A near-infrared absorbing dye and a method for preparing the same

Abstract

The application discloses a near-infrared absorbing dye, which is a symmetrical squarylium cyanine dye with an electron-deficient squarylium ring in the middle and symmetrical electron-rich groups at both ends, and has the characteristics of narrow absorption band, high light absorption coefficient, high thermal stability and good light stability. A method for preparing the near-infrared absorbing dye is also disclosed, which comprises the following steps: coupling reaction, substitution reaction, cyclization reaction, C-N coupling reaction, Fisher reaction, reductive amination and condensation reaction. The structure of the dye is shown in the description.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis, and in particular to a near-infrared absorbing dye and its preparation method. Background Technology

[0002] Squareine dyes are a class of functional dyes with squaric acid as their core structure. First proposed in 1980 by Professor Schmidt's team, the term "squaric acid" originates from its core structural unit, the squaric acid ring, while "squaric" indicates its structural similarity to traditional cyanine dyes. A typical squareine structure consists of an electron-deficient squaric acid ring connected to two electron-rich groups (such as indole, aniline, and naphthylamine) via conjugated double bonds, forming a highly symmetrical π-conjugated system. This electron-donator-electron-acceptor-electron-donor (DAD) charge-transfer transition state gives it excellent storage properties. Therefore, squareine dyes exhibit near-infrared absorption. By adjusting the type of substituents in the electron-donating group, the length of the conjugated double bond system, the anisotropy of molecular absorption, and steric hindrance, the maximum absorption wavelength can be red-shifted or blue-shifted.

[0003] The general structural formula of squaric acid cyanine dyes is:

[0004]

[0005] When D1=D2, it is a symmetric squaricocyanine; when D1≠D2, it is an asymmetric squaricocyanine. This unique structure endows squaricocyanine dyes with excellent optical properties, including strong absorption of visible to near-infrared light, good photostability, and a high molar extinction coefficient.

[0006] The reported squaric acid cyanine dyes can be used to prepare laser protective coatings to counter laser detection technology; they can also be used in multiple fields such as biofluorescent probe technology, sensors, photovoltaic devices, and organic solar cells.

[0007] The electron-rich groups at both ends of squaricocyanine dyes can be continuously adjusted as needed, resulting in a wide variety of types. For example, indole dyes used as fluorescent probes generally have absorption wavelengths concentrated around 645 nm. Patent CN116348555A discloses several asymmetric squaricocyanine dyes with absorption wavelengths concentrated between 724 and 736 nm, while symmetric squaricocyanine dyes cover 688 to 725 nm, with most around 700 nm. CN116348794A also discloses three symmetric squaricocyanine dyes: compound 1 (706 nm), compound 9 (722 nm), and compound 2 (753 nm). Patent CN108603038A discloses a series of symmetric squaricocyanine dyes with absorption compensation mainly concentrated between 688 and 724 nm, and compound A1-8 has an absorption wavelength of 734 nm. Based on multiple literature reports, squaricocyanine dyes with absorption wavelengths above 730 nm are relatively rare, and symmetric squaricocyanine dyes are even rarer.

[0008] Since asymmetric squaric acid cyanine dyes have two strong absorption regions in the near-infrared and visible light regions, they cannot meet the absorption requirements of sensors and other devices for specific wavelengths. Therefore, there is an urgent need to provide a new type of near-infrared absorbing dye. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a near-infrared symmetric squaric acid cyanine dye with an absorption wavelength of 760 nm, which has the characteristics of high extinction coefficient, high transmittance in the visible light region, high thermal stability and high photostability.

[0010] To solve the above-mentioned technical problems, one technical solution adopted by the present invention is: to provide a near-infrared absorbing dye, which is a symmetrical squaric acid cyanine dye containing an electron-deficient squaric acid ring in the middle and symmetrical electron-rich groups at both ends, with the three groups in a π-conjugated system. The structure of the dye is as follows:

[0011]

[0012] In a preferred embodiment of the present invention, the electron-rich group comprises four cyclic structures containing an indoline structure, a thiophene structure, and protective structures for the indoline and thiophene.

