JP2004264448A - Optical recording medium and optical recording / reproducing method - Google Patents

Abstract

（上記一般式（Ｉ）において、Ｒ^１およびＲ^２はそれぞれ独立に、炭素数１〜６の直鎖または分岐のアルキル基、或いは炭素数１〜６の直鎖または分岐のアルコキシ基を表す。Ｘ^１およびＸ^２は、各々独立に硫黄原子または酸素原子を表し、Ｙ^１およびＹ^２は、各々独立に窒素原子または−ＣＲ^５−基（但し、Ｒ^５は水素原子または任意の置換基を表す。）を表す。Ｒ^３およびＲ^４は各々独立に、水素原子または任意の置換基を表す。
なお、Ｙ^１および／またはＹ^２が−ＣＲ^５−であり、該Ｒ^５が任意の置換基である場合には、隣接するＲ^５とＲ^３および／またはＲ^５とＲ^４が結合し、置換基を有しうる環を形成していても良い。）
【選択図】 なしInformation is recorded on an optical recording medium using a photochromic compound using light having a wavelength of visible light to ultraviolet light, and a change in absorbance at a specific frequency in an infrared wavelength region is detected and reproduced.
An optical recording medium having a recording layer containing at least one compound selected from the compounds represented by the following general formula (I).

(In the above general formula (I), R ¹ and R ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched alkoxy group having 1 to 6 carbon atoms. X ¹ and X ² each independently represent a sulfur atom or an oxygen atom; Y ¹ and Y ² each independently represent a nitrogen atom or a —CR ⁵ — group (provided that R ⁵ represents a hydrogen atom or an arbitrary substituent; R ³ and R ⁴ each independently represent a hydrogen atom or an optional substituent.
When Y ¹ and / or Y ² is —CR ⁵ — and R ⁵ is an optional substituent, adjacent R ⁵ and R ³ and / or R ⁵ and R ⁴ are bonded, A ring which may have a substituent may be formed. )
[Selection diagram] None

Description

【００１１】
（上記一般式（Ｉ）において、Ｒ^１およびＲ^２はそれぞれ独立に、炭素数１〜６の直鎖または分岐のアルキル基、或いは炭素数１〜６の直鎖または分岐のアルコキシ基を表す。Ｘ^１およびＸ^２は、各々独立に硫黄原子または酸素原子を表し、Ｙ^１およびＹ^２は、各々独立に窒素原子または−ＣＲ^５−基（但し、Ｒ^５は水素原子または任意の置換基を表す。）を表す。Ｒ^３およびＲ^４は各々独立に、水素原子または任意の置換基を表す。
【００１２】
なお、Ｙ^１および／またはＹ^２が−ＣＲ^５−であり、該Ｒ^５が任意の置換基である場合には、隣接するＲ^５とＲ^３および／またはＲ^５とＲ^４が結合し、置換基を有しうる環を形成していても良い。）
前記一般式（Ｉ）で表されるフォトクロミック化合物は、フォトクロミック反応前後の状態の赤外吸収に大きな相違があるので、該化合物を使用した光学的記録媒体は、記録光よりも低エネルギーの電磁波である赤外光を利用して、非破壊的かつ選択的に再生することができる。
【００１３】
すなわち本発明の光学的記録再生方法は、前記光学的記録媒体に対する記録再生方法であって、記録層に含まれる前記一般式（Ｉ）で表される化合物のうち、少なくとも１種類の化合物を光異性化反応せしめるエネルギーの光を照射することにより、情報の記録および／または消去を行い、該記録層の被記録部分について、特定振動数における記録前後の赤外吸収強度変化を検出することにより、情報の再生を行うことを特徴とする。
【００１４】
【発明の実施の形態】
以下に、本発明の光学的記録媒体および光学的記録再生方法について詳しく説明する。
本発明の光学的記録媒体および光学的記録方法は、フォトクロミック反応前後における赤外吸収の変化が大きい、前記一般式（Ｉ）で表されるフォトクロミック化合物を見いだしたことにより達成されたものである。
【００１５】
ジアリールエテン系化合物において、光閉環反応により形成されるＣ＝Ｃ二重結合の非対称結合伸縮振動は、分子軌道計算による詳細な分子科学的解析の結果、ほぼ１６００ｃｍ^−１付近に出現する。その結果、開環体には殆ど出現しないこの帯域の振動を検出することにより、記録された情報の非破壊的かつ選択的な読出しを行うことができる。
【００１６】
本発明の光学的記録媒体および光学的記録再生方法は、フォトクロミック反応前後における赤外吸収の変化が著しく大きい化合物を見出したことにより達成されたものである。
さらに、上述したフォトクロミック化合物に、もともとこの帯域に赤外吸収を持つ官能基を導入すれば、上述したＣ＝Ｃ二重結合の非対称結合伸縮振動とのカップルを期待でき、反応の前後に大きな変化をもたらすことを見いだした。具体的には、フォトクロミック反応前後の分子構造に対し、分子軌道法計算を行ない赤外吸収強度の変化を予測し、導入する官能基を予測して分子設計を行った。
【００１７】
その結果、下記一般式（Ｉ）で表される化合物において、フォトクロミック反応前後の赤外吸収スペクトルが大きく変化することを見いだした。
【００１８】
【化３】

