Recording medium, information recording method, and information reading method

Abstract

A recording medium according to the present disclosure includes a recording layer containing an organic compound having a nonlinear light absorption characteristic, the molar absorption coefficient of the organic compound with respect to light having a wavelength of 400 nm or more and 405 nm or less being 90 mol <-1 > L cm <-1 > or more, and in the transient absorption spectrum of the organic compound, the wavelength of the organic compound is greater than or equal to 50 nm. The absorbance change [Delta] Abs at a wavelength of 400-405 nm (inclusive) is a positive value.

Description

Technical Field

[0001] The present disclosure relates to a recording medium, a method for recording information, and a method for reading information. Background Art

[0002] Among optical materials such as light absorbing materials, materials with nonlinear optical (Non-Linear Optical) effects are called nonlinear optical materials. The so-called nonlinear optical effect means that when a material is irradiated with strong light such as laser, an optical phenomenon that is proportional to the square of the electric field of the irradiated light or a higher order than the square is generated in the material. As optical phenomena, absorption, reflection, scattering, luminescence, etc. can be listed. As secondary nonlinear optical effects proportional to the square of the electric field of the irradiated light, second harmonic generation (SHG), Pockels effect, parametric effect, etc. can be listed. As third-order nonlinear optical effects proportional to the cube of the electric field of the irradiated light, two-photon absorption, multiphoton absorption, third harmonic generation (THG), Kerr effect, etc. can be listed. In this specification, multiphoton absorption such as two-photon absorption is sometimes referred to as nonlinear light absorption. Sometimes a material capable of nonlinear light absorption is referred to as a nonlinear light absorbing material. In particular, sometimes a material capable of two-photon absorption is referred to as a two-photon absorbing material. In addition, nonlinear light absorption is sometimes referred to as nonlinear absorption.

[0003] A large amount of research has been actively conducted so far on nonlinear optical materials. In particular, inorganic materials that can easily prepare single crystals have been developed as nonlinear optical materials. In recent years, the development of nonlinear optical materials formed by organic materials has been expected. Compared with inorganic materials, organic materials not only have a high degree of design freedom, but also have large nonlinear optical constants. Furthermore, for organic materials, nonlinear response is performed at high speed. In this specification, nonlinear optical materials containing organic materials are sometimes referred to as organic nonlinear optical materials.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent No. 6448042

[0007] Patent Document 2: Japanese Patent No. 5738554

[0008] Non-patent literature

[0009] Non-Patent Literature 1: Harry L. Anderson et al., “Two-Photon Absorption and the Design of Two-Photon Dyes”, Angew. Chem. Int. Ed. 2009, Vol. 48, pp. 3244-3266. Summary of the invention

[0010] Problems to be solved by the invention

[0011] New recording media using nonlinear optical materials are required.

[0012] Means for solving problems

[0013] A recording medium in one embodiment of the present disclosure includes a recording layer, wherein the recording layer contains an organic compound having nonlinear light absorption characteristics, wherein the molar absorption coefficient of the organic compound for light having a wavelength of 400 nm or more and 405 nm or less is 90 mol / L. -1 ·L·cm -1 As described above, in the transient absorption spectrum of the organic compound, the absorbance change ΔAbs at a wavelength of 400 nm to 405 nm is a positive value.

[0014] Effects of the Invention

[0015] The present disclosure provides a novel recording medium using a nonlinear optical material. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1A It is a flowchart related to the method of recording information using the recording medium including the nonlinear light absorbing material according to one embodiment of the present disclosure.

[0017] Figure 1B This is a flowchart related to a method of reading information using a recording medium including a nonlinear light absorbing material according to one embodiment of the present disclosure.

[0018] Figure 2 is a compound represented by formula (2) 1 H-NMR spectrum graph.

[0019] Figure 3A This is a graph showing the recording and reproducing characteristics of the resin film of Example 1.

[0020] Figure 3B This is a graph showing the recording and reproducing characteristics of the resin film of Example 2.

[0021] Figure 3C It is a graph showing the recording and reproducing characteristics of the resin film of Comparative Example 1.

[0022] Figure 3D It is a graph showing the recording and reproducing characteristics of the resin film of Comparative Example 2.

[0023] Figure 3E It is a graph showing the recording and reproducing characteristics of the resin film of Comparative Example 3.

[0024] Figure 3F It is a graph showing the recording and reproducing characteristics of the resin film of Comparative Example 4.

[0025] Figure 3G It is a graph showing the recording and reproducing characteristics of the resin film of Comparative Example 5.

[0026] Figure 4A is the transient absorption spectrum of the solution containing the compound of Example 1.

[0027] Figure 4B This is the transient absorption spectrum of the solution containing the compound of Example 1 when the vertical axis is converted from the absorbance change to the molar absorption coefficient of the excited state.

[0028] Figure 5A is the transient absorption spectrum of the thin film containing the compound of Example 1.

[0029] Figure 5B This is the transient absorption spectrum of the thin film containing the compound of Example 1 when the vertical axis is converted from the absorbance change to the molar absorption coefficient of the excited state.

[0030] Fig. 6A is the transient absorption spectrum of the solution containing the compound of Comparative Example 1.

[0031] Figure 6B is the transient absorption spectrum of the solution containing the compound of Comparative Example 2. DETAILED DESCRIPTION

[0032] (Insights that form the basis of this disclosure)

[0033] Among organic nonlinear optical materials, two-photon absorption materials have received particular attention. The so-called two-photon absorption refers to the phenomenon that a compound absorbs two photons almost simultaneously and transitions to an excited state. As two-photon absorption, simultaneous two-photon absorption and step-by-step two-photon absorption are known. Simultaneous two-photon absorption is sometimes also called non-resonant two-photon absorption. Simultaneous two-photon absorption means two-photon absorption in a wavelength range where there is no absorption band of single photons. Step-by-step two-photon absorption is sometimes also called resonant two-photon absorption. In the case of step-by-step two-photon absorption, the compound absorbs the first photon and then further absorbs the second photon, thereby transitioning to a higher-order excited state. In the case of step-by-step two-photon absorption, the compound absorbs 2 photons one by one.

[0034] In simultaneous two-photon absorption, the amount of light absorbed by the compound is generally proportional to the square of the intensity of the irradiated light, showing nonlinear characteristics. The amount of light absorbed by the compound can be used as an indicator of the efficiency of two-photon absorption. In the case where the amount of light absorbed by the compound shows nonlinear characteristics, for example, the absorption of light caused by the compound can occur only near the focus of a laser with a high electric field intensity. That is, in a sample containing a two-photon absorption material, the compound can be excited only at a desired position. In this way, the compound that produces simultaneous two-photon absorption brings extremely high spatial resolution, so the application in the recording layer of a three-dimensional optical memory, a photocurable resin composition for optical modeling, etc. is studied. In the case where the two-photon absorption material also has fluorescence characteristics, the two-photon absorption material can also be applied to fluorescent pigment materials used in two-photon fluorescence microscopes, etc. If the two-photon absorption material is used in a three-dimensional optical memory, it is also possible to adopt a method of reading the ON / OFF state of the recording layer based on the change in fluorescence from the two-photon absorption material. In the case of existing optical memories, a method of reading the ON / OFF state of a recording layer based on changes in the reflectivity and absorptivity of light in a two-photon absorption material is adopted. However, when this method is applied to a three-dimensional optical memory, the two-photon absorption efficiency of existing two-photon absorption materials is low compared to the single-photon absorption efficiency, so crosstalk may occur based on other recording layers different from the recording layer whose ON / OFF state is to be read.

[0035] For two-photon absorption materials, the two-photon absorption cross-sectional area (GM value) is used as an index to indicate the efficiency of two-photon absorption. The unit of two-photon absorption cross-sectional area is GM (10 -50 cm 4 ·s·molecule -1 Photon -1 ). So far, a large number of organic two-photon absorption materials with large two-photon absorption cross-sections have been proposed. For example, a large number of compounds with large two-photon absorption cross-sections exceeding 500GM have been reported (e.g., Non-Patent Document 1). However, in almost all reports, the two-photon absorption cross-section is measured using a laser with a wavelength longer than 600nm. In particular, near-infrared rays with a wavelength longer than 750nm are sometimes used as lasers.

[0036] However, in order to apply two-photon absorption materials to industrial uses, materials that show two-photon absorption characteristics when irradiated with laser light having a shorter wavelength are required. For example, in the field of three-dimensional optical storage, laser light having a short wavelength can achieve finer light focusing points, thereby increasing the recording density of three-dimensional optical storage. In the field of light modeling, laser light having a short wavelength can also achieve higher-resolution modeling. Furthermore, with regard to the specifications of Blu-ray (registered trademark) discs, a laser light having a central wavelength of 405 nm is used. In this way, if a compound having excellent two-photon absorption characteristics for light in the same wavelength range as a laser light having a short wavelength is developed, it will be possible to make a great contribution to the development of the industry.

[0037] Furthermore, light-emitting devices that emit extremely short pulse lasers with high light intensity are large and tend to be unstable. Therefore, such light-emitting devices are difficult to adopt for industrial use from the perspective of versatility and reliability. Considering this point, in order to apply two-photon absorption materials for industrial use, materials that exhibit two-photon absorption characteristics even when irradiated with lasers with low light intensity are required.

