Novel double squaraine dye and its manufacturing method

Abstract

To provide a novel double squaraine dye and a method for producing the same.SOLUTION: Provided is a double squaraine dye that is characterized by being represented by the following formula (I0). (In formula (I0), D1 and D2 each represent a heterocyclic group.).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a novel double squaraine dye and a method for producing the same. [Background technology]

[0002] Highly sensitive detection of metal ions is important for monitoring in the industrial, environmental, and healthcare fields. For example, in the healthcare field, maintaining optimal metal ion concentrations is necessary to maintain various biological processes, and an imbalance can cause various diseases. Among metals, lead (Pb) is a highly toxic heavy metal that can cause anemia, neurological disorders, kidney damage, and other conditions.

[0003] In clinical diagnosis in the healthcare field, it is necessary to measure metal ions such as lead in living organisms, and in environmental pollution investigations, it is necessary to measure metal ions in environmental samples. Under these circumstances, a suitable Pb ion detector, especially one with a near-infrared (NIR) wavelength range, is required. 2+ The design of ion-sensing probes is expected to simplify conventional sample processing and also be applicable to biosensing applications.

[0004] On the other hand, squaraine dyes, which are four-membered ring systems with structural rigidity, have unique photoelectric properties, characterized by very sharp and strong absorption associated with strong fluorescence emission in solution. These favorable properties are expected to be utilized in a variety of applications, including photoconductivity, data storage, light-emitting field-effect transistors, solar cells, and fluorescent histological probes. Specifically, squaraine dyes have been proposed for use in filters for display devices (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2021-504538 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a novel double squaraine dye and a method for producing the same. [Means for solving the problem]

[0007] Through extensive research into squaraine dyes, the present inventors have discovered novel double squaraine dyes containing two squaric acid moieties in the same molecule, as well as a method for preparing the same, leading to the completion of the present invention. As an example, they have discovered novel N-alkyl-substituted benzoindole-based double squaraine dyes with variable alkyl chain lengths, as well as a method for preparing the same.

[0008] That is, the present invention is as follows. [1] A double squaraine dye represented by the following formula (I0): [ka] (In formula (I0), D 1 and D 2 each represents a heterocyclic group. [2] In formula (I0), D 1 and D 2 and each of the groups represented by the following formulae (a-1) to (a-16) is a heterocyclic group. [ka] (In the formula, R 12 represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and * represents the bonding position. [3] In formula (I0), D 1 and D 2is a heterocyclic group represented by the following formula (a-1), (a-3) or (a-5), respectively: [ka] [4] In formula (I0), D 1 and D 2 and are the same heterocyclic group. [5] The double squaraine dye according to any one of [1] to [4] above, which is represented by the following formula (I): [ka] (In formula (I), R 1 and R 2 represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and R 3 ~R 6 represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 4 carbon atoms.) [6] In formula (I), R 1 and R 2 and each represent an aliphatic saturated hydrocarbon group having 1 to 20 carbon atoms. [7] In formula (I), R 3 ~R 6 and each of the groups represented by the formula (5) or (6) is a methyl group. [8] The double squaraine dye according to any one of [5] to [7] above, which is represented by the following formula: [ka] [9] The double squaraine dye according to any one of [1] to [3] above, which is represented by any one of the following formulae: [ka] (In the formula, R′ represents a hydroxyl group, a methoxy group, a bromo group, a cyano group, or a carboxy group.)

[10] A method for detecting metal ions, characterized by detecting metal ions using the double squaraine dye according to any one of [1] to [9] above.

[11] The metal ion detection method according to

[10] above, wherein the metal ion is a divalent metal ion.

[12] The metal ion detection method according to

[11] above, wherein the divalent metal ion is a lead ion.

[13] A method for detecting solvent polarity, comprising detecting the polarity of a solvent using the double squaraine dye according to any one of [1] to [9] above.

[14] In the presence of a mixed organic solvent of a non-polar solvent and a protic polar solvent, The following formula (wherein D 1 and D 2 each represents a heterocyclic group. [ka] A single squaraine compound represented by the formula: [ka] 1. A method for producing a double squaraine dye, comprising the step of obtaining a double squaraine dye represented by the formula:

[15] The method for producing a double squaraine dye according to

[14] above, wherein the mixed organic solvent contains, in volume ratio, 1:1 of a protic polar solvent to 1:1 or more of a nonpolar solvent.

[16] The method for producing a double squaraine dye according to

[14] or

[15] above, wherein the non-polar solvent is toluene.

[17] The method for producing a double squaraine dye according to any one of the above

[14] to

[16] , wherein the protic polar solvent is n-butanol.

[18] The following formula (wherein R 3 , R 4 , R 7 represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 4 carbon atoms.) [ka] For the 1H-benzo[e]indole compound represented by the formula: 1 X(R 1 represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and X represents a halogen atom, The following formula [ka] Step 1 to obtain a compound represented by the formula: The compound obtained in the step 1 is reacted with a dialkyl squarate in the presence of an amine to obtain a compound represented by the following formula (wherein R A represents an alkyl group. [ka] Step 2 to obtain a compound represented by the formula: The compound obtained in the step 2 is reacted with an inorganic base compound to obtain a compound represented by the following formula (M represents an alkali metal): [ka] Step 3 to obtain a compound represented by the formula: The compound obtained in step 3 above is dimerized to obtain a compound represented by the following formula: [ka] Step 4 to obtain a double squaraine dye represented by 1. A method for producing a double squaraine dye, comprising: [Effects of the Invention]

[0009] According to the present invention, a novel double squaraine dye can be provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TM1) of the present invention. [Figure 2] FIG. 1 shows the results of mass spectrometry (HR-MS) of the double squaraine dye (TM2) of the present invention. [Figure 3] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TM3) of the present invention. [Figure 4] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TM4) of the present invention. [Figure 5] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-309) of the present invention. [Figure 6] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-303) of the present invention. [Figure 7] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-195) of the present invention. [Figure 8] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-185) of the present invention. [Figure 9] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-187) of the present invention. [Figure 10] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-176) of the present invention. [Figure 11] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-308) of the present invention. [Figure 12] FIG. 1 shows the results of mass spectrometry (ESI+) of the double squaraine dye (TC-177) of the present invention. [Figure 13] FIG. 1 shows changes in absorption wavelength of the double squaraine dyes (TM1, TM3) of the present invention upon addition of metal ions (Pb 2+ ). [Figure 14] This figure shows the results of adding metal ions (Pb2+) to the double squaraine dyes (TM1, TM3) of the present invention, and shows the results (photographs) of N-ethyl BLANK, N-ethyl + Pb2+, and N-dodecyl + Pb2+ from the left. [Figure 15] FIG. 1 shows the change in absorption wavelength of the double squaraine dye (TM3) of the present invention upon addition of different types of metal ions. [Figure 16] This figure shows the results of adding different types of ions to the double squaraine dye (TM3) of the present invention. From the left, the photographs show the results of adding BLANK, Li+, Na+, K+, Mg2+, Ca2+, Pb2+, Cu2+, Ni2+, and Zn2+. [Figure 17] FIG. 1 shows the change in absorption wavelength when different concentrations of metal ions (Pb 2+ ) are added to the double squaraine dye (TM3) of the present invention in a binary solvent. [Figure 18] FIG. 18 shows the absorbance data at a wavelength of 720 nm in FIG. 17. [Figure 19] This figure shows the results of dissolving the double squaraine dye (TM3) of the present invention in different types of single solvents, from top to bottom, at a wavelength of 600 nm: chloroform, 2-propanol, AcOH, n-butanol, acetonitrile, acetone, toluene, ethyl acetate, THF, methanol, ethanol, DMF, and DMSO. [Figure 20]FIG. 1 shows the change in absorption wavelength of the double squaraine dye (TM3) of the present invention in a binary solvent depending on the polarity of the solvent, from top to bottom at a wavelength of 600 nm: 100% ACN, 1% DMF 99% ACN, 5% DMF 95% ACN, 10% DMF 90% ACN, 20% DMF 80% ACN, 30% DMF 70% ACN, 40% DMF 60% ACN, 50% DMF 50% ACN, 60% DMF 40% ACN, 70% DMF 30% ACN, 80% DMF 20% ACN, 90% DMF 10% ACN, and 100% DMF. DETAILED DESCRIPTION OF THE INVENTION

[0011] The double squaraine dye of the present invention is a compound represented by the following formula (I0).

[0012] [ka]

[0013] In formula (I0), D 1 and D 2 represents a heterocyclic group, which may have a substituent.

[0014] Specifically, in formula (I0), D 1 and D 2 can be exemplified by heterocyclic groups represented by the following formulae (a-1) to (a-16), respectively, and a heterocyclic group represented by formula (a-1), formula (a-3) or formula (a-5) is preferred, and a heterocyclic group represented by formula (a-1) is particularly preferred. 12 represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and * represents the bonding position. The aromatic skeleton may have a substituent.

