JP6607597B2 - Novel organic lithium complex compound, electron injection material comprising the same, and organic EL device using the same - Google Patents
Novel organic lithium complex compound, electron injection material comprising the same, and organic EL device using the same Download PDFInfo
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- 239000007924 injection Substances 0.000 title claims description 33
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- 239000000463 material Substances 0.000 title claims description 18
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Description
本発明は、新規な有機リチウム錯体化合物、それよりなる電子注入材料およびそれを用いた有機EL素子に関する。 The present invention relates to a novel organolithium complex compound, an electron injection material comprising the same, and an organic EL device using the same.
有機ELデバイスの実用性を向上させる手段の一つとして、駆動電圧を下げることが挙げられる。一方、有機ELデバイスの電極から有機層へのエネルギー障壁は高電圧化、低効率化に繋がる。このエネルギー障壁を下げる手法として、電子注入層に用いられる電子注入材料の改良が挙げられる。具体的には、電子輸送層などの有機膜とアルミニウム陰極との界面に仕事関数の低いリチウム(Φ=2.9eV)や、膜厚1nm以下のフッ化リチウム(LiF)の極薄膜層を挿入することで、素子の低駆動電圧化と、従来の有機ELデバイスに比べて1.4倍という発光効率の向上を実現してきた。また、発光層(Alq3)と、アルミニウム陰極との界面に金属リチウムやリチウム化合物を挿入することで、セルフドーピングと呼ばれるメカニズムに基づき、電子注入性が向上することが見出されている。 One means for improving the practicality of organic EL devices is to reduce the drive voltage. On the other hand, the energy barrier from the electrode of the organic EL device to the organic layer leads to higher voltage and lower efficiency. As a technique for lowering the energy barrier, there is an improvement of an electron injection material used for the electron injection layer. Specifically, an ultrathin layer of lithium (Φ = 2.9 eV) having a low work function or lithium fluoride (LiF) having a thickness of 1 nm or less is inserted at the interface between an organic film such as an electron transport layer and an aluminum cathode. As a result, the driving voltage of the element has been reduced and the luminous efficiency has been improved by 1.4 times compared to the conventional organic EL device. Further, it has been found that insertion of metallic lithium or a lithium compound at the interface between the light emitting layer (Alq3) and the aluminum cathode improves the electron injection property based on a mechanism called self-doping.
一方で、金属リチウムは取り扱いが難しく、またフッ化リチウムは沸点が1680℃と非常に高く、デバイス作製にコストがかかること、フッ化リチウムは絶縁体であるために、0.5nmほどの極薄膜でなければ機能せず、膜厚制御がシビアであるといった問題があった。また、フッ化リチウムは溶媒への溶解性に乏しいため、塗布型有機ELデバイスには用いることができないという問題もある。 On the other hand, metallic lithium is difficult to handle, and lithium fluoride has a very high boiling point of 1680 ° C., which makes it expensive to manufacture devices. Since lithium fluoride is an insulator, it is an extremely thin film of about 0.5 nm. Otherwise, there is a problem that the film does not function and the film thickness control is severe. In addition, since lithium fluoride has poor solubility in a solvent, there is a problem that it cannot be used for a coating type organic EL device.
電子注入材料として、Liq、Naq、Liacac、Lidpmを有機層と金属陰極の界面に挿入した素子が報告された(非特許文献1〜3)。これらのアルカリ金属錯体は、大気下での安定性や導電性を兼ね備えた材料である。これらのうち、LiqやNaqは、発光層(Alq3)及びアルミニウム陰極の間に挿入されると、中心金属イオン(Li+、Na+)が、熱的に活性化されたアルミニウムによって還元され、ラジカルアニオンを形成し、アルミニウム陰極からの電子注入を促進すると考えられている。
また、Liqと構造の似た配位子を持つアルカリ金属錯体として、Liqにメチル基を導入したLiMeqが開発され、Liq、LiMeqを電子注入層とした有機EL素子が報告されている(非特許文献4)。
また、電子注入層として膜厚2nmのLiOXDを導入した、ITO(酸化インジウムスズ)/NPB(N,N’−ジフェニル−(1,1’−ビフェニル)−4,4’−ジアミン)/Alq3(トリス(8−キノリノラト)アルミニウム)/LiOXD/Alからなる有機EL素子も報告されている(非特許文献5)。
その後、すでに報告されていたLiqからπ共役長を伸ばした構造を有するLiPP、Li2BPP、LiIQPが開発され、これらを導入した有機EL素子の電子輸送性が向上することが報告されている。特にLiPPでは、膜厚を3nmから40nmにすると、3V以上も駆動電圧が増加したのに対して、Li2BPP、LiIQPでは、厚膜でも低電圧駆動を示し、加えてπ共役が広いために、高い電子輸送性を発揮し、LiPPよりも駆動電圧が低減することが報告されている(非特許文献6)。
これらのうち、Li2BPPを用いた高効率緑色リン光素子が開発され、電子注入層にLiq、Li2BPP、電子輸送層にB4PyPPM、B4PyMPMを使用し、Ir(ppy)3(トリス(2−フェニルピリジナト)イリジウム(III))をドープしたCBP(4,4’−ビス(カルバゾル−9−イル)ビフェニル)を発光層に使用して作製した緑色リン光素子において、駆動電圧を大幅に低減化することに成功している(非特許文献7)。 Among these, a high-efficiency green phosphorescent device using Li2BPP has been developed, and Liq, Li2BPP is used for the electron injection layer, B4PyPPM, B4PyMPM is used for the electron transport layer, and Ir (ppy) 3 (Tris (2-phenylpyridina) G) Driving voltage is greatly reduced in a green phosphor element produced by using CBP (4,4′-bis (carbazol-9-yl) biphenyl) doped with iridium (III)) as a light emitting layer. (Non-Patent Document 7).