【００１９】
（上記一般式（Ｉ）において、Ｒ^１およびＲ^２はそれぞれ独立に、炭素数１〜６の直鎖または分岐のアルキル基、或いは炭素数１〜６の直鎖または分岐のアルコキシ基を表す。Ｘ^１およびＸ^２は、各々独立に硫黄原子または酸素原子を表し、Ｙ^１およびＹ^２は、各々独立に窒素原子または−ＣＲ^５−基（但し、Ｒ^５は水素原子または任意の置換基を表す。）を表す。Ｒ^３およびＲ^４は各々独立に、水素原子または任意の置換基を表す。
【００２０】
なお、Ｙ^１および／またはＹ^２が−ＣＲ^５−であり、該Ｒ^５が任意の置換基である場合には、隣接するＲ^５とＲ^３および／またはＲ^５とＲ^４が結合し、置換基を有しうる環を形成していても良い。）
Ｒ^１とＲ^２は、同一であっても異なっていてもよいが、好ましくは炭素数１〜６のアルキル基であり、より好ましくはメチル基である。
【００２１】
Ｘ^１およびＸ^２は、各々独立に硫黄原子または酸素原子を表し、Ｙ^１およびＹ^２は、各々独立に窒素原子または−ＣＲ^５−基（但し、Ｒ^５は水素原子または任意の置換基を表す。）を表す。またＲ^３およびＲ^４は各々独立に、水素原子または任意の置換基を表す。
なお、Ｙ^１およびＹ^２がともに−ＣＲ^５−である場合、これら２つのＲ^５は同一であっても異なっていてもよい。
【００２２】
（Ｘ^１，Ｙ^１）の組合せ、および（Ｘ^２，Ｙ^２）の組合せとしては、各々独立に、（−Ｏ−，−ＣＲ^５−）、（−Ｓ−，−ＣＲ^５−）、または（−Ｓ−，−Ｎ＝）がより好ましい。
Ｒ^３、Ｒ^４およびＲ^５が任意の置換基である場合、該置換基として、好ましくはハロゲン原子、炭素数１〜１５のアルキル基、炭素数１〜１２のアルコキシ基、炭素数１〜１２のフッ化アルキル基、ニトロ基、シアノ基、および炭素数６〜１０の芳香族炭化水素基等があげられる。なお、アルキル基、アルコキシ基、フッ化アルキル基は、鎖状または環状のいずれであってもよく、また鎖状の場合、直鎖でも分岐していてもよい。
【００２３】
前記一般式（Ｉ）で表される化合物として好ましくは、ハロゲン原子または炭素数１〜１２のアルキル基で置換されているか、或いは無置換である。より好ましくは、ハロゲン原子で置換されているか、無置換の化合物である。
また、Ｙ^１および／またはＹ^２が−ＣＲ^５−であり、該Ｒ^５が任意の置換基である場合には、それぞれ隣接する、Ｒ^５とＲ^３および／またはＲ^５とＲ^４が結合し、置換基を有しうる環を形成していても良い。このような環としては、ベンゼン環等があげられ、該環が有しうる置換基としては、Ｒ^３、Ｒ^４およびＲ^５の例として前述した基等があげられる。
【００２４】
一般式（Ｉ）で表される化合物としては、Ｒ^５とＲ^３および／またはＲ^５とＲ^４が結合している化合物より、これらが各々別の基である化合物の方が好ましい。
上述した化合物の作り方としては、Ｋ．Ｕｃｈｉｄａ ａｎｄ Ｍ．Ｉｒｉｅ， Ｃｈｅｍｉｓｔｒｙ Ｌｅｔｔｅｒｓ，１９９５，（Ｎｏ．１１）９６９−９７０．等に記載の方法を例示することができる。
【００２５】
次に、本発明の光学的記録再生方法について説明する。
本発明の光学的記録再生方法は、上述した本発明の光学的記録媒体に対する記録再生方法であり、記録光照射により情報が記録または消去され、該記録光よりも低エネルギーの電磁波（赤外線）を用いて再生される。詳しくは、記録層に含まれる前記一般式（Ｉ）で表される化合物のうち、少なくとも１種類の化合物を光異性化反応せしめるエネルギーの光を照射することにより、情報の記録または消去を行い、該記録層の被記録部分について、特定振動数における記録前後の赤外吸収強度変化を検出することにより、情報の再生を行う。
【００２６】
前記一般式（Ｉ）で表されるフォトクロミック化合物は、紫外線波長領域〜可視光波長領域の光で、効率的に光異性化反応を生じるものが多いため、この波長領域（具体的には、１９０ｎｍ〜８００ｎｍ程度）の光を記録光または消去光として用いることが好ましい。通常、該波長領域の中で、比較的短波長の光で閉環体が生成し、長波長の光で開環体が生成する。そうした波長の異なる光を照射することにより、上述したフォトクロミック化合物が可逆変化を起こし、情報の記録および消去が行なわれる。なお、光源は特に限定されないが、半導体レーザー等が好ましく適用される。
【００２７】
記録された情報の再生は、上述した記録光よりも低エネルギーの電磁波である赤外線波長領域の光により行なわれる。上述した本発明に係るフォトクロミック化合物は、閉環体と開環体とで赤外吸収に大きな相違があるので、光学的記録媒体の記録層における記録光が照射された部分（被記録部分）に赤外光を照射し、その吸収信号を変換することにより、情報を再生することができる。
【００２８】
本発明における光学的記録媒体の記録層は、例えば、前記フォトクロミック化合物を、シクロオレフィン系樹脂、ポリエステル樹脂、ポリスチレン樹脂、塩化ビニル樹脂、酢酸ビニル樹脂、ポリビニルブチラール樹脂、ポリメチルメタクリル樹脂、ポリカーボネート樹脂、フェノール樹脂、エポキシ樹脂等のバインダ樹脂と共に、ベンゼン、トルエン、ヘキサン、シクロヘキサン、メチルエチルケトン、アセトン、メタノール、エタノール、テトラヒドロフラン、ジオキサン、四塩化炭素、クロロホルム等の溶媒に分散または溶解させて、適当な基板に塗布する方法や、フォトクロミック化合物を上記溶媒に溶解してなる溶液を、基板上に塗布・乾燥することにより成膜する方法、或いはフォトクロミック化合物溶液を、ガラスセル等に封入する方法等により形成される。得られた媒体の扱い易さの点からは、記録層は固体（膜状）であることが好ましく、中でも、アモルファス状の膜が得やすい点から、適当なバインダ樹脂と共に成膜する方法がより好ましい。
【００２９】
本発明に用いられる光学的記録媒体は、例えば適当な基板上に、上述した、フォトクロミック化合物含有樹脂膜からなる記録層を設けることにより作成される。記録層の上に、或いは基板と記録層との間に反射層を設けても良い。また、最外層（記録層や反射層などの積層部分に対し、基板側とは逆の側の最外層）に、各層を保護する保護層を設けても良い。さらに、２枚の基板間に記録層や、必要に応じて反射層などの任意の層を設けても良い。これら以外にも、上述の各層間に、本発明の要旨を超えない範囲で任意の層を有していても良い。
本発明に用いられる光学的記録媒体において、上述の基板、反射層、保護層などは、現在一般的に使用されている材料から適宜選択して使用することができる。
【００３０】
【実施例】
以下に、実施例により本発明をさらに具体的に説明するが、本発明はその要旨を超えない限り、以下の実施例に限定されるものではない。
（実施例１）
フォトクロミック化合物として、下記構造式で表される２位でエテン部位に結合した１，２−ビス（３，５−ジメチル−２−チエニル）パーフルオロペンテン（ｉ３５Ｍｅ）を用いた。
【００３１】
【化４】

