JP2004214050A - Organic electroluminescent element and display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic electroluminescent element in which both light emission brightness and emission efficiency are high, and which is superior in durability, and a display device having this organic electroluminescent element. <P>SOLUTION: This organic electroluminescent element is made to contain a compound expressed as formula (1): (A)<SB>l</SB>-(X)-(B)<SB>n</SB>, wherein A and B are monovalent substituents in which structures are respectively different, X expresses an m-valent coupling group, A or B contains hetero elements, and furthermore, l and n respectively express the number of A and B, m=l+n, m expresses an integer of 2 to 6, and l≥1, and n≥1. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００４２】
ここで、注意するのは、本明細書で定義するところのＥｓ値は、メチル基のそれを０として定義したのではなく、水素原子を０としたものであり、メチル基を０としたＥｓ値から１．２４を差し引いたものである。
【００４３】
一般式（１）において、連結基Ｘは、ｍ価すなわち、２価以上の連結基を表し、ｍは２〜６の整数を表す。好ましくは、炭素、ケイ素、窒素、ホウ素、酸素、硫黄、金属、金属イオンなどで形成される連結基であり、より好ましくは炭素原子、窒素原子、ケイ素原子、ホウ素原子、酸素原子、硫黄原子、芳香族炭化水素環、芳香族へテロ環からなる連結基であり、更に好ましくは炭素原子、ケイ素原子、芳香族炭化水素環、芳香族へテロ環である。連結基Ｘの具体例としては以下のものが挙げられる。
【００４４】
【化１】

【００４５】
上記の連結基は、さらに置換基を有していても良く、好ましくはアリーレン基であり、さらに好ましくは連結位に隣接して前記Ｅｓ値の絶対値が０．５以上の置換基を有している。
【００４６】
以下に、一般式（１）で表される化合物の具体的を示すが、本発明はこれらに限定されない。
【００４７】
【化２】

【００４８】
【化３】

【００４９】
【化４】

【００５０】
【化５】

【００５１】
【化６】

【００５２】
【化７】

【００５３】
【化８】

【００５４】
【化９】

【００５５】
【化１０】

【００５６】
【化１１】

【００５７】
【化１２】

【００５８】
【化１３】

【００５９】
【化１４】

【００６０】
【化１５】

【００６１】
【化１６】

【００６２】
【化１７】

【００６３】
【化１８】

【００６４】
上記一般式（１）で表される化合物は、有機エレクトロルミネッセンス素子を構成する、下記に示すような何れの層（例えば、正孔輸送層、発光層、正孔ブロック層、電子輸送層等）に含有していても良いが、特に、後述するようにホスト化合物として発光層に含有する場合、または、電子輸送層に含有する場合に、より一層、高発光輝度、高発光効率を示し、且つ、耐久性が向上した有機エレクトロルミネッセンス素子が提供できることがわかった。
【００６５】
本発明に係る一般式（１）で表される化合物の、有機エレクトロルミネッセンス素子を構成するいずれか１層中での含有量としては、５０質量％以上であることが好ましく、更に好ましくは、８０質量％〜９５質量％であり、特に好ましくは、９０質量％〜９５質量％である。
【００６６】
本発明に係る、一般式（１）で表される化合物は従来公知の方法によって製造が可能であるが、例えば、下記に示すような合成例１（化合物＊＊の合成）に記載の合成方法を参照して合成出来る。
【００６７】
以下、本発明に係る、一般式（１）で表される化合物の合成例の一態様を示す。
【００６８】
《合成例１：化合物Ａ−１の合成》
【００６９】
【化１９】

【００７０】
【化２０】

【００７１】
３−ヨード−６−メチル−９−エチルカルバゾールの合成
３−アミノ−６−メチル−９−エチルカルバゾール５０ｇよりサンドマイヤー反応により３−ヨード−６−メチル−９−エチルカルバゾールを２５ｇ合成した。
【００７２】
反応生成物１の合成
３−ヨード−６−メチル−９−エチルカルバゾール１．７ｇを含むテトラヒドロフラン溶液を−７８℃下、ｔｅｒｔ−ブチルリチウムを３．５ｍｌ滴下、攪拌し、３０分後、トリメトキシボランを１．５ｍｌ滴下し、１２時間攪拌した。攪拌後の溶液を抽出、濃縮して反応生成物１を得た。
【００７３】
反応生成物２の合成は、以下の文献を参照し、上記スキームに従い合成した。Ｓｈｉｇｅｈｉｒｏ Ｙａｍａｇｕｃｈｉ ｅｔ ａｌ．，Ｏｒｇ．Ｌｅｔｔ．，２０００，４１２９．
化合物Ａ−１の合成
得られた反応生成物１、２を、テトラキストリフェニルフォスフィンパラジウム（Ｐｄ（ＰＰｈ_３）_４）０．４ｇ、炭酸カリウム１．０ｇを含むテトラヒドロフラン３００ｍｌ、水３０ｍｌから構成される混合溶媒に溶解させ、７０℃、６時間攪拌した。
【００７４】
反応溶液を抽出、乾燥、濃縮、カラム精製、昇華精製を行うことにより、化合物Ａ−１（１．５ｇ）得た。
【００７５】
化合物Ａ−１の分子構造は、ＮＭＲ（核磁気共鳴スペクトル）及びマススペクトルにより目的物であることを確認した。
【００７６】
《合成例２：化合物Ａ−７の合成》
３，５−ジブロモ−２，４，６−トリメチルフェニルトリメチルシランの合成
【００７７】
【化２１】

【００７８】
３−ヨード−６−メチル−９−エチルカルバゾールの合成
３−アミノ−６−メチル−９−エチルカルバゾール５０ｇよりサンドマイヤー反応により３−ヨード−６−メチル−９−エチルカルバゾールを２５ｇ合成した。
【００７９】
トリブロモメシチレンの合成は、以下の文献を参照した。
Ｓｈｉｇｅｈｉｒｏ Ｙａｍａｇｕｃｈｉ ｅｔ ａｌ．，Ｏｒｇ．Ｌｅｔｔ．，２０００，４１２９．
３，５−ジブロモ−２，４，６−トリメチルフェニルトリメチルシランの合成トリブロモメシチレン７．２ｇを含むＴＨＦ溶液３００ｍｌにｎ−ブチルリチウム１３０ｍｌを−７８℃で滴下混合し、トリメチルシランクロリド３．７ｍｌ滴下し、室温で６ｈ攪拌することにより得られた生成物をシリカゲルカラムクロマトグラフィーで精製することにより、３，５−ジブロモ−２，４，６−トリメチルフェニルトリメチルシラン７．０ｇを合成した。
【００８０】
化合物Ａ−７の合成
【００８１】
【化２２】

【００８２】
３，５−ジペンタフルオロフェニル−２，４，６−トリメチルフェニルトリメチルシランの合成
３，５−ジブロモ−２，４，６−トリメチルフェニルトリメチルシラン７．０ｇ、ペンタフルオロフェニルボロン酸１２．７ｇ、テトラキストリフェニルフォスフィンパラジウム４．０ｇ、炭酸カリウム１０ｇを含むテトラヒドロフラン５００ｍｌ、水５０ｍｌから構成される混合溶媒に溶解させ、７０℃、８時間攪拌することにより得られた生成物をシリカゲルカラムクロマトグラフィーで精製することにより３，５−ジペンタフルオロフェニル−２，４，６−トリメチルフェニルトリメチルシラン２．６ｇを合成した。
【００８３】
３，５−ジペンタフルオロフェニル−２，４，６−トリメチルブロモベンゼンの合成
３，５−ジペンタフルオロフェニル−２，４，６−トリメチルフェニルトリメチルシラン２．６ｇを含むＤＭＦ溶液２００ｍｌにＮＢＳ０．９ｇを滴下し、４時間攪拌することにより得られた生成物をシリカゲルカラムクロマトグラフィーおよび再結晶により精製し、３，５−ジ（ペンタフルオロフェニル）−２，４，６−トリメチルブロモベンゼン（３．５ｇ）を合成した。
【００８４】
化合物Ａ−７の合成
得られた前記反応生成物１および３，５−ジペンタフルオロフェニル−２，４，６−トリメチルブロモベンゼン（２．４ｇ）を、テトラキストリフェニルフォスフィンパラジウム０．４ｇ、炭酸カリウム１．０ｇを含むテトラヒドロフラン３００ｍｌ、水３０ｍｌから構成される混合溶媒に溶解させ、７０℃、９時間攪拌した。
【００８５】
反応溶液を抽出、乾燥、濃縮、カラム精製、昇華精製を行うことにより、化合物Ａ−７を１．０ｇ得た。
【００８６】
化合物Ａ−７の分子構造は、ＮＭＲ（核磁気共鳴スペクトル）及びマススペクトルにより目的物であることを確認した。
【００８７】
《ホスト化合物》
本発明に係るホスト化合物について説明する。
【００８８】
ここで、「ホスト化合物」とは、２種以上の化合物で構成される発光層中にて混合比（質量）の最も多い化合物のことを意味し、それ以外の化合物については「ドーパント化合物」という。例えば、発光層を化合物ａ、化合物ｂという２種で構成し、その混合比がａ：ｂ＝１０：９０であれば化合物ａがドーパント化合物であり、化合物ｂがホスト化合物である。更に、発光層を化合物ａ、化合物ｂ、化合物ｃの３種から構成し、その混合比がａ：ｂ：ｃ＝５：１０：８５であれば、化合物ａ、化合物ｂがドーパント化合物であり、化合物ｃがホスト化合物である。
【００８９】
ここで、本発明に係るホスト化合物としては、前記一般式（１）で表される化合物、従来公知の燐光性化合物、後述する蛍光性化合物等を用いることができる。
【００９０】
《燐光性化合物》
本発明に係る、ドーパント化合物として用いられる燐光性化合物について説明する。
【００９１】
「燐光性化合物」とは励起三重項からの発光が観測される化合物であり、燐光量子収率が、２５℃において０．００１以上の化合物である。燐光量子収率は好ましくは０．０１以上、更に好ましくは０．１以上である。
【００９２】
上記燐光量子収率は、第４版実験化学講座７の分光ＩＩの３９８頁（１９９２年版、丸善）に記載の方法により測定できる。溶液中での燐光量子収率は種々の溶媒を用いて測定できるが、本発明に係る燐光性化合物は、任意の溶媒の何れかにおいて上記燐光量子収率が達成されることが好ましい。
【００９３】
本発明に係る燐光性化合物としては、元素周期表で８族〜１０族の金属を含有する錯体系化合物が好ましく、更に好ましくは、イリジウム化合物、オスミウム化合物、または、白金化合物（白金錯体系化合物）等が挙げられ、中でも最も好ましく用いられるのはイリジウム化合物である。
【００９４】
本発明においてホスト材料の最低励起三重項エネルギー準位は、発光材料の最低励起三重項エネルギー準位の１．０５倍以上１．３８倍以下であることが好ましい。
【００９５】
また本発明においてホスト材料の最低励起三重項エネルギー準位は、６８ｋｃａｌ／ｍｏｌ（２８４．９ｋＪ／ｍｏｌ）以上９０ｋｃａｌ／ｍｏｌ（３７７．１ｋＪ／ｍｏｌ）以下であることが好ましい。
【００９６】
本発明に係わる有機エレクトロルミネッセンス素子において、発光層に隣接する層に含まれる有機材料の最低励起三重項エネルギー準位は、発光層を構成する材料の最低励起三重項エネルギー準位よりも高いことが好ましい。
【００９７】
本発明に係わる有機エレクトロルミネッセンス素子において、発光層に隣接する層に含まれる有機材料の最低励起三重項エネルギー準位は、発光層を構成する材料の最低励起三重項エネルギー準位の１．０５倍以上１．３８倍以下であることが好ましい。
【００９８】
また、本発明に係わる有機エレクトロルミネッセンス素子において、発光層に隣接する層に含まれる有機材料の最低励起三重項エネルギー準位が、６８ｋｃａｌ／ｍｏｌ（２８４．９ｋＪ／ｍｏｌ）以上９０ｋｃａｌ／ｍｏｌ（３７７．１ｋＪ／ｍｏｌ）以下であることが好ましい。
【００９９】
以下に、本発明に係る燐光性化合物の具体例を示すが、本発明はこれらに限定されない。また、これらの化合物は、例えば、Ｉｎｏｒｇ．Ｃｈｅｍ．４０巻、１７０４〜１７１１に記載の方法等により合成できる。
【０１００】
【化２３】

