Fluorescent rare earth complex and security medium using same

Abstract

To provide a fluorescent rare earth complex that has high solubility in a medium and is superior in emission intensity and durability, and also provide a light-emitting device including the complex.SOLUTION: A rare earth complex comprises a rare earth ion and a phosphine oxide ligand. The phosphine oxide ligand has a phosphorus atom combined with at least one phenyl group with a substituent at the meta position. The para position of the phenyl group should be unsubstituted.SELECTED DRAWING: None

Description

[Technical field]

[0001] The embodiments relate to rare earth complexes having high luminescence intensity and durability, compositions containing the rare earth complexes, and security media carrying the rare earth complexes. [Background technology]

[0002] Rare earth complexes have the characteristics of having an absorption wavelength in the UV region and a sharp emission spectrum, and are expected to be used in many fields such as light-emitting devices, sensors, and security. In order to apply rare earth complexes to such applications, they are required to have excellent emission intensity, solubility in polymers and solvents, and durability. The search for phosphors that simultaneously satisfy all these characteristics is currently ongoing, and phosphors with better properties than conventional phosphors are desired. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3811142 specification [Patent Document 2] Patent No. 5498331 specification DISCLOSURE OF THEINVENTION [Problem to be solved by the invention]

[0004] The embodiments have been made under the above circumstances, and an object of the embodiments is to provide a phosphor that is particularly excellent in luminous intensity and durability. [Means for solving the problem]

[0005] The rare earth complex according to the embodiment comprises Rare earth ions; a diphosphine dioxide ligand; and a β-diketone ligand, The combinations of substituents bonded to the two phosphorus atoms contained in the diphosphine dioxide ligand are different from each other.

[0006] A composition for forming a security medium according to an embodiment contains the rare earth complex and a polymer.

[0007] In addition, a security medium according to an embodiment has the rare earth complex supported on a substrate. [Brief description of the drawings]

[0008] [Figure 1] Fluorescence spectra of Example 1 and Comparative Example 1 [Diagram 2] Excitation spectra of Example 2 and Comparative Example 2 [Diagram 3] Graph showing the results of durability tests for Example 3 and Comparative Example 3. [Figure 4] FIG. 1 shows the quantum yields of Example 1 and Comparative Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, the embodiments will be described in detail.

[0010] <Rare earth complexes> The rare earth complex according to the embodiment includes a rare earth ion, a diphosphine dioxide ligand, and a β-diketone ligand, and is a phosphor that absorbs ultraviolet light and emits light.

[0011] In the embodiment, the rare earth ion can be appropriately selected so as to generate fluorescence of a wavelength according to the application, but is preferably a lanthanide ion, more specifically, europium or terbium is preferable, and europium is particularly preferable in order to realize a fluorescent complex having a wide spectrum in the red region and excellent color rendering.

[0012] The diphosphine dioxide ligand contained in the rare earth complex according to the embodiment has two P=O bonds in its structure, and is a ligand that coordinates to a rare earth ion through these bonds. Various substituents can be bonded to the two phosphorus atoms that constitute the two P=O bonds. In the embodiment, the combinations of the substituents bonded to the two phosphorus atoms are different from each other. That is, the diphosphine dioxide ligand has an asymmetric shape. In this way, the diphosphine dioxide ligand has an asymmetric shape, which causes distortion in the ligand field and increases the quantum yield. Since the emission intensity of the rare earth complex is proportional to the product of the quantum yield and the absorption coefficient, the emission intensity can be increased if the quantum yield is high. In addition, if the diphosphine dioxide ligand is asymmetric, the solubility in a solvent or the like also tends to be high.

[0013] Two substituents can be bonded to each of these phosphorus atoms. In an embodiment, the combination of substituents bonded to one of the two phosphorus atoms is different from the combination of substituents bonded to the other phosphorus atom. For example, (i) An aliphatic hydrocarbon group and an aromatic hydrocarbon group are bonded to one phosphorus atom, and two aliphatic hydrocarbon groups are bonded to the other phosphorus atom; (ii) an aliphatic hydrocarbon group and an aromatic hydrocarbon group attached to one phosphorus atom and two aromatic hydrocarbon groups attached to the other; (iii) Two aliphatic hydrocarbon groups attached to one phosphorus atom and two aromatic hydrocarbon groups attached to the other;

[0014] etc. In the embodiment, the aliphatic hydrocarbon group may be one consisting of only carbon and hydrogen, or may contain a substituent containing oxygen, nitrogen, sulfur, etc., such as a hydroxyl group or an amino group. In the embodiment, the aromatic hydrocarbon group may be one containing nitrogen or sulfur as an element constituting an aromatic ring, such as a pyridyl group or a thienyl group, or may contain a substituent containing oxygen, nitrogen, sulfur, etc., such as a hydroxyl group or an amino group.

