JP4604312B2 - Benzothiophene derivative and organic electroluminescence device using the same - Google Patents

Description

（式中、Ｒ₁〜Ｒ₉はそれぞれ独立して水素原子、炭素数１〜６のアルキル基、炭素数１〜６のアルコキシ基、置換もしくは無置換のアリール基、または置換もしくは無置換のヘテロ環基を示し、このアリール基およびヘテロ環基は、これらが隣接している場合には、互いに縮合した構造のものであってもよい。）
【００１５】
（２）前記（１）に記載のベンゾチオフェン誘導体が用いられていることを特徴とする有機電界発光素子。
【００１６】
（３）前記（１）に記載のベンゾチオフェン誘導体が正孔輸送層に含有されていることを特徴とする、前記（２）に記載の有機電界発光素子。
【００１７】
（４）前記（１）に記載のベンゾチオフェン誘導体が発光層に含有されていることを特徴とする、前記（２）に記載の有機電界発光素子。
【００１８】
（５）前記（１）に記載のベンゾチオフェン誘導体が正孔注入層に含有されていることを特徴とする、前記（２）に記載の有機電界発光素子。
【００１９】
（６）前記（１）に記載のベンゾチオフェン誘導体からなる有機電界発光材料。
【００２０】
（７）前記（１）に記載のベンゾチオフェン誘導体からなる正孔輸送材料。
【００２１】
【発明の実施の形態】
以下、本発明を詳細に説明する。一般式（１）で表わされるベンゾチオフェン誘導体の具体例としては、下記の式（２）〜（１１）で表わされる化合物を挙げることができる。
【００２２】
【化３】

（式中、ｔ−Ｂｕはｔ−ブチル基を示す。）
【００２３】
【化４】

（式中、Ｍｅはメチル基を示す。）
【００２４】
【化５】

（式中、Ｍｅはメチル基を示す。）
【００２５】
これらのベンゾチオフェン誘導体は、ベンゾチオフェン基を含む化合物とハロゲン化トリアリールアミンとを遷移金属触媒を用いてカップリング反応することにより、合成することができる。例えば、本願明細書の合成例に記載の方法により得ることができる。本発明のベンゾチオフェン誘導体はそれ自身蛍光を発し、発光材料として適している。これはベンゾチオフェン基とそれに結合しているアリール基に起因している。特に、本発明のベンゾチオフェン誘導体は発光色が青色であるので、黄、緑、赤色等の他の発光材料を添加することにより、異なる発光色の有機ＥＬ素子を得ることができる。
【００２６】
また、本発明の有機ＥＬ素子は、高効率であるばかりでなく、保存時及び駆動時の耐久性が高い。これは、本発明で使用される一般式（１）で表わされるベンゾチオフェン誘導体のＴｇが高いためである。また、このベンゾチオフェン誘導体は、正孔輸送層および正孔注入層を形成させるための材料として用いられることもできる。
【００２７】
本発明の有機ＥＬ素子の構造としては、各種の態様があるが、基本的には一対の電極（陽極と陰極）間に、上記ベンゾチオフェン誘導体を含有する有機層を挟持した構造であり、所望に応じて、上記ベンゾチオフェン誘導体層に他の材料を用いた正孔注入層、正孔輸送層、発光層、電子注入層あるいは電子輸送層などを組み合わせることができる。また、ベンゾチオフェン誘導体を発光層として使用する場合、この発光層に他の発光材料を添加することにより、異なる波長の光を発生させたり、発光効率を向上させることができるし、正孔注入材料または正孔輸送材料として用いる場合についても、更に機能の向上をはかるために他の材料を併用することができる。
【００２８】
具体的な構成としては、（１）陽極／ベンゾチオフェン誘導体層／陰極、（２）陽極／ベンゾチオフェン誘導体層／発光層／陰極、（３）陽極／ベンゾチオフェン誘導体層／発光層／電子注入層／陰極、（４）陽極／正孔注入層／ベンゾチオフェン誘導体層／発光層／電子注入層／陰極、（５）陽極／ベンゾチオフェン誘導体層／正孔輸送層／発光層／電子注入層／陰極、（６）陽極／正孔注入層／ベンゾチオフェン誘導体層／電子注入層／陰極などの積層構造を挙げることができる。これらの場合、正孔注入層や電子注入層は、必ずしも必要ではないが、これらの層を設けることにより、発光効率を向上させることができる。
【００２９】
本発明の有機ＥＬ素子は、上記のいずれの構造であっても、基板に支持されていることが好ましい。基板としては、機械的強度、熱安定性および透明性を有するものであればよく、ガラス、透明プラスチックフィルムなどを用いることができる。本発明の有機ＥＬ素子の陽極物質としては、４ｅＶより大きな仕事関数を有する金属、合金、電気伝導性化合物およびこれらの混合物を用いることができる。具体例として、Ａｕなどの金属、ＣｕＩ、インジウムチンオキシド（以下、ＩＴＯと略記する）、ＳｎＯ₂、ＺｎＯなどの導電性透明材料が挙げられる。
【００３０】
陰極物質としては、４ｅＶより小さな仕事関数の金属、合金、電気伝導性化合物、およびこれらの混合物を使用できる。具体例としては、アルミニウム、カルシウム、マグネシウム、リチウム、マグネシウム合金、アルミニウム合金等があり、合金としては、アルミニウム／弗化リチウム、アルミニウム／リチウム、マグネシウム／銀、マグネシウム／インジウムなどが挙げられる。有機ＥＬ素子の発光を効率よく取り出すために、電極の少なくとも一方は光透過率を１０％以上とすることが望ましい。電極としてのシート抵抗は数百Ω／ｍｍ以下とすることが好ましい。なお、膜厚は電極材料の性質にもよるが、通常１０ｎｍ〜１μｍ、好ましくは１０〜４００ｎｍの範囲に選定される。このような電極は、上述の電極物質を使用して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。
【００３１】
本発明の有機ＥＬ素子において使用される式（１）で表されるベンゾチオフェン誘導体は十分に高いＴｇを有しているが、正孔注入材料、正孔輸送材料、発光材料、電子注入材料などの他の使用材料についても、Ｔｇが８０℃以上のものが好ましく、１００℃以上のものがより好ましい。
【００３２】
本発明の有機ＥＬ素子に使用される他の正孔注入材料および正孔輸送材料については、光導電材料において、正孔の電荷輸送材料として従来から慣用されているものや、有機ＥＬ素子の正孔注入層および正孔輸送層に使用されてい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。例えば、カルバゾール誘導体（Ｎ−フェニルカルバゾール、ポリビニルカルバゾールなど）、トリアリールアミン誘導体（ＴＰＤ、芳香族第３級アミンを主鎖あるいは側鎖に持つポリマー、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’−ジフェニル−Ｎ，Ｎ’−ジナフチル−４，４'−ジアミノビフェニル、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、J. Chem. Soc. Chem. Comm., 2175(1996)に記載されている化合物、特開昭５７−１４４５５８号公報、特開昭６１−６２０３８号公報、特開昭６１−１２４９４９号公報、特開昭６１−１３４３５４号公報、特開昭６１−１３４３５５号公報、特開昭６１−１１２１６４号公報、特開平４−３０８６８８号公報、特開平６−３１２９７９号公報、特開平６−２６７６５８号公報、特開平７−９０２５６号公報、特開平７−９７３５５号公報、特開平６−１９７２号公報、特開平７−１２６２２６号公報、特開平７−１２６６１５号公報、特開平７−３３１２３８号公報、特開平８−１００１７２号公報または特開平８−４８６５６号公報に記載されている化合物、Adv. Mater., 6, 677(1994)に記載されているスターバーストアミン誘導体など）、スチルベン誘導体（日本化学会第７２春季年会講演予稿集（II）、1392ページ、2PB098に記載のものなど）、フタロシアニン誘導体（無金属、銅フタロシアニンなど）、ポリシランなどがあげられる。
