Novel Compound Capable of White Light Emission and White Fluorescent Composition

Abstract

To provide: a novel fluorescent compound that can alone emit white light instead of using multiple fluorescent compounds; and a light-emitting element based on the compound.SOLUTION: The compound is represented by the formula in the figure, where X1, X2, X3, X4, X5 and X6 each independently represent F, Cl or H; and Ar1 and Ar2 each independently represent an aromatic group.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a novel compound capable of emitting white light, a white fluorescent composition containing the compound, and a light-emitting device manufactured using the white fluorescent composition.

Background Art

[0002] White fluorescence can usually be achieved by mixing a plurality of fluorescent dyes among the three primary colors of light, red, green, and blue, or by mixing two types, blue and yellow. However, since these fluorescent dyes, which are inorganic compounds and organic compounds, have different excitation wavelengths and fluorescence quantum yields, extremely restricted conditions are required for the dye mixing ratio, excitation wavelength, etc. in order to obtain white fluorescence.

[0003] In addition, since the durability of each fluorescent dye is different, it is difficult to maintain the balance between them and maintain the state in which white fluorescence can be obtained for a long period of time. Therefore, for example, when applied to organic EL, there are many technical difficulties such as the need for complicated condition studies and an increase in product price in its commercialization. As a compound without such problems, Patent Document 1 proposes a novel compound having a benzene ring-crosslinked bipyrrole structure.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide a novel fluorescent compound that emits white light with only one kind, without depending on a plurality of fluorescent compounds, and a light-emitting device using the compound.

Means for Solving the Problems

[0006] The inventors of the present invention have conducted studies based on diarylethene derivatives, which are photochromic compounds, and found that derivatives obtained by oxidatively closing the ring of the derivatives and changing the central part to an aromatic ring emit blue and yellow excimer fluorescence from two different intermolecular interaction states in the crystalline state, and white fluorescence is emitted by this blue and yellow, thus completing the present invention.

[0007] That is, the present invention relates to a compound represented by the following formula:

Chemical formula

[0008] Preferably, the fluorescent substance contains only the above compound.

[0009] The present invention also relates to a light-emitting device containing the above white fluorescent composition, an electroluminescence device containing the light-emitting device, or a photoluminescence device.

[0010] Furthermore, the present invention relates to a method for producing a white fluorescent compound, which includes a step of oxidatively closing the ring of a diarylethene derivative.

[0011] Preferably, the white fluorescent compound is the above compound.

[0012]

Advantages of the Invention

Effect of the Invention

[0013] Since the compound of the present invention can emit white light only with the compound as a fluorescent substance, it is not necessary to consider an appropriate mixing ratio when using a plurality of fluorescent compounds, and it is also not necessary to select a narrow excitation wavelength range such that all fluorescent compounds are excited, and a light-emitting device rich in selectivity of an excitation wavelength corresponding to the absorption range of the fluorescent compound can be provided. Further, it is not necessary to individually consider the durability of a plurality of fluorescent compounds, and it is possible to maintain a state in which white fluorescence is obtained for a long period of time.

Brief Description of Drawings

[0014]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Mode for Carrying Out the Invention

[0015] The compound of the present invention has the following formula:

Chemical Formula

[0016] X 1 and X 2 and X 3 and X 4 and X 5 and X 6 each independently is F, Cl or H, but F is preferred in terms of fatigue resistance to light. Ar 1 and Ar 2 each independently is an aromatic group, and examples of the aromatic group include a phenyl group and a naphthyl group. These aromatic groups may have substituents such as an alkyl group. Among them, the following formula:

Chemical formula

[0017] The said compound is a photochromic compound, and it can be synthesized by using a diarylethene derivative (for example, 1,2-bis(2-phenylthiazol-4-yl)perfluorocyclopentene) in which two aromatic groups are respectively bonded to the 1st and 2nd positions of ethylene as a precursor, and oxidatively cyclizing to change the central part into an aromatic ring. Examples of the method of oxidative cyclization include irradiating ultraviolet light in the presence of an oxidizing agent such as iodine or tetrabutylammonium perchlorate in a solution.

[0018] The compound emits white fluorescence in the crystalline state. As shown in Figure 1, when it is dissolved in chloroform and the letter "R" is written on a glass substrate and then dried, it still shows white fluorescence. The emission mechanism of the white light emission is that, as shown in the Jablonski diagram in Figure 2, it is not the emission in solution, but in the crystal which is a molecular aggregate, and it emits blue and yellow light from two different intermolecular interaction states shown below.

[0019] Since the compound fluoresces white, it can be mixed with other components such as organic solvents to form a white fluorescent composition. By applying the composition to a glass substrate or the like, a light-emitting element can be fabricated. As the organic solvent, those that can dissolve the compound can be used, for example, chloroform, methanol, ethanol, hexane, toluene, tetrahydrofuran, dichloromethane, acetone, acetonitrile, and the like. On the other hand, as the fluorescent substance, it is preferably free of fluorescent substances other than the compound.