【０１０１】
【化２４】

【０１０２】
【化２５】

【０１０３】
《蛍光性化合物》
本発明に用いられる蛍光性化合物について説明する。
【０１０４】
本発明では、ホスト化合物と燐光性化合物の他に、燐光性化合物からの発光の極大波長よりも長波な領域に、蛍光極大波長を有する蛍光性化合物を少なくとも１種含有してもよい。この場合、ホスト化合物と燐光性化合物からのエネルギー移動で、有機エレクトロルミネッセンス素子（有機ＥＬ素子）としての電界発光は蛍光性化合物からの発光が得られる。蛍光性化合物として好ましいのは、溶液状態で蛍光量子収率が高いものである。ここで、蛍光量子収率は１０％以上であることが好ましく、更に好ましくは、３０％以上である。
【０１０５】
具体的な蛍光性化合物としては、クマリン系色素、ピラン系色素、シアニン系色素、クロコニウム系色素、スクアリウム系色素、オキソベンツアントラセン系色素、フルオレセイン系色素、ローダミン系色素、ピリリウム系色素、ペリレン系色素、スチルベン系色素、ポリチオフェン系色素、または、希土類錯体系蛍光体等が挙げられる。
【０１０６】
ここでの蛍光量子収率も、前記第４版実験化学講座７の分光ＩＩの３６２頁（１９９２年版、丸善）に記載の方法により測定することが出来る。
【０１０７】
前記燐光性化合物は、前記のような燐光量子収率が、２５℃において０．００１以上である他、前記ホストとなる蛍光性化合物の蛍光極大波長よりも長い燐光発光極大波長を有するものである。これにより、例えば、ホストとなる蛍光性化合物の発光極大波長より長波の燐光性化合物を用いて燐光性化合物の発光、即ち三重項状態を利用した、ホスト化合物の蛍光極大波長よりも長波において電界発光するＥＬ素子を得ることができる。従って、用いられる燐光性化合物の燐光発光極大波長としては特に制限されるものではなく、原理的には、中心金属、配位子、配位子の置換基等を選択することで得られる発光波長を変化させることができる。
【０１０８】
例えば、３５０ｎｍ〜４４０ｎｍの領域に蛍光極大波長を有する蛍光性化合物をホスト化合物として用い、例えば、緑の領域に燐光を有するイリジウム錯体を用いることで緑領域に電界発光する有機ＥＬ素子を得ることが出来る。
【０１０９】
また、別の形態では、前記のように、ホスト化合物としての蛍光性化合物ａと燐光性化合物の他に、燐光性化合物からの発光の極大波長よりも長波な領域に、蛍光極大波長を有するもう一つの蛍光性化合物ｂを少なくとも１種含有する場合もあり、蛍光性化合物ａと燐光性化合物からのエネルギー移動で、有機ＥＬ素子としての電界発光は蛍光性化合物ｂからの発光を得ることも出来る。
【０１１０】
本発明に用いられる蛍光性化合物が発光する色は、「新編色彩科学ハンドブック」（日本色彩学会編、東京大学出版会、１９８５）の１０８頁の図４．１６において、分光放射輝度計ＣＳ−１０００（ミノルタ製）で測定した結果をＣＩＥ色度座標に当てはめたときの色で決定される。
【０１１１】
《有機エレクトロルミネッセンス素子の層構成》
本発明に係る有機エレクトロルミネッセンス素子（有機ＥＬ素子）の層構成について説明する。
【０１１２】
本発明の有機ＥＬ素子は、一対の電極（陽極、陰極）の間に、少なくとも１層の発光層を挟持した構造を有する。ここで、発光層は、広義の意味では、陰極と陽極からなる電極に電流を流した際に発光する層のことであり、具体的には、陰極と陽極からなる電極に電流を流した際に発光する化合物を含有する層のことを指す。
【０１１３】
本発明の有機ＥＬ素子は、必要に応じ発光層の他に、正孔輸送層、電子輸送層、陽極バッファー層及び陰極バッファー層等を有し、陰極と陽極で挟持された構造をとる。具体的には以下に示される構造が挙げられる。
【０１１４】
（ｉ）陽極／発光層／陰極
（ｉｉ）陽極／正孔輸送層／発光層／陰極
（ｉｉｉ）陽極／発光層／電子輸送層／陰極
（ｉｖ）陽極／正孔輸送層／発光層／電子輸送層／陰極
（ｖ）陽極／陽極バッファー層／正孔輸送層／発光層／電子輸送層／陰極バッファー層／陰極
《発光層》
本発明に係る発光層について説明する。
【０１１５】
本発明では、例えば、前記一般式（１）で表される化合物およびリン光性ドーパント化合物を用いて発光層を形成することが好ましい。ここで、その形成方法としては、例えば、蒸着法、スピンコート法、キャスト法、ＬＢ法などの公知の方法により薄膜を形成することが出来るが、本発明では、特に分子堆積膜が好ましい。ここで、分子堆積膜とは、上記化合物の気相状態から沈着され形成された薄膜や、該化合物の溶融状態、または液相状態から固体化され形成された膜のことである。通常、分子堆積膜はＬＢ法により形成された薄膜（分子累積膜）と、凝集構造、高次構造の相違やそれに起因する機能的な相違により区別することができる。
【０１１６】
また、この発光層は、特開昭５７−５１７８１号公報に記載されているように、樹脂などの結着材と共に発光材料として上記化合物を溶剤に溶かして溶液とした後、これをスピンコート法などにより塗布して薄膜形成することにより得ることができる。
【０１１７】
（発光層の膜厚）
このようにして形成された発光層の膜厚については特に制限はなく、状況に応じて適宜選択することができるが、５ｎｍ〜５μｍの範囲に膜厚調整することが好ましい。
【０１１８】
次に、正孔注入層、正孔輸送層、電子注入層、電子輸送層等、発光層と組み合わせて有機ＥＬ素子を構成するその他の層について説明する。
【０１１９】
《正孔注入層、正孔輸送層、電子注入層、電子輸送層》
本発明に用いられる、正孔注入層、正孔輸送層は、陽極より注入された正孔を発光層に伝達する機能を有し、この正孔注入層、正孔輸送層を陽極と発光層の間に介在させることにより、より低い電界で多くの正孔が発光層に注入され、その上、発光層に陰極、電子注入層、または電子輸送層より注入された電子は、発光層と正孔注入層もしくは正孔輸送層の界面に存在する電子の障壁により、発光層内の界面に累積され発光効率が向上するなど発光性能の優れた素子となる。
【０１２０】
《正孔注入材料、正孔輸送材料》
この正孔注入層、正孔輸送層の材料（以下、正孔注入材料、正孔輸送材料という）については、前記の陽極より注入された正孔を発光層に伝達する機能を有する性質を有するものであれば特に制限はなく、従来、光導伝性材料において、正孔の電荷注入輸送材料として慣用されているものやＥＬ素子の正孔注入層、正孔輸送層に使用される公知のものの中から任意のものを選択して用いることができる。
【０１２１】
上記正孔注入材料、正孔輸送材料は、正孔の注入もしくは輸送、電子の障壁性の何れかを有するものであり、有機物、無機物の何れであってもよい。この正孔注入材料、正孔輸送材料としては、例えばトリアゾール誘導体、オキサジアゾール誘導体、イミダゾール誘導体、ポリアリールアルカン誘導体、ピラゾリン誘導体及びピラゾロン誘導体、フェニレンジアミン誘導体、アリールアミン誘導体、アミノ置換カルコン誘導体、オキサゾール誘導体、スチリルアントラセン誘導体、フルオレノン誘導体、ヒドラゾン誘導体、スチルベン誘導体、シラザン誘導体、アニリン系共重合体、または、導電性高分子オリゴマー、特にチオフェンオリゴマーなどが挙げられる。正孔注入材料、正孔輸送材料としては、上記のものを使用することができるが、ポルフィリン化合物、芳香族第三級アミン化合物及びスチリルアミン化合物、特に芳香族第三級アミン化合物を用いることが好ましい。
【０１２２】
上記芳香族第三級アミン化合物及びスチリルアミン化合物の代表例としては、Ｎ，Ｎ，Ｎ′，Ｎ′−テトラフェニル−４，４′−ジアミノフェニル；Ｎ，Ｎ′−ジフェニル−Ｎ，Ｎ′−ビス（３−メチルフェニル）−〔１，１′−ビフェニル〕−４，４′−ジアミン（ＴＰＤ）；２，２−ビス（４−ジ−ｐ−トリルアミノフェニル）プロパン；１，１−ビス（４−ジ−ｐ−トリルアミノフェニル）シクロヘキサン；Ｎ，Ｎ，Ｎ′，Ｎ′−テトラ−ｐ−トリル−４，４′−ジアミノビフェニル；１，１−ビス（４−ジ−ｐ−トリルアミノフェニル）−４−フェニルシクロヘキサン；ビス（４−ジメチルアミノ−２−メチルフェニル）フェニルメタン；ビス（４−ジ−ｐ−トリルアミノフェニル）フェニルメタン；Ｎ，Ｎ′−ジフェニル−Ｎ，Ｎ′−ジ（４−メトキシフェニル）−４，４′−ジアミノビフェニル；Ｎ，Ｎ，Ｎ′，Ｎ′−テトラフェニル−４，４′−ジアミノジフェニルエーテル；４，４′−ビス（ジフェニルアミノ）クオードリフェニル；Ｎ，Ｎ，Ｎ−トリ（ｐ−トリル）アミン；４−（ジ−ｐ−トリルアミノ）−４′−〔４−（ジ−ｐ−トリルアミノ）スチリル〕スチルベン；４−Ｎ，Ｎ−ジフェニルアミノ−（２−ジフェニルビニル）ベンゼン；３−メトキシ−４′−Ｎ，Ｎ−ジフェニルアミノスチルベンゼン；Ｎ−フェニルカルバゾール、更に、米国特許第５，０６１，５６９号明細書に記載されている２個の縮合芳香族環を分子内に有するもの、例えば、４，４′−ビス〔Ｎ−（１−ナフチル）−Ｎ−フェニルアミノ〕ビフェニル（α−ＮＰＤ）、特開平４−３０８６８８号公報に記載されているトリフェニルアミンユニットが３つスターバースト型に連結された４，４′，４″−トリス〔Ｎ−（３−メチルフェニル）−Ｎ−フェニルアミノ〕トリフェニルアミン（ＭＴＤＡＴＡ）などが挙げられる。
【０１２３】
更に、これらの材料を高分子鎖に導入した、または、これらの材料を高分子の主鎖とした高分子材料を用いることもできる。
【０１２４】
または、ｐ型−Ｓｉ、ｐ型−ＳｉＣなどの無機化合物も正孔注入材料、正孔輸送材料として使用することができる。この正孔注入層、正孔輸送層は、上記正孔注入材料、正孔輸送材料を、例えば真空蒸着法、スピンコート法、キャスト法、ＬＢ法などの公知の方法により、薄膜化することにより形成することができる。
【０１２５】
（正孔注入層の膜厚、正孔輸送層の膜厚）
正孔注入層、正孔輸送層の膜厚については特に制限はないが、５ｎｍ〜５μｍ程度での範囲に調整することが好ましい。この正孔注入層、正孔輸送層は、上記材料の一種または二種以上からなる一層構造であってもよく、同一組成または異種組成の複数層からなる積層構造であってもよい。
【０１２６】
《電子輸送層、電子輸送材料》
本発明に係る電子輸送層は、陰極より注入された電子を発光層に伝達する機能を有していればよく、その材料としては従来公知の化合物の中から任意のものを選択して用いることができる。
【０１２７】
この電子輸送層に用いられる材料（以下、電子輸送材料という）の例としては、ニトロ置換フルオレン誘導体、ジフェニルキノン誘導体、チオピランジオキシド誘導体、ナフタレンペリレンなどの複素環テトラカルボン酸無水物、カルボジイミド、フレオレニリデンメタン誘導体、アントラキノジメタン及びアントロン誘導体、オキサジアゾール誘導体などが挙げられる。更に、上記オキサジアゾール誘導体において、オキサジアゾール環の酸素原子を硫黄原子に置換したチアジアゾール誘導体、電子吸引基として知られているキノキサリン環を有するキノキサリン誘導体も、電子輸送材料として用いることができる。
【０１２８】
更に、これらの材料を高分子鎖に導入した、またはこれらの材料を高分子の主鎖とした高分子材料を用いることもできる。
【０１２９】
または、８−キノリノール誘導体の金属錯体、例えばトリス（８−キノリノール）アルミニウム（Ａｌｑ）、トリス（５，７−ジクロロ−８−キノリノール）アルミニウム、トリス（５，７−ジブロモ−８−キノリノール）アルミニウム、トリス（２−メチル−８−キノリノール）アルミニウム、トリス（５−メチル−８−キノリノール）アルミニウム、ビス（８−キノリノール）亜鉛（Ｚｎｑ）など、及びこれらの金属錯体の中心金属がＩｎ、Ｍｇ、Ｃｕ、Ｃａ、Ｓｎ、ＧａまたはＰｂに置き替わった金属錯体も、電子輸送材料として用いることができる。
【０１３０】
その他、メタルフリーまたはメタルフタロシアニン、更には、それらの末端がアルキル基やスルホン酸基などで置換されているものも、電子輸送材料として好ましく用いることができる。または、発光層の材料として例示したジスチリルピラジン誘導体も、電子輸送材料として用いることができるし、正孔注入層、正孔輸送層と同様に、ｎ型−Ｓｉ、ｎ型−ＳｉＣなどの無機半導体も電子輸送材料として用いることができる。
【０１３１】
この電子輸送層は、上記化合物を、例えば真空蒸着法、スピンコート法、キャスト法、ＬＢ法などの公知の薄膜形成法により製膜して形成することができる。
【０１３２】
（電子輸送層の膜厚）
電子輸送層の膜厚は特に制限はないが、５ｎｍ〜５μｍの範囲に調整することが好ましい。この電子輸送層は、これらの電子輸送材料一種または二種以上からなる一層構造であってもよいし、或いは、同一組成または異種組成の複数層からなる積層構造であってもよい。
【０１３３】
また、本発明においては、蛍光性化合物は発光層のみに限定することはなく、発光層に隣接した正孔輸送層、または電子輸送層に前記燐光性化合物のホスト化合物となる蛍光性化合物と同じ領域に蛍光極大波長を有する蛍光性化合物を少なくとも１種含有させてもよく、それにより更にＥＬ素子の発光効率を高めることができる。これらの正孔輸送層や電子輸送層に含有される蛍光性化合物としては、発光層に含有されるものと同様に蛍光極大波長が３３０ｎｍ〜４４０ｎｍ、更に好ましくは３６０ｎｍ〜４１０ｎｍの範囲にある蛍光性化合物が用いられる。
【０１３４】
または、本発明においては、発光効率、及び耐久性の点から一般式（１）で表される化合物を電子輸送層に含有することが好ましい。
【０１３５】
《基板（支持体ともいう）》
本発明の有機ＥＬ素子に好ましく用いられる基板は、ガラス、プラスチックなどの種類には特に限定はなく、または、透明のものであれば特に制限はない。本発明の有機ＥＬ素子に好ましく用いられる基板としては例えばガラス、石英、光透過性プラスチックフィルムを挙げることができる。
【０１３６】
光透過性プラスチックフィルムとしては、例えばポリエチレンテレフタレート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、ポリエーテルスルホン（ＰＥＳ）、ポリエーテルイミド、ポリエーテルエーテルケトン、ポリフェニレンスルフィド、ポリアリレート、ポリイミド、ポリカーボネート（ＰＣ）、セルローストリアセテート（ＴＡＣ）、セルロースアセテートプロピオネート（ＣＡＰ）等からなるフィルム等が挙げられる。
【０１３７】
次に、該有機ＥＬ素子を作製する好適な例を説明する。例として、前記の陽極／正孔注入層／正孔輸送層／発光層／電子輸送層／電子注入層／陰極からなるＥＬ素子の作製法について説明する。
【０１３８】
まず適当な基板上に、所望の電極用物質、例えば陽極用物質からなる薄膜を、１μｍ以下、好ましくは１０〜２００ｎｍの範囲の膜厚になるように、蒸着やスパッタリングなどの方法により形成させて陽極を作製する。次に、この上に素子材料である正孔注入層、正孔輸送層、発光層、電子輸送層／電子注入層からなる薄膜を形成させる。
【０１３９】
更に、陽極と発光層または正孔注入層の間、及び、陰極と発光層または電子注入層との間にはバッファー層（電極界面層）を存在させてもよい。
【０１４０】
バッファー層とは、駆動電圧低下や発光効率向上のために電極と有機層間に設けられる層のことで、「有機ＥＬ素子とその工業化最前線（１９９８年１１月３０日エヌ・ティー・エス社発行）」の第２編第２章「電極材料」（第１２３頁〜第１６６頁）に詳細に記載されており、陽極バッファー層と陰極バッファー層とがある。
【０１４１】
陽極バッファー層は、特開平９−４５４７９号公報、同９−２６００６２号公報、同８−２８８０６９号公報等にもその詳細が記載されており、具体例として、銅フタロシアニンに代表されるフタロシアニンバッファー層、酸化バナジウムに代表される酸化物バッファー層、アモルファスカーボンバッファー層、ポリアニリン（エメラルディン）やポリチオフェン等の導電性高分子を用いた高分子バッファー層等が挙げられる。
【０１４２】
陰極バッファー層は、特開平６−３２５８７１号公報、同９−１７５７４号公報、同１０−７４５８６号公報等にもその詳細が記載されており、具体的にはストロンチウムやアルミニウム等に代表される金属バッファー層、フッ化リチウムに代表されるアルカリ金属化合物バッファー層、フッ化マグネシウムに代表されるアルカリ土類金属化合物バッファー層、酸化アルミニウム、酸化リチウムに代表される酸化物バッファー層等が挙げられる。
【０１４３】
上記バッファー層はごく薄い膜であることが望ましく、素材にもよるが、その膜厚は０．１〜１００ｎｍの範囲が好ましい。
【０１４４】
更に上記基本構成層の他に必要に応じてその他の機能を有する層を積層してもよく、例えば特開平１１−２０４２５８号公報、同１１−２０４３５９号公報、及び「有機ＥＬ素子とその工業化最前線（１９９８年１１月３０日エヌ・ティー・エス社発行）」の第２３７頁等に記載されている正孔阻止（ホールブロック）層などのような機能層を有していても良い。
【０１４５】
バッファー層は、陰極バッファー層または陽極バッファー層の少なくとも何れか１つの層内に一般式（１）または（２）で表される化合物の少なくとも１種が存在して、発光層として機能してもよい。
【０１４６】
《電極》
次に有機ＥＬ素子の電極について説明する。有機ＥＬ素子の電極は、陰極と陽極からなる。この有機ＥＬ素子における陽極としては、仕事関数の大きい（４ｅＶ以上）金属、合金、電気伝導性化合物及びこれらの混合物を電極物質とするものが好ましく用いられる。このような電極物質の具体例としてはＡｕなどの金属、ＣｕＩ、インジウムチンオキシド（ＩＴＯ）、ＳｎＯ_２、ＺｎＯなどの導電性透明材料が挙げられる。
【０１４７】
上記陽極は蒸着やスパッタリングなどの方法によりこれらの電極物質の薄膜を形成させ、フォトリソグラフィー法で所望の形状のパターンを形成してもよく、或いはパターン精度をあまり必要としない場合（１００μｍ以上程度）は、上記電極物質の蒸着やスパッタリング時に所望の形状のマスクを介してパターンを形成してもよい。この陽極より発光を取り出す場合には、透過率を１０％より大きくすることが望ましく、または、陽極としてのシート抵抗は数百Ω／□以下が好ましい。更に膜厚は材料にもよるが、通常１０ｎｍ〜１μｍ、好ましくは１０ｎｍ〜２００ｎｍの範囲で選ばれる。
【０１４８】
一方、陰極としては、仕事関数の小さい（４ｅＶ以下）金属（電子注入性金属と称する）、合金、電気伝導性化合物及びこれらの混合物を電極物質とするものが好ましく用いられる。このような電極物質の具体例としては、ナトリウム、ナトリウム−カリウム合金、マグネシウム、リチウム、マグネシウム／銅混合物、マグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム（Ａｌ_２Ｏ_３）混合物、インジウム、リチウム／アルミニウム混合物、希土類金属などが挙げられる。これらの中で、電子注入性及び酸化などに対する耐久性の点から、電子注入性金属とこれより仕事関数の値が大きく安定な金属である第二金属との混合物、例えばマグネシウム／銀混合物、マグネシウム／アルミニウム混合物、マグネシウム／インジウム混合物、アルミニウム／酸化アルミニウム（Ａｌ_２Ｏ_３）混合物、リチウム／アルミニウム混合物などが好適である。上記陰極は、これらの電極物質を蒸着やスパッタリングなどの方法で薄膜を形成させることにより作製することができる。または、陰極としてのシート抵抗は数百Ω／□以下が好ましく、膜厚は通常１０ｎｍ〜１μｍ、好ましくは５０ｎｍ〜２００ｎｍの範囲で選ばれる。尚、発光を透過させるため、有機ＥＬ素子の陽極または陰極の何れか一方が、透明または半透明であれば発光効率が向上するので好都合である。
【０１４９】
《有機ＥＬ素子の作製方法》
次に、有機ＥＬ素子の作製方法について説明する。
【０１５０】
薄膜化の方法としては、前記の如くスピンコート法、キャスト法、蒸着法などがあるが、均質な膜が得られやすく、かつピンホールが生成しにくいなどの点から、真空蒸着法が好ましい。薄膜化に真空蒸着法を採用する場合、その蒸着条件は、使用する化合物の種類、分子堆積膜の目的とする結晶構造、会合構造などにより異なるが、一般にボート加熱温度５０〜４５０℃、真空度１０−６〜１０−３Ｐａ、蒸着速度０．０１ｎｍ／秒〜５０ｎｍ／秒、基板温度−５０℃〜３００℃、膜厚５ｎｍ〜５μｍの範囲で適宜選ぶことが望ましい。
【０１５１】
前記の様に、適当な基板上に所望の電極用物質、例えば陽極用物質からなる薄膜を１μｍ以下、好ましくは１０ｎｍ〜２００ｎｍの範囲の膜厚になるように、蒸着やスパッタリングなどの方法により形成させて陽極を作製した後、該陽極上に前記の通り正孔注入層、正孔輸送層、発光層、電子輸送層／電子注入層からなる各層薄膜を形成させた後、その上に陰極用物質からなる薄膜を１μｍ以下、好ましくは５０ｎｍ〜２００ｎｍの範囲の膜厚になるように、例えば蒸着やスパッタリングなどの方法により形成させて陰極を設け、所望の有機ＥＬ素子が得られる。この有機ＥＬ素子の作製は、一回の真空引きで一貫してこの様に正孔注入層から陰極まで作製するのが好ましいが、作製順序を逆にして、陰極、電子注入層、発光層、正孔注入層、陽極の順に作製することも可能である。このようにして得られた有機ＥＬ素子に、直流電圧を印加する場合には、陽極を＋、陰極を−の極性として電圧５〜４０Ｖ程度を印加すると、発光が観測できる。または、逆の極性で電圧を印加しても電流は流れずに発光は全く生じない。更に、交流電圧を印加する場合には、陽極が＋、陰極が−の状態になったときのみ発光する。尚、印加する交流の波形は任意でよい。
【０１５２】
《表示装置》
本発明の有機ＥＬ素子は、照明用や露光光源のような一種のランプとして使用しても良いし、画像を投影するタイプのプロジェクション装置や、静止画像や動画像を直接視認するタイプの表示装置（ディスプレイ）として使用しても良い。動画再生用の表示装置として使用する場合の駆動方式は単純マトリクス（パッシブマトリクス）方式でもアクティブマトリクス方式でもどちらでも良い。または、異なる発光色を有する本発明の有機ＥＬ素子を２種以上使用することにより、フルカラー表示装置を作製することが可能である。
【０１５３】
【発明の実施の形態】
本発明の有機ＥＬ素子から構成される表示装置の一例を図面に基づいて以下に説明する。
【０１５４】
図１は、有機ＥＬ素子から構成される表示装置の一例を示した模式図である。有機ＥＬ素子の発光により画像情報の表示を行う、例えば、携帯電話等のディスプレイの模式図である。
【０１５５】
ディスプレイ１は、複数の画素を有する表示部Ａ、画像情報に基づいて表示部Ａの画像走査を行う制御部Ｂ等からなる。
【０１５６】
制御部Ｂは、表示部Ａと電気的に接続され、複数の画素それぞれに外部からの画像情報に基づいて走査信号と画像データ信号を送り、走査信号により走査線毎の画素が画像データ信号に応じて順次発光して画像走査を行って画像情報を表示部Ａに表示する。
【０１５７】
図２は、表示部Ａの模式図である。
表示部Ａは基板上に、複数の走査線５及びデータ線６を含む配線部と、複数の画素３等とを有する。表示部Ａの主要な部材の説明を以下に行う。
【０１５８】
図においては、画素３の発光した光が、白矢印方向（下方向）へ取り出される場合を示している。
【０１５９】
配線部の走査線５及び複数のデータ線６は、それぞれ導電材料からなり、走査線５とデータ線６は格子状に直交して、直交する位置で画素３に接続している（詳細は図示せず）。
【０１６０】
画素３は、走査線５から走査信号が印加されると、データ線６から画像データ信号を受け取り、受け取った画像データに応じて発光する。発光の色が赤領域の画素、緑領域の画素、青領域の画素を、適宜、同一基板上に並置することによって、フルカラー表示が可能となる。
【０１６１】
次に、画素の発光プロセスを説明する。
図３は、画素の模式図である。
【０１６２】
画素は、有機ＥＬ素子１０、スイッチングトランジスタ１１、駆動トランジスタ１２、コンデンサ１３等を備えている。複数の画素に有機ＥＬ素子１０として、赤色、緑色、青色発光の有機ＥＬ素子を用い、これらを同一基板上に並置することでフルカラー表示を行うことができる。
【０１６３】
図３において、制御部Ｂからデータ線６を介してスイッチングトランジスタ１１のドレインに画像データ信号が印加される。そして、制御部Ｂから走査線５を介してスイッチングトランジスタ１１のゲートに走査信号が印加されると、スイッチングトランジスタ１１の駆動がオンし、ドレインに印加された画像データ信号がコンデンサ１３と駆動トランジスタ１２のゲートに伝達される。
【０１６４】
画像データ信号の伝達により、コンデンサ１３が画像データ信号の電位に応じて充電されるとともに、駆動トランジスタ１２の駆動がオンする。駆動トランジスタ１２は、ドレインが電源ライン７に接続され、ソースが有機ＥＬ素子１０の電極に接続されており、ゲートに印加された画像データ信号の電位に応じて電源ライン７から有機ＥＬ素子１０に電流が供給される。
【０１６５】
制御部Ｂの順次走査により走査信号が次の走査線５に移ると、スイッチングトランジスタ１１の駆動がオフする。しかし、スイッチングトランジスタ１１の駆動がオフしてもコンデンサ１３は充電された画像データ信号の電位を保持するので、駆動トランジスタ１２の駆動はオン状態が保たれて、次の走査信号の印加が行われるまで有機ＥＬ素子１０の発光が継続する。順次走査により次に走査信号が印加されたとき、走査信号に同期した次の画像データ信号の電位に応じて駆動トランジスタ１２が駆動して有機ＥＬ素子１０が発光する。
【０１６６】
すなわち、有機ＥＬ素子１０の発光は、複数の画素それぞれの有機ＥＬ素子１０に対して、アクティブ素子であるスイッチングトランジスタ１１と駆動トランジスタ１２を設けて、複数の画素３それぞれの有機ＥＬ素子１０の発光を行っている。このような発光方法をアクティブマトリクス方式と呼んでいる。
【０１６７】
ここで、有機ＥＬ素子１０の発光は、複数の階調電位を持つ多値の画像データ信号による複数の階調の発光でもよいし、２値の画像データ信号による所定の発光量のオン、オフでもよい。
【０１６８】
また、コンデンサ１３の電位の保持は、次の走査信号の印加まで継続して保持してもよいし、次の走査信号が印加される直前に放電させてもよい。
【０１６９】
本発明においては、上述したアクティブマトリクス方式に限らず、走査信号が走査されたときのみデータ信号に応じて有機ＥＬ素子を発光させるパッシブマトリクス方式の発光駆動でもよい。
【０１７０】
図４は、パッシブマトリクス方式による表示装置の模式図である。図４において、複数の走査線５と複数の画像データ線６が画素３を挟んで対向して格子状に設けられている。
【０１７１】
順次走査により走査線５の走査信号が印加されたとき、印加された走査線５に接続している画素３が画像データ信号に応じて発光する。
【０１７２】
パッシブマトリクス方式では画素３にアクティブ素子が無く、製造コストの低減が計れる。
【０１７３】
【実施例】
以下、実施例を挙げて本発明を詳細に説明するが、本発明の態様はこれに限定されない。
【０１７４】
実施例１
《ＷｉｎＭＯＰＡＣを用いる置換基ＡおよびＢのＨＯＭＯ−ＬＵＭＯ計算》
化合物例Ａ−１〜Ｄ−８において示したような置換基に分けて富士通製ＷｉｎＭＯＰＡＣ ｖｅｒ．３を用い、キーワードとしてＥＦおよびＡＭ１を使用して収束条件がｇｒａｄ＜１．０になるように計算した。また、各置換基のヘテロ元素を炭素原子に換えて計算を行ない、以下に示した２つの条件式のうちどちらかを満足する方を置換基Ａ、置換基Ｂと定義した。ここにおいて、置換基のＨＯＭＯおよびＬＵＭＯとしては、各置換基の結合位を水素で置換した化合物についてそれぞれ計算を行って得られた結果を置換基のＨＯＭＯおよびＬＵＭＯとした。
【０１７５】
《条件式》
置換基Ａ：
ＨＯＭＯ（Ｈ）−ＨＯＭＯ（Ｃ）＞０ かつ、
│ＨＯＭＯ（Ｈ）−ＨＯＭＯ（Ｃ）│−│ＬＵＭＯ（Ｈ）−ＬＵＭＯ（Ｃ）│＞０
置換基Ｂ：
ＬＵＭＯ（Ｈ）−ＬＵＭＯ（Ｃ）＜０ かつ、
│ＨＯＭＯ（Ｈ）−ＨＯＭＯ（Ｃ）│−│ＬＵＭＯ（Ｈ）−ＬＵＭＯ（Ｃ）│＜０
＊（Ｈ）：ヘテロ元素を含む置換基。＊（Ｃ）：ヘテロ元素を炭素に置換した比較置換基。
【０１７６】
ここで、置換するヘテロ原子の結合箇所が２箇所（２価）である場合、置換した炭素のうち結合に寄与しない２つの結合には２つの炭素−水素結合を形成させたものを用いて計算する。即ちヘテロ原子が１価である場合には、３つの炭素−水素結合、ヘテロ原子が３価である場合には、１つの炭素−水素結合を形成させたものを用いて計算する。計算結果を以下に示す（単位ｅＶ）。
【０１７７】
【化２６】