本発明は、新たな電子注入材料を開発して、さらなる低電圧駆動を実現することを目的としており、新規有機リチウム錯体化合物、それを用いた電子注入材料及び有機EL素子を提供することを目的とする。 An object of the present invention is to develop a new electron injection material and realize further low voltage driving, and to provide a novel organic lithium complex compound, an electron injection material using the same, and an organic EL device And
本発明の有機リチウム錯体化合物は、下記式(1)で表されることを特徴とする。
本発明の電子注入材料は、上記有機リチウム錯体化合物からなることを特徴とする。
本発明の有機EL素子は、上記有機リチウム錯体化合物からなることを特徴とする。
The organolithium complex compound of the present invention is represented by the following formula (1).
The electron injection material of the present invention is characterized by comprising the above organolithium complex compound.
The organic EL device of the present invention is characterized by comprising the above organic lithium complex compound.
本発明によれば、有機EL素子の電子注入材料として好適な有機リチウム錯体化合物を高い収率で合成することができる。具体的には、2,6−ジブロモピリジンと2−ヒドロキシフェニルボロン酸との鈴木・宮浦カップリングにより、ブロモ体2BrPPを高収率で合成し、該ブロモ体2BrPPと対応するピリジンボロン酸エステルとの鈴木・宮浦カップリングにより3BPP、4BPPを高収率で合成し、さらに該3BPP、4BPPと水酸化リチウムとの反応により、ほぼ定量的にLi3BPP、Li4BPPを合成することができる。
本発明の有機リチウム錯体化合物は、電子注入層として、電子輸送層と陰極金属との間に数ナノメートル程度、挿入することで、デバイスの大幅な低電圧化が可能となる。特にLi3BPP、Li4BPPでは、電子吸引性の高い3−ピリジル基や4−ピリジル基を有するため、HOMO及びLUMOがともに深くすることができ、電子注入障壁を低減化できることが期待できる。
さらに、本発明の有機リチウム錯体化合物は、高い熱安定性及び昇華性を持ち、蒸着温度も300℃程度と低く、比較的厚膜でも素子として機能する。また、空気中で安定であるため、取り扱いが容易である。
本発明の有機リチウム錯体化合物は、有機化合物からなる配位子を有するため、一般的な有機溶媒に可溶であり、溶液法による塗布製膜が可能である。
ADVANTAGE OF THE INVENTION According to this invention, the organolithium complex compound suitable as an electron injection material of an organic EL element is compoundable with a high yield. Specifically, the bromo compound 2BrPP was synthesized in a high yield by Suzuki-Miyaura coupling of 2,6-dibromopyridine and 2-hydroxyphenylboronic acid, and the corresponding pyridine boronic acid ester with the bromo compound 2BrPP 3BPP and 4BPP can be synthesized in high yield by Suzuki-Miyaura coupling, and Li3BPP and Li4BPP can be synthesized almost quantitatively by reaction of the 3BPP and 4BPP with lithium hydroxide.
When the organolithium complex compound of the present invention is inserted as an electron injection layer between the electron transport layer and the cathode metal by about several nanometers, the voltage of the device can be greatly reduced. In particular, Li3BPP and Li4BPP have high electron-withdrawing 3-pyridyl and 4-pyridyl groups, so that both HOMO and LUMO can be deepened, and the electron injection barrier can be reduced.
Furthermore, the organolithium complex compound of the present invention has high thermal stability and sublimation properties, has a low deposition temperature of about 300 ° C., and functions as an element even with a relatively thick film. Moreover, since it is stable in the air, it is easy to handle.
Since the organolithium complex compound of the present invention has a ligand composed of an organic compound, the organolithium complex compound is soluble in a general organic solvent and can be coated and formed by a solution method.
以下、本発明について、詳細に説明する。
[有機リチウム錯体化合物]
本発明の有機リチウム錯体化合物は、下記一般式(1)で表される:
[Organic lithium complex compound]
The organolithium complex compound of the present invention is represented by the following general formula (1):
芳香族炭化水素基としては、例えば、フェニル基、ピリミジン(ピリミジニル基)、トリアジン(トリアジニル基)、ピリジン(3−ピリジル基、4−ピリジル基)などが挙げられる。これらのうち、合成化学的観点及び電子物性の理由から、ピリミジン、トリアジン、3−ピリジル基及び4−ピリジル基が好ましく、3−ピリジル基及び4−ピリジル基がより好ましい。
一般式(1)で表される化合物は、具体的には、下記構造式を有する化合物が好ましい。
Specifically, the compound represented by the general formula (1) is preferably a compound having the following structural formula.
上記一般式(1)で表される化合物は、種々の公知の方法により製造することができる。例えば、Li3BPPは、以下に示すように、鈴木・宮浦カップリング反応を用いて合成することができる。
すなわち、三口フラスコに2,6−ジブロモピリジン及び2−ヒドロキシフェニルボロン酸を入れて、Pd(0)触媒の存在下、炭酸カリウムなどの塩基とともに攪拌することにより、収率80%で2BrPPを得る。次いで、三口フラスコに、得られた2BrPPと、3−ピリジンボロン酸エステルとを入れて、Pd(0)触媒及び配位子の存在下、リン酸三カリウムなどの塩基とともに加熱還流することにより、収率96%で3BPPを得る。得られた3BPPを水酸化リチウムと反応させることにより、ほぼ定量的にLi3BPPを得る。
ただし、本発明の一般式(1)で表される化合物は、上記方法に限られることなく、公知の種々の方法を組み合わせて製造することができる。
That is, 2,6-dibromopyridine and 2-hydroxyphenylboronic acid are placed in a three-necked flask and stirred with a base such as potassium carbonate in the presence of a Pd (0) catalyst to obtain 2BrPP at a yield of 80%. . Next, the obtained 2BrPP and 3-pyridineboronic acid ester are put into a three-necked flask and heated and refluxed with a base such as tripotassium phosphate in the presence of a Pd (0) catalyst and a ligand. 3BPP is obtained with a yield of 96%. Li3BPP is obtained almost quantitatively by reacting the obtained 3BPP with lithium hydroxide.
However, the compound represented by General formula (1) of this invention is not restricted to the said method, It can manufacture by combining a well-known various method.
