Thiazole-bridged benzothiadiazole high dichromatic ratio dichroic dyes, synthesis and application thereof

Abstract

The present application relates to the field of dichroic dye preparation, in particular to a thiazole bridged benzothiadiazole high dichroic ratio dichroic dye and synthesis and application thereof. The dichroic dye prepared by the present application has a molecular skeleton comprising a benzoheterodiazole acceptor unit, thiazole bridged units on both sides of the benzoheterodiazole acceptor unit and terminal group substituted aromatic donor units. The nitrogen atom in the thiazole bridged unit is conducive to enhancing the intramolecular charge transfer effect, and forms intramolecular S...N weak interaction with the adjacent sulfur-containing heteroaromatic structure to improve the planarity of the conjugated skeleton and the liquid crystal orientation order. The dichroic dye prepared by the method provided by the present application has good solubility, dichroic ratio and light stability in a liquid crystal host, and is suitable for liquid crystal light adjusting film, liquid crystal light adjusting glass, vehicle-mounted light adjusting sunroof, electronic paper and guest-host type liquid crystal display device.

Description

Technical Field

[0001] This invention relates to the field of dichroic dye preparation, specifically to a thiazole-bridged benzothiadiazole type high dichroic ratio dichroic dye and its synthesis and application. Background Technology

[0002] Dichroic dyes are organic functional materials that exhibit different absorption capabilities for specific wavelengths of polarized light along their long and short axes. When dichroic dye molecules are arranged in an orderly fashion within a liquid crystal matrix, the difference in absorption of light with different polarization directions can be used to adjust light transmittance. Guest-host type liquid crystal displays and dimming technologies typically use dichroic dyes as guest materials dispersed within the liquid crystal matrix. Under an applied electric field, the liquid crystal molecules undergo orientation changes, and the guest dye molecules rotate in tandem with the liquid crystal orientation, thereby altering the device's light transmittance. This type of technology features relatively simple structure, wide viewing angle, high brightness, low driving voltage, fast response, and low power consumption, making it suitable for applications such as smart dimming windows, car sunroofs, photochromic glasses, electronic paper, and low-power display devices.

[0003] Existing dichroic dyes mainly include azo dyes, anthraquinone dyes, and benzothiadiazole dyes. Azo dyes have a high dichroism ratio and good solubility, but the azo bonds are prone to cis-trans isomerism or breakage under ultraviolet light or heat, leading to fading with prolonged use. Anthraquinone dyes have good photostability, but their solubility is relatively poor and their dichroism ratio is low, usually requiring higher addition amounts to achieve the desired light-blocking effect, which may lead to increased viscosity, reduced response speed, and increased cost of the liquid crystal system. Benzothiadiazole dyes have strong electron-accepting ability and good photostability, making them the most promising dichroic dye system currently. Patent (CN105377995A) discloses benzothiadiazole dichroic dyes that use bisthiophene as the conjugated bridging unit, but still have the following problems: (1) Insufficient molecular planarity: The thiophene rings are connected by single bonds, with a large degree of freedom of rotation, making the molecules prone to distortion, which leads to the interruption of the conjugated system and low dichroic ratio and order parameter (usually dichroic ratio <6.5); (2) Electron Poor effect matching: Thiophene is an electron-rich heterocycle, and its DA (donor-acceptor) interaction with benzothiadiazole acceptor is limited. The intramolecular charge transfer (ICT) effect is insufficient, the molar extinction coefficient is low, and a higher addition amount is required; (3) There is still room for improvement in photothermal stability: The C=C double bond of the thiophene ring is prone to oxidation and cracking under long-term ultraviolet irradiation and high temperature conditions; (4) The compatibility with liquid crystal needs to be optimized: The polarity of the full thiophene structure is low, and its compatibility with some polar nematic liquid crystals is insufficient. High concentration addition is prone to crystallization.

