JP4608044B2 - Novel arylamine-containing vinyl polymer and organic electroluminescent device using the same - Google Patents

Description

（式中、Ｒ^１は水素またはアルキル基、Ｒ^２とＲ^３は、水素、メチル基およびエチル基よりなる群からそれぞれ独立して選ばれた基であり、Ａｒ^１とＡｒ^２は、アルキル基を有していてもよいアリール基よりなる群からそれぞれ独立して選ばれた基）
の構造を有するアリールアミン含有ビニルモノマーを生成し、
【０００７】
このアリールアミン含有ビニルモノマーを重合して一般式（２）で示されるアリールアミン含有ビニルポリマーを生成するにおいて、
【化７】

（式中、Ｒ^１は水素またはアルキル基、Ｒ^２とＲ^３は、水素、メチル基およびエチル基よりなる群からそれぞれ独立して選ばれた基であり、Ａｒ^１とＡｒ^２は、アルキル基を有していてもよいアリール基よりなる群からそれぞれ独立して選ばれた基）
一般式（１）のアリールアミン含有ビニルモノマーが上記一般式（２）で示される数平均分子量１，０００〜１，０００，０００のアリールアミン含有ビニルポリマーを基本骨格とするものであり、
【０００８】
アリールアミン含有ビニルポリマーの基本骨格として、下記の一般式（３）（４）（５）を有するものである。
一般式（３）
【化８】

（式中、Ｒ^１、Ｒ^４、Ｒ^５、Ｒ^６、Ｒ^７、Ｒ^８、Ｒ^９、Ｒ^１０およびＲ^１１は水素およびアルキル基よりなる群からそれぞれ独立して選ばれた基であり、Ｒ^２とＲ^３は、水素、メチル基およびエチル基よりなる群からそれぞれ独立して選ばれた基であり、Ａｒ^３、Ａｒ^４およびＡｒ^５は、アルキル基を有していてもよいアリール基よりなる群からそれぞれ独立して選ばれた基である）
で示される繰り返し単位を含有するアリールアミン含有ビニルポリマー。
又は、上記一般式（３）のＡｒ^４とＡｒ^５が結合しているＮと一体になる下記の複素環基を形成するもの。
一般式（４）
【化９】

（前記式中、Ｒ^１２、Ｒ^１３、Ｒ^１４、Ｒ^１５、Ｒ^１６、Ｒ^１７、Ｒ^１８およびＲ^１９は、水素およびアルキル基よりなる群からそれぞれ独立して選ばれた基）で示される繰り返し単位を含有するアリールアミン含有ビニルポリマー。
又は、下記の一般式（５）で示されるもの。
一般式（５）
【化１０】

（式中、Ｒ^１、Ｒ^２０、Ｒ^２１、Ｒ^２２、Ｒ^２３、Ｒ^２４、Ｒ^２５、Ｒ^２６およびＲ^２７は、水素およびアルキル基よりなる群からそれぞれ独立して選ばれた基であり、Ｒ^２とＲ^３は、水素、メチル基およびエチル基よりなる群からそれぞれ独立して選ばれた基であり、Ａｒ^３、Ａｒ^４およびＡｒ^５は、アルキル基を有していてもよいアリール基よりなる群からそれぞれ独立して選ばれた基である）
で示される繰り返し単位を含有するアリールアミン含有ビニルポリマー。
【０００９】
本発明の第二は、請求項１に記載のアリールアミン含有ビニルポリマーのいずれかを用いたことを特徴とする有機エレクトロルミネッセント素子に関する。
【００１０】
本発明の第三は、請求項１に記載のアリールアミン含有ビニルポリマーが正孔輸送層として使用されていることを特徴とする有機エレクトロルミネッセント素子に関する。
【００１１】
本発明に用いるビニルモノマーは、スチレンのようなアリール系ビニルモノマーの通常の重合開始剤を用い、通常の方法により重合して、請求項１のポリマーとすることができる。必要に応じて他のビニルモノマーと共重合することもできる。
【００１２】
本発明の有機エレクトロルミネッセント素子は、前記高分子材料を含有する有機層を備えていれば、素子構造は特に限定されず、有機層一層からなる単層型でも二層以上の多層型であってもよい。要するに前記高分子材料を備えた種々の素子構造に適用できる。
【００１３】
本発明で用いられる高分子層を含む素子を構成する各層の膜厚については、特に限定されない。高分子層は高分子を適当な溶媒に溶解した溶液からの塗布法のほかにもインクジェット法、ラングミュア−ブロジェット法によっても形成できる。他の有機層は真空蒸着法などの気相成長法や溶液塗布法によって形成することができる。
【００１４】
有機エレクトロルミネッセント素子では大きな仕事関数を有する陽極すなわち正孔注入電極から正孔が有機層へ注入され、小さな仕事関数を有する陰極電極から電子が有機層へ注入される。正孔輸送層と電子輸送性発光層からなる二層型素子の場合、注入された正孔は正孔輸送層を通り発光層との界面付近で、発光層に注入されてきた電子と再結合し発光層中で励起子を生ずる。この結果、発光層より発光が生じる。
【００１５】
このとき、高い発光効率、輝度を得るには、各層の電荷の輸送特性の向上ばかりでなく電極からの電荷の注入効率を上げることが重要である。また、通電によるジュール熱による有機層の再結晶化、凝集の促進、すなわち素子劣化を防ぐためにもガラス転移点の高い材料を選択する必要がある。
【００１６】
本発明においては、正孔輸送層に高い正孔輸送特性を有する新規高分子を用いることにより、電極との密着性を高め電荷の注入特性を上げるものである。また、高いガラス転移点を有する高分子を使用するため、結晶化や凝集による素子劣化が抑制され、良好な特性を有する有機エレクトロルミネッセント素子を得ることができる。
【００１７】
本発明のアリールアミン含有ビニルポリマーは、繰り返し単位構造中−Ｃ（Ｒ^２，Ｒ^３）−の個所を中心にしてジアリールアミン基が自由に回転することができる構造を有することにより、重合反応においてダイマーなどの低分子成分が生成せず、結果的に生成したポリマーのガラス転移温度を高くすることに成功したものである。したがって−Ｃ（Ｒ^２，Ｒ^３）−としては、−ＣＨ^２−や、−ＣＨＭｅ−（Ｍｅはメチル）が最も好ましい。また、−Ｃ（Ｒ^２，Ｒ^３）−の存在により図１に示すように分子の重なり合うエキシマー現象が抑制できるのも大きなメリットである。
この基本的技術思想を害しないかぎり、Ａｒ^１とＡｒ^２は芳香族系の広い範囲の基を包含することができる。請求項１に示すものはＡｒ^２の１つの具体例を示すにすぎない。
【００１８】
【実施例】
以下に実施例を挙げて本発明を説明するが、本発明はこれにより何ら限定されるものではない。
【００１９】
実施例１
▲１▼ベンジル誘導体の合成
空冷管、温度計、マグネットと窒素導入管のついた１００ｍｌの３つ口フラスコに、Ｎ，Ｎ′−ジフェニルベンジジン２０．２ｇ（６０ｍｍｏｌ）、ヨードベンゼン１２．５ｇ（６０ｍｍｏｌ）、銅粉３８ｇと炭酸カリウム１６．６ｇ（１２０ｍｍｏｌ）を加え、窒素気流下マッドヒーターで２３０℃で２４時間反応した。反応後、室温まで冷却し５００ｍｌのエチレンジクロリドで希釈した。この液を濾過し不溶物を分離し、溶媒を減圧下回収した。得られた残渣は、カラムクロマトグラフィー（展開液クロロホルム：ｎ−ヘキサン＝１：１）で精製し、下記式（６）で示される目的物を４．６ｇ（１１．１ｍｍｏｌ）得た（収率１８．６％）。
【化１１】