[0013] Furthermore, the indoline is protected by alkyl groups at positions 1, 2, and 3. The presence of two alkyl groups at position 3 of the indoline significantly improves its ester solubility.

[0014] Furthermore, the 2' and 3' positions of the thiophene are protected by cyclohexyl groups. While adding a thiophene ring significantly increases the conjugation of the system and causes a noticeable red shift in wavelength, it also results in poor thermal and optical stability. Therefore, this invention protects the reactive 2' and 3' positions of the thiophene ring, forming a new ring structure that significantly increases its thermal and optical stability, while further red-shifting the absorption wavelength to 761 nm.

[0015] To solve the above-mentioned technical problems, another technical solution adopted by the present invention is: to provide a method for preparing a near-infrared absorbing dye as described in any of the preceding claims, wherein the preparation process includes coupling reaction, substitution reaction, cyclization reaction, CN coupling reaction, Fisher reaction, reductive ammoniation, and condensation reaction, and the synthetic route is as follows:

[0016]

[0017] The preparation of compound a:

[0018] Starting with 1,3-dibromo-2-iodobenzene and cyclohexanone, a palladium catalyst, an organophosphorus ligand, and a carbonate as a base are added. The reaction is carried out in toluene and dioxane by heating. The preferred catalyst is Pd2(dba)3, the preferred ligand is Xantphos, and the preferred base is cesium carbonate, which can make the reaction proceed rapidly and reduce the formation of impurities.

[0019] Preparation of compound b:

[0020] Compound a is first mixed with an organic sulfur reagent, and a sulfur-oxygen exchange reaction is carried out under the action of HMDSO to generate thioketone; the organic sulfur reagent is preferably P2S5 or Lawson's reagent, more preferably P2S5; the amount of P2S5 is preferably 0.2 to 0.5 equivalents, more preferably 0.25 equivalents; the reaction temperature is preferably 80 to 100°C, more preferably 90°C.

[0021] Preparation of compound c:

[0022] Compound b undergoes an intramolecular coupling reaction in the presence of a palladium catalyst, an organophosphorus ligand, and a base to generate a condensation product. The palladium catalyst is preferably Pd2(dba)3, Pd(PPh3)4, or Pd(PPh3)2Cl2, with Pd2(dba)3 being more preferred. The organophosphorus ligand is preferably Xantphos, DPEphos, or JohnPhos, with DPEphos being more preferred. The base is preferably potassium carbonate, cesium carbonate, or sodium tert-butoxide, with cesium carbonate being more preferred. The solvent is preferably toluene, dioxane, or tetrahydrofuran, with toluene being more preferred. The reaction temperature is preferably 90–120 °C, with 100 °C being more preferred.

[0023] Preparation of compound d:

[0024] Compound c undergoes a classic CN coupling reaction in the presence of a palladium catalyst, an organophosphorus ligand, and a base to generate an organohydrazine compound. The palladium catalyst is preferably Pd2(dba)3, Pd(PPh3)4, or Pd(PPh3)2Cl2, with Pd2(dba)3 being more preferred. The organophosphorus ligand is preferably Xantphos, DPEphos, or JohnPhos, with Xantphos being more preferred. The base is preferably potassium tert-butoxide, cesium carbonate, or sodium tert-butoxide, with sodium tert-butoxide being more preferred. The solvent is preferably toluene, dioxane, or tetrahydrofuran, with toluene being more preferred. The reaction temperature is preferably 90–120 °C, with 100 °C being more preferred.

[0025] Preparation of compound e:

[0026] The preparation of compound e is achieved in two steps: an acid de-BOC reaction and a Fisher indole synthesis reaction. First, compound d is stirred in an acidic solution at room temperature to remove BOC, generating a hydrazine compound. Then, the hydrazine compound and a ketone are reacted under acid catalysis to synthesize Fisher indole to produce e. The acidic reagent for BOC removal is preferably a hydrogen chloride EA solution, a hydrogen chloride dioxane solution, or a hydrogen chloride ethanol solution, with a hydrogen chloride EA solution being more preferred. The acidic catalyst for Fisher indole synthesis is preferably hydrochloric acid, glacial acetic acid, or sulfuric acid, with glacial acetic acid being more preferred.

