Perfluoropolyphenylene compound, method for producing compound, and blue fluorescent material comprising compound

Abstract

To provide a thermally activated delayed fluorescent material that exhibits excellent photostability and prolonged lifetime in blue light emission.SOLUTION: There are provided a perfluoropolyphenylene compound represented by the following formula (1) (where X1, X2, X3, and X4 are fluorine atoms, and n is 3 to 5), a method for producing the compound, and a blue fluorescent material comprising the compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel perfluoropolyphenylene compound, a method for producing the compound, and a blue fluorescent material containing the compound, which is useful for clothing, agricultural films, organic electroluminescence devices, etc. [Background technology]

[0002] Materials that absorb light and emit blue fluorescence have been reported to be used as fluorescent whitening agents (hydroxycoumarin, rhodamine 6G, perylene derivatives, diarylanthracene derivatives, etc.) that make yellowing of clothing less visible, agricultural films (benzotriazole derivatives, Patent Document 1, Non-Patent Document 1), and blue-emitting materials in organic electroluminescent devices (Patent Document 2, Non-Patent Document 2). Among such uses, when used as agricultural film, it absorbs ultraviolet light contained in sunlight and artificial light and emits blue light, so the difference between the absorption wavelength (ultraviolet light) and the emission wavelength (blue light), i.e., the Stokes number, must be large. If the difference between the absorption wavelength and the emission wavelength is small, the molecule itself will absorb part of the emitted light, causing a cancellation and preventing the intensity from increasing. The Stokes number of a typical blue fluorescent material is around 100 nm, which is by no means a large value. In addition, since it will be exposed to light irradiation for long periods of time, durability against light is also required. The problem with typical blue fluorescent materials is their low durability against light. On the other hand, the properties required for blue light-emitting materials used in organic EL devices include a small half-width in the emission spectrum, improved luminous efficiency, improved blue purity, and improved durability. Among these, thermally activated delayed fluorescent materials are attracting attention for use in next-generation organic EL devices because they have a theoretically 100% luminous efficiency and high blue purity (Non-Patent Document 2). However, in terms of improving durability, blue fluorescent materials in particular have the problem of poor durability, a short lifespan, and a gradual decrease in luminescence intensity.

[0003] Among fluorescent materials, compounds having carbazole as the donor and perfluorophenylene ring as the acceptor are known to emit thermally activated delayed fluorescence, and to date, compounds in which carbazole is substituted on perfluorophenylene (number of benzene rings: n=1, 2, ...) such as tetrafluorophenylene (n=1) (Patent Document 3) and octafluorobiphenyl (n=2) (Non-Patent Document 3) have been reported. However, there have been no reports on the synthesis or optical properties of polyphenylene derivatives in which benzene rings are linked in a longer linear fashion.

[0004] Thermally activated delayed fluorescent materials are organic light-emitting molecules characterized by having donor and acceptor sites within the molecule. Their light-emitting mechanism involves triplet-state excitons (corresponding to 75%) being converted into singlet-state excitons by thermal energy, followed by the emission of fluorescence. This fluorescence, combined with the fluorescence emitted from the original singlet excitons (corresponding to 25%), theoretically achieves an energy efficiency of 100% (Patent Document 5, Non-Patent Document 4). These materials hold promise as light-emitting materials for next-generation organic electroluminescent (EL) light-emitting devices. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] No. 6131400 (Agricultural film) [Patent Document 2] JP 2010-141059 A (organic electroluminescence, octafluorobiphenyl, triazine disubstituted compound) [Patent Document 3] No. 6628470 (Universal Display, Tetrafluorophenylene, Carbazole Disubstituted Compound) [Patent Document 4] JP 2005-255531 (Patent No. 4344823) (Chemical synthesis of perfluoropolyphenylene, described below) [Patent Document 5] Patent Publication No. 2021-64641 (Kyushu University, thermally activated delayed fluorescence) [Non-patent literature]

[0006] [Non-Patent Document 1] Functional Materials, 2019, 39, 55. (Agricultural Film) [Non-patent document 2] ACS_Materias Lett.,2020,2,28.(Boron-based compounds) [Non-patent document 3] Dyes and Pigments, 2021, 193, 109493. (Octafluorobiphenyl, 2-substituted carbazole) [Non-patent document 4] Science Advances 2017, 3, e1603282. (AIST, Thermally activated delayed fluorescence) Summary of the Invention [Problem to be solved by the invention]