[0038] As a light source, for example, a femtosecond laser such as a titanium sapphire laser or a pulsed laser such as a semiconductor laser having a pulse width of picoseconds to nanoseconds can be used. From the viewpoint of being small, highly versatile, and having stable operation, semiconductor lasers are suitable for industrial use. When a laser having a pulse width of picoseconds to nanoseconds or more is used, and light with a lens that increases the photon density is irradiated onto an organic nonlinear optical material, the electron undergoes single-photon excitation or two-photon excitation at the femtosecond level, and relaxes to the lowest excited state in hundreds of femtoseconds to picoseconds. Even at the moment when the electron relaxes to the lowest excited state, pulse irradiation is being performed. Therefore, sometimes excitation from the lowest excited state to a higher excited state occurs. This phenomenon is called excited state absorption (ESA). Then, as long as the pulse irradiation continues, excited state absorption and relaxation to the lowest excited state are repeated. Except for special cases such as azulene, this relaxation is a very fast process that is completed at the latest in picoseconds, and there is no radiation deactivation. That is, deactivation occurs not by emission of light such as fluorescence or phosphorescence, but by heat generation. In this way, when a nonlinear light absorbing material is locally excited using a laser with a pulse width of picoseconds to nanoseconds or more, heat can be locally generated when the nonlinear light absorbing material further undergoes excited state absorption. This makes it possible to utilize the nonlinear light absorbing material as a heat source for locally deteriorating the recording medium, and even to perform three-dimensional recording.

[0039] Excited state absorption occurs, for example, as follows.

[0040] (1-1) Through single-photon absorption or two-photon absorption, electrons transition from the ground state (S0) to an excited state and rapidly relax to the first excited state (singlet state, S1).

[0041] (1-2) Further single-photon absorption from the S1 state excites the electron to a higher-order singlet excited state (S n ).

[0042] or,

[0043] (2-1) Through single-photon absorption or two-photon absorption, electrons transition from the ground state (S0) to an excited state and rapidly relax to the first excited state (singlet state, S1).

[0044] (2-2) Intersystem crossing (ISC) occurs from the S1 state to the triplet excited state (T1).

[0045] (2-3) Single photon absorption is further performed from the T1 state to excite the electron to a higher-order triplet excited state (T n ).

[0046] When excited state absorption does not occur, for example, electron transition proceeds as follows.

[0047] (3-1) Through single-photon absorption or two-photon absorption, electrons transition from the ground state (S0) to an excited state and rapidly relax to the first excited state (singlet state, S1).

[0048] (3-2) The electron relaxes from the S1 state to the S0 state and becomes deactivated.

[0049] or

[0050] (4-1) Through single-photon absorption or two-photon absorption, electrons transition from the ground state (S0) to an excited state and rapidly relax to the first excited state (singlet state, S1).

[0051] (4-2) Intersystem crossing occurs from the S1 state to the triplet excited state (T1).

[0052] (4-3) The electron relaxes from the T1 state to the S0 state and becomes deactivated.

[0053] As mentioned above, excited state absorption is a type of nonlinear light absorption, which is successive multiphoton absorption. Like two-photon absorption, excited state absorption only occurs when a sample is irradiated with high-intensity light. The probability of excited state absorption occurring when a sample is irradiated with low-intensity light is negligibly small.

[0054] In a compound having nonlinear light absorption characteristics, the relationship between the light intensity and the absorption characteristics when irradiated with a laser having a pulse width of picoseconds to nanoseconds or more is represented by the following formulas (i) and (ii). In this specification, a compound having nonlinear light absorption characteristics is sometimes referred to as a nonlinear light absorption compound. Formulas (i) and (ii) are calculation formulas for calculating the decrease in light intensity -dI when a sample containing a nonlinear light absorption compound and having a small thickness dz is irradiated with light of intensity I.

[0055] [Mathematical formula number 1]

[0056]

[0057] In formula (ii), α is the single photon absorption coefficient (cm -1 ). β is the simultaneous two-photon absorption coefficient (cm / W). γ is the simultaneous three-photon absorption coefficient (cm 3 / W 2 ). ESA is the excited state absorption cross-sectional area (cm 2 ). τ is the lifetime of the excited state (s). - is the Dirac constant (J·s). ω is the angular frequency of the incident light (rad / s).

[0058] Furthermore, α and β can be represented by the following formulas (iii) and (iv), respectively. In the formulas (iii) and (iv), ε is the molar absorption coefficient (mol -1 ·L·cm -1 ). N is the number of molecules of the compound per unit volume of the sample (mol·cm -3 ). A is Avogadro's constant. σ is the two-photon absorption cross-sectional area (GM).

[0059] [Mathematical formula number 2]

[0060]

[0061] Absorption coefficient (cm -1 ) refers to the ratio of photons absorbed per unit length when light travels through a substance. -1 cm -1 ) refers to the ratio of photons absorbed by each 1 mole of molecules when light travels through a substance. Absorption cross-sectional area (cm 2 ) refers to the ratio of photons absorbed by each particle (molecule) when light travels through a substance. The absorption coefficient can be converted to the absorption cross-sectional area by dividing it by the number of molecules per unit volume of the sample (molecular number density). The absorption cross-sectional area is calculated by multiplying the Avogadro constant (6.02×10 23 mol -1) and convert the units to convert it into the molar absorption coefficient.

[0062] When the irradiation light intensity is low, the contribution of the third-order nonlinear light absorption becomes small. For example, when irradiating light from a small, highly versatile semiconductor laser, the third-order term in equation (i) is considered to be small enough to be ignored. For simplicity, the CI is ignored. 3 The following formula (v) explains the nonlinear characteristics of light absorption.

[0063] [Formula No. 3]

[0064]

[0065] From formula (v), we can see that in the sample, the linear absorption (first order: AI) and the nonlinear absorption (second order: BI) 2 ) are equal to each other, and the intensity I of the incident light is represented by A / B. That is, when the intensity I of the incident light is smaller than A / B, linear light absorption is preferentially produced in the sample. When the intensity I of the incident light is larger than A / B, nonlinear light absorption is preferentially produced in the sample. Therefore, there is the following tendency: the smaller the value of A / B in the sample, the more nonlinear light absorption can be preferentially manifested by using a laser with a small light intensity. Here, A / B is represented by the following formula (vi).

[0066] [Formula No. 4]

[0067]

[0068] In the case of materials without excited state absorption, due to σ ESA =0, so the following formula (vii) holds. Therefore, when the incident light intensity ratio α / β is smaller, linear light absorption occurs preferentially over nonlinear light absorption.

[0069] [Formula No. 5]

[0070]

[0071] On the other hand, in the case of a material that causes excited state absorption, the term on the left side of formula (vii) has a value, and formula (vii) does not hold. Therefore, the threshold value of the incident light intensity I for causing nonlinear light absorption to occur preferentially over linear light absorption can be lowered. If the material has large excited state absorption, nonlinear light absorption can occur preferentially even at very low incident light intensity.

[0072] Patent document 1 discloses that a light information recording material containing a nonlinear absorption pigment and a multilayer diffraction grating is irradiated with a laser having a central wavelength of 401 nm and a pulse width of 8 nanoseconds, and the diffraction grating is locally destroyed to form a recording mark. As the nonlinear absorption pigment, 1,1,4,4-tetraphenyl-1,3-butadiene, 1,3,6,8-tetraphenylpyrene, pyrene-ethylene glycol-pyrene, 1,4-bis(phenylethynyl)benzene, 1,2,4,5-tetra(phenylethynyl)benzene, 9,10-diphenylanthracene, 5,6,11,12-tetraphenyl tetracene, fluorene, 2,7-dibromofluorene, 1-bromopyrene, 4-bromopyrene and pyrene are disclosed.

[0073] Patent Document 2 discloses a holographic recording medium containing a nonlinear sensitizer that transitions to a higher-order triplet excited state by laser irradiation with a wavelength of 405 nm and a pulse width of 5 nanoseconds. A platinum ethynyl complex is disclosed as the nonlinear sensitizer.

[0074] But, if the absorption coefficient under the ground state of nonlinear absorption pigment is too small, then the value of-dI / dz in formula (v) tapers, and recording sensitivity becomes insufficient.In addition, in the nonlinear absorption pigment absorption light and exciting back before returning to the ground state through the triplet excited state, worry that light resistance is insufficient.The oxygen molecule in the atmosphere exists with triplet state under the ground state, is to be used for the pigment generation energy transfer reaction that is positioned at the triplet excited state, generates singlet oxygen.When the triplet excited state returns to the ground state, with the inversion of spin, therefore long life-span, if life-span is very long, then has the excitation life-span of hundreds of milliseconds.After exciting, the number of the pigment via the triplet excited state is more, namely the quantum yield of the intersystem crosstalk of pigment is higher, then the probability of reacting with oxygen molecule is more raised.The life-span of the triplet excited state is longer, then the probability of reacting with oxygen molecule is more further raised.The electronic deficiency of singlet oxygen, activity is very high, and it is deteriorated with the pigment or the macromolecular compound reaction existing in the periphery.The optical characteristics such as the pigment fading that reacts with singlet oxygen change.

[0075] The inventors of the present invention have conducted intensive research and have newly discovered that the following properties are required for a recording medium using an organic compound as a nonlinear light absorbing material. That is, for light having a wavelength in the short wavelength range, (a) the single-photon absorption coefficient α must be within an appropriate range, and (b) the excited state absorption cross-sectional area σ must be within a certain range. ESAHas a high value. In this case, there is the following tendency: in addition to the above-mentioned -dI / dz value being large enough, the value of the ratio A / B (formula (vi)) of the magnitude B of linear light absorption to the magnitude A of nonlinear light absorption is small, and the nonlinear characteristic of light absorption is high. In addition, when the excited state absorption generated in the short wavelength range comes from a singlet excited state, the lifetime of the excited state is not too long and it is not easy to react with oxygen in the atmosphere. Therefore, it is also not easy to deteriorate due to the generation of singlet oxygen. In this specification, the short wavelength range means a wavelength range including 405nm, for example, a wavelength range of more than 390nm and less than 420nm.

[0076] (Overview of one aspect of the present disclosure)

[0077] A recording medium according to a first aspect of the present disclosure includes a recording layer, wherein the recording layer contains an organic compound having a nonlinear light absorption property, wherein the molar absorption coefficient of the organic compound for light having a wavelength of 400 nm or more and 405 nm or less is 90 mol / L. -1 ·L·cm -1 As described above, in the transient absorption spectrum of the organic compound, the absorbance change ΔAbs at a wavelength of 400 nm to 405 nm is a positive value.