【０１７８】
実施例２
《有機ＥＬ素子の作製》
有機ＥＬ素子ＯＬＥＤ１−１〜１−９を以下のように作製した。
【０１７９】
（有機ＥＬ素子ＯＬＥＤ１−１の作製）
陽極として１００ｍｍ×１００ｍｍ×１．１ｍｍのガラス基板上にＩＴＯ（インジウムチンオキシド）を１５０ｎｍの膜厚で製膜した透明基板（ＮＨテクノグラス社製ＮＡ−４５）にパターニングを行った後、このＩＴＯ透明電極（陽極）を設けた透明支持基板をイソプロピルアルコール中で超音波洗浄し、乾燥窒素ガスで乾燥し、ＵＶオゾン洗浄を５分間行なった。
【０１８０】
この透明支持基板を市販の真空蒸着装置の基板ホルダーに固定し、一方、モリブデン製抵抗加熱ボートにα−ＮＰＤを２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにカルバゾール誘導体（ＣＢＰ）を２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートにバソクプロイン（ＢＣＰ）を２００ｍｇ入れ、別のモリブデン製抵抗加熱ボートに燐光性化合物（Ｉｒ−１２）を１００ｍｇ入れ、更に別のモリブデン製抵抗加熱ボートにＡｌｑ_３を２００ｍｇ入れ、真空蒸着装置に取付けた。
【０１８１】
次いで、真空槽を４×１０^−４Ｐａまで減圧した後、α−ＮＰＤの入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／秒で透明支持基板に蒸着し、膜厚４５ｎｍの正孔輸送層を設けた。更に、ＣＢＰ（ホスト化合物として使用）と燐光性化合物Ｉｒ−１２（ドーパント化合物として使用）の入った前記加熱ボートに通電して加熱し、各々蒸着速度０．１ｎｍ／秒、０．０１ｎｍ／秒で前記正孔輸送層上に共蒸着して膜厚２０ｎｍの発光層を設けた。尚、蒸着時の基板温度は室温であった。更に、ＢＣＰの入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／秒で前記発光層の上に蒸着して膜厚１０ｎｍの正孔阻止の役割も兼ねた電子輸送層を設けた。その上に、更に、Ａｌｑ_３の入った前記加熱ボートに通電して加熱し、蒸着速度０．１ｎｍ／秒で前記電子輸送層の上に蒸着して更に膜厚４０ｎｍの電子注入層を設けた。尚、蒸着時の基板温度は室温であった。
【０１８２】
引き続きフッ化リチウム０．５ｎｍ及びアルミニウム１１０ｎｍを蒸着して、陰極バッファー層、陰極を各々形成し、有機ＥＬ素子ＯＬＥＤ１−１（比較例）を作製した。
【０１８３】
図５に、有機ＥＬ素子ＯＬＥＤ１−１の概略模式図を示す。
（有機ＥＬ素子ＯＬＥＤ１−２〜１−９の作製）
上記有機ＥＬ素子ＯＬＥＤ１−１の作製において、発光層の形成に用いたホスト化合物ＣＢＰの代わりに、以下の化合物を用いた以外は全く同様にして、表２に示す有機ＥＬ素子ＯＬＥＤ１−２〜１−９を作製した。
【０１８４】
【化２７】

