A hair dyeing molecule for improving the hair dyeing fastness and the hair antioxidant performance of plant dye molecules, and a synthesis method and application thereof

Abstract

The application discloses a hair dyeing molecule for improving hair dyeing color fastness and hair oxidation resistance performance and a synthesis method thereof. The hair dyeing molecule is prepared by esterification or amidation reaction of a natural pigment molecule with a phenolic hydroxyl group, an alcoholic hydroxyl group, an amino group or an imino group structure and an organic acid containing an alpha, beta-carbon-carbon double bond, so as to obtain a natural pigment molecule derivative with an alpha-carbonyl carbon-carbon double bond structure. The improved pigment molecule is connected to the keratin of the hair through a chemical bond by a thiol click reaction, so that the pigment residence performance is greatly improved, and the color fastness effect is improved.

Description

Technical Field

[0001] This invention belongs to the field of hair product technology, and particularly relates to a hair dye molecule that enhances the color fastness of plant dye molecules and the antioxidant properties of hair, as well as its synthesis method and application. Background Technology

[0002] Plant dyes, as the name suggests, are dyes extracted from plants and used for dyeing fabrics. In the early 20th century, with the advent of chemically synthesized dyes, plant dyes gradually withdrew from the dye market due to their superior dyeing properties, wide variety, and low cost. In recent years, however, with increased environmental awareness, people have begun to recognize the serious harm and damage that chemically synthesized dyes cause to human health and the environment, leading to a renewed interest in plant dyes.

[0003] Plant dyes are a class of molecules that absorb visible light. They possess a large system of conjugated π bonds and typically contain a certain amount of functional groups, including amino, alcoholic, and phenolic hydroxyl groups. For example, hematoxylin is extracted from the heartwood of the hematoxylin tree in tropical regions, and its chemical formula is C2. 16 H 14 O6, whose structure includes a large conjugated system and four phenolic hydroxyl groups and one alcoholic hydroxyl group, is shown in the following structural formula:

[0004]

[0005] In hair dyeing, hematoxylin, as a plant-based hair dye, adheres to the hair surface through physical adsorption. This method results in a short residence time for the dye molecules on the hair, making them susceptible to external environmental influences and leading to low color fastness. This problem is widespread and common to plant-based dyes. Although plant-based dyes are safer and more environmentally friendly, their poor color fastness remains a bottleneck restricting their application in hair dyeing.

[0006] Click chemistry, also known as "dynamic combinatorial chemistry" or "linked chemistry," is a novel modular organic synthesis concept proposed in 2001 by Nobel laureate chemist Sharpless. It aims to synthesize organic compounds rapidly, efficiently, and reliably by assembling small unit molecules, much like "buttoning up" a mortise and tenet. This concept aligns with the era of green synthesis and atom economy, paving an efficient path for constructing functionalized molecules. Today, click chemistry has become a research hotspot in various fields, including medicine, materials science, and chemistry, both domestically and internationally, and has become a paradigm of modern synthetic chemistry. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a hair dye molecule that enhances the color fastness and antioxidant properties of hair, along with its synthesis method and applications. Unlike the physical adsorption of traditional plant-based hair dyes, this invention chemically bonds pigment molecules to the keratin of hair, thereby significantly improving pigment retention and ultimately enhancing color fastness. To achieve this, the technology proposed in this invention requires the external attachment of thiol groups to the hair and the derivatization and modification of the pigment molecules.

[0008] This invention first protects a hair dye molecule that enhances the color fastness of natural pigment molecules and the antioxidant properties of hair. The hair dye molecule is prepared by esterification or amidation of natural pigment molecules with phenolic hydroxyl, alcoholic hydroxyl, amino or imino structures and organic acids with olefin structures containing α-unsaturated bonds, to obtain natural pigment molecule derivatives with α-unsaturated bonds, i.e., hair dye molecules.

