JP2006185506A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium which is highly sensitive and whose recording data are stable to heat. <P>SOLUTION: The optical recording medium using a multiphoton absorption reaction of a photochromic compound is characterized in that recording is performed in a direction in which the absorption wavelength of the compound is made short. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical recording medium using a photochromic compound, and in particular, an optical recording medium having a large multiphoton absorption cross-sectional area and a large efficiency of optical property change accompanying a structural change of a compound excited by multiphoton absorption, that is, excellent recording sensitivity. About.

  Nonlinear optical effects are various phenomena based on the interaction between strong light and a substance, and among the nonlinear optical properties of organic compounds, multiphoton, particularly two-photon absorption phenomena are attracting attention. Two-photon absorption is a phenomenon in which a compound absorbs two photons and transitions from a ground state to an excited state. Using light having a wavelength about twice the one-photon excitation wavelength, two photons are converted into one photon. It can be excited by hitting a molecule. The probability that two photons hit one molecule at a time is proportional to the square of the photon density, and as the laser beam is focused on the sample, the photon density is proportional to the square of the distance as it moves away from the focal plane. Decrease. Accordingly, the probability that two-photon absorption occurs decreases as the distance from the focal plane increases in proportion to the fourth power of the distance. Utilizing this phenomenon, application of two-photon absorption is expected in the fields of optical memory, two-photon modeling, two-photon photodynamic therapy, and the like.

By the way, a photochromic compound is a compound that reversibly produces two isomers with different coloring states by the action of light, and research and development are actively progressing with the aim of application to light control lenses, dosimeters, optical recording media, and the like. It has been. In addition, among optical recording media, vigorous studies have been conducted on optical recording media that utilize a multiphoton absorption phenomenon when a photochromic compound changes its structure by absorbing light. In general, the quantum yield in the isomerization reaction of the photochromic compound is 0.1 or more from the short wavelength body to the long wavelength body, whereas in the reverse reaction, the quantum yield is only about 1/10 to 1/1000. In conventional multiphoton absorption recording using a photochromic compound, recording is performed by utilizing a molecular structure change in a direction in which the absorption wavelength of the compound becomes longer (see Patent Documents 1 and 2). However, multiphoton absorption is generally very low in efficiency, and in order to actually perform multiphoton recording, it is necessary to use a high-power and extremely expensive titanium sapphire laser. There is a need for optical recording media.
JP 2004-039009 A JP 2003-308634 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a more sensitive optical recording medium.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the long absorption wavelength body is higher than the short absorption wavelength body and the absorption wavelength of the compound is shortened with respect to the multiphoton absorption cross section of the photochromic compound. In this way, the present inventors have found that an optical recording medium that can be recorded with lower energy, has high recording data stability, and high sensitivity can be obtained by performing recording in (1). That is, the gist of the present invention resides in an optical recording medium using a multiphoton absorption reaction of a photochromic compound, and recording is performed in a direction in which the absorption wavelength of the compound becomes shorter.

  According to the present invention, an optical recording medium having high sensitivity and recording data stable against heat is provided.

Hereinafter, typical contents of the present invention will be specifically described. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention. it can.
The optical recording medium according to the present invention contains a photochromic compound as at least a part of the constituent components. The fact that the photochromic compound is contained in the optical recording medium means that the material is decomposed, extracted, etc., and then subjected to, for example, liquid chromatography mass spectrometry (LC-MS) or nuclear magnetic resonance spectroscopy (NMR). This can be confirmed by analysis. In addition, the photochromic compound may contain only 1 type, or may contain 2 or more types by arbitrary combinations and arbitrary ratios.

  As a photochromic compound, a photochromic compound having heat irreversibility such as diarylethene and fulgide is preferable because the state after isomerization is stable, that is, the recorded data is stable against heat. Therefore, the diarylethene type is more preferable because of its high repetitive durability. The heat irreversible photochromic compound should not substantially lose the record due to heat change under normal working environment. Specifically, it is usually 50% or more after storage at 80 ° C. for 200 hours, Preferably, 70% or more, more preferably 90% or more, is not thermally changed.

  The diarylethene-based photochromic compound has a structure represented by any of the following general formulas (Ia) to (Id).