[0015] [ka]

[0016] The substituent in the aromatic skeleton is preferably an electron-donating group. Specific examples include an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a hydroxyl group. These substituents are preferably substituted at positions that function as electron-donating groups. Alternatively, they may be halogen groups.

[0017] The heterocyclic group contains a nitrogen atom, a sulfur atom, or an oxygen atom, and preferably contains a nitrogen atom. 1 and D 2 is preferably a nitrogen-containing heterocyclic group containing a nitrogen atom. 1 and D 2 When the nitrogen-containing heterocyclic group is a nitrogen-containing heterocyclic group, the nitrogen atom may have a substituent, and the substituent is preferably an aliphatic hydrocarbon group having 1 to 30 carbon atoms. The aliphatic hydrocarbon group may be a linear hydrocarbon group or a branched hydrocarbon group, but a linear hydrocarbon group is preferred. Also, it may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but a saturated hydrocarbon group is preferred. As mentioned above, the number of carbon atoms is preferably 1 to 30, more preferably 1 to 25, even more preferably 2 to 20, and particularly preferably 5 to 18. Specifically, -CH3, -C2H5, -CH 13 , -C 12 H 25 , -C 18 H 37 , -C 24 H 49 The substituents on the nitrogen atoms of the nitrogen-containing heterocyclic group may be the same or different, but are preferably the same.

[0018] In the above formula (I0), D 1 and D 2 may be the same heterocyclic group or different heterocyclic groups, but are preferably the same heterocyclic group. That is, the double squaraine dye of the present invention may be a double squaraine dye having the same heterocyclic group (symmetric double squaraine dye) or a double squaraine dye having different heterocyclic groups (asymmetric double squaraine dye), but is preferably a double squaraine dye having the same heterocyclic group.

[0019] Preferred double squaraine dyes of the present invention having a nitrogen-containing heterocyclic group represented by formula (a-1) are described below. Preferred double squaraine dyes of the present invention are, for example, compounds represented by the following formula (I):

[0020] [ka]

[0021] In formula (I), R 1 and R 2 R represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms. 1 and R 2 may be a linear hydrocarbon group or a branched hydrocarbon group, but a linear hydrocarbon group is preferred. Also, may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but a saturated hydrocarbon group is preferred. As mentioned above, the number of carbon atoms is 1 to 30, but 1 to 25 is preferred, 2 to 20 is more preferred, and 5 to 18 is even more preferred. Specifically, -CH3, -C2H5, -CH 13 , -C 12 H 25 , -C 18 H 37 , -C 24 H 49 Examples include: R 1 and R 2 may be the same or different, but are preferably the same.

[0022] R 3 ~R 6 R each represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 4 carbon atoms. 3 ~R 6 R may be a linear hydrocarbon group or a branched hydrocarbon group, but a linear hydrocarbon group is preferred. It may be a saturated hydrocarbon group or an unsaturated hydrocarbon group, but a saturated hydrocarbon group is preferred. The number of carbon atoms is 1 to 4, as described above, but 1 to 2 is preferred, and 1 is more preferred. 3 ~R 6may be the same or different, but are preferably the same.

[0023] The aromatic skeleton in the above formula (I) may have a substituent. The substituent is preferably an electron-donating group. Specific examples include an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and a hydroxyl group. These substituents are preferably substituted at a position that functions as an electron-donating group. Alternatively, the substituent may be a halogen group.

[0024] D 1 and D 2 Specific examples of double squaraine dyes in which is a nitrogen-containing heterocyclic group represented by formula (a-1) include the compounds shown below.

[0025] [ka]

[0026] In addition to the compound represented by formula (I), the following can be exemplified as double squaraine dyes having a nitrogen-containing heterocyclic group represented by formula (a-1), formula (a-3) or formula (a-5). 1 and D 2 In the following formula, R' represents a hydroxyl group, a methoxy group, a bromo group, a cyano group, or a carboxy group. [ka]

[0027] Squaraine dyes, which are four-membered ring systems with structural rigidity, possess unique photoelectric properties and are characterized by very sharp and strong absorption associated with strong fluorescence emission in solution. Furthermore, the novel double squaraine dyes of the present invention, which incorporate a four-membered ring, allow electronic conjugation to occur in the double four-membered ring, resulting in strong absorption in the near-infrared region. Therefore, they can be used in fields such as photoconductivity, data storage, light-emitting field-effect transistors, solar cells, nonlinear optical materials, optical bioimaging, NIR-fluorescent probes, and label optical detection. They are particularly suitable for biosensing as metal ion detection probes. Furthermore, the novel double squaraine dyes of the present invention exhibit solvatochromism, which changes color (wavelength) and emission intensity depending on the polarity of the solvent, making them suitable for use in detecting solvent polarity.

[0028] Next, a method for producing the double squaraine dye of the present invention will be described.

[0029] [Method of producing the novel double squaraine dye of the present invention (1)] The novel double squaraine dye of the present invention can be produced, for example, from a single squaraine compound represented by the following chemical formula as a starting material: The single squaraine compound can be obtained by the same method as steps 1 and 2 of the method for producing the novel double squaraine dye of the present invention (2), which will be described below following this method.

[0030] [ka]

[0031] In the above structural formula, D 1 and D 2 is the same as that explained in the above formula (I0).

[0032] The single squaraine compound is reacted with squaric acid in the presence of a mixed organic solvent of a non-polar solvent and a protic polar solvent (Step 1-3 of Example 1). In this reaction, reflux treatment is preferably carried out.

[0033] The mixed organic solvent used in this step preferably contains 1 part of the protic polar solvent to 0.3 or more of the nonpolar solvent, more preferably 1 or more, and even more preferably 2 or more, by volume. On the upper limit side, the ratio is preferably 10 or less, more preferably 7 or less, and even more preferably 6 or less, by volume, by 1 part of the protic polar solvent to 1 part of the nonpolar solvent.

[0034] Suitable non-polar solvents include, for example, toluene, benzene, hexane, xylene, heptane, etc. Suitable protic polar solvents include, for example, alcohols such as n-butanol, n-pentanol, 2-propanol, etc.

[0035] This allows the double squaraine dye shown below to be obtained.

[0036] [ka]

[0037] [Method of producing the novel double squaraine dye of the present invention (2)] The novel double squaraine dye of the present invention can be produced, for example, using a 1H-benzo[e]indole compound represented by the following chemical formula as a starting material.

[0038] [ka]

[0039] In the above structural formula, R 3 ~R 6 is the same as that explained in the above formula (I). 7 and R8 is R 3 ~R 6 is the same as: Hereinafter, as a starting material, the 1H-benzo[e]indole compound (R 3 , R 4 and R 7 The following will explain the case where a compound having the formula (I) is used as an example.

[0040] (Process 1) The starting material, 1H-benzo[e]indole compound, is reacted with a halogenated aliphatic hydrocarbon (R 1 X) is reacted (Step 2-1 of Example 2). In this reaction, reflux treatment is preferably carried out.

[0041] The halogen X of the halogenated aliphatic hydrocarbon may be chlorine, bromine, iodine, or the like, with iodine being preferred. 1 ) are the same as those explained in formula (I) above. Specific examples of halogenated aliphatic hydrocarbons include iodoethane, 1-iodohexane, 1-iododecane, and 1-iodooctadecane. In addition, as the solvent used in step 1, nitrile solvents such as acetonitrile and propionitrile can be suitably used.

[0042] This gives the compound shown below.

[0043] [ka]

[0044] (Process 2) Subsequently, the compound obtained in the above step 1 is reacted with a dialkyl squarate in the presence of an amine (step 2-2 of Example 2).

[0045] Alkyl (R) in dialkyl squarate A) can be an alkyl having about 1 to 6 carbon atoms, such as methyl, ethyl, butyl, etc. As the solvent used in step 2, an alcohol solvent such as ethanol can be suitably used.

[0046] This gives the compound shown below.

[0047] [ka]

[0048] (Step 3) Subsequently, the compound obtained in the above step 2 is reacted with an inorganic base compound such as sodium hydroxide, potassium hydroxide, or lithium hydroxide (step 2-3 of Example 2).

[0049] As the solvent used in this step 3, an alcohol solvent such as ethanol can be suitably used.

[0050] As a result, the compound shown below (M represents an alkali metal) is obtained.

[0051] [ka]

[0052] (Step 4) Subsequently, the compound obtained in the above step 3 is dimerized to obtain the double squaraine dye shown below (step 2-4 of Example 2).

[0053] [ka]

[0054] In this step, for example, thionyl chloride, hydrochloric acid, or acetic acid is added to the compound obtained in step 3 above, and the reaction is carried out at a low temperature, followed by refluxing to obtain a crude product. The crude product can be purified by known means such as chromatography.

[0055] As a solvent for the reaction in which thionyl chloride, hydrochloric acid, or acetic acid is added, an ether-based solvent can be used. In the reflux treatment, toluene, butanol, etc. can be used, and a mixture of toluene and butanol is preferred.