【００２０】
▲２▼モノマーの合成
前記式（６）で示されるベンジジン誘導体２．０ｇ（５ｍｍｏｌ）は、２５ｍｌの滴下ロート、水冷管、温度計、マグネットと窒素導入管のついた１００ｍｌの３つ口フラスコに、トリエチルアミン２．０ｇ（２０ｍｍｏｌ）と共にジメチルスルホキシド（ＤＭＳＯ）２５ｍｌに溶解させた。これに滴下ロートから、１．５ｇ（１０ｍｍｏｌ）のα−クロロメチルｐ−スチレンを室温で滴下した。この後、マッドヒーターで１００℃、２４時間反応した。反応後、室温まで冷却し沈殿物を濾過し、濾液は減圧下回収した。得られた残渣は、カラムクロマトグラフィー（展開液クロロホルム：ｎ−ヘキサン＝２：１）で単離した。これにより目的の式（７）で示されるスチレンモノマーを１．０ｇ（１．９ｍｍｏｌ）、収率１８．９％で得た。融点５８．５〜６０．２℃。図３は、このものの^１Ｈ−ＮＭＲチャートであり、図４は、ＩＲチャートである。
【化１２】

【００２１】
▲３▼ポリマー（ＰＴＰＤ−２）の合成
前記式（７）で示されるモノマー０．５ｇ（０．９５ｍｍｏｌ）とアゾビスイソブチロニトリル（以下ＡＩＢＮと略する）０．００５ｇ（０．０３ｍｍｏｌ）を、水冷管、窒素導入管、水銀温度計そして、マグネットのついた３０ｍｌの４つ口フラスコに加えテトラヒドロフラン（以下ＴＨＦと略す）４ｍｌに溶かした。そして、液体窒素で凍結脱気を３回くり返した。
このＴＨＦ溶液は、マッドヒーターで窒素気流下６０℃、２４時間ラジカル重合を行った。その後、室温まで冷却し１０００ｍｌのアセトン中にあけ、析出したポリマーを回収した。得られた粗製のポリマーは、その後ＴＨＦ−アセトンで３回再沈精製を行い０．３ｇ（収率６０％）の後記式（８）にその繰り返し単位を示すポリ〔ｐ−Ｎ′−（ｐ−Ｎ，Ｎ−ジフェニルアミノ）ビフェニル〕Ｎ′−フェニルアミノメチル〕スチレン（以下ＰＴＰＤ−２と略する）を得た。
【００２２】
▲４▼ポリマー（ＰＴＰＤ−２）の構造と物性
式（８）に示す繰り返し単位をもつ前記ポリマーを、ＴＨＦを移動層としたＧＰＣ分析（日立製Ｌ７１００シリーズ）を行ったところ、重量平均分子量（Ｍｗ）１９０００、数平均分子量（Ｍｎ）１４５００であった（いずれもポリスチレン換算）。示差走査熱量計（パーキンエルマー社製ＤＴＡ７）で測定したガラス転移温度は１４２℃であり、熱重量計（パーキンエルマー社製ＤＴＡ７）で測定した窒素ガス中での分解温度も４０３℃と高く、高い熱安定性を示した。理研計器社製表面分析装置（ＡＣ−１）で測定したイオン化ポテンシャルは５．６ｅＶであり、ホール輸送性材料としては十分に小さいイオン化ポテンシャルを有することが分った。
ＰＴＰＤ−２の有機溶媒に対する溶解性を下記表１に示す。
【表１】