[0027] Preparation of compound f:

[0028] Compound d is reduced to a secondary amine using acidic sodium borohydride, then dehydrated and condensed with acetaldehyde to form an imine, and finally reduced to compound f using basic sodium borohydride. Alternatively, a large excess of acetaldehyde can be mixed with the compound, and the two reactions can be carried out simultaneously using acidic sodium cyanoborohydride for reduction and amination. Since acetaldehyde also has the opportunity to be reduced, the amount of acetaldehyde used needs to be increased, preferably 10 equivalents, more preferably 20 equivalents. Acidity can be adjusted using hydrochloric acid, sulfuric acid, phosphoric acid, glacial acetic acid, methanesulfonic acid, p-toluenesulfonic acid, etc., preferably methanesulfonic acid and glacial acetic acid, more preferably glacial acetic acid. The reaction temperature is preferably -10 to 30°C, more preferably 0 to 5°C.

[0029] Preparation of compound Y-761:

[0030] Compound f is mixed with squaric acid in an appropriate ratio, and a toluene-n-butanol mixed solvent is added. The mixture is heated to reflux, while an oil-water separator is used to remove water from the system. The feed ratio of compound i to squaric acid is 1:0.5 to 1:1, preferably 1:0.5; the volume ratio of toluene to n-butanol is 5:1 to 1:5, preferably 1:1 to 1:5, and more preferably 1:4.

[0031] The beneficial effects of this invention are:

[0032] (1) This invention provides a novel symmetrical squaric acid cyanine dye with a maximum absorption wavelength of 761 nm, filling the gap in squaric acid cyanine dyes with an absorption wavelength of around 760 nm.

[0033] (2) Compared with other squaric acid cyanine dyes with similar structures, it has better thermal stability;

[0034] (3) Compared with other squaric acid cyanine dyes with similar structures, it has better photostability;

[0035] (4) The synthetic routes designed in this invention are all classic organic reactions, which are easy to implement and do not use special reagents, providing a better solution for industrialization. Attached Figure Description

[0036] Figure 1 This is a transmittance curve of Y-761 dye before and after high temperature in an embodiment of the present invention;

[0037] Figure 2 This is a transmittance curve of Y-761 dye xenon lamp before and after irradiation according to an embodiment of the present invention;

[0038] Figure 3 This is a graph showing the transmittance curves of dye A1-4 before and after high temperature in comparative example A of this invention.

[0039] Figure 4 This is a transmittance curve of dye-xenon lamp before and after irradiation, which is the comparative example A1-4 of this invention. Detailed Implementation

[0040] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0041] Example 1:

[0042] A method for preparing a near-infrared absorbing dye Y-761 includes coupling reaction, substitution reaction, cyclization reaction, CN coupling reaction, Fisher reaction, reductive ammoniation, and condensation reaction. The synthetic route is shown below:

[0043]

[0044] The preparation of compound a:

[0045] 35 g of 1,3-dibromo-2-iodobenzene, 19 g of cyclohexanone, and 140 ml of dioxane were added to a three-necked reaction flask. Stirring was started, and under nitrogen protection, 69.3 g of cesium carbonate, 30.28 g of Pd2(dba) and 0.67 g of Xantphos were added. The mixture was heated to 80 °C and reacted for 24 h. After the reaction was completed, water and DCM were added, and the organic phase was dried with anhydrous sodium sulfate after extraction. The mixture was filtered, and the filtrate was concentrated to dryness to obtain 24.7 g, with a yield of 77%.

[0046] Preparation of compound b:

[0047] 25 g of compound a and 120 ml of toluene were added to a three-necked reaction flask. Stirring was started, and 54 g of P2S was added under nitrogen protection. The mixture was stirred at room temperature for 10 minutes. 20 g of HMDSO was added, and the temperature was raised to 90 °C for 21 h. After the reaction was completed, the mixture was filtered, and the filtrate was concentrated to obtain 17.6 g, with a yield of 70%.

