Patent Grant
11499093
This application is a National Stage of International Application No. PCT/JP2018/006466, filed on Feb. 22, 2018, which claims priority from Japanese Patent Application No. 2017-035043, filed on Feb. 27, 2017.
The present invention relates to a rare earth complex and a light emitting element.
A rare earth complex which exhibits emission of red light is expected to be applied to, for example, as fluorescent substance to constitute a white LED light source. As the rare earth complex which exhibits emission of red light, for example, a europium complex having a hexafluoroacetylacetonate (hfa) derivative and a phosphine oxide compound as ligands has been reported (Patent Literature 1).
Patent Literature 1: Japanese Unexamined Patent Publication No. 2016-166139
The excitation wavelength band (absorption wavelength) of an intensive light-emitting rare earth light-emitting substance is typically at 400 nm or less. On the other hand, the general-purpose excitation wavelength of light-emitting substance of a white LED light source is in the vicinity of 460 nm in the visible light region excited by a blue LED. When it becomes possible that a rare earth light-emitting substance is excited by a blue LED, creation of a new market is expected due to an advantage of excellent color rendering.
A main object of the present invention is to provide a novel rare earth complex which efficiently emits light by excitation using visible light in the vicinity of 460 nm.
In an aspect of the present invention, there is provided a rare earth complex comprising a rare earth ion and a ligand coordinated with the rare earth ion and having a condensed polycyclic aromatic group. The condensed polycyclic aromatic group is a residue formed by removing a hydrogen atom bonded to a condensed aromatic ring in the following formula (I) or formula (II) from a condensed polycyclic aromatic compound represented by formula (I) or (II). The condensed polycyclic aromatic compound optionally has a substituent bonded to the condensed aromatic ring in formula (I) or formula (II).
The present invention also relates to a light emitting element comprising the rare earth complex described above. The light emitting element is usable as various light sources such as a white LED and an optical coherence tomography apparatus.
According to the present invention, there is provided a novel rare earth complex which efficiently emits light by excitation using visible light (for example, 420 to 480 nm). Further, the rare earth complex in an embodiment of the present invention tends to exhibit emission in a relatively narrow emission band in the emission spectrum, so that application to a light emitting element is advantageous from this point of view.
Embodiments of the present invention are described in detail in the following. The present invention, however, is not limited to the following embodiments.
The rare earth complex in an embodiment comprises a rare earth ion and a plurality of ligands coordinated with the rare earth ion.
The rare earth ion is an ion of rare earth element selected from the group consisting of, for example, europium (Eu), neodymium (Nd), ytterbium (Yb), and gadolinium (Gd). For example, europium as a trivalent cation (Eu3+) forms a complex.
The rare earth complex in an embodiment has a ligand having a condensed polycyclic aromatic group derived from a condensed polycyclic aromatic compound represented by the following formula (I) or (II). The condensed polycyclic aromatic group is a residue formed by removing a hydrogen atom bonded to a condensed aromatic ring in formula (I) or formula (II) from a condensed polycyclic aromatic compound represented by the following formula (I) or (II). The condensed polycyclic aromatic compound of formula (I) or (II) and a condensed polycyclic aromatic group derived therefrom may have or may not have a substituent (for example, a methyl group) bonded to the condensed ring in formula (I) or formula (II). The condensed polycyclic aromatic group has a π conjugated system having a large area and a large width, which contributes to efficient emission by excitation using visible light in the vicinity of 460 nm. This is supported by calculation of the absorption properties through a semiempirical molecular orbital method as described below.
Specific examples of the condensed polycyclic aromatic group as a residue formed by removing a hydrogen atom from the condensed polycyclic aromatic compound of formula (I) include a monovalent condensed polycyclic aromatic group represented by the following formula (Ia) and a divalent condensed polycyclic aromatic group represented by the following formula (Ib). In these formulas, * represents a bond, which is the same in other formulas.
Specific examples of the condensed polycyclic aromatic group as a residue formed by removing a hydrogen atom from the condensed polycyclic aromatic compound of formula (II) include a monovalent condensed polycyclic aromatic group represented by the following formula (IIa) and a divalent condensed polycyclic aromatic group represented by the following formula (IIb).
The ligand having a condensed polycyclic aromatic group may be, for example, at least either one of a phosphine oxide ligand represented by the following formula (10) and a diketone ligand represented by the following formula (20).