[0004] Therefore, it is very promising to invent a benzothiadiazole dichroic dye that has a high dichroism ratio, good solubility, good photostability and liquid crystal compatibility, and to provide a suitable synthetic route for preparing the dye. Summary of the Invention

[0005] To address the aforementioned technical problems, the dichroic dye prepared by this invention comprises a benzo[a]diazolium acceptor unit, thiazole bridging units flanking the benzo[a]diazolium acceptor unit, and terminal-substituted aromatic donor units. The nitrogen atom in the thiazole bridging unit enhances intramolecular charge transfer and forms weak intramolecular S…N interactions with adjacent sulfur-containing heteroaromatic structures, thereby improving the planarity of the conjugated framework and the orientation order of the liquid crystal. The dichroic dye prepared by the method provided by this invention exhibits good solubility, dichroism ratio, and photostability in liquid crystal substrates, making it suitable for liquid crystal dimming films, liquid crystal dimming glasses, automotive dimming sunroofs, electronic paper, and host-guest type liquid crystal display devices.

[0006] This invention discloses a thiazole-bridged benzothiadiazole-based high dichroism dye, the structure of which is shown in formula (I):

[0007]

[0008] Formula (I) Wherein, X, Y, and Z are each independently selected from O, S, or Se; M, L, W, T, U, and V are each independently selected from C or N, and the bridged heteroaromatic rings formed by W, T, and Z, as well as the bridged heteroaromatic rings formed by U, V, and Y, each contain at least one C and one N; R and Q are each independently selected from F, Cl, or CN; K and P are each independently selected from methylene, oxygen atom, N-alkyl linker, or ester linker; n is an integer from 1 to 20; and the terminal hydrocarbon groups in formula (I) are each independently a straight-chain alkyl, branched alkyl, or cyclic alkyl.

[0009] Preferably, the bridged heteroaromatic ring is a thiazole ring, and the two sides of the benzothiadiazole core in formula (I) are respectively connected to the substituted phenyl groups through the thiazole ring to form a donor-acceptor-donor linear conjugated structure.

[0010] Preferably, the nitrogen atom in the thiazole ring is oriented toward the adjacent sulfur-containing heteroaryl structure.

[0011] This invention also discloses a method for preparing a thiazole-bridged benzothiadiazole-based high dichroism dye, comprising the following steps: Step (1): Add a haloalkoxy-substituted aromatic compound to a solvent, cool it, metallize it with an organolithium reagent, and then react it with a borate ester to obtain an arylboronic acid intermediate. Step (2): The arylboronic acid intermediate prepared in step (1) is coupled with halothiazole in the presence of palladium catalyst and base to obtain thiazole-bridged aromatic intermediate; Step (3): The thiazole-bridged aromatic intermediate obtained in step (2) is metallized with an organolithium reagent and then reacted with a borate ester to obtain the thiazole-bridged arylboronic acid intermediate. Step (4): The thiazole-bridged arylboronic acid intermediate obtained in step (3) is coupled with a dihalobenzothiadiazole acceptor compound in the presence of a palladium catalyst and a base to obtain the dichroic dye compound.

[0012] Preferably, in steps (1) and (3), the organolithium reagent is n-butyllithium; the borate ester is triisopropyl borate; the solvent is tetrahydrofuran; and the metallization reaction temperature is... 65 ℃.

[0013] Preferably, in step (1), the molar ratio of the haloalkoxy-substituted aromatic compound to the organolithium reagent is 1:1; the molar ratio of the haloalkoxy-substituted aromatic compound to the borate ester is 1:2; and the mass ratio of the haloalkoxy-substituted aromatic compound to tetrahydrofuran is 1:10.

[0014] Preferably, in step (2), the palladium catalyst is bis(triphenylphosphine)palladium(II) dichloride; in step (4), the palladium catalyst is tetratriphenylphosphine palladium, the base is a 20% potassium carbonate aqueous solution; and the molar ratio of the arylboronic acid intermediate to potassium carbonate is 1:2.5.

