JP7470357B2 - Pyrene fluorescent dye - Google Patents

Description

The present invention relates to a fluorescent dye that has a relatively long maximum absorption wavelength and maximum fluorescence wavelength and has excellent photostability.

Fluorescent dyes are organic compounds with a highly π-conjugated structure, and when they absorb light of a specific wavelength and become excited, the energy is not wasted in intramolecular vibration or rotational motion, but is instead emitted as light of a specific wavelength. In addition to the difference between absorption and emission wavelengths, fluorescent light is sensitive to lasers and has the ability to convert light energy into electrical energy, so it is expected to be used in a variety of fields, such as as a dye for optical recording media or photoelectric conversion dye in silver halide photography, displays, solar cells, and other fields. In addition, due to its high visibility, it is also used as a fluorescent labeling dye in the bio field.

Although ultraviolet light, which has high energy, is sometimes used as the light absorbed by fluorescent dyes, in recent years, infrared light has been attracting attention due to its safety and high transmittance. For example, Patent Document 1 discloses a silaxanthenium core-based fluorescent compound that is sufficiently red-shifted by using a substituent selected to correspond to the far-infrared and NIR spectrum. Patent Document 2 discloses a near-infrared fluorescent compound containing a pyridinium structure in the 5-position substituted imino group of benzo[a]phenoxatin. Patent Documents 3 and 4 disclose cyanine-based compounds that are useful as contrast components of near-infrared fluorescent contrast agents. However, in recent years, there has been a tendency for fluorescent dyes to not be newly developed.

The structure of a cyanine dye, a typical fluorescent dye, has nitrogen-containing heterocycles at both ends of a polymethine skeleton. It is known that the absorption and fluorescence wavelengths can be shifted to longer wavelengths by lengthening this polymethine skeleton. In other words, the absorption wavelength of the cyanine dye shifts to the longer wavelength side by approximately 100 nm for every two methine groups (-CH=) added.

JP 2016-521254 A JP 2014-166975 A JP 2011-46663 A JP 2011-46662 A

As mentioned above, fluorescent dyes with longer absorption and fluorescence wavelengths have been developed. For example, it is known that the absorption and fluorescence wavelengths can be shifted to longer wavelengths by lengthening the polymethine skeleton of a cyanine dye. However, it is also known that the photostability decreases when the polymethine skeleton is lengthened, and the fluorescence intensity in response to excitation light decreases over time.
Therefore, an object of the present invention is to provide a fluorescent dye which has relatively long maximum wavelengths of excitation light and fluorescence and is excellent in photostability.

The present inventors have conducted extensive research to solve the above problems, and as a result have discovered that introducing a pyrene ring into the structure of a fluorescent dye not only shifts the absorption wavelength and fluorescence wavelength to longer wavelengths, but also surprisingly improves the photostability, thereby completing the present invention.
The present invention will now be described.

［式中、
Ｒ¹は、カルボキシ基、スルホ基、アジド基、またはエチニル基で置換されていてもよいＣ_1-18アルキル基を示し、
Ｘ¹は、＞ＣＲ²Ｒ³（式中、Ｒ²とＲ³は独立してＣ_1-18アルキル基を示す。）、－Ｏ－、または－Ｓ－を示し、
Ｙは、下記式（ｉ）～（ｉｖ）で表される基から選択されるいずれかの基を示す。

（式中、
Ｘ²とＸ³は、独立して、＞ＣＲ¹⁰Ｒ¹¹（式中、Ｒ¹⁰とＲ¹¹は独立してＣ_1-18アルキル基を示す。）、－Ｏ－、または－Ｓ－を示し、
Ｚは＝Ｏまたは＝Ｓを示し、
Ｒ⁴～Ｒ⁹は、独立して、カルボキシ基、スルホ基、アジド基、またはエチニル基で置換されていてもよいＣ_1-18アルキル基を示し、
ｌは、１以上、５以下の整数を示し、
ｍは、０以上、５以下の整数を示し、
ｎは、１以上、５以下の整数を示す。）］ [1] A pyrene fluorescent dye represented by the following formula (I):

[Wherein,
R ¹ represents a C _1-18 alkyl group optionally substituted with a carboxy group, a sulfo group, an azide group, or an ethynyl group;
^X1 represents > ^CR2R3 (wherein ^R2 and ^R3 each independently represent a _C1-18 alkyl group), -O-, or ^-S- ;
Y represents any group selected from the groups represented by the following formulas (i) to (iv).