[0078] According to the first aspect, a new type of recording medium using a nonlinear optical material can be provided.

[0079] In the second embodiment of the present disclosure, for example, according to the recording medium involved in the first embodiment, the molar absorption coefficient of the organic compound may be 1000 mol -1 ·L·cm -1 the following.

[0080] In a third embodiment of the present disclosure, for example, according to the recording medium involved in the first or second embodiment, the molar absorption coefficient of the organic compound may be 100 mol -1 ·L·cm -1 Above 500mol - 1 L cm -1 the following.

[0081] In a fourth aspect of the present disclosure, for example, according to the recording medium pertaining to any one of the first to third aspects, the lifetime of the excited state of the organic compound may be 1 millisecond or less.

[0082] The organic compounds having the characteristics described in the second to fourth aspects are suitable for the recording medium of the present disclosure.

[0083] In a fifth aspect of the present disclosure, for example, according to the recording medium involved in the first to fourth aspects, the organic compound may be a compound capable of causing a change in stereostructure in an excited state. By having such a property, the excited state absorption cross-sectional area σ of the organic compound in the short wavelength range ESA High values ​​can be displayed.

[0084] A sixth aspect of the present disclosure is a method for recording information, comprising: preparing a light source that emits light having a wavelength of 390 nm to 420 nm; and focusing the light from the light source and irradiating the light onto a recording layer in the recording medium according to any one of the first to fifth aspects.

[0085] According to the sixth aspect, in the recording medium, the nonlinear light absorption characteristic for light having a wavelength in the short wavelength range is improved. According to the information recording method using the recording medium containing the organic compound having the nonlinear light absorption characteristic, information can be recorded at a high recording density.

[0086] The seventh scheme of the present disclosure involves a method for reading information, for example, a method for reading information recorded using the recording method involved in the fifth scheme, and the reading method includes: irradiating light to the recording layer in the recording medium to thereby measure the optical properties of the recording layer; and reading information from the recording layer.

[0087] In an eighth aspect of the present disclosure, for example, according to the information reading method pertaining to the seventh aspect, the optical characteristic may be the intensity of light reflected by the recording layer.

[0088] According to the seventh or eighth aspect, when reading information, the occurrence of crosstalk due to other recording layers can be suppressed.

[0089] The following describes embodiments of the present disclosure with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0090] (Implementation Method)

[0091] The recording medium of this embodiment includes a recording layer, wherein the recording layer contains an organic compound having nonlinear light absorption characteristics. The molar absorption coefficient of the organic compound for light having a wavelength of 400 nm or more and 405 nm or less is 90 mol -1 ·L·cm -1 In the transient absorption spectrum of an organic compound, the absorbance change ΔAbs at a wavelength of 400 nm or more and 405 nm or less is a positive value.

[0092] The absorbance change ΔAbs is the absorbance Abs from the excited state ex Subtract the absorbance of the ground state Abs noexThe absorbance Abs is obtained using the Lambert-Beer law. A positive value of the absorbance change ΔAbs indicates that excited state absorption (ESA) occurs predominantly in this wavelength range. That is, by light having a wavelength of more than 400nm and less than 405nm, excited state absorption can be caused and the heat generated during relaxation can be utilized. On the other hand, even if low-intensity light having the same wavelength is irradiated, almost no heat is generated. Such properties are suitable for the formation of recording marks on recording media and the reading of information.

[0093] Transient absorption refers to transient light absorption. According to transient absorption spectroscopy, the instantaneous excited state absorption generated by pulsed laser irradiation can be tracked with high time resolution. In transient absorption spectroscopy, for example, after a single wavelength pump light is irradiated to the sample and it transitions to the excited state, a white probe light is irradiated to the sample with an appropriate delay time. The transient absorption spectrum is obtained by detecting the difference ΔAbs between the absorbance of the excited state and the ground state. By comparing with the ground state, the increase in absorbance is paid attention to, so that the wavelength range in which the excited state absorption occurs can be known. In the absorption wavelength range of the ground state, the number of molecules in the ground state decreases due to light absorption, thereby reducing the absorbance, and sometimes a fading (bleaching) phenomenon in which the absorbance change takes a negative value is found.

[0094] As for the determination performed by transient absorption spectroscopy, both solution-like samples and film-like samples can be performed in the same manner. In order to prevent the excited state from being deactivated by oxygen in the atmosphere, it is preferred to perform an operation to remove dissolved oxygen. When the sample is a solution, by bubbling argon or nitrogen for a certain period of time, when the sample is a film, by replacing the gas in the tank with argon or nitrogen, deoxygenation can be performed. In addition, the life of the excited state can be read by the time change of the transient absorption spectrum. In the case where the life of the excited state observed by tracking the transient absorption spectrum is about picoseconds to hundreds of nanoseconds, it can generally be considered to be a transition from a singlet excited state to a higher-order singlet excited state. On the other hand, in the case where the life of the excited state is more than microseconds, it can generally be considered to be a transition from a triplet excited state to a higher-order triplet excited state. Furthermore, the triplet excited state is very low in stability to oxygen compared to the singlet excited state. Thus, if there is almost no change in the transient absorption intensity due to the presence or absence of oxygen, it can be judged that the observed state is from the singlet excited state. When the transient absorption intensity changes significantly depending on the presence or absence of oxygen, it can be determined that the observed state is from a triplet excited state.

[0095] Excited state absorption is the successive light absorption that occurs after single photon absorption or two-photon absorption. In order to efficiently cause excited state absorption, it is desirable to cause single photon absorption by an organic compound, thereby forming an excited state. The preferred range of the molar absorption coefficient of an organic compound when the organic compound causes single photon absorption is, for example, 90 mol -1 ·L·cm -1 When single-photon absorption and excited-state absorption satisfy preferred conditions, desired nonlinear light absorption characteristics can be achieved.

[0096] The molar absorption coefficient of the above organic compound can be 1000 mol -1 ·L·cm -1 Below, can be 100 mol -1 ·L·cm - 1 or more and 500 mol -1 ·L·cm -1 When the molar absorption coefficient is not too small, a sufficient amount of excited species can be formed. When the molar absorption coefficient is not too large, nonlinear absorption tends to be dominant over linear absorption.

[0097] The lifetime of the excited state of the organic compound is, for example, less than 1 millisecond. The lifetime of the excited state being less than 1 millisecond means that the excited state is a singlet excited state. The singlet excited state is more stable to oxygen in the air than the long-lived triplet excited state. This is beneficial to the improvement of the light resistance of the recording medium.

[0098] An example of an organic compound having the above-mentioned characteristics is a compound a represented by the following formula (1).

[0099] [Chemical formula number 1]

[0100]

[0101] In formula (1), R 1 To R 12 independently of one another represent a group containing at least one atom selected from H, B, C, N, O, F, Si, P, S, Cl, I and Br.

[0102] As for compound a, the absorption amount of light with a wavelength in the short wavelength range is sufficiently large. As a detail of the absorption amount, there is a tendency that the value of the ratio A / B of the magnitude A of linear light absorption to the magnitude B of nonlinear light absorption is small, that is, the nonlinear characteristics of light absorption tend to be high. Compound a has excellent light resistance because it does not pass through a triplet excited state during the relaxation process. In this way, compound a is improved in terms of both nonlinear light absorption characteristics and light resistance for light with a wavelength in the short wavelength range. Furthermore, the recording sensitivity is improved. Compound a is excited by irradiation with a laser with a wavelength in the short wavelength range, relaxes to the lowest singlet excited state while accompanied by structural changes, further absorbs laser light from the lowest singlet excited state and migrates to a higher-order singlet excited state. The structural change after excitation occurs by the distortion of the double bond connecting the two 6-membered rings. In the adiabatic state, the π electron conjugated system becomes shorter. As a result, the light absorption band of the excited state is blue-shifted to the short wavelength range, and the σ in the short wavelength range is reduced. ESA Displays high values.

[0103] In formula (1), R 1 To R 12 Independently of each other, they may be a hydrogen atom, a halogen atom, a hydrocarbon group, a halogenated hydrocarbon group, a group containing an oxygen atom, a group containing a nitrogen atom, a group containing a sulfur atom, a group containing a silicon atom, a group containing a phosphorus atom, or a group containing a boron atom.

[0104] Examples of the halogen atom include F, Cl, Br, and I. In this specification, a halogen atom may be referred to as a halogen group.

[0105] The hydrocarbon group is an alkyl group or an unsaturated hydrocarbon group.

[0106] The carbon number of the alkyl group is not particularly limited, for example, it is 1 or more and 20 or less. The carbon number of the alkyl group can be 1 or more and 10 or less, or 1 or more and 5 or less, from the viewpoint of being able to easily synthesize compound a. By adjusting the carbon number of the alkyl group, the solubility in a solvent or a resin composition can be adjusted for compound a. The alkyl group can be linear, branched, or cyclic. At least one hydrogen atom contained in the alkyl group can be substituted by a group containing at least one atom selected from N, O, P, and S. As the alkyl group, methyl, ethyl, propyl, butyl, 2-methylbutyl, pentyl, hexyl, 2,3-dimethylhexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecanyl, octadecyl, nonadecanyl, eicosyl, 2-methoxybutyl, 6-methoxyhexyl, etc. can be listed.

[0107] The unsaturated hydrocarbon group contains unsaturated bonds such as carbon-carbon double bonds and carbon-carbon triple bonds. The number of unsaturated bonds contained in the unsaturated hydrocarbon group is, for example, greater than 1 and less than 5. The carbon number of the unsaturated hydrocarbon group is not particularly limited, for example, greater than 2 and less than 20, greater than 2 and less than 10, or greater than 2 and less than 5. The unsaturated hydrocarbon group may be linear, branched, or cyclic. At least one hydrogen atom contained in the unsaturated hydrocarbon group may be substituted by a group containing at least one atom selected from N, O, P, and S. Examples of the unsaturated hydrocarbon group include vinyl, ethynyl, and allyl.