[0009] Furthermore, the general structural formula of the hair dye molecule is as follows:

[0010]

[0011] in:

[0012] R1 is a dye molecule group that absorbs visible light;

[0013] R4 is selected from any of the following groups:

[0014]

[0015]

[0016] In group (Ⅰ): R3 is selected from hydrogen atoms and has the general formula C n H 2n+1 The group is a group or carboxyl group with n ≥ 1. Further, the dye molecule group with visible light absorption includes one of the following structures:

[0017]

[0018]

[0019] 3. The hair dye molecule according to any one of claims 1-2, characterized in that the specific structure of the hair dye molecule is any one of the following structures:

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027] A method for synthesizing the hair dye molecule, wherein the method comprises: mixing natural pigment, organic acid and solvent to obtain a mixed solution, stirring and reacting, evaporating the solvent to obtain the hair dye molecule.

[0028] Furthermore, the natural pigment is a molecule having multiple phenolic hydroxyl groups, alcoholic hydroxyl groups, amino groups, or imino groups, where multiple refers to ≥2.

[0029] Furthermore, the natural pigment includes one or more of hematoxylin, betaine, anthocyanin, indigo, malvidin, alizarin, and shikonin; the solvent is acetone.

[0030] Furthermore, the organic acid includes organic acids with an olefin structure containing an α-unsaturated bond.

[0031] Furthermore, the organic acid includes one or more of acrylic acid, methacrylic acid, 3-butenoic acid, 3-pentenoic acid, maleic acid, fumaric acid, and shikimic acid.

[0032] Further, the unit molar ratio of the organic acid to the natural pigment is 2:1-1:1, preferably 1.5:1-1:1, and most preferably 1.25:1; the mass ratio of the total amount of the natural pigment and organic acid to the solvent is 10-50:100, preferably 20-40:100, and most preferably 30:100; the reaction temperature is 40℃-70℃, preferably 40℃-50℃, and most preferably 45℃; the reaction time is 1-6h, preferably 6h.

[0033] A hair dye prepared from the aforementioned hair dyeing molecules.

[0034] Furthermore, the hair dye comprises agent A and agent B; agent A comprises 2-aminoisothiazolidinyl hydrochloride; agent B comprises the hair dye molecule;

[0035] Further, the mass ratio of agent A to agent B is 1:2-2:1; the mass fraction of 2-aminoisothiazolidinyl hydrochloride in agent A is 0.5-2%, and the pH value of agent A is 8-11; the mass fraction of hair dye molecules in agent B is 0.1-5%.

[0036] Further, agent A comprises, by mass percentage, 0.5-2% of 2-aminoisothiazolidinyl hydrochloride, with the remainder being water and / or other components. Other components include one or more of carbomer, hydroxyethyl cellulose, and Kathon.

[0037] Furthermore, agent B, by mass percentage, comprises 0.1-5% hair dye molecules and other components; the other components include polyols and / or an oil phase.

[0038] The beneficial technical effects of this invention are as follows:

[0039] This invention involves reacting hair keratin with reagents such as 2-aminoisothiazolidinyl hydrochloride to infuse a certain amount of free thiol groups into the hair. Simultaneously, natural pigment molecules with phenolic hydroxyl, alcoholic hydroxyl, or amino / imino structures are esterified or amidated to prepare natural pigment molecule derivatives with α-unsaturated bonds in an olefin structure.

[0040] Furthermore, based on the aforementioned modification of hair keratin and natural pigment molecules, this invention endows them with reactivity. Through a click chemical reaction between the α-carbonyl carbon-carbon double bond group of the natural pigment molecule derivative and the thiol group, the natural pigment molecule is covalently linked to the keratin. This significantly improves pigment retention performance, thereby enhancing color fastness. Simultaneously, since natural pigments have antioxidant properties, the method described in this invention also enhances the hair's antioxidant capacity. Attached Figure Description

[0041] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the hematoxylin acrylate prepared in Example 1 of this invention.

[0042] Figure 2 The images shown are fluorescence micrographs obtained by using Rhodamine B to quench the fluorescence before and after treatment with agent A and after staining with agent B, as described in Example 1 of this invention.