【００３２】
この化合物は、原料である３，５−ジメチルチオフェン、およびｎ−ブチルリチウム、オクタフルオロペンテン、テトラヒドロフランを用いて、Ｋ．Ｕｃｈｉｄａ ａｎｄ Ｍ．Ｉｒｉｅ，Ｃｈｅｍｉｓｔｒｙ Ｌｅｔｔｅｒｓ，１９９５，（Ｎｏ．１１）９６９−９７０．に準じて合成した。
この化合物（開環体）２００ｍｇをヘキサン２Ｌに溶解し、該ヘキサン溶液中の開環体（ｉ３５Ｍｅ−Ｏ）に波長３６５ｎｍの光を照射して閉環体（ｉ３５Ｍｅ−Ｃ）を生成させ、閉環体を含む光定常状態に至らせた（２．５×１０^−４Ｍ）。この光定常状態（ｉ３５Ｍｅ−Ｏ＋ｉ３５Ｍｅ−Ｃ）の溶液を減圧下、溶剤を留去した。得られた光定常状態混合物の赤外吸収（ＩＲ）スペクトルをＮａＣｌ錠剤法により測定した。次に、この光定常状態混合物を含むＮａＣｌ錠剤に対し、光源としてキセノンランプを使用し、これにカットオフフィルタを組み合わせて、波長４５０ｎｍ以下の光をカットしたものを照射し、全てを開環体（ｉ３５Ｍｅ−Ｏ）に変換して、同様にＩＲ測定を行った。（以下の実施例および比較例における「可視光」も、同様に、キセノンランプとカットオフフィルタを組み合わせて得られた光である。）
【００３３】
この２つの状態（光定常状態および開環体）に対応した（すなわちフォトクロミック反応前後の）該化合物の赤外吸収スペクトル変化を図１に示した。閉環体（ｉ３５Ｍｅ−Ｃ）を含む光定常状態のスペクトルには、開環体（ｉ３５Ｍｅ−Ｏ）では吸収のない１５９３、１６３０、１６５１ｃｍ^−１の３本の大きな吸収ピークがみられ、後述する比較例１と較べて、より明瞭に反応前後のＩＲスペクトル変化が生じていることが分かる。
【００３４】
（実施例２）
実施例１にて使用したフォトクロミック化合物（ｉ３５Ｍｅ）の赤外吸収スペクトルを、６−３１Ｇ基底を用いた非経験的分子軌道法（Ｈａｒｔｒｅｅ−Ｆｏｃｋ法、ＨＦ／６−３１Ｇ法と略）でシミュレートした結果を、図２に示す。下が実測の赤外吸収、上が計算結果である。ＨＦ／６−３１Ｇ法は、市販ソフトのＧａｕｓｓｉａｎ９８を利用して行った。ＨＦ／６−３１Ｇ法の計算は、赤外吸収の波数を過大に計算することが知られているので、０．９倍した。
図２より、分子軌道法計算は、実施例１の化合物が、開環体は１６００ｃｍ^−１付近に赤外吸収を持たないが、閉環体（実測では、開環体を含む光定常状態）は大きな赤外吸収があることを、再現できていることが分かる。
【００３５】
（実施例３〜５）
以下、下記構造式（ａ）〜（ｃ）で表される化合物につき、実施例２と同様にシミュレーションを行った。結果を図３〜図５に示す。いずれの化合物についても、振動数１６００ｃｍ^−１付近で、開環体と閉環体の赤外吸収強度に大きな差があることが分かる。
【００３６】
【化５】