（＋＋）可溶、（＋）一部可溶、（−）不溶
【化１３】

【００２３】
実施例２
▲１▼モノマーの合成
水冷管、２５ｍｌの滴下ロート、マグネットそして水銀温度計のついた２００ｍｌの３つ口フラスコ内において、ジフェニルアミン１０．２ｇ（６．０ｍｍｏｌ）と炭酸水素ナトリウム５．０ｇ（４．００ｍｍｏｌ）をメタノール１００ｍｌに溶解させた。これに滴下ロートから、３．１ｇ（２．００ｍｍｏｌ）のα−クロロメチルｐ−スチレンを室温で滴下した。この後、マッドヒーターで還流下８時間反応した。反応後、室温まで冷却した沈殿物を濾過し、濾液は減圧下回収した。得られた残渣は、カラムクロマトグラフィー（展開液ｎ−ヘキサン：クロロホルム＝４：１）で単離した。これにより目的の下記式（９）で示されるスチレンモノマーを１．１ｇ（０．３４ｍｍｏｌ）、収率１７．３％で得た。融点６５．０〜６６．０℃。図５は、このものの^１Ｈ−ＮＭＲチャートであり、図６は、ＩＲチャートである。
【化１４】

【００２４】
▲２▼ポリマー（ＰＤＰＡＭＳ）の合成
前記式（９）で示されるモノマー１．０ｇとアゾビスブチロニトリル（以下ＡＩＢＭと略す）０．０１ｇ（０．０６ｍｍｏｌ）を、水冷管、窒素導入管、水銀温度計そしてマグネットのついた５０ｍｌの４つ口フラスコに加えテトラヒドロフラン（以下ＴＨＦと略す）４ｍｌに溶かした。そして、液体窒素で凍結脱気を３回くり返した。
このＴＨＦ溶液は、マッドヒーターで窒素気流下還流させながら２４時間ラジカル重合を行った。その後、室温まで冷却し１０００ｍｌのメタノール中にあけ、析出したポリマーを回収した。得られた粗製のポリマーは、その後ＴＨＦ−メタノールで２回再沈精製を行い０．８９ｇ（収率８９．０％）のポリ（ｐ−Ｎ，Ｎ−ジフェニルアニリノメチル）スチレン（以下ＰＤＰＡＭＳと略する）を得た〔下記式（１０）にその繰り返し単位を示す〕。
【化１５】

【００２５】
▲３▼ポリマー（ＰＤＰＡＭＳ）の構造と物性
式（１０）に示す繰り返し単位をもつ前記ポリマーを、ＴＨＦを移動層としたＧＰＣ分析（日立製Ｌ７１００シリーズ）を行ったところ、重量平均分子量（Ｍｗ）３４０００、数平均分子量（Ｍｎ）１８０００であった（いずれもポリスチレン換算）。示差走査熱量計（パーキンエルマー社製ＤＴＡ７）で測定したガラス転移温度は８０℃であり、熱重量計（パーキンエルマー社製ＤＴＡ７）で測定した窒素ガス中での分解温度も３７８℃と高く、高い熱安定性を示した。理研計器社製表面分析装置（ＡＣ−１）で測定したイオン化ポテンシャルは５．６ｅＶであり、ホール輸送性材料としては十分に小さいイオン化ポテンシャルを有することが分った。
ＰＤＰＡＭＳの有機溶媒に対する溶解性を下記表２に示す。
【表２】

（＋＋）可溶、（＋）一部可溶、（−）不溶
【００２６】
実施例３
実施例１の方法に準拠し、下記化学反応式に従って、カルバゾール基を有するアリールアミン含有ビニルポリマーを得た。
【化１６】

得られたポリマーは、カルバゾール基を含有しているため、実施例１や２のポリマーに較べて耐熱性に優れている。
【００２７】
実施例４
実施例１の方法に準拠し、下記化学反応式に従って、フルオレン基をもつアリールアミン含有ビニルポリマーを得た。
【化１７】

得られたポリマーは、フルオレン基を含有しているため、実施例１や２のポリマーに較べて耐熱性に優れている。
【００２８】
実施例５
＜ＥＬ素子の作製＞
図２は本発明の一実施例の断面図である。１はガラス基板で２のシート抵抗１５Ω／□のＩＴＯ（インジウム−チン−オキサイド）がコートされている。その上に正孔輸送性高分子層３として実施例２で得られた式（１０）で示される繰り返し単位をもつアリールアミン含有ビニルポリマー（ＰＤＰＡＭＳ）をクロロホルム溶液からディップコーティング法により４００Å厚に形成した。その上から、発光層４として下記式
【化１８】

で示される電子輸送性のトリス（８−キノリノラト）アルミニウム錯体を７００Å、１０^−５Ｔｏｒｒの真空下で蒸着して形成した。最後に陰極電極としてＭｇとＡｇ（１０：１）を同じ真空度で２０００Å共蒸着した。発光領域の領域は縦０．５ｃｍ、横０．５ｃｍの正方形状とした。
【００２９】
前記の有機エレクトロルミネッセント素子においてＩＴＯを陽極、Ｍｇ：Ａｇを陰極として、直流電圧を印加してガラス基板を通して発光を観察した。輝度はトプコン輝度計ＢＭ−８により測定した。この素子は初期駆動５Ｖの印加により緑色の発光が得られ、発光スペクトルから発光層のトリス（８−キノリノラト）アルミニウム錯体が発光していることを確認した。輝度は１４Ｖで２５００ｃｄ／ｍ^２と高い値を示した。また、作製後３カ月間、室温下、乾燥窒素雰囲気中で保存した素子においても初期特性がほとんど変わらず、素子の保存安定性は極めて良好であることを確認した。さらに、乾燥窒素雰囲気中で１００℃の条件で１００時間保存した素子においてもおおきな劣化は見られず、この素子が高い耐熱性を有することが確認された。また一定電流値で連続駆動を行った場合においても、３カ月後に輝度の大幅な低下は見られなかった。
【００３０】
比較例１
低分子モデル化合物である下記式
【化１９】