[0043] In the figure: a is the pre-thiol hair strand, b is the post-thiol hair strand, and c is after staining.

[0044] Figure 3 These are images showing the hair dyeing effects under different treatment conditions according to the present invention.

[0045] In the figure: a is a hair strand before dyeing, b is hair dyed using Example 1, c is hair dyed using Comparative Example 1, d is hair dyed using Example 1 after washing, and e is hair dyed using Comparative Example 1 after washing.

[0046] Figure 4 The ESR graphs show the antioxidant properties of Application Example 1 and Comparative Example 6 of this invention.

[0047] In the figure: a is application example 1; b is application comparison example 6.

[0048] Figure 5 The nuclear magnetic resonance hydrogen spectrum of anthocyanin methacrylate prepared in Example 2 of this invention.

[0049] Figure 6 The 1H NMR spectrum of anthocyanin fumarate prepared in Example 4 of this invention.

[0050] Figure 7 The 1H NMR spectrum of betaine maleate prepared in Example 5 of this invention.

[0051] Figure 8 The 1H NMR spectrum of betaine acrylate prepared in Example 6 of this invention. Detailed Implementation

[0052] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0053] This invention proposes a method using click chemistry to pre-attach thiol groups to hair and derivatize plant dye molecules, thereby constructing a Michael addition reaction between thiol groups and olefins. Specifically, the technical route proposed in this invention fixes plant dye molecules onto hair in the form of chemical bonds, thereby improving the color fastness of pigment molecules. At the same time, due to the antioxidant properties of natural pigments, the method described in this invention also enhances the antioxidant function of hair.

[0054] The hair dye molecules are obtained by reacting the phenolic hydroxyl, alcoholic hydroxyl, or amino groups of natural pigments with organic acids.

[0055] The hair dye achieves its effect through the reaction of dye molecules with thiol groups. Taking hematoxylin as an example, after esterification with acrylic acid, hematoxylin acrylate is obtained. Through thiol click reaction, the CH2=CH-COO- group in hematoxylin acrylate reacts with the thiol groups pre-attached to the hair shaft to form covalent bonds, thereby improving the retention performance of pigment molecules inside the hair. In addition, hematoxylin has phenolic hydroxyl groups, which can play a good role in anti-oxidation and promote the hair's resistance to ultraviolet radiation.

[0056] When the dye molecule is hematoxylin, the synthetic route of hematoxylin and acrylic acid is as follows:

[0057]

[0058] When the dye molecule is anthocyanin, the synthetic route for modifying anthocyanins by reacting anthocyanins with methacrylic acid is as follows:

[0059]

[0060] The synthetic route for modifying anthocyanins by combining anthocyanins with fumaric acid is as follows:

[0061]

[0062] The synthetic route for modifying betaine from betaine and maleic acid is as follows:

[0063]

[0064] After obtaining the hair dye molecules, the hair dye agent is prepared and the hair dyeing process is carried out.

[0065] The hair dye comprises agent A and agent B; agent A comprises 2-aminoisothiazolidin hydrochloride; agent B comprises the hair dye molecule.

[0066] In one embodiment of the present invention, the mass ratio of agent A to agent B is 1:2; 1:1, 1.5:1 or 2:1; the mass fraction of 2-aminoisothiazoline hydrochloride in agent A is 0.5%, 1%, 1.5% or 2%, and the pH value of agent A is 8, 9, 10 or 11; the mass fraction of hair dye molecules in agent B is 0.1%, 0.5%, 1%, 2%, 3%, 4% or 5%.

[0067] In one embodiment of the invention, agent A comprises, by weight percentage, 0.5%, 1%, 1.5%, or 2% 2-aminoisothiazolidinyl hydrochloride, with the remainder being water and / or other components. Other components include one or more of carbomer, hydroxyethyl cellulose, and Kathon.

