JP2004259408A - Optical recording medium and multiple recording and reproducing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multiple recording and reproducing method capable of performing multiple recording and reproduction to an optical recording medium by recording information by using light beams having a plurality of kinds of wavelengths and detecting change of absorbances in a plurality of frequencies in an IR (infrared) wavelength region to perform reproduction to the optical recording medium using photochromic compounds. <P>SOLUTION: The multiple recording and reproducing method of the optical recording medium wherein recording and/or erasure of information are performed by irradiating the optical recording medium having a recording layer containing plural kinds of the photochromic compounds with a light beam having energy for optically isomerizing at least one compound of the compounds and reproduction of information is performed by detecting the change between IR absorbances before and after recording is performed in a specific frequency about a recorded part of the recording layer, is characterized in that recording and/or erasure are performed using plural kinds of recording light beams having wavelengths different from each other and reproduction is performed by detecting the change of IR absorbances in a plurality of frequencies different from each other. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００２１】
（式中、Ｒ^１〜Ｒ^４は各々独立に、炭素数１〜６のアルキル基を表す。）
上記化合物は、式（Ｉ）で表される化合物の開環体、該化合物の閉環体、式（ＩＩ）で表される化合物の開環体、および該化合物の閉環体で、形状が大きく異なる赤外吸収スペクトルを示すため、これらを用いることにより、効果的に多重記録再生方法が達成される。例えば、式（Ｉ）および式（ＩＩ）で表される化合物を各１種類含有する記録層をもつ光学的記録媒体の場合、一方または両方を、開環反応または閉環反応させる光を照射することにより信号を記録した後、記録後の記録層について赤外吸収スペクトルを測定することにより、結果として生じる４つの状態（２化合物とも開環体、２化合物とも閉環体、式（Ｉ）で表される化合物が開環体で式（ＩＩ）で表される化合物が閉環体、および式（Ｉ）で表される化合物が閉環体で式（ＩＩ）で表される化合物が開環体、の４状態）を、再生し分けることができ、多重記録再生方法が実現する。
【００２２】
なお上述した各化合物は、本発明の光学的記録媒体に使用できるフォトクロミック化合物の一部であり、本発明はこれらに限定されるものではない。
本発明の光学的記録媒体に対する記録再生方法は、波長の異なる複数種の記録光を用いて記録および／または消去を行い、かつ異なる複数の振動数における赤外吸収強度変化の検出により、再生を行うことを特徴とする多重記録再生方法である。記録時および／または消去時には、再生時より高エネルギーの記録光を使用する。フォトクロミック化合物には、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（具体的には、１９０ｎｍ〜８００ｎｍ程度）の光を記録光および／または消去光として用いることが好ましい。
【００２３】
記録光および／または消去光としては、記録層に含まれる複数種のフォトクロミック化合物のうち、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使用する。記録光および／または消去光は、記録層中の１種類の化合物のみを光異性化反応させるものであってもよいし、同時に複数種の化合物につき光異性化反応を生じさせるものであってもよく、これらを適宜組み合わせることにより、所望の多重度を有する記録や、該記録の消去や上書きを実施すればよい。
【００２４】
また、情報の再生は赤外吸収強度の変化を検出することにより行う。具体的には、まず記録層に含有される各フォトクロミック化合物の、光異性化反応前後の赤外吸収スペクトルを測定する。次に、そのスペクトル形状を全て比較し、どの化合物の、いずれの異性体が生成したか、見分けやすい振動数をピックアップする。情報が記録された光学的記録媒体に対し、記録層における被記録部分に赤外光を照射し、予めピックアップしておいた振動数における吸収強度の変化を検出する。検出された吸収信号を変換することにより、被記録部分に存在する各化合物の異性体を判別することが可能となり、多重記録が実現する。
【００２５】
本発明において、記録光、再生光および消去光に使用する光源に特に制限はないが、半導体レーザーを光源として使用することが好ましい。
本発明における光学的記録媒体の記録層は、例えば、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。
【００２６】