【００３７】
（比較例１）
フォトクロミック材料として、下記構造式で表される１，２−ビス（２，４，５−トリメチル−３−チエニル）パーフルオロペンテン（Ｔ−Ｏ（開環体）、Ｔ−Ｃ（閉環体））を用いた。
【００３８】
【化６】

【００３９】
これは、既存文献（Ｆ．Ｓｔｅｌｌａｃｃｉ、Ｃ．Ｂａｒｔａｒｅｌｌｉ， Ｔ．Ｔｏｓｃａｎｏ， Ｍ．Ｃ．Ｇａｌｌａｚｚｉ， Ｇ．Ｚｅｒｂｉ， Ｃｈｅｍ． Ｐｈｙｓ． Ｌｅｔｔｅｒｓ， ３０２， ５６３−５７０ （１９９９））の追試を比較対照のために行ったものである。
この化合物をヘキサンに溶解し、ヘキサン溶液中の開環体（Ｔ−Ｏ）に波長３１３ｎｍの光を照射して閉環体（Ｔ−Ｃ）を生成させた（１．２×１０^−４Ｍ）。閉環体（Ｔ−Ｃ）は５３８ｎｍに吸収極大をもち、溶液は赤色を呈していた。その状態、即ち光定常状態での開環体（Ｔ−Ｏ）と閉環体（Ｔ−Ｃ）の比は、約２０：８０であった。この溶液から溶媒を留去し、メタノールより再結晶して閉環体（Ｔ−Ｃ）の結晶を単離した。得られた閉環体（Ｔ−Ｃ）結晶のＩＲスペクトルを、ＮａＣｌ錠剤法により測定した。次に、この閉環体（Ｔ−Ｃ）を含むＮａＣｌ錠剤に対して可視光を照射し、全てを開環体（Ｔ−Ｏ）に変換してＩＲを測定した。
【００４０】
この２つの状態（閉環体および開環体）に対応した（すなわちフォトクロミック反応前後の）赤外吸収スペクトル変化を図２に示した。反応前後の赤外吸収のチャートが殆ど重なっておりこの分子では赤外吸収の変化は小さい。
（実施例６）
フォトクロミック化合物として、チオフェン環の２位でエテン部位に結合したベンゾチエニル基を持つ１，２−ビス（３−メチルベンゾ［ｂ］チオフェン−２−イル）パーフルオロシクロペンテン（ｉＢｚ）を用いた。
【００４１】
【化７】