[0068] In one embodiment of the present invention, agent B comprises, by weight percentage, 0.1%, 0.5%, 1%, 2%, 3%, 4%, or 5% hair dye molecules and other components; the other components include polyols and / or an oil phase.

[0069] When dyeing hair, first use agent A containing 2-aminoisothiazolidinyl hydrochloride to treat the hair, introducing free thiol groups; then use agent B containing natural pigment modifiers to dye the hair. The specific method is as follows: apply agent A to the hair strands, leave it for 0.25h, 0.4h, or 0.5h, then rinse and blow-dry; then apply agent B to the surface of the hair strands, wrap the hair strands, heat for 0.5h, 0.75h, or 1h, rinse, and blow-dry.

[0070] The hair dye is produced by pre-conjugating thiol groups to the hair, and then using the reaction of these thiol groups with olefins containing α-unsaturated bonds in the modified hair dye molecules to achieve the binding of hair keratin with the dye molecules, thus achieving hair dyeing.

[0071] In one embodiment of the present invention, the pH of agent A is in the range of 8, 9, 10 or 11.

[0072] Using agent A to pre-add thiol groups to the hair, the reaction pathway for thiol group addition to the hair is as follows:

[0073]

[0074] In the formula: R is -CH2CH2CH2CH2 or -CH2CH2CH2NHC=NH. When R is CH2CH2CH2CH2, it corresponds to lysine. When R is CH2CH2CH2NHC=NH, it corresponds to arginine.

[0075] When hair pre-treated with thiol groups is treated with agent B, the reaction pathway by which the dye molecules are chemically bonded to the hair is as follows (taking hematoxylin acrylate as an example):

[0076]

[0077] The present invention will be further described below through examples and other means.

[0078] Examples 1-6

[0079] New hair dye molecules are obtained by modifying natural pigment molecules. The specific modification method is as follows:

[0080] First, natural pigments and organic acids were used as starting materials to modify the natural pigments. This involved dissolving the raw materials in acetone and stirring the mixture to obtain natural pigment derivatives. The specific types of natural pigments, organic acids, raw material ratios, reaction times, and reaction temperatures used in each example differed. Specific experimental conditions were carried out according to Table 1 below. Here, "raw materials" refers to natural pigments and organic acids, and the mass of the natural raw materials is the total mass of the natural pigments and organic acids.

[0081] The structural characteristic spectrum of the modified molecule obtained in Example 1 is shown in the figure. Figure 1 .

[0082] Comparative Examples 1-4

[0083] New hair dye molecules are obtained by modifying natural pigment molecules. The specific method is as follows:

[0084] First, natural pigments and organic acids were used as starting materials to modify the natural pigments. The raw materials were dissolved in acetone and stirred to react, and natural pigment derivatives were obtained. The specific experimental conditions for each comparative example were carried out according to Table 1 below.

[0085] Table 1. Raw materials and reaction conditions used in the examples and comparative examples.

[0086]

[0087] The reaction products of Examples 1-6 and Comparative Examples 1-4 were analyzed and detected. The composition of the system at the end of the reaction was analyzed by high-performance liquid chromatography (HPLC) to calculate the conversion rate of the dye molecules, as shown in Table 2. Specific testing methods: Taking pure hematoxylin as an example, a hematoxylin standard sample was first prepared. The amount of unreacted natural pigment in the reaction product was calculated using the external standard method to obtain the conversion rate. The conversion rates of other modified natural pigment molecules were obtained using a similar method.

[0088] Conversion rate (%) = (Amount of natural pigment added - Amount of unreacted natural pigment) * 100% / Amount of natural pigment added

[0089] The conversion rates of the products synthesized using different methods in the examples and comparative examples are shown in Table 2 below.

[0090] Table 2. Conversion rates of the synthesized products in the examples and comparative examples.