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。
【００２７】
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。
【００２８】
【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、まず化合物１（１，２−ビス（２，５−ジメチル−３−チエニル）パーフルオロシクロペンテン）を、Ｓ．Ｋｏｂａｔａｋｅ， Ｔ．Ｙａｍａｄａ， Ｋ．Ｕｃｈｉｄａ， Ｎ．Ｋａｔｏ， ａｎｄ Ｍ．Ｉｒｉｅ， Ｊ．Ａｍ．Ｃｈｅｍ．Ｓｏｃ．， １９９９， １２１， ２３８０−２３８６．に記載の手法に基づいて合成し、次に化合物２（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）を、Ｋ．Ｕｃｈｉｄａ ａｎｄ Ｍ．Ｉｒｉｅ， Ｃｈｅｍ．Ｌｅｔｔ．， １９９５， ９６９−９７０．に記載の手法に基づいて合成した。
【００２９】
【化２】

【００３０】
得られた化合物１および化合物２について、開環体と紫外光照射によってできる光定常状態（開環体と閉環体の混合物）の、ヘキサン溶液中の吸収スペクトルを図１および図２に示す。化合物１は３１３ｎｍよりも短い波長の光で閉環し、５２０ｎｍに極大をもつ吸収があり、４００ｎｍには吸収がない。化合物２は、３８０ｎｍより短い波長の光で閉環し、４３０ｎｍに極大をもつ吸収があり、５６０ｎｍには吸収がない。よって、波長４００ｎｍの光を用いて化合物２のみの開環反応を生じさせることができ、また波長５６０ｎｍの光を用いて化合物１のみの開環反応を生じさせることができる。なお、それぞれの閉環体は光吸収と同時に開環反応を起こすので、可視光を用いた非破壊読み出しはできない。
【００３１】
次に、化合物１を２．８ｍｇ、化合物２を３．０ｍｇ、および非晶質ポリオレフィン樹脂（日本ゼオン（株）製「Ｚｅｏｎｅｘ４８０」）４３．５ｍｇをクロロホルム４ｍｌで溶かし、直径５ｃｍのシャーレ上に溶液キャストした。シャーレを６０℃に加熱し、シャーレ上に溶液が均一に広がるように調製し、アルミホイルを被せ、徐々に溶媒を蒸発させ、フォトクロミック膜（膜中のフォトクロミック化合物の重量分率が１２ｗｔ％）を作成した。
【００３２】
続いて、得られたフォトクロミック膜（光学的記録媒体の記録層に相当する）を用いて、情報の多重記録・再生・消去を行う。このフォトクロミック膜において、記録光および／または消去光照射により生じる４つの状態と、各状態に至るために照射される光の波長を、図４に模式的に示す。なお図４では、Ａ〜Ｄの各状態間の遷移を分かりやすく示すために、Ａ〜Ｄの各状態において、化合物１および化合物２は、各々開環体または閉環体のいずれか一方の構造異性体しか存在しないように記載してある。しかし、以下に述べる実験では、光異性化反応は光定常状態までしか進行していないため、化合物１および化合物２のいずれも、各状態において開環体および閉環体が混在した状態になっている。
【００３３】
まず、得られたフォトクロミック膜（該膜中に含まれる化合物１及び化合物２は、いずれも開環体の状態（状態Ａ。（１−Ｏ＋２−Ｏ））の赤外吸収スペクトルを測定した。結果を図３に示す。この測定で、１５００ｃｍ^−１〜１７００ｃｍ^−１の領域に目立った吸収がないことが分かる。
次に、同じフォトクロミック膜に波長３１３ｎｍの光を照射し、化合物１及び化合物２を光定常状態（状態Ｄ。（（１−Ｏ＋１−Ｃ）＋（２−Ｏ＋２−Ｃ）））にし、赤外吸収スペクトルを測定した。結果を図３に示す。この測定では、１５４５ｃｍ^−１付近、１５９０ｃｍ^−１付近と１６７０ｃｍ^−１〜１６２５ｃｍ^−１にかけて４本の赤外吸収を観測できた。
【００３４】
続いて、同じフォトクロミック膜に、波長５６０ｎｍ以上の光を照射し、化合物１のみを開環体にした状態（状態Ｃ。（１−Ｏ＋（２−Ｏ＋２−Ｃ）））とし、赤外吸収スペクトルを測定した。結果を図３に示す。この測定では、１５４５ｃｍ^−１付近の吸収はないが、１５９０ｃｍ^−１付近と１６７０ｃｍ^−１〜１６２５ｃｍ^−１にかけて３本の赤外吸収が観測できた。
【００３５】
さらに、同フォトクロミック膜（化合物１と化合物２が共に光定常状態にある状態Ｄのフォトクロミック膜）に、波長４０３ｎｍの光をあてると、化合物２のみを開環体である状態（状態Ｂ。（（１−Ｏ＋１−Ｃ）＋２−Ｏ）にすることができ、その赤外吸収スペクトルを測定した。結果を図３に示す。この測定では、１５４５ｃｍ^−１付近の吸収はあるが、１５９０ｃｍ^−１付近と１６７０ｃｍ^−１〜１６２５ｃｍ^−１の吸収は無くなる。
【００３６】
最後に、同フォトクロミック膜に波長４６０ｎｍの光を照射すると、化合物１及び化合物２が共に開環体だけの状態、（状態Ａ。（１−Ｏ＋２−Ｏ））に戻る。この赤外吸収を測定すると、１５００ｃｍ^−１〜１７００ｃｍ^−１の領域に目立った吸収はない。
これらを整理すると、１５４５ｃｍ^−１付近の赤外吸収と、１５９０ｃｍ^−１（あるいは１６５５ｃｍ^−１）の赤外吸収強度を検出することにより、表１に示すように、図４記載の４つの状態（状態Ａ〜Ｄ）を再生し分けることが可能であり、多重記録再生が可能であることが示された。
【００３７】
【表１】

【００３８】
【発明の効果】
このように、情報の記録光として複数種類の波長の光を用い、記録光よりも低エネルギーの電磁波、特に赤外線波長領域の複数の振動数における吸光度変化を検出することにより、光学的記録媒体への多重記録および再生方法が可能となり、記録媒体の高密度化が容易に実現できる。
【図面の簡単な説明】
【図１】実施例１にて測定した、化合物１の開環体（合成にて得られた異性体）および光定常状態の、ヘキサン溶液中の吸収スペクトルである。
【図２】実施例１にて測定した、化合物２の開環体（合成にて得られた異性体）および光定常状態の、ヘキサン溶液中の吸収スペクトルである。
【図３】実施例１における、状態Ａ〜Ｄの赤外吸収スペクトルである。