[0056] In the method for producing the novel double squaraine dye of the present invention, a symmetrical double squaraine dye can be obtained by using one heterocyclic compound, and an asymmetrical double squaraine dye can be obtained by using a different heterocyclic compound. Both the symmetrical and asymmetrical double squaraine dyes can be obtained by the production methods (1) and (2) of the present invention.

[0057] [Method for detecting metal ions using the novel double squaraine dye of the present invention] The metal ion detection method of the present invention is characterized by using the double squaraine dye of the present invention. The dye of the present invention exhibits a purple color with absorption at 500 to 600 nm in, for example, an acetonitrile / DMF solvent. When a metal ion is added, the metal ion coordinates, shifting the absorption wavelength to the longer wavelength side, resulting in a color change. For example, Pb 2+ When added, it changes to cyan, which has absorption in the range of 650 to 800 nm.

[0058] Therefore, by detecting such a change in color (change in absorption wavelength), the presence of metal ions can be detected easily and with high accuracy.

[0059] The metal ions to be detected are Na + , K. + Monovalent metal ions such as Mg 2+ , Ca 2+ , Pb 2+ Among these, divalent metal ions are preferred, and Pb 2+ is particularly preferred.

[0060] [Method for detecting solvent polarity using the novel double squaraine dye of the present invention] The method for detecting solvent polarity of the present invention is characterized by using the double squaraine dye of the present invention. The dye of the present invention changes color depending on the polarity of the solvent. For example, in aprotic polar solvents, it exhibits red-shifted NIR absorption. Therefore, by detecting this color change (change in absorption wavelength), solvent polarity can be detected and used to measure polarity parameters. [Example]

[0061] The present invention will be described in more detail below with reference to examples. [Example 1] Double squaraine dyes TM1 to TM4 of the present invention were produced. The outline of the production process (steps 1-1 to 1-3) is shown below.

[0062] [ka]

[0063] Each step will be specifically described below. [Process 1-1] (Production of Compound 1a)

[0064] [ka]

[0065] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (6.3 g, 30.0 mmol), was placed in 50 mL of acetonitrile and iodoethane (9.6 mL, 120.0 mmol) was added. The resulting mixture was refluxed for 18 hours. Thin layer chromatography (TLC) confirmed complete consumption of the starting material. The reaction was cooled to room temperature, and 150 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound 1a (11.0 g, 100% yield) as a gray solid.

[0066] Mass spectrometry (HRMS) of compound 1a was performed. HRMS calculation for C 17 H 20 N + [M+] 238.16, found 238.16.

[0067] (Production of Compound 1b)

[0068] [ka]

[0069] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (4.2 g, 20.0 mmol), was placed in 40 mL of acetonitrile and 1-iodohexane (8.5 mL, 40.0 mmol) was added. The resulting mixture was refluxed for 24 hours. TLC confirmed complete consumption of the starting material. The reaction was cooled to room temperature, and 200 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound 1b (8.0 g, 95% yield) as a gray solid.

[0070] Mass spectrometry (HRMS) of compound 1b was carried out. HRMS calculation for C 21 H 28 N + [M+] 294.22, found 294.22.

[0071] (Production of Compound 1c)

[0072] [ka]

[0073] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (2.1 g, 10.0 mmol), was placed in 20 mL of propionitrile and 1-iodododecane (5.0 mL, 20.0 mmol) was added. The resulting mixture was refluxed for 36 hours. TLC confirmed complete consumption of the starting material. The reaction was cooled to room temperature, and 100 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound 1c (5.0 g, 100% yield) as a gray solid.

[0074] Mass spectrometry (HRMS) of compound 1c was performed. HRMS calculation for C 27 H 40 N + [M+] 378.32, found 378.32.

[0075] (Preparation of Compound 1d)

[0076] [ka]

[0077] 1,1,2-Trimethyl-1H-benzo[e]indole (6.3 g, 30.0 mmol) was placed in 60 mL of propionitrile and 1-iodooctadecane (13.7 mg, 36.0 mmol) was added. The resulting mixture was refluxed for 48 hours. TLC confirmed that the starting material was nearly consumed. The reaction was cooled to room temperature, and 250 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound 1d (12.6 g, 75% yield) as a gray solid.

[0078] Mass spectrometry (HRMS) of compound 1d was carried out. HRMS calculation for C 33 H 52 N + [M+] 462.41, found 462.41.

[0079] [Step 1-2] (Production of Compound 2a)

[0080] [ka]

[0081] To a solution of compound 1a (3.65 g, 10.0 mmol) in 40 mL of anhydrous toluene / n-butanol (v / v = 1 / 1), squaric acid (0.57 g, 5.0 mmol) was added. The resulting reaction mixture was subjected to azeotropic reflux overnight at 120 °C using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using chloroform-methanol as the eluent. The pure fractions were collected, evaporated, and dried under vacuum to give compound 2a (2.1 g, 76% yield) as a blue-black solid.

[0082] Mass spectrometry (HRMS) of compound 2a was performed. HRMS calculation for C 38 H 36 N2O2[M+H] 553.28, found 553.28.

[0083] Compound 2a 1 H-NMR analysis, 13 C-NMR analysis was performed. 1 H NMR (500 MHz, DMSO-d6) δ 8.23 ​​(d, J = 8.5 Hz, 1H), 8.03 (d, J = 6.0 Hz, 1H), 8.02 (d, J = 5.2 Hz, 1H), 7.71 (d, J = Hz8.9, 1H), (7.62dd, J = 6.9, 15.2 Hz, 1H), (7.45dd, J = 7.8, 14.9 Hz, 1H), (5.86s, 1H), 4.27 (q, J = 6.9 Hz, 2H), (1.96 s, 6H), (1.35t, J = 7.1 Hz, 3H). 13C NMR (500 MHz, DMSO-d6) δ 177.51, 169.81, 139.29, 133.15, 130.84, 129.79, 129.72, 127.96, 127.41, 124.13, 122.21, 111.09, 85.51, 50.52, 38.14, 26.13, 12.06.

[0084] (Preparation of Compound 2b)

[0085] [ka]

[0086] To a solution of compound 1b (4.21 g, 10.0 mmol) in 40 mL of anhydrous toluene / n-butanol (v / v = 1 / 1), squaric acid (0.57 g, 5.0 mmol) was added. The resulting reaction mixture was subjected to azeotropic reflux overnight at 120 °C using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using chloroform-methanol as the eluent. The pure fractions were collected, evaporated, and dried under vacuum to give compound 2b (2.6 g, 79% yield) as a blue-black solid.

[0087] Mass spectrometry (HRMS) of compound 2b was performed. HRMS calculation for C 46 H 52 N2O2[M+H] 665.40, found 665.41.

[0088] Compound 2b 1 H-NMR analysis, 13 C-NMR analysis was performed. 1H NMR (500 MHz, CDCl3) δ 8.20 (d, J = 8.5 Hz, 1H), 7.89 (d, J = 8.2 Hz, 1H), 7.87 (d, J = 8.7 Hz, 1H), 7.57 (dd, J = 6.8, 15.3 Hz, 1H), 7.41 (dd, J = 6.9, 15.0 Hz, 1H), 7.28 (dd, J = 8.8, 14.9 Hz, 1H), 6.03 (s, 1H), 4.11 (t, J = 7.1 Hz, 2H), 2.09 (s, 6H), 1.90-1.84 (m, 2H), 1.50-1.44 (m, 2H), 1.39-1.31 (m, 4H), 0.90 (t, J = 7.0 Hz, 3H). 13 C NMR (500 MHz, CDCl3) δ 178.04, 171.34, 139.65, 134.39, 131.18, 129.69, 129.61, 128.71, 127.28, 124.23, 122.57, 110.13, 86.26, 51.17, 43.83, 31.52, 27.33, 26.79, 26.74, 22.55, 13.99.

[0089] (Preparation of Compound 2c)

[0090] [ka]

[0091] To a solution of compound 1c (5.05 g, 10.0 mmol) in 40 mL of anhydrous toluene / n-butanol (v / v = 1 / 1), squaric acid (0.57 g, 5.0 mmol) was added. The resulting reaction mixture was subjected to azeotropic reflux overnight at 120 °C using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using hexane-ethyl acetate as the eluent. The pure fractions were collected, evaporated, and dried under vacuum to give compound 2c (3.0 g, 65% yield) as a blue-black solid.

[0092] The mass analysis (HRMS) of compound 2c was carried out. HRMS calcd. for C 58 H 76 N2O2[M+H] 833.59, found 833.60.