[0015] Preferably, in step (2), the molar ratio of the arylboronic acid intermediate to the halothiazole is 1:1.1; and the molar ratio of the arylboronic acid intermediate to bis(triphenylphosphine)palladium(II) chloride is 1:0.001.

[0016] Preferably, in step (4), the molar ratio of the thiazole-bridged arylboronic acid intermediate to the dihalobenzothiadiazole acceptor compound is 2.5:1; the molar ratio of the thiazole-bridged arylboronic acid intermediate to potassium carbonate is 1:2; and the mass ratio of the thiazole-bridged arylboronic acid intermediate to tetrahydrofuran is 1:8.2.

[0017] The application of a thiazole-bridged benzothiadiazole high dichroic ratio dichroic dye: the dichroic dye synthesized by any of the above-mentioned methods for synthesizing a thiazole-bridged benzothiadiazole high dichroic ratio dichroic dye is dispersed as a guest dye in the nematic liquid crystal matrix to prepare a guest-host liquid crystal composition.

[0018] Preferably, the mass percentage of the dichroic dye compound in the host-guest liquid crystal composition is 0.5-2.0%.

[0019] Compared with the prior art, the beneficial effects of the present invention are: This invention provides a thiazole-bridged benzothiadiazole-based high dichroism dye, its synthesis, and its application, which has the following characteristics: (1) The present invention uses thiazole bridging units to construct a DAD strong conjugated structure. The thiazole ring introduces electronegative N atoms, and the S…N weak hydrogen bonds in the molecule lock the conjugated skeleton, reducing the free rotation of aromatic ring single bonds and the degree of molecular twisting is much smaller than that of the full thiophene structure. The overall coplanarity of the conjugated chain is better, the orientation regularity of the molecule in the nematic liquid crystal is improved, the dichroism ratio (DA) and the order parameter S are higher, the dichroism ratio is 7.8~8.1, and the contrast ratio can reach (18~20):1, which meets the requirements of high-end guest and host display / dimming film.

[0020] (2) The benzothiadiazole receptor unit of the present invention has good photostability, the benzothiadiazole parent nucleus is photoresistant, and the residual rate after 500h ultraviolet irradiation is ≥94%, which is far superior to the residual rate of 72% after 500h ultraviolet irradiation of azo compounds, making it suitable for long-term outdoor or vehicle-mounted scenarios.

[0021] (3) The N atom of thiazole in the dichroic dye of the present invention can form intermolecular hydrogen bonds with liquid crystal molecules (cyano-based and ester-based liquid crystals), and its compatibility with commercial nematic liquid crystals is better than that of the full thiophene structure.

[0022] (4) The preparation method of the present invention mainly uses borate reaction and Suzuki coupling reaction as the main steps. The reaction conditions are mild, the raw materials are readily available, and the use of organotin reagents is avoided, making it suitable for large-scale preparation. Attached Figure Description

[0023] Figure 1 This is the general structural formula of the dichroic dye compound shown in formula (I) of this invention.

[0024] Figure 2 The reaction route for preparing compound B from compound A in Example 1 is shown.

[0025] Figure 3 The reaction route for preparing compound D by coupling compound B and compound C in Example 1 is shown.

[0026] Figure 4 The reaction route for preparing compound E from compound D in Example 1 is shown.

[0027] Figure 5 The reaction route for preparing DTzBT-1 by coupling compound E and compound F in Example 1 is shown.

[0028] Figure 6 This is the specific structural formula for DTzBT-1.

[0029] Figure 7 For comparison, the specific structural formula of compound DTBT-1 is shown.