【図４】実施例１における、状態Ａ〜Ｄの状態遷移図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a multiplex recording / reproducing method for an optical recording medium, and more specifically, to use a plurality of wavelengths of light as information recording light, and a plurality of vibrations in an electromagnetic wave having a lower energy than the recording light, particularly in an infrared wavelength region. The present invention relates to a method for multiplex recording / reproducing on an optical recording medium, wherein information is reproduced by detecting a change in absorbance of the number.
[0002]
[Prior art]
In recent years, as the amount of information has increased, a recording medium capable of recording / reproducing information at a high density has been demanded. As means for achieving high-density information recording, reduction of the minimum unit of recording such as recording marks and multiplex recording of information have been proposed, and by combining these as appropriate, more effective information can be obtained. It is considered that high densification is achieved.
[0003]
Regarding multiplex recording of information, for example, Patent Literature 1 describes multiplex recording on an optical recording medium having a recording layer mainly composed of a plurality of types of dyes having (maximum) light absorption wavelengths different by 100 nm or more.
However, the recording layer of the optical recording medium described in the document uses a dye similar to an organic dye-based optical recording medium generally used at present, such as a CD-R or a DVD-R. There are problems such as the inability to rewrite and the limitation of reduction of recording marks due to heat mode recording.
[0004]
Incidentally, in addition to the above-mentioned non-rewritable optical recording medium, a rewritable organic dye-based optical recording medium using a photochromic compound has been proposed.
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).
[0005]
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 causes unnecessary recording with reproduction light. In other words, repeated recording destroys the recorded portion. There was a problem. 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).
[0006]
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).
[0007]
[Patent Document 1]
JP-A-2-24846 [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).
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of such a situation, and realizes extremely high-density optical information recording by using a material capable of miniaturizing a recorded portion itself and realizing multiplex recording. did.
[0009]
[Means for Solving the Problems]
The present inventors have conducted intensive studies, and as a result, by using a recording layer containing a plurality of types of photochromic compounds, the state before and after the photochromic reaction of each compound was detected at a plurality of types of wavelengths (frequency) to record the state. By non-destructively and selectively reading out information, multiple recording / reproduction on an optical recording medium has been achieved, and the present invention has been achieved.
