Novel fluorane compound and preparation method thereof

Abstract

The invention relates to a novel fluorane compound and a preparation method thereof, belongs to the technical field of thermosensitive dyes, and is used for solving at least one of the problems of higher color development temperature, non-bright color after color development, low color density, complex synthesis method, low purity and the like of pink dyes in the prior art. The novel fluorane compound which has a conjugated structure with the parent nucleus is synthesized, the color development temperature of the compound is relatively low, color development can be performed when the temperature reaches about 70 DEG C, the color development capability of the fluorane parent nucleus is enhanced, the fluorane parent nucleus is pink in color development, the color is brighter after color development, and the color density value is higher.

Description

Technical Field

[0001] The invention relates to the technical field of thermosensitive dyes, and in particular to a novel fluorane compound and a preparation method thereof. Background Art

[0002] Fluoran compounds are widely used in thermal and pressure-sensitive printing due to the special nature of their lactone ring structure. The color-developing raw material is a closed-loop lactone ring, which is usually hidden or non-color-developing. After the lactone ring is destroyed and contacts the developer, it will show another color in the visible light range, thus realizing the function of printing text and patterns of different colors.

[0003] The diversity of colors of fluorane thermosensitive materials mainly comes from the different substituents on the fluorane parent core, as shown in formula (III):

[0004]

[0005] Among them, the substituents of R1 to R8 are completely different or partially the same structure, and the lactone ring opens to show different colors after contacting the developer. The existing pink thermosensitive materials have high color development temperature, dull color after color development, low color density, complex synthesis method, and low purity. Summary of the invention

[0006] In view of the above analysis, the present invention aims to provide a novel fluorane compound and a preparation method thereof, which is used to solve at least one of the problems of the prior art, namely, high color development temperature of pink dyes, dull color after development, low color density, complex synthesis method, and low purity.

[0007] In the first aspect, the present invention provides a novel fluorane compound, the compound having a structural formula as shown in formula (I) or formula (II), and a specific structural formula as follows:

[0008]

[0009] In a second aspect, the present invention provides a method for preparing a novel fluorane compound, comprising the following steps:

[0010] (1) reacting 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid with 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol under strongly acidic conditions, and then cooling to obtain a reaction solution;

[0011] (2) adding the reaction solution into water or alkaline water, then adding an organic solvent, separating the layers, and concentrating the organic layer to obtain a concentrate;

[0012] (3) adding a crystallization agent to dissolve the concentrate, cooling and crystallizing, filtering, and drying to obtain the novel fluorane compound.

[0013] Furthermore, in step (1), the molar ratio of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid to 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol is 1:1-2.

[0014] Furthermore, in step (1), the acid is sulfuric acid, methanesulfonic acid or nitric acid.

[0015] Furthermore, in step (1), the reaction temperature is 60-160° C., and the reaction time is 0.5-6 h.

[0016] Furthermore, in step (2), the organic solvent is one or more of ethyl acetate, dichloromethane or dichloroethane.

[0017] Furthermore, in step (2), the alkaline water includes but is not limited to strong inorganic alkaline solutions of sodium hydroxide and potassium hydroxide.

[0018] Furthermore, in step (3), the crystallization agent is one or more of methanol, ethanol, isopropanol or toluene.

[0019] Furthermore, in step (3), the mass ratio of the concentrate to the crystallization agent is 1:5-20.

[0020] In a third aspect, the present invention provides a thermosensitive dye, comprising the fluorane compound.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0022] (1) The present invention synthesizes a novel fluorane compound having a conjugated structure with a fluorescent mother core. The color development temperature of the compound is relatively low, and the color can be developed at a temperature of about 70°C, thereby enhancing the color development ability of the fluorane mother core. The color is pink, and the color after development is brighter and the color density value is higher. The color density value at 160°C is 0.96-1.0.

[0023] (2) The preparation method of the novel fluorane compound of the present invention is simple, the production cost is low, and the purity of the product can reach above 97.1%, which is suitable for large-scale industrial production.

[0024] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description. DETAILED DESCRIPTION

[0025] A specific embodiment of the present invention discloses a novel fluorane compound, the compound has a structural formula as shown in formula (I) or formula (II), and the specific structural formula is as follows:

[0026]

[0027] Compared with the prior art, the present invention discloses a novel fluorane compound having a conjugated structure with a fluorescent mother nucleus. The present invention synthesizes a novel fluorane compound having a conjugated structure with a fluorescent mother nucleus. The color development temperature of the compound is relatively low and the color can be developed at a temperature of about 70°C, thereby enhancing the color development ability of the fluorane mother nucleus and developing a pink color. After color development, the color is brighter and the color density is higher.

