A highly conjugated photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole and its application

Abstract

The present invention relates to a highly conjugated photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole and its application in 4D printing intelligent manufacturing, belonging to the technical field of liquid crystal materials. The structural general formula is as shown in Formula (I). In the present invention, carbazole and thiophene groups with good optoelectronic response are introduced into the photocurable liquid crystal molecular system to replace the low-conjugated phenyl structure bridged by traditional ester bonds, which not only realizes a lower driving voltage for 4D printing structures, but also the position of carbazole-NH is convenient for introducing flexible side chains, further realizing the regulation of the phase transition temperature of liquid crystal materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal materials, and particularly relates to a highly conjugated photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole and its application. Background Art

[0002] 4D printing is based on 3D printing and utilizes smart materials to generate structure, shape, and performance changes over time under external stimuli (such as light, heat, water, electricity, magnetism, etc.), thereby realizing self-deformation, self-repair, self-assembly, etc. of products. It is an important embodiment of advanced intelligent manufacturing technology. Currently, 4D printing technology has broad application prospects in many fields such as national defense and industry, including soft robots, invisibility cloaks, aircraft and firearm printing, artificial muscles, sensors, flexible electronics, etc.

[0003] Currently, the research on 4D printing smart materials mainly focuses on the development of stimulus-responsive polymers. Compared with shape memory metals and ceramics, smart polymers have many advantages, such as multiple stimulus-responsive properties, large deformation amounts, wide material sources, strong designability, and so on. However, when traditional shape memory polymers, such as polylactic acid, polyurethane, polydimethylsiloxane, etc., are used as 4D printing materials, it is difficult to truly realize the advantages of the 4D printing shape memory effect due to the limitations of small thermal expansion amplitude and isotropy. Although anisotropic swelling hydrogels can achieve large-scale shape changes and can automatically bend and twist at the macroscopic scale without mechanical programming, the limitations of the aqueous environment and insufficient gel strength have imposed many restrictions on the application of 4D printing.

[0004] Liquid crystal elastomers (LCEs) prepared from photocurable liquid crystal monomers are a class of stimuli-responsive polymers that undergo large, reversible, and anisotropic shape changes when exposed to various stimuli (e.g., heat and light) (ACS Applied Materials & Interfaces, 2017, 9, 37332; Advanced Materials, 2018, 30, 1706164; ACS Applied Materials & Interfaces, 2019, 11, 19514). If these photocurable liquid crystals are cross-linked in an oriented state, they will shrink along the orientation direction and expand in the vertical direction, making them ideal for 4D printing smart materials. However, the conventional phenyl ester liquid crystal monomers (RM82 and RM257) reported so far, whether by adding additional chain extenders to reduce the liquid crystal phase transition temperature, or by doping with inorganic materials and using multilayer structures to improve strength, have led to problems such as poor compatibility of doped materials in the printing system, weak interfacial adhesion between layers, and inconsistent orientation synergy. In addition, various additives increase the complexity and variable factors of the printing system, further limiting the resolution and accuracy of the printed structure. In addition, the traditional phenyl ester liquid crystal molecules with ester bonds interrupting the conjugation require a higher voltage to achieve photoelectric driving performance, which has created certain obstacles to further effectively promote the application of 3D / 4D printing in cutting-edge technology fields such as organic optoelectronic devices and millimeter wave communication antennas. Therefore, from the perspective of the essential molecular structure, optimizing the liquid crystal material structure system has important research significance for improving the performance and application of 4D printing. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a highly conjugated photocurable discotic liquid crystal monomer based on benzoterthiophene-bridged carbazole and its application. The liquid crystal monomer uses a quaternary large condensed ring benzoterthiophene with a highly conjugated system as the core of the discotic liquid crystal, and symmetrically bridges three highly conjugated carbazole groups with sensitive photoelectric response, which plays an important role in improving the photoelectric response and mechanical properties of the 4D printing structure. Compared with the traditional nematic or smectic phase of phenyl ester liquid crystals, the discotic liquid crystal layers are more closely stacked, and the large planar condensed ring conjugation derived from benzoterthiophene-bridged carbazole is very beneficial to the improvement of carrier transport and photoelectric response performance. The introduction of stable and efficient imide diene at the end of the molecule to replace the traditional acrylate further improves the 4D printing photocuring cross-linking efficiency. In addition, the carbazole-NH position is convenient for introducing flexible side chains, which is beneficial to the regulation of the liquid crystal phase transition temperature.