[0010]
That is, the gist of the present invention is as described in [1] to [10] below.
[1] An optical recording medium having a recording layer containing a plurality of types of light-responsive materials, wherein multiplex recording is performed on the recording layer using ultraviolet light or visible light, and multiplex recording is performed using infrared light. Rewritable optical recording medium, characterized by performing non-destructive reading of information. The light-responsive material is a material that undergoes a chemical and / or physical change by light irradiation.
[2] The optical recording medium according to [1], wherein the photoresponsive material is a photochromic compound.
[3] The optical recording medium according to the above [1] or [2], wherein the photochromic compound is a diarylethene-based compound.
[4] The recording layer contains n types (where n is an integer of 2 or more) of photochromic compounds, and each of the photochromic compounds has a wavelength region satisfying the following a) and b) of 5 nm or more. The optical recording medium according to any one of [1] to [3].
a) In the first absorption band of one structural isomer, a wavelength region in which the molar extinction coefficient of the isomer is 550 or more.
b) A wavelength region in which the molar extinction coefficient of each of the two structural isomers of the other structural isomer and the other (n-1) compounds is 500 or less.
[0011]
Note that the first absorption band means an absorption band located on the longest wavelength side in the absorption spectrum of the compound.
[5] The optical recording medium according to any one of [1] to [4], wherein the photochromic compound contained in the recording layer satisfies the following c) and d).
c) The photochromic reaction is a ring-opening / ring-closing reaction, and there is a frequency at which a difference in infrared transmittance between the photo-steady state and the ring-opened state of the same compound is 1% or more.
d) The frequencies defined in c) above are all different for each type of photochromic compound contained in the recording layer.
[6] An optical recording medium having a recording layer containing n types (where n is an integer of 2 or more) of photochromic compounds. For each of the photochromic compounds contained in the recording layer, the following a) and b) are used. An optical recording medium having a wavelength region satisfying 5 nm or more.
a) In the first absorption band of one structural isomer, a wavelength region in which the molar extinction coefficient of the isomer is 550 or more.
b) A wavelength region in which the molar extinction coefficient of each of the two structural isomers of the other structural isomer and the other (n-1) compounds is 500 or less.
[7] The optical recording medium according to the above [6], wherein the photochromic compounds contained in the recording layer both satisfy the following c) and d).
c) The photochromic reaction is a ring-opening / ring-closing reaction, and there is a frequency at which a difference in infrared transmittance between the photo-steady state and the ring-opened state of the same compound is 1% or more.
d) The frequencies defined in c) above are all different for each type of photochromic compound contained in the recording layer.
[8] An optical recording medium having a recording layer containing n types (where n is an integer of 2 or more) of photochromic compounds, wherein each of the photochromic compounds contained in the recording layer satisfies the following c) and d): Optical recording medium.
c) The photochromic reaction is a ring-opening / ring-closing reaction, and there is a frequency at which a difference in infrared transmittance between the photo-steady state and the ring-opened state of the same compound is 1% or more.
d) The frequencies defined in c) above are all different for each type of photochromic compound contained in the recording layer.
[9] The optical recording medium according to any one of [2] to [8] is irradiated with light having an energy to cause a photoisomerization reaction of at least one of the photochromic compounds contained in the recording layer. To record and / or erase information,
For a recorded portion of the recording layer, a recording method for reproducing information by detecting a change in infrared absorption intensity before and after recording at a specific frequency,
A multiplex optical recording medium characterized by performing recording and / or erasing using a plurality of types of recording light having different wavelengths and performing reproduction by detecting a change in infrared absorption intensity at a plurality of different frequencies. Recording and playback method.
[10] An optical recording medium having a recording layer containing a plurality of types of photochromic compounds,
By irradiating at least one compound among the compounds with light having an energy to cause a photoisomerization reaction, information is recorded and / or erased,
For a recorded portion of the recording layer, a recording method for reproducing information by detecting a change in infrared absorption intensity before and after recording at a specific frequency,
A multiplex optical recording medium characterized by performing recording and / or erasing using a plurality of types of recording light having different wavelengths and performing reproduction by detecting a change in infrared absorption intensity at a plurality of different frequencies. Recording and playback method.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention relates to an optical recording medium having a recording layer containing a plurality of types of photoresponsive materials, particularly a plurality of types of photochromic compounds, and an optical recording / reproducing method suitable for the recording layer.