(Wherein,
^X2 and ^X3 independently ^represent > ^CR10R11 (wherein ^R10 and ^R11 independently represent a _C1-18 alkyl group), -O-, or -S-;
Z represents ═O or ═S;
R ⁴ to R ⁹ each independently represent a C _1-18 alkyl group optionally substituted by a carboxy group, a sulfo group, an azide group, or an ethynyl group;
l represents an integer of 1 to 5,
m represents an integer of 0 to 5,
n represents an integer of 1 or more and 5 or less.

[2] The pyrene fluorescent dye according to the above [1], wherein Y is a group represented by formula (i).
[3] The pyrene fluorescent dye according to the above [2], wherein X ² is >CR ¹⁰ R ^{11 .}
[4] The pyrene fluorescent dye according to the above [2] or [3], wherein R ⁴ is an unsubstituted C _1-18 alkyl group.
[5] The pyrene fluorescent dye according to any one of the above [1] to [4], wherein X ¹ is >CR ² R ³ .
[6] The pyrene fluorescent dye according to any one of the above [1] to [5], wherein R ¹ is an unsubstituted C _1-18 alkyl group.

In the present invention, the term "C _1-18 alkyl group" refers to a linear or branched monovalent saturated aliphatic hydrocarbon group having 1 to 18 carbon atoms. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl, n-pentyl, n-hexyl, n-octyl, n-decane, n-dodecane, n-tetradecane, n-hexadecane, and n-octadecane. When steric hindrance is taken into consideration, a C _1-10 alkyl group is preferred, a C _1-6 alkyl group or a C _1-4 alkyl group is more preferred, and a C _1-2 alkyl group is even more preferred. When a substituent such as a carboxy group is present, a C _1-6 alkyl group is preferred, and a C _2-4 alkyl group is more preferred. When it is desired to increase the fat solubility of the pyrene fluorescent dye, a C _6-18 alkyl group is preferred, a C _8-18 alkyl group is more preferred, and a C _10-16 alkyl group is even more preferred.

The pyrene fluorescent dye of the present invention has a relatively long maximum absorption wavelength and a long maximum fluorescence wavelength, and has excellent photostability. For example, according to the examples described below, compared to a conventional squaraine dye that has the same structure except that it does not have a pyrene ring, the maximum absorption wavelength and the maximum fluorescence wavelength are shifted to the long wavelength side by about 100 nm, and the photostability is improved. Therefore, the pyrene fluorescent dye of the present invention has the potential to replace conventional fluorescent dyes used in various fields.

FIG. 1 shows a ¹ H-NMR spectrum of an example of the pyrene fluorescent dye according to the present invention. FIG. 2 shows the absorption wavelength spectrum and the fluorescence wavelength spectrum of an example of the pyrene fluorescent dye according to the present invention and a conventional fluorescent dye. FIG. 3 is a graph showing the photostability of an example of the pyrene fluorescent dye according to the present invention and a conventional fluorescent dye.

The pyrene fluorescent dye according to the present invention can be produced by a person skilled in the art in accordance with the conventionally known production method of a cyanine dye. For example, a pyrene fluorescent dye represented by formula (I) in which Y is a group represented by formula (i) can be produced by the following synthesis scheme. Hereinafter, Q represented by formula (P) may be abbreviated as "Q(P)".