上記のようにして得られる本発明の有機リチウム錯体化合物は、融点(Tm)及び分解点(Td5)のいずれも十分に高く、熱安定性に優れる。特に、L3BPP、L4BPPは、従来技術の項において説明したL2BPPと同じ分子量であるにもかかわらず、L2BPPよりも融点(Tm)及び分解点(Td5)が高い。これは、ピリジルフェノレート部位から離れた位置に窒素が存在することから、分子間で水素結合や配位結合が形成され、分子間相互作用が強くなるためと考えられる。 The organolithium complex compound of the present invention obtained as described above has a sufficiently high melting point (T m ) and decomposition point (T d5 ), and is excellent in thermal stability. In particular, L3BPP and L4BPP have higher melting points (T m ) and decomposition points (T d5 ) than L2BPP, despite having the same molecular weight as L2BPP described in the section of the prior art. This is probably because nitrogen exists at a position distant from the pyridylphenolate site, so that hydrogen bonds and coordination bonds are formed between the molecules, and the intermolecular interaction is strengthened.
上記有機リチウム錯体化合物は、HOMO(Highest OccupiedMolecular Orbital)、LUMO(Lowest Unoccupied Molecular Orbital)が深くなる傾向がみられる。特にL3BPP及びL4BPPは、L2BPPに比べて、電子吸引性の高い3−ピリジル基や4−ピリジル基を有することで、ピリジルフェノレート側の電子密度が下がるためと考察される。なお、L2BPPはピリジン環上の窒素がピリジルフェノレート側に存在する場合、バンドギャップが狭まり、LUMOが大幅に深くなることが知られている。 The organolithium complex compounds tend to have deep HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital). In particular, L3BPP and L4BPP are considered to have a lower electron density on the pyridylphenolate side by having a 3-pyridyl group or 4-pyridyl group having higher electron-withdrawing properties than L2BPP. It is known that L2BPP has a narrow band gap and a significantly deep LUMO when nitrogen on the pyridine ring is present on the pyridylphenolate side.
[電子注入材料、有機EL素子]
本発明の電子注入材料又は有機EL素子は、上記した有機リチウム錯体化合物よりなる。
有機EL素子は、機能の異なる複数の有機材料を積層した1μm以下の極薄膜層(以下「有機層」ともいう。)を、透明電極であるITO(酸化インジウムスズ)を成膜したガラス基板と金属陰極とで挟んだ構造をしており、典型的には、陰極、電子注入層、電子輸送層、発光層、正孔輸送層、正孔注入層、陽極が順次積層された素子構造を有する。なお、前記素子構造において、電子輸送層は発光層を兼ねたものであってもよいし、正孔輸送層が発光層の機能を兼ねたものであってもよい。また、発光層を電子輸送層と正孔輸送層で挟んだ三層型構造(ダブルへテロ構造)であってもよい。
[Electron injection material, organic EL element]
The electron injection material or the organic EL device of the present invention comprises the above-described organic lithium complex compound.
An organic EL element has an ultrathin film layer (hereinafter also referred to as “organic layer”) of 1 μm or less in which a plurality of organic materials having different functions are laminated, and a glass substrate on which ITO (indium tin oxide) as a transparent electrode is formed; It has a structure sandwiched between metal cathodes and typically has an element structure in which a cathode, an electron injection layer, an electron transport layer, a light emitting layer, a hole transport layer, a hole injection layer, and an anode are sequentially stacked. . In the element structure, the electron transport layer may also serve as the light emitting layer, or the hole transport layer may serve as the function of the light emitting layer. Alternatively, a three-layer structure (double hetero structure) in which the light-emitting layer is sandwiched between an electron transport layer and a hole transport layer may be used.
有機EL素子に電圧を印加すると、有機層中に陽極側からホールが、陰極からは電子が注入される。ホール及び電子の移動は、ホールではHOMO、電子ではLUMOの電子雲の重なりを利用している。これらのキャリアを化学的に分類すると、ホールはラジカルカチオン、電子はラジカルアニオンに相当する。電極から有機層へキャリアが注入されると、有機分子がイオンラジカル状態となり、隣接する分子へπ電子の授受を行いながら片側の電極へと移動する。そして発光性の有機材料においてラジカルカチオンとラジカルアニオンとが再結合することで、ホール・電子対を成し励起子を生成する。この励起子が失活する際に光が観測される。 When a voltage is applied to the organic EL element, holes are injected into the organic layer from the anode side, and electrons are injected from the cathode. The movement of holes and electrons uses the overlap of electron clouds of HOMO for holes and LUMO for electrons. When these carriers are chemically classified, holes correspond to radical cations and electrons correspond to radical anions. When carriers are injected from the electrode into the organic layer, the organic molecule enters an ionic radical state and moves to one electrode while transferring π electrons to adjacent molecules. The radical cation and radical anion recombine in the light-emitting organic material to form a hole-electron pair and generate excitons. Light is observed when the exciton is deactivated.
有機EL素子の発光効率を維持又は向上させるためには、電極から有機層へのエネルギー障壁を下げることが有効である。 In order to maintain or improve the luminous efficiency of the organic EL element, it is effective to lower the energy barrier from the electrode to the organic layer.
本発明では、上記有機リチウム錯体化合物を電子注入材料として、有機EL素子中の有機層に導入することにより、外部量子効率−輝度特性及び電力効率−輝度特性において高効率を示し、深いLUMOを有することがわかった。特にL3BPP及びL4BPPは、L2BPPに比べて、分子内での水素結合や配位結合が形成されるため、エネルギーギャップが小さく、LUMOがより深くなり、高い電子注入性をもつと考えられることから、有機EL材料における電子注入材料として好適である。 In the present invention, the above-described organolithium complex compound is introduced into the organic layer in the organic EL device as an electron injection material, thereby showing high efficiency in external quantum efficiency-luminance characteristics and power efficiency-luminance characteristics, and having a deep LUMO. I understood it. In particular, L3BPP and L4BPP are considered to have a high energy injecting property due to a smaller energy gap and a deeper LUMO, because hydrogen bonds and coordination bonds are formed in the molecule than L2BPP. It is suitable as an electron injection material for organic EL materials.