In the recording method in the multiplex recording / reproducing method of the present invention, among the photochromic compounds contained in the recording layer, only one isomer of a certain compound has absorption, and the other isomer of the compound is contained in the recording layer. Any isomers of other compounds that are defined as having no absorption wavelength are the recording light of the compound. For all types of photochromic compounds contained in the recording layer, “recording light” is similarly determined for each compound, and these are used separately to realize multiplex recording. In the present invention, "" having absorption "at a certain wavelength" means that the molar extinction coefficient at the wavelength is 550 or more, and "no absorption" means that the molar extinction coefficient at the wavelength is 500 or more. It means the following.
[0013]
Further, the reproducing method in the multiplex recording / reproducing method of the present invention comprises the steps of: picking up a wavelength at which infrared transmittance differs by 1% or more between one isomer state and a photo-steady state of the same compound; By determining the above-mentioned wavelength differently from the above and using this as the reproduction wavelength, it becomes possible to reproduce the multiplex-recorded information.
[0014]
Information is erased by irradiating a compound forming a signal (information) to be erased with light having a wavelength that causes a photochromic reaction corresponding to information erasure. Erasure of information may be performed by irradiating the entire surface with light. For example, light of a certain wavelength may cause one compound to be in the “recording” state and another compound to be in the “erased” state. If possible, the information can be overwritten.
[0015]
The optical recording medium of the present invention is a medium most suitable for the above-described multiplex recording / reproducing method, and is preferably a medium in which a plurality of types of photochromic compounds are combined so that the above-mentioned recording / reproducing method can be effectively performed.
Hereinafter, the optical recording medium and the optical recording method of the present invention will be described in detail.
[0016]
The multiplex recording / reproducing method of the present invention can be easily achieved by combining a plurality of photochromic compounds including molecular vibrations having a large infrared absorption intensity change before and after the photoisomerization reaction of the photochromic compound. We analyzed molecular vibrations related to infrared absorption of photochromic compound isomers in detail, and studied molecular design to increase the change of molecular vibrations. Analysis of molecular vibrations was performed using theoretical chemical calculations, especially molecular orbital calculations.
[0017]
Examples of the photochromic compound used in the present invention include a diarylethene compound, a fulgide compound, a spironaphthoxazine compound, and an azobenzene compound. Of these, diarylethene compounds are more preferably used. In this diarylethene-based compound, the asymmetric bond stretching vibration of the C 二 重 C double bond formed by the photocyclic ring-closing reaction appears at about 1600 cm ^{−1 as} a result of detailed molecular science analysis by molecular orbital calculation. 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.
[0018]
Further, by using a plurality of the above-described photochromic compounds, a difference in infrared absorption intensity between the ring-opened body and the ring-closed body can be detected at a plurality of frequencies, and nondestructive reading can be performed. Specifically, for example, in the case of a diarylethene-based compound, a large absorption other than around 1600 cm ⁻¹ is exhibited depending on the type and direction of the functional group and aromatic group (aryl group) contained in the compound. Multiple detection is possible by additionally detecting the intensity change of the typical infrared absorption peak before and after the photochromic reaction. About 1 compound, considering the two structural isomers, with respect to the recording layer containing the n types of photochromic compounds, so that the signal as 2 ⁿ can be recorded.
[0019]
As a combination of a plurality of photochromic compounds for realizing such multiple recording, for example, at least one of diarylethene compounds represented by the following general formulas (I) and (II) is used (included in the recording layer). It is mentioned.
[0020]
Embedded image

[0021]
(In the formula, R ^{1 to} R ⁴ each independently represent an alkyl group having 1 to 6 carbon atoms.)
The shape of the above compound is largely different among a ring-opened form of the compound represented by the formula (I), a ring-closed form of the compound, a ring-opened form of the compound represented by the formula (II), and a ring-closed form of the compound. By using these because they show an infrared absorption spectrum, a multiple recording / reproducing method can be effectively achieved. For example, in the case of an optical recording medium having a recording layer containing one kind of each of the compounds represented by the formulas (I) and (II), irradiating one or both of them with light that causes a ring opening reaction or a ring closing reaction. After recording a signal, the infrared absorption spectrum of the recording layer after recording is measured, and the resulting four states (both compounds are ring-opened, both compounds are ring-closed and represented by the formula (I)) Wherein the compound represented by the formula (II) is a ring-opened compound and the compound represented by the formula (I) is a ring-closed compound and the compound represented by the formula (II) is a ring-opened compound. State) can be reproduced and separated, and a multiplex recording / reproducing method is realized.