【００４２】
この化合物は、原料である３−メチルベンゾ［ｂ］チオフェン、およびｎ−ブチルリチウム、オクタフルオロペンテン、テトラヒドロフランを用いて、Ｋ．Ｕｃｈｉｄａ ａｎｄ Ｍ．Ｉｒｉｅ，Ｃｈｅｍｉｓｔｒｙ Ｌｅｔｔｅｒｓ，１９９５，（Ｎｏ．１１）９６９−９７０に準じて合成した。
この化合物をヘキサンに溶解し、ヘキサン溶液中の開環体（ｉＢｚ−Ｏ）に波長３６５ｎｍの光を照射して閉環体（ｉＢｚ−Ｃ）を生成させ、閉環体のみを単離した（２．０×１０^−４Ｍ）。単離した閉環体（ｉＢｚ−Ｃ）について、比較例１と同様にＩＲ測定を行なった。次に、この閉環体溶液に可視光を照射し、全てを開環体（ｉＢｚ−Ｏ）に変換して、同様にＩＲ測定を行った。
【００４３】
この２つの状態（閉環体と開環体）に対応した（すなわちフォトクロミック反応前後の）赤外吸収スペクトル変化を図３に示した。閉環体（ｉＢｚ−Ｃ）のスペクトルには、開環体（ｉＢｚ−Ｏ）では吸収のない１５８７ｃｍ^−１および１６３７ｃｍ^−１に２本の大きな吸収ピークがみられた。
【００４４】
【発明の効果】
以上説明したように、本発明の光学的記録媒体および光学的記録方法によれば、フォトクロミック反応前後の状態の赤外吸収に大きな相違を有するフォトクロミック材料を含むので、記録光よりも低エネルギーの電磁波である赤外光を利用して、非破壊的かつ選択的に情報の再生を行うことができる。
【図面の簡単な説明】
【図１】実施例１の化合物の、フォトクロミック反応前後の赤外吸収スペクトル線図である。
【図２】実施例２にて行った、ＨＦ／６−３１Ｇ法による本発明化合物（ｉ３５Ｍｅ）のシミュレート結果である。
【図３】実施例３にて行った、ＨＦ／６−３１Ｇ法による本発明化合物（ａ）のシミュレート結果である。
【図４】実施例４にて行った、ＨＦ／６−３１Ｇ法による本発明化合物（ｂ）のシミュレート結果である。
【図５】実施例５にて行った、ＨＦ／６−３１Ｇ法による本発明化合物（ｃ）のシミュレート結果である。
【図６】比較例１の化合物の、フォトクロミック反応前後の赤外吸収スペクトル線図である。
【図７】実施例６の化合物の、フォトクロミック反応前後の赤外吸収スペクトル線図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical recording medium using a photochromic compound and an optical recording / reproducing method for the medium, and more specifically, a non-destructive method using electromagnetic waves of lower energy than light used for recording, particularly light in an infrared wavelength region. The present invention relates to an optical recording medium for reading and an optical recording / reproducing method.
[0002]
[Prior art]
A photochromic compound is a molecule that reversibly generates two states (structural isomers) having different optical characteristics including color by the action of light.
This photochromic compound is being studied for application to the field of optoelectronics such as an optical recording medium or an optical switch element by utilizing a change in optical characteristics based on such a photoisomerization reaction (referred to as photochromic reaction).
[0003]
Further, as a method for recording and reproducing on an optical recording medium using a photochromic compound, light having a wavelength having a large difference in absorbance between structural isomers is used for recording information, and the intensity is weak at the same wavelength. The most common method is to use light for reproduction. However, when light of the same (or close) wavelength is used for recording and reproduction, repeated recording may cause unintended recording with reproduced light. In other words, recording may be destroyed by repeated reproduction. There was a problem that would go. Therefore, it has been pointed out that in order for the photochromic compound to be widely used as an information recording material, it is necessary to introduce a nondestructive read function. (For example, see Non-Patent Document 1).
[0004]
Under these circumstances, it has recently been found that there is a difference in infrared absorption intensity between before and after the photochromic reaction depending on the photochromic compound (for example, see Non-Patent Document 2).
[0005]
[Non-patent document 1]
M. Irie, Chem. Rev .. , 100, 1685-1716 (2000).
[Non-patent document 2]
F. Stellacci, C.I. Bartarelli, T.W. Toscano, M .; C. Gallazzi, G .; Zerbi, Chem. Phys. Letters, 302, 563-570 (1999).
[Non-Patent Document 3]
Proceedings of the 81st Annual Meeting of the Chemical Society of Japan (2002), p138, lower right column, lecture number 3C4-13
[0006]
[Problems to be solved by the invention]
On the other hand, the present inventors have also analyzed in detail the molecular vibration related to the change in the infrared absorption intensity (spectrum) before and after the photoisomerization reaction of the photochromic compound, and have designed the molecular design to increase the change in the molecular vibration. I have been studying about. By introducing a benzene ring or a carbonyl group into a diarylethene-based molecule in which the 3-position of the thiophene group is bonded to the ethene moiety, it was already possible to increase the change in infrared absorption intensity before and after the photochromic reaction. It has already been reported (see Non-Patent Document 3).
[0007]
As a result of further research, the present inventors have found that, among compounds other than the above, there are also compounds in which the amount of change in infrared absorption intensity is large before and after the photochromic reaction, and have led to the present invention.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors conducted detailed analysis of molecular vibrations related to infrared absorption before and after a photochromic reaction, and studied a molecular design for increasing a change in molecular vibration. Analysis of molecular vibrations was performed using theoretical chemical calculations, especially molecular orbital calculations. First, a diarylethene-based molecule was examined, and it was clarified that the difference in the infrared absorption intensity between before and after the photochromic reaction of the compound largely involves a mode of molecular vibration around 1600 cm ⁻¹ . Next, in the isomers before and after the photochromic reaction, trials were conducted with the aim of a molecule whose infrared absorption intensity changes significantly due to its vibration or a molecule whose interaction with the vibration changes its infrared absorption intensity. Made mistakes and ingenuity. Finally, a molecular design having an absorption band existing only in one of the states before and after the reaction was realized. The present invention has been made for the first time by finding out that the change in infrared absorption of a new molecule thus designed before and after the photochromic reaction is remarkable.
[0009]
That is, the optical recording medium of the present invention that achieves the above object has a recording layer containing at least one compound selected from the compounds represented by the following general formula (I).
[0010]
Embedded image

