functional was optimized using the optDFTω program; the optimal ω value for both the g-eutectic and y-eutectic structures was 0.1724 Bohr. -1The SOC constant was calculated using the Beijing Density Functional Procedure (BDF), and the phosphorescence emission transition dipole moment was calculated using Dalton software.

[0032] Results and Analysis: (1) Synthesis and characterization In this invention, electron donor 1-BrDBT and electron acceptor TCNB are selected as building blocks, and two polymorphic organic cocrystals are prepared by solution self-assembly, denoted as g-cocrystal and y-cocrystal, respectively. The basis for the design of this invention is: (1) the introduction of sulfur atoms in the donor is conducive to (n, π*) transitions, and the heavy atom effect of bromine atoms can enhance SOC, thereby promoting the ISC process; (2) the CT interaction between DA pairs helps to reduce the singlet-triplet energy level difference (ΔE). ST (3) The one-dimensional micro rod-shaped micro-nano crystal structure can effectively block oxygen and form a rigid framework, which is beneficial to stabilizing triplet excitons.

[0033] like Figure 1 As shown in Figure a, the prepared g-eutectic and y-eutectic microrods exhibit bright green and yellow edge emission, respectively, under 365 nm ultraviolet light excitation, while the main body emits weaker light, indicating that they possess good optical waveguide properties. The PLQY values ​​of the g-eutectic and y-eutectic microrods, measured by the direct method, are 16.69% and 28.39%, respectively. Figure 1 b shows the steady-state photoluminescence spectra of the two eutectics at room temperature: the g-eutectic exhibits a single strong emission peak at 475 nm (green line), while the y-eutectic spectrum shows a bimodal characteristic at 475 nm and 558 nm (orange line). The corresponding International Commission on Illumination (CIE) chromaticity coordinates for the emission colors are (0.21, 0.40) and (0.47, 0.50), respectively. Figure 2 ).

[0034] Depend on Figure 1 As can be seen from b, the emission of single-component TCNB and 1-BrDBT before 400 nm is invisible to the naked eye. However, the g-eutectic and γ-eutectic exhibit distinctly broad, structureless, and redshifted emission spectra, indicating the formation of a eutectic structure dominated by CT interactions. Furthermore, the corresponding redshifted absorption bands in the diffuse reflectance absorption spectra and the enhanced excitation band before 450 nm further confirm the effective CT interactions in the polymorphic eutectic. Figure 3 Both eutectic types formed uniform one-dimensional microrods. Figure 4 XRD patterns showed that the eutectic exhibited characteristic diffraction peaks different from those of the single-component crystalline phase, confirming the formation of a new crystalline phase. Figure 5 ).

[0035] To verify the composition and distribution of polymorphic eutectics, elemental scanning analysis was performed on individual g-eutectic and γ-eutectic microrods grown on quartz sheets. Figure 6 As shown, nitrogen is uniformly distributed in the g-eutectic, indicating that TCNB molecules are uniformly present in the g-eutectic microrods; simultaneously, sulfur and bromine are also uniformly distributed, proving that 1-BrDBT molecules are uniformly distributed in the g-eutectic microrods. The elemental distribution of the γ-eutectic also shows the uniform coexistence of the two molecules. Figure 7 The above results demonstrate that a polycrystalline organic eutectic material with uniform composition and good crystallinity was successfully obtained via solution self-assembly.

[0036] (2) Study of photophysical processes This invention further explores the photophysical dynamics of g-eutectic and γ-eutectic processes, and the relevant photophysical parameters are shown in Table 1. The excited-state decay behavior of the two eutectic types was systematically analyzed using variable-temperature photoluminescence spectroscopy and time-resolved spectroscopy.