のアリールアミン蒸着膜を正孔輸送層に用いた同様の素子では輝度半減時間が２５時間である。
【００３１】
前記実施例５と比較例１から、実施例５で用いた新規高分子（ＰＤＰＡＭＳ）の高いガラス転移温度により有機層の安定性が大幅に改善されていることがわかる。
また、本発明の素子は発光層がトリス（８−キノリノラト）アルミニウム錯体以外の有機材料の時でも同様に安定性の向上が認められた。
【００３２】
実施例６
正孔輸送高分子層３を形成するポリマーとして実施例１で得られた式（８）で示される繰り返し単位をもつアリールアミン含有ビニルポリマー（ＰＴＰＤ−２）を用いた以外は実施例３を繰り返した。
【００３３】
前記の有機エレクトロルミネッセント素子においてＩＴＯを陽極、Ｍｇ：Ａｇを陰極として、直流電圧を印加してガラス基板を通して発光を観察した。輝度はトプコン輝度計ＢＭ−８にて測定した。この素子からは直流電圧の印加により緑色の発光が得られ、発光スペクトルから発光層のトリス（８−キノリノラト）アルミニウム錯体が発光していることを確認した。図９は輝度−電圧特性を示し、図１０は電流密度−電圧特性を示す。本発明においては、アリールアミン含有ビニルポリマーよりなる正孔輸送性高分子層３の膜厚が２００Åのときが膜厚を３００Åとしたときや４００Åとしたときに比べて同じ電圧をかけた場合、最も高い輝度を示す。その最高輝度は１１Ｖにおいて８７００ｃｄ／ｍ^２であった。
【００３４】
また、作製後３カ月間、室温にて乾燥窒素雰囲気中で保存した素子においても初期特性がほとんど変わらず、素子の保存安定性は極めて良好であることを確認した。さらに、乾燥窒素雰囲気中で１００℃の条件で１００時間保存した素子においてもおおきな劣化は見られず、この素子が高い耐熱性を有することが確認された。また一定電流値で連続駆動を行った場合においても、３カ月後に輝度の大幅な低下は見られなかった。
【００３５】
比較例２
低分子モデル化合物である下記式
【化２０】

のアリールアミン蒸着膜を正孔輸送層に用いた同様の素子では輝度半減時間が１０時間である。
【００３６】
前記実施例６と比較例２から、実施例６で用いた新規高分子（ＰＴＰＤ−２）の高いガラス転移温度により有機層の安定性が大幅に改善されていることがわかる。
また、本発明の素子は発光層がトリス（８−キノリノラト）アルミニウム錯体以外の有機材料のときでも同様に安定性の向上が認められた。
【００３７】
【発明の効果】
（１） 本発明により新規なアリールアミン含有ビニルモノマーおよびそのポリマーが提供できた。
（２） 本発明によれば発光特性および長期間の安定性に優れた有機エレクトロルミネッセント素子が提供される。したがって、本発明の有機エレクトロルミネッセント素子は実用化に十分な信頼性を有し、表示、照明の分野で広く利用できる。
【図面の簡単な説明】
【図１】本発明のアリールアミン含有ビニルポリマーが従来のアリールアミン含有ビニルポリマーに較べてエキシマーを抑制する理由を説明するためのモデル図である。
【図２】本発明実施例で用いる有機ＥＬ素子の断面構造を示すモデル図である。
【図３】実施例１のモノマーの^１Ｈ−ＮＭＲチャートを示す。
【図４】実施例１のモノマーのＩＲチャートを示す。
【図５】実施例２のモノマーの^１Ｈ−ＮＭＲチャートを示す。
【図６】実施例２のモノマーのＩＲチャートを示す。
【図７】実施例５のＥＬ素子にかかる輝度−電圧曲線を示す図である。
【図８】実施例５のＥＬ素子にかかる電流密度−電圧曲線を示す図である。
【図９】実施例６のＥＬ素子にかかる輝度−電圧曲線を示す図である。
【図１０】実施例６のＥＬ素子にかかる電流密度−電圧曲線を示す図である。
【符号の説明】
１ ガラス基板
２ ＩＴＯ膜
３ 正孔輸送性高分子層
４ 発光層
５ 電極[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel arylamine-containing vinyl polymer and an organic electroluminescent device (organic EL device) used for a planar light source and a display device using the same.
[0002]
[Prior art]
An organic EL element in which a light emitting layer is composed of an organic thin film is attracting attention as a low-voltage driven large area display element. A device structure in which organic layers with different carrier transport properties are stacked is effective for improving device efficiency, and devices using low-molecular aromatic amines for the hole transport layer and aluminum chelate complexes for the electron transport light-emitting layer have been reported. [C. W. Tang, Appl. Phys. Lett. 51, p. 913 (1987)]. In this element, high luminance sufficient for practical use of 1000 cd / m ² is obtained with an applied voltage of 10 V or less.
[0003]
However, in the hole transport layer of a low molecular aromatic amine that is generally used, the glass transition temperature of the material is as low as about 60 ° C. to 100 ° C., and the device structure is destroyed by recrystallization or aggregation, or at a high environmental temperature. Deterioration of the element during storage is a problem. For this reason, even an element with good initial characteristics is not suitable for long-time use, and has a shortage of a drive element life of about several thousand hours, which is shorter than existing inorganic light-emitting elements such as light-emitting diodes.
[0004]
[Problems to be solved by the invention]
Therefore, the present inventors have developed an arylamine-containing vinyl polymer having a high glass transition point, and by using it instead of the conventional low-molecular aromatic amine, the device structure can be destroyed by recrystallization or aggregation. The object of the present invention is to provide a novel organic EL device that prevents deterioration of the device during storage at a high ambient temperature.
[0005]
[Means for Solving the Problems]
In order to solve the above-described problems, the present inventors have focused on polymer materials that are less likely to cause crystallization and aggregation and have high film stability, and have studied to polymerize arylamine derivatives having hole transport properties. The resulting new polymer material has a glass transition temperature (140 ° C or higher) that is much higher than that of low molecular weight model compounds, and it has excellent film storage stability and is a good hole transport layer in organic EL devices. The present invention has been completed by finding that it is functionally effective, showing high luminous efficiency and luminous luminance, and is extremely effective in improving the stability of the device.
[0006]
That is, the present invention provides the following general formula (1)
[Chemical 6]