以下、本発明を実施例に基づいてさらに具体的に説明するが、本発明は下記実施例により制限されるものではない。 EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not restrict | limited by the following Example.
合成物の同定に使用した機器及び測定条件は以下のとおりである。
(1)1H核磁気共鳴(NMR)法:
日本電子(株)製(400MHz)JNM−EX270FT−NMR型
(2)質量分析法(MS)
日本電子(株)製JMS−K9[卓上GCQMS]及びWaters(株)製Zspray(SQ検出器2))
(3)元素分析
Perkin Elmer 2400II CHNS/O アナライザー
測定モード:CHNモード
The equipment and measurement conditions used for the identification of the composites are as follows.
(1) 1 H nuclear magnetic resonance (NMR) method:
JEOL Ltd. (400 MHz) JNM-EX270FT-NMR type (2) mass spectrometry (MS)
JEOL Ltd. JMS-K9 [Desktop GCQMS] and Waters Ltd. Zspray (SQ detector 2))
(3) Elemental analysis Perkin Elmer 2400II CHNS / O analyzer Measurement mode: CHN mode
[合成例1]2BrPPの合成
三口フラスコに、2,6−ジブロモピリジン、2−ヒドロキシフェニルボロン酸、トルエン、エタノール及び2M炭酸カリウム水溶液を入れた後、1〜2時間窒素バブリングし、テトラキス(トリフェニルホスフィン)パラジウム(0)(Pd(PPh)4)を加えて2〜3時間加熱撹拌した。薄層クロマトグラフィー(TLC;thinlayer chromatography)及びMSにて、これらの原料の消費を確認し、反応混合物を室温に戻した。反応混合物を飽和食塩水で洗浄し、トルエンで抽出し、無水硫酸マグネシウムで乾燥した。硫酸マグネシウムを濾別後、濃縮することで黄色結晶固体を得た。この黄色固体をヘキサン/クロロホルム=3/2(vol/vol)(約100mL)に溶解し、シリカゲルを充填したカラムに乗せた。シリカゲルカラムクロマトグラフィー(シリカゲル:500cc、展開溶媒:約5L(ヘキサン/クロロホルム=3/2(vol/vol))により精製し、収率80%で白色固体である2BrPPを得た。
[Synthesis Example 1] Synthesis of 2BrPP Into a three-necked flask, 2,6-dibromopyridine, 2-hydroxyphenylboronic acid, toluene, ethanol and a 2M aqueous potassium carbonate solution were added, and then nitrogen bubbling was performed for 1 to 2 hours. Phenylphosphine) palladium (0) (Pd (PPh) 4 ) was added, and the mixture was heated and stirred for 2 to 3 hours. The consumption of these raw materials was confirmed by thin layer chromatography (TLC) and MS, and the reaction mixture was returned to room temperature. The reaction mixture was washed with saturated brine, extracted with toluene, and dried over anhydrous magnesium sulfate. Magnesium sulfate was filtered off and concentrated to obtain a yellow crystalline solid. This yellow solid was dissolved in hexane / chloroform = 3/2 (vol / vol) (about 100 mL) and placed on a column packed with silica gel. Purification by silica gel column chromatography (silica gel: 500 cc, developing solvent: about 5 L (hexane / chloroform = 3/2 (vol / vol)) gave 2BrPP as a white solid in a yield of 80%.
2BrPPの1H−NMR及びMSの結果を以下に示す。
1H NMR (400 MHz, CDCl3):δ = 12.71 (s, 1H), 7.84 (d, 1H, J=7.6 Hz), 7.67~7.75 (m, 2H), 7.32~7.46 (m,2H), 7.04 (dd, 1H, J=8.2, 1.2 Hz), 6.93 (dt, 1H, J=7.6, 1.6 Hz) ppm
MS:m/z 250 [M]+
The results of 1 H-NMR and MS of 2BrPP are shown below.
1 H NMR (400 MHz, CDCl 3 ): δ = 12.71 (s, 1H), 7.84 (d, 1H, J = 7.6 Hz), 7.67 to 7.75 (m, 2H), 7.32 to 7.46 (m, 2H), 7.04 (dd, 1H, J = 8.2, 1.2 Hz), 6.93 (dt, 1H, J = 7.6, 1.6 Hz) ppm
MS: m / z 250 [M] +
[合成例2]3BPPの合成
三口フラスコに、合成例1で得られた2BrPP、3−ピリジンボロン酸エステル、トルエン、エタノール及び1.25Mリン酸三カリウム水溶液を入れ、1〜2時間窒素バブリングした。その後、Pd2(dba)3及びトリシクロヘキシルホスフィン(PCy3)を加え、19〜21時間加熱撹拌した。TLC及びMSにて原料の消費を確認し、反応混合物を室温に戻した後、吸引濾過しつつ水、エタノールで洗浄した。濾液を飽和食塩水で洗浄、トルエンで抽出し、無水硫酸マグネシウムで乾燥した。硫酸マグネシウムを濾別後、濃縮することで黄色粘性液体を得た。この橙色粘体をクロロホルムに溶解し、シリカゲルを充填したカラムに乗せた。シリカゲルカラムクロマトグラフィー(シリカゲル:500cc、展開溶媒:約1L(クロロホルム/酢酸エチル=19/1(vol/vol))⇒約3L(9:1(vol/vol))により精製し、収率96%で橙色飴状固体である3BPPを得た。
[Synthesis Example 2] Synthesis of 3BPP Into a three-necked flask, 2BrPP obtained in Synthesis Example 1, 3-pyridineboronic acid ester, toluene, ethanol, and 1.25M tripotassium phosphate aqueous solution were placed, and nitrogen bubbling was performed for 1 to 2 hours. . Thereafter, Pd 2 (dba) 3 and tricyclohexylphosphine (PCy 3 ) were added, followed by heating and stirring for 19 to 21 hours. The consumption of the raw materials was confirmed by TLC and MS, the reaction mixture was returned to room temperature, and then washed with water and ethanol while suction filtration. The filtrate was washed with saturated brine, extracted with toluene, and dried over anhydrous magnesium sulfate. Magnesium sulfate was filtered off and concentrated to obtain a yellow viscous liquid. This orange viscous body was dissolved in chloroform and placed on a column packed with silica gel. Purified by silica gel column chromatography (silica gel: 500 cc, developing solvent: about 1 L (chloroform / ethyl acetate = 19/1 (vol / vol)) => about 3 L (9: 1 (vol / vol)), yield 96% 3BPP was obtained as an orange candy-like solid.
