A three-phase luminescent phasmid liquid crystal element and its preparation method and application

Abstract

The present invention discloses a three-phase luminescent phasmid liquid crystal unit and its preparation method and application. The phasmid liquid crystal unit of the present invention has branch units at both ends and a long rod-shaped core in the middle; the long rod-shaped core is composed of diphenylbutadiene units and diphenylcyanoethylene units; the former is a typical aggregation-induced fluorescence quenching unit, and the latter is a typical aggregation-induced luminescence unit; the cyano group is a strong electron-withdrawing group, so the long rod-shaped core is a D-A-π-A-D structure. The phasmid molecules of the present invention can be dissolved in ordinary solvents; in selective solvents, columnar micelles are formed with good micelle stability; and a hexagonal columnar liquid crystal phase is formed in the solid state. In the single molecule state, the D-A effect is strong. The phasmid molecules of the present invention exhibit high luminescence efficiency in both the gel state and the liquid crystal state, which are 58.5% and 85.5%, respectively.

Description

Technical Field

[0001] The invention belongs to the technical field of luminescent liquid crystal materials and relates to a three-phase luminescent phasmid liquid crystal element and a preparation method and application thereof. Background Art

[0002] Although organic light-emitting materials have been applied in numerous fields, their applications are constrained by two opposing luminescence phenomena: aggregation-induced quenching (ACQ) and aggregation-induced emission (ALE). Luminescent molecules with ACQ properties are hereafter referred to as ACQ molecules, while those with AIE properties are hereafter referred to as AIE molecules. ACQ molecules exhibit strong luminescence in the single-molecule state (e.g., in dilute solutions), but their luminescence is diminished or even absent in the aggregated state (e.g., in the solid state). In contrast, AIE molecules are silent in the single-molecule state but emit light in the aggregated state. This single-state luminescence characteristic severely restricts the application of these luminescent molecules. Therefore, the development of multi-state luminescent molecules (single-molecule and aggregated states) is of great significance as it can bridge the gap between ACQ and AIE molecules and broaden the application of luminescent materials. However, ACQ and AIE are two opposing photophysical phenomena, making it difficult for a single molecule to possess both ACQ and AIE properties. Developing multi-state luminescent molecules is a significant challenge. One straightforward approach is to directly link ACQ and AIE units via covalent bonds, thereby synthesizing "ACQ+AIE" molecules to bridge the gap between ACQ and AIE molecules. Numerous "ACQ+AIE" molecules have been synthesized, and the results indicate that these molecules typically exhibit high solid-state luminescence efficiencies but low solution luminescence efficiencies. This is due to the nonradiative energy transfer generated by the intramolecular motion of the AIE unit, which reduces the solution luminescence efficiency of these molecules. Therefore, it is conceivable that if the AIE group and the ACQ group could form a conjugated, coplanar structure in solution, the low solution luminescence efficiency of these "ACQ+AIE" units would be overcome. Such "ACQ+AIE" units would undoubtedly exhibit high luminescence efficiency in both the single-molecule and aggregated states.

[0003] Recently, the YL Zhao and Zhu Liangliang research groups collaborated to confirm this concept. The authors designed a luminescent unit with the structure "diphenylethylene cyanide + diacetylene + diphenylethylene cyanide." Diphenylethylene cyanide and diacetylene are typical AIE and ACQ units, respectively. In solution, due to the strong electron-withdrawing ability of the cyanide group, a strong intramolecular charge transfer effect occurs within the molecule, forcing the entire molecule to adopt a planar conformation, resulting in high solution luminescence efficiency. In the solid state, however, diphenylethylene cyanide adopts a twisted conformation, effectively preventing close packing between diacetylene units and enabling efficient luminescence from the diacetylene units. Since diphenylethylene cyanide in a twisted conformation is a typical AIE unit and can emit light efficiently in the solid state, the diphenylethylene cyanide units and diacetylene units synergistically emit light, giving the entire molecule high luminescence efficiency. However, the authors' designed structure has single alkyl chains or short forked chains at both ends, resulting in poor self-assembly ability and difficulty in forming polymorphic structures such as gels and liquid crystals, limiting the application of this type of material.