[0007] However, it has been pointed out that thermally activated delayed fluorescent materials have problems with low light resistance and short lifespan when it comes to blue light emission. [Means for solving the problem]

[0008] To solve the above problems, the present inventors have linearly increased the number of benzene rings in the perfluorophenylene chain serving as the acceptor moiety, thereby increasing the torsion angle between the donor and acceptor moieties and making the HOMO and LUMO localization more pronounced. They also carried out molecular design by optimizing the combination of donor moieties such as carbazole, and conducted research into the synthesis of novel materials, which has led to the completion of the present invention. Therefore, the present invention provides the following. [1] The following formula (1): [ka] (In the formula, X 1 , X 2 , X 3 and X 4is a fluorine atom, and n is 3 to 5. A perfluoropolyphenylene compound represented by the formula: [2] The following formula (1): [ka] (In the formula, X 1 , X 2 , X 3 and X 4 is a fluorine atom, and n is 3 to 5. A method for producing a perfluoropolyphenylene compound represented by the formula: The following formula (2): [ka] (In the formula, X 1 , X 2 , X 3 and X 4 is a fluorine atom, and n is 3 to 5. The method includes a step of reacting a perfluoropolyphenylene represented by the formula (I) with carbazole in the presence of a base. [3] The following formula (1): [ka] (In the formula, X 1 , X 2 , X 3 and X 4 is a fluorine atom, and n is 3 to 5. A blue fluorescent material containing a perfluoropolyphenylene compound represented by the formula: [Effects of the Invention]

[0009] A problem with blue materials is that they have lower durability than red and green materials. Although compounds such as those described in Non-Patent Document 2 have been shown to have high blue purity, the durability issue has not been discussed. In the present invention, as a result of intensive research aimed at achieving both higher blue purity and durability, a novel perfluoropolyphenylene compound represented by formula (1) is provided. This novel compound satisfies the requirements for the characteristic molecular structure of thermally activated delayed fluorescent materials. Compared to known biphenyl compounds (n = 2), this novel compound has succeeded in emitting blue light closer to the wavelength with high blue purity while improving durability. Based on the above, the present invention solves the problems with thermally activated delayed fluorescent materials and provides a thermally activated delayed fluorescent material that has high light resistance and a long lifetime for blue emission. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a graph showing the change in fluorescence intensity over time of a compound (biphenyl compound) where n=2 in formula (1). [Figure 2] FIG. 1 is a graph showing the change in fluorescence intensity over time of a compound (terphenyl compound) where n=3 in formula (1). [Figure 3] FIG. 1 is a graph showing the change in fluorescence intensity over time of a compound (quarterphenyl compound) in which n=4 in formula (1). [Figure 4] FIG. 1 is a graph showing the change in fluorescence intensity over time for a compound (quinquephenyl derivative) in which n=5 in formula (1). [Figure 5] FIG. 1 is a diagram showing a comparison of changes in fluorescence intensity over time for compounds of formula (1) where n=2, 3, 4, and 5. DETAILED DESCRIPTION OF THE INVENTION

[0011] [Effect] The present invention provides a perfluoropolyphenylene compound represented by formula (1). For an organic molecule to emit thermally activated delayed fluorescence, the donor and acceptor groups must have a twisted structure to localize the HOMO and LUMO orbitals at the donor and acceptor sites, respectively. The inventors used carbazole, which has high steric hindrance and excellent donor performance, as the donor group. For the acceptor group, they focused on the fact that substituting all hydrogen atoms on the molecular backbone corresponding to the acceptor with fluorine, i.e., perfluorination, is an effective way to achieve a twisted structure. Because fluorine is sterically bulkier than hydrogen, its steric effect causes the π planes constituting the donor site and the π planes constituting the acceptor site to have a significantly twisted structure, which is expected to further localize the HOMO and LUMO orbitals. Furthermore, as a novel approach in this invention, they investigated increasing the length of the perfluorophenylene chain (n = 3 to 5). This resulted in an increase in the number of fluorines, further improving the acceptor performance, and an increase in the twisted structure, which succeeded in improving the fluorescence quantum yield, blue purity, and durability, i.e., extending the lifetime.