3BPPの1H−NMR及びMSの結果を以下に示す。
1H-NMR (400 MHz,DMSO-d6): δ = 9.22 (d, 1H, J=1.6 Hz), 8.73 (dd, 1H, J=4.8, 1.6 Hz), 8.38 (td,1H, J=8.0, 2.0 Hz), 8.26 (d, 1H, J=7.6 Hz), 8.04~8.17 (m, 3H), 7.63 (q, 1H,J=4.0 Hz), 7.36 (dt, 1H, J=8.0, 1.6 Hz), 6.96~7.00 (m, 2H) ppm
MS:m/z 249 [M]+
The results of 1 H-NMR and MS of 3BPP are shown below.
1 H-NMR (400 MHz, DMSO-d6): δ = 9.22 (d, 1H, J = 1.6 Hz), 8.73 (dd, 1H, J = 4.8, 1.6 Hz), 8.38 (td, 1H, J = 8.0 , 2.0 Hz), 8.26 (d, 1H, J = 7.6 Hz), 8.04 to 8.17 (m, 3H), 7.63 (q, 1H, J = 4.0 Hz), 7.36 (dt, 1H, J = 8.0, 1.6 Hz ), 6.96 ~ 7.00 (m, 2H) ppm
MS: m / z 249 [M] +
[合成例3]4BPPの合成
三口フラスコに、合成例1で得られた2BrPP、4−ピリジンボロン酸エステル、トルエン、エタノール及び1.25Mリン酸三カリウム水溶液を入れ、1〜2時間窒素バブリングした。その後、Pd2(dba)3及びトリシクロヘキシルホスフィン(PCy3)を加え、19〜21時間加熱撹拌した。TLCとMSにて原料の消費を確認し、反応混合物を室温に戻した後、吸引濾過しつつ水、エタノールで洗浄した。濾液を飽和食塩水で洗浄、トルエンで抽出し、無水硫酸マグネシウムで乾燥した。硫酸マグネシウムを濾別後、濃縮することで黄色粘性液体を得た。この黄色粘性液体をクロロホルムに溶解し、シリカゲルを充填したカラムに乗せた。そのままシリカゲルカラムクロマトグラフィー(シリカゲル=500cc,展開溶媒:クロロホルム/酢酸エチル=19/1(1L)⇒9:1(3L))により精製することで、収率89%で橙色粘体である4BPPを得た。
[Synthesis Example 3] Synthesis of 4BPP 2BrPP, 4-pyridineboronic acid ester obtained in Synthesis Example 1, toluene, ethanol and a 1.25M tripotassium phosphate aqueous solution were placed in a three-necked flask and bubbled with nitrogen for 1-2 hours. . Thereafter, Pd 2 (dba) 3 and tricyclohexylphosphine (PCy 3 ) were added, followed by heating and stirring for 19 to 21 hours. The consumption of the raw materials was confirmed by TLC and MS, the reaction mixture was returned to room temperature, and then washed with water and ethanol while suction filtration. The filtrate was washed with saturated brine, extracted with toluene, and dried over anhydrous magnesium sulfate. Magnesium sulfate was filtered off and concentrated to obtain a yellow viscous liquid. This yellow viscous liquid was dissolved in chloroform and placed on a column packed with silica gel. Purification by silica gel column chromatography (silica gel = 500 cc, developing solvent: chloroform / ethyl acetate = 19/1 (1 L) => 9: 1 (3 L)) to obtain 4BPP as an orange viscous body with a yield of 89% It was.
4BPPの1H−NMR及びMSの結果を以下に示す。
1H-NMR (400 MHz,DMSO-d6): δ = 8.78 (d, 2H, J=4.8 Hz), 8.30 (d, 1H, J=8.4 Hz),8.08~8.19 (m, 3H), 7.97 (d, 2H, J=4.4 Hz), 7.35 (t, 1H, J=8.0Hz), 6.95~6.99 (m, 2H) ppm
MS:m/z 249 [M]+
The results of 1 H-NMR and MS of 4BPP are shown below.
1 H-NMR (400 MHz, DMSO-d6): δ = 8.78 (d, 2H, J = 4.8 Hz), 8.30 (d, 1H, J = 8.4 Hz), 8.08 to 8.19 (m, 3H), 7.97 ( d, 2H, J = 4.4 Hz), 7.35 (t, 1H, J = 8.0Hz), 6.95 to 6.99 (m, 2H) ppm
MS: m / z 249 [M] +
[実施例1]Li3BPPの合成
ナスフラスコ内で水酸化リチウム水和物をメタノールに完全に溶解し、そこに合成例2で得られた3BPPをメタノールに溶解した溶液を1ml/minの速度で滴下した。滴下後13時間撹拌した後、反応溶液を濃縮することで、檸檬色粉末固体をほぼ定量的に得た。
[Example 1] Synthesis of Li3BPP Lithium hydroxide hydrate was completely dissolved in methanol in an eggplant flask, and a solution of 3BPP obtained in Synthesis Example 2 dissolved in methanol was added dropwise at a rate of 1 ml / min. did. After stirring for 13 hours after the dropwise addition, the reaction solution was concentrated to obtain an amber powder solid almost quantitatively.
