Nonlinear optical absorption material, recording medium, information recording method, and information reading method

Abstract

A nonlinear light absorbing material according to one embodiment of the present disclosure contains, as a main component, a compound that is represented by formula (1).　In formula (1), each of R1 to R6 independently represents a hydrocarbon group.

Description

[Technical Field]

[0001] The present disclosure relates to nonlinear optically absorbing materials, recording media, methods for recording information, and methods for reading information. [Background technology]

[0002] Among optical materials such as light-absorbing materials, materials that exhibit nonlinear optical effects are called nonlinear optical materials. Nonlinear optical effects refer to the occurrence of optical phenomena in a material when irradiated with strong light such as laser light, which are proportional to the square or higher-order of the electric field of the irradiated light. Examples of optical phenomena include absorption, reflection, scattering, and light emission. Examples of second-order nonlinear optical effects proportional to the square of the electric field of the irradiated light include second-harmonic generation (SHG), the Pockels effect, and the parametric effect. Examples of third-order nonlinear optical effects proportional to the cube of the electric field of the irradiated light include two-photon absorption, multi-photon absorption, third-harmonic generation (THG), and the Kerr effect. In this specification, multi-photon absorption, such as two-photon absorption, is sometimes referred to as nonlinear optical absorption. Materials capable of nonlinear optical absorption are sometimes referred to as nonlinear optical absorption materials. In particular, materials capable of two-photon absorption are sometimes referred to as two-photon absorption materials.

[0003] Much research has been conducted on nonlinear optical materials. In particular, inorganic materials that can be easily prepared as single crystals have been developed as nonlinear optical materials. In recent years, the development of nonlinear optical materials made from organic materials has been anticipated. Compared to inorganic materials, organic materials not only have a high degree of design freedom but also have large nonlinear optical constants. Furthermore, organic materials exhibit high-speed nonlinear response. In this specification, nonlinear optical materials containing organic materials may be referred to as organic nonlinear optical materials. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5769151 [Patent Document 2] Patent No. 5659189 [Patent Document 3] Patent No. 5821661 [Non-patent literature]

[0005] [Non-Patent Document 1] Harry L. Anderson et al, “Two-Photon Absorption and the Design of Two-Photon Dyes”, Angew. Chem. Int. Ed. 2009, Vol. 48, p. 3244-3266. Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional nonlinear optical absorption materials have room for improvement in terms of nonlinear absorption properties for light having wavelengths in the short wavelength range. [Means for solving the problem]

[0007] In one embodiment of the present disclosure, the nonlinear optical absorption material is The compound represented by the following formula (1) is contained as the main component. [ka] In the formula (1), R 1 From R 6 are each independently a hydrocarbon group. [Effects of the Invention]

[0008] The present disclosure provides a nonlinear optically absorbing material with improved nonlinear absorption properties for light having wavelengths in the short wavelength range. [Brief explanation of the drawings]

[0009] [Figure 1A]FIG. 1A is a flowchart illustrating a method for recording information using a recording medium including a nonlinear optically absorbing material according to an embodiment of the present disclosure. [Figure 1B] FIG. 1B is a flowchart illustrating a method for reading information using a recording medium including a nonlinear optically absorbing material according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Findings that formed the basis of this disclosure) Among organic nonlinear optical materials, two-photon absorption materials have attracted particular attention. Two-photon absorption refers to the phenomenon in which a compound absorbs two photons almost simultaneously and transitions to an excited state. Known two-photon absorption types include simultaneous two-photon absorption and stepwise two-photon absorption. Simultaneous two-photon absorption is sometimes called non-resonant two-photon absorption. Simultaneous two-photon absorption refers to two-photon absorption in a wavelength range where no single-photon absorption band exists. Stepwise two-photon absorption is sometimes called resonant two-photon absorption. In stepwise two-photon absorption, a compound absorbs the first photon and then absorbs the second photon, transitioning to a higher excited state. In stepwise two-photon absorption, a compound absorbs two photons sequentially.

[0011] In simultaneous two-photon absorption, the amount of light absorbed by a compound is typically proportional to the square of the irradiated light intensity and exhibits nonlinearity. The amount of light absorbed by a compound can be used as an indicator of the efficiency of two-photon absorption. When the amount of light absorbed by a compound exhibits nonlinearity, for example, light absorption by the compound can occur only near the focus of a laser beam with a high electric field strength. In other words, in a sample containing a two-photon absorbing material, the compound can be excited only at the desired position. Compounds that exhibit simultaneous two-photon absorption thus provide extremely high spatial resolution and are therefore being considered for use in applications such as recording layers for three-dimensional optical memories and photocurable resin compositions for stereolithography. If the two-photon absorbing material also possesses fluorescent properties, it can also be used as a fluorescent dye material for two-photon fluorescence microscopes. Using this two-photon absorbing material in three-dimensional optical memories may enable the adoption of a method for reading the ON / OFF state of the recording layer based on changes in fluorescence from the two-photon absorbing material. Current optical memories use a method to read the ON / OFF state of a recording layer based on changes in the reflectivity and absorbance of light in two-photon absorbing materials. However, when this method is applied to three-dimensional optical memories, crosstalk can occur due to recording layers other than the one whose ON / OFF state should be read.