[0037] From Table 1 and Figure 8 It can be seen that for g-eutectic, as the temperature decreases from 298K to 77K, its spectral intensity at 475nm gradually weakens, while a new emission peak appears at 495nm, which significantly strengthens from 160K and persists until 77K (see...). Figure 8 a and Figure 9 a). Time-resolved spectroscopy shows that the decay curve of the g-eutectic at 475 nm at 298 K exhibits a double-exponential characteristic with an instantaneous component of 0.87 ns (see [link to study]). Figure 8 b) and a delay component of 1.34 μs ( Figure 8 (Green line in b). When the temperature drops to 77K, the decay lifetime at 475nm is significantly shortened ( Figure 8 (b blue line), while at 495nm, there is a long lifetime decay of 8.53ms ( Figure 8 c (blue line). Furthermore, the delayed PL spectrum of the g-eutectic is essentially consistent with the steady-state PL spectrum profile ( Figure 10 This indicates that their emissions all originate from the same excited state. Combining the temperature-varying spectra and lifetime decay characteristics, it can be confirmed that the g-eutectic exhibits typical TADF properties. For the γ-eutectic, the trend of spectral intensity change at 475 nm is similar to that of the g-eutectic as the temperature decreases; however, the emission peak at 558 nm slowly increases with decreasing temperature. Figure 9 b). In the range of 160K to 77K, two new and significantly enhanced emission peaks appear at 495nm and 525nm ( Figure 8 d). Time-resolved spectroscopy shows that the decay curve at 475 nm at 298 K also exhibits a double-exponential characteristic, showing an instantaneous component of 1.07 ns (see [reference]). Figure 8 (Illustration in e) and a delay component of 0.38 μs (see illustration in e) and 0.38 μs (see illustration in e) Figure 8(The orange line in e), and this lifetime is significantly shortened at 77K ( Figure 8 The e-purple line indicates that the emission at 475 nm exhibits TADF characteristics, consistent with g-eutectic. The lifetime at 558 nm increases from 3.83 ms (298 K) to 14.85 ms (77 K) with decreasing temperature, while long lifetimes are also observed at 77 K at 495 nm and 525 nm, at 14.51 ms and 13.62 ms respectively. Figure 8 f). Delayed spectral analysis showed that at 298 K, with a delay of 5 μs, the emission signal was detected only at 558 nm, while at 77 K, the delayed spectrum covered a broad spectral range of 495 nm, 525 nm, and 558 nm. Figure 11 ).

[0038] Table 1. Relevant photophysical parameters of g-eutectic and γ-eutectic

[0039] Note: [a] Measured at 298K; [b] Transient decay component (τ) at 298K P ) and delayed decay component (τ) ) PL lifetime; [c] measured at 77K.

[0040] In summary, the short-lived emission of the γ-eutectic at 475 nm is attributed to TADF, while the long-lived emission at 495 nm, 525 nm, and 558 nm is attributed to room-temperature phosphorescence (RTP). It is noteworthy that the energy difference between the three phosphorescence emission peaks at 77 K is approximately 0.14 eV, and their lifetimes are similar, suggesting that they may originate from transitions from the same triplet excited state to different vibrational energy levels of the ground state.

[0041] (3) Single crystal structure analysis and intermolecular interaction study To reveal the structural origin of the differences in TADF and RTP emission behaviors between g-eutectic and y-eutectic, this invention obtained single crystals of the two polymorphic eutectic by slow solvent evaporation and used single crystal X-ray diffraction for structural analysis. The relevant crystallographic data are detailed in Table 2.

[0042] As shown in Table 2, both g-eutectic and γ-eutectic belong to the monoclinic crystal system, but their cell parameters differ significantly. The cell parameters of g-eutectic are a=9.5340(6)Å, b=13.7110(9)Å, c=14.4099(9)Å, α=90°, β=93.211(6), γ=90° (CCDC No. 2405529); the cell parameters of γ-eutectic are a=9.4397(2)Å, b=36.2855(9)Å, c=7.2215(2)Å, α=90°, β=92.972(2), γ=90° (CCDC No. 2405534). Figure 12-13It can be seen that in both eutectic structures, the electron donor 1-BrDBT and the electron acceptor TCNB are stacked alternately in a stoichiometric ratio of 1:1, forming an ordered alternating DA stacking pattern.