[0011]
(In the above general formula (I), R ¹ and R ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched alkoxy group having 1 to 6 carbon atoms. X ¹ and X ² each independently represent a sulfur atom or an oxygen atom; Y ¹ and Y ² each independently represent a nitrogen atom or a —CR ⁵ — group (provided that R ⁵ represents a hydrogen atom or an arbitrary substituent; R ³ and R ⁴ each independently represent a hydrogen atom or an optional substituent.
[0012]
When Y ¹ and / or Y ² is —CR ⁵ — and R ⁵ is an optional substituent, adjacent R ⁵ and R ³ and / or R ⁵ and R ⁴ are bonded, A ring which may have a substituent may be formed. )
Since the photochromic compound represented by the general formula (I) has a large difference in infrared absorption before and after the photochromic reaction, an optical recording medium using the compound is exposed to electromagnetic waves having lower energy than recording light. Using certain infrared light, nondestructive and selective reproduction can be performed.
[0013]
That is, the optical recording / reproducing method of the present invention is a method for recording / reproducing on / from the optical recording medium, wherein at least one compound of the compounds represented by the general formula (I) contained in the recording layer is optically reproduced. By irradiating light of energy to cause an isomerization reaction, information is recorded and / or erased, and for a recorded portion of the recording layer, a change in infrared absorption intensity before and after recording at a specific frequency is detected. It is characterized by reproducing information.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the optical recording medium and the optical recording / reproducing method of the present invention will be described in detail.
The optical recording medium and the optical recording method of the present invention have been attained by finding a photochromic compound represented by the general formula (I), which has a large change in infrared absorption before and after a photochromic reaction.
[0015]
In the diarylethene-based compound, the asymmetric bond stretching vibration of the C ＝ C double bond formed by the photocyclization reaction appears at around 1600 cm ^{−1 as} a result of detailed molecular science analysis by molecular orbital calculation. As a result, non-destructive and selective reading of recorded information can be performed by detecting vibrations in this band which hardly appear in the ring-opened body.
[0016]
The optical recording medium and the optical recording / reproducing method of the present invention have been attained by finding a compound having a significantly large change in infrared absorption before and after a photochromic reaction.
Furthermore, by introducing a functional group having infrared absorption into this band from the photochromic compound, a couple with the asymmetric bond stretching vibration of the C = C double bond described above can be expected, and a large change occurs before and after the reaction. Has been found to bring. More specifically, molecular orbital calculations were performed on the molecular structure before and after the photochromic reaction to predict changes in infrared absorption intensity, and a functional group to be introduced was predicted to perform molecular design.
[0017]
As a result, it has been found that, in the compound represented by the following general formula (I), the infrared absorption spectrum before and after the photochromic reaction significantly changes.
[0018]
Embedded image

[0019]
(In the above general formula (I), R ¹ and R ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched alkoxy group having 1 to 6 carbon atoms. X ¹ and X ² each independently represent a sulfur atom or an oxygen atom; Y ¹ and Y ² each independently represent a nitrogen atom or a —CR ⁵ — group (provided that R ⁵ represents a hydrogen atom or an arbitrary substituent; R ³ and R ⁴ each independently represent a hydrogen atom or an optional substituent.
[0020]
When Y ¹ and / or Y ² is —CR ⁵ — and R ⁵ is an optional substituent, adjacent R ⁵ and R ³ and / or R ⁵ and R ⁴ are bonded, A ring which may have a substituent may be formed. )
R ¹ and R ² may be the same or different, but are preferably an alkyl group having 1 to 6 carbon atoms, and more preferably a methyl group.
[0021]
X ¹ and X ² each independently represent a sulfur atom or an oxygen atom; Y ¹ and Y ² each independently represent a nitrogen atom or a —CR ⁵ — group (provided that R ⁵ represents a hydrogen atom or an arbitrary substituent; Represents). R ³ and R ⁴ each independently represent a hydrogen atom or an arbitrary substituent.
When both Y ¹ and Y ² are —CR ⁵ —, these two R ⁵ may be the same or different.
[0022]
As the combination of (X ¹ , Y ¹ ) and the combination of (X ² , Y ² ), (—O—, —CR ⁵ —), (—S—, —CR ⁵ —), or (-S-, -N =) is more preferable.
When R ³ , R ⁴ and R ⁵ are optional substituents, the substituents are preferably a halogen atom, an alkyl group having 1 to 15 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, and 1 to 12 carbon atoms. And a nitro group, a cyano group, and an aromatic hydrocarbon group having 6 to 10 carbon atoms. In addition, the alkyl group, the alkoxy group, and the fluorinated alkyl group may be any of a chain or a ring. In the case of a chain, they may be linear or branched.
[0023]
The compound represented by the general formula (I) is preferably substituted with a halogen atom or an alkyl group having 1 to 12 carbon atoms, or unsubstituted. More preferred are compounds substituted or unsubstituted with a halogen atom.
When Y ¹ and / or Y ² is —CR ⁵ — and R ⁵ is an arbitrary substituent, adjacent R ⁵ and R ³ and / or R ⁵ and R ⁴ are bonded to each other. However, a ring which may have a substituent may be formed. Examples of such a ring include a benzene ring and the like, and the substituents that the ring may have include the groups described above as examples of R ³ , R ⁴ and R ⁵ .
[0024]
As the compound represented by the general formula (I), a compound in which each of R ⁵ and R ³ and / or R ⁵ and R ⁴ is a different group is more preferable than a compound in which R ⁵ and R ³ are bonded.
As a method of preparing the above-mentioned compound, K. Uchida and M.S. Irie, Chemistry Letters, 1995, (No. 11) 969-970. And the like.
[0025]
Next, the optical recording / reproducing method of the present invention will be described.
The optical recording / reproducing method of the present invention is a recording / reproducing method for the above-described optical recording medium of the present invention, in which information is recorded or erased by irradiating recording light, and electromagnetic waves (infrared rays) having lower energy than the recording light are emitted. Reproduced using Specifically, information is recorded or erased by irradiating at least one compound among the compounds represented by the general formula (I) contained in the recording layer with light that causes photoisomerization reaction, The information is reproduced by detecting a change in the infrared absorption intensity of the recorded portion of the recording layer before and after recording at a specific frequency.
[0026]
The photochromic compound represented by the general formula (I) often emits light in an ultraviolet wavelength region to a visible light wavelength region and efficiently causes a photoisomerization reaction. (About 800 nm) is preferably used as recording light or erasing light. Usually, in the wavelength region, a ring-closed body is generated by light having a relatively short wavelength and a ring-opened body is generated by light having a long wavelength. By irradiating such light having different wavelengths, the above-described photochromic compound undergoes a reversible change, and information is recorded and erased. The light source is not particularly limited, but a semiconductor laser or the like is preferably applied.
[0027]
Reproduction of the recorded information is performed by light in the infrared wavelength region, which is an electromagnetic wave having lower energy than the recording light described above. Since the photochromic compound according to the present invention described above has a large difference in infrared absorption between the ring-opened body and the ring-opened body, a portion of the recording layer of the optical recording medium irradiated with the recording light (recorded portion) has a red color. Information can be reproduced by irradiating external light and converting the absorption signal.
[0028]
The recording layer of the optical recording medium in the present invention, for example, the photochromic compound, cycloolefin resin, polyester resin, polystyrene resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, polymethyl methacryl resin, polycarbonate resin, Disperse or dissolve in a solvent such as benzene, toluene, hexane, cyclohexane, methyl ethyl ketone, acetone, methanol, ethanol, tetrahydrofuran, dioxane, carbon tetrachloride, chloroform, etc. A method of applying, a method of forming a film by applying and drying a solution obtained by dissolving a photochromic compound in the above-described solvent on a substrate, or enclosing a photochromic compound solution in a glass cell or the like It is formed by that method and the like. The recording layer is preferably solid (film-like) from the viewpoint of easy handling of the obtained medium, and among them, the method of forming a film with an appropriate binder resin is more preferable because an amorphous film is easily obtained. preferable.
[0029]
The optical recording medium used in the present invention is produced, for example, by providing the above-mentioned recording layer comprising a photochromic compound-containing resin film on an appropriate substrate. A reflective layer may be provided on the recording layer or between the substrate and the recording layer. Further, a protective layer for protecting each layer may be provided on the outermost layer (the outermost layer on the side opposite to the substrate with respect to the laminated portion such as the recording layer and the reflective layer). Further, an arbitrary layer such as a recording layer and, if necessary, a reflection layer may be provided between the two substrates. In addition to these, any layers may be provided between the above-mentioned layers without departing from the scope of the present invention.
In the optical recording medium used in the present invention, the above-described substrate, reflective layer, protective layer, and the like can be appropriately selected and used from currently generally used materials.
[0030]
【Example】
Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist of the present invention.
(Example 1)
As the photochromic compound, 1,2-bis (3,5-dimethyl-2-thienyl) perfluoropentene (i35Me) bonded to the ethene moiety at the 2-position represented by the following structural formula was used.
[0031]
Embedded image