[0012] In two-photon absorption materials, the two-photon absorption cross section (GM value) is used as an index of two-photon absorption efficiency. The unit of the two-photon absorption cross section is GM (10 -50 cm 4 ·s·molecule -1 photon -1 ) Up to now, many organic two-photon absorption materials with large two-photon absorption cross sections have been proposed. For example, many compounds with large two-photon absorption cross sections exceeding 500 GM have been reported (e.g., Non-Patent Document 1). However, in most reports, the two-photon absorption cross section was measured using laser light with a wavelength longer than 600 nm. In particular, near-infrared light with a wavelength longer than 750 nm is sometimes used as the laser light.

[0013] However, in order to apply two-photon absorption materials to industrial applications, materials that exhibit two-photon absorption properties when irradiated with laser light having a shorter wavelength are required. For example, in the field of three-dimensional optical memory, laser light having a shorter wavelength can realize a finer focused spot, thereby improving the recording density of three-dimensional optical memory. In the field of stereolithography, laser light having a shorter wavelength can realize modeling with higher resolution. Furthermore, the Blu-ray (registered trademark) disc standard uses laser light with a central wavelength of 405 nm. Thus, the development of compounds that exhibit excellent two-photon absorption properties for light in the same wavelength range as short-wavelength laser light would greatly contribute to industrial development.

[0014] Furthermore, light-emitting devices that emit ultrashort pulsed lasers with high optical intensity tend to be large and unstable in operation. Therefore, such light-emitting devices are difficult to adopt for industrial applications from the viewpoints of versatility and reliability. In consideration of this, in order to apply two-photon absorption materials to industrial applications, materials that exhibit two-photon absorption properties even when irradiated with low-intensity laser light are required.

[0015] In a compound having two-photon absorption properties, the relationship between light intensity and two-photon absorption properties is expressed by the following formula (i). In this specification, a compound having two-photon absorption properties may be referred to as a two-photon absorption compound. Formula (i) is a calculation formula for calculating the decrease in light intensity -dI when a sample containing a two-photon absorption compound and having a minute thickness dz is irradiated with light of intensity I. As can be seen from formula (i), the decrease in light intensity -dI is expressed as the sum of a term proportional to the first power of the intensity I of the light incident on the sample and a term proportional to the square of the intensity I.

number

[0016] In formula (i), α is the one-photon absorption coefficient (cm -1 ) α (2)is the two-photon absorption coefficient (cm / W). From equation (i), it is clear that the intensity I of the incident light when the one-photon absorption amount and the two-photon absorption amount are equal in the sample is α / α (2) In other words, the intensity of the incident light I is expressed as α / α (2) When the incident light intensity I is smaller than α / α, one-photon absorption occurs predominantly in the sample. (2) When the α / α ratio in the sample is larger than α, two-photon absorption occurs preferentially. (2) The smaller the value of , the more likely it is that two-photon absorption can be preferentially exhibited by laser light with a lower light intensity.

[0017] Furthermore, α and α (2) can be expressed by the following formulas (ii) and (iii), respectively. In formulas (ii) and (iii), ε is the molar absorption coefficient (mol -1 L cm -1 ) where N is the number of molecules of the compound per unit volume of the sample (mol cm -3 ) N A is the Avogadro constant. σ is the two-photon absorption cross section (GM). h-(Hbar) is the Dirac constant (J·s). ω is the angular frequency of the incident light (rad / s).

number

[0018] From equations (ii) and (iii), α / α (2) is determined by ε / σ. In other words, in order to preferentially induce two-photon absorption using low-intensity laser light, it is desirable that the ratio σ / ε of the two-photon absorption cross section σ to the molar extinction coefficient ε be large for the wavelength of the irradiated laser light. When the ratio σ / ε is large at a specific wavelength for a compound, it can be said that the nonlinearity of light absorption at that wavelength is high.

[0019] Patent Documents 1 and 2 disclose compounds having a large two-photon absorption cross section for light having a wavelength around 405 nm. Patent Document 3 discloses an optical information recording medium that can shorten the writing time when using laser light having a wavelength around 405 nm, and a compound contained in the optical information recording medium.

[0020] Patent Documents 1 and 3 describe compounds with large π-electron conjugated systems. Furthermore, Patent Document 2 describes a benzophenone derivative with a large π-electron conjugated system. However, when the π-electron conjugated system of a compound is enlarged, the two-photon absorption cross section increases, while the peak resulting from one-photon absorption tends to shift to a longer wavelength region. In this specification, the shift of the peak resulting from one-photon absorption to a longer wavelength region is sometimes referred to as a long-wavelength shift or red shift. As a result of the long-wavelength shift of the peak resulting from one-photon absorption, part of the wavelength region where one-photon absorption occurs may overlap with the wavelength of the excitation light. An example of the wavelength of the excitation light is 405 nm, as specified in the Blu-ray (registered trademark) standard. In a compound, when the one-photon absorption due to the excitation light is large, the nonlinearity of the optical absorption tends to decrease. Compounds with low nonlinearity of optical absorption are not suitable for the recording layer of a multilayered three-dimensional optical memory.