[0028] In the structure of formula (I) of the present invention, the two bridge carbons C13 and C14 form a fluorane compound with a large conjugated structure, and in the structure of formula (II), the two bridge carbons C12 and C13 form a fluorane compound with a large conjugated structure.

[0029] The spectral absorption and color development characteristics of the dye are determined by the combined effects of the molecular structure with the fluorane structure as the parent core, the length and symmetry of the conjugated system, the polar groups within the molecule, the coplanarity and spatial hindrance of the molecule. The presence of the diethylamine group in the parent core structure has the above-mentioned properties, thereby affecting the color development temperature and effect of the dye.

[0030] The presence of conjugated structure and the increase in the number of conjugated double bonds have a significant impact on the color of the substance. By affecting the mobility of the electron cloud and reducing the energy level difference between molecules, the conjugated structure enables the substance to absorb and transmit more light energy, thereby affecting the color performance of the substance; at the same time, the color of the conjugated system is also affected by certain functional groups and substituents. The introduction of certain substituents can change the electron cloud density distribution and spatial configuration in the conjugated system, thereby affecting the light absorption capacity of the system; therefore, different substituents can lead to different color changes, and the presence of methoxynaphthalene rings increases the number of conjugated double bonds of the parent nucleus, while the electron donation effect of the methoxy group makes the electron cloud density on the conjugated structure higher, thereby making the color of the dye relatively more vivid. The color development temperature of the compound prepared by the present invention is 69.3-70.3°C, and the color density value at 160°C is 0.96-1.0.

[0031] Another specific embodiment of the present invention discloses a method for preparing the novel fluorane compound, comprising the following steps:

[0032] (1) reacting 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid with 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol under strongly acidic conditions, and then cooling to obtain a reaction solution;

[0033] (2) adding the reaction solution into water or alkaline water, then adding an organic solvent, separating the layers, and concentrating the organic layer to obtain a concentrate;

[0034] (3) adding a crystallization agent to dissolve the concentrate, cooling and crystallizing, filtering, and drying to obtain the novel fluorane compound.

[0035] The chemical equation of the above reaction in the present invention is as follows:

[0036]

[0037] In a specific embodiment, in step (1), the molar ratio of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid to 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol is 1:1-2. For example, the molar ratio is 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2.

[0038] In a specific embodiment, further, in step (1), the acid is sulfuric acid, methanesulfonic acid, or nitric acid.

[0039] In a specific embodiment, in step (1), the reaction temperature is 60-160°C, and the reaction time is 0.5-6h. For example, the reaction temperature is 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, and the reaction time is 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h.

[0040] In a specific embodiment, in step (2), the organic solvent is one or more of ethyl acetate, dichloromethane or dichloroethane.

[0041] In a specific embodiment, in step (2), the alkaline water includes but is not limited to strong inorganic alkaline solutions such as sodium hydroxide and potassium hydroxide. Exemplarily, the mass fraction of sodium hydroxide in the sodium hydroxide solution is 10%.

[0042] In a preferred embodiment, in step (2), the layers are specifically divided into an aqueous layer and an organic solvent layer. The aqueous layer needs to be extracted with an organic solvent at least once until the color of the organic solvent layer becomes lighter. The organic solvent layers are combined each time and extracted with clean water until the pH value of the aqueous layer is 7 to 8.

[0043] In a specific embodiment, in step (3), the crystallization agent is one or more of methanol, ethanol, isopropanol or toluene.

[0044] In a specific embodiment, in step (3), the mass ratio of the concentrate to the crystallization agent is 1:5-20. For example, the mass ratio is 1:5, 1:7, 1:9, 1:11, 1:13, 1:15, 1:17, 1:19, 1:20.

[0045] In a specific embodiment, in step (3), the temperature for cooling and crystallization is -15 to 25°C. For example, the temperature is -15°C, -10°C, -5°C, 0°C, 5°C, 10°C, 15°C, 20°C, or 25°C.

[0046] The purity of the compound prepared by the method of the invention is greater than 97.1%, and the yield is greater than 25.4%.

[0047] In a third aspect, the present invention provides a thermosensitive dye, comprising the fluorane compound.