Li3BPPの1H−NMR及び元素分析の結果を以下に示す。
1H-NMR (400 MHz,DMSO-d6): δ = 9.28 (d, 1H, J=2.4 Hz), 9.12~9.17 (m, 1H), 8.57 (dd, 1H, J=4.8,1.6 Hz), 8.46 (td, 1H, J=8.0, 2.0 Hz), 8.01 (dd, 1H, J=8.2, 2.0Hz), 7.57~7.66 (m, 2H), 7.48 (dd, 1H, J=8.0, 4.4 Hz), 6.77~6.82 (m, 1H),6.32~6.37 (m, 1H), 6.07 (t, 1H, J=7.2 Hz) ppm (図1参照)
Anal.Calcd for C16H11LiN2O; C, 75.59; H, 4.36; N,11.02 %. Found: C, 75.64; H, 4.24; N, 10.98%
The results of 1 H-NMR and elemental analysis of Li3BPP are shown below.
1 H-NMR (400 MHz, DMSO-d6): δ = 9.28 (d, 1H, J = 2.4 Hz), 9.12 to 9.17 (m, 1H), 8.57 (dd, 1H, J = 4.8, 1.6 Hz), 8.46 (td, 1H, J = 8.0, 2.0 Hz), 8.01 (dd, 1H, J = 8.2, 2.0Hz), 7.57 to 7.66 (m, 2H), 7.48 (dd, 1H, J = 8.0, 4.4 Hz) , 6.77 to 6.82 (m, 1H), 6.32 to 6.37 (m, 1H), 6.07 (t, 1H, J = 7.2 Hz) ppm (see Fig. 1)
Anal.Calcd for C 16 H 11 LiN 2 O; C, 75.59; H, 4.36; N, 11.02%. Found: C, 75.64; H, 4.24; N, 10.98%
[実施例2]Li4BPPの合成
ナスフラスコ内で水酸化リチウム水和物をメタノールに完全に溶解し、そこに4BPPをメタノールに溶解した溶液を1ml/minの速度で滴下した。滴下後12時間撹拌した後、反応溶液を濃縮することで、黄色粉末固体をほぼ定量的に得た。
[Example 2] Synthesis of Li4BPP Lithium hydroxide hydrate was completely dissolved in methanol in a recovery flask, and a solution of 4BPP dissolved in methanol was added dropwise thereto at a rate of 1 ml / min. After stirring for 12 hours after the dropping, the reaction solution was concentrated to obtain a yellow powdered solid almost quantitatively.
Li4BPPの1H−NMR及び元素分析の結果を以下に示す。
1H-NMR (400 MHz,DMSO-d6): δ = 9.20 (br, 1H), 8.69 (d, 2H, J­=6.4 Hz), 8.07~8.11 (m, 3H),7.74 (d, 2H, J­=4.4 Hz), 6.86 (t, 1H, J­=8.0 Hz), 6.41 (d, 1H, J­=8.8Hz), 6.17 (t, 1H, J­=5.6 Hz) ppm (図2参照)
Anal.Calcd for C16H11LiN2O; C, 75.59; H, 4.36; N,11.02 %. Found: C, 75.43; H, 4.25; N, 11.00%
The results of 1 H-NMR and elemental analysis of Li4BPP are shown below.
1 H-NMR (400 MHz, DMSO-d6): δ = 9.20 (br, 1H), 8.69 (d, 2H, J ­ = 6.4 Hz), 8.07 to 8.11 (m, 3H), 7.74 (d, 2H, J ­ = 4.4 Hz), 6.86 (t, 1H, J ­ = 8.0 Hz), 6.41 (d, 1H, J ­ = 8.8 Hz), 6.17 (t, 1H, J ­ = 5.6 Hz) ppm (see Figure 2) )
Anal.Calcd for C 16 H 11 LiN 2 O; C, 75.59; H, 4.36; N, 11.02%. Found: C, 75.43; H, 4.25; N, 11.00%
[参考例]
参考例として、下記構造式で表されるLi2BPPを使用した。
As a reference example, Li2BPP represented by the following structural formula was used.
[熱物性評価]
(1)分解点(Td5)
実施例1、2で得られた試料(Li3BPP、Li4BPP)、及び参考例の試料(Li2BPP)をそれぞれアルミパンにのせ、示差熱重量計((株)パーキンエルマージャパン製;TGAダイアモンド)を用いて、窒素ガス中で昇温速度10℃/minで5%重量減少温度(Td5)の測定を行った。
(2)融点(Tm)
各試料をそれぞれアルミパンに封入し、示差走査熱量計((株)パーキンエルマージャパン製;DSCDTA)を用いて窒素ガス中で昇温速度10℃/minで融点(Tm)の測定を行った。
(3)昇華点(Ts)
各試料をそれぞれ白金製のパンにのせ、有機色素材熱挙動測定装置((株)アルバック製;VAP−9000特型)を用いて真空中(10-4Pa)で昇温速度10℃/minで昇華点(Ts)の測定を行った。
結果を表1に示す。
[Thermal properties evaluation]
(1) Decomposition point (T d5 )
The samples (Li3BPP, Li4BPP) obtained in Examples 1 and 2 and the sample of the reference example (Li2BPP) were each placed on an aluminum pan, and a differential thermogravimeter (manufactured by PerkinElmer Japan, Inc .; TGA diamond) was used. The 5% weight loss temperature (T d5 ) was measured in a nitrogen gas at a heating rate of 10 ° C./min.
(2) Melting point ( Tm )
Each sample was sealed in an aluminum pan, and the melting point (T m ) was measured at a heating rate of 10 ° C./min in nitrogen gas using a differential scanning calorimeter (manufactured by Perkin Elmer Japan; DSCDTA). .
(3) Sublimation point (T s )
Each sample is placed on a platinum pan, and the temperature rise rate is 10 ° C./min in vacuum (10 −4 Pa) using an organic color material thermal behavior measuring device (manufactured by ULVAC, Inc .; VAP-9000 special model). The sublimation point (T s ) was measured at.
The results are shown in Table 1.