[0021] Furthermore, the quantum yield of intersystem crossing is almost 100% in the benzophenone derivative disclosed in Patent Document 2. This benzophenone derivative undergoes a rapid transition from the singlet excited state to the triplet excited state, and therefore emits almost no fluorescence.

[0022] As a result of extensive research, the present inventors have newly discovered that a compound represented by the formula (1) described below has high nonlinear optical absorption properties for light having a wavelength in the short wavelength range, and have completed the nonlinear optical absorption material of the present disclosure. Specifically, the present inventors have discovered that the compound represented by formula (1) has a large value of the ratio σ / ε of the two-photon absorption cross section σ to the molar extinction coefficient ε for light having a wavelength in the short wavelength range, and thus has high nonlinear optical absorption. Furthermore, this compound also tends to have fluorescent properties. In this specification, the short wavelength range refers to a wavelength range including 405 nm, for example, a wavelength range of 390 nm to 420 nm.

[0023] (Summary of one aspect of the present disclosure) The nonlinear optical absorption material according to the first aspect of the present disclosure comprises: The compound represented by the following formula (1) is contained as the main component. [ka] In the formula (1), R 1 From R 6 are each independently a hydrocarbon group.

[0024] According to the first aspect, the nonlinear light-absorbing material tends to have a large ratio σ / ε of the two-photon absorption cross section σ to the molar extinction coefficient ε for light having a wavelength in the short wavelength range, and thus has high nonlinearity in light absorption. Thus, the nonlinear light-absorbing material has improved nonlinear light absorption properties for light having a wavelength in the short wavelength range. The nonlinear light-absorbing material according to the first aspect also tends to have fluorescent properties.

[0025] In the second aspect of the present disclosure, for example, in the nonlinear optical absorption material according to the first aspect, the R 1 From the R 6 may be, independently of each other, an alkyl group.

[0026] In the third aspect of the present disclosure, for example, in the nonlinear optical absorption material according to the first or second aspect, the R 1 From the R 6may be, independently of each other, a methyl group or an ethyl group.

[0027] In a fourth aspect of the present disclosure, for example, in the nonlinear optical absorption material according to any one of the first to third aspects, the R 1 From the R 6 are the same as each other and may be a methyl group or an ethyl group.

[0028] In a fifth aspect of the present disclosure, for example, in the nonlinear optical absorption material according to any one of the first to fourth aspects, the compound may have a nonlinear optical absorption effect.

[0029] In a sixth aspect of the present disclosure, for example, the nonlinear optically absorbing material according to any one of the first to fifth aspects may be used in a device that utilizes light having a wavelength of 390 nm or more and 420 nm or less.

[0030] According to the second to sixth aspects, the nonlinear optical absorption properties of the nonlinear optical absorption material are improved for light having a wavelength in the short wavelength region. The nonlinear optical absorption materials according to the second to fifth aspects also tend to have fluorescent properties. This nonlinear optical absorption material is suitable for use in devices that utilize light having a wavelength of 390 nm or more and 420 nm or less.

[0031] A recording medium according to a seventh aspect of the present disclosure includes: The optical recording medium comprises a recording layer containing the nonlinear optical absorption material according to any one of the first to sixth aspects.

[0032] According to the seventh aspect, the nonlinear light-absorbing material has improved nonlinear absorption characteristics for light having a wavelength in the short wavelength region. The nonlinear light-absorbing material used in the seventh aspect also tends to have fluorescent properties. A recording medium including such a nonlinear light-absorbing material can record information at a high recording density.

[0033] An information recording method according to an eighth aspect of the present disclosure includes: providing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and condensing the light from the light source and irradiating the light onto the recording layer of the recording medium according to the seventh aspect.

[0034] According to the eighth aspect, the nonlinear light-absorbing material has improved nonlinear absorption characteristics for light having a wavelength in the short wavelength region. The nonlinear light-absorbing material used in the eighth aspect also tends to have fluorescent properties. According to an information recording method using a recording medium containing such a nonlinear light-absorbing material, information can be recorded at a high recording density.

[0035] A method for reading information according to a ninth aspect of the present disclosure is, for example, a method for reading information recorded by the recording method according to the eighth aspect, The reading method includes: measuring optical characteristics of the recording layer by irradiating the recording layer of the recording medium with light; and reading the information from the recording layer.

[0036] In a tenth aspect of the present disclosure, for example, in the information reading method according to the ninth aspect, the optical property may be the intensity of fluorescent light emitted from the recording layer.

[0037] According to the ninth or tenth aspect, when reading out information, it is possible to suppress the occurrence of crosstalk due to other recording layers.