(Wherein R ¹ is hydrogen or an alkyl group, R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ¹ and Ar ² are alkyl groups. Each independently selected from the group consisting of aryl groups optionally having
Producing an arylamine-containing vinyl monomer having the structure:
[0007]
In polymerizing this arylamine-containing vinyl monomer to produce an arylamine-containing vinyl polymer represented by the general formula (2),
[Chemical 7]

(Wherein R ¹ is hydrogen or an alkyl group, R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ¹ and Ar ² are alkyl groups. Each independently selected from the group consisting of aryl groups optionally having
The arylamine-containing vinyl monomer of the general formula (1) is based on an arylamine-containing vinyl polymer having a number average molecular weight of 1,000 to 1,000,000 represented by the general formula (2).
[0008]
The basic skeleton of the arylamine-containing vinyl polymer has the following general formulas (3), (4) and (5).
General formula (3)
[Chemical 8]

(Wherein R ¹ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are groups independently selected from the group consisting of hydrogen and alkyl groups, R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ³ , Ar ⁴ and Ar ⁵ are aryl groups optionally having an alkyl group Each group independently selected from the group consisting of:
An arylamine-containing vinyl polymer containing a repeating unit represented by:
Or what forms the following heterocyclic group united with N to which Ar ⁴ and Ar ⁵ of the general formula (3) are bonded.
General formula (4)
[Chemical 9]

(Wherein R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ and R ¹⁹ are groups independently selected from the group consisting of hydrogen and an alkyl group). An arylamine-containing vinyl polymer containing repeating units.
Or what is shown by the following general formula (5).
General formula (5)
Embedded image

Wherein R ¹ , R ²⁰ , R ²¹ , R ²² , R ²³ , R ²⁴ , R ²⁵ , R ²⁶ and R ²⁷ are groups independently selected from the group consisting of hydrogen and an alkyl group. , R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ³ , Ar ⁴ and Ar ⁵ are aryl optionally having an alkyl group Each group independently selected from the group consisting of groups)
An arylamine-containing vinyl polymer containing a repeating unit represented by:
[0009]
A second aspect of the present invention relates to an organic electroluminescent device using any of the arylamine-containing vinyl polymers according to claim 1 .
[0010]
A third aspect of the present invention relates to an organic electroluminescent device characterized in that the arylamine-containing vinyl polymer according to claim 1 is used as a hole transport layer.
[0011]
The vinyl monomer used in the present invention can be polymerized by a usual method using a usual polymerization initiator of an aryl vinyl monomer such as styrene, and the polymer of claim 1 can be obtained. If necessary, it can be copolymerized with other vinyl monomers.
[0012]
The organic electroluminescent device of the present invention is not particularly limited as long as the organic electroluminescent device of the present invention includes an organic layer containing the polymer material. The device structure may be a single layer type composed of one organic layer or a multilayer type of two or more layers. There may be. In short, the present invention can be applied to various element structures provided with the polymer material.
[0013]
The film thickness of each layer constituting the element including the polymer layer used in the present invention is not particularly limited. The polymer layer can be formed by an ink jet method or a Langmuir-Blodgett method in addition to a coating method from a solution in which a polymer is dissolved in an appropriate solvent. The other organic layer can be formed by a vapor deposition method such as a vacuum deposition method or a solution coating method.
[0014]
In the organic electroluminescent device, holes are injected into the organic layer from an anode having a large work function, that is, a hole injection electrode, and electrons are injected into the organic layer from a cathode electrode having a small work function. In the case of a two-layer device consisting of a hole transport layer and an electron transporting light emitting layer, the injected holes recombine with the electrons injected into the light emitting layer through the hole transport layer and in the vicinity of the interface with the light emitting layer. Then, excitons are generated in the light emitting layer. As a result, light emission occurs from the light emitting layer.
[0015]
At this time, in order to obtain high luminous efficiency and luminance, it is important not only to improve the charge transport characteristics of each layer, but also to increase the charge injection efficiency from the electrodes. In addition, it is necessary to select a material having a high glass transition point in order to prevent recrystallization and aggregation of the organic layer due to Joule heat by energization, that is, to prevent element deterioration.
[0016]
In the present invention, the use of a novel polymer having high hole transport characteristics for the hole transport layer enhances the adhesion with the electrode and improves the charge injection characteristics. In addition, since a polymer having a high glass transition point is used, device deterioration due to crystallization and aggregation is suppressed, and an organic electroluminescent device having good characteristics can be obtained.
[0017]
The arylamine-containing vinyl polymer of the present invention has a structure in which a diarylamine group can freely rotate around a position of —C (R ² , R ³ ) — in the repeating unit structure, thereby allowing polymerization reaction. A low molecular component such as a dimer is not generated, and as a result, the glass transition temperature of the resulting polymer has been successfully increased. Accordingly, —C (R ² , R ³ ) — is most preferably —CH ² — or —CHMe— (Me is methyl). In addition, the presence of -C (R ² , R ³ )-can greatly suppress the excimer phenomenon of overlapping molecules as shown in FIG.
As long as this basic technical idea is not harmed, Ar ¹ and Ar ² can include a wide range of aromatic groups. What is shown in claim 1 shows only one specific example of Ar ² .
[0018]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
[0019]
Example 1
(1) Synthesis of benzyl derivative In a 100 ml three-necked flask equipped with an air-cooled tube, a thermometer, a magnet and a nitrogen introducing tube, 20.2 g (60 mmol) of N, N'-diphenylbenzidine and 12.5 g (60 mmol) of iodobenzene were added. ), 38 g of copper powder and 16.6 g (120 mmol) of potassium carbonate were added, and the mixture was reacted at 230 ° C. for 24 hours with a mud heater under a nitrogen stream. After the reaction, the reaction mixture was cooled to room temperature and diluted with 500 ml of ethylene dichloride. This liquid was filtered to separate insoluble matters, and the solvent was recovered under reduced pressure. The obtained residue was purified by column chromatography (developing solution chloroform: n-hexane = 1: 1) to obtain 4.6 g (11.1 mmol) of the target compound represented by the following formula (6) (yield) 18.6%).
Embedded image