In the above reaction, a pyrene compound (II) is reacted with a squaric acid derivative (III) in a solvent in the presence of a base to produce a pyrene-squaraine dye (I ¹ ).

The solvent is not particularly limited as long as it has an appropriate solubility in the pyrene compound (II) and the squaric acid derivative (III) and does not inhibit the reaction. Examples of the solvent include _C1-4 alcohols such as methanol, ethanol, and 1-butanol; aromatic hydrocarbon solvents such as benzene, toluene, and chlorobenzene; and mixed solvents thereof.

Examples of bases include organic bases such as quinoline and pyridine, and inorganic bases such as sodium acetate.

The reaction conditions may be adjusted as appropriate. For example, the amount of pyrene compound (II) relative to the squaric acid derivative (III) may be 1.9 or more times by mol and 2.1 or less times by mol. The amounts of pyrene compound (II) and squaric acid derivative (III) in the reaction solution may be adjusted as appropriate according to the solubility, etc. It is preferable to use an excess amount of base. The reaction temperature may be from room temperature to 150°C or less, and the reaction may be performed under heating under reflux. The reaction time may be determined by thin layer chromatography or the like until the raw material compound is consumed, or by a preliminary experiment, and may be, for example, 1 hour or more and 60 hours or less.

The pyrene fluorescent dye (I) in which Y is a group (ii) to (iv) can be produced by the following synthesis scheme. The synthesis scheme for the pyrene fluorescent dye (I ² ) in which Y is a group (ii) is shown below as a representative example.

The pyrene-cyanine fluorescent dye (I ² ) can be produced under the same conditions as the pyrene-squaraine fluorescent dye (I ¹ ), except that the polymethine compound (IV) is used instead of the squaric acid derivative (III). The pyrene-merocyanine fluorescent dye (I ³ ) and the pyrene-LDS fluorescent dye (I ⁴ ) can be produced in the same manner as the pyrene-cyanine fluorescent dye (I 2 ), except that instead of the polymethine compound (IV), a compound in which one end of the polymethine compound (IV) is substituted with an oxopyrimidine ring or an aniline ring is used, and these compounds and the pyrene compound ( ^II ) are used in a molar ratio of about 1:1.

The pyrene compound (II) can be produced by applying the conventionally known indole synthesis method, benzoxazole synthesis method, or benzothioxazole synthesis method. However, when ^X1 is > ^CR2R3 , the following method using a metal catalyst (Matyas ^Tursky et al., Organic & Biomolecular Chemistry, 2010, 8, 5576-5582) is very efficient.

When ^X1 is -O-, hydroxypyrene is acylated, and the resulting acylated product is subjected to a Fries rearrangement reaction to give an acylhydroxypyrene, which is then oximed and then subjected to a cyclization transfer reaction to form an oxazole ring. When ^X1 is -S-, pyrenethiol is used instead of hydroxypyrene.

The pyrene fluorescent dye (I) and the intermediate compound may be purified by known methods, or the intermediate compound may be used in the next reaction without purification or after only crude purification depending on the purity. In addition, the reactive functional groups may be appropriately protected and deprotected.

Squaraine dyes, also known as squarylium dyes, are classified as cyanine dyes, but have a unique structure, a zwitterionic structure in which a squaric acid (squaric acid) moiety is located at the center of a polymethine conjugated system and a cationic group and an anionic group coexist in one molecule. Squaraine dyes are used as charge generating agents for electrophotographic photoreceptors and sensitizing dyes for organic solar cells.

Indocyanine dyes have a structure with nitrogen-containing heterocycles at both ends of a polymethine skeleton. One of the nitrogens is an ammonium with a cationic structure and acts as an electron acceptor, while the other nitrogen is a tertiary amine and acts as an electron donor. They usually exist as a salt with an anion. Examples of anions include halide ions, sulfonate ions, perchlorate ions, tetrafluoroborate, and hexafluoroantimonate. Indocyanine dyes are used as dyes for optical recording media, etc.