[0048] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0049] Example 1

[0050] The present embodiment provides a method for preparing a fluorane compound represented by formula (I), which is specifically as follows:

[0051] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 13.5 g of 8-methoxynaphthalene-1-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 80° C. for 3 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0052] (2) adding 60 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of dichloroethane, stirring for 10 min, transferring the solution to a separatory funnel, standing to separate the layers, and extracting the aqueous layer with dichloroethane twice, 200 ml / time, until the color of the dichloroethane layer becomes lighter, combining the dichloroethane, extracting the dichloroethane with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0053] (3) Add 30 g of the concentrate to 150 g of methanol, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -5°C for 3 h, filter and dry to obtain 20.74 g of a light pink solid with a yield of 71.9% and a content of 98.52%.

[0054] The fluorane compounds obtained in this example were subjected to nuclear magnetic resonance testing, and the results were as follows:

[0055] Mp:200.1-201.3℃;1HNMR(400MHz,DMSO)δ8.02(dd,1H),7.72–7.66(m,1H),7.67–7.62(m,1H),7.59–7.52(m,2H),7.50(d d,1H),7.44–7.34(m,2H),7.22(d,1H),6.90(dd,1H),6.67(dd,1H),6.31(d,1H),3.92(s,2H),3.52(q,4H),1.16(t,6H).

[0056] After ultraviolet scanning test, the absorption wavelength of the compound prepared in this example is 518nm, which is in the pink absorption band.

[0057] Example 2

[0058] The present embodiment provides a method for preparing a fluorane compound represented by formula (I), which is specifically as follows:

[0059] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 11.2 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 85° C. for 3 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0060] (2) Add 60 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stir for 10 min, then add 200 ml of dichloroethane, stir for 10 min, transfer the solution to a separatory funnel, let stand to separate the layers, extract the water layer with dichloroethane twice, 200 ml / time, until the color of the dichloroethane layer becomes lighter, combine the dichloroethane, extract the dichloroethane with clean water, measure the pH value of the water layer to be 7-8, and concentrate the dichloroethane layer to dryness under reduced pressure at 45-70° C. to obtain a concentrate;

[0061] (3) Add 30 g of the concentrate to 360 g of methanol, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -5°C for 3 h, filter and dry to obtain 16.24 g of light pink solid with a yield of 56.35% and a content of 99.34%.

[0062] The results of nuclear magnetic resonance and ultraviolet scanning tests on the fluorane compounds obtained in this example are basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0063] Example 3

[0064] The present embodiment provides a method for preparing a fluorane compound represented by formula (I), which is specifically as follows:

[0065] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 13.5 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 90° C. for 3 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0066] (2) adding 60 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of dichloroethane, stirring for 10 min, transferring the solution to a separatory funnel, standing to separate the layers, and extracting the aqueous layer with dichloroethane twice, 200 ml / time, until the color of the dichloroethane layer becomes lighter, combining the dichloroethane, extracting the dichloroethane with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0067] (3) Add 30 g of the concentrate to 450 g of toluene, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -5°C for 3 h, filter and dry to obtain 13.64 g of a light pink solid with a yield of 47.3% and a content of 99.43%.

[0068] The results of nuclear magnetic resonance and ultraviolet scanning tests on the fluorane compounds obtained in this example are basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0069] Example 4

[0070] The present embodiment provides a method for preparing a fluorane compound represented by formula (I), which is specifically as follows:

[0071] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 13.5 g of 8-methoxynaphthalen-1-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 100° C. for 6 h. After the reaction was completed, the temperature was lowered to obtain a reaction solution;

[0072] (2) adding 60 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of dichloroethane, stirring for 10 min, transferring the solution to a separatory funnel, standing to separate the layers, and extracting the aqueous layer with dichloroethane twice, 200 ml / time, until the color of the dichloroethane layer becomes lighter, combining the dichloroethane, extracting the dichloroethane with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0073] (3) Add 30 g of the concentrate to 600 g of toluene, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -5°C for 3 h, filter and dry to obtain 10.58 g of a light pink solid with a yield of 36.71% and a content of 99.85%.

[0074] The results of nuclear magnetic resonance and ultraviolet scanning tests on the fluorane compounds obtained in this example are basically consistent with those in Example 1, and are not listed one by one due to limited space.