[0022]
Each of the above-mentioned compounds is a part of the photochromic compound that can be used in the optical recording medium of the present invention, and the present invention is not limited to these.
According to the recording / reproducing method for an optical recording medium of the present invention, recording and / or erasing are performed using a plurality of types of recording light having different wavelengths, and reproduction is performed by detecting changes in infrared absorption intensity at a plurality of different frequencies. This is a multiplex recording / reproducing method characterized by performing. At the time of recording and / or erasing, recording light having higher energy than at the time of reproduction is used. Since many photochromic compounds generate light isomerization efficiently with light in the ultraviolet wavelength region to the visible light wavelength region, light of this wavelength (specifically, about 190 nm to 800 nm) is used as a recording light and It is preferably used as erasing light.
[0023]
As the recording light and / or the erasing light, light having an energy that causes at least one of the plural types of photochromic compounds included in the recording layer to undergo a photoisomerization reaction is used. The recording light and / or the erasing light may be one that causes only one kind of compound in the recording layer to undergo a photoisomerization reaction, or one that causes a plurality of kinds of compounds to cause a photoisomerization reaction at the same time. By appropriately combining these, it is only necessary to perform recording with a desired multiplicity, or erase or overwrite the recording.
[0024]
Reproduction of information is performed by detecting a change in infrared absorption intensity. Specifically, first, infrared absorption spectra of the photochromic compounds contained in the recording layer before and after the photoisomerization reaction are measured. Next, the spectrum shapes are all compared, and a frequency at which it is easy to identify which isomer of which compound has been generated is picked up. The optical recording medium on which information is recorded is irradiated with infrared light on a recording portion of the recording layer, and a change in absorption intensity at a frequency previously picked up is detected. By converting the detected absorption signal, it is possible to determine the isomer of each compound present in the recorded portion, and multiplex recording is realized.
[0025]
In the present invention, the light source used for the recording light, the reproducing light and the erasing light is not particularly limited, but it is preferable to use a semiconductor laser as the light source.
The recording layer of the optical recording medium in the present invention, for example, a photochromic compound, cycloolefin resin, polyester resin, polystyrene resin, vinyl chloride resin, vinyl acetate resin, polyvinyl butyral resin, polymethyl methacryl resin, polycarbonate resin, phenol Disperse or dissolve in a solvent such as benzene, toluene, hexane, cyclohexane, methyl ethyl ketone, acetone, methanol, ethanol, tetrahydrofuran, dioxane, carbon tetrachloride, chloroform, etc. with a binder resin such as resin and epoxy resin, and apply it to an appropriate substrate To form a film by coating and drying a solution obtained by dissolving a photochromic compound in the above-mentioned solvent on a substrate, or enclosing the photochromic compound solution in a glass cell or the like. Formed by law or 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.
[0026]
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.
[0027]
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.
[0028]
【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)
Compound 1 (1,2-bis (2,5-dimethyl-3-thienyl) perfluorocyclopentene) was first used as a photochromic compound in S.P. Kobatake, T .; Yamada, K .; Uchida, N .; Kato, and M.S. Irie, J.M. Am. Chem. Soc. , 1999, 121, 2380-2386. Compound 2 (1,2-bis (3,5-dimethyl-2-thienyl) perfluoropentene) was then synthesized according to the method described in K. Uchida and M.S. Irie, Chem. Lett. , 1995, 969-970. Were synthesized based on the method described in (1).
[0029]
Embedded image

[0030]
FIG. 1 and FIG. 2 show absorption spectra of the obtained compound 1 and compound 2 in a hexane solution in a light-steady state (a mixture of a ring-opened body and a ring-closed body) formed by irradiation with UV light. Compound 1 is closed with light having a wavelength shorter than 313 nm, has absorption having a maximum at 520 nm, and has no absorption at 400 nm. Compound 2 is closed with light having a wavelength shorter than 380 nm, has absorption having a maximum at 430 nm, and has no absorption at 560 nm. Therefore, the ring-opening reaction of only compound 2 can be caused by using light having a wavelength of 400 nm, and the ring-opening reaction of compound 1 alone can be caused by using light having a wavelength of 560 nm. In addition, since each ring closure causes a ring opening reaction simultaneously with light absorption, nondestructive readout using visible light cannot be performed.