[0015] In order to make the diphosphine dioxide ligand asymmetric, it is possible to combine aliphatic hydrocarbon groups having different carbon numbers, for example, but in order to increase the distortion of the ligand field, it is preferable to realize the asymmetry by combining an aliphatic hydrocarbon group with an aromatic hydrocarbon group. Specifically, it is preferable that at least one aliphatic hydrocarbon group is bonded to one of the two phosphorus atoms and at least one aromatic hydrocarbon group is bonded to the other phosphorus atom, and it is particularly preferable that two aliphatic hydrocarbon groups are bonded to one phosphorus atom and two aromatic hydrocarbon groups are bonded to the other (corresponding to the above (iii)).

[0016] The two substituents bonded to each phosphorus atom may be bonded to each other to form a ring.

[0017] The β-diketone ligand contained in the rare earth complex according to the embodiment can be arbitrarily selected from commonly known ligands. This β-diketone ligand is a counter ion for the rare earth ion, which is a cation, and also contributes to the formation of the ligand field of the complex. The rare earth complex according to the embodiment has high durability due to the presence of a specific β-diketone ligand.

[0018] The β-diketone ligand according to the embodiment preferably has a halogenated hydrocarbon group, since the emission intensity is higher. This is believed to be because the halogenated hydrocarbon group has electron-withdrawing properties, and activates the C-H bond of the β-diketone ligand, thereby increasing the luminous intensity. This linking group is generally bonded to the 1-position and / or 3-position of the β-diketone ligand skeleton. In addition, if the β-diketone ligand has an asymmetric shape, the emission intensity tends to be higher.

[0019] The rare earth complex according to the embodiment includes a β-diketone ligand as a counter ion of the rare earth ion, but may include other anions as counter ions, such as halogen ions, hydroxy ions, carboxylate ions, and the like.

[0020] Among such rare earth complexes, those represented by the following formula (1): [ka] During the ceremony, Each Ar is independently an aryl group; R is independently a linear or branched alkyl group; R F are each independently a perfluoroalkyl group, n is an integer from 3 to 5; p is an integer of 1 or 2, q is an integer from 1 to 3; X is absent when q is 3, and is an anion with a valence of 3-q when q is 1 or 2. This complex is a diphosphine dioxide ligand and a β-diketone ligand bonded to a europium(III) ion.

[0021] In formula (1), one of the two phosphine oxides (P=O) has two aryl groups bonded to it, and the other has two alkyl groups bonded to it. This asymmetric structure improves the emission intensity.

[0022] In formula (1), the two aryl groups Ar may be the same or different. The aryl group is not limited, but from the viewpoint of the solubility and durability of the rare earth complex, the number of carbon atoms of the aryl group is preferably 6 to 20, more preferably 6 to 12. The aryl group may contain a substituent such as a hydroxyl group or an alkoxy group, within a range that does not impair the effects of the embodiment. More specifically, the aryl group is preferably phenyl, 2-methylphenyl, 1-ethoxyphenyl, or naphthyl, and more preferably phenyl. When the phenyl has a substituent, the solubility tends to be higher when the phenyl has a substituent at the 2-position. In addition, the two Ar may be bonded to each other to form a ring structure containing a phosphorus atom. Specifically, a structure in which phenylene is bonded to one phosphorus atom via two hydrocarbon chains can be formed.

[0023] In formula (1), the two alkyl groups R may be the same or different. The alkyl group is not limited, but from the viewpoint of the solubility and durability of the rare earth complex, the number of carbon atoms in the alkyl group is preferably 3 to 10, more preferably 4 to 8. The group may contain a substituent such as a hydroxyl group or an alkoxy group within a range that does not impair the effects of the embodiment. More specifically, examples of the alkyl group include n-butyl, 1-methylpropyl, t-butyl, n-hexyl, 2-ethylbutyl, and n-octyl. The two R may be bonded to each other to form a ring structure containing a phosphorus atom. Specifically, a structure in which an alkylene chain is bonded to one phosphorus atom may be formed.

