JP7770645B2 - Photochromic Compounds - Google Patents

Description

The present invention relates to a photochromic compound.

The phenomenon of reversible color change upon exposure to light is called photochromism, and compounds that exhibit this phenomenon are called photochromic compounds. Photochromic compounds are expected to be used in light-adjusting materials, optical recording materials, holographic materials, and more.

Diarylethenes, which have a five-membered heterocyclic ring as the aryl group, are known as photochromic compounds. Such diarylethenes are generally colorless in their open-ring form, but their closed-ring forms exhibit various colors depending on their structure.

For example, Patent Document 1 discloses a compound that has strong absorption around 450 nm and can produce a brown color. Furthermore, Non-Patent Document 1 discloses a compound that can produce a blue color.

Patent No. 5337927

C. Zheng et al. , Dyes and Pigments, 2013, vol. 98, p. 565-574

The compounds described in Patent Document 1 and Non-Patent Document 1 can produce brown or blue colors. However, for purposes such as anti-glare, they are required to absorb light uniformly across the entire visible range.

However, when using the compounds described in Patent Document 1 and Non-Patent Document 1 as light-modulating materials, the light-modulating material must be mixed in order to uniformly absorb light across the entire visible range, requiring a large amount of material. As a result, for example, when forming a film, the material concentration in the film becomes high, which can cause the material to aggregate, potentially resulting in color unevenness.

Therefore, the object of the present invention is to provide a photochromic compound that is transparent in its open-ring form and can absorb light across the entire visible range in its closed-ring form, with more uniform absorption.

The inventors conducted extensive research to solve the above-mentioned problems. As a result, they discovered that a hetero-fused ring structure having a structure in which a substituted amino group is bonded can absorb light across the entire visible range in its closed ring state, and can achieve more uniform absorption, leading to the completion of the present invention.

That is, according to one aspect of the present invention, there is provided a compound represented by either one of the following formulas (I) and (I)':

In each of formulas (I) and (I)′,
R ₁ to R ₄ are each independently a group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted hydrocarbon group, a substituted or unsubstituted silyl group, a substituted or unsubstituted heterocyclic group, an electron-withdrawing group, an electron-donating group, and a substituent containing a heteroatom, and R ₁ and R ₂ may be bonded to each other to form a ring;
_X1 is a heteroatom;
A is a group derived from a heterocyclic compound.

The present invention provides a photochromic compound that is transparent in its open-ring form and can absorb light across the entire visible range in its closed-ring form, with more uniform absorption.

1 is a graph showing the absorption spectrum of Compound 1' of an example. 1 is a graph showing the absorption spectra of compounds A to C of the examples. 1 is a graph showing the absorption spectra of compounds 1 and 1' of the examples. 1 is a graph showing the absorption spectra of compounds D to F of the examples.

The following describes one embodiment of the present invention. The present invention is not limited to the following embodiment.

In this specification, the range "X to Y" means "X or more and Y or less." Unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20-25°C) and a relative humidity of 40-50% RH.

One aspect of the present invention is a compound represented by either formula (I) or (I)' below.

In each of formulas (I) and (I)′,
R ₁ to R ₄ are each independently a group selected from the group consisting of a hydrogen atom, a substituted or unsubstituted hydrocarbon group, a substituted or unsubstituted silyl group (—SiH ₃ ), a substituted or unsubstituted heterocyclic group, an electron-withdrawing group, an electron-donating group, and a substituent containing a heteroatom; R ₁ and R ₂ may be bonded to each other to form a ring; X ₁ is a heteroatom; and A is a group derived from a heterocyclic compound.

In this specification, a compound represented by either formula (I) or (I)' above is also referred to simply as the "compound according to the present invention."

The compounds of the present invention are transparent in their open-ring form (compounds represented by formula (I)), while their closed-ring form (compounds represented by formula (I)') can absorb light across the entire visible range, with the absorption being more uniform. Reversible interconversion between the open-ring form and the closed-ring form occurs only upon irradiation with light.

The compound described in Non-Patent Document 1 has low absorption around 470 nm and is unable to absorb uniformly across the entire visible range. Therefore, if uniform absorption across the entire visible range is required, for example, for anti-glare purposes, it is necessary to mix multiple light-adjusting materials. As a result, when producing anti-glare film, for example, the concentration of the light-adjusting material in the film increases, which can lead to aggregation of the light-adjusting material. This can easily result in color unevenness.

On the other hand, the compound according to the present invention contains a structure with a substituted amino group (the structure on the left side in formulas (I) and (I)'), and therefore can achieve higher absorption in the 400 to 500 nm range compared to the compound described in Non-Patent Document 1. This makes it possible to achieve more uniform absorption across the entire visible range.