[0006] The present invention provides a highly conjugated photocurable discotic liquid crystal monomer based on benzoterithiophene-bridged carbazole, the general structural formula of which is shown in formula (I):

[0007]

[0008] In formula (I), R1, R2, and R3 are each independently selected from one of H, D, F, -CN, -NO2, -CF3, alkenyl, alkynyl, amino, acyl, amido, cyano, isocyano, alkoxy, hydroxy, carbonyl, sulfonyl, alkyl having 1 to 60 carbon atoms, cycloalkyl having 3 to 60 carbon atoms, aromatic group having 6 to 60 carbon atoms, heteroaromatic group having 3 to 60 carbon atoms, fused polycyclic aromatic group having 7 to 60 carbon atoms, and fused heteroaromatic group having 4 to 60 carbon atoms;

[0009] R4, R5, and R6 are each independently selected from one of alkyl having 1 to 60 carbon atoms, cycloalkyl having 3 to 60 carbon atoms, aromatic group having 6 to 60 carbon atoms, heteroaromatic group having 3 to 60 carbon atoms, fused polycyclic aromatic group having 7 to 60 carbon atoms, and fused heteroaromatic group having 4 to 60 carbon atoms.

[0010] Preferably, it further includes: R1, R2, and R3 are each independently selected from one of H, D, F, -CN, -NO2, -CF3, alkenyl, alkynyl, amino, acyl, amido, cyano, isocyano, alkoxy, hydroxy, carbonyl, sulfonyl, alkyl having 1 to 60 carbon atoms, cycloalkyl having 3 to 60 carbon atoms, aromatic group having 6 to 60 carbon atoms, heteroaromatic group having 3 to 60 carbon atoms, fused polycyclic aromatic group having 7 to 60 carbon atoms, and fused heteroaromatic group having 4 to 60 carbon atoms, and rings formed by multiple groups bonding to each other among them form a monocyclic or polycyclic aliphatic or aromatic ring system.

[0011] Preferably, it further includes: R4, R5, and R6 are each independently selected from one of alkyl having 1 to 60 carbon atoms, cycloalkyl having 3 to 60 carbon atoms, aromatic group having 6 to 60 carbon atoms, heteroaromatic group having 3 to 60 carbon atoms, fused polycyclic aromatic group having 7 to 60 carbon atoms, and fused heteroaromatic group having 4 to 60 carbon atoms, and rings formed by multiple groups bonding to each other among them form a monocyclic or polycyclic aliphatic or aromatic ring group.

[0012] Preferably, it is specifically any one of the following liquid crystal monomers:

[0013]

[0014]

[0015]

[0016]

[0017] The present invention also provides a polymer, and the structural formula of the polymer at least includes the structural formula of the above liquid crystal monomer.

[0018] The present invention also provides a mixture, which comprises the above-mentioned liquid crystal monomer; or comprises the above-mentioned polymer.

[0019] The present invention also provides a 4D printing intelligent material, which comprises the above-mentioned liquid crystal monomer, or comprises the above-mentioned polymer, or comprises the above-mentioned mixture.

[0020] The present invention also provides an application of the 4D printing intelligent material in 4D printing intelligent manufacturing.

[0021] Preferably, it includes: passing a precursor solution containing the 4D printing intelligent material through a 4D printing device and obtaining a formed liquid crystal elastomer device by means of photocuring.

[0022] More preferably, the 4D printing device includes a fused deposition modeling device, a direct writing ink printing device, a digital light processing printing device or a two-photon printing device.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] A highly conjugated photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole provided by the present invention provides excellent carrier transport and optoelectronic response performance through discotic liquid crystal monomers with closely packed columnar discs. The chemically stable photopolymerizable imide olefin can effectively improve the photocuring crosslinking efficiency. The highly conjugated structure of benzotrithiophene-bridged carbazole with a large planar fused ring is not only beneficial to achieving a lower driving voltage, but also the rigid fused ring aromatic group can effectively improve the mechanical properties of the 4D printing structure.