In formula (10), Z represents a condensed polycyclic aromatic group derived from a condensed polycyclic aromatic compound of the formula (I) or (II) described above, and R11 and R12 each independently represent an aryl group different from the condensed polycyclic aromatic group. In formula (20), Z represents a condensed polycyclic aromatic group derived from a condensed polycyclic aromatic compound of the formula (I) or (II) described above, and R21 and R22 each independently represent a hydrogen atom, an alkyl group, a halogenated alkyl group, an aryl group different from the condensed polycyclic aromatic group, or a heteroaryl group.
The aryl group as R11 or R12 may be a residue formed by removing a hydrogen atom from an aromatic compound. The aryl group may have, for example, 6 to 14 carbon atoms. Specific examples of the aryl group include a residue formed by removing a hydrogen atom from a substituted or unsubstituted benzene, a substituted or unsubstituted naphthalene, a substituted or unsubstituted anthracene, and a residue formed by removing a hydrogen atom from a substituted or unsubstituted phenanthrene. In particular, R11 and R12 may be a substituted or unsubstituted phenyl group.
The alkyl group and the halogenated alkyl group as R21 or R22 may have 1 to 15, 1 to 5, or 1 to 3 carbon atoms. The halogenated alkyl group may be a fluorinated alkyl group such as trifluoromethyl group. Examples of the aryl group and the heteroaryl group as R21 or R22 include a phenyl group, a naphthyl group, and a thienyl group. R21 may be a methyl group, a trifluoromethyl group, a tert-butyl group, or a phenyl group. R22 may be a hydrogen atom (including a deuterium atom).
The ligand having a condensed polycyclic aromatic group may be, for example, a bidentate phosphine oxide ligand represented by the following formula (30). Z, R11 and R12 in formula (30), are similarly defined as Z, R11 and R12 in formula (10). The phosphine oxide ligand of formula (30) may be coordinated with two rare earth ions such that the rare earth ions are linked.
The rare earth complex may further comprise other ligands in addition to the ligand having a condensed polycyclic aromatic group. Examples of the other ligands include a phosphine oxide ligand represented by the following formula (11) and a diketone ligand represented by the following formula (21).
In formula (11), R13, R14 and R15 each independently represent an aryl group different from a condensed polycyclic aromatic group derived from the condensed polycyclic aromatic compound of the formula (I) or (II) described above. Examples of the aryl group as R13, R14 or R15 include those which are the same as R11 or R12 in formula (10). R13, R14 and R15 may be a substituted or unsubstituted phenyl group.
In formula (21), R23, R24 and R25 each independently represent a hydrogen atom, an alkyl group, a halogenated alkyl group, an aryl group different from a condensed polycyclic aromatic group derived from the condensed polycyclic aromatic compound of the formula (I) or (II) described above, or a heteroaryl group. Examples of R23, R24 and R25 include those which are the same as R21 and R22 in formula (20). R23 and R25 may be each independently a methyl group, a trifluoromethyl group, a tert-butyl group or a phenyl group, and R24 may be a hydrogen atom (including a deuterium atom).
The rare earth complex containing a diketone ligand represented by formula (20) or (21) is able to have further excellent properties from the viewpoints of intensive emission and the like. As a ligand of the rare earth complex, a combination of a diketone ligand represented by formula (20) having a condensed polycyclic aromatic group and a phosphine oxide ligand represented by formula (11), or a combination of a diketone ligand represented by formula (21) and a ligand represented by formula (10) having a condensed polycyclic aromatic group, may be therefore selected. For example, the rare earth complex may be a complex represented by the following formula (C1) or (C2). In formulas (C1) and (C2), Ln (III) represents a trivalent rare earth ion.
The rare earth complex having a diketone ligand may have a bidentate ligand represented by formula (30). Examples thereof include a complex represented by the following (C3). The definition of each symbol in formula (C3) is the same as described above. In the complex represented by formula (C3), two rare earth ions Ln (III) are linked through two bidentate ligands.
The light emitting element comprising the rare earth complex of the present embodiment is expected to be applied to, for example, the light source of a white LED element excited by a blue LED and an optical coherence tomography (OCT) apparatus. A rare earth complex in several embodiments allows a light emitting element with a wide band width of 140 nm or more, or 200 nm or more, to be provided at a low cost. The band width, for example, directly affects the resolution of OCT, and high resolution can be obtained by using a light source having a wide band width.
The present invention will be described in further detail based on Examples as follows. However, the present invention is not limited to the following Examples.