[0032]
This compound was prepared using the starting material 3,5-dimethylthiophene, n-butyllithium, octafluoropentene, and tetrahydrofuran. Uchida and M.S. Irie, Chemistry Letters, 1995, (No. 11) 969-970. Synthesized according to
200 mg of this compound (ring-opened product) was dissolved in 2 L of hexane, and the ring-opened product (i35Me-O) in the hexane solution was irradiated with light having a wavelength of 365 nm to produce a closed-ring product (i35Me-C). (2.5 × 10 ⁻⁴ M). The solvent in this photo-steady state (i35Me-O + i35Me-C) solution was distilled off under reduced pressure. The infrared absorption (IR) spectrum of the resulting photosteady state mixture was measured by the NaCl tablet method. Next, a xenon lamp was used as a light source for the NaCl tablet containing the photo-steady state mixture, and a cut-off filter was combined with the xenon lamp to irradiate a cut-off light having a wavelength of 450 nm or less, and all were opened. (I35Me-O) and similarly measured IR. ("Visible light" in the following Examples and Comparative Examples is also light obtained by combining a xenon lamp and a cutoff filter.)
[0033]
FIG. 1 shows changes in the infrared absorption spectrum of the compound corresponding to these two states (the photo-steady state and the ring-opened form) (that is, before and after the photochromic reaction). In the photosteady state spectrum including the closed form (i35Me-C), three large absorption peaks of 1593, 1630, and 1651 cm ^{-1 having} no absorption in the open form (i35Me-O) were observed. It can be seen that a change in the IR spectrum before and after the reaction occurs more clearly than in Example 1.
[0034]
(Example 2)
The infrared absorption spectrum of the photochromic compound (i35Me) used in Example 1 was simulated by the ab initio molecular orbital method using the 6-31G basis (Harttree-Fock method, abbreviated as HF / 6-31G method). The results obtained are shown in FIG. The lower part is the measured infrared absorption, and the upper part is the calculation result. The HF / 6-31G method was performed using commercially available software Gaussian98. The calculation by the HF / 6-31G method was multiplied by 0.9 because it is known that the wave number of infrared absorption is excessively calculated.
From FIG. 2, the molecular orbital calculation shows that the compound of Example 1 shows that the ring-opened body does not have infrared absorption near 1600 cm ⁻¹ , but the closed-ring body (in the actual measurement, the photo-steady state including the ring-opened body) It can be seen that large infrared absorption can be reproduced.
[0035]
(Examples 3 to 5)
Hereinafter, simulations were performed for the compounds represented by the following structural formulas (a) to (c) in the same manner as in Example 2. The results are shown in FIGS. It can be seen that there is a large difference in the infrared absorption intensities of the ring-opened product and the closed-ring product at a frequency of around 1600 cm ⁻¹ for all compounds.
[0036]
Embedded image