[0093] Compound 2cの 1 H-NMR analysis, 13 C-NMR analysis was carried out. 1 H NMR (500 MHz, CDCl3) δ 8.20 (d, J = 8.5 Hz, 1H), 7.89 (d, J = 8.1, Hz, 1H), 7.86 (d, J = 8.7 Hz, 1H), 7.57 (dd, J = 6.8, 15.3 Hz, 1H), 7.41 (dd, J = 7.9, 15.0 Hz, 1H), 7.28 (dd, J = 8.8, 15.4 Hz, 1H), 6.03 (s, 1H), 4.10 (t, J = 7.1 Hz, 2H), 2.09 ( s, 6H), 1.90-1.84 (m, 2H), 1.49-1.43 (m, 2H), 1.38-1.35 (m, 2H), 1.30-1.25 (m, 14H), 0.87 (t, J = 6.8 Hz, 3H). 13 C NMR (500 MHz, CDCl3) δ 178.02, 171.34, 139.66, 134.40, 131.18, 129.69, 129.60, 128.72, 127.28, 124.23, 122.58, 110.14, 86.28, 51.17, 43.84, 31.91, 29.60, 29.53, 29.51, 29.40, 29.33, 27.38, 27.10, 26.80, 22.69, 14.14

[0094] (Manufacture of Compound 2d)

[0095]

change

[0096] To a solution of compound 1d (5.89 g, 10.0 mmol) in 40 mL of anhydrous toluene / n-butanol (v / v = 1 / 1), squaric acid (0.57 g, 5.0 mmol) was added. The resulting reaction mixture was subjected to azeotropic reflux overnight at 120 °C using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using chloroform-methanol as the eluent. The pure fractions were collected, evaporated, and dried under vacuum to give compound 2d (2.2 g, 44% yield) as a blue-black solid.

[0097] Mass spectrometry (HRMS) of compound 2d was carried out. HRMS calculation for C 70 H 100 N2O2[M+H] 1001.78, found 1001.78.

[0098] Compound 2d 1 H-NMR analysis, 13 C-NMR analysis was performed. 1 H NMR (500 MHz, CDCl3) δ 8.20 (d, J = 8.5 Hz, 1H), 7.90 (d, J = 8.1 Hz, 1H), 7.87 (d, J = 8.7 Hz, 1H), 7.57 (dd, J = 6.8, 15.3 Hz, 1H), 7.41 (dd, J = 7.8, 14.9 Hz, 1H), 7.28 (dd, J = 8.8, 15.8 Hz, 1H), 6.03 (s, 1H), 4.12 (m, 2H), 2.09 (s, 6H), 1.90-1.84 (m, 2H), 1.48-1.43 (m, 2H), 1.41-1.35 (m, 2H), 1.30-1.21 (m, 26H), 0.87 (t, J = 6.8 Hz, 3H). 13C NMR (500 MHz, CDCl3) δ 177.95, 171.36, 139.66, 134.41, 131.19, 128.72, 129.69, 129.60, 127.28, 124.23, 122.59, 110.14, 86.28, 51.17, 43.85, 31.93, 29.71, 29.66, 29.62, 29.56, 29.53, 29.42, 29.37, 27.39, 26.80, 26.70, 22.70, 14.13.

[0099] [Step 1-3] (Production of the double squaraine dye TM1 of the present invention)

[0100] [ka]

[0101] To a solution of compound 2a (0.55 g, 1.0 mmol) in 12 mL of anhydrous toluene / n-butanol (v / v = 5 / 1), squaric acid (0.11 g, 1.1 mmol) was added. The resulting reaction mixture was azeotropically refluxed at 120 °C overnight using a Dean-Stark apparatus. TLC confirmed that more than half of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 10 h. TLC confirmed that approximately 30% of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 8 h. TLC confirmed that no further reduction of the starting material occurred. The mixture was removed from the heat and cooled to room temperature. The solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using chloroform-methanol as the eluent. The pure blue fractions were collected, the solvent evaporated and dried in vacuo to give the double squaraine dye TM1 (160 mg, 25% yield) as a purple-black solid.

[0102] Mass spectrometry (ESI+) of the double squaraine dye TM1 was performed. TOF mass ESI+ calcd. for C46 H 36 N2O5[M+H] 649.26, found 649.27.

[0103] ダブルスクアライン pigment TM1の 1 H-NMR analysis, 13 C-NMR analysis was carried out. 1 H NMR (500 MHz, DMSO-d6) δ 8.42 (d, J = 2.6 Hz, 1H), 8.40 (d, J = 3.8 Hz, 1H), 8.30 (d, J = 7.2 Hz, 1H), 8.29 (d, J = 1.6 Hz, 1H), 8.07 (d, J = 8.46 Hz, 1H), 7.92 (d, J = 8.6 Hz, 1H), 7.78-7.84 (m, 2H), 7.53 (d, J = 8.9 Hz, 1H), 7.48 (t, J = 7.4, 7.8 Hz, 1H), 7.34 (t, J = 7.7, 7.2 Hz, 1H), 5.48 (s, 1H), 4.63 (dd, J = 7.1, 8.0 Hz, 2H), 4.05 (d, J = 7.2 Hz, 2H), 1.78 (s, 6H), 1.74 (s, 6H), 1.46 (t, J = 7.2 Hz, 3H), 1.23 (t, J = 7.7 Hz, 3H), 1.26 (s, 1H). 13C NMR (500 MHz, CDCl3) δ 197.31, 194.61, 193.41, 192.65, 180.61, 178.31, 167.91, 167.19, 158.25, 157.59, 139.75, 139.62, 137.30, 133.82, 132.50, 130.97, 130.66, 129.98, 129.72, 129.61, 128.75, 128.52, 128.30, 127.72, 127.05, 123.54, 123.41, 122.10, 112.60, 109.51, 83.91, 82.69, 58.65, 49.78, 45.13, 37.82, 26.45, 26.24, 23.19, 22.73, 13.01, 11.93.

[0104] (Production of the double squaraine dye TM2 of the present invention)

[0105] [ka]

[0106] To a solution of compound 2b (0.66 g, 1.0 mmol) in 12 mL of anhydrous toluene / n-butanol (v / v = 5 / 1), squaric acid (0.11 g, 1.1 mmol) was added. The resulting reaction mixture was azeotropically refluxed at 120 °C overnight using a Dean-Stark apparatus. TLC confirmed that more than half of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 10 h. TLC confirmed that approximately 20% of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 8 h. TLC confirmed that no further reduction of the starting material occurred. The mixture was removed from the heat and cooled to room temperature. The solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using chloroform-methanol as the eluent. The pure blue fractions were collected, the solvent evaporated and dried in vacuo to give the double squaraine dye TM2 (200 mg, 26% yield) as a purple-black solid.

[0107] Mass spectrometry (HRMS) of the double squaraine dye TM2 was performed. HRMS calculation for C 50 H 52 N2O5[M] 760.39 found 760.39.

[0108] Double squaraine dye TM2 1 H-NMR analysis, 13 C-NMR analysis was performed. 1 H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.2 Hz, 1 H), 8.13 (d, J = 8.9 Hz, 1 H), 8.09 (d, J = 8.0 Hz, 1 H), 8.04 (d, J = 8.5 Hz, 1 H), 7.84 (d, J = 8.1 Hz, 1 H), 7.81 (d, J = 8.8 Hz, 1 H), 7.69-7.76 (m, 3 H), 7.46 ( dd, J = 7.8, 15.2 Hz, 1 H), 7.33 (dd, J = 7.8, 15.0 Hz, 1 H), 7.19 (d, J = 8.8Hz, 1H), 5.56(s, 1 H), 4.30-4.43 (m, 2 H), 3.92 (t, J = 7.5 Hz, 2 H), 1.92 (s, 6 H), 1.88 (s, 3 H), 1.86 (s, 3 H), 1.25-1.49 (m, 16 H), 0.89 (t, J = 7.0 Hz, 3 H), 0.84 (t, J = 6.9 Hz, 3 H). 13C NMR (500 MHz, CDCl3) δ 197.39, 194.50, 193.12, 192.61, 180.51, 178.34, 167.94, 167.63, 158.26, 157.69, 140.14, 139.61, 137.69, 133.78, 132.39, 130.89, 130.63, 129.96, 129.71, 129.52, 128.69, 128.49, 128.25, 127.68, 127.05, 123.54, 123.40, 122.12, 112.67, 109.78, 84.10, 83.04, 58.66, 49.98, 49.75, 43.16, 31.50, 31.06, 29.70, 27.71, 26.90, 26.69, 26.63, 26.49, 26.32, 23.24, 22.97, 22.50, 22.28, 13.97, 13.89.

[0109] (Production of the double squaraine dye TM3 of the present invention)

[0110] [ka]

[0111] To a solution of compound 2c (0.83 g, 1.0 mmol) in 12 mL of anhydrous toluene / n-butanol (v / v = 5 / 1), squaric acid (0.11 g, 1.1 mmol) was added. The resulting reaction mixture was azeotropically refluxed at 120 °C overnight using a Dean-Stark apparatus. TLC confirmed that more than half of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 10 h. TLC confirmed that approximately 15% of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 8 h. TLC confirmed that no further reduction of the starting material occurred. The mixture was removed from the heat and cooled to room temperature. The solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using hexane-ethyl acetate as the eluent. The pure blue fractions were collected, the solvent evaporated and dried in vacuo to give the double squaraine dye TM3 (250 mg, 27% yield) as a purple-black solid.