[0031]
Next, 2.8 mg of the compound 1, 3.0 mg of the compound 2, and 43.5 mg of an amorphous polyolefin resin (“Zeonex480” manufactured by Nippon Zeon Co., Ltd.) were dissolved in 4 ml of chloroform, and the solution was placed on a Petri dish having a diameter of 5 cm. Cast. The Petri dish is heated to 60 ° C., prepared so that the solution is evenly spread on the Petri dish, covered with aluminum foil, and the solvent is gradually evaporated to form a photochromic film (the weight fraction of the photochromic compound in the film is 12 wt%). Created.
[0032]
Subsequently, multiplex recording, reproduction, and erasure of information are performed using the obtained photochromic film (corresponding to the recording layer of the optical recording medium). FIG. 4 schematically shows four states of the photochromic film caused by the irradiation of the recording light and / or the erasing light, and the wavelength of light irradiated to reach each state. In FIG. 4, in order to clearly show the transition between the states A to D, in each of the states A to D, the compound 1 and the compound 2 are each a structural isomer of one of an open form and a closed form. It is described as having only a body. However, in the experiments described below, since the photoisomerization reaction has progressed only to the photo-steady state, both the compound 1 and the compound 2 are in a state in which the ring-opened form and the ring-closed form are mixed in each state. .
[0033]
First, an infrared absorption spectrum of the obtained photochromic film (both compound 1 and compound 2 contained in the film were in the state of a ring-opened body (state A. (1-O + 2-O)) was measured. are shown in Figure 3. in this ^measurement, it is found that no absorption noticeable in the area of 1500cm ^-1 ~1700cm -1.
Next, the same photochromic film is irradiated with light having a wavelength of 313 nm to bring compound 1 and compound 2 into a photo-steady state (state D. ((1-O + 1-C) + (2-O + 2-C))), The absorption spectrum was measured. The results are shown in FIG. In this measurement, 1545cm around ^-1, was able to observe the four infrared absorption over to 1590cm ^-1 and near ^{1670cm -1 ~1625cm} -1.
[0034]
Subsequently, the same photochromic film is irradiated with light having a wavelength of 560 nm or more to make only compound 1 into a ring-opened body (state C. (1-O + (2-O + 2-C))), and an infrared absorption spectrum is obtained. Was measured. The results are shown in FIG. In this measurement, there is no absorption in the vicinity of 1545cm ^-1, 3 pieces of infrared absorption over to 1590cm ^-1 and near ^{1670cm -1 ~1625cm} -1 could be observed.
[0035]
Further, when light having a wavelength of 403 nm is applied to the photochromic film (the photochromic film in the state D in which both the compound 1 and the compound 2 are in the photo-steady state), only the compound 2 is in a ring-opened state (state B ((B)). 1-O + 1-C) + 2-O) that can be show to measure the infrared absorption spectrum. the results in Figure 3. in this measurement, albeit absorption around 1545 cm ^-1, 1590 cm around ^-1 And absorption of 1670 cm ^{-1 to} 1625 cm ^-1 disappears.
[0036]
Finally, when the photochromic film is irradiated with light having a wavelength of 460 nm, both the compound 1 and the compound 2 return to the state of only the ring-opened form (state A. (1-O + 2-O)). When measuring the infrared ^absorption, no absorption noticeable in the region of 1500cm ^-1 ~1700cm -1.
To summarize these, the infrared absorption at around 1545 cm ^-1, by detecting the infrared absorption intensity of 1590 cm ^-1 (or 1655 cm ^-1), as shown in Table 1, four in FIG. 4, wherein the state ( The states A to D) can be reproduced and divided, and it has been shown that multiplex recording / reproduction is possible.
[0037]
[Table 1]

[0038]
【The invention's effect】
In this way, by using light of a plurality of wavelengths as information recording light, and detecting changes in absorbance at a plurality of frequencies in the infrared wavelength region, particularly electromagnetic waves having lower energy than the recording light, the optical recording medium can be recorded. Multiplex recording and reproduction methods can be performed, and the density of the recording medium can be easily increased.