[0108] The so-called halogenated hydrocarbon group means a group in which at least one hydrogen atom contained in the hydrocarbon group is replaced by a halogen atom. The halogenated hydrocarbon group may be a group in which all hydrogen atoms contained in the hydrocarbon group are replaced by halogen atoms. Examples of the halogenated hydrocarbon group include halogenated alkyl groups and halogenated alkenyl groups.

[0109] Examples of the halogenated alkyl group include -CF3, -CH2F, -CH2Br, -CH2Cl, -CH2I, and -CH2CF3. Examples of the halogenated alkenyl group include -CH=CHCF3.

[0110] The group containing an oxygen atom is, for example, a substituent having at least one selected from a hydroxyl group, a carboxyl group, an aldehyde group, an ether group, an acyl group, and an ester group.

[0111] As a substituent having a hydroxyl group, for example, a hydroxyl group itself and a hydrocarbon group having a hydroxyl group can be listed. In the substituent, the hydroxyl group can be deprotonated to -O - As the hydrocarbon group having a hydroxyl group, there are -CH2OH, -CH(OH)CH3, -CH2CH(OH)CH3, -CH2C(OH)(CH3)2 and the like.

[0112] As a substituent having a carboxyl group, for example, a carboxyl group itself and a hydrocarbon group having a carboxyl group can be listed. Among the substituents, the carboxyl group can be deprotonated to -CO2 - As hydrocarbon groups having a carboxyl group, -CH2CH2COOH, -C(COOH)(CH3)2, -CH2CO2 - wait.

[0113] Examples of the substituent having an aldehyde group include an aldehyde group itself and a hydrocarbon group having an aldehyde group. Examples of the hydrocarbon group having an aldehyde group include -CH=CHCHO and the like.

[0114] As the substituent having an ether group, for example, an alkoxy group, a halogenated alkoxy group, an alkenyloxy group, an ethylene oxide group, and a hydrocarbon group having at least one of these functional groups can be listed. At least one hydrogen atom contained in the alkoxy group can be substituted by a group containing at least one atom selected from N, O, P and S. As the alkoxy group, a methoxy group, an ethoxy group, a 2-methoxyethoxy group, a butoxy group, a 2-methylbutoxy group, a 2-methoxybutoxy group, a 4-ethylthiobutoxy group, a pentyloxy group, a hexyloxy group, a heptyloxy group, an octyloxy group, a nonyloxy group, a decyloxy group, an undecyloxy group, a dodecyloxy group, a tridecyloxy group, a tetradecyloxy group, a pentadecyloxy group, a hexadecyloxy group, a heptadecyloxy group, an octadecyloxy group, a nonadecyloxy group, an eicosyloxy group, -OCH2O can be listed. - 、-OCH2CH2O - 、-O(CH2)3O - Examples of halogenated alkoxy groups include -OCHF2, -OCH2F, -OCH2Cl, etc. Examples of alkenyloxy groups include -OCH=CH2, etc. Examples of hydrocarbon groups having a functional group such as an alkoxy group include -CH2OCH3, -C(OCH3)3, 2-methoxybutyl, 6-methoxyhexyl, etc.

[0115] Examples of the substituent having an acyl group include an acyl group itself and a hydrocarbon group having an acyl group. Examples of the acyl group include -COCH3 and the like. Examples of the hydrocarbon group having an acyl group include -CH=CHCOCH3 and the like.

[0116] As a substituent having an ester group, for example, an alkoxycarbonyl group, an acyloxy group, and a hydrocarbon group having at least one of these functional groups can be listed. As an alkoxycarbonyl group, -COOCH3, -COO(CH2)3CH3, -COO(CH2)7CH3, etc. can be listed. As an acyloxy group, -OCOCH3, etc. can be listed. As a hydrocarbon group having a functional group such as an acyloxy group, -CH2OCOCH3, etc. can be listed.

[0117] The group containing a nitrogen atom is, for example, a substituent having at least one selected from an amino group, an imino group, a cyano group, an azido group, an amide group, a carbamate group, a nitro group, a cyanamide group, an isocyanate group, and an oxime group.

[0118] Examples of substituents having an amino group include primary amino groups, secondary amino groups, tertiary amino groups, quaternary amino groups, and hydrocarbon groups having at least one of these functional groups. In the substituents, the amino group may be protonated. Examples of tertiary amino groups include -N(CH3)2. Examples of hydrocarbon groups having functional groups such as primary amino groups include -CH2NH2, -CH2N(CH3)2, -(CH2)4N(CH3)2, -CH2CH2NH3 + 、-CH2CH2NH(CH3)2 +、-CH2CH2N(CH3)3 + wait.

[0119] Examples of the substituent having an imino group include the imino group itself and a hydrocarbon group having an imino group. Examples of the imino group include -N=CCl2 and the like.

[0120] Examples of the substituent having a cyano group include a cyano group itself and a hydrocarbon group having a cyano group. Examples of the hydrocarbon group having a cyano group include -CH2CN, -CH=CHCN, and the like.

[0121] Examples of the substituent having an azide group include an azide group itself and a hydrocarbon group having an azide group.

[0122] As a substituent having an amide group, for example, an amide group itself and a hydrocarbon group having an amide group can be listed. As an amide group, -CONH2, -NHCHO, -NHCOCH3, -NHCOCF3, -NHCOCH2Cl, -NHCOCH(CH3)2, etc. can be listed. As a hydrocarbon group having an amide group, -CH2CONH2, -CH2NHCOCH3, etc. can be listed.

[0123] Examples of the substituent having a carbamate group include a carbamate group itself and a hydrocarbon group having a carbamate group. Examples of the carbamate group include -NHCOOCH3, -NHCOOCH2CH3, and -NHCO2(CH2)3CH3.

[0124] Examples of the substituent having a nitro group include the nitro group itself and a hydrocarbon group having a nitro group. Examples of the hydrocarbon group having a nitro group include -C(NO2)(CH3)2 and the like.

[0125] Examples of the substituent having a cyanamide group include a cyanamide group itself and a hydrocarbon group having a cyanamide group. The cyanamide group is represented by -NHCN.

[0126] Examples of the substituent having an isocyanate group include an isocyanate group itself and a hydrocarbon group having an isocyanate group. The isocyanate group is represented by -N=C=O.

[0127] Examples of the substituent having an oxime group include an oxime group itself and a hydrocarbon group having an oxime group. The oxime group is represented by -CH=NOH.

[0128] The group containing a sulfur atom is, for example, a substituent having at least one selected from a thiol group, a thioether group, a sulfinyl group, a sulfonyl group, a sulfinyl group, a sulfonic acid group, an acylthio group, a sulfenamide group, a sulfonamide group, a thioamide group, a thiocarbamate group and a thiocyanate group.

[0129] Examples of the substituent having a thiol group include a thiol group itself and a hydrocarbon group having a thiol group. The thiol group is represented by -SH.

[0130] As a substituent having a thioether group, for example, an alkylthio group, an alkyldisulfide group, an alkenylthio group, an alkynylthio group, a thiirane group, and a hydrocarbon group having at least one of these functional groups can be listed. At least one hydrogen atom contained in the alkylthio group can be substituted by a halogen group. As an alkylthio group, -SCH3, -S(CH2)F, -SCH(CH3)2, -SCH2CH3, etc. can be listed. As an alkyldisulfide group, -SSCH3, etc. can be listed. As an alkenylthio group, -SCH=CH2, -SCH2CH=CH2, etc. can be listed. As an alkynylthio group, -SC≡CH, etc. can be listed. As a hydrocarbon group having a functional group such as an alkylthio group, -CH2SCF3, etc. can be listed.

[0131] Examples of the substituent having a sulfinyl group include a sulfinyl group itself and a hydrocarbon group having a sulfinyl group. Examples of the sulfinyl group include -SOCH3 and the like.

[0132] As the substituent having a sulfonyl group, for example, a sulfonyl group itself and a hydrocarbon group having a sulfonyl group can be listed. As the sulfonyl group, -SO2CH3 can be listed. As the hydrocarbon group having a sulfonyl group, -CH2SO2CH3, -CH2SO2CH2CH3, etc. can be listed.

[0133] Examples of the substituent having a sulfinyl group include a sulfinyl group itself and a hydrocarbon group having a sulfinyl group. In the substituent, the sulfinyl group may be deprotonated to be in a state of -SO2-.

[0134] Examples of the substituent having a sulfonic acid group include the sulfonic acid group itself and a hydrocarbon group having a sulfonic acid group. In the substituent, the sulfonic acid group may be deprotonated to be in the state of -SO3-.

[0135] Examples of the substituent having an acylthio group include an acylthio group itself and a hydrocarbon group having an acylthio group. Examples of the acylthio group include -SCOCH3 and the like.

[0136] Examples of the substituent having a sulfenamide group include the sulfenamide group itself and a hydrocarbon group having a sulfenamide group. Examples of the sulfenamide group include -SN(CH3)2 and the like.

[0137] Examples of the substituent having a sulfonamide group include the sulfonamide group itself and a hydrocarbon group having a sulfonamide group. Examples of the sulfonamide group include -SO2NH2, -NHSO2CH3, and the like.

[0138] As a substituent having a thioamide group, for example, a thioamide group itself and a hydrocarbon group having a thioamide group can be listed. As a thioamide group, -NHCSCH3 can be listed. As a hydrocarbon group having a thioamide group, -CH2SC(NH2)2 can be listed. + wait.

[0139] Examples of the substituent having a thiourethane group include a thiourethane group itself and a hydrocarbon group having a thiourethane group. Examples of the thiourethane group include -NHCSNHCH2CH3 and the like.

[0140] Examples of the substituent having a thiocyanate group include the thiocyanate group itself and a hydrocarbon group having a thiocyanate group. Examples of the hydrocarbon group having a thiocyanate group include -CH2SCN and the like.