【００３３】
なお、本発明の有機ＥＬ素子における正孔注入層および正孔輸送層は、上記の化合物の一種以上を含有する一つの層で構成されていてもよいし、また、異種の化合物を含有する複数の層を積層したものであってもよい。
【００３４】
本発明の有機ＥＬ素子に使用される他の電子注入材料および電子輸送材料については特に制限はなく、光導電材料において、電子伝達化合物として従来から慣用されているもの、有機ＥＬ素子の電子注入層および電子輸送層に使用されてい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。このような電子伝達化合物の好ましい例として、ジフェニルキノン誘導体（電子写真学会誌、30, 3(1991)などに記載のもの）、ペリレン誘導体（J. Apply. Phys., 27, 269(1988)等に記載のもの）や、オキサジアゾール誘導体（前記文献、Jpn. J. Aplly. Phys., 27, L713(1988)）、Appl. Phys. Lett., 55, 1489(1989)などに記載のもの）、チオフェン誘導体（特開平４−２１２２８６号公報などに記載のもの）、トリアゾール誘導体（Jpn. J. Appl. Phys., 32, L917(1993)などに記載のもの）、チアジアゾール誘導体（第４３回高分子学会予稿集、（III）P1a007などに記載のもの）、オキシン誘導体の金属錯体（電子情報通信学会技術研究報告、92(311), 43(1992)などに記載のもの）、キノキサリン誘導体のポリマー（Jpn. J. Appl. Phys., 33, L250(1994)などに記載のもの）、フェナントロリン誘導体（第４３回高分子討論会予稿集、14J07などに記載のもの）などを挙げることができる。
【００３５】
本発明の有機ＥＬ素子の発光層に用いる他の発光材料としては、高分子学会編高分子機能材料シリーズ”光機能材料”、共同出版(1991)、P236に記載されているような昼光蛍光材料、蛍光増白剤、レーザー色素、有機シンチレータ、各種の蛍光分析試薬などの公知の発光材料を用いることができる。具体的には、アントラセン、フェナントレン、ピレン、クリセン、ペリレン、コロネン、ルブレン、キナクリドンなどの多環縮合化合物、クオーターフェニルなどのオリゴフェニレン系化合物、１，４−ビス（２−メチルスチリル）ベンゼン、１，４−ビス（４−メチルスチリル）ベンゼン、１，４−ビス（４−フェニル−５−オキサゾリル）ベンゼン、１，４−ビス（５−フェニル−2−オキサゾリル）ベンゼン、２，５−ビス（５−ターシャリー−ブチル−2−ベンズオキサゾリル）チオフェン、１，４−ジフェニル−１，３−ブタジエン、１，６−ジフェニル−１，３，５−ヘキサトリエン、１，１，４，４−テトラフェニル−１，３−ブタジエンなどの液体シンチレーション用シンチレータ、特開昭６３−２６４６９２号公報記載のオキシン誘導体の金属錯体、クマリン染料、ジシアノメチレンピラン染料、ジシアノメチレンチオピラン染料、ポリメチン染料、オキソベンズアントラセン染料、キサンテン染料、カルボスチリル染料、およびペリレン染料、独国特許２５３４７１３号公報に記載のオキサジン系化合物、第40回応用物理学関係連合講演会講演予稿集、1146(1993)に記載のスチルベン誘導体、特開平７−２７８５３７号公報記載のスピロ化合物および特開平４−３６３８９１号公報記載のオキサジアゾール系化合物などが好ましい。
【００３６】
本発明の有機ＥＬ素子を構成する各層は、各層を構成すべき材料を蒸着法、スピンコート法およびキャスト法などの公知の方法で薄膜とすることにより、形成することができる。このようにして形成された各層の膜厚については特に限定はなく、素材の性質に応じて適宜選定することができるが、通常２ｎｍ〜５０００ｎｍの範囲に選定される。なお、ベンゾチオフェン誘導体を薄膜化する方法としては、均質な膜が得やすく、かつピンホールが生成しにくいなどの点から蒸着法を適するのが好ましい。蒸着法を用いて薄膜化する場合、その蒸着条件は、ベンゾチオフェン誘導体の種類、分子累積膜の目的とする結晶構造および会合構造などにより異なるが、一般的に、ボート加熱温度５０〜４００℃、真空度１０^-6〜１０^-3Ｐａ、蒸着速度０．０１〜５０ｎｍ／秒、基板温度−１５０〜＋３００℃、膜厚５ｎｍ〜５μｍの範囲で適宜選定することが好ましい。
【００３７】
次に、本発明のベンゾチオフェン誘導体を用いて有機ＥＬ素子を作成する方法の一例として、前述の陽極／ベンゾチオフェン誘導体／陰極からなる有機ＥＬ素子の作成法について説明する。適当な基板上に、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法により形成させて陽極を作製した後、この陽極上にベンゾチオフェン誘導体の薄膜を形成させて発光層とし、この発光層の上に陰極用物質からなる薄膜を蒸着法により、１μｍ以下の膜厚になるように形成させて陰極とすることにより、目的の有機ＥＬ素子が得られる。なお、上述の有機ＥＬ素子の作製においては、作製順序を逆にして、陰極、発光層、陽極の順に作製することも可能である。
【００３８】
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−の極性として印加すればよく、電圧２〜４０Ｖ程度を印加すると、透明又は半透明の電極側（陽極又は陰極、及び両方）より発光が観測できる。また、この有機ＥＬ素子は、交流電圧を印加した場合にも発光する。なお、印加する交流の波形は任意でよい。
【００３９】
【実施例】
次に、本発明を実施例に基づいて更に詳しく説明する。
【００４０】
合成例１
トリス［４−（２−ベンゾチエニル）フェニル］アミン（式（２）で表わされる化合物、以下、ＢｔＰ−３と略記する。）の合成
ベンゾチオフェン１．６６ｇおよびｔ−ブチルメチルエーテル４０ｍｌをフラスコに入れて、窒素雰囲気下で−７８℃に冷却後、濃度１．５ｍｏｌ／Ｌのｎ−ブチルリチウム／ｎ−ヘキサン溶液８．５ｍｌを滴下した。−１０〜−５℃まで昇温後、Ｎ，Ｎ，Ｎ’，Ｎ’−テトラメチルエチレンジアミン１．９ｍｌおよびジクロロ（Ｎ，Ｎ，Ｎ’，Ｎ’−テトラメチル−エチレンジアミン）亜鉛３．４３ｇを入れて室温まで加熱した。次にトリよう化フェニルアミン２．４９ｇおよびビス(トリフェニルホスフィン)パラジウムクロライド０．０８４ｇを入れて還流温度（５６℃）で２時間加熱した。反応終了後、室温まで冷却して純水を加え、有機層を抽出した。それをエバポレータにより濃縮したものをトルエン中からの再結晶により精製して、目的とする化合物１ｇを得た。この化合物のトルエン中での発光色は青色であり、Ｔｇは１３０℃であった。
¹Ｈ−ＮＭＲ（ＣＤＣｌ₃）δ＝7.2(d, 6H)、7.2(m, 9H)、7.3−7.4(m, 6H)、7.5(s, 3H)、7.6−7.7(d, 6H)、7.8(d, d, 6H).