(In the formula (Id), X represents an alkyl group which may have a substituent, an alkoxy group which may have a substituent, an aryl group which may have a substituent, or a substituted sulfonyl group; And B represents an aromatic ring.)
In the present invention, the simple term “aromatic ring” represents a ring having aromaticity, that is, a ring having a (4n + 2) π electron system (n is a natural number), and includes aromatic hydrocarbons and aromatics. Any heterocycle having a property is included. Further, the aromatic ring may have a substituent as long as the aromaticity is not significantly impaired.

Of the above (Ia) to (Id), the structures (Ia) and (Ib) are preferable, and the structure (Ia) is particularly preferable.
The alkyl group of X in the general formula (Id) is usually a chain alkyl group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, and more preferably 1 to 10 carbon atoms. Group, ethyl group, n-propyl group, i-propyl group and the like.

The alkoxy group of X in the general formula (Id) is usually a linear alkoxy group having 1 to 30 carbon atoms, preferably 1 to 20 carbon atoms, and more preferably 1 to 10 carbon atoms. Group, ethoxy group, n-propoxy group, i-propoxy group and the like.
The aryl group of X in the general formula (Id) is usually an aromatic ring having 5 to 30 carbon atoms, preferably 5 to 20 carbon atoms, and more preferably 5 to 15 carbon atoms. The carbon atom in the atom may be substituted with an oxygen atom, a nitrogen atom or a sulfur atom. Specific examples include a phenyl group, a naphthyl group, a thienyl group, a pyrrolyl group, and a furyl group.

When X in the general formula (Id) is an alkyl group, an alkoxy group, or a sulfonyl group, examples of the substituent include a halogen atom such as one or two or more fluorine atoms and chlorine atoms, a cyano group, a nitro group, and a carboxyl group. Amide group, alkoxy group, alkylthio group and the like. Preferred examples of the substituent include a halogen atom and a cyano group. Specifically, for example, halogenated alkyl groups (fluorinated alkyl groups, chloroalkyl groups, etc.), cyanoalkyl groups, alkoxyalkyl groups, halogenated alkoxy groups (fluorinated alkoxy groups, chloroalkoxy groups, etc.), cyanoalkoxy groups And alkoxyalkoxy groups.

  In addition, when the general formula (Id) is an aryl group, the substituents it has include one or more alkyl groups, alkoxy groups, halogen atoms such as fluorine atoms and chlorine atoms, cyano groups, nitro groups, carboxyls Group, amide group, alkylthio group and the like. Specific examples include halogenated aryl groups such as alkylaryl groups, alkoxyaryl groups, fluorinated aryl groups, and chloroaryl groups, cyanoaryl groups, and nitroaryl groups.

A and B in the above general formula (I) each independently represent an aromatic ring which may have a substituent. The skeletal structures of A and B are usually 5- or 6-membered, monocyclic or aromatic rings composed of 2 to 6 condensed rings, which include aromatic hydrocarbons, heteroaromatics, and anthracene rings. In addition, a ring such as a carbazole ring or an azulene ring is also included. Specific examples of the skeleton structure of A and B include benzene ring, naphthalene ring, phenanthrene ring, azulene ring, pyridine ring, pyrazine ring, furan ring, thiophene ring, pyrrole ring, pyrene ring, imidazole ring, oxadiazole ring, Examples include a quinoline ring, an isoquinoline ring, a quinoxaline ring, a benzofuran ring, a carbazole ring, a thiazole ring, a dibenzothiophene ring, and an anthracene ring. Of these, a thiophene ring, a thiazole ring, and a benzothiazole ring are particularly preferable from the viewpoint that the absorption spectrum corresponds to a red semiconductor laser beam having a wavelength of about 800 nm or a wavelength of about 650 nm in the near infrared.