[0024] In formula (1), the two phosphorus atoms are linked by an alkylene chain having n carbon atoms. n is an integer of 3 to 5, and is preferably 4. By setting n within this range, high durability can be achieved. When n is 2 or less, the positional relationship between the two phosphine oxides is limited, suppressing distortion of the ligand field and decreasing the emission intensity. On the other hand, when n exceeds 6, one diphosphine dioxide ligand forms a binuclear complex linking two rare earth ions, which may decrease the solubility.

[0025] In formula (1), the β-diketone ligand has two perfluoroalkyl groups R at the 1- and 3-positions. F The β-diketone ligand has a perfluoroalkyl group, and when the complex absorbs light, the energy efficiency from the excited ligand to the rare earth ion is high, so that high luminescence intensity can be realized. The number of carbon atoms in the perfluoroalkyl group is not limited, but in order to realize high solubility, the number of carbon atoms is preferably 8 or less, and more preferably 1 to 3. Specifically, the perfluoroalkyl group is particularly preferably CF3, C2F5, or C3F7. In addition, when two R F may be the same or different, but the two R FThe difference in the β-diketone ligand makes the β-diketone ligand asymmetric, which increases the distortion of the ligand field and increases the emission intensity, which is preferable.

[0026] In addition, it is generally known that in rare earth complexes, when the two substituents of the β-diketone ligand are perfluoroalkyl groups, the light resistance and quantum yield are improved. However, it is also known that such a structure reduces the solubility in polymers and solvents, and reduces the transparency of a composition containing a rare earth complex (a rare earth complex dissolved in a polymer or solvent). If the transparency of the composition is reduced, it is disadvantageous, especially when applied to a security medium. In the embodiment, the diphosphine dioxide ligand is made to have a specific structure, thereby maintaining high solubility and ensuring the transparency of the composition.

[0027] In the rare earth complex according to the embodiment, it is preferable that the diphosphine dioxide ligand is asymmetric and the β-diketone ligand is also asymmetric. The present inventors consider the reason for this to be as follows.

[0028] In the case of β-diketone, the proton at the active methylene site dissociates, becomes an anion, and coordinates with the rare earth ion, neutralizing the rare earth ion. Therefore, when the proton returns to the β-diketone anion and the charge becomes neutral, it is released from the rare earth ion, and as a result, the rare earth complex does not emit light. Comparing the anion state with the charge neutral state, the greater the stabilization energy for neutralization, the easier it is for the β-diketone ligand to be released from the rare earth ion. [ka]

[0029] We investigated how the stabilization energy of the anionization reaction of such β-diketones is affected by the substituents. a and R b ) is changed, the stabilization energy E when a proton binds to the anion Swas calculated using the density generalized functional theory. The results are shown in the chemical table. [Table 1] In the table, Me is methyl, t-Bu is t-butyl, and Naph is naphthyl.

[0030] From this calculation, In the case of the combination of (Me,Me) or (t-Bu,t-Bu), the stabilization energy E S is the largest, indicating that the β-diketone ligand is easily removed. The stabilization energy is significantly reduced with the combinations (C3F7,t-Bu), (C3F7,naph) or (CF3,Naph). However, these combinations contain substituents that are not perfluoroalkyl groups, so the light durability of the complexes is insufficient. When both substituents are perfluoroalkyl groups, the stabilization energy E S is 310~314 kcal / mol, the smallest, indicating that the β-diketone ligand is difficult to remove.

[0031] Of these, the combination (CF3,CF3) tends to have low solubility in the solvent. The combination (C3F7,C3F7) can improve solubility by reducing the interaction between solutes due to the steric hindrance effect of the substituents. In addition, solubility can also be improved by making the molecular structure asymmetric, as in the combination (C3F7,CF3).

[0032] On the other hand, the phosphine oxide ligand and the rare earth ion form a coordinate bond as a Lewis base and a Lewis acid. When one diphosphine dioxide ligand is coordinated, a chelate effect occurs, making it difficult to remove, compared to when two phosphine oxide ligands are coordinated. However, when the diphosphine dioxide ligand is symmetric, the quantum yield is limited and the emission intensity of the rare earth complex may be insufficient. The rare earth complex according to the embodiment achieves a higher quantum yield by using an "asymmetric diphosphine dioxide".