[0012] [Perfluoropolyphenylene compounds] As shown in the formula (1), the compound according to the present invention has two functional groups with high steric hindrance and donor properties at both ends of the molecule, with an acceptor group sandwiched between the two donor groups. The acceptor group is characterized as a polyphenylene group to which an electron-withdrawing substituent is bonded. The donor group may be an amino group with a cyclic structure, but the present invention employs a carbazole group. The acceptor group is a substituent (X) on the carbon of the polyphenylene group. 1 , X 2 , X 3 and X 4 ) is a fluorine atom. In the polyphenylene group, the number (n) of linearly connected benzene rings is 2 to 5, and among these, a polyphenylene group where n≧3, that is, 3 to 5 benzene rings are linearly connected, is preferred. As described above, a fluorescent material can be produced by combining two donor groups and one acceptor group at both ends.

[0013] [Method of producing perfluoropolyphenylene compounds] The perfluoropolyphenylene compound of formula (1) is represented by the following formula (2): [ka] (In the formula, X 1 , X 2 , X 3 and X 4 is a fluorine atom, and n is 3 to 5. The compound can be produced by a method including a step of reacting a perfluoropolyphenylene represented by the following formula (I) with carbazole in the presence of a base.

[0014] Perfluoroterphenyl (n=3), perfluoroquaterphenyl (n=4), and perfluoroquinquephenyl (n=5), which are generally called perfluoropolyphenylenes, can be produced, for example, by the method described in Patent Document 4, JP-A-2005-255531 (Patent No. 4344823) (Chemical Synthesis of Perfluoropolyphenylene).

[0015] The carbazole and base that can be used are commercially available as reagents. Examples of the base include alkali metal hydroxides (e.g., sodium hydroxide, potassium hydroxide), alkali metal carbonates (e.g., sodium carbonate, potassium carbonate), quaternary ammonium salts (e.g., tetrabutylammonium fluoride), tertiary amines (e.g., triethylamine), and strong organic bases (e.g., 1,5-diazabicyclo[4.3.0]non-5-ene (DBN), 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) (MTBD)). Sodium carbonate and potassium carbonate are preferred, and potassium carbonate is more preferred.

[0016] The reaction is usually carried out in the presence of a solvent by appropriately adjusting the concentration of the reagents, such as a polar solvent, preferably dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), or an alcohol such as methanol, ethanol, propanol, or butanol, and more preferably dimethylformamide.

[0017] The reaction temperature is −78 to 200° C., preferably 0 to 100° C., and more preferably 25 to 60° C. The reaction can be carried out under atmospheric pressure, and no pressure vessel or the like is required.

[0018] The reaction time is 1 hour to 96 hours, preferably 1 hour to 48 hours, and more preferably 4 hours to 24 hours.

[0019] Other reaction conditions include the need to add carbazole in an amount at least twice the molar equivalent of the perfluoropolyphenylene of formula (2) in the reaction system; considering reaction efficiency, this amount is preferably 2 to 10 times, and more preferably 2 to 2.1 times. The molar equivalent of the base is 1 to 10 molar equivalents, preferably 2 to 5 molar equivalents, and more preferably 3.9 to 4.1 molar equivalents relative to the perfluoropolyphenylene of formula (2). The amount of solvent used is not particularly limited, but considering reaction efficiency, it is preferable to use the solvent appropriately so that the concentration of the perfluoropolyphenylene of formula (2) is 0.001 to 1 mol / L, preferably 0.01 to 0.1 mol / L, and more preferably 0.02 to 0.03 mol / L.

[0020] [Blue fluorescent material] The blue fluorescent material of the present invention is characterized by containing the perfluoropolyphenylene compound of formula (1). As experimentally demonstrated in the examples described below, the perfluoropolyphenylene compound of formula (1) exhibits stable and strong blue fluorescence. The blue fluorescent material of the present invention is formed by dispersing the compound of formula (1) in a solvent or a resin matrix and adjusting the concentration of the compound of formula (1) in the material.