When A and / or B has a substituent, the substituent may be an organic group, an inorganic element, or an inorganic functional group, but is preferably one that does not significantly affect the electron density of the diarylethene compound. When the substituent is an organic group, the substituent preferably has 20 or less carbon atoms. In terms of ease of synthesis, A and B are preferably the same.
The substituents A and B have include alkyl groups, alkenyl groups, alkynyl groups, hydrocarbon ring groups, heterocyclic groups, alkoxy groups, (hetero) aryloxy groups, (hetero) aralkyloxy groups, and further substituents. An amino group, a nitro group, a cyano group, an ester group, a halogen atom, a hydroxyl group and the like, which may be used, are mentioned. Among these, an alkyl group, a hydrocarbon ring group, and an amino group which may further have a substituent are preferable, and an amino group which may further have a substituent is more preferable.

  Specifically, an alkyl group having 1 to 20 carbon atoms, an alkenyl group having 1 to 20 carbon atoms, an alkynyl group having 1 to 20 carbon atoms, a hydrocarbon ring group having 3 to 20 carbon atoms, a single unit of a 5- or 6-membered ring. A heterocyclic group derived from a ring or a 2-6 condensed ring, an alkoxy group having 1 to 9 carbon atoms, a (hetero) aryloxy group having 2 to 18 carbon atoms, a (hetero) aralkyloxy group having 3 to 18 carbon atoms, an amino group , An alkylamino group having 2 to 20 carbon atoms, a (hetero) arylamino group having 2 to 30 carbon atoms, a jurodinyl group, a nitro group, a cyano group, an ester group having 1 to 6 carbon atoms, a halogen atom, a hydroxyl group, and the like. . Of these, a (hetero) arylamino group having 2 to 30 carbon atoms is preferable.

Examples of the alkyl group having 1 to 20 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, iso-butyl group, sec-butyl group, tert-butyl group, hexyl group and octyl group. Can be mentioned.
Examples of the alkenyl group having 1 to 20 carbon atoms include a vinyl group, a propenyl group, a butenyl group, a 2-methyl-1-propenyl group, a hexenyl group, and an octenyl group.

Examples of the alkynyl group having 1 to 20 carbon atoms include ethynyl group, propynyl group, butynyl group, 2-methyl-1-propynyl group, hexynyl group, octynyl group and the like.
Examples of the hydrocarbon ring group having 3 to 20 carbon atoms include a cyclopropyl group, a cyclohexyl group, a cyclohexenyl group, a tetradecahydroanthranyl group, a phenyl group, an anthranyl group, a phenanthryl group, and a ferrocenyl group.

Heterocyclic groups derived from 5- or 6-membered monocyclic or 2-6 condensed rings include pyridyl, thienyl, benzothienyl, carbazolyl, quinolinyl, 2-piperidinyl, 2-piperazinyl, octahydroxy Examples include a nolinyl group.
Examples of the alkoxy group having 1 to 9 carbon atoms include methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, iso-butoxy group, sec-butoxy group, tert-butoxy group, hexyloxy group, octyloxy Groups and the like.

Examples of the (hetero) aryloxy group having 2 to 18 carbon atoms include a phenoxy group, a naphthyloxy group, a 2-thienyloxy group, a 2-furyloxy group, and a 2-quinolyloxy group.
Examples of the (hetero) aralkyloxy group having 3 to 18 carbon atoms include benzyloxy group, phenethyloxy group, naphthylmethoxy group, 2-thienylmethoxy group, 2-furylmethoxy group, 2-quinolylmethoxy group and the like. It is done.

Examples of the alkylamino group having 2 to 20 carbon atoms include dimethylamino group, methylethylamino group, dibutylamino group, ditolylamino group, di (2-thienyl) amino group, di (2-furyl) amino group, phenyl ( 2-thienyl) amino group and the like.
Examples of the (hetero) arylamino group having 2 to 30 carbon atoms include diphenylamino group, dinaphthylamino group, naphthylphenylamino group, ditolylamino group, di (2-thienyl) amino group, and di (2-furyl) amino. Group, phenyl (2-thienyl) amino group and the like. Of these, a diphenylamino group is preferred.

Examples of the ester group having 1 to 6 carbon atoms include a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, and an isopropoxycarbonyl group.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.
In addition, when each A and / or B has two or more substituents, the substituents may be bonded to form a cyclic structure.