[0004] Liquid crystals are a class of substances between crystals and liquids, combining both processability and order, making them an important soft matter platform for designing functional materials. Substances that can form liquid crystals are generally called mesogens. Based on their shape, mesogens can be broadly categorized as rod-shaped and disc-shaped. Mesogens of other shapes can be considered a combination of rods and / or discs. Phasmid mesogens have a long, rod-shaped core in the center, flanked by wedge-shaped tail chains (typically three alkyl chains) at either end. Phasmid mesogens can be considered intermediate between rods and discs, boasting large, easily controllable molecular size and a rich, easily tunable phase structure. Their self-assembly properties are determined by the length of the rigid core and the number, length, and position of the tail chains, making phasmid liquid crystal molecules an ideal platform for designing polymorphic luminescent materials. Summary of the Invention

[0005] To address the shortcomings of existing luminescent materials in their single-state (single-molecule or aggregated) luminescence, the present invention aims to provide a three-phase luminescent phasmid liquid crystal element that exhibits high luminescence efficiency in solution, gel, and liquid crystal states. Another technical problem addressed by the present invention is a method for preparing the aforementioned three-phase luminescent phasmid liquid crystal element. A further technical problem addressed by the present invention is to provide an application for the three-phase luminescent phasmid liquid crystal element.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A three-phase luminescent phasmid liquid crystal unit, the structural formula of which is shown in formula (IV-n):

[0008]

[0009] Where n is a natural number between 8 and 12.

[0010] A method for preparing a three-phase luminescent phasmid liquid crystal unit (IV-n), the reaction equation is as follows:

[0011]

[0012] Where n is a natural number between 8 and 12.

[0013] The specific steps include:

[0014] Compounds (II-n) and (III) can be synthesized according to the methods reported in the literature (J. Mater. Chem. C. 2014, 2, 5168., Angew. Chem. Int. Ed. 2019, 58, 11419.).

[0015] Under nitrogen protection, compound (III) was dissolved in a two-necked flask containing dry THF and stirred at room temperature until most of (III) was dissolved. Dry NEt3 was then added to the reaction flask (the molar ratio of NEt3 to (III) was 4:1), and the reaction flask was then placed in an ice bath; compound (II-n) was dissolved in an appropriate amount of dry THF, and the THF solution of (II-n) was slowly dripped into the above-mentioned cooled reaction flask through a constant pressure dropping funnel. After the temperature rose to room temperature, stirring was continued for 24 hours; an appropriate amount of silica gel was added to the reaction flask, and the reaction liquid was removed by rotary evaporation until a loose powder was obtained; the powder was then separated by dry loading column chromatography (eluent: DCM) to obtain the target compound (IV-n).

[0016] The application of the three-phase luminescent phasmid liquid crystal unit in the preparation of organic luminescent materials.

[0017] In this invention, the inventors introduced "ACQ+AIE" units into the design of phasmid mesogens, utilizing them to achieve multi-state luminescence and multi-state phase transitions through the self-assembly of phasmid mesogens. Ultimately, they prepared a polymer with high luminescence efficiency in solution, gel, and liquid crystal states, achieving efficient three-state luminescence from the same molecule. The chemical structure of the molecule is shown in Formula (IV-n, n=8-12):

[0018]

[0019] This phasmid liquid crystal unit has dendrimer units at both ends and a long rod-shaped core in the middle. The long rod-shaped core is composed of diphenylbutadiyne units and diphenylcyanoethylene units. The former is a typical aggregation-induced fluorescence quenching (ACQ) unit, and the latter is a typical aggregation-induced emission (AIE) unit. The cyano group is a strong electron-withdrawing group, so the long rod-shaped core has a DA-π-AD structure (D represents the electron donor and A represents the electron acceptor). This phasmid molecule is soluble in common solvents such as THF and DCM. In selective solvents such as dodecane, it forms columnar micelles with excellent stability, existing stably at 100°C. Lowering the temperature allows micelle growth to induce gelation. In the solid state, it forms a hexagonal columnar liquid crystal phase, with a single cell with a monolayer thickness of ~0.44 nm containing ~4 molecules. In the single-molecule state (in a good solvent), the DA effect is strong, and the long rod-shaped core adopts a planar structure, inhibiting non-radiative energy transfer. As a result, the phasmid molecules of the present invention exhibit a high luminescence efficiency (~90.3%) in good solvents. In the aggregated state (gel or liquid crystal state), the DA effect is weak, and the diphenylcyanoethylene units adopt a twisted conformation, exhibiting AIE properties, resulting in efficient luminescence. Furthermore, the twisted conformation effectively prevents the close packing of the diacetylene units, weakening their ACQ effect, thus also enabling efficient luminescence. The synergistic luminescence of these two units enables the phasmid molecules of the present invention to exhibit high luminescence efficiencies in both the gel and liquid crystal states (58.5% and 85.5%, respectively).

