A fluorinated benzodipyrrole liquid crystal compound and its preparation method

Abstract

This invention belongs to the field of liquid crystal materials technology, specifically relating to a fluorinated benzo[a]pyrrole liquid crystal compound and its preparation method. This invention utilizes the benzo[a]pyrrole ring as a crystallizing unit in a polar aromatic heterocyclic liquid crystal monomer and provides a method for preparing such polar aromatic heterocyclic liquid crystal monomers. This invention uses 2,5-difluoro-1,4-diphenylamine as a raw material and performs a Bischler-indole synthesis reaction to obtain such polar aromatic heterocyclic liquid crystal monomers. The operation is simple, and the product yield and purity are high. These polar aromatic heterocyclic liquid crystal monomers are nematic liquid crystal compounds and can be used in special liquid crystal materials.

Description

Technical Field

[0001] This invention belongs to the field of liquid crystal material technology, specifically relating to a fluorinated benzodipyrrole liquid crystal compound and its preparation method. Background Technology

[0002] With the rapid development of liquid crystal displays (LCDs), liquid crystal materials have been extensively studied. Among the many research areas, polar aromatic heterocyclic liquid crystal materials are one of the important areas of liquid crystal research. The crystallizing unit is a rigid part in the molecular structure of a liquid crystal material, which allows the liquid crystal material to maintain an ordered arrangement under specific conditions, forming a liquid crystal phase. This rigid part plays a core role in the molecular structure, maintaining the stability of the liquid crystal material and influencing its physical and chemical properties. Polar aromatic heterocyclic compounds, due to their polar heteroatoms, can change the molecular polarity. In the field of liquid crystal material technology, benzopyrrole rings, as important substituents of crystallizing units, can change the phase transition temperature range, electrical anisotropy, and optical anisotropy of liquid crystal molecules, thereby functionally modifying liquid crystal materials. However, polar aromatic heterocyclic liquid crystal monomers with benzopyrrole rings as crystallizing units have been rarely studied, and the performance of these liquid crystal compounds as liquid crystal monomers remains unknown. Summary of the Invention

[0003] The purpose of this invention is to provide a class of polar aromatic heterocyclic liquid crystal monomers with benzopyrrole rings as crystallizing units.

[0004] To achieve the above objectives, the present invention provides a fluorinated benzodipyrrole liquid crystal compound and a method for preparing the same to meet this need in the field.

[0005] On one hand, the present invention relates to a fluorinated benzodipyrrole liquid crystal compound, the structure of which is shown in Formula I.

[0006]

[0007] Wherein, R represents a C2-5 straight-chain alkyl group.

[0008] On the other hand, the present invention relates to a method for preparing a fluorinated benzodipyrrole liquid crystal compound, comprising: using 2,5-difluoro-1,4-diphenylamine, a base, and a compound of formula II as raw materials, performing a Bischler–Möhlau indole synthesis reaction to obtain the fluorinated benzodipyrrole liquid crystal compound.

[0009]

[0010] Furthermore, the method for preparing the fluorinated benzodipyrrole liquid crystal compound provided by the present invention includes: adding 2,5-difluoro-1,4-diphenylamine, a base, and the compound shown in Formula II to ethanol, stirring, and heating to react, to obtain the compound shown in Formula III;

[0011]

[0012] The compound shown in Formula III was mixed with a solvent and reacted under microwave to obtain the compound shown in Formula I.

[0013] Furthermore, in the method for preparing the fluorinated benzodipyrrole liquid crystal compound provided by the present invention, the solvent is selected from DMAC, DMF, and DMSO.

[0014] Furthermore, in the method for preparing the fluorinated benzodipyrrole liquid crystal compound provided by the present invention, the reaction temperature for obtaining the compound shown in Formula III is 50-78°C, and the reaction time is 4-10 h.

[0015] The reaction temperature for obtaining the compound shown in Formula I is 100–140 °C, and the reaction time is 10–60 min.

[0016] Furthermore, in the method for preparing the fluorinated benzodipyrrole liquid crystal compound provided by the present invention, the molar ratio of 2,5-difluoro-1,4-diphenylamine to the base is 1:2 to 4;

[0017] The molar ratio of 2,5-difluoro-1,4-diphenylamine to the compound shown in Formula II is 1:2.

[0018] Furthermore, in the preparation method of the fluorinated benzodipyrrole liquid crystal compound provided by the present invention, the alkali is selected from K2CO3, Na2CO3, sodium tert-butoxide, and potassium tert-butoxide.

[0019] On the other hand, the present invention relates to a liquid crystal composition comprising at least one of the above-mentioned fluorinated benzodipyrrole liquid crystal compounds.