[0025] The present invention applies the photocurable highly conjugated discotic liquid crystal to the 4D printing structure. It can not only achieve good solubility of small molecule materials to facilitate the preparation of the printing resin precursor solution, but also realize large, reversible and anisotropic shape change and deformation recovery ability through photocuring orientation crosslinking.

[0026] The present invention introduces carbazole and thiophene groups with good optoelectronic response into the photocurable liquid crystal molecular system, replacing the low-conjugated phenyl structure bridged by traditional ester bonds, which not only realizes a lower driving voltage for the 4D printing structure, but also the position of carbazole - NH is convenient for introducing flexible side chains, further realizing the regulation of the phase transition temperature of the liquid crystal material. Detailed Embodiments

[0027] The following further elaborates the present invention in conjunction with specific embodiments, but it should be understood that the listed embodiments are only for facilitating the understanding of the core methods and application fields of the present invention, but the scope of the present invention is not limited thereto.

[0028] In the following embodiments, the experimental methods and detection methods are conventional methods unless otherwise specified; the reagents and materials can be obtained commercially unless otherwise specified.

[0029] The high-conjugation photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole provided by the present invention has a structural general formula as shown in Formula (I):

[0030]

[0031] In Formula (I), R1, R2, and R3 are each independently selected from one of H, D, F, -CN, -NO2, -CF3, alkenyl, alkynyl, amino, acyl, amide, cyano, isocyano, alkoxy, hydroxyl, carbonyl, sulfone, an alkyl group having 1 to 60 carbon atoms, a cycloalkyl group having 3 to 60 carbon atoms, an aromatic group having 6 to 60 carbon atoms, a heteroaromatic group having 3 to 60 carbon atoms, a fused polycyclic aromatic group having 7 to 60 carbon atoms, and a fused heteroaromatic group having 4 to 60 carbon atoms;

[0032] R4, R5, and R6 are each independently selected from one of an alkyl group having 1 to 60 carbon atoms, a cycloalkyl group having 3 to 60 carbon atoms, an aromatic group having 6 to 60 carbon atoms, a heteroaromatic group having 3 to 60 carbon atoms, a fused polycyclic aromatic group having 7 to 60 carbon atoms, and a fused heteroaromatic group having 4 to 60 carbon atoms.

[0033] The high-conjugation photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole provided by the present invention mainly utilizes the discotic liquid crystal with closely stacked columnar discs to provide excellent carrier transport and optoelectronic response properties. The chemically stable photo-polymerizable imide olefin can effectively improve the photocuring crosslinking efficiency. The high-conjugation structure of the large planar fused polycyclic benzotrithiophene-bridged carbazole is not only beneficial to achieving a lower driving voltage, but also the rigid fused polycyclic aromatic group improves the mechanical properties of the 4D printing structure.

[0034] The following shows specific examples of the high-conjugation photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole of the present invention:

[0035]

[0036]

[0037]

[0038] The present invention also provides a polymer, and the structural formula of the polymer contains at least the structural formula of the liquid crystal monomer provided by the present invention.

[0039] The present invention also provides a mixture, and the mixture includes the liquid crystal monomer provided by the present invention; or includes the polymer provided by the present invention.

[0040] The present invention also provides a 4D printing intelligent material, which includes the liquid crystal monomer provided by the present invention, or includes the polymer provided by the present invention, or includes the mixture provided by the present invention.

[0041] The present invention also provides an application of the 4D printing intelligent material in 4D printing intelligent manufacturing.

[0042] In the specific application process of the 4D printing intelligent material of the present invention, it includes: passing a precursor solution containing the 4D printing intelligent material through a 4D printing device and obtaining a formed liquid crystal elastomer device by means of photocuring.