なお、この合成例と全く同様の方法で、ベンゾチオフェンを３−ｔ−ブチルベンゾチオフェンに替えることにより式（３）で表わされる化合物（トリス｛４−［２−（３−ｔ−ブチルベンゾチエニル）］フェニル｝アミン）を、ベンゾチオフェンを３−フェニルベンゾチオフェンに替えることにより式（５）で表わされる化合物（トリス｛４−［２−（３−フェニルベンゾチエニル）］フェニル｝アミン）を、それぞれ合成することができる。
【００４１】
実施例１
２５ｍｍ×７５ｍｍ×１．１ｍｍのガラス基板上にＩＴＯを５０ｎｍの厚さに蒸着したもの（東京三容真空(株)製）を透明支持基板とした。この透明支持基板を市販の蒸着装置（真空機工（株）製）の基盤ホルダーに固定し、合成例１で合成したＢｔＰ−３をいれたモリブデン製蒸着用ボート、トリス（８−ヒドロキシキノリン）アルミニウム（以下、ＡＬＱと略記する。）をいれたモリブデン製蒸着用ボート、弗化リチウムをいれたモリブデン製蒸着用ボート、およびアルミニウムをいれたタングステン製蒸着用ボートを装着した。真空槽を１×１０^-3Ｐａまで減圧し、ＢｔＰ−３入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＢｔＰ−３を蒸着して正孔輸送層を形成し、次いで、ＡＬＱ入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＡＬＱを蒸着して発光層を形成した。蒸着速度は０．１〜０．２ｎｍ／秒であった。その後、弗化リチウム入りの蒸着用ボートを加熱して、膜厚０．５ｎｍになるように０．００３〜０．０１ｎｍ／秒の蒸着速度で蒸着し、次いで、アルミニウム入りの蒸着用ボートを加熱して、膜厚１００ｎｍになるように０．２〜０．５ｎｍ／秒の蒸着速度で蒸着することにより、有機ＥＬ素子を得た。ＩＴＯ電極を陽極、弗化リチウム／アルミニウム電極を陰極として、約４Ｖの直流電圧を印加すると、約４ｍＡ／ｃｍ²の電流が流れ、輝度は約１００ｃｄ／ｍ²、発光効率２．１ｌｍ／Ｗで波長５２０ｎｍの緑色発光を得た。また、６．５Ｖの直流電圧を継続して印加したが、３時間経過後も発光が持続されていた。また、１００℃に加熱しても発光の低下は見られなかった。
【００４２】
実施例２
実施例１と同様に、透明支持基板を蒸着装置の基板ホルダーに固定し、合成例１で合成したＢｔＰ−３をいれたモリブデン製蒸着用ボート、Ｎ，Ｎ’−ジナフチルーＮ，Ｎ’−ジフェニル−４，４’−ジアミノビフェニル（以下、ＮＰＤと略記する。）をいれたモリブデン製蒸着用ボート、ＡＬＱをいれたモリブデン製蒸着用ボート、弗化リチウムをいれたモリブデン製蒸着用ボート、およびアルミニウムをいれたタングステン製蒸着用ボートを装着した。真空槽を１×１０^-3Ｐａまで減圧し、ＢｔＰ−３入りの蒸着用ボートを加熱して、膜厚１０ｎｍになるようにＢｔＰ−３を蒸着して正孔注入層を形成し、次いで、ＮＰＤ入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＮＰＤを蒸着して正孔輸送層を形成した。次に、ＡＬＱ入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＡＬＱを蒸着して発光層を形成した。以上の蒸着速度は０．１〜０．２ｎｍ／秒であった。その後、弗化リチウム入りの蒸着用ボートを加熱して、膜厚０．５ｎｍになるように０．００３〜０．０１ｎｍ／秒の蒸着速度で蒸着し、次いで、アルミニウム入りの蒸着用ボート加熱して、膜厚１００ｎｍになるように０．２〜０．５ｎｍ／秒の蒸着速度で蒸着することにより、有機ＥＬ素子を得た。ＩＴＯ電極を陽極、弗化リチウム／アルミニウム電極を陰極として、約４Ｖの直流電圧を印加すると、約３ｍＡ／ｃｍ²の電流が流れ、輝度は約１００ｃｄ／ｍ²であった。
【００４３】
実施例３
実施例１と同様に、透明支持基板を蒸着装置の基板ホルダーに固定し、合成例１で合成したＢｔＰ−３をいれたモリブデン製蒸着用ボート、ＮＰＤをいれたモリブデン製蒸着用ボート、９，９’−スピロビシラフルオレンをいれたモリブデン製蒸着用ボート、弗化リチウムをいれたモリブデン製蒸着用ボート、およびアルミニウムをいれたタングステン製蒸着用ボートを装着した。真空槽を１×１０^-3Ｐａまで減圧し、ＮＰＤ入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＮＰＤを蒸着して正孔輸送層を形成し、次いで、ＢｔＰ−３入りの蒸着用ボートを加熱して、膜厚２０ｎｍになるようにＢｔＰ−３を蒸着して発光層を形成した。次に、９，９’−スピロビシラフルオレン入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるように９，９’−スピロビシラフルオレンを蒸着して電子輸送層を形成した。以上の蒸着速度は０．１〜０．２ｎｍ／秒であった。その後、弗化リチウム入りの蒸着用ボートを加熱して、膜厚０．５ｎｍになるように０．００３〜０．０１ｎｍ／秒の蒸着速度で蒸着し、次いでアルミニウム入りの蒸着用ボート加熱して、膜厚１００ｎｍになるように０．２〜０．５ｎｍ／秒の蒸着速度で蒸着することにより、有機ＥＬ素子を得た。ＩＴＯ電極を陽極、弗化リチウム／アルミニウム電極を陰極として、１０Ｖの直流電圧を印加すると、約５０ｍＡ／ｃｍ²の電流が流れ、ＢｔＰ−３からの青色発光が得られた。
【００４４】
実施例４
実施例１と同様に、透明支持基板を蒸着装置の基板ホルダーに固定し、合成例１で合成したＢｔＰ−３をいれたモリブデン製蒸着用ボート、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をいれたモリブデン製蒸着用ボート、ＡＬＱをいれたモリブデン製蒸着用ボート、弗化リチウムをいれたモリブデン製蒸着用ボート、およびアルミニウムをいれたタングステン製蒸着用ボートを装着した。真空槽を１×１０^-3Ｐａまで減圧し、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入りの蒸着用ボートを加熱して、膜厚５ｎｍになるように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を蒸着して正孔注入層を形成し、次いで、ＢｔＰ−３入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＢｔＰ−３を蒸着して正孔輸送層を形成した。次に、ＡＬＱ入りの蒸着用ボートを加熱して、膜厚５０ｎｍになるようにＡＬＱを蒸着して発光層を形成した。以上の蒸着速度は０．１〜０．２ｎｍ／秒であった。その後、弗化リチウム入りの蒸着用ボートを加熱して、膜厚０．５ｎｍになるように０．００３〜０．０１ｎｍ／秒の蒸着速度で蒸着し、次いで、アルミニウム入りの蒸着用ボート加熱して、膜厚１００ｎｍになるように０．２〜０．５ｎｍ／秒の蒸着速度で蒸着することにより、有機ＥＬ素子を得た。ＩＴＯ電極を陽極、弗化リチウム／アルミニウム電極を陰極として、３Ｖの直流電圧を印加すると、約３ｍＡ／ｃｍ²の電流が流れ、輝度約１００ｃｄ／ｃｍ²の緑色の発光を得た。
【００４５】
比較例１
実施例１を用いたＢｔＰ−３をＮＰＤに代えた以外は、実施例１と同様な方法で有機ＥＬ素子を作成した。 ＩＴＯ電極を陽極、弗化リチウム／アルミニウム電極を陰極として、直流電圧約４Ｖを印加すると約４ｍＡ／ｃｍ²が流れ、輝度約１００ｃｄ／ｃｍ²、発光効率１．９ｌｍ／Ｗであった。また、１００℃に加熱したところ、発光が見られなくなった。
【００４６】
比較例２
実施例１で用いたＢｔＰ−３をトリス［４−（２−チエニル）フェニル］アミンに代えた以外は、実施例１と同様な方法で有機ＥＬ素子を作成した。 ＩＴＯ電極を陽極、弗化リチウム／アルミニウム電極を陰極として、直流電圧約４Ｖを印加すると約２０ｍＡ／ｃｍ²が流れた。また、８０℃で直流電圧を印加すると数秒後に発光しなくなった。
【００４７】
【発明の効果】