Merocyanine dyes have a large absorption coefficient and are widely used as light absorbers, sensitizers, dyes, etc. in optical filters used in displays and optical lenses, photosensitive photographic materials, dyes, paints, inks, electrophotographic photoreceptors, toners, thermal recording paper, transfer ribbons, optical recording dyes, solar cells, photoelectric conversion elements, semiconductor materials, clinical test reagents, dyes for laser therapy, and dyes.

Since LDS dyes have a relatively long life and can be easily replaced with Ti:Sapphire, LDS dye lasers are promising light sources for DIAL systems.

Furthermore, the pyrene-squaraine dye (I ¹ ), pyrene-cyanine fluorescent dye (I ² ), pyrene-merocyanine fluorescent dye (I ³ ), and pyrene-LDS fluorescent dye (I ⁴ ) according to the present invention have maximum absorption and fluorescence wavelengths shifted to the long wavelength side and exhibit excellent photostability. Furthermore, the pyrene fluorescent dyes of the present invention, which are highly water-soluble due to the substitution of a carboxyl group or a sulfo group on the _C 1-18 alkyl group, may be usable in vivo for bioimaging, photodynamic therapy, and the like.

The present invention will be explained in more detail below with reference to examples. However, the present invention is not limited to the following examples, and it is of course possible to carry out the invention with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included in the technical scope of the present invention.

Example 1: Synthesis of pyrene-squaraine dyes

(1) Synthesis of Compound 1 1-Aminopyrene (3 g, 13.8 mmol), RuCl ₃ ·H ₂ O (28.6 mg, 0.138 mmol), and Xantphos (239.6 mg, 0.414 mmol) were placed in a recovery flask, and the gas phase in the flask was replaced with argon. Then, 2,3-butanediol (1.27 mL, 13.8 mmol) was added and the mixture was heated at 110°C for 1 hour, and then heated to 180°C for 2 days. The temperature of the reactant was returned to room temperature, and the reactant was dissolved in chloroform, and the insoluble matter was filtered off. The filtrate was concentrated under reduced pressure, and the target product was isolated as a yellow solid by silica gel column chromatography (eluent: chloroform) (yield: 2.62 g, yield: 70%). The production of the target product was confirmed by ¹ H-NMR.

(2) Synthesis of Compound 2 Pd ₂ (dba) ₃ (170.3 mg, 0.186 mmol) and P(2-furyl) ₃ (85.9 mg, 0.37 mmol) were placed in a two-necked eggplant flask, and the gas phase in the flask was replaced with argon. Allyl methyl carbonate (1.69 mL, 14.9 mmol) and dehydrated dichloromethane (18.6 mL) were then added and stirred at room temperature for 10 minutes. This solution was added to a separately prepared solution of compound 1 (2 g, 7.43 mmol) in dehydrated dichloromethane (18.6 mL), and stirred at room temperature for 3 hours. After removing the solvent with an evaporator, the target product, which was an orange-brown viscous liquid, was isolated by silica gel column chromatography (eluent: ethyl acetate/hexane = 1/3) (yield: 1.25 g, yield: 55%). The production of the target product was confirmed by ¹ H-NMR.

(3) Synthesis of Compound 3 Compound 2 (1.2 g, 3.88 mmol) and Pd/C (120 mg, 10 w%) were placed in a two-necked eggplant flask, and the gas phase in the flask was replaced with hydrogen, after which methanol (19.4 mL) was added. Hydrogen gas was then bubbled into the solution, and the mixture was stirred at room temperature for 4 hours. After removing insoluble matter with pleated filter paper, the filtrate was concentrated under reduced pressure, and the target product was isolated as an orange solid by silica gel column chromatography (eluent: hexane/ethyl acetate = 5/1) (yield: 954 mg, yield: 79%). The production of the target product was confirmed by ¹ H-NMR.