[0112] Mass spectrometry (HRMS) of the double squaraine dye TM3 was performed. HRMS calculation for C 62 H 76 N2O5[M+H] 929.58, found 929.58.

[0113] Double squaraine dye TM3 1 H-NMR analysis, 13 C-NMR analysis was performed. 1H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.4 Hz, 1 H), 8.13 (d, J = 8.9 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H), 8.04 (d, J = 8.6 Hz, 1 H), 7.84 (d, J = 8.1 Hz, 1 H), 7.81 (d, J = 8.8 Hz, 1 H), 7.68-7.76 (m, 3 H), 7.46 ( dd, J = 7.1, 14.5 Hz, 1 H), 7.33 (dd, J = 7.4, 14.6 Hz, 1 H), 7.19 (d, J = 8.8 Hz, 1 H), 5.56 (s, 1 H), 4.29-4.43 (m, 2 H), 3.92 (t, J = 7.5 Hz, 2 H), 1.92 ( s, 6 H), 1.88 (s, 3 H), 1.86 (s, 3 H), 1.20-1.48 (m, 40 H), 0.87 (t, J = 6.9 Hz, 3 H), 0.84 (t, J = 6.9 Hz, 3H). 13 C NMR (500 MHz, CDCl3) δ 197.38, 194.50, 193.10, 192.62, 180.49, 178.35, 167.93, 167.60, 158.27, 157.71, 140.14, 139.60, 137.69, 133.77, 132.39, 130.89, 130.63, 129.96, 129.70, 129.52, 128.69, 128.49, 128.24, 127.67, 127.04, 123.53, 123.40, 122.11, 112.68, 109.78, 84.09, 83.04, 58.66, 49.97, 49.75, 43.17, 31.89, 31.86, 29.70, 29.59, 29.57, 29.53, 29.48, 29.47, 29.39, 29.32, 29.28, 29.26, 28.98, 27.76, 27.07, 26.98, 26.79, 26.51, 26.33, 23.23, 22.97, 22.67, 22.64, 14.12, 14.09.

[0114] (Production of the double squaraine dye TM4 of the present invention)

[0115] [ka]

[0116] To a solution of compound 2d (1.0 g, 1.0 mmol) in 12 mL of anhydrous toluene / n-butanol (v / v = 5 / 1), squaric acid (0.11 g, 1.1 mmol) was added. The resulting reaction mixture was azeotropically refluxed at 120 °C overnight using a Dean-Stark apparatus. TLC confirmed that more than half of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 10 h. TLC confirmed that approximately 10% of the starting material remained. Squaric acid (0.1 g, 1.0 mmol) was added to the resulting reaction mixture, and the mixture was refluxed for an additional 8 h. TLC confirmed that no further reduction of the starting material occurred. The mixture was removed from the heat and cooled to room temperature. The solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using chloroform-methanol as the eluent. The pure blue fractions were collected, the solvent evaporated and dried in vacuo to give the double squaraine dye TM4 (360 mg, 33% yield) as a purple-black solid.

[0117] Mass spectrometry (HRMS) of the double squaraine dye TM4 was performed. HRMS calculation for C 74 H 100 N2O5[M+H] 1097.76, found 1097.77.

[0118] Double squaraine dye TM4 1 H-NMR analysis, 13 C-NMR analysis was performed. 1H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.4 Hz, 1 H), 8.13 (d, J = 8.9 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H), 8.04 (d, J = 8.6 Hz, 1 H), 7.84 (d, J = 8.1 Hz, 1 H), 7.81 (d, J = 8.8 Hz, 1 H), 7.68-7.76 (m, 3 H), 7.45 ( dd, J = 7.1, 15.3 Hz, 1 H), 7.32 (dd, J = 7.4, 15.1 Hz, 1 H), 7.19 (d, J = 8.8 Hz, 1 H), 5.56 (s, 1 H), 4.29-4.43 (m, 2 H), 3.91 (t, J = 7.5 Hz, 2 H), 1.92 ( s, 6 H), 1.88 (s, 3 H), 1.86 (s, 3 H), 1.20-1.49 (m, 64 H), 0.88 (t, J = 3.4 Hz, 3 H), 0.86 (t, J = 3.6 Hz, 3H). 13 C NMR (500 MHz, CDCl3) δ 197.38, 194.51, 193.12 192.63, 180.50, 178.36, 167.91, 167.57, 158.26, 157.73, 140.15, 139.60, 137.69, 133.77, 132.39, 130.88, 130.63, 129.96, 129.71, 129.51, 128.69, 128.48, 128.25, 127.67, 127.04, 123.53, 123.40, 122.11, 112.68, 109.77, 84.11, 83.04, 58.66, 49.97, 49.74, 43.17, 31.92, 29.68, 29.65, 29.61, 29.56, 29.50, 29.41, 29.36, 29.27, 28.98, 27.76, 27.08, 26.98, 26.51, 26.33, 23.23, 22.97, 22.69, 14.13.

[0119] (Confirmation of yield by solvent mixing ratio) The double squaraine dye TM3 was produced and its yield was confirmed by changing the mixing ratio of the mixed solvents in steps 1-3 of the double squaraine dye production method of Example 1. Specifically, the following procedure was carried out.

[0120] Compound 2c (100 mg, 0.12 mmol) was dissolved in 2 mL of a toluene / n-butanol mixture at different ratios, and 3 to 5 equivalents of squaric acid were added. The mixture was then refluxed for 6 to 8 hours to obtain the target product. Table 1 shows the relationship between the solvent ratio and the yield of the resulting double squaraine dye TM3.

[0121] [Table 1]

[0122] As shown in Table 1, the double squaraine dye TM3 was produced when the toluene / n-butanol mixture ratio was in the range of 1 / 3 to 9 / 1. When the toluene / n-butanol mixture ratio was in the range of 1 to 7 / 1, the double squaraine dye TM3 was produced in a high yield of 10% or more.

[0123] (Confirmation of yield based on substrate concentration (solvent volume)) The double squaraine dye TM3 was produced and its yield was confirmed by varying the substrate concentration in steps 1-3 of the double squaraine dye production method of Example 1. Specifically, the procedure was as follows.

[0124] Compound 2c (100 mg, 0.12 mmol) was dissolved in various amounts of a toluene / n-butanol mixed solvent (v / v = 5 / 1), and 3 to 5 equivalents of squaric acid were added. The mixture was then refluxed for 6 to 8 hours to obtain the desired product. Table 2 shows the relationship between the amount of solvent used and the yield of the resulting double squaraine dye TM3.

[0125] [Table 2]

[0126] As shown in Table 2, the yield varied depending on the substrate concentration. In this test, a higher yield was obtained when 2 ml of solvent was used.

[0127] [Example 2] The double squaraine dyes TM1 to TM4 of the present invention were produced using a method different from that used in Example 1. An outline of the production steps of the production method of Example 2 (steps 2-1 to 2-4) is shown below.

[0128] [ka]

[0129] Each step will be specifically described below. [Step 2-1] (Production of Compound TD11)

[0130] [ka]

[0131] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (6.3 g, 30.0 mmol), was placed in 50 mL of acetonitrile and iodoethane (9.6 mL, 120.0 mmol) was added. The resulting mixture was refluxed for 18 hours. Thin layer chromatography (TLC) confirmed complete consumption of the starting material. The reaction was cooled to room temperature, and 150 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound TD11 (11.0 g, 100% yield) as a gray solid.

[0132] Mass spectrometry (HRMS) of compound TD11 was performed. HRMS calculation for C 17 H 20 N + [M+] 238.16, found 238.16.

[0133] (Production of Compound TD21)

[0134] [ka]

[0135] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (4.2 g, 20.0 mmol), was placed in 40 mL of acetonitrile and 1-iodohexane (8.5 mL, 40.0 mmol) was added. The resulting mixture was refluxed for 24 hours. TLC confirmed complete consumption of the starting material. The reaction was cooled to room temperature, and 200 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound TD21 (8.0 g, 95% yield) as a gray solid.

[0136] Mass spectrometry (HRMS) of compound TD21 was performed. HRMS calculation for C 21 H 28 N + [M+] 294.22, found 294.22.

[0137] (Production of Compound TD31)

[0138] [ka]

[0139] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (2.1 g, 10.0 mmol), was placed in 20 mL of propionitrile and 1-iodododecane (5.0 mL, 20.0 mmol) was added. The resulting mixture was refluxed for 36 hours. TLC confirmed complete consumption of the starting material. The reaction was cooled to room temperature, and 100 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound TD31 (5.0 g, 100% yield) as a gray solid.

[0140] Mass spectrometry (HRMS) of compound TD31 was performed. HRMS calculation for C 27 H 40 N + [M+] 378.32, found 378.32.