[0038] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0039] (Embodiment) The nonlinear optical absorption material of this embodiment contains a compound A represented by the following formula (1). [ka]

[0040] In formula (1), R 1 From R 6are each independently a hydrocarbon group. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. Furthermore, the aliphatic hydrocarbon group may be a saturated aliphatic hydrocarbon group or an unsaturated aliphatic hydrocarbon group. A specific example of an aliphatic saturated hydrocarbon group is an alkyl group. R 1 From R 6 may be, independently of each other, an alkyl group. The alkyl group may be linear, branched, or cyclic. The number of carbon atoms in the alkyl group is not particularly limited and may be, for example, 1 to 20. From the viewpoint of facilitating the synthesis of compound A, the number of carbon atoms in the alkyl group may be 1 to 10, or 1 to 5. By adjusting the number of carbon atoms in the alkyl group, the solubility of compound A in a solvent or resin composition can be adjusted. At least one hydrogen atom contained in the alkyl group may be substituted with a group containing at least one atom selected from the group consisting of N, O, P, and S. Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, a butyl group, a 2-methylbutyl group, a pentyl group, a hexyl group, a 2,3-dimethylhexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, an eicosyl group, a 2-methoxybutyl group, and a 6-methoxyhexyl group. 1 From R 6 may be, independently of each other, a methyl group or an ethyl group.

[0041] The aliphatic unsaturated hydrocarbon group contains an unsaturated bond such as a carbon-carbon double bond or a carbon-carbon triple bond. The number of unsaturated bonds contained in the aliphatic unsaturated hydrocarbon group is, for example, 1 to 5. The number of carbon atoms in the aliphatic unsaturated hydrocarbon group is not particularly limited and is, for example, 2 to 20, or may be 2 to 10, or may be 2 to 5. The aliphatic unsaturated hydrocarbon group may be linear, branched, or cyclic. Examples of the aliphatic unsaturated hydrocarbon group include a vinyl group and an ethynyl group.

[0042] The aromatic hydrocarbon group contains an aromatic ring. The aromatic ring is composed of, for example, carbon atoms. Examples of aromatic rings include a benzene ring, a naphthalene ring, and an anthracene ring. The number of carbon atoms in the aromatic hydrocarbon group is not particularly limited and is, for example, 6 to 20. Examples of aromatic hydrocarbon groups include a phenyl group and a benzyl group.

[0043] R 1 From R 6 may be the same or different. 1 From R 6 are the same and may be a methyl group or an ethyl group. Specifically, specific examples of compound A include 10,15-dihydro-5,5,10,10,15,15-hexamethyl-5H-diindeno[1,2-a:1',2'-c]fluorene of the following formula (2) and 10,15-dihydro-5,5,10,10,15,15-hexaethyl-5H-diindeno[1,2-a:1',2'-c]fluorene of the following formula (3). [ka]

[0044] Compound A represented by formula (1) has excellent two-photon absorption properties and tends to have small one-photon absorption with respect to light having a wavelength in the short wavelength region. For example, when compound A is irradiated with light having a wavelength of 405 nm, two-photon absorption may occur in compound A, but one-photon absorption may hardly occur.

[0045] The two-photon absorption cross section of compound A for light having a wavelength of 405 nm may be greater than 1 GM or even 10 GM or greater. The upper limit of the two-photon absorption cross section of compound A is not particularly limited and may be, for example, 1000 GM. The two-photon absorption cross section 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, a measurement sample is moved along the direction of irradiation of a laser beam near the focal point where the beam is focused. At this time, changes in the amount of light transmitted through the measurement sample are recorded. In the Z-scan method, the power density of the incident light changes depending on the position of the measurement sample. Therefore, if the measurement sample exhibits nonlinear optical absorption, the amount of transmitted light will be attenuated when the measurement sample is positioned near the focal point of the laser beam. The two-photon absorption cross section can be calculated by fitting the change in the amount of transmitted light to a theoretical curve predicted from the intensity of the incident light, the thickness of the measurement sample, the concentration of compound A in the measurement sample, etc.

[0046] The molar absorption coefficient of compound A for light with a wavelength of 405 nm is 100 mol -1 L cm -1 may be less than 10 mol -1 L cm -1 It may be less than 1 mol -1 L cm -1 It may be 0.1 mol or less. -1 L cm -1 The lower limit of the molar extinction coefficient of compound A is not particularly limited, and may be, for example, 0.00001 mol -1 L cm -1The molar extinction coefficient can be measured, for example, by a method conforming to the provisions of Japanese Industrial Standards (JIS) K0115:2004. In measuring the molar extinction coefficient, a light source is used that irradiates light with a photon density that causes almost no two-photon absorption by compound A. Furthermore, in measuring the molar extinction coefficient, the concentration of compound A is adjusted to 100 mmol / L or more and 500 mmol / L or less. This concentration is much higher than the concentration used in the measurement test for the molar extinction coefficient of the light absorption peak. The molar extinction coefficient can be used as an index of one-photon absorption.

[0047] Compound A has a molar absorption coefficient ε (mol -1 L cm -1 The ratio σ / ε of the two-photon absorption cross section σ(GM) to the wavelength of light having a wavelength of 405 nm of compound A may be 100 or more, 300 or more, 500 or more, 700 or more, or 900 or more. The upper limit of the ratio σ / ε of compound A is not particularly limited, and is, for example, 5,000.