In formulas (I) and (I)', the hydrocarbon group may be, for example, a straight-chain, branched-chain, or cyclic hydrocarbon group. From the perspective of further demonstrating the effects of the present invention, the hydrocarbon group is preferably a saturated or unsaturated hydrocarbon group having 1 to 20 carbon atoms, and more preferably a straight-chain or branched-chain alkyl group having 1 to 20 carbon atoms, a straight-chain or branched-chain alkynyl group having 2 to 20 carbon atoms, a straight-chain or branched-chain alkenyl group having 2 to 20 carbon atoms, or an aromatic hydrocarbon group having 6 to 20 carbon atoms.

In formulas (I) and (I)', examples of alkyl groups having 1 to 20 carbon atoms include straight-chain alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-pentadecyl, and n-hexadecyl; isopropyl, isobutyl, sec-butyl, tert-butyl, and isoamyl. Examples of branched-chain alkyl groups include tert-pentyl, neopentyl, 1-methylpentyl, 4-methyl-2-pentyl, 3,3-dimethylbutyl, 2-ethylbutyl, 1-methylhexyl, tert-octyl, 1-methylheptyl, 2-ethylhexyl, 2-propylpentyl, 2,2-dimethylheptyl, 2,6-dimethyl-4-heptyl, 3,5,5-trimethylhexyl, 1-methyldecyl, and 1-hexylheptyl.

In formulas (I) and (I)', examples of alkynyl groups having 2 to 20 carbon atoms include ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl, 3-butynyl, 3-methyl-1-propynyl, 2-methyl-3-propynyl, pentynyl, 1-hexynyl, 3-methyl-1-butynyl, and 3,3-dimethyl-1-butynyl.

In formulas (I) and (I)', examples of alkenyl groups having 2 to 20 carbon atoms include vinyl, allyl, isopropenyl, 1-butenyl, 2-butenyl, 2-methyl-2-propenyl, 1-methyl-2-propenyl, 2-methyl-1-propenyl, pentenyl, 1-hexenyl, and 3,3-dimethyl-1-butenyl.

In formulas (I) and (I)', examples of aromatic hydrocarbon groups having 6 to 20 carbon atoms include phenyl, biphenyl, 1-naphthyl, 2-naphthyl, anthryl, phenanthryl, pyrenyl, naphthacenyl, indenyl, azulenyl, anthracenyl, triphenylenyl, and chrysenyl.

In formulas (I) and (I)', the heterocyclic group may be either an aromatic heterocyclic group having 2 to 20 carbon atoms or a non-aromatic heterocyclic group having 2 to 20 carbon atoms.

Examples of aromatic heterocyclic groups having 2 to 20 carbon atoms include thienyl, furanyl, pyrrolyl, pyrazolyl, imidazolyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, triazolyl, tetrazolyl, triazinyl, benzothienyl, benzimidazolyl, indolyl, isoindolyl, quinolinyl, isoquinolinyl, quinazolinyl, quinoxalinyl, naphthyridinyl, acridinyl, carbazolyl, and dibenzothienyl.

Examples of non-aromatic heterocyclic groups having 2 to 20 carbon atoms include pyrrolidinyl, tetrahydrofuranyl, tetrahydrothienyl, piperidinyl, tetrahydropyranyl, tetrahydrothiopyranyl, dioxanyl, morpholyl, and dioxolanyl.

In formulas (I) and (I)', electron-withdrawing groups, also known as electron-accepting groups, are atomic groups that attract electrons from the substituted atomic group due to the inductive effect or resonance effect in organic electronics. Examples of electron-withdrawing groups include those with a positive value for the Hammett's substituent constant (σp(para)). The Hammett's substituent constant (σp(para)) can be found in the Revised 5th Edition of the Basic Chemistry Handbook (page II-380; edited by the Chemical Society of Japan, Maruzen Co., Ltd.).

Examples of electron-withdrawing groups include halogeno groups (preferably fluoro, chloro, or bromo groups), halogenoalkyl groups (preferably perhalogenoalkyl groups having 1 to 3 carbon atoms), cyano groups, alkoxycarbonyl groups (ester groups), carboxy groups (carboxylic acid groups), carboxylic acid ester groups, carboxylic acid amide groups, sulfo groups (sulfonic acid groups), nitro groups, dicyanoethylene groups, and aldehyde groups.

In formulas (I) and (I)', the electron-donating group is an atomic group that, in organic electronics theory, donates electrons to the substituted atomic group due to the inductive effect or resonance effect. Examples of electron-donating groups include those with a negative value for the Hammett's substituent constant (σp(para)). The Hammett's substituent constant (σp(para)) can be found in the Revised 5th Edition of the Basic Chemistry Handbook (page II-380; edited by the Chemical Society of Japan, Maruzen Co., Ltd.).