Specific examples of the skeleton structure of the diarylethene compound used in the optical recording medium according to the present invention (in the diazole compound according to the present invention, hydrogen atoms of the skeleton structure exemplified below may be substituted with the above-described substituents) Examples are given below, but the diarylethene compound used in the optical recording medium according to the present invention is not limited to these examples.

The photochromic compound can be synthesized, for example, by the method described in Chem. Rev. 2000, 100, 1685-1716.

  In general, in an optical recording medium using a photochromic compound, the photochromic compound is dispersed in a polymer binder as a recording layer. The photochromic compound is preferably contained in an amount of 5 to 95% by weight, more preferably 10 to 70% by weight based on the total solid content. When the amount of the photochromic compound is too small, it becomes difficult to read out, and when it is too large, the compatibility with the polymer binder is lowered and the film is easily crystallized.

  The polymer binder used for forming the recording layer is not particularly limited as long as the diarylethene compound is suitably dissolved or dispersed. Specifically, acrylic resin, methacrylic resin, vinyl acetate resin, vinyl chloride resin, polyethylene resin, polypropylene resin, polystyrene resin, polynaphthalene resin, polycarbonate resin, polyethylene terephthalate resin, polyvinyl butyral resin, etc. Acrylic resin or methacrylic resin is preferred.

  When the recording layer is prepared by the above method, as the solvent (dispersion medium), the diarylethene compound is preferably dissolved or dispersed, and the polymer binder is suitably dissolved or dispersed, and film formation processing is performed. If it does not become a hindrance at the time of, it will not specifically limit. Specific examples include various organic solvents such as aromatic solvents such as benzene and toluene, aliphatic solvents such as hexane, ether solvents such as tetrahydrofuran, and chlorine solvents such as chloroform.

Alternatively, a polymerizable compound may be used as the polymer binder, and this may be polymerized and cured by irradiation with an ultraviolet ray such as a high-pressure mercury lamp, or an active energy ray such as an electron beam or a visible ray to form a recording layer. In this case, the amount of the polymerizable compound is preferably 50 to 99.8% by weight, more preferably 80 to 99% by weight based on the total solid content.
The polymerizable compound component used in the present invention may be either a monofunctional or polyfunctional polymerizable monomer or resin oligomer. However, in order to increase the crosslink density of the recording layer and maintain the strength, the polyfunctional component It is preferable to contain a certain amount.

  Examples of the monofunctional monomer component include 2-ethylhexyl (meth) acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, phenoxyethyl (meth) acrylate, nonylphenoxyethyl (meth) acrylate, N-vinylpyrrolidone, 2-hydroxyethylacryloyl phosphate, tetrahydrofurfuryl (meth) acrylate, tetrahydrofurfuryloxyethyl (meth) acrylate, tetrahydrofurfuryloxyhexanolide (meth) acrylate, ε of 1,3-dioxane alcohol -Caprolactone adduct (meth) acrylate, 1,3-dioxolane (meth) acrylate and the like.

  Examples of the polyfunctional monomer component include cyclopentenyl (meth) acrylate, 1,6-hexanediol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, dicyclopentadienyl di (meth) acrylate, and diethylene glycol. Di (meth) acrylate, tripropylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, polyethylene glycol (400) di (meth) acrylate, hydroxypivalate ester neopentyl glycol di (meth) acrylate, neopentyl Di (meth) acrylate of glycol adipate, di (meth) acrylate of ε-caprolactone adduct of neopentyl glycol hydroxypivalate, 2- (2-hydroxy-1,1- Ε-caprolactone addition of methylethyl) -5-hydroxymethyl-5-ethyl-1,3-dioxane di (meth) acrylate, tricyclodecane dimethylol di (meth) acrylate, tricyclodecane dimethylol di (meth) acrylate Bisphenol A diglycidyl ether di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol tri (meth) acrylate propionate, hydroxypivalaldehyde modified dimethylolpropane tri Examples include (meth) acrylate, tetra (meth) acrylate of dipentaerythritol propionate, and ditrimethylolpropane tetra (meth) acrylate. In particular, the polymerizable compound having the tricyclo structure represented by the following general formula (II) has high heat resistance and light transmittance of the cured product, low saturated water absorption, and compatibility with the photochromic compound. It is excellent and is particularly preferable as a recording layer according to the present invention.