(4) Synthesis of Compound 4 Compound 3 (694 mg, 2.23 mmol), iodomethane (2 mL), and acetonitrile (11.2 mL) were placed in a recovery flask and heated at 80° C. for 24 hours. The precipitate was collected by filtration to obtain the target product as a yellow powder solid (yield: 512 mg, 51%). The formation of the target product was confirmed by ¹ H-NMR.

(5) Synthesis of pyrene-squaraine dye (PYSQ) Compound 4 (200 mg, 0.44 mmol), 3,4-diethoxy-3-cyclobutene-1,2-dione (32 μL, 0.22 mmol), and a mixture of 1-butanol/pyridine (1/1) (1.1 mL/1.1 mL) were placed in a recovery flask and heated to reflux at 120° C. for 21 hours. The reaction solution was concentrated under reduced pressure and isolated by silica gel column chromatography (eluent: dichloromethane/methanol (99/1)). The product was further washed with hot methanol to obtain the target product as a green powder solid (yield: 40.6 mg, 13%). The ¹ H-NMR spectrum of the obtained PYSQ is shown in FIG. 1.

Test Example 1: Fluorescence properties The fluorescence properties of the pyrene-squaraine dye (PYSQ) synthesized in Example 1 were evaluated. For comparison, the fluorescence properties of a conventionally known squaraine dye (SQ) were also evaluated in the same manner. The results are shown in Table 1 and FIG. 2.

As shown in the results in Table 1 and Figure 2, PYSQ exhibited optical absorption and fluorescence wavelengths that were nearly 100 nm longer than those of SQ. In addition, its brightness (the product of the molar absorption coefficient and the fluorescence quantum yield) was almost the same as that of SQ, which is known as a highly luminous dye.

Test Example 2: Photostability Test The pyrene-squaraine dye (PYSQ) synthesized in Example 1 was dissolved in toluene and irradiated with 657 nm excitation light, and the change in fluorescence intensity over time was monitored. For comparison, the concentration of the solution of a conventionally known squaraine dye (SQ) was adjusted so that the absorbance at 657 nm was consistent, and the change in fluorescence intensity over time was similarly monitored. The results are shown in FIG. 3.
As shown in Figure 3, after 3 hours of light irradiation, the fluorescence intensity of SQ attenuated to about 83% of the initial state, while that of PYSQ was maintained at 90% or more. Therefore, it was found that the photostability of PYSQ is superior to that of SQ. SQ is a dye with far superior photostability to commercially available dyes such as Nile Red.

Claims (6)

A pyrene fluorescent dye represented by the following formula (I):

[Wherein,
R ¹ represents a C _1-18 alkyl group optionally substituted with a carboxy group, a sulfo group, an azide group, or an ethynyl group;
^X1 represents > ^CR2R3 (wherein ^R2 and ^R3 each independently represent a _C1-18 alkyl group), -O-, or ^-S- ;
Y represents any group selected from groups represented by the following formula (i) or (ii) .

(Wherein,
^X2 and ^X3 independently ^represent > ^CR10R11 (wherein ^R10 and ^R11 independently represent a _C1-18 alkyl group), -O-, or -S- ;
R4 and R5 ^{independently} represent a _C1-18 alkyl group optionally substituted with ^a carboxy group, a sulfo group, an azide group, or an ethynyl group;
and l represents an integer of 1 or more and 5 or less. The pyrene fluorescent dye according to claim 1, wherein Y is a group represented by formula (i). The pyrene fluorescent dye according to claim 2, wherein ^X2 is > ^{CR10R11 .} The pyrene fluorescent dye according to claim 2 or 3, wherein R ⁴ is an unsubstituted C _1-18 alkyl group. The pyrene fluorescent dye according to any one of claims 1 to 4, wherein X ¹ is >CR ² R ³ . The pyrene fluorescent dye according to any one of claims 1 to 5, wherein R ¹ is an unsubstituted C _1-18 alkyl group.

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