[0037]
(Comparative Example 1)
As a photochromic material, 1,2-bis (2,4,5-trimethyl-3-thienyl) perfluoropentene represented by the following structural formula (TO (open ring), TC (ring closed)) Was used.
[0038]
Embedded image

[0039]
This is a comparison of existing literature (F. Stellacci, C. Bartarelli, T. Toscano, MC Gallazzzi, G. Zerbi, Chem. Phys. Letters, 302, 563-570 (1999)) for comparison. It is what went to.
This compound was dissolved in hexane, and the ring-opened form (TO) in the hexane solution was irradiated with light having a wavelength of 313 nm to form a closed form (TC) (1.2 × 10 ⁻⁴ M). . The closed form (TC) had an absorption maximum at 538 nm, and the solution was red. In that state, that is, the ratio between the ring-opened form (TO) and the closed form (TC) in the photo-steady state was about 20:80. The solvent was distilled off from this solution, and the solution was recrystallized from methanol to isolate a ring-closed product (TC). The IR spectrum of the obtained closed-ring (TC) crystal was measured by a NaCl tablet method. Next, this NaCl tablet containing the closed form (TC) was irradiated with visible light, and all were converted to the open form (TO) to measure IR.
[0040]
FIG. 2 shows changes in infrared absorption spectra corresponding to these two states (ring-closed form and ring-opened form) (that is, before and after the photochromic reaction). The infrared absorption charts before and after the reaction are almost overlapped, and the change in infrared absorption is small in this molecule.
(Example 6)
As the photochromic compound, 1,2-bis (3-methylbenzo [b] thiophen-2-yl) perfluorocyclopentene (iBz) having a benzothienyl group bonded to the ethene site at the 2-position of the thiophene ring was used.
[0041]
Embedded image

[0042]
This compound was prepared using 3-methylbenzo [b] thiophene as a raw material, n-butyllithium, octafluoropentene, and tetrahydrofuran. Uchida and M.S. It was synthesized according to Irie, Chemistry Letters, 1995, (No. 11) 969-970.
This compound was dissolved in hexane, and the ring-opened form (iBz-O) in the hexane solution was irradiated with light having a wavelength of 365 nm to form a ring-closed form (iBz-C), and only the closed form was isolated (2. 0 × 10 ⁻⁴ M). IR measurement was carried out on the isolated ring-closed product (iBz-C) in the same manner as in Comparative Example 1. Next, this closed-ring solution was irradiated with visible light, and all of the solution was converted into a ring-opened product (iBz-O), and IR measurement was similarly performed.
[0043]
FIG. 3 shows changes in infrared absorption spectra corresponding to these two states (ring-closed form and ring-opened form) (that is, before and after the photochromic reaction). In the spectrum of the closed form (iBz-C), two large absorption peaks were observed at 1587 cm ^-1 and 1637 cm ^-1, which had no absorption in the open form (iBz-O).
[0044]
【The invention's effect】
As described above, according to the optical recording medium and the optical recording method of the present invention, since a photochromic material having a large difference in infrared absorption between before and after the photochromic reaction is included, an electromagnetic wave having a lower energy than the recording light is used. The information can be reproduced non-destructively and selectively using the infrared light.
[Brief description of the drawings]
FIG. 1 is an infrared absorption spectrum of a compound of Example 1 before and after a photochromic reaction.
FIG. 2 is a simulation result of the compound of the present invention (i35Me) performed in Example 2 by the HF / 6-31G method.
FIG. 3 shows the results of a simulation of the compound (a) of the present invention performed in Example 3 by the HF / 6-31G method.
FIG. 4 is a simulation result of the compound (b) of the present invention performed in Example 4 by the HF / 6-31G method.
FIG. 5 shows the results of a simulation of the compound (c) of the present invention performed in Example 5 by the HF / 6-31G method.
FIG. 6 is an infrared absorption spectrum diagram of a compound of Comparative Example 1 before and after a photochromic reaction.
FIG. 7 is an infrared absorption spectrum of a compound of Example 6 before and after a photochromic reaction.

Claims (2)

An optical recording medium having a recording layer, comprising at least one compound selected from the compounds represented by the following general formula (I).

(In the above general formula (I), R ¹ and R ² each independently represent a linear or branched alkyl group having 1 to 6 carbon atoms, or a linear or branched alkoxy group having 1 to 6 carbon atoms. X ¹ and X ² each independently represent a sulfur atom or an oxygen atom; Y ¹ and Y ² each independently represent a nitrogen atom or a —CR ⁵ — group (provided that R ⁵ represents a hydrogen atom or an arbitrary substituent; R ³ and R ⁴ each independently represent a hydrogen atom or an optional substituent.
When Y ¹ and / or Y ² is —CR ⁵ — and R ⁵ is an optional substituent, adjacent R ⁵ and R ³ and / or R ⁵ and R ⁴ are bonded, A ring which may have a substituent may be formed. ) The recording / reproducing method for an optical recording medium according to claim 1,
Information is recorded or erased by irradiating at least one compound among the compounds represented by the general formula (I) contained in the recording layer with light that causes photoisomerization reaction,
An optical recording / reproducing method, wherein information is reproduced by detecting a change in infrared absorption intensity of a recording portion of the recording layer before and after recording at a specific frequency.

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