1. Synthesis of Rare Earth Complex
(1) Synthesis of Gd(hfa)3(DPPTO)3
In toluene (15 mL), tris(hexafluoroacetylacetonate)gadolinium (Gd(hfa)3(H2O)2, 350 mg, 0.430 mmol) and 2-diphenylphosphoryltriphenylene DPPTO (500 mg, 1.17 mmol) were dissolved, and the resulting reaction solution was heated to reflux at 85° C. for 12 hours. Subsequently, the reaction solution was dried and solidified by an evaporator. Using a mixed solvent of dichloromethane/hexane, the residue was re-precipitated, and the precipitate was washed with hexane to obtain Gd(hfa)3(DPPTO)3 (white powder), (yield: 78 mg, yield rate: 13%).
Elemental analysis (%): calcd for C105H66GdF18O9P3:C 61.11, H 3.22. Found: C 62.53, H 3.53.
ESI-MS: m/z calcd for C100H65GdF12O7P3 [M-hfa]+=1856.30; found: 1856.35.
(2) Synthesis of Eu(hfa)3(DPPTO)3
In toluene (10 mL), tris(hexafluoroacetylacetonate) europium (Eu(hfa)3(H2O)2, 350 mg, 0.430 mmol) and 2-diphenylphosphoryltriphenylene (DPPTO, 300 mg, 0.701 mmol) were dissolved, and the resulting reaction solution was heated to reflux at 85° C. for 12 hours. Subsequently, the reaction solution was dried and solidified by an evaporator. Using a mixed solvent of dichloromethane/hexane, the residue was re-precipitated, and the precipitate washed with hexane to obtain Eu(hfa)3(DPPTO)3 (white powder), (yield: 82 mg, yield rate: 17%).
Elemental analysis (%): calcd for C105H66EuF18O9P3:C 61.26, H 3.23. Found: C 61.40, H 3.41
ESI-MS: m/z calcd for C100H65EuF12O7P3 [M-hfa]+=1851.30; found: 1851.32.
(3) Synthesis of Eu2(hfa)6(BDPPC)2
Synthesis of 1,6-bis(diphenylphosphoryl)coronene (BDPPC):
In chlorobenzene (300 mL), coronene (6.3 g, 20.9 mmol) was suspended, and a mixture of chlorobenzene (100 mL) and bromine (10.0 g, 62.6 mmol) was added dropwise thereto. The formed reaction liquid was heated at 70° C. for 15 minutes while stirring, and then cooled with ice for 20 minutes. After completion of stirring, the reaction liquid was left standing and subjected to decantation. A solid taken out by suction filtration was washed with chlorobenzene and hexane and then dried, so that a yellow solid containing dibromocoronene (7.4 g) was obtained.
The resulting yellow solid was suspended in ultra-dehydrated THF (250 mL). Thereto, n-butyllithium (8.5 mL, 14 mmol) was added and the suspension was stirred. After 2 hours, chlorodiphenylphosphine (2.4 mL, 13 mmol) was added thereto, so that the suspension turned into a transparent solution. To the solution, H2O2 (2 mL) was added and stirred for 3 hours. Subsequently, extraction from the solution was performed three times with dichloromethane and brine. The dichloromethane layer was dried and solidified, and the resulting crude product solid was purified by silica column chromatography (dichloromethane/ethyl acetate), so that BDPPC was obtained.
1H-NMR (CDCl3, 400 MHz): /ppm=10.03-8.60 (m, 10H), 7.99-7.40 (m, 20H)
Synthesis of Eu2(hfa)6(BDPPC)2
In dichloromethane (20 mL), tris(hexafluoroacetylacetonate)europium (Eu(hfa)3(H2O)2, 65 mg, 0.08 mmol) and BDPPC (50 mg, 0.07 mmol) were dissolved, and the resulting reaction solution was stirred at room temperature for 4 hours. Subsequently, the reaction solution was dried and solidified by an evaporator. The solidified crude product was purified by recrystallization using a mixed solvent of dichloromethane/hexane, so that Eu2(hfa)6(BDPPC)2 (yellow powder) was obtained (yield: 10 mg, yield rate: 5%).
ESI-MS: m/z calcd for C121H65Eu2F30O14P4 [M-hfa]+=2740.13; found: 2740.08.