[0030] Figure 8 For comparison, the specific structural formula of compound DTdzBT-1 is shown. Detailed Implementation

[0031] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0032] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0033] Example 1: Preparation of a thiazole-bridged benzothiadiazole high dichroism dye DTzBT-1: Step 1: As Figure 2 As shown, 40 g of compound A and 400 g of tetrahydrofuran were added to a three-necked flask, and the mixture was cooled to approximately [temperature missing] under nitrogen protection. 65 °C. Add a 2.5 M n-butyllithium solution (68 mL volume) dropwise, controlling the system temperature to not exceed [temperature value missing] during the addition process. 60℃. After the addition is complete, maintain the temperature for 1.5 h. Then add 60 g of triisopropyl borate, controlling the temperature during the addition process to approximately [temperature missing]. The reaction was carried out at 60 °C for 2 h after the addition was complete. After the reaction was completed, the temperature was allowed to rise naturally to room temperature. 2 M dilute hydrochloric acid was added to adjust the pH to 5 or 6. After stirring for 5 min, the mixture was separated. The aqueous phase was extracted with ethyl acetate, and the organic phases were combined and dried over anhydrous sodium sulfate. After filtration, the filtrate was concentrated until no droplets remained. 100 g of petroleum ether was added, and the mixture was stirred at room temperature for 3 h. The mixture was then filtered, and the filter cake was washed with petroleum ether. The mixture was dried at 40 °C to constant weight to give 24 g of compound B, with a yield of 70.5%.

[0034] Step 2: As Figure 3As shown, 24 g of compound B, 20.4 g of compound C, 240 g of tetrahydrofuran, 200 g of a 20% potassium carbonate aqueous solution, and 0.1 g of palladium catalyst were added sequentially to a three-necked flask. After nitrogen purging, the mixture was heated to reflux for 12 h. After the reaction of the starting materials was monitored by thin-layer chromatography until complete, the system was cooled to room temperature, 200 g of water was added, and then 200 g of ethyl acetate was added for extraction. The organic phases were separated, combined, dried, and concentrated until no droplets remained. 50 g of petroleum ether was added for dispersion, and the mixture was passed through a rapid silica gel column, eluted with petroleum ether. The product was collected and concentrated under reduced pressure to give 22.7 g of a colorless oily liquid compound D, with a yield of 80%.

[0035] Step 3: As Figure 4 As shown, 22 g of compound D and 250 g of tetrahydrofuran were added to a three-necked flask, and the mixture was cooled to approximately [temperature missing] under nitrogen protection. 65 °C. Add a 2.5 M, 37 mL n-butyllithium solution dropwise, controlling the temperature not to exceed [temperature value missing] during the addition process. 60 ℃. After the addition was complete, the reaction was maintained at this temperature for 1.5 h. Then, 33 g of triisopropyl borate was added dropwise, with the temperature controlled at approximately [temperature missing] during the addition process. The reaction was carried out at 60 °C for 2 h after the addition was complete. After the reaction was completed, the temperature was allowed to rise naturally to room temperature. 2 M dilute hydrochloric acid was added to adjust the pH to 5-6. After stirring for 5 min, the mixture was separated. The aqueous phase was extracted with ethyl acetate, and the organic phases were combined and dried over anhydrous sodium sulfate. After filtration, the filtrate was concentrated until no droplets remained. 50 g of petroleum ether was added and the mixture was stirred at room temperature for 2 h. The mixture was then filtered and the filter cake was washed with petroleum ether. The mixture was dried at 40 °C to constant weight to give 17 g of compound E, with a yield of 65.2%.

[0036] Step 4: As Figure 5 As shown, 17 g of compound E, 6.7 g of compound F, 140 g of tetrahydrofuran, 80 g of a 20% potassium carbonate aqueous solution, and 0.1 g of palladium catalyst were added sequentially to a three-necked flask. After nitrogen purging, the mixture was heated to reflux for 12 h. After the reaction of the starting materials was monitored by thin-layer chromatography until complete, the system was cooled to room temperature, 300 g of water was added, the mixture was filtered and washed with methanol, and dried at 70 °C to obtain the crude product. The crude product was added to 200 g of tetrahydrofuran, heated to 60 °C and stirred for 1 h until completely dissolved, cooled to 40 °C and filtered through silica gel. The filtrate was concentrated to approximately 20 g. The concentrated solution was heated to 60 °C and stirred for 1 h, 50 g of methanol was added, and the mixture was slurried at 50 °C for 2 h. After cooling to room temperature, the mixture was filtered, the filter cake was washed with methanol, and dried at 65 °C to constant weight to obtain DTzBT-18.6 g, with a yield of 60.4%.