[0141] The group containing a silicon atom is, for example, a substituent having at least one selected from a silyl group and a siloxy group.

[0142] As a substituent having a silyl group, a silyl group itself and a hydrocarbon group having a silyl group can be listed. As a silyl group, -Si(CH3)3, -SiH(CH3)2, -Si(OCH3)3, -Si(OCH2CH3)3, -SiCH3(OCH3)2, -Si(CH3)2OCH3, -Si(N(CH3)2)3, -SiF(CH3)2, -Si(OSi(CH3)3)3, -Si(CH3)2OSi(CH3)3, etc. can be listed. As a hydrocarbon group having a silyl group, -(CH2)2Si(CH3)3, etc. can be listed.

[0143] Examples of the substituent having a silyloxy group include the silyloxy group itself and a hydrocarbon group having a silyloxy group. Examples of the hydrocarbon group having a silyloxy group include -CH2OSi(CH3)3 and the like.

[0144] The group containing a phosphorus atom is, for example, a substituent having at least one selected from a phosphine group and a phosphono group.

[0145] As a substituent having a phosphino group, for example, a phosphino group itself and a hydrocarbon group having a phosphino group can be listed. As a phosphino group, -PH2, -P(CH3)2, -P(CH2CH3)2, -P(C(CH3)3)2, -P(CH(CH3)2)2, etc. can be listed.

[0146] Examples of the substituent having a phosphonyl group include a phosphonyl group itself and a hydrocarbon group having a phosphonyl group. Examples of the hydrocarbon group having a phosphonyl group include -CH2PO(OCH2CH3)2 and the like.

[0147] The group containing a boron atom is, for example, a substituent having a boronic acid group. Examples of the substituent having a boronic acid group include a boronic acid group itself and a hydrocarbon group having a boronic acid group.

[0148] In formula (1), R 5 To R 12 Each may be a hydrogen atom. In this case, the aromatic ring in the compound a represented by formula (1) has no substituent. Therefore, due to the electron-withdrawing or electron-donating property of the substituent, the energy increase of the highest occupied molecular orbital (HOMO: Highest Occupied Molecular Orbital) and the energy decrease of the lowest unoccupied molecular orbital (LUMO: Lowest Unoccupied Molecular Orbital) in the compound can be suppressed. That is, the energy gap between HOMO and LUMO can be suppressed from decreasing. Thus, the peak from single-photon absorption can be suppressed from migrating to long wavelengths, and the value of the ratio of linear light absorption to nonlinear light absorption A / B (formula (vi)) can be suppressed from increasing.

[0149] In formula (1), R 1 and R 2 can be the same group. Alternatively, R 1 and R 3 According to such a constitution, the compound represented by formula (1) can be easily synthesized.

[0150] In formula (1), R 1 To R 4 According to such a constitution, the compound represented by formula (1) can be easily synthesized.

[0151] In formula (1), R 1 To R 4 Each may be a hydrocarbon group or a halogenated hydrocarbon group having 5 or less carbon atoms. 1 To R 4 Each may be a methyl group or a CF3 group.

[0152] In formula (1), R 1 To R 12 It may be a group not containing an aromatic ring.

[0153] Specifically, the compound in the present disclosure can be represented by the following formula (2).

[0154] [Chemical formula number 2]

[0155]

[0156] In the compound represented by formula (2), there are cis-isomers and trans-isomers as isomers. 1 To R 4Compared with compounds composed entirely of hydrogen atoms, the stability of the cis-isomer is low due to steric hindrance. Even in the case of isomerization by light irradiation, the compound represented by formula (2) will quickly return to the trans-isomer at room temperature. Due to this characteristic, the ratio of the trans-isomer: cis-isomer obtained during synthesis is 100:0 (Michael Oelgemoller et al., "Synthesis, structural characterization and photoisomerization of cyclic stilbenes", Tetrahedron, 2012, 68, 4048-4056.). Therefore, the material or device containing the compound represented by formula (2) does not need to be stored in a light-shielding environment, and the original characteristics can be stably exhibited.

[0157] The synthesis method of compound a is not particularly limited, and for example, the McMurray coupling reaction can be used. Compound a represented by formula (1) can be synthesized, for example, by the following method: First, compound b represented by the following formula (3) and compound c represented by the following formula (4) are prepared.

[0158] [Chemical formula number 3]

[0159]

[0160]

[0161] Next, a coupling reaction is performed between compound b and compound c. Thus, compound a can be synthesized. The conditions of the coupling reaction can be appropriately adjusted according to the types of substituents contained in each of compound b and compound c, for example.

[0162] The compound b represented by the formula (3) can be synthesized, for example, by the following method. First, a tetralone derivative compound d represented by the following formula (5) and a tetralone derivative represented by R are prepared. 1 -X and R 2 - A halogenated compound represented by X. X is a halogen atom. Examples of the halogen atom include Br and I.

[0163] [Chemical formula number 4]

[0164]

[0165] Next, compound d and R 1 -X. Thus, compound e represented by the following formula (6) can be synthesized. The coupling reaction conditions can be adjusted according to the conditions of compound d and R 1 -X can be appropriately adjusted by the type of substituent contained in each of them.

[0166] [Chemical formula number 5]

[0167]

[0168] Next, compound e was reacted with R 2 -X. Thus, compound b represented by formula (3) can be synthesized. The coupling reaction conditions can be adjusted according to the conditions of compound e and R 2 -X can be appropriately adjusted by the type of substituent contained in each of them.

[0169] Other examples of organic compounds suitable for the recording medium of the present disclosure include compound a' represented by the following formula (7).

[0170] [Chemical formula number 6]

[0171]

[0172] In formula (7), R 21 To R 30 Each of the following independently represents a group containing at least one atom selected from the group consisting of H, B, C, N, O, F, Si, P, S, Cl, I and Br. 21 To R 30 For example, it is applicable to R of the compound a represented by formula (1) 1 To R 12 In addition, the following description about compound a is also applicable to compound a'.

[0173] Compound a represented by formula (1) and compound a' represented by formula (7) are both compounds that can cause a change in stereostructure in an excited state. By having such properties, the excited state absorption cross-sectional area σ of these compounds in the short wavelength range is ESA A high value may be shown. The "change in the stereostructure" typically refers to distortion of the periphery of the carbon-carbon double bond.

[0174] The compound a represented by formula (1) has excellent nonlinear light absorption characteristics for light having a wavelength in the short wavelength range. The quadratic nonlinear absorption coefficient is represented by the sum of the product of the single-photon absorption coefficient, the excited state absorption cross-sectional area, and the excited state lifetime and the two-photon absorption coefficient.

[0175] The two-photon absorption cross-sectional area of ​​compound a for light having a wavelength of 405 nm may be greater than 1GM, may be greater than 10GM, may be greater than 20GM, may be greater than 100GM, may be greater than 400GM, may be greater than 600GM. There is no particular limitation on the upper limit of the two-photon absorption cross-sectional area of ​​compound a, for example, it may be 10000GM, or may be 1000GM. The two-photon absorption cross-sectional area can be measured, for example, by the Z-scan method described in J.Opt.Soc.Am.B, 2003, Vol. 20, p. 529. The Z-scan method is widely used as a method for measuring nonlinear optical constants. In the Z-scan method, the measurement sample is moved along the irradiation direction of the beam near the focus of the laser beam. At this time, the change in the amount of light transmitted through the measurement sample is recorded. In the Z-scan method, the power density of the incident light changes according to the position of the measurement sample. Therefore, in the case where the measurement sample undergoes nonlinear light absorption, if the measurement sample is located near the focus of the laser beam, the amount of light transmitted by the light is attenuated. The two-photon absorption cross-sectional area can be calculated by fitting the change in the amount of transmitted light to a theoretical curve predicted from the intensity of incident light, the thickness of the measurement sample, the concentration of compound a in the measurement sample, and the like.

[0176] The molar absorption coefficient of compound a for light having a wavelength of 405 nm is, for example, less than 4000 mol -1 ·L·cm -1 , can be 2000mol -1 ·L·cm -1 Below, can be 1000mol -1 ·L·cm -1 Below, can be 500mol -1 ·L·cm - 1 or less. There is no particular limitation on the lower limit of the molar absorption coefficient of compound a, for example, 90 mol -1 ·L·cm -1 The molar absorption coefficient can be measured, for example, by a method in accordance with Japanese Industrial Standard (JIS) K0115:2004. For the determination of the molar absorption coefficient, a light source is used that irradiates light with a photon density that hardly generates two-photon absorption caused by compound a. Furthermore, for the determination of the molar absorption coefficient, for example, the concentration of compound a is adjusted to 1 mmol / L. The molar absorption coefficient can be used as an indicator of single-photon absorption.

[0177] When compound a undergoes two-photon absorption, compound a absorbs about twice the energy of light irradiated to compound a. The wavelength of light having about twice the energy of light having a wavelength of 405 nm is, for example, 200 nm. When light having a wavelength of around 200 nm is irradiated to compound a, single-photon absorption may occur in compound a. Furthermore, compound a may undergo single-photon absorption for light having a wavelength near the wavelength range in which two-photon absorption occurs.

[0178] Compound a represented by formula (1) can be used as a component of a light absorbing material, for example. That is, the present disclosure provides a light absorbing material comprising compound a represented by formula (1) from another aspect thereof. The light absorbing material, for example, comprises compound a as a main component. "Main component" means the component that is contained most in the light absorbing material by weight ratio. The light absorbing material, for example, is substantially formed of compound a. "Substantially formed of..." means that other components that change the essential characteristics of the material mentioned are excluded. However, the light absorbing material may also contain impurities in addition to compound a.