[0020] Beneficial effects: Compared with the prior art, the advantages of this application are:

[0021] 1) The phasmid liquid crystal element of the present invention has excellent self-assembly ability due to the introduction of the rigid structure of "diphenylethylene cyano-diphenylbutadiyne-diphenylethylene cyano" and the dendron units at both ends. It can be dissolved in a good solvent and can form columnar micelles in a selective solvent. The micelles have good stability and can induce gelation of the system, forming a hexagonal columnar liquid crystal phase in the bulk state.

[0022] 2) The phasmid liquid crystal unit of the present invention has a DA-π-AD structure, has a strong intramolecular charge transfer ability in a good solvent, and the entire molecule adopts a conjugated coplanar structure, with a high luminous efficiency (~90.3%):

[0023] 3) The phasmid liquid crystal element of the present invention, due to the introduction of diphenylcyanoethylene units, adopts a relatively distorted conformation in the aggregated state, exhibiting AIE properties. On the other hand, this distorted conformation destroys the close packing between the diacetylene units and weakens their ACQ effect, resulting in the diphenylcyanoethylene units and the diacetylene units synergistically emitting light in the aggregated state. The entire molecule exhibits a high luminescence efficiency, with a luminescence efficiency of up to 58.5% in the gel state and up to 85.5% in the bulk liquid crystal state. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is compound (I-12) 1 H NMR spectra;

[0025] Figure 2 is compound (III) 1 H NMR spectra;

[0026] Figure 3 is compound (IV-12) 1 H NMR spectra;

[0027] Figure 4 is the DSC curve of compound (IV-12) at a heating and cooling rate of 10°C / min;

[0028] Figure 5 is the PLM graph of compound (IV-12) when the temperature is slowly decreased from the isotropic temperature to room temperature;

[0029] Figure 6 is the 1D XRD pattern of compound (IV-12) when the temperature is slowly decreased from the isotropic temperature to room temperature;

[0030] Figure 7 This is a molecular arrangement model diagram of compound (IV-12);

[0031] Figure 8 Compound (IV-12) in DMF, THF, CHCl3, C 12 H 26 In the UV-visible absorption spectrum, the molar concentration of (IV-12) is 10 μmol / L;

[0032] Figure 9 Compound (IV-12) in DMF, THF, CHCl3, C 12 H 26 In the fluorescence emission spectrum, the molar concentration of (IV-12) is 10 μmol / L, and the excitation wavelength of the spectrum is 365 nm;

[0033] Figure 10is the UV-visible absorption spectrum of compound (IV-12) in its bulk state;

[0034] Figure 11 It is the fluorescence emission spectrum of compound (IV-12) in the bulk state, and the excitation wavelength of the spectrum is 365 nm. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] Example 1: Synthesis of Compound (IV-12)

[0037] The synthetic route of compound (IV-12) is as follows:

[0038]

[0039] 1) Synthesis of compound (I-12)

[0040] A 250 mL round-bottom flask was charged with 20 mmol of methyl 3,4,5-trihydroxybenzoate, 62 mmol of 1-bromododecane, 40 mmol of KCO, 100 mL of acetone, and a catalytic amount of TBAB. The mixture was refluxed under nitrogen until TLC analysis indicated complete reaction of methyl 3,4,5-trihydroxybenzoate. The reaction mixture was cooled to room temperature, and the acetone was removed by rotary evaporation. The residue was extracted with DCM, washed with saturated NaCl solution, and dried over anhydrous MgSO to yield a crude product. The crude product was recrystallized twice from acetone to yield 11.02 g of methyl 3,4,5-triacontoxybenzoate as a white powdery solid (80% yield). The product was used directly in the next step without further characterization.

[0041] 14.50 mmol of methyl 3,4,5-triadecyloxybenzoate was added to a 500 mL single-necked round-bottom flask, followed by 50 mL of THF and 25 mL of ethanol. The mixture was refluxed at 80°C for 10 min until the solution became clear. 25 mL of aqueous KOH solution (containing 29.00 mmol of KOH) was then slowly poured from the upper end of the condenser tube and refluxed at 80°C for 2 h. The reaction solution was cooled to room temperature, acidified with concentrated HCl to a pH value close to 2, and most of the reaction solution was removed by rotary evaporation. The residue was extracted with ether, washed with a saturated aqueous NaCl solution, and dried over anhydrous MgSO4 to obtain 9.30 g (yield 95%) of white powdery 3,4,5-triadecyloxybenzoic acid, i.e., compound (I-12). 1 H NMR results are shown in Figure 1 .