以上説明してきたように、本発明のベンゾチオフェン誘導体はＴｇが１００℃以上と高く、しかもアモルファス状態になり易いので、これを有機ＥＬ素子の発光材料、正孔輸送材料および正孔注入材料として使用することにより、有機ＥＬ素子の高効率、長寿命化を可能とすることができる。すなわち、本発明の有機ＥＬ素子は、ベンゾチオフェン誘導体を有機層とすることにより、高効率、長寿命、フルカラー化が容易である。従って、本発明の有機ＥＬ素子を用いることにより、フルカラーディスプレーなどの高効率なディスプレイ装置が作成できる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic electroluminescent element (hereinafter abbreviated as an organic EL element) and a material thereof.
[0002]
[Prior art]
In recent years, organic EL elements have attracted attention as next-generation full-color flat panel displays, and active research and development have been made. The organic EL element is an injection type light emitting element in which a light emitting layer is sandwiched between two electrodes, and emits light by injecting electrons and holes into the organic light emitting layer and recombining them. There are low molecular weight materials and high molecular weight materials used, and it has been shown that a high-brightness organic EL element can be obtained.
[0003]
There are two types of such organic EL elements. One uses an electron transport material with a fluorescent dye added by CW Tang et al. As a light emitting layer (J. Appl. Phys., 65, 3610 (1989)). The fluorescent dye itself is used as a light emitting layer (for example, an element described in Appl. Phys. 27, L269 (1988)).
[0004]
The types using fluorescent dyes as the light emitting layer are roughly divided into three types. The first is a three-layer structure in which a light-emitting layer is sandwiched between an electron-transport layer and a hole-transport layer. The second is a two-layer structure in which a hole-transport layer and a light-emitting layer are stacked. The eye is formed by stacking an electron transport layer and a light emitting layer into two layers. It is known that the light emission efficiency of the organic EL element is improved by adopting such a laminated structure.
[0005]
The electron transport layer in the organic EL device having the above-described configuration contains an electron transfer compound, and has a function of transmitting electrons injected from the cathode to the light emitting layer. The hole transport layer and the hole injection layer are layers containing a hole transfer compound, and have a function of transmitting holes injected from the anode to the light emitting layer. By interposing a hole injection layer between the anode and the light emitting layer, a large number of holes are transferred from the anode to the light emitting layer with a lower electric field, and electrons injected from the electron transport layer or the electron injection layer are further emitted. Therefore, it is possible to obtain an organic EL element having excellent light emitting performance such as improved luminous efficiency.
[0006]
However, these organic EL elements did not have sufficient performance for practical use. A major cause of this is the lack of durability of the materials used, particularly the poor durability of the hole transport material. When an inhomogeneous portion such as a crystal grain boundary is present in the organic layer of the organic EL element, it is considered that the electric field concentrates on the portion and leads to deterioration and destruction of the element. Therefore, the organic layer is often used in an amorphous state. The organic EL element is an electron injection type element. If the glass transition point of the material used is low, the organic EL element deteriorates due to heat generation during driving. Therefore, the organic EL element is abbreviated as Tg. ) Is required. In addition, the hole transporting material used does not have sufficient hole transportability, and the light emitting efficiency of the device was not practically sufficient.