[0020]
(2) Synthesis of monomer 2.0 g (5 mmol) of the benzidine derivative represented by the above formula (6) was placed in a 100 ml three-necked flask equipped with a 25 ml dropping funnel, a water-cooled tube, a thermometer, a magnet and a nitrogen introducing tube. And 2.0 g (20 mmol) of triethylamine were dissolved in 25 ml of dimethyl sulfoxide (DMSO). From this dropping funnel, 1.5 g (10 mmol) of α-chloromethyl p-styrene was added dropwise at room temperature. Then, it reacted at 100 degreeC with the mud heater for 24 hours. After the reaction, the reaction mixture was cooled to room temperature, the precipitate was filtered, and the filtrate was collected under reduced pressure. The obtained residue was isolated by column chromatography (developing solution chloroform: n-hexane = 2: 1). As a result, 1.0 g (1.9 mmol) of a target styrene monomer represented by the formula (7) was obtained in a yield of 18.9%. Melting point 58.5-60.2 ° C. FIG. 3 is a ¹ H-NMR chart of this product, and FIG. 4 is an IR chart.
Embedded image

[0021]
(3) Synthesis of polymer (PTPD-2) 0.5 g (0.95 mmol) of the monomer represented by the formula (7) and 0.005 g (0.03 mmol) of azobisisobutyronitrile (hereinafter abbreviated as AIBN) Was dissolved in 4 ml of tetrahydrofuran (hereinafter abbreviated as THF) in addition to a water-cooled tube, a nitrogen introduction tube, a mercury thermometer, and a 30 ml four-necked flask equipped with a magnet. Then, freeze deaeration was repeated three times with liquid nitrogen.
This THF solution was subjected to radical polymerization with a mud heater under a nitrogen stream at 60 ° C. for 24 hours. Then, it cooled to room temperature and opened in 1000 ml of acetone, and the deposited polymer was collected. The obtained crude polymer was then purified by reprecipitation three times with THF-acetone, and 0.3 g (yield 60%) of poly [p-N '-(p -N, N-diphenylamino) biphenyl] N'-phenylaminomethyl] styrene (hereinafter abbreviated as PTPD-2) was obtained.
[0022]
(4) Structure of polymer (PTPD-2) and physical properties The polymer having the repeating unit represented by the formula (8) was subjected to GPC analysis (Hitachi L7100 series) using THF as a moving bed. Mw) 19000 and number average molecular weight (Mn) 14500 (all in terms of polystyrene). The glass transition temperature measured with a differential scanning calorimeter (Perkin Elmer DTA7) is 142 ° C., and the decomposition temperature in nitrogen gas measured with a thermogravimetric meter (Perkin Elmer DTA7) is as high as 403 ° C., which is high. It showed thermal stability. The ionization potential measured with a surface analyzer (AC-1) manufactured by Riken Keiki Co., Ltd. was 5.6 eV, and it was found to have a sufficiently small ionization potential as a hole transporting material.
Table 1 below shows the solubility of PTPD-2 in organic solvents.
[Table 1]

(++) soluble, (+) partially soluble, (-) insoluble

[0023]
Example 2
(1) Synthesis of monomer In a 200 ml three-necked flask equipped with a water-cooled tube, 25 ml dropping funnel, magnet and mercury thermometer, 10.2 g (6.0 mmol) of diphenylamine and 5.0 g of sodium hydrogen carbonate (4. 00 mmol) was dissolved in 100 ml of methanol. From this dropping funnel, 3.1 g (2.00 mmol) of α-chloromethyl p-styrene was added dropwise at room temperature. Then, it reacted for 8 hours under reflux with a mud heater. After the reaction, the precipitate cooled to room temperature was filtered, and the filtrate was collected under reduced pressure. The obtained residue was isolated by column chromatography (developing solution n-hexane: chloroform = 4: 1). As a result, 1.1 g (0.34 mmol) of the desired styrene monomer represented by the following formula (9) was obtained in a yield of 17.3%. Melting point 65.0-66.0 ° C. FIG. 5 is a ¹ H-NMR chart of this product, and FIG. 6 is an IR chart.
Embedded image