[0020] The light-emitting element can be fabricated by applying, vapor-depositing, or printing the white fluorescent composition onto a substrate such as glass. And by mounting the light-emitting element, an electroluminescence device or a photoluminescence device can be fabricated.

Examples

[0021] Hereinafter, examples of the present invention will be described, but the present invention is not limited to the following examples.

[0022] Example 1 1,2-Bis(2-phenylthiazol-4-yl)perfluorocyclopentene, which is a diarylethene derivative, and iodine were dissolved in chloroform at a molar ratio of 1:1, and irradiated with ultraviolet light (λ = 365 nm, 810 μW / cm -2 ) for 1 hour to oxidatively cyclize to obtain the following formula in which the central part becomes an aromatic ring:

Chemical formula

[0023] 50 mg of Compound A synthesized in Example 1 was dissolved in 5 ml of chloroform, and the letter "R" was written on a glass substrate and dried. Ultraviolet light (wavelength = 365 nm, intensity 277 mW / cm -2 ) was irradiated on the letter. Photographs of the letter before and after irradiation with ultraviolet light are shown in Fig. 1, and it emitted white light upon irradiation with ultraviolet light. The mechanism of luminescence is shown in the Jablonski diagram of Fig. 2. The white luminescence is because, in the crystal which is a molecular aggregate rather than in solution, blue and yellow luminescence occurs from two different intermolecular interaction states shown in Fig. 2.

[0024] To confirm that the white luminescence is due to the condensation of molecules, water was added to the ethanol solution of Compound A to decrease the solubility, and Compound A was condensed and precipitated. As shown in Fig. 4, it was observed that the fluorescence color shifted from blue to white with aggregation and precipitation. When representing the color change at this time in the Commission Internationale de l’Eclair-age (CIE) 1931 color space coordinates, as shown in Fig. 5, it can be recognized that it shifted from blue to white.

[0025] Experimental results regarding the fluorescence emission of the crystal of Compound A are shown in Fig. 6. As shown in a~f of Fig. 6, when the crystal is irradiated with ultraviolet light, it shows white fluorescence. When the crystal emitting the white light is passed through a cut-off filter of 426 < λ < 446 nm, it appears blue as shown in d, and when passed through a cut-off filter of λ > 500 nm, it appears yellow as shown in f. When measuring the fluorescence excitation spectrum of the crystal of Compound A, as shown in Fig. 7, there is only one absorption band in the absorption below 400 nm, indicating that it has a single composition. On the other hand, as shown in Fig. 8, there are blue emission and yellow emission bands in the fluorescence emission spectrum, and their fluorescence lifetimes τ are 0.81 ns for the blue emission and 6.70 ns for the yellow emission.

[0026] The packing structure of the molecules in the crystalline state is shown in Fig. 11. In the crystal, there are two conformers (rotational isomers of the phenyl group) of Compound A, which are distinguished as black (Conformer A) and gray (Conformer B) molecular frameworks. They have a herringbone structure arranged alternately as shown in Fig. 11. Each conformer consists of a pair of structural units that overlap in an antiparallel manner, and furthermore, they are arranged in a configuration where they overlap slightly separated and adjacent dimers. Therefore, a pair of dimers shows the appearance of a J-aggregate. The face-to-face distances between the dimers of Conformer A and Conformer B are 3.414 and 3.511 Å, respectively, and the distances between each adjacent dimer are 3.493 and 3.445 Å, respectively. It is considered that blue emission corresponding to single-molecule emission emerges from the state of Conformer A with a small molecular overlap, and yellow emission corresponding to excimer emission emerges from the state where two molecules of Conformer B with a large overlap face each other.

Industrial Applicability

[0027] The compound of the present invention is a new material that emits white fluorescence with a single material. It has the potential as a new material for EL, and if it is put into practical use as an EL material, it can revolutionize the technology of organic EL.

Claims

1. A compound represented by the following formula: 【Chemical Formula 1】 (wherein X １ , X ２ , X ３ , X ４ , X ５ , and X ６ each independently represents F, Cl or H, and Ar １ , and Ar ２ each independently represents an aromatic group.)

2. A white fluorescent composition comprising the compound according to Claim 1.

3. The white fluorescent composition according to Claim 2, comprising only the compound according to Claim 1 as a fluorescent substance.

4. A light-emitting device comprising the white fluorescent composition according to Claim 2 or 3.

5. An electroluminescence device or a photoluminescence device comprising the light-emitting device according to Claim 4.

6. A method for producing a white fluorescent compound, comprising a step of oxidatively cyclizing a diarylethene derivative, wherein the white fluorescent compound is the compound according to Claim 1. ​

Images