Li2BPP、Li3BPP、Li4BPPはいずれも同じ分子量であり、ピリジンの置換位置のみの違いであるにもかかわらず、物性値に明確な差異がみられた。すなわち、Td5はLi2BPP<Li3BPP<Li4BPPの順に上昇する結果が得られた。この理由として、Li2BPPはピリジルフェノレート部位に最も近い位置に窒素が存在するため、分子内水素結合やリチウムとの分子内での配位結合を形成しやすいが、Li3BPP及びLi4BPPでは、ピリジルフェノレート部位から離れた位置に窒素が存在するために、分子間での水素結合や配位結合が形成され、分子間の相互作用が強くなるためと考えられる。 Li2BPP, Li3BPP, and Li4BPP all had the same molecular weight, and despite the difference only in the substitution position of pyridine, there was a clear difference in physical property values. That is, Td 5 was obtained in the order of Li2BPP <Li3BPP <Li4BPP. The reason for this is that Li2BPP has nitrogen in the position closest to the pyridylphenolate moiety, so it is easy to form an intramolecular hydrogen bond or an intramolecular coordination bond with lithium, but in Li3BPP and Li4BPP, pyridylphenolate This is probably because the presence of nitrogen at a position distant from the site results in the formation of hydrogen bonds and coordination bonds between molecules, and the interaction between molecules is strengthened.
[光学特性評価]
(1)UV−vis吸収スペクトル
石英基板上に真空蒸着したLi2BPP、Li3BPP、Li4BPPの薄膜、及びLi2BPP、Li3BPP、Li4BPPをテトラヒドロフランに溶解させた1×10-5Mテトラヒドロフラン溶液を1cm×1cm×1cmの石英セル中に入れたサンプルについて測定を行った。測定には、(株)島津製作所UV−3150を使用した。測定条件としては、スキャンスピードを中速、測定範囲を200〜800nm、サンプリングピッチを0.5nm、スリット幅を0.5nmとした。
(2)電気化学特性の評価
ITOガラス基板上に真空蒸着したLi2BPP、Li3BPP、Li4BPPの薄膜を、住友重機械工業(株)製イオン化ポテンシャル測定装置(PYS)を使用して真空中でイオン化ポテンシャル(Ip)の測定を行った。また、UV−vis吸収スペクトルの吸収端よりエネルギーギャップ(Eg)を見積もり、電子親和力(Ea)を算出した。
(3)蛍光スペクトル
石英基板上に真空蒸着したLi2BPP、Li3BPP、Li4BPPの薄膜について蛍光スペクトルの測定を行った。測定には、インスツルメンツS.A.社製Fluoro MAX−2を使用した。
[Optical characteristics evaluation]
(1) UV-vis absorption spectrum A thin film of Li2BPP, Li3BPP, Li4BPP vacuum-deposited on a quartz substrate, and a 1 × 10 −5 M tetrahydrofuran solution in which Li2BPP, Li3BPP, Li4BPP are dissolved in tetrahydrofuran are 1 cm × 1 cm × 1 cm. Measurements were made on samples placed in a quartz cell. Shimadzu Corporation UV-3150 was used for the measurement. As measurement conditions, the scan speed was medium speed, the measurement range was 200 to 800 nm, the sampling pitch was 0.5 nm, and the slit width was 0.5 nm.
(2) Evaluation of electrochemical properties Li2BPP, Li3BPP, and Li4BPP thin films vacuum-deposited on an ITO glass substrate were subjected to ionization potential in vacuum using an ionization potential measuring device (PYS) manufactured by Sumitomo Heavy Industries, Ltd. Ip) was measured. Moreover, the energy gap (Eg) was estimated from the absorption edge of the UV-vis absorption spectrum, and the electron affinity (Ea) was calculated.
(3) Fluorescence spectrum The fluorescence spectrum was measured about the thin film of Li2BPP, Li3BPP, and Li4BPP vacuum-deposited on the quartz substrate. For the measurement, Instruments S.D. A. Fluoro MAX-2 manufactured by the company was used.
結果を表2、3及び図3〜6に示す。
Li3BPP及びLi4BPPでは、Li2BPPに対してピリジン環の窒素位置が異なることで、計算値と同様にHOMO、LUMOが深くなる傾向が見られた。Li2BPP及びLi3BPPのLUMOにおいては、計算値に差が見られなかったのに対して、実測値では0.3eVという大きな開きがあった。この結果から、電子求引性の高い3−ピリジル基や4−ピリジル基を導入することで、LUMOを深くすることができると考えられる。しかし、HOMO、LUMOが深くなった一方で、エネルギーギャップには大きな差が見られなかった。これは、Li2BPP、Li3BPP及びLi4BPPでは、エネルギーギャップに差異が生じるほど、分子構造を大きく相違しないためと考えられる。 In Li3BPP and Li4BPP, the nitrogen position of the pyridine ring was different from that of Li2BPP, so that HOMO and LUMO tended to be deeper, similar to the calculated values. In the LUMO of Li2BPP and Li3BPP, there was no difference in the calculated value, but there was a large difference of 0.3 eV in the actually measured value. From this result, it is considered that LUMO can be deepened by introducing a 3-pyridyl group or a 4-pyridyl group having high electron withdrawing properties. However, while HOMO and LUMO became deeper, there was no significant difference in the energy gap. This is presumably because Li2BPP, Li3BPP, and Li4BPP do not differ greatly in molecular structure as the energy gap differs.
[素子特性評価1]
(i)塗布型黄緑色素子の作製
図7に示すように、ITOガラス基板上に、正孔注入層として、ポリスチレンスルホン酸(PEDOT:PSS)をスピンコートし、ベイクし、成膜した。同様に、正孔輸送層に、インターレイヤーHT12(住友化学(株)製、熱架橋性ポリマー材料)、発光層にF8BT、電子注入層(EIL)の各層を重ねて成膜した。電子注入層にはLi3BPP、Li4BPP、及びLi2BPPのそれぞれを用いた。
前記層上に重ねて、陰極としてアルミニウムを真空蒸着により成膜した。
すなわち、素子構造を[ITO/PEDOT:PSS(30nm)/IL(20nm)/F8BT(80nm)/EIL(1nm)/Al(100nm)](EIL=Li3BPP、Li4BPP、Li2BPP)とした。
また、比較として、電子注入層を用いない素子(NonEIL)を作製した。
[Element characteristic evaluation 1]
(I) Fabrication of coating type yellow-green element As shown in FIG. 7, polystyrene sulfonic acid (PEDOT: PSS) was spin-coated on an ITO glass substrate as a hole injection layer, baked, and formed into a film. Similarly, an interlayer HT12 (manufactured by Sumitomo Chemical Co., Ltd., thermally crosslinkable polymer material) was formed on the hole transport layer, and F8BT and an electron injection layer (EIL) were stacked on the light emitting layer. Each of Li3BPP, Li4BPP, and Li2BPP was used for the electron injection layer.