[0007]
As a hole transport material used for such an organic EL element, there are few materials suitable for practical use, although a wide variety of materials are known centering on a triphenylamine derivative. For example, N, N′-diphenyl-N, N′-di (3-methylphenyl) -4,4′-diaminobiphenyl (hereinafter abbreviated as TPD) has been reported (Appl. Phys. Lett. 57, 6, 531 (1990)), but this compound has poor thermal stability and has a problem in the lifetime of the device. U.S. Pat. No. 5,047,687, U.S. Pat. No. 4,049,948, U.S. Pat. No. 4,536,457, JP-B-6-32307, JP-A-5-234681, JP-A-5-239455, JP-A-8-87122, and Although many triphenylamine derivatives are described in JP-A-8-259940, there are no compounds having sufficient characteristics.
[0008]
Starburst amine derivatives described in JP-A-4-308688, JP-A-6-1972 and Adv. Mater., 6, 677 (1994), JP-A-7-126226, JP-A-7-126615 No. 7, JP-A-7-33238, JP-A-7-97355, JP-A-8-48656, JP-A-8-100192, and J. Chem. Soc. Chem. Comm., 2175, (1996 None of the compounds described in (1) have the practically essential properties of high luminous efficiency and long life. Furthermore, in JP-A-9-194441, an example using a naphthylamine derivative is reported, and it is described that it is improved from the characteristics of TPD, but also in these cases, hole transportability and durability are described. Was not enough.
[0009]
JP-A-4-33918, JP-A-4-93078, JP-A-4-359922, Synth. Mater., 89, 227 (1997), J. Am. Chem. Soc., 120, 589 (1998) ), Chem. Mater., 10, 1487 (1998), Acta. Chem. Scand., 52, 131 (1998) and Mol. Cryst. Liq. Cryst., 296, 445 (1997). 4- (2-thienyl) phenyl] amine and its polymer have been clarified to have a hole transporting property, and device characteristics in a configuration in which the above compound is sandwiched between an anode and a cathode are shown. The brightness is 100 cd / cm ² Applied voltage 8V, current density 100mA / cm ² Met. Moreover, Tg is as low as 70 ° C. and does not have practically sufficient characteristics.
[0010]
As described above, hole transport materials used in conventional organic EL elements do not have practically sufficient performance, and use of excellent materials increases the efficiency and lifetime of organic EL elements. Is desired. Further, most organic EL devices emit light from a light emitting layer or an electron transport layer provided separately from the charge transport layer, and few are obtained from the hole transport layer. The reason is that there is a problem of compatibility with the electron transport layer used at the same time, but the emission color and emission intensity of the hole transport material itself are considered to be important factors. Despite the expectation of higher practical value if light emission can be extracted from the hole transport layer, there are few such materials. In addition, in many cases, such materials have a problem that the emission wavelength is long and the emission of short wavelengths cannot be extracted.
[0011]
[Problems to be solved by the invention]
The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an organic EL device having a high luminous efficiency and a long lifetime, a novel compound used therefor, and a hole transporting method. It is to provide a material and an organic electroluminescent material.
[0012]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems of the conventional organic EL elements, the present inventors have obtained a high Tg, high efficiency, and long life organic EL element by using a specific benzothiophene derivative. The present invention has been completed.
[0013]
That is, the present invention has the following configuration.
[0014]
(1) A benzothiophene derivative represented by the general formula (1).
[Chemical 2]

(Wherein R ₁ ~ R ₉ Each independently represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group, or a substituted or unsubstituted heterocyclic group, When they are adjacent to each other, the heterocyclic groups may have a structure condensed with each other. )
[0015]
(2) An organic electroluminescent device using the benzothiophene derivative according to (1).
[0016]
(3) The organic electroluminescence device according to (2), wherein the benzothiophene derivative according to (1) is contained in a hole transport layer.
[0017]
(4) The organic electroluminescent element according to (2) above, wherein the benzothiophene derivative according to (1) is contained in a light emitting layer.
[0018]
(5) The organic electroluminescence device according to (2), wherein the benzothiophene derivative according to (1) is contained in a hole injection layer.
[0019]
(6) An organic electroluminescent material comprising the benzothiophene derivative according to (1).
[0020]
(7) A hole transport material comprising the benzothiophene derivative according to (1).
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail. Specific examples of the benzothiophene derivative represented by the general formula (1) include compounds represented by the following formulas (2) to (11).
[0022]
[Chemical 3]

(In the formula, t-Bu represents a t-butyl group.)
[0023]
[Formula 4]

(In the formula, Me represents a methyl group.)
[0024]
[Chemical formula 5]

(In the formula, Me represents a methyl group.)
[0025]
These benzothiophene derivatives can be synthesized by a coupling reaction of a compound containing a benzothiophene group and a halogenated triarylamine using a transition metal catalyst. For example, it can be obtained by the method described in the synthesis examples of the present specification. The benzothiophene derivative of the present invention emits fluorescence itself and is suitable as a light emitting material. This is due to the benzothiophene group and the aryl group bonded to it. In particular, since the benzothiophene derivative of the present invention has a blue emission color, organic EL elements having different emission colors can be obtained by adding other light-emitting materials such as yellow, green, and red.
[0026]
The organic EL device of the present invention is not only highly efficient, but also has high durability during storage and driving. This is because the Tg of the benzothiophene derivative represented by the general formula (1) used in the present invention is high. The benzothiophene derivative can also be used as a material for forming a hole transport layer and a hole injection layer.
[0027]
Although there are various modes as the structure of the organic EL device of the present invention, it is basically a structure in which an organic layer containing the benzothiophene derivative is sandwiched between a pair of electrodes (anode and cathode), which is desired. Accordingly, a hole injection layer, a hole transport layer, a light emitting layer, an electron injection layer, an electron transport layer, or the like using other materials can be combined with the benzothiophene derivative layer. In addition, when a benzothiophene derivative is used as a light emitting layer, by adding another light emitting material to the light emitting layer, it is possible to generate light of different wavelengths, improve the light emission efficiency, Alternatively, when used as a hole transport material, other materials can be used in combination in order to further improve the function.
[0028]
Specifically, (1) anode / benzothiophene derivative layer / cathode, (2) anode / benzothiophene derivative layer / light emitting layer / cathode, (3) anode / benzothiophene derivative layer / light emitting layer / electron injection layer / Cathode, (4) anode / hole injection layer / benzothiophene derivative layer / light emitting layer / electron injection layer / cathode, (5) anode / benzothiophene derivative layer / hole transport layer / light emitting layer / electron injection layer / cathode (6) A laminated structure such as anode / hole injection layer / benzothiophene derivative layer / electron injection layer / cathode can be mentioned. In these cases, the hole injection layer and the electron injection layer are not necessarily required, but the light emission efficiency can be improved by providing these layers.