[0075] Example 5

[0076] The present embodiment provides a method for preparing a fluorane compound represented by formula (II), which is specifically as follows:

[0077] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 12.8 g of 8-methoxynaphthalene-2-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid aqueous solution (135 g of sulfuric acid was added to 45 g of water) was added, and the mixture was reacted at 80° C. for 5 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0078] (2) adding 100 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of ethyl acetate, stirring for 10 min, transferring the solution to a separatory funnel, standing to separate the layers, and extracting the aqueous layer with ethyl acetate twice, 200 ml / time, until the color of the ethyl acetate layer becomes lighter, combining the ethyl acetate, extracting the ethyl acetate with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the ethyl acetate layer under reduced pressure at 35-70° C. to dryness to obtain a concentrate;

[0079] (3) Add 30 g of the concentrate to 150 g of methanol, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -5°C for 3 h, filter and dry to obtain 13.65 g of light pink solid with a yield of 47.36% and a content of 97.1%.

[0080] The fluorane compounds obtained in this example were subjected to nuclear magnetic resonance testing, and the results were as follows:

[0081] Mp:198.3-199.2℃; 1H-NMR (400MHz, DMSO) δ8.02(dd,1H),7.77(s,1H),7.72–7.66(m,1H),7.64(ddd,1H),7.56(td,1 H),7.52–7.44(m,3H),7.22(d,1H),7.00(dd,1H),6.67(dd,1H),6.31(d,1H),3.95(s,2H),3.52(q,4H),1.16(t,6H).

[0082] After ultraviolet scanning test, the absorption wavelength of the compound prepared in this example is 526nm, which is in the pink absorption band.

[0083] Example 6

[0084] The present embodiment provides a method for preparing a fluorane compound represented by formula (II), which is specifically as follows:

[0085] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 12.8 g of 8-methoxynaphthalene-2-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid solution was added, and the mixture was reacted at 85° C. for 6 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0086] (2) adding 100 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of dichloroethane, stirring for 10 min, transferring the solution to a separatory funnel, standing to separate the layers, and extracting the aqueous layer with dichloroethane twice, 200 ml / time, until the color of the dichloroethane layer becomes lighter, combining the dichloroethane, extracting the dichloroethane with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the dichloroethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0087] (3) Add 30 g of the concentrate to 450 g of toluene, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -15°C for 4 h, filter and dry to obtain 10.28 g of a light pink solid with a yield of 35.32% and a content of 97.8%.

[0088] The results of nuclear magnetic resonance and ultraviolet scanning tests on the fluorane compounds obtained in this example are basically consistent with those in Example 5, and are not listed one by one due to limited space.

[0089] Example 7

[0090] The present embodiment provides a method for preparing a fluorane compound represented by formula (II), which is specifically as follows:

[0091] (1) 20 g of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid and 15.5 g of 8-methoxynaphthalene-2-ol were placed in a 500 ml four-necked bottle, 180 g of a 75% sulfuric acid solution was added, and the mixture was reacted at 90° C. for 8 h. After the reaction was completed, the mixture was cooled to obtain a reaction solution;

[0092] (2) adding 100 ml of 10% sodium hydroxide aqueous solution to the reaction solution, stirring for 10 min, then adding 200 ml of dichloroethane, stirring for 10 min, transferring the solution to a separatory funnel, standing to separate the layers, and extracting the aqueous layer with dichloromethane twice, 200 ml / time, until the color of the dichloromethane layer becomes lighter, combining the dichloromethane, extracting the dichloromethane with clean water, measuring the pH value of the aqueous layer to be 7-8, and concentrating the dichloromethane layer under reduced pressure at 45-70° C. to dryness to obtain a concentrate;

[0093] (3) Add 30 g of the concentrate to 600 g of toluene, heat and reflux for 30 min to completely dissolve the solid, then crystallize at -5°C for 5 h, filter and dry to obtain 7.32 g of a light pink solid with a yield of 25.4% and a content of 99.1%.

[0094] The results of nuclear magnetic resonance and ultraviolet scanning tests on the fluorane compounds obtained in this example are basically consistent with those in Example 5, and are not listed one by one due to limited space.