[0048] When compound A undergoes two-photon absorption, compound A absorbs approximately twice the energy of light irradiated onto compound A. The wavelength of light having approximately twice the energy of light having a wavelength of 405 nm is, for example, 200 nm. When compound A is irradiated with light having a wavelength around 200 nm, one-photon absorption may occur in compound A. Furthermore, compound A may undergo one-photon absorption with light having a wavelength close to the wavelength range in which two-photon absorption occurs.

[0049] Compound A also tends to emit fluorescent light. The wavelength of the fluorescent light emitted by compound A may be 405 nm or more and 660 nm or less, and in some cases, may be 300 nm or more and 650 nm or less. The fluorescence quantum yield Φf of compound A may be 0.05 or more, 0.1 or more, or 0.5 or more. The upper limit of the fluorescence quantum yield Φf of compound A is not particularly limited, and is, for example, 0.99. In this specification, "quantum yield" specifically means internal quantum yield. The fluorescence quantum yield can be measured, for example, using a commercially available absolute PL quantum yield measurement device.

[0050] The nonlinear light-absorbing material of this embodiment may contain compound A represented by formula (1) as a main component. "Main component" means the component contained in the nonlinear light-absorbing material in the largest amount by weight. The nonlinear light-absorbing material may, for example, consist essentially of compound A. "Consisting essentially of" means excluding other components that alter the essential characteristics of the referenced material. However, the nonlinear light-absorbing material may contain impurities in addition to compound A. The nonlinear light-absorbing material of this embodiment containing compound A functions, for example, as a two-photon absorption material.

[0051] Generally, to improve the nonlinearity of optical absorption by a compound in the wavelength range of 390 nm to 420 nm, the compound must not only have nonlinear optical absorption properties in that wavelength range, but also have very low one-photon absorption by the compound in that wavelength range. When adjusting the optical properties of a material with a low concentration of nonlinear optical absorbing compounds, the optical properties of the compound itself can be taken into consideration. That is, by using a compound with a minimum one-photon absorption level corresponding to the energy of light with a wavelength sufficiently shorter than the wavelength range of 390 nm to 420 nm and a low oscillator strength, the molar extinction coefficient in the wavelength range of 390 nm to 420 nm can be reduced. However, industrial applications sometimes require materials with a high concentration of nonlinear optical absorbing compounds. When the concentration of nonlinear optical absorbing compounds is high, the compounds may come into close proximity and associate through π-π interactions, etc. This association can change the optical properties of the compound itself.

[0052] Unsubstituted truxene is a hydrocarbon compound that is non-polar and has high planarity. 1 From R 6 corresponds to a compound in which is a hydrogen atom. In this specification, unsubstituted truxene may be simply referred to as truxene. In truxene, π stacking between molecules is likely to occur, and truxene tends to have low solubility in solvents or resin monomers. For example, when chloroform is used as a solvent, the solubility of truxene is about several mmol / L. When the concentration of truxene in a material is high, the truxene molecules come close to each other and associate in various forms. This results in the formation of multiple new levels at energy positions lower than the minimum one-photon absorption allowable level of truxene itself. Therefore, when the one-photon absorption spectrum of a material containing truxene at a high concentration is measured, it can be confirmed that the peak resulting from one-photon absorption is tailing. In contrast, when R in formula (1) 1 From R 6 Compound A, in which R is a hydrocarbon group, tends to be able to suppress the formation of associations between compounds without substantially changing the size of the π-electron conjugated system of truxene. Therefore, compound A suppresses the tailing of peaks resulting from one-photon absorption even when present at a high concentration in a material. That is, compound A tends to have a small molar absorption coefficient for light in the wavelength range of 390 nm to 420 nm, and high nonlinearity in light absorption, even when present at a high concentration in a material. Furthermore, compound A also tends to have high solubility in solvents or resin monomers. For example, when chloroform is used as a solvent, R in formula (1) 1 From R 6 The solubility of compounds where is a methyl group is 100 mmol / L or more.

[0053] The nonlinear optical absorption material of this embodiment is used, for example, in devices that use light having a wavelength in the short wavelength range. As an example, the nonlinear optical absorption material of this embodiment is used in devices that use light having a wavelength of 390 nm or more and 420 nm or less. Examples of such devices include recording media, modeling machines, and fluorescence microscopes. Examples of recording media include three-dimensional optical memories. A specific example of three-dimensional optical memories is a three-dimensional optical disk. Examples of modeling machines include stereolithography machines such as 3D printers. Examples of fluorescence microscopes include two-photon fluorescence microscopes. 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, 0.1 W / cm. 2 Over 1.0 x 10 20 W / cm 2 The power density near the focal point of this light is 1.0 W / cm 2 It may be 1.0 x 10 or more. 2 W / cm 2 It may be 1.0 x 10 or more. 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.