【０１８５】
【化２８】

【０１８６】
得られた有機ＥＬ素子ＯＬＥＤ１−１〜ＯＬＥＤ１−９の各々について下記のような評価を行った。
【０１８７】
《有機ＥＬ素子の評価》
以下のようにして有機ＥＬ素子の評価を行い、結果を表２に示す。
【０１８８】
《発光輝度》
有機ＥＬ素子ＯＬＥＤ１−１では、初期駆動電圧３Ｖで電流が流れ始め、発光層のドーパントである燐光性化合物（Ｉｒ−１２）からの青色の発光を示した。
【０１８９】
まず、上記有機ＥＬ素子ＯＬＥＤ１−１を温度２３℃、乾燥窒素ガス雰囲気下の測定条件下において、１０Ｖ直流電圧を印加した時の発光輝度（ｃｄ／ｍ^２）を測定した。ここで、発光輝度の測定は、ＣＳ−１０００（ミノルタ製）を用いた。
【０１９０】
次いで、有機ＥＬ素子ＯＬＥＤ１−１の測定と同様にして、有機ＥＬ素子ＯＬＥＤ１−２〜１−９について発光輝度を求めた。
【０１９１】
表２に記載の発光輝度、発光効率は、有機ＥＬ素子ＯＬＥＤ１−１の測定値を各々１００としたときの相対値で示す。
【０１９２】
《耐久性》
有機ＥＬ素子ＯＬＥＤ１−１〜１−９の各々において、１０ｍＡ／ｃｍ^２の一定電流で駆動したときの初期輝度が半分に低下するのに要した時間、即ち、半減時間（耐久性）を耐久性の指標として示す。表２において、各有機ＥＬ素子の半減時間（耐久性）は有機ＥＬ素子ＯＬＥＤ１−１を１００とした時の相対値で表した。
【０１９３】
得られた結果を表２に示す。
【０１９４】
【表２】

【０１９５】
表２から得られた結果を詳細に説明すると、ＣＢＰや比較化合物２のように、平面性が高い化合物ではバンドギャップが狭く、青色に発光する燐光性化合物のホスト化合物としては発光輝度、発光効率の点で劣っていることが判る。また、比較化合物１においては、従来用いられているＣＢＰと比べてバンドギャップが広く、発光輝度および発光効率の点では改善されているが、耐久性の点では満足な結果が得られないことが判る。
【０１９６】
一方、本発明に係る一般式（１）で表されるカルバゾール誘導体化合物をホスト化合物として用いた有機エレクトロルミネッセンス素子（有機ＥＬ素子）は、発光輝度が高く、発光効率が向上し、且つ、耐久性が良好なことから、有機ＥＬ素子として非常に有用であることがわかった。
【０１９７】
また、燐光性化合物Ｉｒ−１２を、Ｉｒ−１またはＩｒ−９に変更した以外は有機ＥＬ素子ＯＬＥＤ１−１〜１−９と同様にして作製した有機ＥＬ素子の性能を評価した場合にも上記と同様の効果が得られた。特に、耐久性については大幅な改善がみられた。尚、Ｉｒ−１を用いた素子からは緑色の発光が、Ｉｒ−９を用いた素子からは赤色の発光が得られた。
【０１９８】
実施例３
《有機ＥＬ素子ＯＬＥＤ２−１〜２−７の作製》
実施例１の有機ＥＬ素子ＯＬＥＤ１−１の電子輸送層におけるＢＣＰを表２に示す様に前記の化合物に置き換えた以外は同様にして、有機ＥＬ素子ＯＬＥＤ２−１〜２−７を作製した。
【０１９９】
次いで、得られた有機ＥＬ素子ＯＬＥＤ２−１〜２−７について、実施例１と同様の方法を用いて発光輝度、発光効率及び半減時間（耐久性）を測定した。得られた結果を表３に示す。
【０２００】
【表３】