[0024]
(2) Synthesis of polymer (PDPAMS) 1.0 g of the monomer represented by the formula (9) and 0.01 g (0.06 mmol) of azobisbutyronitrile (hereinafter abbreviated as AIBM) were added to a water-cooled tube, a nitrogen introducing tube, In addition to a 50 ml four-necked flask equipped with a mercury thermometer and a magnet, it was dissolved in 4 ml of tetrahydrofuran (hereinafter abbreviated as THF). Then, freeze deaeration was repeated three times with liquid nitrogen.
This THF solution was subjected to radical polymerization for 24 hours while being refluxed with a mud heater under a nitrogen stream. Thereafter, it was cooled to room temperature and poured into 1000 ml of methanol, and the precipitated polymer was recovered. The obtained crude polymer was purified by reprecipitation twice with THF-methanol, and then 0.89 g (yield 89.0%) of poly (p-N, N-diphenylanilinomethyl) styrene (hereinafter referred to as PDPAMS). Abbreviated) (the repeating unit is shown in the following formula (10)).
Embedded image

[0025]
(3) Structure of polymer (PDPAMS) and physical properties When the polymer having the repeating unit represented by the formula (10) was subjected to GPC analysis (L7100 series manufactured by Hitachi) using THF as a moving bed, the weight average molecular weight (Mw) 34,000 and a number average molecular weight (Mn) of 18000 (all in terms of polystyrene). The glass transition temperature measured with a differential scanning calorimeter (Perkin Elmer DTA7) is 80 ° C., and the decomposition temperature in nitrogen gas measured with a thermogravimetric meter (Perkin Elmer DTA7) is also high and high at 378 ° C. It showed thermal stability. The ionization potential measured with a surface analyzer (AC-1) manufactured by Riken Keiki Co., Ltd. was 5.6 eV, and it was found to have a sufficiently small ionization potential as a hole transporting material.
The solubility of PDPAMS in organic solvents is shown in Table 2 below.
[Table 2]

(++) soluble, (+) partially soluble, (-) insoluble
Example 3
Based on the method of Example 1, an arylamine-containing vinyl polymer having a carbazole group was obtained according to the following chemical reaction formula.
Embedded image

Since the obtained polymer contains a carbazole group, it is excellent in heat resistance as compared with the polymers of Examples 1 and 2.
[0027]
Example 4
In accordance with the method of Example 1, an arylamine-containing vinyl polymer having a fluorene group was obtained according to the following chemical reaction formula.
Embedded image

Since the obtained polymer contains a fluorene group, it is excellent in heat resistance as compared with the polymers of Examples 1 and 2.
[0028]
Example 5
<Production of EL element>
FIG. 2 is a cross-sectional view of one embodiment of the present invention. A glass substrate 1 is coated with ITO (indium-tin-oxide) 2 having a sheet resistance of 15Ω / □. On top of that, an arylamine-containing vinyl polymer (PDPAMS) having a repeating unit represented by the formula (10) obtained in Example 2 as a hole transporting polymer layer 3 is formed to a thickness of 400 mm from a chloroform solution by a dip coating method. did. From there, the light emitting layer 4 has the following formula:

The electron-transporting tris (8-quinolinolato) aluminum complex represented by formula (1) was formed by vapor deposition under a vacuum of 700 ^-5 and 10 ^-5 Torr. Finally, Mg and Ag (10: 1) were co-deposited as a cathode electrode at the same degree of vacuum for 2000 mm. The region of the light emitting region was a square shape having a length of 0.5 cm and a width of 0.5 cm.
[0029]
In the organic electroluminescent device, light emission was observed through a glass substrate by applying a direct current voltage using ITO as an anode and Mg: Ag as a cathode. The luminance was measured with a Topcon luminance meter BM-8. This device obtained green light emission by applying an initial drive of 5 V, and it was confirmed from the emission spectrum that the tris (8-quinolinolato) aluminum complex in the light emitting layer was emitting light. The luminance was as high as 2500 cd / m ^{2 at} 14V. In addition, it was confirmed that the storage characteristics of the device were very good even when the device was stored in a dry nitrogen atmosphere at room temperature for 3 months after the production. Furthermore, no significant deterioration was observed even in the element stored for 100 hours under the condition of 100 ° C. in a dry nitrogen atmosphere, and it was confirmed that this element has high heat resistance. Further, even when continuous driving was performed at a constant current value, no significant reduction in luminance was observed after 3 months.
[0030]
Comparative Example 1
The following formula, which is a low molecular weight model compound:

In a similar device using the arylamine vapor-deposited film as the hole transport layer, the luminance half-life is 25 hours.
[0031]
From Example 5 and Comparative Example 1, it can be seen that the stability of the organic layer is greatly improved by the high glass transition temperature of the novel polymer (PDPAMS) used in Example 5.
Further, in the device of the present invention, the improvement in stability was recognized even when the light emitting layer was an organic material other than the tris (8-quinolinolato) aluminum complex.
[0032]
Example 6
Example 3 was repeated except that the arylamine-containing vinyl polymer (PTPD-2) having the repeating unit represented by the formula (8) obtained in Example 1 was used as the polymer for forming the hole transporting polymer layer 3. It was.
[0033]
In the organic electroluminescent device, light emission was observed through a glass substrate by applying a direct current voltage using ITO as an anode and Mg: Ag as a cathode. The luminance was measured with a Topcon luminance meter BM-8. From this element, green light emission was obtained by applying a DC voltage, and it was confirmed from the emission spectrum that the tris (8-quinolinolato) aluminum complex in the light emitting layer was emitting light. FIG. 9 shows luminance-voltage characteristics, and FIG. 10 shows current density-voltage characteristics. In the present invention, when the film thickness of the hole-transporting polymer layer 3 made of an arylamine-containing vinyl polymer is 200 mm, when the same voltage is applied compared to when the film thickness is 300 mm or 400 mm, Shows the highest brightness. Its maximum luminance was 8700 cd / m ² at 11V.
[0034]
In addition, it was confirmed that the storage characteristics of the device were very good even when the device was stored in a dry nitrogen atmosphere at room temperature for 3 months after fabrication, and the initial characteristics were hardly changed. Furthermore, no significant deterioration was observed even in the element stored for 100 hours under the condition of 100 ° C. in a dry nitrogen atmosphere, and it was confirmed that this element has high heat resistance. Further, even when continuous driving was performed at a constant current value, no significant reduction in luminance was observed after 3 months.
[0035]
Comparative Example 2
The following formula, which is a low molecular weight model compound

In a similar device using the arylamine vapor-deposited film as the hole transport layer, the luminance half-life is 10 hours.
[0036]
From Example 6 and Comparative Example 2, it can be seen that the stability of the organic layer is greatly improved by the high glass transition temperature of the novel polymer (PTPD-2) used in Example 6.
Further, in the device of the present invention, improvement in stability was recognized even when the light emitting layer was an organic material other than tris (8-quinolinolato) aluminum complex.
[0037]
【The invention's effect】
(1) The present invention can provide a novel arylamine-containing vinyl monomer and a polymer thereof.
(2) According to the present invention, an organic electroluminescent device excellent in light emission characteristics and long-term stability is provided. Therefore, the organic electroluminescent device of the present invention has sufficient reliability for practical use and can be widely used in the fields of display and illumination.
[Brief description of the drawings]
FIG. 1 is a model diagram for explaining the reason why an arylamine-containing vinyl polymer of the present invention suppresses an excimer as compared with a conventional arylamine-containing vinyl polymer.
FIG. 2 is a model diagram showing a cross-sectional structure of an organic EL element used in an embodiment of the present invention.
3 shows a ¹ H-NMR chart of the monomer of Example 1. FIG.
4 shows an IR chart of the monomer of Example 1. FIG.
5 shows a ¹ H-NMR chart of the monomer of Example 2. FIG.
6 shows an IR chart of the monomer of Example 2. FIG.
7 is a diagram showing a luminance-voltage curve according to an EL element of Example 5. FIG.
8 is a graph showing a current density-voltage curve applied to the EL element of Example 5. FIG.
FIG. 9 is a diagram showing a luminance-voltage curve according to an EL element of Example 6.
10 is a diagram showing a current density-voltage curve applied to the EL element of Example 6. FIG.
[Explanation of symbols]
1 Glass substrate 2 ITO film 3 Hole transporting polymer layer 4 Light emitting layer 5 Electrode

Claims (3)

The following general formula (1)

(Wherein R ¹ is hydrogen or an alkyl group, R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ¹ and Ar ² are alkyl groups. Each independently selected from the group consisting of aryl groups optionally having
An arylamine-containing vinyl polymer represented by the following general formula (2) obtained by polymerizing an arylamine-containing vinyl monomer represented by

(Wherein R ¹ is hydrogen or an alkyl group, R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ¹ and Ar ² are alkyl groups. Each independently selected from the group consisting of aryl groups optionally having
In the arylamine-containing vinyl polymer represented by the general formula (2), the repeating unit is any one of the number average molecular weights 1,000 to 1,000,000 represented by the following general formulas (3), (4), and (5). An arylamine-containing vinyl polymer, characterized in that
General formula (3)

(Wherein R ¹ , R ⁴ , R ⁵ , R ⁶ , R ⁷ , R ⁸ , R ⁹ , R ¹⁰ and R ¹¹ are groups independently selected from the group consisting of hydrogen and alkyl groups, R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ³ , Ar ⁴ and Ar ⁵ are aryl groups optionally having an alkyl group Group independently selected from the group consisting of:
Also, Ar ⁴ and Ar ⁵ are combined, and Ar ⁴ , Ar ⁵ and N are combined,
General formula (4)

(Wherein R ¹² , R ¹³ , R ¹⁴ , R ¹⁵ , R ¹⁶ , R ¹⁷ , R ¹⁸ and R ¹⁹ are groups independently selected from the group consisting of hydrogen and an alkyl group)
An arylamine-containing vinyl polymer containing a repeating unit represented by:
General formula (5)

Wherein R ¹ , R ²⁰ , R ²¹ , R ²² , R ²³ , R ²⁴ , R ²⁵ , R ²⁶ and R ²⁷ are groups independently selected from the group consisting of hydrogen and an alkyl group. , R ² and R ³ are groups independently selected from the group consisting of hydrogen, methyl group and ethyl group, and Ar ³ , Ar ⁴ and Ar ⁵ are aryl optionally having an alkyl group Groups independently selected from the group consisting of groups)
An arylamine-containing vinyl polymer containing a repeating unit represented by: An organic electroluminescent device using the arylamine-containing vinyl polymer according to claim 1 . 2. An organic electroluminescent device, wherein the arylamine-containing vinyl polymer according to claim 1 is used as a hole transport layer.

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