(In the formula (II), the substituents R ₁ and R ₂ each independently represent a hydrogen atom or a methyl group, and the linking groups R ₃ and R ₄ each independently represent a single bond or an alkylene having 1 to 4 carbon atoms. Represents a group.)
In the general formula (II), R ₁ and R ₂ are preferably methyl groups, and the linking groups R ₃ and R ₄ are preferably alkylene groups having 1 or 2 carbon atoms.
Examples of the resin oligomer component include various (meth) acrylates such as epoxy (meth) acrylate, urethane (meth) acrylate, polyester (meth) acrylate, and polyether (meth) acrylate.

These polymerizable compounds may be used alone or in combination of two or more.
The polymerization initiator is preferably a radical photopolymerization initiator. The photo radical polymerization initiator generates active radicals by irradiation with ultraviolet rays such as high-pressure mercury lamps widely used in industry, and active energy rays such as electron beams and visible rays. Specifically, for example, benzoin isopropyl ether, benzophenone, 2-hydroxy-2-methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, 2,4-diethylthioxanthone, methyl o-benzoylbenzoate, 4,4-bis Diethylaminobenzophenone, 2,2-diethoxyacetophenone, benzyl, 2-chlorothioxanthone, diisopropylthioxanthone, 9,10-anthraquinone, benzoin, benzoin methyl ether, 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy- 2-methylpropiophenone, 4-isopropyl-2-hydroxy-2-methylpropiophenone, α, α-dimethoxy-α-phenylacetone, 2-hydroxy-2-methyl-1-phenylpropane- - one, 2,6-dimethyl-benzoyl phenyl phosphine oxide, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, and the like. Any one photopolymerization initiator may be used alone, or two or more photoinitiators may be used in combination.

The amount of the polymerization initiator is preferably 0.1% by weight to 10% by weight based on the total solid content. More preferably, it is 0.5 to 5% by weight. If the amount is too small, the amount of radicals generated is reduced, and the rate of photopolymerization is reduced. On the other hand, if the amount is too large, radicals generated by light irradiation recombine with each other, and the contribution to photopolymerization is reduced, and the rate of photopolymerization may also be slow.
In the recording layer of the present invention, if necessary, a thermal polymerization initiator, a chain transfer agent, a polymerization terminator, a storage stabilizer, a dispersant, an antifoaming agent, a plasticizer, a polymer binder other than the polymerizable compound, etc. Additives may be added. The amount of these additives is 0 to 20% by weight, preferably 0 to 10% by weight, based on the total solid content.

The optical recording medium according to the present invention may be coated on a transparent support without solvent, or may be mixed by adding a solvent or an additive to the composition. A recording layer is formed by irradiating and curing a line.
The active energy ray to be irradiated is not limited as long as the polymerizable compound can be cured and at the same time the photochromic compound can be colored, and examples thereof include an electron beam, visible light, and ultraviolet rays, and ultraviolet rays having a wavelength of 200 to 400 nm are particularly preferable. Specific examples of the lamp used include a chemical lamp, a xenon lamp, a low-pressure mercury lamp, a high-pressure mercury lamp, an ultrahigh-pressure mercury lamp, and a metal halide lamp. Introducing a step of coloring the photochromic compound at the same time as curing the polymerizable compound has the effect of increasing the coloring efficiency of the photochromic compound and increasing the signal intensity, and can simplify the process of creating the recording medium. It is possible and useful.

  The irradiation amount of the active energy ray is arbitrary as long as the polymerization initiator generates radicals. However, when the amount is extremely small, the polymerization is too incomplete and the heat resistance and mechanical properties of the recording layer are not sufficiently exhibited. On the contrary, when the amount is extremely large, the photochromic compound or the polymerizable compound contained in the recording layer is deteriorated by light, which is not preferable. Irradiation is usually preferably in the range of 0.1 to 20 J according to the composition of the recording layer composition, the type and amount of the polymerization initiator.