[0179] Compound a is used, for example, in devices that utilize light having a wavelength in a short wavelength range. As an example, compound a is used in devices that utilize light having a wavelength of more than 390nm and less than 420nm. As such devices, recording media, modeling machines, fluorescence microscopes, etc. can be listed. As recording media, for example, three-dimensional optical storage can be listed. A specific example of a three-dimensional optical storage is a three-dimensional optical disc. As a modeling machine, for example, optical modeling machines such as 3D printers can be listed. As a fluorescence microscope, for example, a two-photon fluorescence microscope can be listed. The light used in these devices has a high photon density, for example, near its focus. The power density near the focus of the light used in the device is, for example, 0.1W / cm 2 Above and 1.0×10 20 W / cm 2 The power density near the focal point of the light can be 1.0 W / cm 2 Above, can be 1.0×10 2 W / cm 2 Above, can be 1.0×10 5 W / cm 2 As the light source of the device, for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser having a pulse width of picoseconds to nanoseconds such as a semiconductor laser can be used.

[0180] The recording medium includes, for example, a thin film called a recording layer. In the recording medium, information is recorded in the recording layer. As an example, the thin film as the recording layer contains compound a. That is, the present disclosure provides a recording medium containing the above-mentioned compound a from another aspect.

[0181] The recording layer may further include a polymer compound that functions as a binder in addition to the compound a. The recording medium may include a dielectric layer in addition to the recording layer. The recording medium may include, for example, a plurality of recording layers and a plurality of dielectric layers. In the recording medium, a plurality of recording layers and a plurality of dielectric layers may be alternately stacked.

[0182] Next, a method of recording information using the above-mentioned recording medium will be described. Figure 1A This is a flow chart related to a method for recording information using the above-mentioned recording medium. First, in step S11, a light source that emits light with a wavelength of more than 390nm and less than 420nm is prepared. As the light source, for example, a femtosecond laser such as a titanium sapphire laser or a pulse laser such as a semiconductor laser with a pulse width of picoseconds to nanoseconds can be used. Secondly, in step S12, the light from the light source is focused by a lens or the like, and irradiated onto the recording layer in the recording medium. Specifically, the light from the light source is focused by a lens or the like, and irradiated onto the recording area in the recording medium. There is no particular restriction on the NA (numerical aperture) of the lens used to focus the light. As an example, a lens with an NA in the range of more than 0.8 and less than 0.9 can be used. The power density near the focus of the light is, for example, 0.1W / cm 2 Above and 1.0×10 20 W / cm 2 The power density near the focal point of the light can be 1.0 W / cm 2 Above, can be 1.0×10 2 W / cm 2 Above, can be 1.0×10 5 W / cm 2 In this specification, the recording area refers to a site existing in the recording layer and capable of recording information by irradiation with light.

[0183] In the recording area irradiated with the above-mentioned light, a physical change or a chemical change occurs. For example, when the compound a that absorbs the light returns to the ground state from the transition state, heat is generated. Due to the heat, the adhesive present in the recording area deteriorates. As a result, the optical properties of the recording area change. For example, the intensity of the light reflected in the recording area, the reflectivity of the light in the recording area, the absorptivity of the light in the recording area, the refractive index of the light in the recording area, etc. change. In the recording area irradiated with light, sometimes the intensity of the fluorescent light radiated from the recording area or the wavelength of the fluorescent light also changes. As a result, information can be recorded in the recording layer, specifically in the recording area (step S13).

[0184] Next, a method of reading information using the above-mentioned recording medium will be described. Figure 1BThis is a flowchart related to a method for reading information using the above-mentioned recording medium. First, in step S21, the recording layer in the recording medium is irradiated with light. Specifically, the recording area in the recording medium is irradiated with light. The light used in step S21 may be the same as or different from the light used to record information in the recording medium. Next, in step S22, the optical properties of the recording layer are measured. Specifically, the optical properties of the recording area are measured. In step S22, for example, as the optical properties of the recording area, the intensity of light reflected in the recording area is measured. In step S22, as the optical properties of the recording area, the reflectivity of light in the recording area, the absorptivity of light in the recording area, the refractive index of light in the recording area, the intensity of fluorescent light emitted from the recording area, the wavelength of fluorescent light, etc. can be measured. Next, in step S23, information is read from the recording layer, specifically, from the recording area.

[0185] In the information reading method, the recording area where the information is recorded can be found by the following method. First, light is irradiated to a specific area of ​​the recording medium. The light may be the same as or different from the light used to record the information on the recording medium. Next, the optical characteristics of the area irradiated with light are measured. As optical characteristics, for example, the intensity of light reflected in the area, the reflectivity of light in the area, the absorptivity of light in the area, the refractive index of light in the area, the intensity of fluorescent light emitted from the area, the wavelength of fluorescent light emitted from the area, etc. can be listed. Based on the measured optical characteristics, it is determined whether the area irradiated with light is a recording area. For example, when the intensity of light reflected in the area is below a specific value, it is determined that the area is a recording area. On the other hand, when the intensity of light reflected in the area exceeds a specific value, it is determined that the area is not a recording area. Furthermore, the method for determining whether the area irradiated with light is a recording area is not limited to the above method. For example, when the intensity of light reflected in the area exceeds a specific value, it can be determined that the area is a recording area. In addition, when the intensity of light reflected in the area is below a specific value, it can be determined that the area is not a recording area. When it is determined that the area is not a recording area, the same operation is performed on other areas of the recording medium. In this way, the recording area can be found.

[0186] The information recording method and reading method using the above-mentioned recording medium can be performed by using a known recording device, for example, including a light source for irradiating light to a recording area in the recording medium, a measuring device for measuring the optical characteristics of the recording area, and a controller for controlling the light source and the measuring device.

[0187] Example

[0188] The present disclosure will be described in more detail below using examples. Note that the following examples are just examples, and the present disclosure is not limited to the following examples.

[0189] [Example 1]

[0190] The compound (2) represented by the formula (2) was synthesized by the following steps.

[0191] First, 50 g (0.342 mol) of α-tetralone (manufactured by Tokyo Chemical Industry Co., Ltd.) and 500 mL of anhydrous tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a 2 L reactor under an argon atmosphere. After the obtained solution was cooled to -20°C, 376 mL (0.376 mol) of sodium bis(trimethylsilyl)amide (tetrahydrofuran solution with a concentration of 1.0 mol / L) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added dropwise. After stirring at -20°C for 15 minutes, 23.4 mL (0.376 mol) of iodomethane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was slowly added dropwise. In this way, the temperature was raised to room temperature over 3 hours. The obtained suspension was added to 1.5 L of hydrochloric acid (0.5 mol / L), separated into two phases, and the aqueous phase was extracted with toluene. The organic phase was washed with sodium bicarbonate water, tap water, and 1 L of saturated saline in sequence, and dried using anhydrous magnesium sulfate. Next, the extract was concentrated to obtain a light brown liquid. The light brown liquid was purified by distillation to obtain a precursor of compound (2) as a colorless liquid.

[0192] Next, 480 mL of anhydrous tetrahydrofuran (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was placed in a 1 L reactor under an argon atmosphere and cooled to -15°C. Then, 11.0 mL (100 mmol) of titanium (IV) chloride (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was slowly added dropwise. After stirring at -15°C for 30 minutes, 19.7 g (301 mmol) of zinc powder (manufactured by Aldrich) was added at once, and stirred at -15°C for 30 minutes. To the obtained bluish-brown suspension, 12.0 g (66.9 mmol) of the precursor of compound (2) diluted with 120 mL of anhydrous tetrahydrofuran was added dropwise over 10 minutes. The cooling bath was removed, the bath temperature was raised to 75°C, and stirred at 75°C for 30 minutes. The obtained dark brown suspension was added dropwise to a 2.0 mol / L potassium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) aqueous solution (1 L) and stirred at room temperature for 1 hour. The precipitated solid was filtered through celite, and the filter bed was washed with 500 mL of ethyl acetate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.). The aqueous phase in the filtrate was extracted with 500 mL of a mixture of heptane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) / ethyl acetate = 1 / 1. The mixed solution of the extract and the organic phase was washed successively with tap water and saturated brine, and dried using anhydrous magnesium sulfate. The liquid obtained by drying was concentrated with a rotary evaporator. The obtained light brown liquid was purified by silica gel column chromatography to obtain a light yellow liquid. 12 mL of ethanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) was added to the pale yellow liquid, and ultrasonic irradiation was performed. The precipitated solid was filtered, and the filter bed was washed with methanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) and dried to synthesize compound (2) as a colorless powder. Figure 2 is the compound (2) 1 H-NMR spectrum of compound (2) 1 The H-NMR spectrum is as follows.

[0193] 1 H-NMR (400 MHz, chloroform-D) δ7.22-7.07 (m, 8H), 2.85-2.79 (m, 4H), 1.77-1.74 (m, 4H), 1.06 (s, 6H), 0.64 (s, 6H).

[0194] [Example 2 and Comparative Examples 1 to 5]

[0195] Compounds of Example 2 and Comparative Examples 1 to 5 were prepared. The compound of Example 2 is represented by the following formula (8). The compounds of Comparative Examples 1 to 5 are represented by the following formulas (9) to (13), respectively. The compounds of formula (8), formula (10), formula (11) and formula (12) were obtained from Aldrich. The compounds of formula (9) and formula (13) were obtained from Tokyo Chemical Industry Co., Ltd.

[0196] [Chemical formula number 7]

[0197]

[0198] <Measurement of two-photon absorption cross-sectional area>

[0199] For the compounds of Example 1, Example 2 and Comparative Examples 1 to 5, the two-photon absorption cross-sectional area of ​​light having a wavelength of 405nm was measured. The two-photon absorption cross-sectional area was measured using the Z-scan method described in J.Opt.Soc.Am.B, 2003, Vol. 20, p. 529. As a light source for measuring the two-photon absorption cross-sectional area, a titanium sapphire pulse laser was used. Specifically, the sample was irradiated with the second harmonic of a titanium sapphire pulse laser. The pulse width of the laser was 80fs. The repetition frequency of the laser was 1kHz. The average power of the laser was varied in a range of 0.01mW to 0.08mW. The light from the laser was light having a wavelength of 405nm. Specifically, the light from the laser had a central wavelength of 403nm to 405nm. The full width at half maximum of the light from the laser was 4nm.