[0029]
The organic EL device of the present invention is preferably supported by a substrate in any of the structures described above. As the substrate, any substrate having mechanical strength, thermal stability and transparency can be used, and glass, a transparent plastic film and the like can be used. As the anode material of the organic EL device of the present invention, metals, alloys, electrically conductive compounds and mixtures thereof having a work function larger than 4 eV can be used. Specific examples include metals such as Au, CuI, indium tin oxide (hereinafter abbreviated as ITO), SnO. ₂ And conductive transparent materials such as ZnO.
[0030]
As the cathode material, metals, alloys, electrically conductive compounds, and mixtures thereof having a work function smaller than 4 eV can be used. Specific examples include aluminum, calcium, magnesium, lithium, magnesium alloy, and aluminum alloy. Examples of the alloy include aluminum / lithium fluoride, aluminum / lithium, magnesium / silver, and magnesium / indium. In order to efficiently extract light emitted from the organic EL element, it is desirable that at least one of the electrodes has a light transmittance of 10% or more. The sheet resistance as an electrode is preferably several hundred Ω / mm or less. Although the film thickness depends on the properties of the electrode material, it is usually selected in the range of 10 nm to 1 μm, preferably 10 to 400 nm. Such an electrode can be produced by forming a thin film by a method such as vapor deposition or sputtering using the electrode material described above.
[0031]
The benzothiophene derivative represented by the formula (1) used in the organic EL device of the present invention has a sufficiently high Tg, but a hole injection material, a hole transport material, a light emitting material, an electron injection material, etc. Other materials used also preferably have a Tg of 80 ° C. or higher, more preferably 100 ° C. or higher.
[0032]
Other hole injection materials and hole transport materials used in the organic EL device of the present invention are those conventionally used as a charge transport material for holes in photoconductive materials, Any one of known materials used for the hole injection layer and the hole transport layer can be selected and used. For example, carbazole derivatives (N-phenylcarbazole, polyvinylcarbazole, etc.), triarylamine derivatives (TPD, polymers having aromatic tertiary amine in the main chain or side chain, 1,1-bis (4-di-p- Tolylaminophenyl) cyclohexane, N, N′-diphenyl-N, N′-dinaphthyl-4,4′-diaminobiphenyl, 4,4 ′, 4 ″ -tris {N- (3-methylphenyl) -N-phenyl Amino} triphenylamine, compounds described in J. Chem. Soc. Chem. Comm., 2175 (1996), JP-A 57-144558, JP-A 61-62038, JP-A 61 -124949, JP-A-61-134354, JP-A-61-134355, JP-A-61-112164, JP-A-4-308688, JP-A-312979, JP-A-6-267658, JP-A-7-90256, JP-A-7-97355, JP-A-6-1972, JP-A-7-126226, JP-A-7-126615. No. 7, JP-A-7-33238, JP-A-8-100192 or JP-A-8-48656, star described in Adv. Mater., 6, 677 (1994) Burstamine derivatives, etc.), stilbene derivatives (Proceedings of the 72nd Annual Meeting of the Chemical Society of Japan (II), pages 1392, 2PB098, etc.), phthalocyanine derivatives (metal-free, copper phthalocyanine, etc.), polysilane, etc. It is done.
[0033]
In addition, the hole injection layer and the hole transport layer in the organic EL device of the present invention may be composed of one layer containing one or more of the above compounds, or a plurality of different compounds containing different compounds. These layers may be laminated.
[0034]
Other electron injection materials and electron transport materials used in the organic EL device of the present invention are not particularly limited, and those conventionally used as electron transfer compounds in photoconductive materials, the electron injection layer of organic EL devices In addition, any of known materials used for the electron transport layer can be selected and used. Preferred examples of such electron transfer compounds include diphenylquinone derivatives (described in Journal of Electrophotographic Society, 30, 3 (1991), etc.), perylene derivatives (J. Apply. Phys., 27, 269 (1988), etc. Oxadiazole derivatives (the above-mentioned document, Jpn. J. Aplly. Phys., 27, L713 (1988)), Appl. Phys. Lett., 55, 1489 (1989), etc. ), Thiophene derivatives (described in JP-A-4-212286, etc.), triazole derivatives (described in Jpn. J. Appl. Phys., 32, L917 (1993), etc.), thiadiazole derivatives (the 43rd Proceedings of the Society of Polymer Science, (III) as described in P1a007, etc.), metal complexes of oxine derivatives (as described in IEICE Technical Report, 92 (311), 43 (1992), etc.), quinoxaline derivatives Polymers (as described in Jpn. J. Appl. Phys., 33, L250 (1994), etc.), phenanthroline derivatives (No. 3 times polymer debate proceedings, and the like can be mentioned ones) such as described in 14J07.
[0035]
Other light-emitting materials used in the light-emitting layer of the organic EL device of the present invention include daylight fluorescence as described in Polymer Functional Materials Series “Functional Functional Materials” edited by the Society of Polymer Sciences, Joint Publication (1991), P236. Known light-emitting materials such as materials, fluorescent brighteners, laser dyes, organic scintillators, and various fluorescent analysis reagents can be used. Specifically, polycyclic condensed compounds such as anthracene, phenanthrene, pyrene, chrysene, perylene, coronene, rubrene and quinacridone, oligophenylene compounds such as quarterphenyl, 1,4-bis (2-methylstyryl) benzene, 1 , 4-bis (4-methylstyryl) benzene, 1,4-bis (4-phenyl-5-oxazolyl) benzene, 1,4-bis (5-phenyl-2-oxazolyl) benzene, 2,5-bis ( 5-tertiary-butyl-2-benzoxazolyl) thiophene, 1,4-diphenyl-1,3-butadiene, 1,6-diphenyl-1,3,5-hexatriene, 1,1,4,4 -A scintillator for liquid scintillation such as tetraphenyl-1,3-butadiene, which is disclosed in JP-A 63-264692. Synthetic metal complexes, coumarin dyes, dicyanomethylenepyran dyes, dicyanomethylenethiopyran dyes, polymethine dyes, oxobenzanthracene dyes, xanthene dyes, carbostyryl dyes, and perylene dyes, oxazines described in German Patent No. 2534713 Compound, Preliminary Proceedings of the 40th Applied Physics Related Conference, 1146 (1993), stilbene derivatives described in JP-A-7-278537, and oxadiazoles described in JP-A-4-363891 Preference is given to system compounds.