[0141] (Production of Compound TD41)

[0142] [ka]

[0143] The starting material, 1,1,2-trimethyl-1H-benzo[e]indole (6.3 g, 30.0 mmol), was placed in 60 mL of propionitrile and 1-iodooctadecane (13.7 mg, 36.0 mmol) was added. The resulting mixture was refluxed for 48 hours. TLC confirmed that the starting material was nearly consumed. The reaction was cooled to room temperature, and 250 mL of ethyl acetate was added. The resulting precipitate was filtered and washed with ethyl acetate to give compound TD41 (12.6 g, 75% yield) as a gray solid.

[0144] Mass spectrometry (HRMS) of compound TD41 was performed. HRMS calculation for C 33 H 52 N + [M+] 462.41, found 462.41.

[0145] [Step 2-2] (Production of Compound TD12) Preparation of compound TD12 from compound TD11

[0146] [ka]

[0147] To a 50 mL ethanol solution of compound TD11 (9.0 g, 24.6 mmol), diethyl squarate (4.2 g, 24.6 mmol) and triethylamine (10.3 mL, 73.8 mmol) were added. The resulting solution was stirred at room temperature for 15 hours, and a yellow precipitate was observed. TLC confirmed that compound TD11 was almost consumed. The resulting yellow precipitate was filtered and washed with 100 mL of cold ethanol to give compound TD12 (8.5 g, 97% yield) as a yellow solid.

[0148] Mass spectrometry (ESI+) of compound TD12 was performed. TOF mass ESI+ calcd. for C 23 H 23 NO3[M+Na] 384.17, found 384.16.

[0149] (Production of Compound TD22) Preparation of compound TD22 from compound TD21

[0150] [ka]

[0151] To a 25 mL ethanol solution of compound TD21 (4.2 g, 10.0 mmol), diethyl squarate (1.7 g, 10.0 mmol) and triethylamine (4.2 mL, 30.0 mmol) were added. The resulting solution was stirred at room temperature for 15 hours, and a yellow precipitate was observed. TLC confirmed that compound TD21 was almost consumed. The resulting yellow precipitate was filtered and washed with 60 mL of cold ethanol to give compound TD22 (3.8 g, 91% yield) as a yellow solid.

[0152] Mass spectrometry (ESI+) of compound TD22 was performed. TOF mass ESI+ calcd. for C 27 H 31 NO3[M+Na] 440.23, found 440.22.

[0153] (Production of Compound TD32) Preparation of compound TD32 from compound TD31

[0154] [ka]

[0155] To a solution of compound TD31 (5.0 g, 10.0 mmol) in 25 mL of ethanol, diethyl squarate (1.7 g, 10.0 mmol) and triethylamine (4.2 mL, 30.0 mmol) were added. The resulting solution was stirred at room temperature for 15 hours, and a yellow precipitate was observed. TLC confirmed that compound TD31 was almost consumed. The resulting yellow precipitate was filtered and washed with 60 mL of cold ethanol to obtain compound TD32 (4.0 g, 80% yield) as a yellow solid.

[0156] Mass spectrometry (ESI+) of compound TD32 was performed. TOF mass ESI+ calcd. for C 33 H 43 NO3[M+Na] 524.32, found 532.31; TOF mass ESI+ calcd. For C 33 H 43 NO3[M+H] 502.32, found 502.33; TOF mass ESI+ calcd. For C 33 H 43 NO3[2M+Na] 1002.64, found 1025.64.

[0157] (Production of Compound TD42) Preparation of compound TD42 from compound TD41

[0158] [ka]

[0159] To a 20 mL ethanol solution of compound TD41 (5.0 g, 8.5 mmol), diethyl squarate (1.4 g, 8.5 mmol) and triethylamine (3.6 mL, 25.5 mmol) were added. The resulting solution was stirred at room temperature for 36 hours, and a yellow precipitate was observed. TLC confirmed that compound TD41 was almost consumed. The resulting yellow precipitate was filtered and washed with 50 mL of cold ethanol to give compound TD42 (4.0 g, 80% yield) as a yellow solid.

[0160] Mass spectrometry (ESI+) of compound TD42 was performed. TOF mass ESI+ calcd. for C 39 H 55 NO3[M+Na] 608.42, found 608.41; TOF mass ESI+ calcd. For C 39 H 55 NO3[2M+Na] 1193.84, found 1193.83.

[0161] [Step 2-3] (Production of Compound TD13) Preparation of compound TD13 from compound TD12

[0162] [ka]

[0163] To a solution of compound TD12 (1.5 g, 4.2 mmol) in 8 mL of ethanol, 0.8 mL of 40% aqueous NaOH was added. The resulting mixture was stirred at room temperature overnight, and a yellow precipitate was observed. TLC confirmed that compound TD12 had been consumed. The resulting yellow precipitate was filtered and washed with 10 mL of cold ethanol to give compound TD13 (1.3 g, 85% yield) as a yellow solid.

[0164] Mass spectrometry (HRMS) of compound TD13 was performed. HRMS calculation for C 21 H 18NNaO3[M+] 355.12, found 355.12.

[0165] (Production of Compound TD23) Preparation of compound TD23 from compound TD22

[0166] [ka]

[0167] To a 5 mL ethanol solution of compound TD22 (1.0 g, 2.4 mmol), 0.5 mL of 40% aqueous NaOH was added. The resulting mixture was stirred at room temperature overnight, and a yellow precipitate was observed. TLC confirmed that compound TD22 had been consumed. The resulting yellow precipitate was filtered and washed with 10 mL of cold ethanol to give compound TD23 (0.8 g, 80% yield) as a yellow solid.

[0168] Mass spectrometry (ESI+) of compound TD23 was performed. TOF mass ESI+ calcd. for C 25 H 26 NNaO3[M+Na] 434.18, found 434.17.

[0169] (Production of Compound TD33) Preparation of compound TD33 from compound TD32

[0170] [ka]

[0171] To a 5 mL ethanol solution of compound TD32 (1.0 g, 2.0 mmol), 0.4 mL of 40% aqueous NaOH was added. The resulting mixture was stirred at room temperature overnight, and a yellow precipitate was observed. TLC confirmed that compound TD32 had been consumed. 1.0 mL of 4N aqueous HCl was added. The resulting yellow precipitate was filtered and washed with 10 mL of cold ethanol to obtain the hydroxide of compound TD33 (0.7 g, 70% yield) as a yellow solid.

[0172] Mass spectrometry (HRMS) of the hydroxide of compound TD33 was carried out. HRMS calculation for C 31 H 39 NO3[M+] 473.29, found 473.29.

[0173] (Production of Compound TD43) Preparation of compound TD43 from compound TD42

[0174] [ka]

[0175] To a solution of compound TD42 (1.5 g, 2.6 mmol) in 8 mL of ethanol, 0.5 mL of 40% aqueous NaOH was added. The resulting mixture was stirred at room temperature overnight, and a yellow precipitate was observed. TLC confirmed that compound TD42 had been consumed. The resulting yellow precipitate was filtered and washed with 10 mL of cold ethanol to give compound TD43 (1.2 g, 80% yield) as a yellow solid.

[0176] Mass spectrometry (ESI-) of compound TD43 was performed. TOF mass ESI-calcd. for C 37 H 51 NNaO3[MH] 556.39, found 556.38.

[0177] [Step 2-4] (Production of the double squaraine dye TM1 of the present invention) Preparation of double squaraine dye TM1 from compound TD13

[0178] [ka]

[0179] To a suspension of compound TD13 (0.36 g, 1.0 mmol) in 10 mL of anhydrous ether, thionyl chloride (0.145 mL, 2.0 mmol) was added. The resulting mixture was stirred at 0–5°C for 30 min. The solvent and excess thionyl chloride were gently evaporated under reduced pressure, and the residue was dissolved in 12 mL of anhydrous toluene / n-butanol (5:1 v / v) mixture. The reaction mixture was azeotropically refluxed overnight using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using hexane-ethyl acetate as the eluent. The pure purple fraction was collected and dried under a stream of nitrogen gas to give the double squaraine dye TM1 (65 mg, 10% yield) as a purple-black solid.

[0180] Mass spectrometry (ESI+) of the double squaraine dye TM1 was performed, and the measurement results are shown in Figure 1. TOF mass ESI+ calcd. for C 46 H 36 N2O5[M+H] 649.26, found 649.27.

[0181] Double squaraine dye TM1 1 H-NMR analysis was performed. 1H NMR (500 MHz, DMSO-d6) δ 8.42 (d, J = 2.6 Hz, 1 H), 8.40 (d, J = 3.8 Hz, 1 H), 8.30 (d, J = 7.2 Hz, 1 H), 8.29 (d, J = 1.6 Hz, 1 H), 8.07 (d, J = 8.46 Hz, 1 H), 7.92 (d, J = 8.6 Hz, 1 H), 7.78-7.84 (m, 2 H), 7.53 (d, J = 8.9 Hz, 1 H), 7.48 (dd, J = 7.4, 7.8 Hz, 1 H), 7.34 (dd, J = 7.7, 7.2Hz, 1H), 5.48(s, 1 H), 4.63 (dd, J = 7.1, 8.0 Hz, 2 H), 4.05 (d, J = 7.2 Hz, 2 H), 1.78 (s, 6 H), 1.74 (s, 6 H), 1.46 (t, J = 7.2 Hz, 3 H), 1.23 (t, J = 7.7 Hz, 3 H), 1.26 (s, 1 H).