[0048] Preparation of compound c:

[0049] 7.2 g of compound b1 and 86 ml of toluene were added to a three-necked reaction flask. Stirring was started, and 24.1 g of cesium carbonate, 30.85 g of Pd2(dba) and 1.59 g of DPEphos were added under nitrogen protection. The mixture was heated to 100 °C and reacted for 20 h. After the reaction was completed, the mixture was filtered, and the filtrate was concentrated to dryness. 9.24 g of the product was obtained by column chromatography, with a yield of 70%.

[0050] Preparation of compound d:

[0051] Compound C 9.1g, tert-butyl hydrazide carboxylate 5.4g and toluene 91ml were added to a three-necked reaction flask. Stirring was started, and sodium tert-butoxide 8.2g, Pd2(dba)3 0.97g and Xantphos 1.97g were added under nitrogen protection. The mixture was heated to 100℃ and reacted for 24h. After the reaction was completed, the mixture was filtered, and the filtrate was concentrated to dryness. Column chromatography yielded 7.37g, with a yield of 68%.

[0052] Preparation of compound e:

[0053] 7.2 g of compound d and 100 ml of 4M hydrogen chloride EA solution were added to a three-necked reaction flask. The mixture was stirred at room temperature for 6 h, filtered, and the filter cake was washed with EA. After vacuum filtration, the filter cake was added to the three-necked reaction flask. Under stirring, 0.27 g of glacial acetic acid, 80 ml of anhydrous ethanol, and 2.84 g of 3-ethyl-2-pentanone were added. The mixture was heated to reflux and reacted for 4 h. After the reaction was completed, the mixture was concentrated to dryness, DCM and water were added, and the organic phase was dried with anhydrous sodium sulfate after extraction. The mixture was filtered, and the filtrate was concentrated to dryness to obtain 5.71 g, with a yield of 85%.

[0054] Preparation of compound f:

[0055] 5.6 g of compound e and 56 ml of acetonitrile were added to a three-necked reaction flask. 41.4 g of 40% acetaldehyde aqueous solution and 5.6 ml of glacial acetic acid were added while stirring. The mixture was cooled to 0 °C, and 5.9 g of sodium cyanoborohydride was added in portions. The reaction was carried out for 2 h. Water and EA were added, the organic phase was collected, dried, filtered, and concentrated to obtain 5.8 g, with a yield of 94%.

[0056] Preparation of compound Y-761:

[0057] 5.7 g of compound f, 1 g of squaric acid, 60 ml of toluene and 240 ml of n-butanol were added to a three-necked reaction flask. The mixture was heated to reflux and reacted for 14 h. The mixture was then concentrated to dryness and column chromatography was used to obtain 1.61 g of the compound, with a yield of 25%.

[0058]

[0059] Comparative Example 1:

[0060] The structural formula of Comparative Example 1 is as follows:

[0061]

[0062] Compound A1-4 was synthesized using the same method as Y-761, except that the starting material c in the step of synthesizing compound d of Y-761 was changed to 4-bromothiophene.

[0063] The following performance tests were performed on the two compounds prepared in Example 1 and Comparative Example 1:

[0064] (1) The maximum absorption wavelength of the above infrared absorbing dyes in N,N-dimethylformamide:

[0065] Take 0.3 parts by mass of the above-synthesized infrared absorbing dye, add 9.7 parts by mass of N,N-dimethylformamide (Aladdin reagent), stir and dissolve at room temperature, and then use a UV-Vis spectrophotometer (UV-1600PC, Shanghai Xipu Instrument Co., Ltd.) to measure the maximum absorption wavelength of the dye solution. The results are shown in the table below.

[0066]

[0067] Example 1-1: 4.5 parts by mass of infrared absorbing dye Y-761 and 45 parts by mass of N,N-dimethylformamide (Aladdin reagent) were added to a beaker and heated at 60℃~80℃ for 30 minutes under sealed conditions until all dye particles were dissolved. The solution was then cooled to room temperature to obtain a pigment solution. 50 parts by mass of C-3G30G (manufactured by Mitsubishi Gas Chemical Co., Ltd.), 0.4 parts by mass of KH-550 (Aladdin reagent), and 0.1 parts by mass of BYK-3550 (manufactured by BYK Chemical Co., Ltd.) were added to the pigment solution. The mixture was stirred at room temperature for 30 minutes and then spin-coated onto quartz glass using a spin coater. The glass was then placed on a 100℃ hot plate (DB-XAB, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.) for heating and drying to obtain an infrared absorbing dye filter with an absorption layer thickness of 2μm.