[0020] On the other hand, the present invention relates to the application of the above-mentioned fluorinated benzodipyrrole liquid crystal compound in the preparation of liquid crystal display materials or electro-optical display materials or liquid crystal displays.

[0021] On the other hand, the present invention relates to liquid crystal display materials or optical display materials or liquid crystal displays that are prepared by comprising the above-mentioned fluorinated benzodipyrrole liquid crystal compound.

[0022] Compared with the prior art, the present invention has the following beneficial effects or advantages:

[0023] This invention provides a class of liquid crystal compounds using bisbenzopyrrole as the crystallizing unit, alkyl chains as flexible groups, and fluorine atoms as lateral substituents. These compounds exhibit a liquid crystal state, displaying a nematic phase, and can be used in specialty liquid crystal materials. This invention also provides a simple method for preparing these compounds, resulting in high product yield and purity. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The image shows the H-NMR spectrum of the liquid crystal compound prepared in Example 1.

[0026] Figure 2 This is a differential scanning calorimetry (DSC) curve of the liquid crystal compound prepared in Example 1.

[0027] Figure 3 The image shows the schlieren texture of the liquid crystal compound prepared in Example 1 at a temperature of 96°C during the heating process.

[0028] Figure 4 The image shows the schlieren texture of the liquid crystal compound prepared in Example 1 at a temperature of 98°C during the heating process.

[0029] Figure 5 The image shows the H-NMR spectrum of the liquid crystal compound obtained in Example 2.

[0030] Figure 6 The H-NMR spectrum of the liquid crystal compound prepared in Example 3. Detailed Implementation

[0031] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0032] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below in conjunction with specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention.

[0033] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0034] This invention provides the reaction pathway of the compound represented by Formula I.

[0035]

[0036] Wherein, R represents a C2-5 straight-chain alkyl group.

[0037] The reaction pathway of the compound represented by Formula I is as follows:

[0038]

[0039]

[0040] Example 1

[0041] This embodiment provides a method for preparing 4,8-difluoro-2,6-bis(4-propylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole, where R in the compound corresponding to Formula I represents a C3 straight-chain alkyl group, and its structural formula is shown below:

[0042]

[0043] (1) Preparation of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-propylcyclohexyl)ethane-1-one, the raw materials used and their preparation methods are as follows:

[0044]

[0045] 49.4 g of 2-bromo-1-(4-propylcyclohexyl)ethane-1-one, 41.4 g of potassium carbonate, and 14.4 g of 2,5-difluoro-1,4-diphenylamine were added to 500 mL of ethanol, stirred, and reacted at 70 °C for 6 h. After the reaction was complete, the mixture was filtered and recrystallized to prepare 39.5 g of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-ethylcyclohexyl)ethane-1-one), with a yield of 83% and a purity of 97.8%.

[0046] (2) Preparation of 4,8-difluoro-2,6-bis(4-propylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole, the raw materials used and their preparation methods are as follows:

[0047]

[0048] 23.8 g of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-propylcyclohexyl)ethane-1-one) was added to 47 mL of DMF and microwaved at 120 °C for 30 min. The mixture was then recrystallized with 238 mL of petroleum ether to prepare 14.8 g of 4,8-difluoro-2,6-bis(4-propylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole. Yield: 63%, Purity: 99.3%. 1 H-NMR (CDCl3, 300MHz) is attached. Figure 1 As shown.

[0049] The differential scanning calorimetry (DSC) curve of 4,8-difluoro-2,6-bis(4-propylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole is shown in Figure 1. Figure 2 As shown.

[0050] The liquid crystal schlieren texture pattern at a temperature of 96℃ during the heating process is as follows: Figure 3 As shown.

[0051] The liquid crystal schlieren texture pattern at a temperature of 98℃ during the heating process is as follows: Figure 4 As shown.

[0052] The spectrum obtained from the differential scanning spectroscopy test reflects the phase transition range of the liquid crystal and that it belongs to the nematic liquid crystal. This schlieren texture is further evidence of the nematic liquid crystal.

[0053] Example 2

[0054] This embodiment provides a method for preparing 4,8-difluoro-2,6-bis(4-pentylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole, where R in the compound corresponding to Formula I represents a C5 straight-chain alkyl group, and its structural formula is shown below:

[0055]

[0056] (1) Preparation of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-pentylcyclohexyl)ethane-1-one, the raw materials used and the preparation method are as follows:

[0057]

[0058] 55 g of 2-bromo-1-(4-pentylcyclohexyl)ethane-1-one, 42.4 g of sodium carbonate, and 14.4 g of 2,5-difluoro-1,4-diphenylamine were added to 500 mL of ethanol, stirred, and reacted at 78 °C for 5 h. After the reaction was complete, the mixture was filtered and recrystallized to prepare 44.7 g of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-ethylcyclohexyl)ethane-1-one), with a yield of 84% and a purity of 98.4%.