[0043] Preferably, the 4D printing device includes a fused deposition modeling device, a direct writing ink printing device, a digital light processing printing device or a two-photon printing device.

[0044] The following examples provide specific synthesis methods for preparing the above compounds and several corresponding intermediates.

[0045] Example 1

[0046] Synthesis of benzotrithiophene-bridged carbazole photocurable discotic liquid crystal monomer (6):

[0047]

[0048]

[0049] Synthesis of intermediate (3)

[0050] Add 2,5,8-tribromobenzotrithiophene (1) (10.00 g, 20.70 mmol), methoxycarbazole boronic acid (2) (26.05 g, 68.32 mmol) and 250 mL of toluene solvent to a two-necked flask, install the device, and stir until completely dissolved under nitrogen protection. Then weigh potassium carbonate (9.44 g, 68.32 mmol), dissolve it in 40 mL of water, and pour its aqueous solution into the above two-necked flask. Finally, weigh Pd(PPh3)4 (1.20 g, 1.04 mmol) into the flask, pump out the air in the bottle with an oil pump, maintain a nitrogen atmosphere, heat and reflux the reaction at a constant temperature for 24 hours, and then cool. Transfer the reaction solution to a rotary evaporation flask, rotary evaporate most of the solvent, extract with dichloromethane, wash three times with water, dry with anhydrous magnesium sulfate, filter and spin dry, and purify to obtain intermediate (3) (21.26 g) with a yield of 82%.

[0051] Synthesis of intermediate (4)

[0052] Under nitrogen protection, the intermediate (3) (10.00 g, 7.98 mmol) was placed in a two-necked flask and dissolved in 250 mL of chloroform solvent. Then the flask was installed in an ice-water bath at 0 °C, and a solution of boron tribromide (2.54 mL, 26.34 mmol) in dichloromethane (25 mL) was added dropwise to the flask. After the addition was completed, the ice-water bath was maintained for 30 minutes, then the ice-water bath was removed, and the temperature was raised to 30 °C for reaction for 24 hours, and then cooled. The reaction solution was transferred to a rotary evaporation flask, and most of the solvent was evaporated by rotary evaporation. It was extracted with chloroform and washed with water three times, dried over anhydrous magnesium sulfate, filtered and rotary evaporated to dryness, and purified to obtain the intermediate (4) (6.96 g), with a yield of 72%.

[0053] Synthesis of Benzotrithiophene-Bridged Carbazole Photocurable Discotic Liquid Crystal (6)

[0054] Under nitrogen protection, the intermediate (4) (5.00 g, 4.13 mmol), potassium carbonate (1.88 g, 13.63 mmol), and 200 mL of N,N-dimethylformamide were added to a two-necked flask, and stirred at room temperature for two hours. Then the intermediate (5) (4.50 g, 13.63 mmol) was added to the flask, and the temperature was raised to 90 °C for reaction for 48 hours, and then cooled. The reaction solution was transferred to a rotary evaporation flask, and most of the solvent was evaporated by rotary evaporation. It was extracted with dichloromethane and washed with water three times, dried over anhydrous magnesium sulfate, filtered and rotary evaporated to dryness, and purified to obtain the benzotrithiophene-bridged carbazole photocurable discotic liquid crystal (6) (5.74 g), with a yield of 71%.

[0055] Example 2

[0056] Synthesis of Benzotrithiophene-Bridged Carbazole Photocurable Discotic Liquid Crystal Monomer (10):

[0057]

[0058]

[0059] Synthesis of Intermediate (8):

[0060] Add 2,5,8-tribromobenzotrithiophene (1) (10.00 g, 20.70 mmol), methoxycarbazole boronic acid (7) (32.76 g, 68.32 mmol), and 250 mL of toluene solvent into a two-necked flask. Install the device and stir until completely dissolved under nitrogen protection. Then weigh potassium carbonate (9.44 g, 68.32 mmol), dissolve it in 40 mL of water, and pour its aqueous solution into the above two-necked flask. Finally, weigh Pd(PPh3)4 (1.20 g, 1.04 mmol) into the flask, evacuate the air in the flask with an oil pump, maintain the nitrogen atmosphere, and heat under reflux at a constant temperature for 24 hours, then cool. Transfer the reaction solution to a rotary evaporation flask, rotary evaporate most of the solvent, extract with dichloromethane, wash three times with water, dry with anhydrous magnesium sulfate, filter and rotary dry, and purify to obtain intermediate (8) (25.00 g) with a yield of 78%.