[0043] Table 2. Relevant crystallographic data for g-eutectic and γ-eutectic.

[0044] To further confirm the microstructure, this invention performed TEM and SAED analyses on individual g-eutectic and γ-eutectic microrods. Figure 14 It can be seen that both types of microrods have a uniform and smooth morphology. The lattice spacings in the g-eutectic are 7.20 Å and 7.81 Å, respectively, corresponding to Bragg reflections on the (002) and (110) crystal planes; the lattice spacings in the y-eutectic are 7.22 Å and 7.82 Å, respectively, corresponding to Bragg reflections on the (001) and (130) crystal planes.

[0045] This invention compares the XRD patterns of two eutectic structures with the theoretical patterns simulated based on single-crystal data. The two patterns show a high degree of agreement, confirming that the prepared microrods have high phase purity and good crystallinity. Figure 15 Furthermore, theoretical simulations of the crystal morphology were performed using MaterialsStudio software. Figure 16 It can be seen that the exposed crystal planes of the two one-dimensional assembled structures are consistent with the principal crystal planes simulated in the theory, further verifying the preferred orientation of the crystal growth direction. The above structural analysis provides a structural basis for understanding the different excited-state dynamic behaviors in the two polymorphic eutectics.

[0046] To further reveal the structural origins of the different luminescence behaviors exhibited by the two polymorphic eutectics, this invention systematically analyzes the intermolecular interactions in g-eutectics and γ-eutectics. For example... Figure 17As shown, both eutectics exhibit various non-covalent interactions of different strengths, including halogen bonds (C-Br···C≡N / C-Br···Br / C-Br···H), heteroatom bonds (CH···S), CT interactions (CH···π), and hydrogen bonds (C≡N···HC). In the g-eutectic, the distances of halogen bonds, heteroatom bonds, and CT interactions are significantly shorter than in the y-eutectic: the distances of C-Br···C≡N and C-Br···Br are 3.136 Å and 3.220 Å, respectively, the distance of CH···S is 2.962 Å, and the distance of CH···π is 3.285 Å; while in the y-eutectic, the corresponding interaction distances are 3.490 Å (C-Br···H), 3.154 Å (CH···S), and 3.444 Å (CH···π), respectively. The above data indicate that halogen bonds, heteroatom bonds, and CT interactions are stronger in g-eutectic. Stronger halogen bond interactions can produce a significant heavy atom effect, enhancing SOC and thus promoting ISC and RISC processes; enhanced heteroatom bonds help increase molecular rigidity and accelerate singlet radiative decay (S1→S0); while enhanced CT interactions effectively reduce ΔE. ST This further promotes the RISC process. Therefore, the synergistic enhancement of halogen bonds, heteroatom bonds, and CT interactions collectively leads to more pronounced TADF properties in the g-eutectic. In contrast, the hydrogen bond interaction distance (C≡N···HC) in the y-eutectic is 2.711 Å, significantly shorter than the 2.795 Å in the g-eutectic, indicating that the y-eutectic possesses stronger intermolecular hydrogen bonds. Existing research shows that strong hydrogen bonds can effectively restrict molecular vibrations and rotations, stabilize triplet excited states, and suppress their nonradiative transitions (T1→S0), thus favoring RTP emission.

[0047] Furthermore, the molecular stacking modes of the two cocrystals also differ: in the g-cocrystal, acceptor molecules are arranged in an alternating "...DA-DA-DA..." pattern, while in the y-cocrystal, they are stacked in a "...DADADADA..." pattern. These different stacking modes provide a structural basis for the differences in radiation decay kinetics between the two crystal forms. In summary, the enhanced halogen bonds, heteroatom bonds, and CT interactions in the g-cocrystal synergistically promote the TADF process, while the stronger hydrogen bonding in the y-cocrystal favors RTP emission. This structure-property relationship provides theoretical guidance for the regulation of triplet excitons in polymorphic organic cocrystal materials.