[0033] From the above considerations, the best form of the rare earth complex according to the embodiment is one in which the substituent of the β-diketone ligand is (C3F7,C3F7) or (C3F7,CF3), and two aromatic hydrocarbon groups are bonded to one phosphorus atom of the asymmetric diphosphine dioxide ligand, and two aliphatic hydrocarbon groups are bonded to the other phosphorus atom.

[0034] The rare earth complex according to the embodiment has p diphosphine dioxide ligands and q β-diketone ligands, where p is an integer of 1 or 2, and q is an integer of 1 to 3. Most typically, the complex has one diphosphine dioxide ligand (p=1) and three β-diketone ligands (q=3), forming an 8-coordinate structure. In this case, the charge of the rare earth ion is offset by the three β-diketone ligands, so that there is no counter ion X.

[0035] It is also possible to have two or less β-diketone ligands. In this case, typically two diphosphine dioxide ligands can be coordinated, but a counterion X is required to balance the charge of the entire complex. The counterion in this case may be one divalent anion or two monovalent anions.

[0036] The rare earth complex according to the embodiment may contain a diphosphine dioxide ligand or a β-diketone ligand as long as the effect of the embodiment is not impaired.

[0037] Specific examples of rare earth complexes according to the embodiment include the following (1-1) to (1-35). Among these, (1-1) to (1-12) are particularly preferred. [ka]

[0038] [ka]

[0039] [ka]

[0040] [ka]

[0041] <Composition for forming security medium> The rare earth complex according to the embodiment has a feature that it has a high saturation solubility in a medium, for example, a solvent or a polymer. Therefore, by dissolving the rare earth complex in, for example, a polymer to prepare a composition and applying it to an appropriate substrate, it is possible to realize a decorative item or a security medium that is colorless and transparent under indoor light and emits strong light under ultraviolet light or near ultraviolet light. More specifically, by applying a composition in which the rare earth complex according to the embodiment is dissolved in a polymer or the like to a substrate such as a security card to create a barcode, it is possible to obtain a security medium that is completely colorless under visible light but emits strong light under ultraviolet light. With such a security medium, it is difficult to even know the existence of the barcode under visible light, so that higher security can be realized.

[0042] The composition for forming the security medium can be prepared by dissolving the rare earth complex according to the embodiment in a suitable solvent or polymer. The rare earth complex according to the embodiment has high durability or stability, and is therefore highly stable even when dissolved in a solvent or polymer, and is unlikely to decompose even when dissolved in a strongly acidic or strongly basic solvent. As the solvent, an appropriate one can be selected from among commonly known organic solvents. Specific examples of the solvent include esters such as ethyl acetate, fluorinated aliphatic hydrocarbons such as perfluoropentane, aromatic hydrocarbons such as toluene or xylene, and alcohols such as ethanol, methanol, isopropanol, and butanol.

[0043] When the rare earth complex according to the embodiment is dissolved in a polymer, it is preferable to use a transparent resin such as an acrylic resin, a polyester resin, a vinyl chloride-vinyl acetate copolymer resin, etc. As described above, the rare earth complex according to the embodiment is stable even under strongly acidic conditions, and therefore, even if dispersed or dissolved in an acidic resin, it is an advantage of the present invention that it can maintain high durability.

[0044] Such acidic resins are, for example, resins having carboxyl groups, such as alkyd resins, such as linseed oil-modified maleic acid alkyd resins and acrylic-modified alkyd resins, and polyacrylic acid resins. In addition, resins having sulfonic acid include resins having polystyrene sulfonic acid. Many acidic cation exchange resins also fall into this category.

[0045] The composition may contain additives such as surfactants, defoamers, preservatives, and pH adjusters, as necessary. In addition, when the composition according to the embodiment is used as a security medium, it is preferable that the composition has low visibility under visible light, and therefore it is generally preferable that the composition is colorless and transparent. However, dyes and pigments can be combined as necessary. In addition, in order to keep the rare earth complex stable, the rare earth complex can be encapsulated in microcapsules and blended.

[0046] <Security media> The security medium according to the embodiment has the above-mentioned rare earth complex held on a substrate. Such a medium can be manufactured by, for example, applying the above-mentioned composition to a substrate. The substrate can be any material such as paper, plastic, cloth, nonwoven fabric, ceramics, etc. The application method is not particularly limited, but generally, a identifiable mark is formed by drawing or transferring a certain shape onto the substrate by printing or the like.