[0036]
Each layer constituting the organic EL element of the present invention can be formed by forming a material to constitute each layer into a thin film by a known method such as a vapor deposition method, a spin coating method, or a casting method. The film thickness of each layer formed in this way is not particularly limited, and can be appropriately selected according to the properties of the material, but is usually selected in the range of 2 nm to 5000 nm. As a method of thinning the benzothiophene derivative, it is preferable to use a vapor deposition method from the viewpoint that a homogeneous film can be easily obtained and pinholes are hardly generated. In the case of thinning using a vapor deposition method, the vapor deposition conditions vary depending on the type of benzothiophene derivative, the target crystal structure and association structure of the molecular accumulation film, etc. Degree of vacuum 10 ^-6 -10 ^-3 It is preferable to select appropriately within the ranges of Pa, vapor deposition rate of 0.01 to 50 nm / second, substrate temperature of −150 to + 300 ° C., and film thickness of 5 nm to 5 μm.
[0037]
Next, as an example of a method for producing an organic EL device using the benzothiophene derivative of the present invention, a method for producing an organic EL device comprising the aforementioned anode / benzothiophene derivative / cathode will be described. A thin film made of a material for an anode is formed on a suitable substrate by vapor deposition so as to have a film thickness of 1 μm or less, preferably in the range of 10 to 200 nm, and then a benzothiophene derivative is formed on the anode. A thin film made of a cathode material is formed on the light emitting layer by a vapor deposition method so as to have a film thickness of 1 μm or less to form a cathode, thereby obtaining a target organic EL device. Is obtained. It should be noted that in the production of the organic EL element described above, the production order can be reversed, and the cathode, the light emitting layer, and the anode can be produced in this order.
[0038]
When a DC voltage is applied to the organic EL element thus obtained, the anode may be applied with a positive polarity and the cathode with a negative polarity. When a voltage of about 2 to 40 V is applied, a transparent or translucent electrode is applied. Luminescence can be observed from the side (anode or cathode and both). The organic EL element also emits light when an alternating voltage is applied. The alternating current waveform to be applied may be arbitrary.
[0039]
【Example】
Next, the present invention will be described in more detail based on examples.
[0040]
Synthesis example 1
Synthesis of tris [4- (2-benzothienyl) phenyl] amine (compound represented by formula (2), hereinafter abbreviated as BtP-3)
1.66 g of benzothiophene and 40 ml of t-butyl methyl ether are placed in a flask, cooled to −78 ° C. under a nitrogen atmosphere, and 8.5 ml of a 1.5 mol / L n-butyllithium / n-hexane solution is added dropwise. did. After raising the temperature to −10 to −5 ° C., 1.9 ml of N, N, N ′, N′-tetramethylethylenediamine and 3.43 g of dichloro (N, N, N ′, N′-tetramethylethylenediamine) zinc were added. And heated to room temperature. Next, 2.49 g of phenyliodine triiodide and 0.084 g of bis (triphenylphosphine) palladium chloride were added and heated at reflux temperature (56 ° C.) for 2 hours. After completion of the reaction, the mixture was cooled to room temperature, pure water was added, and the organic layer was extracted. The concentrated product was purified by recrystallization from toluene to obtain 1 g of the desired compound. The emission color of this compound in toluene was blue, and the Tg was 130 ° C.
¹ H-NMR (CDCl _Three ) Δ = 7.2 (d, 6H), 7.2 (m, 9H), 7.3-7.4 (m, 6H), 7.5 (s, 3H), 7.6-7.7 (d, 6H), 7.8 (d, d, 6H) .
The compound represented by the formula (3) (tris {4- [2- (3-t-butylbenzothienyl) is obtained by replacing benzothiophene with 3-t-butylbenzothiophene in the same manner as in this synthesis example. )] Phenyl} amine), the compound represented by formula (5) (tris {4- [2- (3-phenylbenzothienyl)] phenyl} amine) by replacing benzothiophene with 3-phenylbenzothiophene, Each can be synthesized.
[0041]
Example 1
A transparent support substrate was obtained by depositing ITO to a thickness of 50 nm on a glass substrate of 25 mm × 75 mm × 1.1 mm (manufactured by Tokyo Sanyo Vacuum Co., Ltd.). This transparent support substrate is fixed to a base holder of a commercially available vapor deposition apparatus (manufactured by Vacuum Kiko Co., Ltd.), and a molybdenum vapor deposition boat containing BtP-3 synthesized in Synthesis Example 1, Tris (8-hydroxyquinoline) aluminum (Hereinafter abbreviated as ALQ), a molybdenum vapor deposition boat containing lithium fluoride, a tungsten vapor deposition boat containing aluminum fluoride, and a tungsten vapor deposition boat containing aluminum were mounted. 1 × 10 vacuum chamber ^-3 Depressurize to Pa, heat the deposition boat containing BtP-3, deposit BtP-3 to a film thickness of 50 nm to form a hole transport layer, and then heat the deposition boat containing ALQ Then, ALQ was deposited to a thickness of 50 nm to form a light emitting layer. The deposition rate was 0.1 to 0.2 nm / second. Thereafter, the vapor deposition boat containing lithium fluoride is heated to deposit at a deposition rate of 0.003 to 0.01 nm / second so that the film thickness becomes 0.5 nm, and then the vapor deposition boat containing aluminum is heated. Then, an organic EL element was obtained by vapor deposition at a vapor deposition rate of 0.2 to 0.5 nm / second so as to have a film thickness of 100 nm. When a direct current voltage of about 4 V is applied using an ITO electrode as an anode and a lithium fluoride / aluminum electrode as a cathode, about 4 mA / cm ² Current flows and the brightness is about 100 cd / m ² A green light emission having a light emission efficiency of 2.1 lm / W and a wavelength of 520 nm was obtained. Further, although a DC voltage of 6.5 V was continuously applied, light emission was continued even after 3 hours. In addition, no decrease in light emission was observed even when heated to 100 ° C.