[0037] Example 2: Compound C (2-bromothiazole) was replaced with compound G (2-bromothiophene), while the remaining steps, methods, parameters, and starting materials were the same as in Example 1, yielding 5.6 g of DTBT-1 in 64% yield. The structural formula of DTBT-1 is shown below. Figure 7 As shown.

[0038] Example 3: Compound C (2-bromothiazole) was replaced with compound H (2-bromo-1,3,4-thiadiazole), and the remaining steps, methods, parameters and raw materials were the same as in Example 1. Finally, 5.1 g of DTdzBT-1 was obtained, with a yield of 62%.

[0039] Application Examples: The dichroic dyes obtained in Examples 1-3 were respectively added to the liquid crystal host material to form guest-host liquid crystal compositions. Details are shown in the table below: Components content Remark Nematic liquid crystal matrix 97.5~98.5% Transtop conventional nematic liquid crystal The present invention relates to a dichroic dye (DTzBT-1 / DTBT-1 / DTdzBT-1). 0.5~2.0% Preferred 1.6wt% Light stabilizer (UV-327) 0.3~0.5% Optional, improves weather resistance The host-guest liquid crystal composition was prepared according to the table above and tested using the following method: Test conditions: Test box: 9μm liquid crystal cell; Wavelength: 550nm (center of visible light); Temperature: 25℃; Comparison samples: commercially available azo dye Azo-1, anthraquinone dye Anq-1, and existing benzothiadiazole dye BTD-0.

[0040] The test results are shown in the table below: dye Dichroism ratio D (550nm) Solubility (in liquid crystals, wt%) Photostability (500h@365nm, residual rate) Absorption peak (nm) Contrast ratio (9μm box) Azo-1 (azo) 6.2 1.8 72% 530 14:1 Anq-1 (anthraquinone) 5.1 0.4 94% 570 11:1 DTBT-1 (This invention) 6.5 0.9 92% 530 13:1 DTzBT-1 (This invention) 7.8 1.4 94% 550 18:1 DTdzBT-1 (This invention) 8.1 1.7 95% 575 20:1 The data in the table above shows that the dye of this invention has a dichroism ratio ≥7.8, solubility ≥1.4wt%, photostability ≥92%, and contrast ratio ≥18:1, all of which are superior to existing nitrogen dyes Azo-1, anthraquinone dye Anq-1, and existing benzothiadiazole dye BTD-0. This invention replaces the thiophene bridging unit with a thiazole bridging unit, utilizing the electronegativity of the N atom in the thiazole ring to form intramolecular S…N weak hydrogen bonds, locking the conjugated framework planarity, and simultaneously enhancing the DA conjugation effect. This achieves a simultaneous improvement in four core performance indicators: dichroism ratio, extinction coefficient, photothermal stability, and liquid crystal compatibility. All performance indicators meet or exceed the application requirements of high-end guest / host displays and intelligent dimming films. Furthermore, the preparation process is environmentally friendly, easy to scale up, and has good industrialization prospects.

[0041] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A thiazole-bridged bibenzothiadiazole high dichroism dye, characterized in that, The structure of the dichroic dye compound is shown in formula (I): Formula (I) Wherein, X, Y, and Z are each independently selected from O, S, or Se; M, L, W, T, U, and V are each independently selected from C or N, and the bridged heteroaromatic rings formed by W, T, and Z, as well as the bridged heteroaromatic rings formed by U, V, and Y, each contain at least one C and one N; R and Q are each independently selected from F, Cl, or CN; K and P are each independently selected from methylene, oxygen atom, N-alkyl linker, or ester linker; n is an integer from 1 to 20; and the terminal hydrocarbon groups in formula (I) are each independently a straight-chain alkyl, branched alkyl, or cyclic alkyl.