[0048] (4) Theoretical calculation research To further reveal the microscopic origins of the different luminescence mechanisms of g-eutectic and y-eutectic, this invention performs TD-DFT calculations based on the structural units extracted from single-crystal structures at the theoretical level of ωB97-XD / def2-TZVP. The optimal ω values ​​for g-eutectic and y-eutectic are shown in Tables 3-4.

[0049] Table 3 Optimal g-eutectic value

[0050] Table 4 Optimal γ-eutectic value

[0051] According to perturbation theory, the intersystem crossing rate constant ( k ISC ) and spin-orbit coupling matrix elements S m | SOC |T n ² is proportional to the square of the energy difference between the single triplet states (ΔE) Sm–Tn The SOC constant is inversely proportional to ΔE. Therefore, a larger SOC constant results in a smaller ΔE. Sm–Tn Beneficial k ISC(RISC) The energy levels of the g- and y-eutectic are significantly lower and more densely packed than those of the single-component eutectic, resulting in an increase in ΔE. ST Reduce and form multiple effective ISC channels. Figure 18 a and Figure 18 b shows the singlet and triplet energy level diagrams, main orbital transition paths, and oscillator strength for the two eutectic types, respectively. f ) and SOC constant ( ξ In the two polymorphic eutectics, at |S1 T n Within the range of |<0.3 eV, three excited states exist, namely T1, T2, and T3, indicating the existence of three ISC channels in the crystal state. Among them, the g-eutectic... ξ S1 / T3 (1.97cm) -1 ) and γ-eutectic ξ S1 / T1 (1.53cm) -1 The relatively large values ​​indicate that the S1→T3 (0.102 eV) of the g-eutectic and the S1→T1 (0.148 eV) of the y-eutectic are the main ISC transition channels, respectively. Singlet excitons transition from S1 to T1, T2, and T3 through efficient ISC processes, then undergo a rapid internal transition to T1, and finally return to the S1 state via RISC before emitting delayed fluorescence.

[0052] Oscillator strength of g-eutectic S1 state f The value is 0.0087, much larger than the 0.0011 for the γ-eutectic, according to Einstein's expression for spontaneous emission. k r,f =f E g 2 / 1.499 indicates that the radiative attenuation of S1 is significantly enhanced in the g-eutectic, while the radiative attenuation of S1 is suppressed in the y-eutectic. Furthermore, under spin-orbit coupling, both singlet and triplet states of the two eutectics possess non-negligible transition dipole moments ( μ For the S1 state, g-eutectic μ ( μ <s1>=0.92) compared to y-eutectic μ ( μ <s1>=0.35) is large, which leads to strong TADF emission in the g-eutectic. However, for the T1 state, the y-eutectic... μ ( μ <t1>=8.58×10 -2 ) compared to g-eutectic μ ( μ <t1>=4.06×10 -3 The efficiency is about 20 times higher, which significantly enhances the radiative transition of the T1 state in the γ-eutectic, thereby inducing significant phosphorescence emission.

[0053] According to the El-Sayed rule, the degree of mixing (n, π*) and (π, π*) between singlet and triplet states directly affects the SOC intensity. For example... Figure 18 As shown in c, the S1 state of both polymorphic eutectics undergoes a (π, π*) transition and exhibits strong CT characteristics, which helps to reduce ΔE. ST Unlike g-eutectic, y-eutectic exhibits a higher proportion of n→π* transitions in the T1 state, stemming from the lone pair electrons of the Br atom and the synergistic contribution of the dibenzothiophene conjugated framework. Specifically, HOMO-6 and HOMO-3 in g-eutectic contain single-electron n-orbital components. Although the HOMO-6→LUMO transition configuration accounts for 22.43% of T1, the n component in this orbital is small, while the HOMO-3→LUMO has a large n component, but only accounts for 2.58% of T1. Compared to g-eutectic, the total transition rate of HOMO-5→LUMO and HOMO-3→LUMO in y-eutectic is 72.93%. Furthermore, the large proportion of n component in the T1 state of y-eutectic may induce electrons to directly transition from the T1 state to the S0 state, resulting in phosphorescence.