[0042] 2) Synthesis of compound (II-12)

[0043] To a 100 mL single-necked round-bottom flask, 10.00 mmol of compound (I-12) was added, followed by 25 mL of DCM, and the mixture was stirred at room temperature for 10 min. Then, 1.66 mL (10.00 mmol) of thionyl chloride (SOCl2) was slowly added dropwise, followed by a drop of N,N-dimethylformamide (DMF), and the mixture was stirred at room temperature for 2 h under nitrogen. The reaction solution was removed by rotary evaporation, and 25 mL of petroleum ether was added to the reaction flask. The petroleum ether was then removed by rotary evaporation, and 25 mL of petroleum ether was added. The mixture was then spin-dried to obtain a viscous residue, the crude product of compound (II-12). The crude product was not further characterized and was used directly in the next step after 25 mL of THF was added to the reaction flask.

[0044] 3) Synthesis of compound (IV-12)

[0045] Compound (III) was synthesized according to the method of reference (Angew.Chem.Int.Ed.2019, 58, 11419.), 1 HNMR results are shown in Figure 2 . Under nitrogen protection, 5.00 mmol of compound (III), 150 mL of dry THF and 2.77 mL of dry NEt3 were added to a 500 mL two-necked round-bottom flask, and stirred at room temperature for 30 min. The reaction flask was then placed in an ice bath, and the THF solution of compound (II-12) (10.00 mmol) prepared in the previous step was slowly dripped into the flask through a constant pressure dropping funnel. After the temperature rose to room temperature, stirring was continued for 24 h. An appropriate amount of silica gel was added to the reaction flask, and the reaction liquid was removed by a rotary evaporator until a loose powder was obtained. The powder was then separated by dry column chromatography (eluent: DCM) to obtain 6.76 g (yield 75%) of the target compound (IV-12). Compound (IV-12) 1 H NMR results are shown in Figure 3 .

[0046] Example 2: Bulk self-assembly properties of compound (IV-12)

[0047] Firstly, the phase transition behavior of compound (IV-12) was investigated by differential scanning calorimetry (DSC). Figure 4 ) shows an endothermic peak at around 120℃, and an exothermic peak appears at around 110℃ in the cooling curve. The enthalpy values of the endothermic and exothermic peaks are very small, indicating that compound (IV-12) has formed a liquid crystal phase. Then, the birefringence properties of compound (IV-12) were examined by polarizing microscope (PLM). The PLM diagram ( Figure 5) showed that the sample (IV-12) has obvious birefringence and the isotropy temperature is about 120℃. To further determine the phase structure of the sample, the sample was analyzed by one-dimensional X-ray diffraction (1D XRD). The room temperature 1D XRD diffraction curve ( Figure 6 ) Three sharp diffraction peaks appeared in the low-angle region, with d values of 4.83, 2.73, and 2.38 nm, respectively. The ratio is The results show that the sample forms a hexagonal columnar liquid crystal phase, with three peaks indexed as (100), (110) and (200) in sequence. The d value corresponding to the more diffuse diffraction package in the wide-angle region is 0.44 nm, indicating that the average thickness h of the monolayer is about 0.44 nm. The sample density ρ measured by the suspension method is 0.97 g / cm 3 According to the formula μ=(Sh)ρ(N A / M) can calculate the number of molecules contained in a single-molecule-thick unit cell μ = 4, where the unit cell area M is the molecular weight of compound (IV-12) (M=1802.66 g / mol), N A is the Avogadro constant. According to the results of 1D XRD, the arrangement model of compound (IV-12) in the molecular column is as follows Figure 7 As shown, the four molecules in a single cell of monolayer thickness are approximately arranged in parallel, and different molecular layers are stacked into supramolecular columns by rotating at a certain angle. The supramolecular columns are arranged in parallel to form a hexagonal columnar liquid crystal phase.

[0048] Example 3: Self-assembly properties of compound (IV-12) in solution

[0049] Although compound (IV-12) has a long rigid core, it contains dendron units composed of alkyl chains at both ends, so it should have good solubility. Solubility experiments show that compound (IV-12) can be well dissolved in common solvents such as THF, DCM, etc., and no obvious Tyndall phenomenon is observed under laser irradiation (365nm or 245nm). However, compound (IV-12) is not soluble in dodecane (C 12 H 26 ) and n-hexane showed obvious Tyndall phenomenon, indicating that it formed micelles. Alkanes can be regarded as selective solvents for compound (IV-12), which can effectively dissolve the dendritic units at both ends, but are precipitants for the rigid core in the middle. Therefore, compound (IV-12) can self-assemble to form micelles in alkanes. According to its characteristic of forming supramolecular columns in the bulk state, it can be known that the micelles formed in alkanes are columnar micelles. Since the further growth of columnar micelles can induce the gelation of the system, the next step is to investigate the reaction of compound (IV-12) in n-hexane (C6H 14 ) in the gelation behavior. The experimental results show that compound (IV-12) in C6H14 It can indeed gel, and its gelation temperature (T gel ) is a function of concentration (see Table 1). For example, the sample weight fraction (w t ) 1% solution can gel at -15℃, w t =20% solution can gel at 10℃.