[Brief description of the drawings]
FIG. 1 shows absorption spectra of a ring-opened compound (an isomer obtained by synthesis) of compound 1 and a photosteady state in a hexane solution measured in Example 1.
FIG. 2 shows absorption spectra of a ring-opened compound (isomer obtained by synthesis) of compound 2 and a photo-steady state in a hexane solution, which were measured in Example 1.
FIG. 3 is an infrared absorption spectrum in states A to D in Example 1.
FIG. 4 is a state transition diagram of states A to D in the first embodiment.

Claims (10)

An optical recording medium having a recording layer containing a plurality of types of light-responsive materials. A rewritable optical recording medium for performing non-destructive reading. The optical recording medium according to claim 1, wherein the photoresponsive material is a photochromic compound. 3. The optical recording medium according to claim 1, wherein the photochromic compound is a diarylethene compound. 4. The recording layer contains n kinds (where n is an integer of 2 or more) of photochromic compounds, and each of the photochromic compounds has a wavelength region satisfying the following a) and b) of 5 nm or more. The optical recording medium according to any one of the above.
a) In the first absorption band of one structural isomer, a wavelength region in which the molar extinction coefficient of the isomer is 550 or more.
b) A wavelength region in which the molar extinction coefficient of each of the two structural isomers of the other structural isomer and the other (n-1) compounds is 500 or less. The optical recording medium according to any one of claims 1 to 4, wherein the photochromic compound contained in the recording layer satisfies the following c) and d).
c) The photochromic reaction is a ring-opening / ring-closing reaction, and there is a frequency at which a difference in infrared transmittance between the photo-steady state and the ring-opened state of the same compound is 1% or more.
d) The frequencies defined in c) above are all different for each type of photochromic compound contained in the recording layer. An optical recording medium having a recording layer containing n types (where n is an integer of 2 or more) of photochromic compounds, and a wavelength region satisfying the following a) and b) for each of the photochromic compounds contained in the recording layer. Is an optical recording medium having a thickness of 5 nm or more.
a) In the first absorption band of one structural isomer, a wavelength region in which the molar extinction coefficient of the isomer is 550 or more.
b) A wavelength region in which the molar extinction coefficient of each of the two structural isomers of the other structural isomer and the other (n-1) compounds is 500 or less. The optical recording medium according to claim 6, wherein each of the photochromic compounds contained in the recording layer satisfies the following c) and d).
c) The photochromic reaction is a ring-opening / ring-closing reaction, and there is a frequency at which a difference in infrared transmittance between the photo-steady state and the ring-opened state of the same compound is 1% or more.
d) The frequencies defined in c) above are all different for each type of photochromic compound contained in the recording layer. An optical recording medium having a recording layer containing n types (where n is an integer of 2 or more) of photochromic compounds, wherein each of the photochromic compounds contained in the recording layer satisfies the following c) and d). Medium.
c) The photochromic reaction is a ring-opening / ring-closing reaction, and there is a frequency at which a difference in infrared transmittance between the photo-steady state and the ring-opened state of the same compound is 1% or more.
d) The frequencies defined in c) above are all different for each type of photochromic compound contained in the recording layer. The information is obtained by irradiating the optical recording medium according to any one of claims 2 to 8 with light having an energy to cause at least one kind of photochromic compound contained in the recording layer to undergo a photoisomerization reaction. Record and / or delete the
For a recorded portion of the recording layer, a recording method for reproducing information by detecting a change in infrared absorption intensity before and after recording at a specific frequency,
A multiplex optical recording medium characterized by performing recording and / or erasing using a plurality of types of recording light having different wavelengths and performing reproduction by detecting a change in infrared absorption intensity at a plurality of different frequencies. Recording and playback method. Containing a plurality of types of photochromic compounds, for an optical recording medium having a recording layer,
By irradiating at least one compound among the compounds with light having an energy to cause a photoisomerization reaction, information is recorded and / or erased,
For a recorded portion of the recording layer, a recording method for reproducing information by detecting a change in infrared absorption intensity before and after recording at a specific frequency,
A multiplex optical recording medium characterized by performing recording and / or erasing using a plurality of types of recording light having different wavelengths and performing reproduction by detecting a change in infrared absorption intensity at a plurality of different frequencies. Recording and playback method.

Images