[0200] <Determination of molar absorption coefficient>

[0201] The molar absorption coefficient of the compounds of Example 1, Example 2 and Comparative Examples 1 to 5 was measured by the method specified in JIS K0115:2004. Specifically, first, a measurement sample in which the concentration of the compound was adjusted to 500 mmol / L was prepared. The absorption spectrum of the measurement sample was measured. From the obtained spectrum, the absorbance at a wavelength of 405 nm was read. The molar absorption coefficient was calculated based on the concentration of the compound in the measurement sample and the optical path length of the cell used for the measurement.

[0202] The two-photon absorption cross-sectional area σ(GM) and molar absorption coefficient ε(mol -1 ·L·cm -1 ) are shown in Table 1. In Table 1, "SA" means that absorption saturation (Saturated Absorption) occurred in two-photon absorption measurement by a Z-scan method and a value of a cross-sectional area was not obtained.

[0203] Table 1

[0204]

[0205] The molar absorption coefficients of the compounds of Example 1 and Example 2 for 405 nm light are 160 mol -1 ·L·cm -1 and 435mol -1 ·L·cm -1 , at 90mol -1 ·L·cm -1 Above 1000mol -1 ·L·cm -1 The molar absorption coefficients of the compounds of Comparative Examples 1 and 2 are large. The molar absorption coefficients of the compounds of Comparative Examples 4 and 5 are very small.

[0206] <Recording and playback characteristics>

[0207] [Production of pigment-containing film]

[0208] First, by adopting stirring, the following materials are mixed, thereby obtained the coating liquid mixed evenly. The weight ratio of resin is fixed at 9wt% relative to solvent. According to the difference of pigment, the solubility of solvent is different, and each is dissolved to the upper limit of solubility. As resin, poly (9-vinyl carbazole) (Aldrich company system) is used. As solvent, chlorobenzene (Fuji Film Wako Pure Chemical Industries, Ltd. system) is used. The composition ratio of the coating liquid made by the compound containing embodiment 1, embodiment 2 and comparative example 1 to 5 as the film of pigment is shown in table 2.

[0209] Table 2

[0210]

[0211] Next, prepare a glass substrate. The size of the glass substrate is 26 mm in length, 38 mm in width, and 0.9 mm in thickness. The glass substrate is placed on a spin coater, and 400 μL of the coating solution prepared by the above method is dripped onto the glass substrate, and the coating solution is rotated for 30 seconds at a rotation speed of 3000 rpm. Then, a resin film containing a compound of any one of Example 1, Example 2, and Comparative Examples 1 to 5 is obtained by drying the glass substrate on a hot plate at 80° C. for 30 minutes. Hereinafter, these resin films are recorded as the film of Example 1, the film of Example 2, and the films of Comparative Examples 1 to 5.

[0212] [Reproduction operation before recording]

[0213] A pulse light with a central wavelength of 405 nm, a peak power of 3 mW, a pulse width of 200 nanoseconds, and a repetition frequency of 100 Hz is passed through a lens of NA0.85 and irradiated in a focused state onto the resin film on the glass substrate. The reflected light signal intensity at this time is obtained as the initial reflected light signal intensity. If the reflected light signal intensity after the recording operation changes relative to the initial reflected light signal intensity, it is determined that a recording mark has been formed.

[0214] [Record operation]

[0215] Recording was performed by passing a recording light beam having a central wavelength of 405 nm and a peak power of 100 mW through a lens of NA 0.85 and irradiating with one pulse. The pulse width was adjusted between 10 nanoseconds and 5 milliseconds.

[0216] [Replay operation]

[0217] Light with a central wavelength of 405 nm, a peak power of 3 mW, and a pulse width of 200 nanoseconds was passed through a lens of NA0.85 and irradiated onto the recording portion of the resin film at a repetition frequency of 100 Hz to obtain the reflected light signal intensity. The change rate of the reflected light signal intensity after the recording operation relative to the reflected light signal intensity before the recording operation was calculated.

[0218] [Evaluation of recording and reproducing characteristics]

[0219] Since the molar absorption coefficient and solubility of the pigments are different, the produced resin films have different light absorption characteristics. In order to make an equal comparison of the recording and reproducing characteristics, the incident light intensity during recording is converted into the energy (J / cm2) of the light with a wavelength of 405nm absorbed by the resin film with a thickness of 1cm. The energy (J / cm2) of the light absorbed by the resin film with a thickness of 1cm is calculated by multiplying the intensity (W) of the irradiated light by the recording time (seconds) and the absorption coefficient (cm2) of the resin film. -1 The absorption coefficient of the resin film is calculated by multiplying the pigment concentration (mol / L) in the film with the molar absorption coefficient (mol -1 ·L·cm -1 The curve diagram showing the change rate of the reflected light signal intensity relative to the energy of light absorbed by the resin film with a thickness of 1 cm is shown in Figures 3A to 3G .

[0220] Figures 3A to 3G These are graphs showing the recording and reproducing characteristics of the resin films of Example 1, Example 2, and Comparative Examples 1 to 5, respectively. Figures 3A to 3G In FIG. 1 , the horizontal axis represents the absorbed light energy that changes with the irradiation time (pulse width) of the laser light, and the vertical axis represents the change rate of the reflected light signal intensity after the recording operation relative to the reflected light signal intensity before the recording operation. Figures 3A to 3GIn the above, a small change in the intensity of the reflected light signal means that the resin film is hardly degraded even when irradiated with laser light, while a large change in the intensity of the reflected light signal means that the resin film is degraded by irradiation with laser light, forming a recording mark.

[0221] Depend on Figure 3A and Figure 3B It can be seen that in Example 1 and Example 2, if the irradiation time (pulse width) of the laser is increased to increase the absorbed light energy, the change rate of the reflected light signal intensity increases sharply around 3mJ / cm. That is, the film of Example 1 and Example 2 has the following threshold characteristics: even if a weak intensity light is irradiated, the reflected light signal intensity hardly changes, but by irradiating a high intensity light, the reflected light signal intensity changes greatly. That is, the film of Example 1 and Example 2 hardly deteriorates even if the reproduction operation is repeated, and has high durability and high reliability. Since the film of Example 1 and Example 2 is difficult to deteriorate with weak light during reproduction, although the recording operation is not performed, the formation of recording marks can be avoided.

[0222] Furthermore, in Examples 1 and 2, the change rate of the reflected light signal intensity is less likely to be saturated and increases to more than 50%. The higher the change rate of the reflected light signal intensity, the greater the difference between the reflected light signal intensity of the recording mark and the reflected light signal intensity around the recording mark. That is, the ratio of the signal to the noise, i.e., the S / N ratio, is improved, making it easier to read the recording mark.

[0223] The threshold characteristics of the thin films of Examples 1 and 2 show that nonlinear light absorption, specifically, excited state absorption, significantly occurs in the range where the absorbed light energy exceeds 3 mJ / cm.

[0224] Compound (2) of Example 1 has a structure in which a tetralin ring is connected by a carbon-carbon double bond. Due to this structure, it can be inferred that the recording and reproducing characteristics are good results. Compound (8) of Example 2 has a structure in which two benzene rings are connected to a hexatriene skeleton. Both compounds (2) and (8) are compounds whose stereostructures can change in an excited state. Due to such properties, it can be inferred that the recording and reproducing characteristics are good results. In addition, compound (2) can also be considered to be a compound having a structure in which the benzene ring and the double bond carbon of trans-diphenylethylene are bound by an alkyl chain. It is believed that such a structure can increase the isomerization rate of the compound, which has an impact on the improvement of the recording and reproducing characteristics.

[0225] On the other hand, by Figure 3C and Figure 3GIt can be seen that in Comparative Examples 1 to 5, the change rate of the reflected light signal intensity increases linearly with respect to the absorbed light energy, and saturates at a low change rate. In addition, in Comparative Examples 1 to 3, even if the absorbed light energy is less than 1 mJ / cm, a change of about 8% to 30% in the reflected light signal intensity occurs. This means that the resin film is easily deteriorated by repeated reproduction operations. That is, the film is deteriorated by weak light during reproduction, which means that a recording mark is formed even if no recording operation is performed.

[0226] In Comparative Example 4, the change rate of the reflected light signal intensity changes linearly with respect to the absorbed light energy, but the change rate of the reflected light signal intensity with respect to the absorbed light energy is small, which means that the S / N ratio is small and it is difficult to read the presence or absence of a recording mark.

[0227] In the case of the film of Comparative Example 5, no change in the intensity of the reflected light signal occurred within the range of light intensity used in the experiment.

[0228] <Measurement of transient absorption spectrum>

[0229] The transient absorption spectrum of the pigment (compound) of Example 1 was measured. The sample was dissolved in chloroform to prepare a solution, and the solution was placed in a quartz cell with an optical path length of 1 cm. The concentration of the solution was prepared in such a way that the absorbance at a wavelength of 355 nm with an optical path length of 1 cm was in the range of 0.1 to 0.2. The quartz cell was sealed and degassed by bubbling with argon for 30 minutes. In the transient absorption spectrum measurement, the UNISOKU TSP-2000 system was used. For the excitation light, SureliteII was used, and light with a wavelength of 355 nm, a repetition frequency of 10 Hz, an average power of 8 mW, and a beam diameter of 6 mm was irradiated to the sample with an optical path length of 1 cm. The results are shown in Figure 4A .