2. The thiazole-bridged benzothiadiazole high dichroism dye according to claim 1, characterized in that, The bridged heteroaromatic ring is a thiazole ring. The two sides of the benzothiadiazole core in formula (I) are connected to substituted phenyl groups through the thiazole ring to form a donor-acceptor-donor linear conjugated structure.

3. The thiazole-bridged benzothiadiazole high dichroism dye according to claim 2, characterized in that, The nitrogen atom in the thiazole ring is oriented toward the adjacent sulfur-containing heteroaromatic structure.

4. A method for preparing a thiazole-bridged benzothiadiazole-based high dichroism dye, characterized in that, Includes the following steps: Step (1): Add a haloalkoxy-substituted aromatic compound to a solvent, cool it, metallize it with an organolithium reagent, and then react it with a borate ester to obtain an arylboronic acid intermediate. Step (2): The arylboronic acid intermediate prepared in step (1) is coupled with halothiazole in the presence of palladium catalyst and base to obtain thiazole-bridged aromatic intermediate; Step (3): The thiazole-bridged aromatic intermediate obtained in step (2) is metallized with an organolithium reagent and then reacted with a borate ester to obtain the thiazole-bridged arylboronic acid intermediate. Step (4): The thiazole-bridged arylboronic acid intermediate obtained in step (3) is coupled with a dihalobenzothiadiazole acceptor compound in the presence of a palladium catalyst and a base to obtain the dichroic dye compound.

5. The method for preparing a thiazole-bridged benzothiadiazole high dichroism dye according to claim 4, characterized in that, In steps (1) and (3), the organolithium reagent is n-butyllithium; the borate ester is triisopropyl borate; the solvent is tetrahydrofuran; and the metallization reaction temperature is... 65 ℃.

6. The method for preparing a thiazole-bridged benzothiadiazole high dichroism dye according to claim 4, characterized in that, In step (1), the molar ratio of the haloalkoxy-substituted aromatic compound to the organolithium reagent is 1:1; the molar ratio of the haloalkoxy-substituted aromatic compound to the borate ester is 1:2; and the mass ratio of the haloalkoxy-substituted aromatic compound to tetrahydrofuran is 1:

10.

7. The method for preparing a thiazole-bridged benzothiadiazole high dichroism dye according to claim 4, characterized in that, In step (2), the palladium catalyst is bis(triphenylphosphine)palladium(II) dichloride; in step (4), the palladium catalyst is tetratriphenylphosphine palladium, the base is a 20% potassium carbonate aqueous solution; the molar ratio of the arylboronic acid intermediate to potassium carbonate is 1:2.

5.

8. The method for preparing a thiazole-bridged benzothiadiazole high dichroism dye according to claim 4, characterized in that, In step (2), the molar ratio of the arylboronic acid intermediate to the halothiazole is 1:1.1; the molar ratio of the arylboronic acid intermediate to bis(triphenylphosphine)palladium(II) dichloride is 1:0.

001.

9. The method for preparing a thiazole-bridged benzothiadiazole high dichroism dye according to claim 4, characterized in that, In step (4), the molar ratio of the thiazole-bridged arylboronic acid intermediate to the dihalobenzothiadiazole acceptor compound is 2.5:1; the molar ratio of the thiazole-bridged arylboronic acid intermediate to potassium carbonate is 1:2; and the mass ratio of the thiazole-bridged arylboronic acid intermediate to tetrahydrofuran is 1:8.

2.

10. The application of a thiazole-bridged benzothiadiazole high dichroism dye, characterized in that, The dichroic dye is dispersed as a guest dye in the nematic liquid crystal matrix to prepare a guest-host liquid crystal composition.

Images