[0091] Example Conversion rate / % Comparative Example Conversion rate / % Example 1 79.41 Comparative Example 1 9.41 Example 2 71.57 Comparative Example 2 1.57 Example 3 78.18 Comparative Example 3 29.41 Example 4 63.14 Comparative Example 4 73.14 Example 5 53.41 Example 6 58.76

[0092] As can be seen from the table above, under the reaction conditions selected in Examples 1-6, the conversion rate of natural pigments was relatively good, generally greater than 50%, with Example 1 showing the best conversion rate. However, under the reaction conditions of Comparative Examples 1-3, the conversion rate of natural pigments was poor. Although Comparative Example 4 had a higher conversion rate, it did not use the organic acid containing an alpha-unsaturated olefin structure required by this invention, thus failing to achieve the click reaction of the thiol group and thus failing to achieve a firm hair dye (see Application Comparative Example 4). The following application test uses Example 1, which has a higher conversion rate.

[0093] Hair dyeing application

[0094] Application Example 1

[0095] A hair dye was prepared using the hair dye molecules prepared in Example 1. The hair dye included agent A and agent B, which were prepared according to Table 3, with a mass ratio of agent A to agent B of 6:4. The hair dye molecules used were those obtained in Example 1.

[0096] Table 3 Composition of hair dye

[0097]

[0098] The hair dyeing method proposed in this invention includes the following steps:

[0099] (1) Take 0.6g of the hair to be dyed (the hair to be dyed is bleached hair, provided by Shanghai Canyu Co., Ltd., model is Level 2 bleached Chinese / 27cm x 1g, free 25cm), use a soft small brush to apply 0.6g of Agent A evenly to the hair at room temperature, keep it at room temperature for 0.5h; rinse clean and blow dry.

[0100] (2) Apply 0.4g of Agent B evenly to the hair treated in step (1) using the same method. Wrap it with plastic wrap and heat it at 343K for 1 hour. Remove it, rinse it clean, blow it dry, and the dyeing is complete.

[0101] The mass ratio of hair to hair dye is 3:5.

[0102] Application Example 2:

[0103] Similar to Application Example 1, except that in step (2) of Application Example 1, the temperature of Agent B is reduced from 343K to 313K.

[0104] Application Example 3:

[0105] Similar to Application Example 1, except that in Application Example 1, the hair dyeing molecules in Agent B are replaced with the hair dyeing molecules in Example 3, and in step (2), after using Agent B, the heating time is increased from 1 hour to 2 hours.

[0106] Application Comparative Example 1:

[0107] Similar to Application Example 1, except that no thiol group is pre-attached in Application Example 1 and no 2-aminoisothiazolidin hydrochloride is added to Agent A. In this case, Agent A is prepared by mixing 98.5% water, 1.48% hydroxyethyl cellulose, and 0.02% Kathon by mass percentage, and then adjusting the pH to 10 with triethanolamine.

[0108] Application Comparative Example 2:

[0109] Similar to Application Example 1, except that in step (2) of Application Example 1, agent B reacts at room temperature.

[0110] Application Comparative Example 3:

[0111] Similar to Application Example 1, except that in step (2) of Application Example 1, the reaction time of agent B is changed to 0.5h.

[0112] Application Comparative Example 4:

[0113] Similar to Application Example 1, except that the dye molecule of Agent B in Application Example 1 is the same as the hair dye molecule in Comparative Example 4.

[0114] Application Comparative Example 5:

[0115] Similar to Application Example 1, except that in Application Example 1, the hair dye molecule of Agent B uses unmodified hematoxylin.

[0116] Application Comparative Example 6:

[0117] Similar to Application Example 1, except that no thiol group is pre-conjugated in Application Example 1 and no 2-aminoisothiazolidin hydrochloride is added to Agent A. In this case, Agent A is prepared by mixing 98.5% water, 1.48% hydroxyethyl cellulose, and 0.02% Kathon by mass percentage, and then adjusting the pH to 10 with triethanolamine. Meanwhile, the hair dye molecule in Agent B uses unmodified hematoxylin.