[0230] Figure 4A It is the transient absorption spectrum of the solution containing the compound of Example 1. The vertical axis represents the difference ΔAbs between the absorbance of the excited state and the ground state. The horizontal axis represents the wavelength of light. The "0 nanosecond" graph represents the absorbance change when the delay time from the irradiation of the excitation light (pump light) to the irradiation of the detection light is 0 nanoseconds, and is the ΔAbs measured approximately simultaneously with the irradiation of the excitation light. The ΔAbs at 0 nanoseconds is the value when the delay time is closest to zero in the device used, and can be regarded as the value closest to the ΔAbs at the moment of excitation at this wavelength. ΔAbs varies depending on the pulse width of the excitation light and the time resolution of the device. As Figure 4A It can be seen that the transient absorption spectrum of the compound of Example 1 has a large peak at a wavelength of 400 nm to 405 nm, and shows a large excited state absorption in the short wavelength range. The absorbance change ΔAbs at a wavelength of 400 nm to 405 nm is a positive value. Figure 4A The graph shows that the lifetime of the observed excited species is about 10 nanoseconds. After the transient absorption spectrum is measured, even if the quartz cell is opened and the sample solution is exposed to the atmosphere and the measurement is repeated, the same transient absorption spectrum is obtained. This shows that the observed transient absorption is not affected by oxygen in the atmosphere, and is therefore light absorption from the singlet excited state.

[0231] Figure 4B This is the transient absorption spectrum of the solution of the compound of Example 1 when the vertical axis is converted from the absorbance change to the molar absorption coefficient in the excited state. The calculation method of the molar absorption coefficient in the excited state is as follows.

[0232] As shown in the following formula (viii), the molar absorption coefficient ε1 (mol -1 ·L·cm -1 ) is obtained by dividing the absorbance change ΔAbs obtained by transient absorption spectroscopy by the product of the concentration c1 (mol / L) of molecules transitioning to the excited state and the optical path length z (cm).

[0233] [Formula No. 6]

[0234]

[0235] As shown in the following formula (ix), the concentration c1 of molecules transitioning to an excited state is obtained as follows: the number density N1 (molecules / cm2) of molecules transitioning to an excited state by absorption of pump light is: 3 ) divided by Avogadro's number N A (mol -1 ) to convert units.

[0236] [Formula No. 7]

[0237]

[0238] As shown in the following formula (x), the number density N1 of molecules that transition to the excited state is calculated by the number of photons n (photons / (s·cm 2 It is obtained by dividing the product of )) and the pulse width τ (s) of the laser by the optical path length z (cm).

[0239] [Formula No. 8]

[0240]

[0241] The number of photons n is calculated using the incident photon flux Φ (photons / (s·cm 2 )) and transmittance T are expressed by the following equation (xi). The incident photon flux Φ is obtained by dividing the laser power W (W) by the irradiation area S (cm 2) and the light power density (W / cm 2 ) is further divided by the photon energy (J / photon) of the irradiating light.

[0242] [Formula No. 9]

[0243] n=Φ×(1-T) (xi)

[0244] Depend on Figure 4B It can be seen that the molar absorption coefficient of the excited state (singlet excited state) of the compound of Example 1 at a wavelength of 400 nm to 405 nm is in the range of 2000 to 3000 mol -1 ·L·cm -1 range.

[0245] Transient absorption spectra were measured for the compound of Example 1 on a thin film prepared by the method described in [Preparation of a film containing a pigment]. The film was hung in a quartz cell with a light path length of 1 cm, the cell was purged with argon and sealed, and the measurement was performed in the same manner as for the solution.

[0246] Figure 5A is the transient absorption spectrum of the thin film containing the compound of Example 1. Figure 5B : is the transient absorption spectrum of the thin film containing the compound of Example 1 when the vertical axis is converted from the absorbance change to the molar absorption coefficient of the excited state. Figure 4A and Figure 4B Same. Figure 5A It can be seen that the compound of Example 1 has a large transient absorption peak near 400nm even in a polymer film with different polarity and dispersion state from that in a chloroform solution, and shows large excited state absorption in a short wavelength range. The lifetime of the observed excited species is about several nanoseconds to 10 nanoseconds, which is the same as that in a chloroform solution.

[0247] Next, solutions of the compounds of Comparative Examples 1 and 2 were prepared in the same manner as in Example 1, and transient absorption spectra were measured. The results are shown in Fig. 6A and Figure 6B middle.

[0248] Fig. 6A is the transient absorption spectrum of the solution containing the compound of Comparative Example 1. Figure 4A Same. Fig. 6AAs shown, the compound of Comparative Example 1 fades in the wavelength region below 420nm, and the molar absorption coefficient of the excited state cannot be calculated. Fading is a phenomenon in which the number of pigments in the ground state is greatly reduced when the single-photon absorption at the observation wavelength is large, so that the absorbance change becomes a negative value. Fading is sometimes also called bleaching. However, in the wavelength region of 430nm to 500nm, it is possible to confirm the downward swing of the transient absorption peak that increases toward the short wavelength side. This teaches that the compound of Comparative Example 1 produces excited state absorption in the short wavelength region near 400nm. However, the lifetime of the excited state is about 1 millisecond, which is very long. After the measurement, the quartz cell was opened to allow the sample solution to contain the atmosphere, and the measurement was performed again. As a result, the lifetime was shortened. From these facts, it can be considered that Fig. 6A The transient absorption that appears in the graph is due to the influence of oxygen in the atmosphere and is therefore based on light absorption from the triplet excited state. By confirming that the lifetime and absorption intensity differ depending on the presence or absence of oxygen in the surrounding environment, it is possible to determine whether the light absorption is from the singlet excited state or the triplet excited state.

[0249] Figure 6B is the transient absorption spectrum of the solution containing the compound of Comparative Example 2. The vertical axis and the horizontal axis are Figure 4A Same. Figure 6B As shown, similarly to the compound of Comparative Example 1, in the compound of Comparative Example 2, also fades in the wavelength region below 430nm, and fails to calculate the molar absorptivity of the excited state. On the other hand, different from the compound of Comparative Example 1, for the compound of Comparative Example 2, in the region of the long wavelength of 430nm less than the influence of fading, fails to confirm the swing of the transient absorption peak. Thus taught: the pigment of Comparative Example 2 is in the short wavelength region near 400nm, and almost no excited state absorption occurs. The life span of the excited state that can be confirmed slightly is also very long, for about several milliseconds. After the measurement, the quartz tank pool is opened, the sample solution is contained in the atmosphere, and the result is measured again, and the life span is shortened. By these facts, it can be considered that the compound of Comparative Example 2 rapidly transitions to the triplet excited state after excitation.

[0250] The transient absorption spectrum of the compound of Example 2 is recorded in the literature Nicole Marie Dickson, "Exploration of the Excited States of Organic Molecules and Metal Complexes Using Ultrafast Laser Spectroscopy", Dissertation, Ohio State Univ. (2011). The transient absorption spectrum of the compound of Example 2 has a peak at about 440 nm. It can be seen from the transient absorption spectrum recorded in the literature that a large excited state absorption also occurs near 400 nm, that is, the absorbance change ΔAbs is positive.

[0251] The transient absorption spectrum of the derivative of the compound of Comparative Example 3, i.e., trans, trans-1,4-distyrylbenzene (unsubstituted), is recorded in the literature Gabriella Ginocchietti et al., "Photobehaviour of thio-analogues of stilbene and 1,4-distyrylbenzene studied by time-resolved absorption techniques", Chem.Phys.2008,352, pages 28-34. From the transient absorption spectrum recorded in the literature, it can be seen that the light absorption from the singlet excited state has a peak at about 750nm, no excited state absorption occurs near 400nm, and the absorbance change ΔAbs is negative.

[0252] The transient absorption spectrum of the compound of Comparative Example 5 is recorded in the literature Paolo Foggi et al., "Transient absorption and vibrational relaxation dynamics of the lowest excited singletstate of pyrene in solution", J. Phys. Chem. 1995, 99, pp. 7439-7445. The transient absorption spectrum recorded in the literature has a peak at about 460 nm. It can be seen from the transient absorption spectrum recorded in the literature that excited state absorption occurs at around 400 nm, although it is small.

[0253] As described above, it is clear that the light absorption characteristics required of an organic compound as a dye in order to have sufficient recording sensitivity and at the same time have nonlinear characteristics (threshold characteristics) are clarified.

[0254] Industrial Applicability

[0255] The compounds disclosed herein can be used as nonlinear light absorption materials for recording layers of three-dimensional optical storage devices, photocurable resin compositions for optical modeling, and the like. The compounds disclosed herein have light absorption characteristics that show high nonlinear characteristics for light with a wavelength in a short wavelength range. Therefore, the compounds disclosed herein can achieve extremely high spatial resolution in applications such as three-dimensional optical storage devices and modeling machines. According to the compounds disclosed herein, even when irradiated with a laser of low light intensity, nonlinear light absorption can occur that is superior to single-photon absorption, compared to existing compounds.

Claims

1. A recording medium comprising a recording layer, wherein the recording layer contains an organic compound having nonlinear light absorption characteristics, wherein the molar absorption coefficient of the organic compound for light having a wavelength of not less than 400 nm and not more than 405 nm is 90 mol -1 ·L·cm -1 As described above, in the transient absorption spectrum of the organic compound, the absorbance change ΔAbs at a wavelength of 400 nm to 405 nm is a positive value.

2. The recording medium according to claim 1, in, The molar absorption coefficient of the organic compound is 1000 mol -1 ·L·cm -1 the following.

3. The recording medium according to claim 1, in, The molar absorption coefficient of the organic compound is 100 mol -1 ·L·cm -1 Above 500mol -1 ·L·cm -1 the following.

4. The recording medium according to claim 1, in, The lifetime of the excited state of the organic compound is 1 millisecond or less.

5. The recording medium according to claim 1, in, The organic compound is a compound that can cause a change in stereostructure in an excited state.

6. A method for recording information, wherein include: preparing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and collecting the light from the light source and irradiating the light to the recording layer in the recording medium according to any one of claims 1 to 5.

7. A method for reading information, which is a method for reading information recorded by the recording method according to claim 6, wherein the reading method include: irradiating the recording layer in the recording medium with light to thereby measure optical properties of the recording layer; and reading information from the recording layer.

8. The reading method according to claim 7, in, The optical characteristic is the intensity of light reflected by the recording layer.

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