[0061] Synthesis of intermediate (9):

[0062] Under nitrogen protection, place intermediate (8) (10.00 g, 6.46 mmol) in a two-necked flask and dissolve it in 250 mL of chloroform solvent. Then install the flask in an ice-water bath at 0 °C, and gradually add a dichloromethane (20 mL) solution of boron tribromide (2.05 mL, 21.33 mmol) dropwise to the flask. After the addition is complete, maintain the ice-water bath for 30 minutes, then remove the ice-water bath, raise the temperature to 30 °C and react for 24 hours, then cool. Transfer the reaction solution to a rotary evaporation flask, rotary evaporate most of the solvent, extract with chloroform, wash three times with water, dry with anhydrous magnesium sulfate, filter and rotary dry, and purify to obtain intermediate (9) (7.10 g) with a yield of 73%.

[0063] Synthesis of benzotrithiophene-bridged carbazole photocurable discotic liquid crystal monomer (10):

[0064] Under nitrogen protection, add intermediate (9) (5.00 g, 3.32 mmol), potassium carbonate (1.51 g, 10.96 mmol), and 200 mL of N,N-dimethylformamide into a two-necked flask, and stir at room temperature for two hours. Then add intermediate (5) (3.62 g, 10.96 mmol) into the flask, raise the temperature to 90 °C and react for 48 hours, then cool. Transfer the reaction solution to a rotary evaporation flask, rotary evaporate most of the solvent, extract with dichloromethane, wash three times with water, dry with anhydrous magnesium sulfate, filter and rotary dry, and purify to obtain benzotrithiophene-bridged carbazole photocurable discotic liquid crystal (10) (5.01 g) with a yield of 67%.

[0065] Example 3

[0066] A polymer, the structural formula of the polymer contains at least the structural formula of the liquid crystal monomer provided in Example 1, specifically as follows:

[0067]

[0068] Example 4

[0069] A mixture, which comprises the polymer provided in Example 4 and 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone (abbreviated as II-369).

[0070] Example 5

[0071] A 4D printing intelligent material, which comprises the liquid crystal monomer in Example 1 herein and 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinobenzylphenyl)butanone (abbreviated as I-369).

[0072] Comparative Example 1

[0073] Phenyl ester-based photocurable rod-like liquid crystal monomer (RM82), the structural formula of which is as follows:

[0074]

[0075] The benzotrithiophene-bridged carbazole-based highly conjugated photocurable discotic liquid crystal monomer provided by the present invention can be used as the main material of a liquid crystal elastomer device, and only the performance of the products provided in the above partial examples is measured below.

[0076] 1. Photocuring crosslinking efficiency:

[0077] In order to compare the photochemical crosslinking performance of the imide diene provided in the examples and the acrylate provided in the comparative examples, the present invention uses an OmniCure S2000 spot UV curing system device to select 100 J / cm under different ultraviolet light flux conditions 2 , 200 J / cm 2 , 400 J / cm 2 , 600 J / cm 2 , 800 J / cm 2 to compare the crosslinking performance of two types of photopolymerizable materials. The ultraviolet light flux settings are selected from the S2000 aperture and UV exposure timing settings and the OmniCure R2000UV spot curing radiometer system. The ultraviolet light energy is selected to be 365 nm. The material is dissolved in chlorobenzene to prepare 10 mg / cm 3The solution was then spin-coated on the surface of the oxygen plasma-treated glass substrate at a rotation speed of 2000 rpm, an acceleration of 2000 units, and a time of 30 seconds. As shown in Table 1, Table 1 is the photocuring cross-linking performance data of the liquid crystal monomers provided in Examples 1 to 2 and Comparative Example 1.