【０２０１】
表３から、本発明の試料は、発光輝度、発光効率が共に高く、且つ、耐久性にも優れていることが明らかである。
【０２０２】
また、本発明に係る、前記一般式（１）で表される化合物を電子輸送層に用いた有機ＥＬ素子は、発光輝度、発光効率が改善されているのが分かるが、特に耐久性の面で、半減時間（耐久性）が顕著に改善されることが判る。
【０２０３】
実施例４
実施例１で作製したそれぞれ赤色、緑色、青色発光有機ＥＬ素子を同一基板上に並置し、図１に記載のような形態を有するアクティブマトリクス方式フルカラー表示装置を作製し、図２には、作製した前記表示装置の表示部Ａの模式図のみを示した。即ち同一基板上に、複数の走査線５及びデータ線６を含む配線部と、並置した複数の画素３（発光の色が赤領域の画素、緑領域の画素、青領域の画素等）とを有し、配線部の走査線５及び複数のデータ線６はそれぞれ導電材料からなり、走査線５とデータ線６は格子状に直交して、直交する位置で画素３に接続している（詳細は図示せず）。前記複数画素３は、それぞれの発光色に対応した有機ＥＬ素子、アクティブ素子であるスイッチングトランジスタと駆動トランジスタそれぞれが設けられたアクティブマトリクス方式で駆動されており、走査線５から走査信号が印加されると、データ線６から画像データ信号を受け取り、受け取った画像データに応じて発光する。この様に各赤、緑、青の画素を適宜、並置することによって、フルカラー表示が可能となる。
【０２０４】
該フルカラー表示装置を駆動することにより、輝度の高く耐久性の良好な、鮮明なフルカラー動画表示が得られた。
【０２０５】
【発明の効果】
本発明により、発光輝度、発光効率が共に高く、且つ、耐久性に優れた有機エレクトロルミネッセンス素子、及び、前記素子を有する表示装置を提供することが出来た。
【図面の簡単な説明】
【図１】有機ＥＬ素子から構成される表示装置の一例を示した模式図である。
【図２】表示部Ａの模式図である。
【図３】画素の模式図である。
【図４】パッシブマトリクス方式による表示装置の模式図である。
【図５】有機ＥＬ素子ＯＬＥＤ１−１の概略模式図である。
【符号の説明】
１ ディスプレイ
３ 画素
５ 走査線
６ データ線
７ 電源ライン
１０ 有機ＥＬ素子
１１ スイッチングトランジスタ
１２ 駆動トランジスタ
１３ コンデンサ
Ａ 表示部
Ｂ 制御部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic electroluminescence element (also referred to as an organic EL element) and a display device.
[0002]
[Prior art]
As a light emitting type electronic display device, there is an electroluminescence display (ELD). ELD components include an inorganic electroluminescent element (inorganic EL element) and an organic electroluminescent element (organic EL element). Inorganic electroluminescent devices have been used as flat light sources, but require a high AC voltage to drive the light emitting devices.
[0003]
An organic electroluminescence element has a configuration in which a light-emitting layer containing a compound that emits light is sandwiched between a cathode and an anode. Electrons and holes are injected into the light-emitting layer and recombined to generate excitons (excitons). An element that emits light by utilizing light emission (fluorescence / phosphorescence) when the exciton is generated and deactivated, and can emit light at a voltage of several volts to several tens of volts. Because of this, it is rich in viewing angle, has high visibility, and is a thin-film type completely solid-state device, which has attracted attention from the viewpoint of space saving and portability.
[0004]
However, development of an organic EL element that emits light with high efficiency and low power consumption is desired for an organic EL element for practical use in the future.
[0005]
For example, in Japanese Patent No. 3093796, a stilbene derivative, a distyrylarylene derivative, or a tristyrylarylene derivative is doped with a trace amount of a phosphor, thereby achieving an improvement in light emission luminance and a long life of the device.
[0006]
Further, an element having an organic light emitting layer in which an 8-hydroxyquinoline aluminum complex is used as a host compound and a small amount of a phosphor is added thereto (JP-A-63-264692), and an 8-hydroxyquinoline aluminum complex as a host compound An element having an organic light emitting layer doped with a quinacridone dye (Japanese Patent Laid-Open No. 3-255190) is known. As described above, by doping the phosphor having a high fluorescence quantum yield, the emission luminance is improved as compared with the conventional device.
[0007]
However, the light emission from the doped small amount of phosphor is light emission from an excited singlet. When light emission from an excited singlet is used, the generation ratio between a singlet exciton and a triplet exciton is 1: 1. 3, the probability of generation of the luminescent excited species is 25%, and the light extraction efficiency is about 20%._ext) Is 5%. However, since Princeton University reported an organic EL device using phosphorescence from an excited triplet (MA Baldo et al., Nature, 395, 151-154 (1998)), Research into phosphorescent materials has become active (e.g., MA Baldo et al., Nature, 403, 17, 750-753 (2000); U.S. Patent No. 6,097,147). Specification). When the excited triplet is used, the upper limit of the internal quantum efficiency is 100%, so that the luminous efficiency is up to four times in principle compared to the case of the excited singlet, and the performance almost equal to that of the cold cathode tube is obtained. It is also applicable to applications and is attracting attention.
[0008]
When the phosphorescent compound is used as a dopant, the host needs to have a light emission maximum wavelength in a shorter wavelength region than the light emission maximum wavelength of the phosphorescent compound, but there are other conditions to be satisfied. I understand that.
[0009]
The 10th International Works on Inorganic and Organic Electroluminescence (EL'00, Hamamatsu) reports several reports on phosphorescent compounds. For example, Ikai et al. Use a hole transporting compound as a host for a phosphorescent compound. Further, M. E. FIG. Tompson et al. Use various electron transporting materials as a host of a phosphorescent compound and dope them with a novel iridium complex. Further, Tsutsui et al. Obtain high luminous efficiency by introducing a hole blocking layer.
[0010]
For the host compound of the phosphorescent compound, for example, C.I. Adachi et al. , Appl. Phys. Lett. 77, p. 904 (2000), etc., but it is necessary to take a newer approach to the properties required for the host compound in order to obtain a high-brightness organic electroluminescent device. .
[0011]
However, none of the reports has obtained a configuration capable of achieving both improvement in light emission luminance and durability.
[0012]
On the other hand, in an element having a light emitting layer containing a host compound and a phosphorescent compound as a dopant compound, examples of applying a carbazole derivative as the host compound include 4,4′-N, N′-. Dicarbazole-biphenyl (CBP) and the like are the most common, but the use of these conventional carbazole derivatives has not achieved both luminous efficiency and durability. In particular, satisfactory luminous efficiency has not been obtained for light having a shorter wavelength than green light.
[0013]
As carbazole derivatives other than CBP, polymer types are described in JP-A-2001-257076 and JP-A-2002-105445, and specific structures are described in JP-A-2001-313179 and JP-A-2002-75645. It is described that the carbazole derivative having the carbazole derivative is particularly effective. However, the device using the carbazole derivative other than the CBP or the device using the carbazole derivative described in Patent Document 1 achieves both luminous efficiency and durability. At present, there is no available configuration.
[0014]
[Patent Document 1]
JP 2002-100476 A
[0015]
[Problems to be solved by the invention]
An object of the present invention is to provide an organic electroluminescence element having high light emission luminance and high luminous efficiency and excellent durability, and a display device having the organic electroluminescence element.
[0016]
[Means for Solving the Problems]
The above object of the present invention has been achieved by the following constitutions.
[0017]
1. An organic electroluminescence device comprising a compound represented by the following general formula (1).
[0018]
General formula (1)
(A)_l-(X)-(B)_n
(Wherein, A and B are monovalent substituents having different structures, X represents an m-valent linking group, A or B contains a hetero element, and l and n each represent A , B, m = l + n, m represents an integer of 2 to 6, and l ≧ 1 and n ≧ 1.)
2. The "highest occupied molecular orbital" HOMO (H) and the "lowest unoccupied molecular orbital" LUMO (H) of the substituent A of the compound represented by the general formula (1), and the hetero element of the substituent A is substituted with carbon. The relationship of the substituted substituent A ′ with the “highest occupied molecular orbital” HOMO (C) and the “lowest unoccupied molecular orbital” LUMO (C) is
HOMO (H) -HOMO (C)> 0
And,
│HOMO (H) -HOMO (C) │-│LUMO (H) -LUMO (C) │> 0
And
The “highest occupied molecular orbital” HOMO (H) and the “lowest unoccupied molecular orbital” LUMO (H) of the substituent B of the compound represented by the general formula (1), and the hetero element of the substituent B is substituted by carbon. The relationship between the “highest occupied molecular orbital” HOMO (C) and the “lowest unoccupied molecular orbital” LUMO (C) of the substituent B ′ is as follows:
LUMO (H) -LUMO (C) <0
And,
| HOMO (H) -HOMO (C) |-| LUMO (H) -LUMO (C) | <0
2. The electroluminescent device according to the above item 1, wherein
[0019]
3. The organic electroluminescence element has a plurality of constituent layers including a light emitting layer, the light emitting layer contains a host compound, and a dopant compound that is a phosphorescent compound, and at least one of the plurality of constituent layers has It contains the compound represented by the general formula (1), the emission maximum wavelength on the short wavelength side of the emission spectrum of the organic EL element is 500 nm or less, and the lowest excited triplet energy level of the host material is 3. The organic electroluminescent device according to the above 1 or 2, wherein the energy is higher than the lowest excited triplet energy level of the dopant compound which is a phosphorescent compound.
[0020]
4. At least one of the plurality of constituent layers is an electron transport layer, and the electron transport layer contains at least one kind of the compound represented by the general formula (1). 9. The organic electroluminescent device according to claim 1.
[0021]
5. 5. The organic electroluminescent device according to the above item 3 or 4, wherein the dopant compound that is a phosphorescent compound is an iridium compound, an osmium compound, or a platinum compound.
[0022]
6. The organic electroluminescence device according to claim 5, wherein the dopant compound that is a phosphorescent compound is an iridium compound.
[0023]
7. 7. The organic electroluminescence device according to the above item 6, wherein the substituent A is anisole, carbazole, indole, an amine alone or a derivative residue.
[0024]
8. 8. The organic electroluminescent device according to 7, wherein the linking group X has a substituent having an absolute value of a steric hindrance parameter (Es) of 0.5 or more.
[0025]
9. A display device comprising the organic electroluminescence element according to any one of the above items 1 to 8.
[0026]
Hereinafter, the present invention will be described in detail.
The present inventors have conducted intensive studies on a phosphorescent material, and as a result, the compound comprising the substituents A, B and the linking group X exhibited excellent solubility, whereby purification efficiency was dramatically improved, It has been found that an amorphous thin film can be easily formed even at room temperature, and that phosphorescence is emitted at a relatively short wavelength, and when the compound of the present invention is used to produce an organic electroluminescent device, the emission luminance and lifetime of the device are improved. This led to the present invention.
[0027]
In particular, the present inventors have found that an organic electroluminescent element which achieves both improvement in light emission luminance, light emission efficiency and durability in blue light emission, and a display device having high light emission luminance and good durability can be provided by using the same. Was.
[0028]
<< Compound Consisting of Substituents A and B or Linking Group X >>
The compound according to the present invention comprising the substituents A and B and the linking group X is represented by the general formula (1).
[0029]
The compound represented by Formula (1) will be described.
In the general formula (1), the substituent A and the substituent B are represented by WinMOPAC ver. 3 and the HOMO and LUMO values obtained by using EF and AM1 as keywords and making the convergence condition grad <1.0, and substituting the hetero element contained in each substituent with carbon. By comparing the HOMO and LUMO values obtained by the above-mentioned method with the above-mentioned substituents, those satisfying one of the following conditions are defined as a substituent A or a substituent B, respectively.
Substituent A:
HOMO (H) -HOMO (C)> 0
And,
│HOMO (H) -HOMO (C) │-│LUMO (H) -LUMO (C) │> 0
Substituent B:
LUMO (H) -LUMO (C) <0
And,
| HOMO (H) -HOMO (C) |-| LUMO (H) -LUMO (C) | <0
HOMO (H), LUMO (H): a substituent containing a hetero element.
HOMO (C), LUMO (C): substituents in which a hetero element is substituted by carbon.
[0030]
Here, HOMO, LUMO, and the like of the substituent A and the substituent B are calculated using a compound in which the bonding position of each substituent is replaced with hydrogen.
[0031]
The substituent A and the substituent B are not particularly limited as long as they are compounds satisfying the above formula, but the following compounds are preferable.
[0032]
The candidate for the substituent A is a group obtained by removing one hydrogen atom at the bonding position from a parent compound such as anisole, carbazole, indole, an amine simple substance or a derivative, and a carbazole derivative is particularly preferable as the parent compound for the substituent A. It is.
[0033]
Examples of the substituent B include fluorinated benzene, trifluoromethylbenzene, thiophene, selenophene, pyrrole, imidazole, pyrazole, pyridine, pyrazoline, pyrimidine, pyridazine, triazine, triazole, oxazole, and thiazole. , Oxadiazol, thiadiazol, imidadiale, arylborane (diarylborane, triarylborane, etc.), or a parent compound such as a derivative thereof in which one hydrogen atom has been removed from the parent compound at the bonding position.
[0034]
In the present invention, the general formula (1) is bonded through a linking group X having substituents A and B.
[0035]
Here, the linking group X will be described.
An Es value defined by Tuft et al. Is known as a numerical value of the magnitude of steric hindrance of a substituent [American Chemical Society Professional Reference Book, 'Exploring QSAR', C.I. Hansh A. Leo et al. R. [Hell Edit].
[0036]
Hereinafter, the ES value will be described.
In general, in the ester hydrolysis reaction under acidic conditions, it is known that the effect of the substituent on the progress of the reaction may be considered to be only steric hindrance. The numerical value of the steric hindrance is the Es value.
[0037]
Substituent X₀Es value of the following chemical reaction formula
X₀-CH₂COORx + H₂O → X₀-CH₂COOH + RxOH
Is substituted with one hydrogen atom of the methyl group of acetic acid by a substituent X₀Reaction rate constant kX when hydrolyzing an α-substituted mono-substituted acetic acid ester derived from an α-substituted mono-substituted acetic acid under acidic conditions, and the following chemical reaction formula
CH₃COORy + H₂O → CH₃COOH + RyOH
(Ry is the same as Rx)
Is obtained from the reaction rate constant kH when the acetate corresponding to the above-mentioned mono-substituted acetate at the α-position is hydrolyzed under acidic conditions.
[0038]
Es = log (kX / kH)
Substituent X₀Due to the steric hindrance, the reaction rate decreases, and as a result, kX <kH, so that the Es value is usually a negative value.
[0039]
When the Es value is actually obtained, the above two reaction rate constants kX and kH are obtained and calculated by the above equation.
[0040]
Specific examples of the Es value are described in Unger, S .; H. Hansch, C .; Prog. Phys. Org. Chem. , 12, 91 (1976). Specific values are also described in “Structure-Activity Relationships of Drugs” (Supplement No. 122 of Chemistry, Nankodo) and “American Chemical Society Professional Reference Book, 'Exploring QSAR' p.81 Table 3-3”. There is. The following is a part of it.
[0041]
[Table 1]

[0042]
Here, it should be noted that the Es value as defined in the present specification is not defined as that of a methyl group as 0, but the hydrogen atom is set to 0, and the Es value is set to 0 for a methyl group. This is the value obtained by subtracting 1.24 from the value.
[0043]
In the general formula (1), the connecting group X represents an m-valent, that is, a divalent or higher-valent connecting group, and m represents an integer of 2 to 6. Preferred is a linking group formed of carbon, silicon, nitrogen, boron, oxygen, sulfur, a metal, a metal ion, and more preferably a carbon atom, a nitrogen atom, a silicon atom, a boron atom, an oxygen atom, a sulfur atom, It is a linking group comprising an aromatic hydrocarbon ring and an aromatic hetero ring, and more preferably a carbon atom, a silicon atom, an aromatic hydrocarbon ring and an aromatic hetero ring. Specific examples of the linking group X include the following.
[0044]
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[0045]
The linking group may further have a substituent, and is preferably an arylene group, and more preferably has a substituent having an absolute value of the Es value of 0.5 or more adjacent to the linking position. ing.
[0046]
Hereinafter, specific examples of the compound represented by Formula (1) will be shown, but the present invention is not limited thereto.
[0047]
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[0048]
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[0049]
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[0050]
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[0051]
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[0052]
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[0053]
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[0054]
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[0055]
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[0056]
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[0057]
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[0058]
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[0059]
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[0060]
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[0061]
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[0062]
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[0063]
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[0064]
The compound represented by the general formula (1) may be any of the following layers (for example, a hole transport layer, a light emitting layer, a hole block layer, and an electron transport layer) constituting an organic electroluminescence device. May be contained, particularly, when contained in the light-emitting layer as a host compound as described later, or when contained in the electron transport layer, further exhibit high emission luminance, high luminous efficiency, and It has been found that an organic electroluminescent device having improved durability can be provided.
[0065]
The content of the compound represented by the general formula (1) according to the present invention in any one of the layers constituting the organic electroluminescence device is preferably 50% by mass or more, and more preferably 80% by mass or more. It is from 90% by mass to 95% by mass, particularly preferably from 90% by mass to 95% by mass.
[0066]
The compound represented by the general formula (1) according to the present invention can be produced by a conventionally known method. For example, the synthesis method described in Synthesis Example 1 (synthesis of compound **) shown below. And can be synthesized.
[0067]
Hereinafter, one embodiment of a synthesis example of the compound represented by the general formula (1) according to the present invention will be described.
[0068]
<< Synthesis Example 1: Synthesis of Compound A-1 >>
[0069]
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[0070]
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[0071]
Synthesis of 3-iodo-6-methyl-9-ethylcarbazole
From 50 g of 3-amino-6-methyl-9-ethylcarbazole, 25 g of 3-iodo-6-methyl-9-ethylcarbazole was synthesized by the Sandmeyer reaction.
[0072]
Synthesis of reaction product 1
A tetrahydrofuran solution containing 1.7 g of 3-iodo-6-methyl-9-ethylcarbazole was added dropwise at −78 ° C., 3.5 ml of tert-butyllithium was stirred, and after 30 minutes, 1.5 ml of trimethoxyborane was added dropwise. And stirred for 12 hours. The solution after stirring was extracted and concentrated to obtain a reaction product 1.
[0073]
The reaction product 2 was synthesized according to the above scheme with reference to the following literature. Shigehiro Yamaguchi et al. , Org. Lett. , 2000, 4129.
Synthesis of Compound A-1
The obtained reaction products 1 and 2 were converted to tetrakistriphenylphosphine palladium (Pd (PPh₃)₄) 0.4 g, dissolved in a mixed solvent composed of 300 ml of tetrahydrofuran containing 1.0 g of potassium carbonate and 30 ml of water, and stirred at 70 ° C. for 6 hours.
[0074]
The compound A-1 (1.5 g) was obtained by performing extraction, drying, concentration, column purification, and sublimation purification of the reaction solution.
[0075]
The molecular structure of Compound A-1 was confirmed to be the target compound by NMR (nuclear magnetic resonance spectrum) and mass spectrum.
[0076]
<< Synthesis Example 2: Synthesis of Compound A-7 >>
Synthesis of 3,5-dibromo-2,4,6-trimethylphenyltrimethylsilane
[0077]
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[0078]
Synthesis of 3-iodo-6-methyl-9-ethylcarbazole
From 50 g of 3-amino-6-methyl-9-ethylcarbazole, 25 g of 3-iodo-6-methyl-9-ethylcarbazole was synthesized by the Sandmeyer reaction.
[0079]
For the synthesis of tribromomesitylene, reference was made to the following literature.
Shigehiro Yamaguchi et al. , Org. Lett. , 2000, 4129.
Synthesis of 3,5-dibromo-2,4,6-trimethylphenyltrimethylsilane To 300 ml of a THF solution containing 7.2 g of tribromomesitylene, 130 ml of n-butyllithium was dropped and mixed at -78 ° C, and 3.7 ml of trimethylsilane chloride was added. The product obtained by dropwise addition and stirring at room temperature for 6 hours was purified by silica gel column chromatography to synthesize 7.0 g of 3,5-dibromo-2,4,6-trimethylphenyltrimethylsilane.
[0080]
Synthesis of Compound A-7
[0081]
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[0082]
Synthesis of 3,5-dipentafluorophenyl-2,4,6-trimethylphenyltrimethylsilane
From 7.0 g of 3,5-dibromo-2,4,6-trimethylphenyltrimethylsilane, 12.7 g of pentafluorophenylboronic acid, 4.0 g of tetrakistriphenylphosphine palladium, 500 ml of tetrahydrofuran containing 10 g of potassium carbonate, and 50 ml of water The product obtained by dissolving in a mixed solvent constituted and stirring at 70 ° C. for 8 hours is purified by silica gel column chromatography to obtain 3,5-dipentafluorophenyl-2,4,6-trimethylphenyl. 2.6 g of trimethylsilane was synthesized.
[0083]
Synthesis of 3,5-dipentafluorophenyl-2,4,6-trimethylbromobenzene
0.9 g of NBS was added dropwise to 200 ml of a DMF solution containing 2.6 g of 3,5-dipentafluorophenyl-2,4,6-trimethylphenyltrimethylsilane, and the resulting product was stirred for 4 hours to obtain a product obtained by silica gel column chromatography. Purification by chromatography and recrystallization gave 3,5-di (pentafluorophenyl) -2,4,6-trimethylbromobenzene (3.5 g).
[0084]
Synthesis of Compound A-7
The obtained reaction product 1 and 3,5-dipentafluorophenyl-2,4,6-trimethylbromobenzene (2.4 g) were mixed with 0.4 g of tetrakistriphenylphosphine palladium and 1.0 g of potassium carbonate. It was dissolved in a mixed solvent composed of 300 ml of tetrahydrofuran and 30 ml of water, and stirred at 70 ° C. for 9 hours.
[0085]
The reaction solution was subjected to extraction, drying, concentration, column purification and sublimation purification to obtain 1.0 g of compound A-7.
[0086]
The molecular structure of Compound A-7 was confirmed to be the desired product by NMR (nuclear magnetic resonance spectrum) and mass spectrum.
[0087]
《Host compound》
The host compound according to the present invention will be described.
[0088]
Here, the “host compound” means a compound having the largest mixing ratio (mass) in a light emitting layer composed of two or more compounds, and the other compounds are called “dopant compounds”. . For example, the light-emitting layer is composed of two types of compound a and compound b, and if the mixing ratio is a: b = 10: 90, compound a is a dopant compound and compound b is a host compound. Further, the light emitting layer is composed of three kinds of compound a, compound b and compound c, and if the mixing ratio is a: b: c = 5: 10: 85, compound a and compound b are dopant compounds, Compound c is the host compound.
[0089]
Here, as the host compound according to the present invention, a compound represented by the general formula (1), a conventionally known phosphorescent compound, a fluorescent compound described below, and the like can be used.
[0090]
《Phosphorescent compound》
The phosphorescent compound used as a dopant compound according to the present invention will be described.
[0091]
The “phosphorescent compound” is a compound in which light emission from an excited triplet is observed, and has a phosphorescence quantum yield of 0.001 or more at 25 ° C. The phosphorescence quantum yield is preferably at least 0.01, more preferably at least 0.1.
[0092]
The phosphorescence quantum yield can be measured by the method described in Spectroscopy II, pp. 398 (1992 edition, Maruzen) of the fourth edition of Experimental Chemistry Course 7. Although the phosphorescence quantum yield in a solution can be measured using various solvents, the phosphorescent compound according to the present invention preferably achieves the above-mentioned phosphorescence quantum yield in any of the solvents.
[0093]
The phosphorescent compound according to the present invention is preferably a complex compound containing a metal belonging to Groups 8 to 10 of the periodic table, and more preferably an iridium compound, an osmium compound, or a platinum compound (platinum complex compound). And the like, among which the iridium compound is most preferably used.
[0094]
In the present invention, the lowest excited triplet energy level of the host material is preferably 1.05 to 1.38 times the lowest excited triplet energy level of the light emitting material.
[0095]
In the present invention, the lowest excitation triplet energy level of the host material is preferably 68 kcal / mol (284.9 kJ / mol) or more and 90 kcal / mol (377.1 kJ / mol) or less.
[0096]
In the organic electroluminescence device according to the present invention, the lowest excited triplet energy level of the organic material contained in the layer adjacent to the light emitting layer is higher than the lowest excited triplet energy level of the material forming the light emitting layer. preferable.
[0097]
In the organic electroluminescence device according to the present invention, the lowest excited triplet energy level of the organic material contained in the layer adjacent to the light emitting layer is 1.05 times the lowest excited triplet energy level of the material forming the light emitting layer. It is preferably at least 1.38 times.
[0098]
In the organic electroluminescence device according to the present invention, the lowest excitation triplet energy level of the organic material contained in the layer adjacent to the light emitting layer is 68 kcal / mol (284.9 kJ / mol) or more and 90 kcal / mol (377. (1 kJ / mol) or less.
[0099]
Hereinafter, specific examples of the phosphorescent compound according to the present invention are shown, but the present invention is not limited thereto. These compounds are described, for example, in Inorg. Chem. 40, 1704-1711.
[0100]
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[0101]
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[0102]
Embedded image