2. Photophysical Properties of Gd(hfa)3(DPPTO)3
3. Photophysical Properties of Eu(hfa)3(DPPTO)3
<Excited Emission Spectrum>
In the emission spectrum having excitation wavelength of 380 nm, a broad emission band was observed in the vicinity of 445 nm. The wavelength is shifted to the longer-wavelength side than the phosphorescence wavelength of DPPTO (439 nm) estimated from the emission spectrum of Gd(hfa)3(DPPTO)3. This suggests that an LMCT excited state based on the transition from DPPTO ligand to Eu (III) is mixed with the T1 state.
In the emission spectrum having an excitation wavelength of 280 nm, the fluorescence of DPPTO was observed in the vicinity of 370 nm in the same manner as in the case of Gd(hfa)3(DPPTO)3. This suggests that the DPPTO ligand is not substantially subjected to the internal heavy atom effect of Eu (III).
<Emission Life>
The emission life of Eu(hfa)3(DPPTO)3 in a powder condition was measured. In Table 1, together with the observed emission life τobs, the emission quantum yield ϕff of 4f-4f transition determined from the emission life measurement, the emission quantum efficiency ϕππ* of π-π* transition, the radiative constant κr, the nonradiative constant κnr, and the energy transfer efficiency ηsens are shown. In Table 1, literature data on Eu(hfa)3(TPPO)2 are also shown (A. Nakajima, T. Nakanishi, Y. Kitagawa, T. Seki, H. Ito, K. Fushimi, Y. Hasegawa, Sci. Rep. 6, 24458 (2016)).
Eu(hfa)3(DPPTO)3 exhibited a higher emission quantum yield ϕff than Eu(hfa)3(TPPO)2.
4. Evaluation on Absorption Intensity by Simulation
The optical absorption properties of Eu(hfa)3(DPPTO)3 were compared with those of Eu(hfa)3(HPO)2 by simulation. The simulation was performed by a semiempirical molecular orbital method using a quantum chemistry calculation software Gaussian.
Furthermore, the following rare earth complexes having a diketone ligand with a condensed polycyclic aromatic group (Complex B and Complex C) were designed, of which optical absorption properties were also calculated by simulation.
The molar extinction coefficient c of Eu2(hfa)6(BDPPC)2 in chloroform and the emission efficiency (room temperature) of Eu (III) when organic ligands are excited were measured.
aThe emission efficiency of Eu(hfa)3(HPO)2 was measured at powder.
From the results shown in Table 2, it was suggested that Eu2(hfa)6(BDPPC)2 emits light with an intensity about 2000 times that of Eu(hfa)3(TPPO)2 and with an intensity about 200 times that of Eu(hfa)3(HPO)2, by excitation light of 450 nm. In the case of excitation light of 460 nm also, it is believed that Eu2(hfa)6(BDPPC)2 exhibits high emission intensity in the same manner. When the chloroform solution of Eu2(hfa)6(BDPPC)2 was irradiated with blue light of 458 nm, high-intensity emission of red light of Eu(III) was observed.
The rare earth complex of the present invention and a light emitting element comprising the same are usable as a blue LED-type white LED and a light source for OCT. Further, expected applications include a solvent sensor which uses changes in emission properties depending on types of solvent, a temperature sensor which uses variation in properties with temperature, and a circularly polarized light-emitting substance.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP2017-035043 | Feb 2017 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/006466 | 2/22/2018 | WO |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2018/155557 | 8/30/2018 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5435937 | Bell | Jul 1995 | A |
| 6524727 | Kathirgamanathan | Feb 2003 | B1 |
| 7242443 | Sage | Jul 2007 | B2 |
| 20080171858 | Nagata | Jul 2008 | A1 |
| 20100072424 | Petoud et al. | Mar 2010 | A1 |
| 20160160121 | Hasegawa et al. | Jun 2016 | A1 |
| 20160164012 | Lee et al. | Jun 2016 | A1 |
| Number | Date | Country |
|---|---|---|
| 103320117 | Dec 2012 | CN |
| 102807592 | Sep 2013 | CN |
| 2007269780 | Oct 2007 | JP |
| 2010-77058 | Apr 2010 | JP |
| 2010-278376 | Dec 2010 | JP |
| 2016-128392 | Jul 2016 | JP |
| 2016-166139 | Sep 2016 | JP |
| 10-2016-0043553 | Apr 2016 | KR |
| 10-2016-0069021 | Jun 2016 | KR |
| 2010032395 | Mar 2010 | WO |
| 2015002295 | Jan 2015 | WO |
| 2015115532 | Aug 2015 | WO |
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| Number | Date | Country | |
|---|---|---|---|
| 20200063030 A1 | Feb 2020 | US |