[0078] Table 1 Photocuring crosslinking performance data

[0079] Ultraviolet light flux (365 nm) Example 1 Example 2 Comparative Example 1 <![CDATA[200 J / cm 2 > 85％ 92％ 58％ <![CDATA[600 J / cm 2 > 100％ 100％ 76％

[0080] As can be seen from Table 1, the liquid crystal monomers provided in Examples 1 and 2, i.e., the discotic imide diene groups, have six groups of photopolymerizable double bonds, and have a more efficient photocuring efficiency than acrylates with two groups of double bonds, and the imide bridging group has greater stability than the ester group during the reaction, and exhibits efficient performance in the preparation of 3D printed structures and photocuring cross-linking processes.

[0081] 2. Digital Light Processing (DLP) 3D Printing Structural Performance:

[0082] A certain proportion of the photocurable liquid crystal monomer provided in Example 1 or the liquid crystal monomer provided in Example 2, n-butylamine, 2-phenylbenzyl-2-dimethylamine-1-(4-morpholinebenzylphenyl)butanone (referred to as I-369) is added to a certain amount of toluene solvent to prepare a 4D printing resin precursor solution. The three-dimensional structure is printed using the DLP method, and then the sample is photocured for 5-20 minutes, and finally the product is vacuum dried overnight to obtain an excitable shape memory structure.

[0083] In order to compare the effects of benzoterthiophene-bridged carbazole photocurable disc liquid crystal and phenyl ester photocurable rod-shaped liquid crystal on 4D printing process parameters and product structural performance, the present invention compares the excitation temperature, driving voltage and tensile strength of the shape memory effect of the printed structure, as shown in Table 2. Table 2 is the data of the excitation temperature, driving voltage and tensile strength of the liquid crystal monomer provided in Examples 1 to 2 and Comparative Example 1 in the shape memory effect of the printed structure.

[0084] Table 2 Data of excitation temperature, driving voltage and tensile strength

[0085] Excitation temperature (°C) Driving voltage (V) Tensile strength (J / kg) Example 1 36 2.4 18.5 Example 2 28 2.6 19.3 Comparative Example 1 65 6.7 4.3

[0086] As can be seen from Table 2, the liquid crystal monomer provided by the present invention has a benzotrithiophene-bridged carbazole with a large planar conjugation, a highly efficient photopolymerizable imide diene group with chemical stability, and a discotic liquid crystal with an ordered molecular structure arrangement. These combined advantages are conducive to carrier transport, thereby achieving a lower driving voltage and improving the optoelectronic response performance of the 4D printing structure. The liquid crystal with a rigid large-conjugation structure of the present invention provides a higher tensile strength and mechanical properties for the 4D printing structure. At the same time, multiple long flexible alkyl chains led out by the carbazole unit achieve the shape memory effect drive near room temperature for the 4D printing structure.

[0087] The above embodiments are only partial embodiments listed for facilitating the understanding of the synthesis and application methods of the materials of the present invention, and are not used to limit the present invention. It can be understood that relevant practitioners can easily make appropriate modifications to this structure. Therefore, any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A highly conjugated photocurable discotic liquid crystal monomer based on benzotrithiophene-bridged carbazole, characterized in that, Specifically, any one of the following liquid crystal monomers: 。 2. A polymer, characterized in that, The structural formula of the polymer contains the structural formula of the liquid crystal monomer described in claim 1.

3. A mixture, characterized in that, The mixture includes the liquid crystal monomer described in claim 1; or includes the polymer described in claim 2.

4. A 4D printing intelligent material, characterized in that, The 4D printing intelligent material includes the liquid crystal monomer described in claim 1, or includes the polymer described in claim 2, or includes the mixture described in claim 3.

5. Application of the 4D printing intelligent material described in claim 4 in 4D printing intelligent manufacturing.

6. The application according to claim 5, characterized in that Including: The precursor solution containing the 4D printing intelligent material is passed through a 4D printing device and a formed liquid crystal elastomer device is obtained by means of photocuring.

7. The application according to claim 6, wherein The 4D printing device includes a fused deposition modeling device, a direct writing ink printing device, a digital light processing printing device or a two-photon printing device.

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