[0042]
Example 2
As in Example 1, a transparent support substrate was fixed to a substrate holder of a vapor deposition apparatus, and a molybdenum vapor deposition boat containing BtP-3 synthesized in Synthesis Example 1, N, N′-dinaphthyl-N, N′-diphenyl Molybdenum deposition boat containing -4,4'-diaminobiphenyl (hereinafter abbreviated as NPD), molybdenum deposition boat containing ALQ, molybdenum deposition boat containing lithium fluoride, and aluminum A tungsten vapor deposition boat fitted with was installed. 1 × 10 vacuum chamber ^-3 The pressure is reduced to Pa, the evaporation boat containing BtP-3 is heated, BtP-3 is evaporated to a film thickness of 10 nm to form a hole injection layer, and then the evaporation boat containing NPD is heated. And NPD was vapor-deposited so that it might become a film thickness of 50 nm, and the positive hole transport layer was formed. Next, the evaporation boat containing ALQ was heated, and ALQ was evaporated to a film thickness of 50 nm to form a light emitting layer. The above deposition rate was 0.1 to 0.2 nm / second. Thereafter, the vapor deposition boat containing lithium fluoride is heated to deposit at a deposition rate of 0.003 to 0.01 nm / second so as to have a film thickness of 0.5 nm, and then the vapor deposition boat containing aluminum is heated. Then, an organic EL element was obtained by vapor deposition at a vapor deposition rate of 0.2 to 0.5 nm / second so as to have a film thickness of 100 nm. When a direct current voltage of about 4 V is applied using an ITO electrode as an anode and a lithium fluoride / aluminum electrode as a cathode, about 3 mA / cm ² Current flows and the brightness is about 100 cd / m ² Met.
[0043]
Example 3
As in Example 1, a transparent support substrate is fixed to a substrate holder of a vapor deposition apparatus, and a molybdenum vapor deposition boat containing BtP-3 synthesized in Synthesis Example 1; a molybdenum vapor deposition boat containing NPD; A molybdenum vapor deposition boat containing 9′-spirobisilafluorene, a molybdenum vapor deposition boat containing lithium fluoride, and a tungsten vapor deposition boat containing aluminum were mounted. 1 × 10 vacuum chamber ^-3 Depressurize to Pa, heat the evaporation boat containing NPD, deposit NPD to a film thickness of 50 nm to form a hole transport layer, and then heat the evaporation boat containing BtP-3 Then, BtP-3 was deposited to a thickness of 20 nm to form a light emitting layer. Next, the 9,9′-spirobisilafluorene-containing vapor deposition boat was heated, and 9,9′-spirobisilafluorene was deposited to a film thickness of 50 nm to form an electron transport layer. The above deposition rate was 0.1 to 0.2 nm / second. Thereafter, the vapor deposition boat containing lithium fluoride is heated, vapor deposition is performed at a vapor deposition rate of 0.003 to 0.01 nm / second so that the film thickness is 0.5 nm, and then the vapor deposition boat containing aluminum is heated. The organic EL device was obtained by vapor deposition at a vapor deposition rate of 0.2 to 0.5 nm / second so that the film thickness was 100 nm. When a direct current voltage of 10 V is applied with the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, about 50 mA / cm ² The blue light emission from BtP-3 was obtained.
[0044]
Example 4
Similarly to Example 1, a transparent support substrate is fixed to a substrate holder of a vapor deposition apparatus, and a molybdenum vapor deposition boat containing BtP-3 synthesized in Synthesis Example 1 is used. 4,4 ′, 4 ″ -Tris {N— Molybdenum vapor deposition boat containing (3-methylphenyl) -N-phenylamino} triphenylamine, molybdenum vapor deposition boat containing ALQ, molybdenum vapor deposition boat containing lithium fluoride, and aluminum A tungsten vapor deposition boat was installed, and the vacuum chamber was 1 × 10 ^-3 The pressure is reduced to Pa, and the evaporation boat containing 4,4 ′, 4 ″ -tris {N- (3-methylphenyl) -N-phenylamino} triphenylamine is heated so that the film thickness becomes 4 nm. , 4 ′, 4 ″ -tris {N- (3-methylphenyl) -N-phenylamino} triphenylamine is deposited to form a hole injection layer, and then the deposition boat containing BtP-3 is heated. And BtP-3 was vapor-deposited so that it might become a film thickness of 50 nm, and the positive hole transport layer was formed. Next, the evaporation boat containing ALQ was heated, and ALQ was evaporated to a film thickness of 50 nm to form a light emitting layer. The above deposition rate was 0.1 to 0.2 nm / second. Thereafter, the vapor deposition boat containing lithium fluoride is heated to deposit at a deposition rate of 0.003 to 0.01 nm / second so as to have a film thickness of 0.5 nm, and then the vapor deposition boat containing aluminum is heated. Then, an organic EL element was obtained by vapor deposition at a vapor deposition rate of 0.2 to 0.5 nm / second so as to have a film thickness of 100 nm. When a direct current voltage of 3 V is applied with the ITO electrode as the anode and the lithium fluoride / aluminum electrode as the cathode, about 3 mA / cm ² Current flows, the brightness is about 100 cd / cm ² A green luminescence was obtained.
[0045]
Comparative Example 1
An organic EL device was produced in the same manner as in Example 1 except that BtP-3 in Example 1 was replaced with NPD. When a direct current voltage of about 4 V is applied using an ITO electrode as an anode and a lithium fluoride / aluminum electrode as a cathode, about 4 mA / cm ² Flows and the brightness is about 100 cd / cm ² The luminous efficiency was 1.9 lm / W. Moreover, when it heated at 100 degreeC, light emission was no longer seen.
[0046]
Comparative Example 2
An organic EL device was produced in the same manner as in Example 1 except that BtP-3 used in Example 1 was replaced with tris [4- (2-thienyl) phenyl] amine. When a direct current voltage of about 4 V is applied using an ITO electrode as an anode and a lithium fluoride / aluminum electrode as a cathode, about 20 mA / cm ² Flowed. In addition, when a DC voltage was applied at 80 ° C., light emission stopped after a few seconds.
[0047]
【The invention's effect】
As described above, since the benzothiophene derivative of the present invention has a high Tg of 100 ° C. or more and easily becomes an amorphous state, it is used as a light-emitting material, a hole transport material, and a hole injection material of an organic EL device. By doing so, the organic EL element can be made highly efficient and have a long life. That is, the organic EL element of the present invention can be easily made highly efficient, long-life, and full color by using a benzothiophene derivative as an organic layer. Therefore, by using the organic EL element of the present invention, a highly efficient display device such as a full color display can be created.

Claims (7)

A benzothiophene derivative represented by the general formula (1).

Wherein R _{1 to} R ₉ are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a substituted or unsubstituted aryl group, or a substituted or unsubstituted hetero group. Indicates a cyclic group.) An organic electroluminescence device, wherein the benzothiophene derivative according to claim 1 is used. The organic electroluminescent element according to claim 2, wherein the benzothiophene derivative according to claim 1 is contained in a hole transport layer. The organic electroluminescent element according to claim 2, wherein the benzothiophene derivative according to claim 1 is contained in a light emitting layer. The organic electroluminescent element according to claim 2, wherein the benzothiophene derivative according to claim 1 is contained in a hole injection layer. An organic electroluminescent material comprising the benzothiophene derivative according to claim 1. A hole transport material comprising the benzothiophene derivative according to claim 1.