[0054] In summary, this invention designed and synthesized two polymorphic organic eutectics of 1-BrTC, g-eutectic and y-eutectic, exhibiting distinct green and yellow light emissions, respectively, through a simple solution self-assembly strategy. These two polymorphic eutectics exhibit different photophysical processes. The g-eutectic exhibits TADF properties, while the y-eutectic exhibits dual emission behavior of TADF and RTP. Single-crystal data show that the significant difference in molecular packing leads to multiple intermolecular interactions of varying strengths between DA pairs. Stronger hydrogen bonding in the y-eutectic results in additional RTP emission. Experimental results indicate that the stronger halogen bonds, heteroatom bonds, and CT interactions in the g-eutectic synergistically enhance the oscillator strength and transition dipole moment of the S1 state and optimize the ISC / RISC channel, thus dominating TADF emission; while the stronger hydrogen bonding in the y-eutectic stabilizes the triplet state, and the T1 state exhibits a large transition dipole moment and significant n→π* characteristics, leading to RTP emission dominance. This study reveals the dynamic regulation mechanism of excited state in polymorphic eutectics at the molecular level, providing theoretical guidance for the design of novel TADF / RTP luminescent materials.

[0055] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A polycrystalline organic eutectic material, characterized in that, The polymorphic organic eutectic material is monoclinic and consists of electron acceptor 1,2,4,5-tetracyanobenzene and electron donor 1-bromodibenzothiophene.

2. The polycrystalline organic eutectic material according to claim 1, characterized in that, When the molar ratio of electron donor 1-bromodibenzothiophene to electron acceptor 1,2,4,5-tetracyanobenzene is 1:2, the polycrystalline organic eutectic material is a g-eutectic and exhibits green light emission; when the molar ratio of electron donor 1-bromodibenzothiophene to electron acceptor 1,2,4,5-tetracyanobenzene is 2:1, the polycrystalline organic eutectic material is a γ-eutectic and exhibits yellow light emission.

3. The method for preparing the polycrystalline organic eutectic material according to claim 1 or 2, characterized in that, Synthesized by solution self-assembly, specifically including the following steps: 1,2,4,5-tetracyanobenzene and electron donor 1-bromodibenzothiophene are mixed uniformly in proportion and allowed to stand. Then, the mixed solution is slowly injected into a poorly mixed solution of ethanol and H2O to form a suspension. Finally, the suspension is dropped onto a substrate and the solution is obtained after the solvent evaporates.

4. The preparation method according to claim 3, characterized in that, The solvent for the 1,2,4,5-tetracyanobenzene is acetonitrile; the solvent for the 1-bromodibenzothiophene is tetrahydrofuran.

5. The application of the polycrystalline organic eutectic material according to claim 1 or 2 in the preparation of thermally activated delayed fluorescence materials.

6. A thermally activated delayed fluorescence material, characterized in that, The thermally activated delayed fluorescence material includes the polymorphic organic eutectic material as described in claim 1 or 2.

7. The application of the thermally activated delayed fluorescence material according to claim 6 in the fabrication of optoelectronic devices.

8. The application of the polycrystalline organic eutectic material according to claim 1 or 2 in the preparation of room temperature phosphorescent materials.

9. A room-temperature phosphorescent material, characterized in that, The room-temperature phosphorescent material includes the polycrystalline organic eutectic material as described in claim 1 or 2.

10. The application of the room-temperature phosphorescent material according to claim 9 in the fabrication of optoelectronic devices.

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