  The support may be transparent or opaque. As the transparent support, a transparent glass plate, an acrylic plate, a polycarbonate plate, a polyethylene terephthalate film, a polyethylene film, or the like is used. A glass plate, an acrylic plate, and a polycarbonate plate are preferable. As the opaque support, a single layer of a metal such as an aluminum plate, a reflective coat made of a metal such as gold, silver, or aluminum on the transparent support, or a dielectric such as magnesium fluoride or zirconium oxide, or A multi-layered coating with a dielectric reflection coating is used. These supports may be provided with data address patterning. Patterning can be performed by forming irregularities on the substrate itself, forming a pattern on the reflective coating, or a combination thereof.

The thickness of the support is preferably from 0.2 mm to 1 mm. If it is 0.2 mm or less, the mechanical strength is insufficient, and if it is 1 mm or more, there is no problem in mechanical strength, but the cost increases.
As a coating method, conventionally known methods such as spin coating, wire bar coating, dip coating, air knife coating, roll coating, and blade coating can be used. In addition, when a recording layer having a particularly large thickness is formed, a method of forming in a mold can be used.

In the optical recording medium of the present invention, a support or a protective layer for blocking oxygen can be further provided on the recording layer.
As the protective layer, a known technique for preventing adverse effects such as a decrease in sensitivity due to oxygen and deterioration in storage stability, for example, application of a water-soluble polymer or the like can be used.
When the support is provided above and below the recording layer, at least one of the two upper and lower supports needs to be transparent.

In the case of a medium having a transparent substrate on both sides of the recording layer, a transmissive type or a reflective type can be recorded. Further, when an opaque or reflective support is provided on one side, the reflective type can be recorded. In the case of a reflective recording medium, the reflective layer may be between the support and the recording layer, or may be on the outer surface of the substrate.
In both the transmissive and reflective recording media, an antireflection film may be provided on the side on which recording light and readout light enter and exit, or between the recording layer and the support. These antireflection films function to improve the light use efficiency.

The optical recording medium according to the present invention performs recording by utilizing the change in the direction in which the absorption wavelength of the photochromic compound becomes shorter. The isomerization reaction of a photochromic compound is conventionally a ring-opening and ring-closing reaction, and the ring-closed body has a longer absorption wavelength than that of the ring-opened body. I was going.
On the other hand, the optical recording medium according to the present invention uses a change in the direction in which the absorption wavelength is shortened, but usually has a two-light absorption cross-sectional area as compared with recording using a change in the direction in which the absorption wavelength is increased. Increases the sensitivity. The particularly preferable optical recording medium according to the present invention has a sensitivity that is 50% higher than that of the conventional recording using the change in the direction in which the absorption wavelength becomes longer. The wavelength change due to isomerization is preferably 50 nm, more preferably 100 nm, and particularly preferably 150 nm or more. In general, it is preferably 350 nm or less. If the wavelength change is too large, the absorption wavelength after isomerization is too long and it is easy to absorb the recording light. If it is too small, the optical change is small and the reading becomes difficult.

The light used for recording information uses a light source having a wavelength that does not cause one-photon absorption. Thereby, multilayer recording becomes possible. 800 nm ± 50 nm is preferable.
As described above, in multiphoton absorption recording using a photochromic compound, recording is performed in a direction in which the absorption wavelength of the compound becomes shorter, whereby a highly sensitive optical recording medium can be achieved.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to synthesis examples and examples. However, the present invention is not limited to the following examples unless it exceeds the gist.
<Synthesis of photochromic compounds>
Synthesis Example 1 Synthesis of 1,2-bis (6-diphenylamino-2-methyl-1-benzo [b] thiophen-3-yl) -3,3,4,4,5,5-hexafluorocyclopentene (PC1038 below)
J. et al. Chem. Eur. 2001, vol7, p3466, compound III was synthesized. Compound III (0.72 g, 1.0 mmol), diphenylamine (0.34 g
, 2.0 mmol), sodium-t-butoxide (0.23 g), and toluene (2 cm ³ ) under a nitrogen atmosphere with palladium (II) acetate (2.2 mg) and tri-t
-Butylphosphine (10% by weight hexane solution, 0.1 cm ³ ) was added and heated to reflux for 3 hours. After cooling to room temperature, ethyl acetate and water were added, and the mixture was stirred and filtered through celite. The organic layer was separated and washed with saturated brine. The extract was dried over anhydrous sodium sulfate and concentrated under reduced pressure. Purification by silica gel column chromatography (elution solvent: hexane / ethyl acetate = 50/1 (volume ratio), then 10/1 (volume ratio)), the obtained crystals were suspended and washed with methanol, and the compound ( 0.65 g, yield 81%) was obtained. The mass analysis result was m / z = 802 (M ⁺ ).