[0059] (2) Preparation of 4,8-difluoro-2,6-bis(4-pentylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole, the raw materials used and their preparation methods are as follows:

[0060]

[0061] 26.6 g of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-pentylcyclohexyl)ethane-1-one was microwaved at 140 °C for 20 min using 54 mL of DMAC, and then recrystallized with 266 mL of petroleum ether to prepare 17.6 g of 4,8-difluoro-2,6-bis(4-pentylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole. Yield: 67%, Purity: 99.1%. 1H-NMR (CDCl3, 300MHz) See attached. Figure 5 .

[0062] Example 3

[0063] This embodiment provides a method for preparing 4,8-difluoro-2,6-bis(4-pentylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole, where R in the compound corresponding to Formula I represents a C2 straight-chain alkyl group, and its structural formula is shown below:

[0064]

[0065] (1) Preparation of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-pentylcyclohexyl)ethane-1-one, the raw materials used and the preparation method are as follows:

[0066]

[0067] 46.4 g of 2-bromo-1-(4-ethylcyclohexyl)ethane-1-one, 42.4 g of sodium carbonate, and 14.4 g of 2,5-difluoro-1,4-diphenylamine were added to 500 mL of ethanol, stirred, and reacted at 78 °C for 5 h. After the reaction was complete, the mixture was filtered and recrystallized to prepare 36.3 g of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-ethylcyclohexyl)ethane-1-one), with a yield of 80.9% and a purity of 98.4%.

[0068] (2) Preparation of 4,8-difluoro-2,6-bis(4-ethylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole, the raw materials used and their preparation methods are as follows:

[0069]

[0070] 22.4 g of 2,2'-((2,5-difluoro-1,4-phenylene)bis(azadiyl))bis(1-(4-ethylcyclohexyl)ethane-1-one) was microwaved at 140 °C for 30 min using 54 mL of DMAC, and then recrystallized with 266 mL of petroleum ether to prepare 17.6 g of 4,8-difluoro-2,6-bis(4-ethylcyclohexyl)-1,5-dihydropyrrolo[2,3-f]indole. Yield: 67%, Purity: 99.1%. 1 H-NMR (CDCl3, 300MHz) See attached. Figure 6 .

[0071] As described above, the present invention can be well implemented. The above embodiments are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, all changes and improvements made by those skilled in the art to the technical solutions of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A fluorinated benzodipyrrole liquid crystal compound, characterized in that, The structure is shown in Equation I. Wherein, R represents a C2-5 straight-chain alkyl group.

2. The method for preparing the fluorinated benzodipyrrole liquid crystal compound according to claim 1, characterized in that, include: 2,5-Difluoro-1,4-diphenylamine, a base, and the compound shown in Formula II were added to ethanol, stirred, and heated to react, thus obtaining the compound shown in Formula III. The compound shown in Formula III was mixed with a solvent and reacted under microwave to obtain the compound shown in Formula I. The reaction temperature for obtaining the compound shown in Formula III is 50–78 °C, and the reaction time is 4–10 h. The reaction temperature for obtaining the compound shown in Formula I is 100–140 °C, and the reaction time is 10–60 min.

3. The method for preparing the fluorinated benzodipyrrole liquid crystal compound according to claim 2, characterized in that, The solvent is selected from DMAC, DMF, and DMSO.

4. The method for preparing the fluorinated benzodipyrrole liquid crystal compound according to claim 2, characterized in that, The molar ratio of 2,5-difluoro-1,4-diphenylamine to the base is 1:2 to 4; The molar ratio of 2,5-difluoro-1,4-diphenylamine to the compound shown in Formula II is 1:

2.

5. The method for preparing the fluorinated benzodipyrrole liquid crystal compound according to claim 2, characterized in that, The alkali is selected from K2CO3, Na2CO3, sodium tert-butoxide, and potassium tert-butoxide.

6. A liquid crystal composition, characterized in that, It includes at least one compound from the fluorinated benzodipyrrole liquid crystal compound of claim 1.

7. The use of the fluorinated benzodipyrrole liquid crystal compound of claim 1 in the preparation of liquid crystal display materials, electro-optical display materials, or liquid crystal displays.

8. A liquid crystal display material or optical display material or liquid crystal display comprising the fluorinated benzodipyrrole liquid crystal compound of claim 1.

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