[0118] Test example:

[0119] (1) Test on the effect of pre-conjugated thiol groups:

[0120] Hair before and after application of Example 1's pre-thiol grafting, i.e., hair before and after treatment with Agent A, was respectively treated with I3. - Immersion in a mixed solution of iodine and rhodamine B. Fluorescence micrographs showing the quenching effect of free thiol groups on iodine solution and rhodamine B after pre-conjugation of thiol groups are shown below. Figure 2 As shown in the figure, there is no fluorescence before pre-conjugation of thiol groups, which proves that the bleached hair has no free thiol groups. After pre-conjugation of thiol groups, the hair shows fluorescence, which proves that it has free thiol groups. After dyeing, the fluorescence disappears, which proves that the thiol groups disappear again. That is, the components in hair dye B have undergone a chemical reaction with the free thiol groups.

[0121] (2) Characteristics of hair dyeing adhesion:

[0122] First, the hair was washed using a simulated daily cleaning process, with 0.2g of shampoo applied per gram of hair strand. After 5 minutes, the hair was rinsed with warm water. Each time the hair was rinsed with warm water, the hair was gently stroked ten times with similar force. The hair was then air-dried under constant temperature and humidity conditions. This constituted one cycle, which was repeated seven times. The color difference before washing and after seven cycles was measured to compare the colorfastness of different hair dyes and dyeing methods.

[0123] The color difference is calculated as follows: the hair color characteristic values ​​L*, a*, b*, c*, and h* are measured using a colorimeter, and the calculations are performed using data from the CIE standard light source D65 and a 90° field of view. L* represents lightness, with black having the lowest lightness and white the highest, interspersed with different shades of gray; a* represents the color index from red to green, with red being positive and green being negative; b* represents the color index from blue to yellow, with blue being negative and yellow being positive.

[0124] The color difference of hair dyed with the hair dye described in the application examples and comparative examples of this invention before and after washing is represented by the color difference ΔE. The formula for calculating the color difference is as follows:

[0125] ΔE=[(ΔL*) 2 +(Δa*) 2 +(Δb*) 2 ] 1 / 2

[0126] The specific test results are shown in Table 4 below.

[0127] Table 4. Color difference values ​​of dyed hair strands before and after washing in the examples and comparative cases.

[0128]

[0129]

[0130] As shown in Table 4, the colorfastness of the dyeing in Examples 1-3 is superior to that in Comparative Examples 1-6, indicating that the coloring ability of external thiol dyeing is better than that of direct hair dyeing.

[0131] Meanwhile, this invention also compared the coloring ability and color fastness of hair dyeing using modified natural pigments without pre-conjugation of thiol (Application Comparative Example 1), direct hair dyeing using unmodified natural pigments (Application Comparative Example 6), and hair dyeing using modified natural pigments after pre-conjugation of thiol (Application Example 1). The results showed that the coloring ability and color fastness of hair dyeing using the modified hair dye molecules after pre-conjugation of thiol in Application Example 1 were significantly improved compared to direct hair dyeing. After multiple washes, the color of directly dyed hair decreased by 9.11% compared to before washing, while the color of hair dyed with pre-conjugated thiol only decreased by 6.13% compared to before washing.

[0132] Figure 3 The images visually represent the different colors of the hair strands. From left to right, they are: bleached hair strand, hair strand dyed using Example 1, hair strand dyed using Comparative Example 1, hair strand d after washing using Example 1, and hair strand e after washing using Comparative Example 1. The washing method is the same as described above. Figure 3 It can be seen that the hair strands dyed using Example 1 retained more color after washing, while the hair strands dyed using Comparative Example 1 showed significant color loss after washing.