[0103]
《Fluorescent compound》
The fluorescent compound used in the present invention will be described.
[0104]
In the present invention, in addition to the host compound and the phosphorescent compound, at least one fluorescent compound having a fluorescence maximum wavelength may be contained in a region longer than the maximum wavelength of light emission from the phosphorescent compound. In this case, by the energy transfer from the host compound and the phosphorescent compound, electroluminescence as an organic electroluminescence element (organic EL element) can be obtained from a fluorescent compound. Preferred as the fluorescent compound is a compound having a high fluorescence quantum yield in a solution state. Here, the fluorescence quantum yield is preferably 10% or more, more preferably 30% or more.
[0105]
Specific fluorescent compounds include coumarin dyes, pyran dyes, cyanine dyes, croconium dyes, squarium dyes, oxobenzanthracene dyes, fluorescein dyes, rhodamine dyes, pyrylium dyes, and perylene dyes , A stilbene-based dye, a polythiophene-based dye, or a rare-earth complex-based phosphor.
[0106]
The fluorescence quantum yield here can also be measured by the method described in Spectroscopy II, page 362 (1992 edition, Maruzen) of the 4th edition of Experimental Chemistry Lecture 7.
[0107]
The phosphorescent compound has a phosphorescence quantum yield as described above of not less than 0.001 at 25 ° C. and a phosphorescent emission maximum wavelength longer than the fluorescence maximum wavelength of the fluorescent compound serving as the host. . Thereby, for example, light emission of the phosphorescent compound using a phosphorescent compound having a longer wavelength than the emission maximum wavelength of the fluorescent compound serving as the host, that is, utilizing the triplet state, electroluminescence at a wavelength longer than the fluorescence maximum wavelength of the host compound EL element can be obtained. Accordingly, the maximum phosphorescent emission wavelength of the phosphorescent compound used is not particularly limited, and in principle, the emission wavelength obtained by selecting a central metal, a ligand, a substituent of a ligand, and the like. Can be changed.
[0108]
For example, by using a fluorescent compound having a fluorescent maximum wavelength in a region of 350 nm to 440 nm as a host compound and using, for example, an iridium complex having phosphorescence in a green region, an organic EL element which emits light in the green region can be obtained. I can do it.
[0109]
In another embodiment, as described above, in addition to the fluorescent compound a and the phosphorescent compound as the host compound, another region having a fluorescence maximum wavelength longer than the maximum wavelength of light emission from the phosphorescent compound. In some cases, at least one kind of the fluorescent compound b is contained. By the energy transfer from the fluorescent compound a and the phosphorescent compound, the electroluminescence as the organic EL device can also obtain the light emission from the fluorescent compound b. .
[0110]
The color emitted by the fluorescent compound used in the present invention is shown in FIG. 4.16 on page 108 of “New Edition of Color Science Handbook” (edited by The Japan Society of Color Science, University of Tokyo Press, 1985), and the spectral radiance meter CS-1000. (Minolta) is determined by the color when the result of measurement is applied to the CIE chromaticity coordinates.
[0111]
<< Layer composition of organic electroluminescence device >>
The layer configuration of the organic electroluminescence device (organic EL device) according to the present invention will be described.
[0112]
The organic EL device of the present invention has a structure in which at least one light emitting layer is sandwiched between a pair of electrodes (anode, cathode). Here, in a broad sense, the light-emitting layer is a layer that emits light when an electric current is applied to an electrode formed of a cathode and an anode. Specifically, when an electric current is applied to an electrode formed of a cathode and an anode, Refers to a layer containing a compound that emits light.
[0113]
The organic EL device of the present invention has a structure in which a hole transport layer, an electron transport layer, an anode buffer layer, a cathode buffer layer, and the like are provided in addition to a light emitting layer as necessary, and is sandwiched between a cathode and an anode. Specifically, the structure shown below is mentioned.
[0114]
(I) anode / light-emitting layer / cathode
(Ii) anode / hole transport layer / light-emitting layer / cathode
(Iii) anode / light-emitting layer / electron transport layer / cathode
(Iv) anode / hole transport layer / emission layer / electron transport layer / cathode
(V) anode / anode buffer layer / hole transport layer / emission layer / electron transport layer / cathode buffer layer / cathode
<< Light-emitting layer >>
The light emitting layer according to the present invention will be described.
[0115]
In the present invention, for example, it is preferable to form the light emitting layer using the compound represented by the general formula (1) and a phosphorescent dopant compound. Here, as a forming method, a thin film can be formed by a known method such as a vapor deposition method, a spin coating method, a casting method, and an LB method. In the present invention, a molecular deposition film is particularly preferable. Here, the molecular deposition film refers to a thin film formed by depositing the compound from a gaseous state or a film formed by solidifying the compound from a molten state or a liquid state. In general, a molecular deposition film can be distinguished from a thin film (molecule accumulation film) formed by the LB method by a difference in an aggregated structure and a higher-order structure and a functional difference resulting therefrom.
[0116]
Further, as described in JP-A-57-51781, this light-emitting layer is prepared by dissolving the above compound as a light-emitting material in a solvent together with a binder such as a resin in a solvent, and then spin-coating the solution. It can be obtained by forming a thin film by coating with such as.
[0117]
(Thickness of light emitting layer)
The thickness of the light emitting layer thus formed is not particularly limited and can be appropriately selected depending on the situation, but is preferably adjusted to a range of 5 nm to 5 μm.
[0118]
Next, other layers constituting an organic EL element in combination with a light emitting layer, such as a hole injection layer, a hole transport layer, an electron injection layer, and an electron transport layer, will be described.
[0119]
《Hole injection layer, hole transport layer, electron injection layer, electron transport layer》
The hole injection layer and the hole transport layer used in the present invention have a function of transmitting holes injected from the anode to the light emitting layer, and the hole injection layer and the hole transport layer are connected to the anode and the light emitting layer. By intervening between them, many holes are injected into the light emitting layer at a lower electric field, and furthermore, electrons injected from the cathode, the electron injection layer, or the electron transport layer into the light emitting layer, An electron barrier existing at the interface of the hole injection layer or the hole transport layer accumulates at the interface in the light emitting layer, resulting in an element having excellent light emitting performance, such as improved light emitting efficiency.
[0120]
《Hole injection material, hole transport material》
The material of the hole injection layer and the hole transport layer (hereinafter, referred to as a hole injection material and a hole transport material) has a property of transmitting the holes injected from the anode to the light emitting layer. There is no particular limitation as long as the material is a conventional photoconductive material, a material commonly used as a hole charge injection / transport material, a hole injection layer of an EL element, and a known material used for a hole transport layer. Any one of them can be selected and used.
[0121]
The hole injection material and the hole transport material have any of hole injection or transport and electron barrier properties, and may be any of an organic substance and an inorganic substance. Examples of the hole injection material and the hole transport material include a triazole derivative, an oxadiazole derivative, an imidazole derivative, a polyarylalkane derivative, a pyrazoline derivative and a pyrazolone derivative, a phenylenediamine derivative, an arylamine derivative, an amino-substituted chalcone derivative, and oxazole. Derivatives, styrylanthracene derivatives, fluorenone derivatives, hydrazone derivatives, stilbene derivatives, silazane derivatives, aniline-based copolymers, or conductive polymer oligomers, particularly thiophene oligomers, are mentioned. As the hole injecting material and the hole transporting material, those described above can be used, and porphyrin compounds, aromatic tertiary amine compounds and styrylamine compounds, particularly aromatic tertiary amine compounds may be used. preferable.
[0122]
Representative examples of the aromatic tertiary amine compound and styrylamine compound include N, N, N ', N'-tetraphenyl-4,4'-diaminophenyl; N, N'-diphenyl-N, N' -Bis (3-methylphenyl)-[1,1'-biphenyl] -4,4'-diamine (TPD); 2,2-bis (4-di-p-tolylaminophenyl) propane; 1,1- Bis (4-di-p-tolylaminophenyl) cyclohexane; N, N, N ', N'-tetra-p-tolyl-4,4'-diaminobiphenyl; 1,1-bis (4-di-p- Tolaminophenyl) -4-phenylcyclohexane; bis (4-dimethylamino-2-methylphenyl) phenylmethane; bis (4-di-p-tolylaminophenyl) phenylmethane; N, N'-diphenyl-N, N -Di (4-methoxyphenyl) -4,4'-diaminobiphenyl; N, N, N ', N'-tetraphenyl-4,4'-diaminodiphenyl ether; 4,4'-bis (diphenylamino) quadri Phenyl; N, N, N-tri (p-tolyl) amine; 4- (di-p-tolylamino) -4 '-[4- (di-p-tolylamino) styryl] stilbene; 4-N, N-diphenyl Amino- (2-diphenylvinyl) benzene; 3-methoxy-4'-N, N-diphenylaminostilbenzene; N-phenylcarbazole, and 2 described in U.S. Pat. No. 5,061,569. Having a plurality of condensed aromatic rings in the molecule, for example, 4,4'-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (α-NPD); No. 08688,4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine in which three triphenylamine units are linked in a star burst form MTDATA).
[0123]
Further, a polymer material in which these materials are introduced into a polymer chain, or a polymer material in which these materials are used as a polymer main chain, can also be used.
[0124]
Alternatively, an inorganic compound such as p-type Si or p-type SiC can be used as the hole injection material or the hole transport material. The hole injection layer and the hole transport layer are formed by thinning the hole injection material and the hole transport material by a known method such as a vacuum evaporation method, a spin coating method, a casting method, and an LB method. Can be formed.
[0125]
(Thickness of hole injection layer, thickness of hole transport layer)
The thicknesses of the hole injection layer and the hole transport layer are not particularly limited, but are preferably adjusted to a range of about 5 nm to 5 μm. The hole injecting layer and the hole transporting layer may have a single-layer structure composed of one or two or more of the above materials, or may have a laminated structure composed of a plurality of layers having the same composition or different compositions.
[0126]
《Electron transport layer, electron transport material》
The electron transporting layer according to the present invention may have a function of transmitting electrons injected from the cathode to the light emitting layer, and any material may be selected from conventionally known compounds. Can be.
[0127]
Examples of materials used for the electron transport layer (hereinafter, referred to as electron transport materials) include nitro-substituted fluorene derivatives, diphenylquinone derivatives, thiopyran dioxide derivatives, heterocyclic tetracarboxylic anhydrides such as naphthalene perylene, carbodiimide, Examples include fluorenylidenemethane derivatives, anthraquinodimethane and anthrone derivatives, and oxadiazole derivatives. Further, in the oxadiazole derivative, a thiadiazole derivative in which the oxygen atom of the oxadiazole ring is substituted with a sulfur atom, and a quinoxaline derivative having a quinoxaline ring known as an electron withdrawing group can also be used as the electron transport material.
[0128]
Further, a polymer material in which these materials are introduced into a polymer chain or a polymer material in which these materials are used as a main chain of a polymer can also be used.
[0129]
Or a metal complex of an 8-quinolinol derivative, for example, tris (8-quinolinol) aluminum (Alq), tris (5,7-dichloro-8-quinolinol) aluminum, tris (5,7-dibromo-8-quinolinol) aluminum, Tris (2-methyl-8-quinolinol) aluminum, tris (5-methyl-8-quinolinol) aluminum, bis (8-quinolinol) zinc (Znq), and the like, and the central metals of these metal complexes are In, Mg, Cu , Ca, Sn, Ga or Pb can also be used as the electron transport material.
[0130]
In addition, metal-free or metal phthalocyanine, and those whose terminals are substituted with an alkyl group, a sulfonic acid group, or the like, can also be preferably used as the electron transport material. Alternatively, a distyrylpyrazine derivative exemplified as a material of the light-emitting layer can also be used as an electron transporting material, and, like the hole injection layer and the hole transport layer, inorganic materials such as n-type Si and n-type SiC. Semiconductors can also be used as electron transport materials.
[0131]
The electron transport layer can be formed by forming the above compound by a known thin film forming method such as a vacuum evaporation method, a spin coating method, a casting method, and an LB method.
[0132]
(Thickness of electron transport layer)
The thickness of the electron transport layer is not particularly limited, but is preferably adjusted in the range of 5 nm to 5 μm. The electron transport layer may have a single-layer structure composed of one or more of these electron transport materials, or may have a laminated structure composed of a plurality of layers having the same composition or different compositions.
[0133]
Further, in the present invention, the fluorescent compound is not limited to the light emitting layer alone, and is the same as the fluorescent compound serving as the host compound of the phosphorescent compound in the hole transport layer adjacent to the light emitting layer or the electron transport layer. At least one kind of fluorescent compound having a maximum fluorescence wavelength may be contained in the region, whereby the luminous efficiency of the EL element can be further increased. As the fluorescent compound contained in the hole transporting layer or the electron transporting layer, a fluorescent compound having a fluorescence maximum wavelength in the range of 330 nm to 440 nm, more preferably 360 nm to 410 nm as in the light emitting layer. Compounds are used.
[0134]
Alternatively, in the present invention, it is preferable that the compound represented by the general formula (1) is contained in the electron transport layer from the viewpoint of luminous efficiency and durability.
[0135]
《Substrate (also called support)》
The substrate preferably used for the organic EL device of the present invention is not particularly limited in the type of glass, plastic, or the like, and is not particularly limited as long as it is transparent. Substrates preferably used in the organic EL device of the present invention include, for example, glass, quartz, and light-transmitting plastic films.
[0136]
Examples of the light-transmitting plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, and polycarbonate (PC). , Cellulose triacetate (TAC), cellulose acetate propionate (CAP) and the like.
[0137]
Next, a preferred example of manufacturing the organic EL device will be described. As an example, a method for manufacturing an EL device including the above-described anode / hole injection layer / hole transport layer / light-emitting layer / electron transport layer / electron injection layer / cathode will be described.
[0138]
First, a thin film made of a desired electrode material, for example, an anode material, is formed on a suitable substrate by a method such as evaporation or sputtering so as to have a thickness of 1 μm or less, preferably in the range of 10 to 200 nm. Make the anode. Next, a thin film composed of a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer, which are element materials, is formed thereon.
[0139]
Further, a buffer layer (electrode interface layer) may be present between the anode and the light emitting layer or the hole injection layer and between the cathode and the light emitting layer or the electron injection layer.
[0140]
The buffer layer is a layer provided between the electrode and the organic layer for lowering the driving voltage and improving the luminous efficiency. The “organic EL device and the forefront of its industrialization (published by NTT Corporation on November 30, 1998) )), Vol. 2, Chapter 2, "Electrode Materials" (pages 123 to 166), and includes an anode buffer layer and a cathode buffer layer.
[0141]
The details of the anode buffer layer are also described in JP-A-9-45479, JP-A-9-260062, JP-A-8-288069 and the like. As a specific example, a phthalocyanine buffer layer represented by copper phthalocyanine And an oxide buffer layer represented by vanadium oxide, an amorphous carbon buffer layer, and a polymer buffer layer using a conductive polymer such as polyaniline (emeraldine) or polythiophene.
[0142]
The details of the cathode buffer layer are also described in JP-A-6-325871, JP-A-9-17574, and JP-A-10-74586, and specifically, metals represented by strontium, aluminum, and the like. Examples include a buffer layer, an alkali metal compound buffer layer represented by lithium fluoride, an alkaline earth metal compound buffer layer represented by magnesium fluoride, and an oxide buffer layer represented by aluminum oxide and lithium oxide.
[0143]
The buffer layer is desirably an extremely thin film, and the thickness is preferably in the range of 0.1 to 100 nm, depending on the material.
[0144]
Further, in addition to the above-mentioned basic constituent layers, layers having other functions may be laminated as necessary. For example, JP-A-11-204258, JP-A-11-204359, and "Organic EL Device and Its Industrialization A front layer (published by NTT Corporation on November 30, 1998) ", page 237, etc., may have a functional layer such as a hole blocking (hole block) layer.
[0145]
The buffer layer may function as a light emitting layer when at least one compound represented by the general formula (1) or (2) is present in at least one of the cathode buffer layer and the anode buffer layer. Good.
[0146]
"electrode"
Next, the electrodes of the organic EL element will be described. The electrodes of the organic EL element are composed of a cathode and an anode. As the anode in this organic EL element, a metal, an alloy, an electrically conductive compound, or a mixture thereof having a large work function (4 eV or more) as an electrode material is preferably used. Specific examples of such an electrode material include metals such as Au, CuI, indium tin oxide (ITO), and SnO.₂And a transparent conductive material such as ZnO.
[0147]
The above-mentioned anode may form a thin film of these electrode substances by a method such as vapor deposition or sputtering, and may form a pattern of a desired shape by a photolithography method, or when the pattern accuracy is not so required (about 100 μm or more). In the above, a pattern may be formed via a mask having a desired shape at the time of vapor deposition or sputtering of the electrode material. When light is extracted from the anode, the transmittance is desirably greater than 10%, or the sheet resistance of the anode is preferably several hundred Ω / □ or less. Further, although the thickness depends on the material, it is usually selected in the range of 10 nm to 1 μm, preferably 10 nm to 200 nm.
[0148]
On the other hand, as the cathode, those having a low work function (4 eV or less) metal (referred to as an electron injecting metal), an alloy, an electrically conductive compound, and a mixture thereof as an electrode material are preferably used. Specific examples of such an electrode material include sodium, sodium-potassium alloy, magnesium, lithium, magnesium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al₂O₃) Mixtures, indium, lithium / aluminum mixtures, rare earth metals and the like. Among them, a mixture of an electron injecting metal and a second metal which is a metal having a large work function and a stable work function, such as a magnesium / silver mixture, magnesium, / Aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide (Al₂O₃) Mixtures, lithium / aluminum mixtures and the like are preferred. The above-mentioned cathode can be produced by forming a thin film from these electrode substances by a method such as vapor deposition or sputtering. Alternatively, the sheet resistance as the cathode is preferably several hundred Ω / □ or less, and the film thickness is usually selected in the range of 10 nm to 1 μm, preferably 50 nm to 200 nm. In order to transmit light, if either the anode or the cathode of the organic EL element is transparent or translucent, the luminous efficiency is advantageously improved.
[0149]
<< Method of manufacturing organic EL element >>
Next, a method for manufacturing an organic EL element will be described.
[0150]
Examples of the method for thinning include the spin coating method, the casting method, and the vapor deposition method as described above, but the vacuum vapor deposition method is preferable because a uniform film is easily obtained and pinholes are hardly generated. When a vacuum deposition method is used for thinning, the deposition conditions vary depending on the type of compound used, the target crystal structure of the molecular deposition film, the association structure, and the like. It is desirable to appropriately select a temperature within a range of 10-6 to 10-3 Pa, a deposition rate of 0.01 nm / sec to 50 nm / sec, a substrate temperature of -50 ° C to 300 ° C, and a film thickness of 5 nm to 5 μm.
[0151]
As described above, a thin film made of a desired electrode material, for example, a material for an anode, is formed on an appropriate substrate by a method such as evaporation or sputtering so as to have a thickness of 1 μm or less, preferably in a range of 10 nm to 200 nm. After forming an anode, a layer thin film including a hole injection layer, a hole transport layer, a light emitting layer, and an electron transport layer / electron injection layer is formed on the anode as described above, and then a cathode is formed thereon. A cathode is provided by forming a thin film made of a substance so as to have a thickness of 1 μm or less, preferably in the range of 50 nm to 200 nm, for example, by vapor deposition or sputtering, and a desired organic EL element is obtained. In the production of this organic EL device, it is preferable to consistently produce the hole injection layer to the cathode in this manner by one evacuation, but the production order is reversed, and the cathode, the electron injection layer, the light emitting layer, A hole injection layer and an anode can be formed in this order. When a DC voltage is applied to the organic EL element obtained in this manner, light emission can be observed by applying a voltage of about 5 to 40 V with the positive polarity of the anode and the negative polarity of the cathode. Alternatively, even if a voltage is applied in the opposite polarity, no current flows and no light emission occurs. Further, when an AC voltage is applied, light is emitted only when the anode is in the + state and the cathode is in the-state. The waveform of the applied alternating current may be arbitrary.
[0152]
《Display device》
The organic EL element of the present invention may be used as a kind of lamp for illumination or an exposure light source, a projection device of a type for projecting an image, or a display device of a type for directly viewing a still image or a moving image. (Display). When used as a display device for reproducing moving images, the driving method may be either a simple matrix (passive matrix) method or an active matrix method. Alternatively, a full-color display device can be manufactured by using two or more kinds of the organic EL elements of the present invention having different emission colors.
[0153]
BEST MODE FOR CARRYING OUT THE INVENTION
An example of a display device including the organic EL element of the present invention will be described below with reference to the drawings.
[0154]
FIG. 1 is a schematic diagram illustrating an example of a display device including an organic EL element. FIG. 3 is a schematic diagram of a display such as a mobile phone for displaying image information by light emission of an organic EL element.
[0155]
The display 1 includes a display unit A having a plurality of pixels, a control unit B that performs image scanning of the display unit A based on image information, and the like.
[0156]
The control unit B is electrically connected to the display unit A, sends a scanning signal and an image data signal to each of the plurality of pixels based on image information from the outside, and the pixels for each scanning line are converted into an image data signal by the scanning signal. In response, the light is sequentially emitted, the image is scanned, and the image information is displayed on the display unit A.
[0157]
FIG. 2 is a schematic diagram of the display unit A.
The display section A has a wiring section including a plurality of scanning lines 5 and data lines 6 and a plurality of pixels 3 on a substrate. The main members of the display unit A will be described below.
[0158]
The figure shows a case where the light emitted from the pixel 3 is extracted in the direction of the white arrow (downward).
[0159]
The scanning lines 5 and the plurality of data lines 6 of the wiring portion are each made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a grid pattern and are connected to the pixels 3 at orthogonal positions (for details, FIG. Not shown).
[0160]
When a scanning signal is applied from the scanning line 5, the pixel 3 receives an image data signal from the data line 6 and emits light according to the received image data. By appropriately arranging pixels in a red region, pixels in a green region, and pixels in a blue region on the same substrate, full-color display becomes possible.
[0161]
Next, a light emitting process of the pixel will be described.
FIG. 3 is a schematic diagram of a pixel.
[0162]
Each pixel includes an organic EL element 10, a switching transistor 11, a driving transistor 12, a capacitor 13, and the like. A full-color display can be performed by using red, green, and blue light-emitting organic EL elements as the organic EL elements 10 in a plurality of pixels and juxtaposing them on the same substrate.
[0163]
In FIG. 3, an image data signal is applied from the control unit B to the drain of the switching transistor 11 via the data line 6. When a scanning signal is applied to the gate of the switching transistor 11 from the control unit B via the scanning line 5, the driving of the switching transistor 11 is turned on, and the image data signal applied to the drain is transferred to the capacitor 13 and the driving transistor 12. Transmitted to the gate.
[0164]
By transmitting the image data signal, the capacitor 13 is charged according to the potential of the image data signal, and the driving of the drive transistor 12 is turned on. The driving transistor 12 has a drain connected to the power supply line 7, a source connected to the electrode of the organic EL element 10, and from the power supply line 7 to the organic EL element 10 according to the potential of the image data signal applied to the gate. Current is supplied.
[0165]
When the scanning signal is transferred to the next scanning line 5 by the sequential scanning of the control unit B, the driving of the switching transistor 11 is turned off. However, even when the driving of the switching transistor 11 is turned off, the capacitor 13 holds the potential of the charged image data signal, so that the driving of the driving transistor 12 is kept on and the next scanning signal is applied. The light emission of the organic EL element 10 continues until this. When the next scanning signal is applied by the sequential scanning, the driving transistor 12 is driven according to the potential of the next image data signal synchronized with the scanning signal, and the organic EL element 10 emits light.
[0166]
That is, the organic EL element 10 emits light by providing a switching transistor 11 and a driving transistor 12 as active elements to the organic EL elements 10 of each of the plurality of pixels, and emitting light of the organic EL elements 10 of each of the plurality of pixels 3. It is carried out. Such a light emitting method is called an active matrix method.
[0167]
Here, the light emission of the organic EL element 10 may be light emission of a plurality of gradations based on a multi-valued image data signal having a plurality of gradation potentials, or ON / OFF of a predetermined light emission amount based on a binary image data signal. May be.
[0168]
Further, the holding of the potential of the capacitor 13 may be continued until the next scanning signal is applied, or may be discharged immediately before the next scanning signal is applied.
[0169]
The present invention is not limited to the active matrix method described above, but may be a passive matrix light emission drive in which the organic EL element emits light in accordance with a data signal only when a scanning signal is scanned.
[0170]
FIG. 4 is a schematic view of a display device using a passive matrix system. In FIG. 4, a plurality of scanning lines 5 and a plurality of image data lines 6 are provided in a lattice shape facing each other with the pixel 3 interposed therebetween.
[0171]
When the scanning signal of the scanning line 5 is applied by the sequential scanning, the pixels 3 connected to the applied scanning line 5 emit light according to the image data signal.
[0172]
In the passive matrix system, there is no active element in the pixel 3, and the manufacturing cost can be reduced.
[0173]
【Example】
Hereinafter, the present invention will be described in detail with reference to Examples, but embodiments of the present invention are not limited thereto.
[0174]
Example 1
<< HOMO-LUMO calculation of substituents A and B using WinMOPAC >>
Divided into substituents as shown in Compound Examples A-1 to D-8, and manufactured by Fujitsu's WinMOPAC ver. 3, EF and AM1 were used as keywords, and calculations were performed so that the convergence condition was grad <1.0. In addition, calculations were performed by replacing the hetero element of each substituent with a carbon atom, and those satisfying one of the following two conditional expressions were defined as substituent A and substituent B. Here, as the HOMO and LUMO of the substituent, the results obtained by performing calculations on the compound in which the bonding position of each substituent was substituted with hydrogen were used as the HOMO and LUMO of the substituent.
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《Conditional expression》
Substituent A:
HOMO (H) -HOMO (C)> 0 and
│HOMO (H) -HOMO (C) │-│LUMO (H) -LUMO (C) │> 0
Substituent B:
LUMO (H) -LUMO (C) <0 and
| HOMO (H) -HOMO (C) |-| LUMO (H) -LUMO (C) | <0
* (H): a substituent containing a hetero element. * (C): Comparative substituent in which a hetero element has been substituted with carbon.
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Here, in the case where the substitution site of the hetero atom to be substituted is two (divalent), two of the substituted carbon atoms that do not contribute to the bond are calculated using two carbon-hydrogen bonds. I do. That is, when the hetero atom is monovalent, the calculation is performed using three carbon-hydrogen bonds, and when the hetero atom is trivalent, the calculation is performed using one carbon-hydrogen bond. The calculation results are shown below (unit eV).
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Example 2
<< Preparation of organic EL element >>
Organic EL elements OLED1-1 to 1-9 were produced as follows.
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(Production of organic EL element OLED1-1)
After patterning a transparent substrate (NA-45 manufactured by NH Techno Glass Co., Ltd.) in which ITO (indium tin oxide) was formed to a thickness of 150 nm on a glass substrate of 100 mm × 100 mm × 1.1 mm as an anode, the ITO was formed. The transparent support substrate provided with the transparent electrode (anode) was subjected to ultrasonic cleaning in isopropyl alcohol, dried with dry nitrogen gas, and subjected to UV ozone cleaning for 5 minutes.
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This transparent support substrate was fixed to a substrate holder of a commercially available vacuum evaporation apparatus, while 200 mg of α-NPD was put in a molybdenum resistance heating boat, and 200 mg of carbazole derivative (CBP) was put in another molybdenum resistance heating boat. 200 mg of bathocuproine (BCP) in a molybdenum resistance heating boat, 100 mg of a phosphorescent compound (Ir-12) in another molybdenum resistance heating boat, and Alq in another molybdenum resistance heating boat₃Was placed in a vacuum evaporation apparatus.
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Then, the vacuum chamber was 4 × 10^-4After reducing the pressure to Pa, the heating boat containing α-NPD was energized and heated, and was vapor-deposited on the transparent support substrate at a vapor deposition rate of 0.1 nm / sec to provide a hole transport layer having a film thickness of 45 nm. Further, the heating boat containing the CBP (used as a host compound) and the phosphorescent compound Ir-12 (used as a dopant compound) was heated by being energized at a deposition rate of 0.1 nm / sec and 0.01 nm / sec, respectively. A light-emitting layer having a thickness of 20 nm was provided by co-evaporation on the hole transport layer. In addition, the substrate temperature at the time of vapor deposition was room temperature. Further, the heating boat containing the BCP is energized and heated, and is vapor-deposited on the light-emitting layer at a vapor deposition rate of 0.1 nm / sec to provide a 10-nm-thick electron transport layer also serving as a hole blocking layer. Was. On top of that, Alq₃Was heated by applying a current to the heating boat, and vapor-deposited on the electron-transporting layer at a vapor deposition rate of 0.1 nm / sec to further provide an electron injection layer having a thickness of 40 nm. In addition, the substrate temperature at the time of vapor deposition was room temperature.
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Subsequently, 0.5 nm of lithium fluoride and 110 nm of aluminum were deposited to form a cathode buffer layer and a cathode, respectively, to produce an organic EL device OLED1-1 (comparative example).
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FIG. 5 shows a schematic diagram of the organic EL element OLED1-1.
(Production of Organic EL Element OLED1-2 to 1-9)
In the production of the organic EL elements OLED1-1, the organic EL elements OLED1-2 to -1 shown in Table 2 were completely identical except that the following compound was used instead of the host compound CBP used for forming the light emitting layer. -9 was produced.
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The following evaluation was performed about each of the obtained organic EL elements OLED1-1 to OLED1-9.
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<< Evaluation of organic EL element >>
The organic EL device was evaluated as follows, and the results are shown in Table 2.
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《Emission brightness》
In the organic EL element OLED1-1, current began to flow at an initial driving voltage of 3 V, and blue light was emitted from the phosphorescent compound (Ir-12) that was the dopant of the light emitting layer.
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First, under the measurement conditions of the organic EL element OLED1-1 at a temperature of 23 ° C. and in a dry nitrogen gas atmosphere, the emission luminance (cd / m) when a DC voltage of 10 V is applied.²) Was measured. Here, the measurement of the light emission luminance used CS-1000 (made by Minolta).
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Next, in the same manner as the measurement of the organic EL element OLED1-1, the light emission luminance was obtained for the organic EL elements OLED1-2 to 1-9.
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The light emission luminance and light emission efficiency described in Table 2 are shown as relative values when the measured value of the organic EL element OLED1-1 is 100.
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"durability"
In each of the organic EL elements OLED1-1 to 1-9, 10 mA / cm²The time required for the initial luminance to decrease by half when driven at a constant current of, that is, the half-life (durability) is shown as an index of durability. In Table 2, the half-life (durability) of each organic EL element was represented by a relative value when the organic EL element OLED1-1 was 100.
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Table 2 shows the obtained results.
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[Table 2]