[0021] Specific applications of the blue fluorescent material of the present invention include clothing, agricultural films, organic EL devices, and the like. [Example]

[0022] Decafluorobiphenyl was prepared using a commercially available reagent, and perfluoroterphenyl (trimer), perfluoroquaterphenyl (tetramer), and perfluoroquinquephenyl (pentamer) were synthesized according to the method described in Patent Document 4. Decafluorobiphenylcarbazole disubstituted (a) and novel compounds (b), (c), and (d) were synthesized by the methods described below.

[0023] The optical properties in the solution were measured using a Shimadzu UV-1800 ultraviolet-visible near-infrared spectrophotometer, with a measurement wavelength of 240 nm to 700 nm and a concentration of 1 × 10 -5 ~1×10 -4 Measurements were performed using M (solvent: chloroform) and a quartz cell (two transparent faces, optical path length: 10 mm).

[0024] The fluorescence spectrum was measured using a JASCO FP-8500 spectrofluorometer at a wavelength of 200 nm to 750 nm and a concentration of 1 × 10 -5 ~1×10 -4 Measurements were performed using M (solvent: chloroform) and a quartz cell (transparent on all four sides, optical path length: 10 mm).

[0025] The fluorescence quantum yield was measured using a JASCO FP-8500 spectrofluorometer, with the measurement wavelength adjusted to 200 nm to 750 nm and the absorbance adjusted to 0.05 or less (solvent: chloroform), using a quartz cell (transparent on all four sides, optical path length: 10 mm).

[0026] Interval measurements were performed with sample concentrations of 5 x 10 -6 After adjusting to M (solvent: chloroform), measurements were repeated 1000 times using a JASCO FP-8500 spectrofluorometer with an excitation wavelength λex of 329 nm, measurement wavelengths of 285 nm to 700 nm, and intervals of 30 seconds.

[0027] Example 1 Synthesis of Compound (b) (New Compound) [ka] Under a nitrogen atmosphere, perfluoroterphenyl (24 mg, 0.05 mmol), carbazole (17 mg, 0.1 mmol), potassium carbonate (28 mg, 0.2 mmol), and dimethylformamide (2 mL) were placed in a ground test tube and reacted at 60 °C for 4 hours. After cooling to room temperature, water (10 mL) was added, and the dimethylformamide and water were distilled off under reduced pressure. The mixture was extracted with water (10 mL) and chloroform (10 mL x 3), passed through a short silica gel column, concentrated, and recrystallized from chloroform to obtain compound (b) (white solid, 30.2 mg, 78% yield). 1 H NMR(400MHz,CDCl3) δ 8.17~8.19(m,4H) 7.51~7.55(m,4H) 7.38~7.42(m,4H) 7.28~7.30(m,4H) 19 F NMR(376MHz,CDCl3) δ -135.9~-136.0(m,8F) -140.7~-140.8(m,4F)

[0028] Example 2 Synthesis of Compound (c) (New Compound) [ka] Under a nitrogen atmosphere, perfluoroquatphenyl (32 mg, 0.05 mmol), carbazole (17 mg, 0.1 mmol), potassium carbonate (28 mg, 0.2 mmol), and dimethylformamide (2 mL) were placed in a ground test tube and reacted at 60°C for 4 hours. After cooling to room temperature, water (10 mL) was added, and the dimethylformamide and water were distilled off under reduced pressure. When the liquid volume was reduced to about half, acetone (10 mL) was added, and the precipitated solid was filtered and dried to obtain compound (c) (white solid, 42 mg, yield 91%). 1H NMR(400MHz,CDCl3) δ8.18(d,J=7.6Hz,4H) 7.50~7.54(m,4H) 7.38~7.42(m,4H) 7.27~7.34(m,4H) 19 F NMR(376MHz,CDCl3) δ-135.8~-136.1(m,12F) -140.7~-140.8(m,4F)

[0029] Example 3 Synthesis of compound (d) (new compound) [ka] Under a nitrogen atmosphere, perfluoroquinquephenyl (39 mg, 0.05 mmol), carbazole (17 mg, 0.1 mmol), potassium carbonate (28 mg, 0.2 mmol), and dimethylformamide (2 mL) were placed in a ground test tube and reacted at 100°C for 4 hours. After cooling to room temperature, water (10 mL) was added. The mixture was extracted with water (10 mL) and chloroform (10 mL x 3), passed through a short column of silica gel, concentrated, and recrystallized from chloroform to obtain compound (d) (white solid, 8 mg, 15% yield). 1 H NMR(400MHz,CDCl3) δ 8.17~8.19(m,4H) 7.51~7.54(m,4H) 7.38~7.42(m,4H) 7.28~7.30(m,4H) 19 F NMR(376MHz,CDCl3) δ -135.8~-135.9(m,16F) -140.7~-140.8(m,4F)