[0047] In addition, a rare earth complex can be dissolved in a polymer or the like, and the polymer can then be cured to form a substrate, making the substrate itself a security medium that emits light when exposed to ultraviolet light. EXAMPLES

[0048] Hereinafter, examples of the embodiment will be described, but the embodiment is not limited thereto.

[0049] <Example 1> The Eu(III) complex of formula (1-1) was dissolved in ethyl acetate (2 × 10 -4 The emission spectrum was measured at a concentration of 1.2 mmol / L, and the obtained emission spectrum is shown in FIG. The maximum absolute quantum efficiency of the complex of formula (1-1) in this solution was 0.47. [ka]

[0050] <Comparative Example 1> The emission spectrum of the Eu(III) complex represented by formula (R-1) was measured in the same manner as in Example 1. The maximum absolute quantum yield of the complex represented by formula (R-1) in this solution was 0.40. It was found that the emission intensity of the complex represented by formula (R-1) was smaller than that of the complex represented by formula (1-1). [ka]

[0051] <Example 2> The excitation spectrum was measured for the solution prepared in Example 1. The obtained excitation spectrum is shown in FIG.

[0052] <Comparative Example 2> When the excitation spectrum of the solution prepared in Comparative Example 1 was measured, the obtained excitation spectrum was as shown in Figure 2. It was found that the excitation intensity of the complex of formula (R-1) was smaller than that of the complex of formula (1-1).

[0053] <Example 3> The solution prepared in Example 1 was applied to paper, dried, and the light resistance was evaluated based on JIS B 7754 "Xenon arc lamp type light resistance and weather resistance tester." As shown in Figure 3, the luminance remaining rate after 24 hours of the complex of formula (1-1) was 72%, which was good.

[0054] <Comparative Example 3> The solution prepared in Comparative Example 1 was applied to paper and dried, and the light resistance was evaluated in the same manner as in Example 3. As shown in Fig. 3, the luminance residual rate after 24 hours of the complex of formula (R-1) was 17%, which was found to be significantly inferior to the complex of formula (1-1).

[0055] <Example 4> The absolute quantum yield and light resistance in solution were evaluated using the complex of formula (1-8) as the phosphor for Example 1. The complex of formula (1-8) had an absolute quantum yield about 1.2 times that of the complex of formula (1-1), and had equal or higher light resistance. [ka]

[0056] <Comparative Example 4> The complex of formula (1-1) and the complex of formula (R-2) were used as phosphors to evaluate quantum yield and light resistance. First, the absolute quantum yield in the solid crystalline state for each wavelength was measured for the complex of formula (1-1) and the complex of formula (R-2). The results are shown in FIG. 4, and the absolute quantum yield in the solid state of the complex of formula (R-2) was about 0.7 times that of the complex of formula (1-1). In addition, the fluorescence of the complex of formula (R-2) almost disappeared after 24 hours of light irradiation. [ka]

[0057] As described above, although several embodiments have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various combinations, omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims.

Claims

1. The following formula (1): 【Chemistry 1】 During the ceremony, Each Ar is independently an aryl group; Each R is independently an alkyl group having 6 to 10 carbon atoms; R Ｆ are each independently a halogenated hydrocarbon group; n is an integer from 3 to 5; p is an integer of 1 or 2; q is an integer from 1 to 3; M is a trivalent europium ion; X is absent when q is 3, and is an anion having a valence of 3-q when q is 1 or 2. A rare earth complex represented by the formula:

2. 2. The rare earth complex of claim 1, wherein n=4.

3. Two R's Ｆ The rare earth complex according to claim 1 or 2, wherein the chain lengths of

4. 4. The rare earth complex according to claim 1, wherein p=1 and q=3.

5. 5. The rare earth complex according to claim 1, wherein each of the two Ar's is a substituted or unsubstituted phenyl group.

6. 6. The rare earth complex according to claim 1, wherein each of the two R's is an alkyl group having 6 to 8 carbon atoms.

7. A security medium comprising the rare earth complex according to any one of claims 1 to 6 and a polymer.

8. A security medium comprising the rare earth complex according to any one of claims 1 to 6 supported on a substrate.

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