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The results obtained from Table 2 will be described in detail. As a host compound of a phosphorescent compound which emits blue light, such as CBP and Comparative Compound 2, the compound having a high planarity has a narrow band gap and emits blue light, and the luminous efficiency. It turns out that it is inferior in point. Further, Comparative Compound 1 has a wider band gap than CBP conventionally used and is improved in light emission luminance and light emission efficiency. However, satisfactory results are not obtained in terms of durability. I understand.
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On the other hand, an organic electroluminescent device (organic EL device) using the carbazole derivative compound represented by the general formula (1) according to the present invention as a host compound has high emission luminance, improved luminous efficiency, and durability. Was found to be very useful as an organic EL device.
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Further, when the performance of the organic EL device manufactured in the same manner as the organic EL devices OLED1-1 to 1-9 except that the phosphorescent compound Ir-12 was changed to Ir-1 or Ir-9 was also evaluated. The same effect was obtained. In particular, the durability was greatly improved. In addition, green light emission was obtained from the element using Ir-1, and red light emission was obtained from the element using Ir-9.
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Example 3
<< Preparation of organic EL elements OLED2-1 to 2-7 >>
Organic EL elements OLED2-1 to 2-7 were produced in the same manner as in Example 1, except that the BCP in the electron transport layer of the organic EL element OLED1-1 was replaced with the above compound as shown in Table 2.
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Next, with respect to the obtained organic EL elements OLED2-1 to 2-7, the emission luminance, the emission efficiency, and the half-life (durability) were measured using the same method as in Example 1. Table 3 shows the obtained results.
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[Table 3]