[0050] Table 1. Gelation temperature (T) of compound (IV-12) in n-hexane gle ) and its weight fraction w t Relationship table

[0051] <![CDATA[w t ]]> 1％ 5％ 10％ 15％ 20％ 25％ <![CDATA[T gel (℃)]]> -15 -10 -5 5 10 15

[0052] Example 4: Photophysical property analysis of compound (IV-12)

[0053] Determine the reaction conditions of compound (IV-12) in DMF, THF, CHCl3, C 12 H 26 As well as the UV-visible absorption spectrum and fluorescence emission spectrum of the bulk state, the polarity of the solvent is DMF>THF>CHCl3>C 12 H 26 In DMF, THF, CHCl3, C 12 H 26 Among them, compound (IV-12) showed similar absorption spectrum ( Figure 8 ), with maximum absorption near 380nm. 12 H 26 Among them, compound (IV-12) showed strong emission ( Figure 9 ), in addition to the strong and sharp emission peak in the range of 420-435nm, there is also a slightly weaker and more diffuse emission peak in the range of 440-480nm, which corresponds to the diphenylbutadiyne and phenylcyanoethylene emission groups respectively; with the change of solvent polarity, the former changes less, while the latter changes more. With the increase of solvent polarity, both emission peaks are significantly red-shifted and become diffuse, showing a trend of merging into one peak (such as Figure 9 This also indicates that there is a significant intramolecular charge transfer effect in compound (IV-12). This effect is caused by the DA-π-AD structure within the molecule.

[0054] In the bulk state, compound (IV-12) also exhibits a maximum absorption peak at 375 nm ( Figure 10 ). Compared with the single molecule emission spectrum ( Figure 9 ), the emission spectrum of the bulk state is obviously red-shifted and diffuse ( Figure 11This is due to the excitons formed in the bulk state of the sample. However, compound (IV-12) still exhibits strong emission behavior in the bulk state.

[0055] The luminescence properties of compound (IV-12) in chloroform, dodecane and bulk state were determined by fluorescence quantum yield experiments. The luminescence efficiency of compound (IV-12) in chloroform was 90.3%, and in gel state (w t =40%), with a luminous efficiency of 58.5% in the bulk state and 85.5% in the bulk state. The experimental results demonstrate that compound (IV-12) is a highly efficient luminescent material in solution, gel, and liquid crystal states, overcoming the shortcomings of singlet-state luminescence in ACQ and AIE molecules. It represents a new class of materials capable of highly efficient luminescence in both single-molecule and aggregated states.

Claims

1. A three-phase luminescent phasmid liquid crystal element, characterized in that: The structural formula is as follows: Wherein, n is a natural number between 8 and 12.

2. The three-phase luminescent phasmid liquid crystal element according to claim 1, characterized in that: A hexagonal columnar liquid crystal phase formed in the bulk.

3. The three-phase luminescent phasmid liquid crystal element according to claim 1, characterized in that: Forms organogels in alkanes.

4. The three-phase luminescent phasmid liquid crystal element according to claim 1, characterized in that: The columnar micelles formed in alkanes are stable at 100℃.

5. The three-phase luminescent phasmid liquid crystal element according to claim 1, characterized in that: It can emit light efficiently in the liquid crystal state.

6. The three-phase luminescent phasmid liquid crystal element according to claim 1, characterized in that: It can emit light efficiently in the gel state.

7. The three-phase luminescent phasmid liquid crystal unit according to claim 1, characterized in that: It can emit light efficiently in solution.

8. The method for preparing the phase-luminescent phasmid liquid crystal unit according to claim 1, characterized in that: Under nitrogen, compound (III) was dissolved in a two-necked flask containing dry tetrahydrofuran and dry triethylamine, stirred, then placed in an ice bath, and then slowly added dropwise to the THF solution of compound (II-n) through a constant pressure dropping funnel. After the temperature rose to room temperature, stirring was continued. Silica gel was added to the reaction solution, and the reaction solution was spin-dried to obtain a solid powder, which was then separated by column chromatography to obtain the target compound (IV-n). The specific reaction formula is as follows: Wherein, n is a natural number between 8 and 12.

9. Use of the three-phase luminescent phasmid liquid crystal unit according to claim 1 in the preparation of organic light-emitting materials.

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