[0068] Figure 1 The above are the absorption spectra of the infrared pigment filter prepared in Example 1-1 before and after high temperature. Figure 1 As can be seen, the near-infrared absorption curve (600mm~800mm) of the infrared pigment filter made from the composition of Example 1-1 shows very little attenuation before and after high temperature.

[0069] Examples 1-2: Xenon lamp irradiation was performed using an infrared absorbing pigment filter with an absorption layer thickness of 2 μm prepared in Example 1-1. Figure 2 The images show the absorption spectra of the infrared pigment filters prepared in Examples 1-2 before and after high temperature. Figure 2 It can be seen that the near-infrared absorption curves (600mm~800mm) of the infrared pigment filters prepared by Examples 1-2 before and after xenon lamp irradiation show a small degree of attenuation.

[0070] Comparative Example 2-1: 4.5 parts by mass of infrared absorbing dye A1-4 and 45 parts by mass of N,N-dimethylformamide (Aladdin reagent) were added to a beaker and heated at 60℃~80℃ for 30 minutes under sealed conditions until all dye particles were dissolved. The solution was then cooled to room temperature to obtain a pigment solution. 50 parts by mass of C-3G30G (manufactured by Mitsubishi Gas Chemical Co., Ltd.), 0.4 parts by mass of KH-550 (Aladdin reagent), and 0.1 parts by mass of BYK-3550 (manufactured by BYK Chemical Co., Ltd.) were added to the pigment solution. The mixture was stirred at room temperature for 30 minutes and then spin-coated onto quartz glass using a spin coater. The glass was then placed on a 100℃ hot plate (DB-XAB, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.) for drying to obtain an infrared absorbing dye filter with an absorption layer thickness of 2μm.

[0071] Figure 3The absorption spectra of the infrared pigment filter prepared in Comparative Example 2-1 before and after xenon lamp irradiation are shown in Figure 3. It can be seen from Figure 3 that the absorption curves of the infrared pigment filter prepared in Comparative Example 2-1 in the near-infrared region before and after high temperature are severely attenuated in the visible light region and the infrared region; the attenuation in the (600mm~800mm) region is also very severe.

[0072] Comparative Example 2-2: Xenon lamp irradiation was performed using an infrared absorbing pigment filter with an absorption layer thickness of 2 μm prepared in Example 2-1. Figure 4 The infrared pigment filter prepared in Comparative Example 2-2 has absorption spectra before and after xenon lamp irradiation. Figure 4 It can be seen from the infrared pigment filter made by Comparative Example 2-2 that the absorption curves of the near-infrared region before and after xenon lamp irradiation show severe attenuation in the visible light region and the infrared region; the attenuation in the (600mm~800mm) region is also very severe.

[0073] (2) The heat resistance of the infrared absorbing pigment filters prepared in the above embodiments and comparative examples was evaluated:

[0074] The spectral characteristics of each infrared absorption pigment filter prepared from the infrared pigments in the examples and comparative examples were tested using a UV-Vis spectrophotometer (UV-1600PC, Shanghai Xipu Instrument Co., Ltd.). The minimum transmittance in the absorption spectrum curve at wavelengths of 600nm~800nm ​​was recorded as <initial minimum TC>. Each infrared pigment filter was then placed in a 200℃ forced-air drying oven (LC-101-0B, Shanghai Lichen Bangxi Instrument Technology Co., Ltd.) for 0.5h. The spectral characteristics of the baked infrared absorption pigment filters were then tested, and the minimum transmittance of the infrared absorption pigment filter at wavelengths of 600nm~800nm ​​after high-temperature baking was recorded as <high-temperature minimum Tg>. The pigment residue rate before and after heating was calculated using the following formula: Pigment residue rate (%) = (Minimum transmittance of light at wavelengths of 600nm~800nm ​​before heating) / (Minimum transmittance of light at wavelengths of 600nm~800nm ​​after heating) × 100. The results are shown in the table below. It should be noted that the evaluation criteria for heat resistance are as follows: A: Pigment residue rate is over 90%; B: Pigment residue rate is less than 80%; Results are shown in Table 1.