  (Synthesis Examples 2-7) Synthesis of the following PC1043, PC1015, PC1014, PC1039, PC1019, PC1016

Instead of compound (III) of synthesis example 1 and diphenylamine, each raw material compound may be used.
In the same manner as in Synthesis Example 1, the following PC1043, PC1015, PC1014, PC1039, PC1019, and PC1016 were synthesized.
<Thermal stability of photochromic compounds>
The absorption wavelength of each photochromic compound and the dye residual ratio after leaving the compound at 80 ° C. and 85 RH for 200 hours are as shown in Table 1.

<Preparation of optical recording medium>
A solution was prepared by dissolving 4% by weight of each diarylethene compound and 4% by weight of an acrylic resin (manufactured by Mitsubishi Rayon, trade name: Acrypet VH-5) in tetrahydrofuran / toluene (mixing weight ratio 1: 1). After dropping the above solution onto a slide glass, it was applied with an applicator (gap 100 microns) and dried at 100 ° C. for 30 minutes to prepare a film sample having a thickness of 1 micron. By irradiating both surfaces of this film sample with ultraviolet rays (ultra-high pressure mercury lamp: USH-500BY1 manufactured by USHIO INC., Irradiation intensity: 250 mW / cm ² (
The wavelength was 365 nm), the irradiation time was 1 second), and the color was changed from almost colorless to change the structure of the short wavelength body contained in the film to the long wavelength body.

<Evaluation method of two-photon absorption cross section>
Two-photon absorption cross-sectional area was evaluated with reference to the method described in J. Opt. Soc. Am. B Vol. 14, No. 5 (1997) pp. 1079-1087. A femtosecond titanium sapphire laser (wavelength: 800 nm, pulse width: 100 fs, repetition frequency: 1 kHz, average output: 2 W, peak power: 20 GW) is used for the above film sample, and the output from the laser is appropriately attenuated to give two photons. The absorption cross section was measured. For measurement, the Z-scan method was used to change the excitation light density in the range of 1 to 40 GW / cm ² . As a measurement sample, a solution in which each compound was dissolved in toluene at a concentration of 2.5 mmol / L was used, and this solution was put into a four-sided transparent 1 cm square quartz cell for measurement.

<Recording sensitivity comparison method>
Regarding the two-photon absorption recording sensitivity of each sample, the time required until the color change was visually recognized in the laser irradiated portion of the film sample was compared.
In the case of a wavelength of 800 nm, the average output of the femtosecond titanium sapphire laser was lowered to 68 mW, the laser light was condensed to a beam diameter of 1 mm with a condenser lens, and the color change of the irradiated portion was visually evaluated. In the case of a wavelength of 650 nm, the laser light from the titanium: sapphire laser was converted to 650 nm with a wavelength converter (average output: 33 mW), and then condensed to a beam diameter of 1.7 mm, and an experiment was conducted in the same manner. .

As shown in Table 1, the optical recording medium according to the present invention was found to have a large two-photon absorption cross-sectional area and high sensitivity.
(Comparative example)
About the compound of said synthesis example 1-7, it carried out similarly to the Example, and measured the two-photon absorption cross section and recording sensitivity of the ring-opened body. The results are also shown in Table 1.

  An optical recording medium with high sensitivity and stable recording data against heat is provided.

Claims (4)

  An optical recording medium using a multiphoton absorption reaction of a photochromic compound, wherein the recording is performed in a direction in which the absorption wavelength of the compound becomes shorter.   The optical recording medium according to claim 1, wherein a photochromic compound having thermal irreversibility is used.   The optical recording medium according to claim 1, wherein a light source having a wavelength that does not cause one-photon absorption is used.   4. An optical recording method comprising recording with the optical recording medium according to claim 1.