Over the layer, aluminum was deposited as a cathode by vacuum deposition.
That is, the element structure was [ITO / PEDOT: PSS (30 nm) / IL (20 nm) / F8BT (80 nm) / EIL (1 nm) / Al (100 nm)] (EIL = Li3BPP, Li4BPP, Li2BPP).
For comparison, an element (NonEIL) that does not use an electron injection layer was produced.
(ii)発光評価
素子特性の評価は、フォトニックマルチチャンネル分光器((株)浜松ホトニクス製;PMA−1)を用いたELスペクトルの測定により行った。
発光面を見ると、電子注入層を挿入したすべての素子において黄緑色の発光が観察できたのに対し、電子注入材料を用いなかった素子は発光面の淵のみが発光した。そのため、電子注入材料を用いなかった素子では、各素子特性に必要な輝度が得られず、特性を測ることができなかった。
Li2BPP、Li3BPP及びLi4BPPを各々の電子注入層に用いた場合のそれぞれの素子のELスペクトル、電流密度−電圧特性の関係、輝度−電圧特性の関係、電力効率−輝度特性の関係、電流効率−輝度特性の関係、外部量子効率−輝度特性の関係を図8〜15、及びこれらの結果を表4に示す。
(Ii) Luminescence evaluation Evaluation of element characteristics was performed by measuring an EL spectrum using a photonic multichannel spectrometer (manufactured by Hamamatsu Photonics; PMA-1).
Looking at the light emitting surface, yellow-green light emission could be observed in all the devices in which the electron injection layer was inserted, whereas in the device not using the electron injection material, only the light emitting surface light was emitted. Therefore, in an element that does not use an electron injecting material, the brightness required for each element characteristic cannot be obtained, and the characteristic cannot be measured.
EL spectrum, current density-voltage characteristic relationship, luminance-voltage characteristic relationship, power efficiency-luminance characteristic relationship, current efficiency-luminance relationship of each element when Li2BPP, Li3BPP and Li4BPP are used for each electron injection layer The relationship between the characteristics and the relationship between the external quantum efficiency and the luminance characteristics are shown in FIGS.
ELスペクトルでは、F8BT由来の発光が観測された。電流密度−電圧特性から、電子注入層を挿入しない素子と比較し、挿入することで大幅に低電圧化する結果が得られた。よって、Li3BPP及びLi4BPPは電子注入層として機能していることがわかる。 In the EL spectrum, light emission derived from F8BT was observed. From the current density-voltage characteristics, it was found that the voltage was drastically reduced by insertion compared to a device in which no electron injection layer was inserted. Therefore, it can be seen that Li3BPP and Li4BPP function as an electron injection layer.
[素子特性評価2]
(i)ポリマーバインダーを用いた素子の作製
成膜性の向上を図るべく、電子注入層として、ポリビニルピリジン(PV4Py)をLi2BPP、Li3BPP、Li4BPPのそれぞれに30wt%混合したものを用いて、素子特性評価1と同様にして素子を作製した。
また、比較として、PV4Pyのみを電子注入層に用いた素子を作製した。
[Element characteristic evaluation 2]
(I) Fabrication of device using polymer binder To improve the film-forming property, as an electron injecting layer, a device obtained by mixing 30 wt% of polyvinyl pyridine (PV4Py) with each of Li2BPP, Li3BPP, and Li4BPP is used. A device was fabricated in the same manner as in
For comparison, an element using only PV4Py for the electron injection layer was produced.
(ii)発光評価
素子特性評価1と同様にして発光評価を行った。
それぞれの素子のELスペクトル、電流密度−電圧特性の関係、輝度−電圧特性の関係、電力効率−輝度特性の関係、電流効率−輝度特性の関係、外部量子効率−輝度特性の関係を図16〜21、及びこれらの結果を表5に示す。
(Ii) Luminous evaluation Luminous evaluation was performed in the same manner as in the device
FIG. 16 to FIG. 16 show the EL spectrum, current density-voltage characteristic relationship, luminance-voltage characteristic relationship, power efficiency-luminance characteristic relationship, current efficiency-luminance characteristic relationship, and external quantum efficiency-luminance characteristic relationship of each element. 21 and the results are shown in Table 5.
図14より、ELスペクトルでは、F8BT由来のスペクトルが観察された。
このポリマーバインダーを用いた素子系においても、ポリマーバインダーを用いない素子と同様にLi2BPP<Li3BPP<Li4BPPの順に高電圧化していた(図15)。電力効率、電流効率、外部量子効率においては、Li2BPP>Li3BPP>Li4BPPの順に効率が低下していた(図17、18、19)。一方、ポリマーバインダーを用いない素子と発光開始電圧及び駆動電圧を比較すると、Li2BPPは0.05〜0.34Vの電圧の低減化していた。これに対し、Li3BPP及びLi4BPPは0.02〜0.19V高電圧化していた。
From FIG. 14, in the EL spectrum, a spectrum derived from F8BT was observed.
Even in the element system using the polymer binder, the voltage was increased in the order of Li2BPP <Li3BPP <Li4BPP as in the case of the element not using the polymer binder (FIG. 15). In power efficiency, current efficiency, and external quantum efficiency, the efficiency decreased in the order of Li2BPP>Li3BPP> Li4BPP (FIGS. 17, 18, and 19). On the other hand, when the light emission start voltage and the drive voltage were compared with an element not using the polymer binder, Li2BPP had a voltage reduction of 0.05 to 0.34V. On the other hand, Li3BPP and Li4BPP were increased in voltage by 0.02 to 0.19V.
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