[0054] 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 serving as the recording layer includes the nonlinear optical absorption material of this embodiment. That is, from another aspect thereof, the present disclosure provides a recording medium including the nonlinear optical absorption material including the above-mentioned compound A.

[0055] The recording layer may further contain a polymer compound that functions as a binder in addition to the nonlinear light absorbing material. The recording medium may also 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.

[0056] Next, a method for recording information using the above-mentioned recording medium will be described. FIG. 1A is a flowchart showing the method for recording information using the above-mentioned recording medium. First, in step S11, a light source is prepared that emits light having a wavelength of 390 nm or more and 420 nm or less. As the light source, for example, a femtosecond laser such as a titanium sapphire laser, or a pulsed laser having a pulse width of picoseconds to nanoseconds such as a semiconductor laser can be used. Next, in step S12, the light from the light source is focused using a lens or the like and irradiated onto the recording layer of the recording medium. More specifically, the light from the light source is focused using a lens or the like and irradiated onto the recording region of the recording medium. The power density near the focus of this light is, for example, 0.1 W / cm. 2 Over 1.0 x 10 20 W / cm 2 The power density near the focal point of this light is 1.0 W / cm 2 It may be 1.0 x 10 or more. 2 W / cm 2 It may be 1.0 x 10 or more. 5 W / cm 2 In this specification, the recording area means a spot that exists in the recording layer and that can record information when irradiated with light.

[0057] In the recording area irradiated with the light, a physical or chemical change occurs, changing the optical characteristics of the recording area. For example, the intensity of the fluorescent light emitted from the recording area decreases. In the recording area irradiated with the light, the intensity of the light reflected from the recording area, the reflectance of the light in the recording area, the absorbance of the light in the recording area, the refractive index of the light in the recording area, the wavelength of the fluorescent light emitted from the recording area, etc. may also change. This allows information to be recorded in the recording layer, specifically in the recording area (step S13).

[0058] Next, a method for reading information using the above-described recording medium will be described. FIG. 1B is a flowchart illustrating a method for reading information using the above-described recording medium. First, in step S21, light is irradiated onto the recording layer of the recording medium. More specifically, light is irradiated onto the recording area of ​​the recording medium. The light used in step S21 may be the same as or different from the light used to record information on the recording medium. Next, in step S22, the optical characteristics of the recording layer are measured. More specifically, the optical characteristics of the recording area are measured. In step S22, for example, the intensity of fluorescent light emitted from the recording area may be measured. In step S22, the optical characteristics of the recording area may include the intensity of light reflected from the recording area, the reflectance of light in the recording area, the absorptance of light in the recording area, the refractive index of light in the recording area, and the wavelength of fluorescent light emitted from the recording area. Next, in step S23, information is read from the recording layer, more specifically, the recording area.

[0059] In the information reading method, the recording area where information is recorded can be found by the following method. First, light is irradiated onto a specific area of ​​the recording medium. This light may be the same as or different from the light used to record information on the recording medium. Next, the optical characteristics of the area irradiated with light are measured. Examples of optical characteristics include the intensity of fluorescent light emitted from the area, the intensity of light reflected from the area, the reflectance of light in the area, the absorbance of light in the area, the refractive index of light in the area, and the wavelength of fluorescent light emitted from the area. Whether or not the area irradiated with light is a recorded area is determined based on the measured optical characteristics. For example, if the intensity of fluorescent light emitted from the area is equal to or less than a specific value, the area is determined to be a recorded area. On the other hand, if the intensity of fluorescent light exceeds a specific value, the area is determined to be not a recorded area. Note that the method for determining whether or not the area irradiated with light is a recorded area is not limited to the above method. For example, if the intensity of fluorescent light emitted from the area exceeds a specific value, the area may be determined to be a recorded area. Alternatively, if the intensity of the fluorescent light emitted from the area is equal to or less than a specific value, the area may be determined to be a non-recorded area. If it is determined to be a non-recorded area, the same operation is performed on other areas of the recording medium. This allows the search for a recorded area.

[0060] The information recording and reading methods using the above-mentioned recording medium can be performed, for example, by a known recording device, which includes, for example, a light source that irradiates a recording area of ​​the recording medium with light, a measuring device that measures the optical characteristics of the recording area, and a controller that controls the light source and the measuring device.

[0061] The modeling machine performs modeling by, for example, irradiating a photocurable resin composition with light and curing the resin composition. As an example, a photocurable resin composition for stereolithography contains the nonlinear optical absorption material of this embodiment. The photocurable resin composition contains, for example, a polymerizable compound and a polymerization initiator in addition to the nonlinear optical absorption material. The photocurable resin composition may further contain an additive such as a binder resin. The photocurable resin composition may also contain an epoxy resin.

[0062] The fluorescence microscope can be used to irradiate a biological sample containing a fluorescent dye material with light and observe the fluorescence emitted from the dye material. For example, the fluorescent dye material to be added to the biological sample contains the nonlinear light-absorbing material of this embodiment. [Example]

[0063] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are merely illustrative and the present disclosure is not limited to the following examples.