[0133] (3) Antioxidant performance test:

[0134] Hair samples treated with Application Example 1 and Comparative Example 6 were selected. First, the electron spin resonance intensity was measured using an electron paramagnetic resonance spectrometer under no-light conditions. Then, the hair was exposed to light in a 500W xenon lamp aging chamber for 0.5 hours, and the electron spin resonance intensity was measured again using an electron paramagnetic resonance spectrometer. The electron spin resonance intensities under the two conditions were compared; a higher peak indicates a higher content of free radicals induced by light exposure. The test results are shown in [Figure number missing]. Figure 4 .Depend on Figure 4 It can be seen that in application example 1, the peak height does not change much after illumination (e.g., Figure 4 (As shown by the solid and dashed lines in a), while in Comparative Example 6, the peak height increases significantly after illumination (as shown by...). Figure 4As described in section b, the difference between solid and dashed lines is significant. This indicates that using the hair dyeing technology proposed in this invention can enhance the ability of damaged hair to resist external oxidative stress. The decreased antioxidant performance of damaged hair strands may be due to oxidation during hair bleaching, which damages the hair cuticle and makes the hair more susceptible to UV damage. These conditions are significantly improved after hair dyeing and repair with hematoxylin, thus it can be concluded that the molecules of hematoxylin acrylate can help hair better resist external oxidative stress by interacting with their own phenolic hydroxyl groups.

[0135] The above description is merely a preferred embodiment of the present invention, and the present invention is not limited to the above embodiments. It is understood that other improvements and variations that are directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included within the protection scope of the present invention.

Claims

1. A hair dye molecule that enhances the colorfastness of natural pigment molecules and improves the antioxidant properties of hair, characterized in that... The general structural formula of the hair dye molecule is as follows: in: R1 is a dye molecule group that absorbs visible light; R4 is selected from any of the following groups: （Ⅰ）， （Ⅱ）； In group (Ⅰ): R3 is selected from hydrogen atoms and has the general formula C n H 2n+1 A group or carboxyl group with n=1; The dye molecule groups with visible light absorption are selected from the following structures: （3-5）。 2. A hair dye molecule, characterized in that, The specific structure of the hair dye molecule is any one of the following structures: 。 3. A method for synthesizing the hair dye molecule according to any one of claims 1-2, characterized in that, The synthesis method is as follows: natural pigments, organic acids and solvents are mixed to obtain a mixed solution, and after stirring and reacting, the solvent is evaporated to obtain hair dye molecules; The natural pigment is selected from hematoxylin.

4. The synthesis according to claim 3, characterized in that, The solvent is acetone.

5. The synthesis method according to claim 3, characterized in that, The organic acid is selected from organic acids with an olefin structure containing an α-unsaturated bond.

6. The synthesis method according to claim 3, characterized in that, The organic acid is selected from one or more of acrylic acid, methacrylic acid, 2-butenoic acid, 2-pentenoic acid, maleic acid, fumaric acid, and shikimic acid.

7. The synthesis method according to claim 3, characterized in that, The unit molar ratio of the organic acid to the natural pigment is 2:1 to 1:1; the mass ratio of the total amount of the natural pigment and organic acid to the solvent is 10-50:100; the reaction temperature is 40℃-70℃; and the reaction time is 1-6h.

8. The synthesis method according to claim 3, characterized in that, The unit molar ratio of the organic acid to the natural pigment is 1.5:1 to 1:1; the mass ratio of the total amount of the natural pigment and organic acid to the solvent is 20-40:100; the reaction temperature is 40℃-50℃; and the reaction time is 6 hours.

9. The synthesis method according to claim 3, characterized in that, The unit molar ratio of the organic acid to the natural pigment is 1.25:1; the mass ratio of the total amount of the natural pigment and organic acid to the solvent is 30:100; and the reaction temperature is 45℃.

10. A hair dye prepared using the hair dyeing molecule according to any one of claims 1-2, characterized in that, The hair dye comprises agent A and agent B; agent A comprises 2-aminoisothiazolidinyl hydrochloride; agent B comprises the hair dye molecule according to any one of claims 1-2; the mass ratio of agent A to agent B is 1:2-2:1; the mass fraction of 2-aminoisothiazolidinyl hydrochloride in agent A is 0.5-2%, and the pH value of agent A is 8-11; the mass fraction of hair dye molecule in agent B is 0.1-5%.

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