[0030] Reference Comparative Example 1 Synthesis of Compound (a) [ka] Under a nitrogen atmosphere, decafluorobiphenyl (200 mg, 0.60 mmol), carbazole (200 mg, 1.20 mmol), potassium carbonate (330 mg, 2.39 mmol), and dimethylformamide (10 mL) were placed in a ground test tube and reacted at 40 °C for 24 hours. After cooling to room temperature, water (10 mL) was added, and the dimethylformamide and water were distilled off under reduced pressure. The resulting mixture was then extracted with water (10 mL) and chloroform (10 mL x 3), concentrated, and dried to give compound (a) (white solid, 210 mg, 0.33 mmol, 56% yield). 1 H NMR(300MHz,CDCl3) δ 8.19(d,J=7.5Hz,4H) 7.51~7.54(m,4H) 7.41~7.43(m,4H) 7.21~7.32(m,4H) 19 F NMR(282MHz,CDCl3) δ -136.1~-136.3(m,4F) -140.9~-141.1(m,4F)

[0031] Table 1 shows the optical properties of compound (b) obtained in Example 1, compound (c) obtained in Example 2, compound (d) obtained in Example 3, and compound (a) as a comparative example.

[0032] [Table 1]

[0033] As shown in Table 1, compounds (b), (c), and (d) of the present invention have maximum fluorescence wavelengths of 428 nm, 430 nm, and 431 nm, respectively, which are longer than the 425 nm maximum fluorescence wavelength of known compound (a). Compound (d) even exhibited a value comparable to the blue primary color (435.8 nm) defined by RGB in the CIE 1931 color space, a common chromaticity standard. It can be seen that the blue purity improved as the n value, which indicates the length of the perfluoropolyphenylene moiety, increased. It was also found that the Stokes shift, which indicates the difference between the maximum absorption wavelength and the maximum fluorescence wavelength, shifted toward longer wavelengths in proportion to the n value, which indicates the length of the perfluoropolyphenylene moiety. These results indicate that increasing the n value can shift the maximum fluorescence wavelength further away from the ultraviolet region. In particular, compound (d) has a maximum fluorescence wavelength of 431 nm, which is far from the high-energy ultraviolet region, making it biocompatible and less likely to induce material degradation, making it highly useful. Furthermore, the compounds (b), (c) and (d) of the present invention each had a fluorescence quantum yield of 37 to 41%, which was significantly higher than the fluorescence quantum yield of the known compound (a), which was 27%.

[0034] Figure 1 shows the change in fluorescence intensity during interval scan measurement for compound (a), Figure 2 for compound (b), Figure 3 for compound (c), and Figure 4 for compound (d). Figure 5 compares the interval scan measurement results for the four compounds mentioned above. Compounds (b), (c), and (d) maintained a fluorescence intensity of 75% or more after 1000 measurements, whereas compound (a)'s fluorescence intensity fell below 75% after 1000 measurements. This indicates that a larger n value, i.e., a longer perfluorophenylene chain, results in a stable and long-lived compound.

Claims

1. The following formula (1): 【Chemical 1】 (In the formula, X １ , X ２ , X ３ and X ４ is a fluorine atom, and n is 3 to 5. A perfluoropolyphenylene compound represented by the formula:

2. The following formula (1): 【Chemistry 2】 (In the formula, X １ , X ２ , X ３ and X ４ is a fluorine atom, and n is 3 to 5. A method for producing a perfluoropolyphenylene compound represented by the formula: The following formula (2): 【Chemistry 3】 (In the formula, X １ , X ２ , X ３ and X ４ is a fluorine atom, and n is 3 to 5. The method includes a step of reacting a perfluoropolyphenylene represented by the formula (I) with carbazole in the presence of a base.

3. The following formula (1): 【Chemistry 4】 (In the formula, X １ , X ２ , X ３ and X ４ is a fluorine atom, and n is 3 to 5. A blue fluorescent material containing a perfluoropolyphenylene compound represented by the formula:

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