[0064] First, the compounds of Examples 1 and 2 and Comparative Examples 1 to 6 shown in Table 1 were prepared. The compounds of Comparative Examples 1 to 6 are represented by the following formulas (4) to (9), respectively.

[0065] Here, 10,15-dihydro-5,5,10,10,15,15-hexamethyl-5H-diindeno[1,2-a:1′,2′-c]fluorene, which is the compound of Example 1, and 10,15-dihydro-5,5,10,10,15,15-hexaethyl-5H-diindeno[1,2-a:1′,2′-c]fluorene, which is the compound of Example 2, were synthesized according to the method described in Mao-Sen Yuan et al., “Donor-and-Acceptor Substituted Truxenes as Multifunctionnal Fluorescent Probes”, J. Org. Chem. 2007, Vol. 72, pp. 7915-7922.

[0066] The compound used in Comparative Example 1, truxene (10,15-dihydro-5H-diindeno[1,2-a:1′,2′-c]fluorene), was manufactured by Tokyo Chemical Industry Co., Ltd.; the compound used in Comparative Example 2, truxenone (5H-diindeno[1,2-a:1′,2′-c]fluorene-5,10,15-trione), was manufactured by Tokyo Chemical Industry Co., Ltd.; and the compound used in Comparative Example 3, triazatruxene (10,15-dihydro-5H-5,10,15-triaza-diindeno[1,2-a:1′,2′-c]fluorene), was manufactured by Aldrich Chemicals.

[0067] Hexakis(phenylethynyl)benzene (HPEB), the compound of Comparative Example 4, was synthesized according to the method described in K. Konodo et al., J. Chem. Soc., Chem. Commun. 1995, 55-56; W. Tao, et al., J. Org. Chem. 1990, 55, 63-66. Compound D29, the compound of Comparative Example 5 shown in formula (8) below, was synthesized according to the method described in Japanese Patent No. 5659189, paragraphs

[0222] to

[0230] . Compound 1f, the compound of Comparative Example 6 shown in formula (9) below, was synthesized according to the method described in Japanese Patent No. 5821661, paragraph

[0083] . [ka] [ka]

[0068] The optical properties of the compounds of the examples and comparative examples were measured by the following method. However, the compound of comparative example 2 had low solubility in solvents, and it was not possible to prepare a sample for measuring the optical properties. Furthermore, the compound of comparative example 3 had low stability to light having a wavelength in the short wavelength range, and it was not possible to measure the optical properties. From these results, it can be said that the compounds of comparative examples 2 and 3 are not suitable for use in devices that utilize light having a wavelength of 390 nm or more and 420 nm or less.

[0069] <Measurement of two-photon absorption cross section> The two-photon absorption cross section of the compounds of the examples and comparative examples was measured for light having a wavelength of 405 nm. The two-photon absorption cross section was measured using the Z-scan method described in J. Opt. Soc. Am. B, 2003, Vol. 20, p. 529. A titanium sapphire pulsed laser was used as the light source for measuring the two-photon absorption cross section. Specifically, the second harmonic of the titanium sapphire pulsed laser was irradiated onto the sample. The laser pulse width was 80 fs. The laser repetition rate was 1 kHz. The average laser power was varied in the range of 0.01 mW to 0.08 mW. The light emitted from the laser had a wavelength of 405 nm. Specifically, the light emitted from the laser had a central wavelength of 403 nm to 405 nm. The full width at half maximum of the light emitted from the laser was 4 nm. As described above, the two-photon absorption cross sections of the compounds of Examples 1 and 2 and the compounds of Comparative Examples 1, 4 to 6 were measured.

[0070] <Measurement of molar extinction coefficient> The molar absorption coefficients of the compounds in the Examples and Comparative Examples were measured according to the method specified in JIS K0115:2004. Specifically, a solution in which the compound was dissolved in a solvent was first prepared as a measurement sample. The concentration of the compound in the solution was appropriately adjusted within the range of 100 mmol / L to 500 mmol / L depending on the absorbance of the compound to be measured at a wavelength of 405 nm. Next, the absorption spectrum of the measurement sample was measured. The absorbance at a wavelength of 405 nm was read from the obtained spectrum. 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. In this manner, the molar absorption coefficients of the compounds in Examples 1 and 2 and Comparative Examples 1, 4 to 6 were measured.

[0071] <Measurement of fluorescence quantum yield> The internal quantum yield of fluorescence was measured for the compounds of the Examples and Comparative Examples. Measurement samples were prepared by dissolving the compounds in chloroform (CLF) or tetrahydrofuran (THF) solvent. An absolute PL quantum yield measurement device (C9920-02 manufactured by Hamamatsu Photonics) was used for the measurements. The excitation wavelength was set to the peak wavelength of one-photon absorption of the compound. The measurement wavelength was appropriately adjusted within the range of 350 nm to 650 nm so as not to overlap with the absorption wavelength band of the compound. The solvent used to dissolve the compound was used as a reference. In this manner, the fluorescence quantum yield was measured for the compounds of Examples 1 and 2 and Comparative Examples 1, 4 to 6.