[0182] (Production of the double squaraine dye TM2 of the present invention) Preparation of double squaraine dye TM2 from compound TD23

[0183] [ka]

[0184] To a suspension of compound TD23 (0.41 g, 1.0 mmol) in 10 mL of anhydrous ether, thionyl chloride (0.145 mL, 2.0 mmol) was added. The resulting mixture was stirred at 0–5°C for 30 min. The solvent and excess thionyl chloride were gently evaporated under reduced pressure, and the residue was dissolved in 12 mL of anhydrous toluene / n-butanol (5:1 v / v) mixture. The reaction mixture was azeotropically refluxed overnight using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using hexane-ethyl acetate as the eluent. The pure purple fraction was collected and dried under a stream of nitrogen gas to give the double squaraine dye TM2 (55 mg, 7% yield) as a purple-black solid.

[0185] Mass spectrometry (HR-MS) of the double squaraine dye TM2 was performed, and the measurement results are shown in Figure 2. HR-FAB-calcd. for C 50 H 53 N2O5[M+] 760.39, found 760.38.

[0186] Double squaraine dye TM2 1 H-NMR analysis was performed. 1H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.2 Hz, 1 H), 8.13 (d, J = 8.9 Hz, 1 H), 8.09 (d, J = 8.0 Hz, 1 H), 8.04 (d, J = 8.5 Hz, 1 H), 7.84 (d, J = 8.1 Hz, 1 H), 7.81 (d, J = 8.8 Hz, 1 H), 7.69-7.76 (m, 3 H), 7.46 (dd, J = 7.8, 15.2 Hz, 1 H), 7.33 (dd, J = 7.8, 15.0 Hz, 1 H), 7.19 (d, J = 8.8 Hz, 1 H), 5.56 (s, 1 H), 4.30-4.43 (m, 2 H), 3.92 (t, J = 7.5 Hz, 2 H), 1.92 (s, 6 H), 1.88 (s, 3 H), 1.86 (s, 3 H), 1.25-1.49 (m, 16 H), 0.89 (t, J = 7.0 Hz, 3 H), 0.84 (t, J = 6.9 Hz, 3 H). 13 C NMR (500 MHz, CDCl3) δ 197.39, 194.50, 193.12, 192.61, 180.51, 178.34, 167.94, 167.63, 158.26, 157.69, 140.14, 139.61, 137.69, 133.78, 132.39, 130.89, 130.63, 129.96, 129.71, 129.52, 128.69, 128.49, 128.25, 127.68, 127.05, 123.54, 123.40, 122.12, 112.67, 109.78, 84.10, 83.04, 58.66, 49.98, 49.75, 43.16, 31.50, 31.06, 29.70, 27.71, 26.90, 26.69, 26.63, 26.49, 26.32, 23.24, 22.97, 22.50, 22.28, 13.97, 13.89.

[0187] (Manufactured by Honsen Ming's ブルスクアライン Pigment TM3) Preparation of double squaraine dye TM3 from compound TD33

[0188] [ka]

[0189] To a suspension of compound TD33 (0.5 g, 1.0 mmol) in 10 mL of anhydrous ether, thionyl chloride (0.145 mL, 2.0 mmol) was added. The resulting mixture was stirred at 0–5°C for 20 min. The solvent and excess thionyl chloride were gently evaporated under reduced pressure, and the residue was dissolved in 12 mL of anhydrous toluene / n-butanol (5:1 v / v) mixture. The reaction mixture was azeotropically refluxed overnight using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using hexane-ethyl acetate as the eluent. The pure purple fraction was collected and dried under a stream of nitrogen gas to give the double squaraine dye TM3 (60 mg, 6% yield) as a purple-black solid.

[0190] Mass spectrometry (HRMS) of the double squaraine dye TM3 was performed, and the measurement results are shown in Figure 3. HRMS calculation for C 62 H 76 N2O5[M+H] 929.58, found 929.58.

[0191] Double squaraine dye TM3 1 H-NMR analysis was performed. 1H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.4 Hz, 1 H), 8.13 (d, J = 8.9 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H), 8.04 (d, J = 8.6 Hz, 1 H), 7.84 (d, J = 8.1 Hz, 1 H), 7.81 (d, J = 8.8 Hz, 1 H), 7.68-7.76 (m, 3 H), 7.46 ( dd, J = 7.1, 14.5 Hz, 1 H), 7.33 (dd, J = 7.4, 14.6 Hz, 1 H), 7.19 (d, J = 8.8 Hz, 1 H), 5.56 (s, 1 H), 4.29-4.43 (m, 2 H), 3.92 (t, J = 7.5 Hz, 2 H), 1.92 ( s, 6 H), 1.88 (s, 3 H), 1.86 (s, 3 H), 1.20-1.48 (m, 40 H), 0.87 (t, J = 6.9 Hz, 3 H), 0.84 (t, J = 6.9 Hz, 3H). 13 C NMR (500 MHz, CDCl3) δ 197.38, 194.50, 193.10, 192.62, 180.49, 178.35, 167.93, 167.60, 158.27, 157.71, 140.14, 139.60, 137.69, 133.77, 132.39, 130.89, 130.63, 129.96, 129.70, 129.52, 128.69, 128.49, 128.24, 127.67, 127.04, 123.53, 123.40, 122.11, 112.68, 109.78, 84.09, 83.04, 58.66, 49.97, 49.75, 43.17, 31.89, 31.86, 29.70, 29.59, 29.57, 29.53, 29.48, 29.47, 29.39, 29.32, 29.28, 29.26, 28.98, 27.76, 27.07, 26.98, 26.79, 26.51, 26.33, 23.23, 22.97, 22.67, 22.64, 14.12, 14.09.

[0192] (Production of the double squaraine dye TM4 of the present invention) Preparation of double squaraine dye TM4 from compound TD43

[0193] [ka]

[0194] To a suspension of compound TD43 (0.58 g, 1.0 mmol) in 15 mL of anhydrous ether, thionyl chloride (0.145 mL, 2.0 mmol) was added. The resulting mixture was stirred at 0–5°C for 20 min. The solvent and excess thionyl chloride were gently evaporated under reduced pressure, and the residue was dissolved in 18 mL of anhydrous toluene / n-butanol (5:1 v / v) mixture. The reaction mixture was azeotropically refluxed overnight using a Dean-Stark apparatus. After completion of the reaction, the solvent was evaporated, and the crude product was purified by silica gel flash column chromatography using hexane-ethyl acetate as the eluent. The pure purple fraction was collected and dried under a stream of nitrogen gas to give the double squaraine dye TM4 (85 mg, 8% yield) as a purple-black solid.

[0195] Mass spectrometry (HRMS) of the double squaraine dye TM4 was performed, and the measurement results are shown in Figure 4. HRMS calculation for C 74 H 100 N2O5[M+H] 1097.76, found 1097.77.

[0196] Double squaraine dye TM4 1 H-NMR analysis was performed. 11H NMR (500 MHz, CDCl3) δ 8.16 (d, J = 8.4 Hz, 1 H), 8.13 (d, J = 8.9 Hz, 1 H), 8.09 (d, J = 7.8 Hz, 1 H), 8.04 (d, J = 8.6 Hz, 1 H), 7.84 (d, J = 8.1 Hz, 1 H), 7.81 (d, J = 8.8 Hz, 1 H), 7.68 - 7.76 (m, 3 H), 7.45 (dd, J = 7.1, 15.3 Hz, 1 H), 7.32 (dd, J = 7.4, 15.1 Hz, 1 H), 7.19 (d, J = 8.8 Hz, 1 H), 5.56 (s, 1 H), 4.29 - 4.43 (m, 2 H), 3.91 (t, J = 7.5 Hz, 2 H), 1.92 (s, 6 H), 1.88 (s, 3 H), 1.86 (s, 3 H), 1.20 - 1.49 (m, 64 H), 0.88 (t, J = 3.4 Hz, 3 H), 0.86 (t, J = 3.6 Hz, 3H). 13 13C NMR (500 MHz, CDCl3) δ 197.38, 194.51, 193.12 192.63, 180.50, 178.36, 167.91, 167.57, 158.26, 157.73, 140.15, 139.60, 137.69, 133.77, 132.39, 130.88, 130.63, 129.96, 129.71, 129.51, 128.69, 128.48, 128.25, 127.67, 127.04, 123.53, 123.40, 122.11, 112.68, 109.77, 84.11, 83.04, 58.66, 49.97, 49.74, 43.17, 31.92, 29.68, 29.65, 29.61, 29.56, 29.50, 29.41, 29.36, 29.27, 28.98, 27.76, 27.08, 26.98, 26.51, 26.33, 23.23, 22.97, 22.69, 14.13.