[0075] Table 1

[0076] As can be seen from the test evaluation of the examples and comparative examples in Table 1, the newly prepared Y-761 dye has high stability under high temperature conditions. The absorption spectrum curve of the infrared absorption filter made from it hardly changes before and after high temperature, and it has excellent heat resistance.

[0077] (3) Lightfastness tests were conducted on the filters of Examples 1-2 and Comparative Example 2-2 to evaluate their lightfastness. In the lightfastness test, the filters were irradiated with a xenon lamp.

[0078] The irradiation conditions are as follows:

[0079] Wavelength: 200nm~1000nm

[0080] Temperature: 50℃

[0081] Humidity: 50%

[0082] Irradiation time: 24 hours

[0083] The spectral characteristics of each infrared absorbing pigment filter prepared from the infrared pigments in the examples and comparative examples were tested using a UV-Vis spectrophotometer (UV-1600PC, Shanghai Xipu Instrument Co., Ltd.). The minimum transmittance at wavelengths of 600nm to 800nm ​​in the absorption spectrum before xenon lamp irradiation was recorded as <initial minimum TC>. After light irradiation, the spectral characteristics of the irradiated infrared absorbing pigment filter were tested again, and the minimum transmittance at wavelengths of 600nm to 800nm ​​after irradiation was recorded as <minimum high temperature Tg>. The minimum transmittance of light at wavelengths of 600nm to 800nm ​​before and after irradiation was obtained from the spectral transmittance curves before and after irradiation. The spectral transmittance curves of the filter before and after the lightfastness test were calculated using the following formula.

[0084] The minimum transmittance of light with wavelengths of 600nm~800nm ​​before and after irradiation is obtained from the spectral transmittance curves before and after irradiation, and its variation is calculated by the following formula.

[0085] Minimum transmittance variation [%] = [(Minimum transmittance of light with wavelengths of 600nm~800nm ​​after irradiation) - (Irradiation wavelength variation)]

[0086] [Minimum transmittance of light with wavelengths of 600nm~800nm ​​before irradiation] / (Minimum transmittance of light with wavelengths of 600nm~800nm ​​after irradiation) × 100

[0087] The evaluation criteria for lightfastness are as follows: A: When the minimum transmittance variation [%] is less than 10%; B: When the minimum transmittance variation [%] is greater than 10%; A is evaluated as qualified, and the results are shown in Table 2.

[0088] Table 2

[0089] As can be seen from the test evaluations of the examples and comparative examples in Table 2, the newly prepared Y-761 dye has high stability under xenon lamp irradiation. The absorption spectrum curve of the infrared absorption filter made from it hardly changes before and after irradiation, demonstrating excellent photostability.

[0090] This embodiment is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may use the above content as inspiration to make changes or modifications to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications listed in the above embodiments that do not depart from the technical essence of the claims of the present invention shall still fall within the scope of protection of the claims of the present invention.

Claims

1. A near-infrared absorbing dye, characterized in that, This dye is a symmetrical squaric acid cyanine dye with an electron-deficient squaric acid ring in the middle and symmetrical electron-rich groups at both ends, all three in a π-conjugated system. The structure of the dye is as follows: 。 2. The near-infrared absorbing dye according to claim 1, characterized in that, The electron-rich group comprises four cyclic structures containing an indoline structure, a thiophene structure, and protective structures for indoline and thiophene.

3. The near-infrared absorbing dye according to claim 2, characterized in that, The indoline is protected by alkyl groups at positions 1, 2, and 3.

4. The near-infrared absorbing dye according to claim 2, characterized in that, The 2' and 3' positions of the thiophene are protected with cyclohexyl groups.

5. A method for preparing a near-infrared absorbing dye as described in any one of claims 1 to 4, characterized in that, Its preparation process includes coupling reaction, substitution reaction, cyclization reaction, CN coupling reaction, Fisher reaction, reductive amination, and condensation reaction. The synthetic route is shown below: 。

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