[0095] Comparative Example 1

[0096] The structural formula of the fluorane compound of this comparative example is as follows:

[0097]

[0098] Test Example 1

[0099] The compounds prepared in Examples 1-7 and Comparative Example 1 were respectively prepared into coating solutions;

[0100] (1) Preparing a first mixed solution: 10.5 g of PVA-205MB, 160 g of ultrapure water, and 70 g of the compound prepared in Examples 1-7 and Comparative Example 1 were mixed to prepare a mixed solution with a mass fraction of 29.1%, and then ground in a wet grinder until the solid particles in the mixed solution had a particle size of 0.8 μm to obtain a first mixed solution;

[0101] (2) preparing a second mixed solution: 12.0 g of PVA-205MB, 168.0 g of ultrapure water, 60.0 g of F-108 (D-8, 4-isopropoxy-4'-hydroxydiphenyl sulfone, color developer), and 0.3 g of coating agent SN-522 were mixed to prepare a mixed solution with a mass fraction of 24.9%, and then ground in a wet grinder until the solid particles in the mixed solution had a particle size of 0.8 μm to obtain a second mixed solution;

[0102] (3) Preparation of auxiliary agent emulsion: PVA-205MB 0.3g, ultrapure water 12.7g, kaolin 12.0g were mixed to a mixed solution with a mass fraction of 48.0%, and stirred at high speed for later use;

[0103] (4) Coating liquid: 24.0 g of the first mixed liquid, 22.0 g of the second mixed liquid and 25.0 g of the auxiliary agent emulsion were mixed, and mechanically stirred for 30 minutes to obtain a coating liquid.

[0104] Use a coating machine to coat the prepared base paper with a coating of 4.5 g / m 2 The top coating liquid is applied in a coating amount of , and after drying, a top coating layer is formed to obtain thermal paper.

[0105] The thermal papers obtained in Examples 1-7 and Comparative Example 1 were subjected to thermal color development tests at 70-160° C., and the colors after color development were all pink. The color development temperature and color density values ​​at 160° C. are shown in Table 1.

[0106] Table 1

[0107]

[0108] It can be seen from the above table that the compound of Comparative Example 1 has a higher color development temperature and a lower color density than the compound of the present application. This is because there is a dibutylamino structure and a nitrogen heterocyclic structure on the parent core in Comparative Example 1, and the color development temperature is increased and the color density is reduced compared with the compound of the present invention; the reason is that the nitrogen heterocyclic ring and the benzene ring are connected by a σ bond, and the σ bond can rotate, so that the plane of the nitrogen heterocyclic ring and the benzene ring are not on the same plane, resulting in a decrease in color density; and the dibutylamino group has more carbon numbers than the diethylamino group, and the melting point of the compound is increased, which in turn affects the color development temperature of the compound.

[0109] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A novel fluorane compound, characterized in that: The compound structural formula is shown in formula (I) or formula (II), and the specific structural formula is as follows:

2. A method for preparing a novel fluorane compound, characterized in that: The steps include: (1) reacting 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid with 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol under strongly acidic conditions, and then cooling to obtain a reaction solution; (2) adding the reaction solution into water or alkaline water, then adding an organic solvent, separating the layers, and concentrating the organic layer to obtain a concentrate; (3) adding a crystallization agent to dissolve the concentrate, cooling and crystallizing, filtering, and drying to obtain the novel fluorane compound.

3. The method for preparing a novel fluorane compound according to claim 2, characterized in that: In step (1), the molar ratio of 2-(3-(diethylamino)-2-hydroxybenzoyl)benzoic acid to 8-methoxynaphthalene-1-ol or 8-methoxynaphthalene-2-ol is 1:1-2.

4. The method for preparing a novel fluorane compound according to claim 2, characterized in that: In step (1), the acid is sulfuric acid, methanesulfonic acid or nitric acid.

5. The method for preparing a novel fluorane compound according to claim 2, characterized in that: In step (1), the reaction temperature is 60-160° C. and the reaction time is 0.5-6 h.

6. A method for preparing a novel fluorane compound according to any one of claims 2 to 5, characterized in that: In step (2), the organic solvent is one or more of ethyl acetate, dichloromethane or dichloroethane.

7. A method for preparing a novel fluorane compound according to any one of claims 2 to 5, characterized in that: In step (2), the alkaline water includes but is not limited to sodium hydroxide and potassium hydroxide strong inorganic alkaline solutions.

8. The method for preparing a novel fluorane compound according to claim 2, characterized in that: In step (3), the crystallization agent is one or more of methanol, ethanol, isopropanol or toluene.

9. The method for preparing a novel fluorane compound according to claim 2, characterized in that: In step (3), the mass ratio of the concentrate to the crystallization agent is 1:5-20.

10. A thermosensitive dye, characterized in that: The invention comprises the compound according to claim 1 or the compound prepared by any one of the methods of claims 2 to 9.

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