[0072] The two-photon absorption cross section σ(GM) and molar absorption coefficient ε(mol -1 L cm -1 ), the ratio σ / ε and the fluorescence quantum yield Φf(-) are shown in Table 1.

[0073] [Table 1]

[0074] As can be seen from Table 1, the compounds of Examples 1 and 2, which correspond to compound A represented by formula (1), both had a value of the ratio σ / ε for light having a wavelength of 405 nm that was greater than 500, which was greater than that of the comparative compound. This result shows that compound A has high nonlinearity in optical absorption for light having a wavelength in the short wavelength region, and has improved nonlinear optical absorption properties. Furthermore, the compounds of Examples 1 and 2 also had fluorescent properties.

[0075] In the truxene of Comparative Example 1, the two-photon absorption cross section σ exceeded 100 GM, while the molar absorption coefficient ε was significantly larger than in the Examples. As a result, the ratio σ / ε in Comparative Example 1 was small. As described above, since truxene has high planarity, it is presumed that in the high-concentration measurement sample, the compounds approached each other due to π-π interactions. Therefore, it is presumed that multiple new levels were formed at energy positions lower than the lowest one-photon absorption allowable level of truxene itself. This is presumed to have caused tailing of the peak resulting from one-photon absorption, resulting in an increase in the molar absorption coefficient ε.

[0076] In contrast, in compound A, the substituent R 1 From R 6 For example, in compound A, the substituents extend above and below the plane of the truxene skeleton. 1 From R 6 This is presumably why, in Examples 1 and 2, even when the compound concentrations in the measurement samples were high, peak tailing due to one-photon absorption was suppressed and the molar extinction coefficient ε was small.

[0077] The compounds of Comparative Examples 4 to 6 are compounds different from truxene derivatives. In all of these compounds, the ratio σ / ε for light having a wavelength of 405 nm was below 100. The compounds of Comparative Examples 4 to 6 have large π-electron conjugated systems and therefore large transition dipole moments. Therefore, the two-photon absorption cross-section σ of Comparative Examples 4 to 6 was large. However, in compounds with extended π-electron conjugated systems, the peak resulting from one-photon absorption tends to shift to a longer wavelength region. In the compounds of Comparative Examples 4 to 6, the wavelength region in which one-photon absorption occurs partially overlaps with 405 nm, significantly increasing the molar extinction coefficient ε, which is presumably why the ratio σ / ε was small. [Industrial Applicability]

[0078] The nonlinear optically absorbing material of the present disclosure can be used in applications such as the recording layer of a three-dimensional optical memory and a photocurable resin composition for stereolithography. The nonlinear optically absorbing material of the present disclosure exhibits highly nonlinear optical absorption characteristics for light having a wavelength in the short wavelength range. Therefore, the nonlinear optically absorbing material of the present disclosure can achieve extremely high spatial resolution in applications such as three-dimensional optical memories and modeling machines. Furthermore, the nonlinear optically absorbing material of the present disclosure also tends to have a high fluorescence quantum yield. Therefore, when the nonlinear optically absorbing material is used in the recording layer of a three-dimensional optical memory, a method can be adopted in which the ON / OFF state of the recording layer is read based on changes in fluorescence from the nonlinear optically absorbing material. The nonlinear optically absorbing material of the present disclosure can also be used as a fluorescent dye material used in two-photon fluorescence microscopes, etc. Compared to conventional nonlinear optically absorbing materials, the nonlinear optically absorbing material of the present disclosure can exhibit two-photon absorption in preference to one-photon absorption even when irradiated with laser light of low optical intensity.

Claims

1. Contains a compound represented by the following formula (1) as a main component: Nonlinear optical absorbing materials. 【Chemistry 1】 In the formula (1), R 1 From R 6 are, independently of each other, a hydrocarbon group, When the hydrocarbon group is an alkyl group, the alkyl group has 7 or more and 20 or less carbon atoms.

2. The R 1 From the above R 6 are, independently of each other, an alkyl group; The nonlinear optical absorbing material of claim 1 .

3. The R 1 From the above R 6 are the same as each other, 3. The nonlinear optical absorption material according to claim 1 or 2.

4. The compound has a nonlinear optical absorption effect.

4. The nonlinear optical absorption material according to claim 1.

5. Used in devices that utilize light having a wavelength of 390 nm or more and 420 nm or less, 5. The nonlinear optical absorption material according to claim 1.

6. A recording layer comprising the nonlinear optical absorption material according to any one of claims 1 to 5. Recording medium.

7. providing a light source that emits light having a wavelength of 390 nm or more and 420 nm or less; and irradiating the light from the light source onto the recording layer of the recording medium according to claim 6. How information is recorded.

8. A method for reading information recorded by the recording method according to claim 7, comprising: The reading method includes: measuring optical characteristics of the recording layer by irradiating the recording layer of the recording medium with light; reading the information from the recording layer. How to read the information.

9. the optical property is the intensity of fluorescent light emitted from the recording layer; The reading method according to claim 8.

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