[0197] [Example 3] (Example 3-1) The double squaraine dye (symmetrical double squaraine dye) TC-309 of the present invention was prepared in the same manner as in Example 1. Mass spectrometry (ESI+) of the obtained double squaraine dye TC-309 was performed. The measurement results are shown in Figure 5. TC-309 TOF mass ESI+ calcd. for C 52 H 68 N2O7[M+H] 833.50, found 833.51

[0198] [ka]

[0199] (Example 3-2) In the same manner as in Example 1 above, the double squaraine dyes (asymmetric double squaraine dyes) TC-303, TC-195, TC-185, TC-187, and TC-176 of the present invention shown below were produced.

[0200] [ka]

[0201] The resulting double squaraine dyes TC-303, TC-195, TC-185, TC-187, and TC-176 were subjected to mass spectrometry (ESI+). The measurement results are shown in Figures 6 to 10. TC-303 TOF mass ESI+ calcd. for C 48 H 54 N2O6[M+Na] 777.40, found 777.39 TC-195 TOF mass ESI+ calcd. for C 49 H 56 N2O6[M+H] 769.41, found 769.42 TC-185 TOF mass ESI+ calcd. for C 48 H 53BrN2O5[M+Na] 839.31, found 839.30. TC-187 TOF mass ESI+ calcd. for C 49 H 53 N3O5[M+Na] 786.40, found 786.39. TC-176 TOF mass ESI+ calcd. for C 49 H 54 N2O7[M+Na] 805.39, found 805.38

[0202] (Example 3-3) In the same manner as in Example 1 above, the double squaraine dye (asymmetric double squaraine dye) TC-308 of the present invention was produced.

[0203] [ka]

[0204] The resulting double squaraine dye TC-308 was subjected to mass spectrometry (ESI+), and the measurement results are shown in Figure 11. TC-308 TOF mass ESI+ calcd. for C 47 H 50 N2O5[M+Na] 745.37, found 745.36

[0205] (Examples 3-4) The double squaraine dye (asymmetric double squaraine dye) TC-177 of the present invention was produced.

[0206] [ka]

[0207] The double squaraine dye TC-177 thus obtained was subjected to mass spectrometry (ESI+), and the measurement results are shown in Figure 12. TC-177 TOF mass ESI+ calcd. for C57 H 64 N2O7[M+Na] 911.47, found 911.46

[0208] [Example 4] [Optical property evaluation] (Metal ion sensing test) The double squaraine dyes (TM1 and TM3) of the present invention produced as described above were evaluated for ion sensing according to the properties of metal ions using a spectral sensitivity measurement method.

[0209] The results are shown in Figures 13 and 14. As shown in Figures 13 and 14, the acetonitrile / DMF solvent mixture exhibited a purple color with a predominant absorption at 500-600 nm. 2+ When ions were added, the intensity of the purple color decreased, and clear absorption was observed in the high-wavelength near-infrared region of 650 to 800 nm, resulting in a color change from purple to cyan. In addition, the length of the alkyl chain is dodecyl (C 12 ) double squaraine dye TM3 has a higher Pb 2+ The sensitivity of the ions was high. 12 ) blank is omitted, but it showed a similar color to the ethyl (C2) blank.

[0210] Next, using a double squaraine dye (TM3) at a concentration of 20 μM and different types of ions in DMF solvent, we investigated the influence of the properties of monovalent or divalent ions on ion sensing.

[0211] The results are shown in Figures 15 and 16. As shown in Figures 15 and 16, it was found that the dye preferentially senses divalent ions over monovalent ions.

[0212] Furthermore, the above results indicate that the selection of an appropriate solvent is important for ion detection using double squaraine dyes, since the spectral behavior changes depending on the solvent properties and polarity. For example, the same compound exhibits a cyan color in polar solvents and a blue or purple color in nonpolar solvents. This is thought to be due to the differential interaction between the solvent and the dye, resulting in different conformations of the compound in each solvent.

[0213] Next, using a mixed solvent of 99% acetonitrile and 1% DMF, the double squaraine dye TM3 of the present invention was tested for Pb at 0.01 pM to 1 μM. 2+ The effect of changing the ion concentration was investigated.

[0214] The results are shown in Figure 17. As shown in Figure 17, Pb 2+ As the concentration of ions increases, the absorbance at around 720 nm increases significantly. 2+ It was found that ions can be detected with high sensitivity in the near-infrared wavelength range. In addition, Figure 18 shows the relationship between absorbance at 720 nm and Pb 2+ The relationship between Pb and Pb concentrations is shown. 2+ The absorbance increased as the concentration increased, and the detection limit was 4.35 × 10 -15 It was M.

[0215] (solvatochromism test) The double squaraine dye (TM3) of the present invention produced as described above was examined for changes in near-infrared (NIR) absorption spectrum due to various solvents (single solvent and binary solvent).

[0216] Figure 19 shows the results for the single solvent, and Figure 20 shows the results for the binary solvent. As shown in Figures 19 and 20, it was revealed that the absorption spectrum of the double squaraine dye TM3 of the present invention changes depending on the solvent (polarity). Furthermore, as shown in Figure 19, for example, protic polar solvents exhibited red-shifted near-infrared absorption. Therefore, it was confirmed that the double squaraine dye of the present invention can detect the polarity of a solvent in the near-infrared wavelength region. [Industrial Applicability]

[0217] The novel double squaraine dye of the present invention can be used for detecting metal ions and is therefore industrially useful.

Claims

1. The following formula (I ０ ) A double squaraine dye characterized by being represented by the formula: 【Chemistry 1】 (Formula (I) ０ ) Medium, D １ and D ２ represents a nitrogen-containing heterocyclic group.

2. Formula (I ０ ) Medium, D １ and D ２ and each of the groups represented by the following formula: 【Chemistry 2】 (In the formula, R １２ represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and * represents the bonding position.

3. Formula (I ０ ) Medium, D １ and D ２ and (a-3) are heterocyclic groups represented by the following formula (a-1), (a-3) or (a-5), respectively: 【Transformation 3】

4. Formula (I ０ ) Medium, D １ and D ２ and are the same heterocyclic group.

5. 2. The double squaraine dye according to claim 1, which is represented by the following formula (I): 【Chemistry 4】 (In formula (I), R １ and R ２ represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and R ３ ~R ６ represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 4 carbon atoms.

6. In formula (I), R １ and R ２ and each represent an aliphatic saturated hydrocarbon group having 1 to 20 carbon atoms.

7. In formula (I), R ３ ~R ６ and each represent a methyl group.

8. 6. The double squaraine dye according to claim 5, which is represented by any one of the following formulas: 【Transformation 5】

9. 2. The double squaraine dye according to claim 1, which is represented by any one of the following formulas: 【Transformation 6】 (In the formula, R′ represents a hydroxyl group, a methoxy group, a bromo group, a cyano group, or a carboxy group.)

10. A method for detecting metal ions, comprising detecting metal ions using the double squaraine dye according to claim 1.

11. 11. The method for detecting metal ions according to claim 10, wherein the metal ions are divalent metal ions.

12. 12. The method for detecting metal ions according to claim 11, wherein the divalent metal ion is a lead ion.

13. A method for detecting solvent polarity, comprising detecting the polarity of a solvent using the double squaraine dye of claim 1.

14. In the presence of a mixed organic solvent of a non-polar solvent and a protic polar solvent, The following formula (wherein D １ and D ２ represents a nitrogen-containing heterocyclic group. 【Transformation 7】 A single squaraine compound represented by the formula: 【Transformation 8】 1. A method for producing a double squaraine dye, comprising the step of obtaining a double squaraine dye represented by the formula:

15. 15. The method for producing a double squaraine dye according to claim 14, wherein the mixed organic solvent contains, in volume ratio, 1 protic polar solvent to 1 or more nonpolar solvents.

16. 15. The method for producing a double squaraine dye according to claim 14, wherein the non-polar solvent is toluene.

17. 15. The method for producing a double squaraine dye according to claim 14, wherein the protic polar solvent is n-butanol.

18. The following formula (wherein R ３ , R ４ , R ７ represents a hydrogen atom or an aliphatic hydrocarbon group having 1 to 4 carbon atoms. 【Chemistry 9】 A halogenated aliphatic hydrocarbon R １ X (R １ represents an aliphatic hydrocarbon group having 1 to 30 carbon atoms, and X represents a halogen atom, The following formula 【Chemistry 10】 Step 1 to obtain a compound represented by the formula: The compound obtained in the step 1 is reacted with a dialkyl squarate in the presence of an amine to obtain a compound represented by the following formula (wherein R Ａ represents an alkyl group. 【Chemistry 11】 Step 2 to obtain a compound represented by the formula: The compound obtained in step 2 is reacted with an inorganic base compound to obtain a compound represented by the following formula (M represents an alkali metal): 【Chemistry 12】 Step 3 to obtain a compound represented by the formula: The compound obtained in step 3 above is dimerized to obtain a compound of the following formula: 【Chemistry 13】 Step 4 to obtain a double squaraine dye represented by 1. A method for producing a double squaraine dye, comprising:

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