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From Table 3, it is clear that the sample of the present invention has high luminous luminance and luminous efficiency, and also has excellent durability.
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In addition, it can be seen that the organic EL device according to the present invention, in which the compound represented by the general formula (1) is used for the electron transport layer, has improved light emission luminance and light emission efficiency. It can be seen that the half-life (durability) is significantly improved.
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Example 4
The red, green, and blue light-emitting organic EL elements manufactured in Example 1 were juxtaposed on the same substrate, and an active matrix type full-color display device having the form shown in FIG. 1 was manufactured. Only a schematic diagram of the display unit A of the display device described above is shown. That is, on the same substrate, a wiring portion including a plurality of scanning lines 5 and data lines 6 and a plurality of pixels 3 (pixels in a red region, pixels in a green region, pixels in a blue region, and the like) are arranged side by side. The scanning lines 5 and the plurality of data lines 6 of the wiring portion are each made of a conductive material, and the scanning lines 5 and the data lines 6 are orthogonal to each other in a grid and are connected to the pixels 3 at orthogonal positions (details). Is not shown). The plurality of pixels 3 are driven by an active matrix method provided with an organic EL element corresponding to each emission color, a switching transistor and an driving element as active elements, and a scanning signal is applied from a scanning line 5. Receives an image data signal from the data line 6 and emits light in accordance with the received image data. By arranging the red, green, and blue pixels appropriately as described above, a full-color display can be realized.
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By driving the full-color display device, a clear full-color moving image display with high luminance and good durability was obtained.
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【The invention's effect】
According to the present invention, it is possible to provide an organic electroluminescent element having high light emission luminance and high luminous efficiency and excellent durability, and a display device having the element.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a display device including an organic EL element.
FIG. 2 is a schematic diagram of a display unit A.
FIG. 3 is a schematic diagram of a pixel.
FIG. 4 is a schematic view of a display device using a passive matrix method.
FIG. 5 is a schematic diagram of an organic EL element OLED1-1.
[Explanation of symbols]
1 Display
3 pixels
5 scanning lines
6 Data line
7 Power line
10 Organic EL device
11 Switching transistor
12 Driving transistor
13 Capacitor
A Display
B control unit

Claims (9)

An organic electroluminescence device comprising a compound represented by the following general formula (1).
General formula (1)
(A) _1- (X)-(B) _n
(Where A and B are monovalent substituents having different structures, X represents an m-valent linking group, and A or B contains a hetero element. In the formula, l and n each represent A , B, m = l + n, m represents an integer of 2 to 6, and l ≧ 1 and n ≧ 1.) The "highest occupied molecular orbital" HOMO (H) and the "lowest unoccupied molecular orbital" LUMO (H) of the substituent A of the compound represented by the general formula (1), and the hetero element of the substituent A is substituted with carbon. The relationship of the substituted substituent A ′ with the “highest occupied molecular orbital” HOMO (C) and the “lowest unoccupied molecular orbital” LUMO (C) is as follows:
HOMO (H) -HOMO (C)> 0
And,
│HOMO (H) -HOMO (C) │-│LUMO (H) -LUMO (C) │> 0
And
The “highest occupied molecular orbital” HOMO (H) and the “lowest unoccupied molecular orbital” LUMO (H) of the substituent B of the compound represented by the general formula (1), and the hetero element of the substituent B is substituted with carbon. The relationship of the substituent B ′ with the “highest occupied molecular orbital” HOMO (C) and the “lowest unoccupied molecular orbital” LUMO (C) is
LUMO (H) -LUMO (C) <0
And,
| HOMO (H) -HOMO (C) |-| LUMO (H) -LUMO (C) | <0
The organic electroluminescent device according to claim 1, wherein the following is satisfied. The organic electroluminescent element has a plurality of constituent layers including a light-emitting layer, the light-emitting layer contains a host compound, and a dopant compound that is a phosphorescent compound, and at least one of the plurality of constituent layers has It contains the compound represented by the general formula (1), the emission maximum wavelength on the short wavelength side of the emission spectrum of the organic electroluminescence device is 500 nm or less, and the lowest excited triplet energy level of the host material is The organic electroluminescence device according to claim 1, wherein the energy is higher than the lowest excited triplet energy level of the dopant compound that is the phosphorescent compound. 4. The method according to claim 1, wherein at least one of the plurality of constituent layers is an electron transport layer, and the electron transport layer contains at least one compound represented by the general formula (1). The organic electroluminescence device according to any one of the preceding claims. 5. The organic electroluminescent device according to claim 3, wherein the dopant compound that is a phosphorescent compound is an iridium compound, an osmium compound, or a platinum compound. The organic electroluminescence device according to claim 5, wherein the dopant compound that is a phosphorescent compound is an iridium compound. The organic electroluminescent device according to claim 6, wherein the substituent A is anisole, carbazole, indole, an amine alone or a derivative residue. The organic electroluminescent device according to claim 7, wherein the linking group X has a substituent having an absolute value of a steric hindrance parameter (Es) of 0.5 or more. A display device comprising the organic electroluminescence device according to claim 1.

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