Examples of electron-donating groups include alkyl groups (preferably linear or branched alkyl groups having 1 to 4 carbon atoms), aromatic hydrocarbon groups (preferably aromatic hydrocarbon groups having 6 to 10 or 6 to 20 carbon atoms), alkoxy groups (preferably alkoxy groups having 1 to 4 carbon atoms), alkylthio groups (preferably alkylthio groups having 1 to 2 carbon atoms (methylthio groups, ethylthio groups)), aromatic heterocyclic groups (preferably aromatic heterocyclic groups having 2 to 20 carbon atoms), amino groups, amide groups, sulfonamide groups, hydroxyl groups, thiol groups, benzothiazole groups, and indolinyl groups.

Examples of alkoxy groups include linear alkoxy groups such as methoxy, ethoxy, n-propoxy, n-butoxy, n-pentyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy, n-dodecyloxy, n-tridecyloxy, n-tetradecyloxy, n-pentadecyloxy, and n-hexadecyloxy; isopropoxy, tert-butoxy, and 1-methylpentyloxy. Examples of branched-chain alkoxy groups include 4-methyl-2-pentyloxy, 3,3-dimethylbutyloxy, 2-ethylbutyloxy, 1-methylhexyloxy, tert-octyloxy, 1-methylheptyloxy, 2-ethylhexyloxy, 2-propylpentyloxy, 2,2-dimethylheptyloxy, 2,6-dimethyl-4-heptyloxy, 3,5,5-trimethylhexyloxy, 1-methyldecyloxy, and 1-hexylheptyloxy.

Examples of substituents containing a heteroatom include alkoxy groups (preferably alkoxy groups having 1 to 4 carbon atoms), alkylamino groups, alkyl ether groups, hydroxyalkyl groups, alkylthio groups, acyloxy groups, alkylcarboxylic acid ester groups, alkylcarboxylic acid amide groups, N-alkylcarbamoyl groups, N,N-dialkylcarbamoyl groups, alkylsulfonyl groups, halogenated alkyl groups, pyrrolyl groups, pyridyl groups, naphthyl groups, pyrrolidinyl groups, piperidyl groups, perhydroindolyl groups, perhydroisoindolyl groups, perhydroquinolyl groups, perhydroisoquinolyl groups, perhydrocarbazolyl groups, perhydroacridinyl groups, furyl groups, pyranyl groups, perhydrofuryl groups, and thienyl groups.

When the hydrocarbon group, silyl group, and heterocyclic group have a substituent, the introduced substituent is not particularly limited. Examples of the introduced substituent include a halogeno group, an unsubstituted alkyl group, an unsubstituted alkoxy group, and combinations thereof.

In formulas (I) and (I)′, from the viewpoint of being able to further exhibit the effects of the present invention, R ₁ and R ₂ are each independently preferably a substituted or unsubstituted hydrocarbon group, more preferably a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 20 carbon atoms, a substituted or unsubstituted alkenyl group having 2 to 20 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, and even more preferably a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, or a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms.

In a preferred embodiment, from the viewpoint of further exhibiting the effects of the present invention, _R1 and _R2 each independently represent a linear or branched hydrocarbon group, more preferably a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, a substituted or unsubstituted alkynyl group having 2 to 4 carbon atoms, or a substituted or unsubstituted alkenyl group having 2 to 4 carbon atoms, still more preferably a methyl group, ethyl group, n-propyl group, n-butyl group, isopropyl group, isobutyl group, sec-butyl group, or tert-butyl group, and particularly preferably a methyl group.

In a preferred embodiment, from the viewpoint of achieving more uniform absorption of light throughout the entire visible range, _R1 and _R2 are each independently an unsubstituted phenyl group or a phenyl group substituted with an alkyl group having 1 to 4 carbon atoms, more preferably a phenyl group substituted with an alkyl group having 1 to 4 carbon atoms, even more preferably a methylphenyl group or a tert-butylphenyl group, and particularly preferably a tert-butylphenyl group. When the phenyl group is substituted with an alkyl group having 1 to 4 carbon atoms, the position of the substituent may be any of the ortho-position, meta-position, or para-position, and is preferably the para-position.

In formulas (I) and (I)′, _R3 is, from the viewpoint of being able to more effectively exhibit the effects of the present invention, a substituted or unsubstituted hydrocarbon group or a substituted or unsubstituted heterocyclic group, more preferably a substituted or unsubstituted aromatic hydrocarbon group or a substituted or unsubstituted aromatic heterocyclic group, and particularly preferably an unsubstituted hydrocarbon group.

In a preferred embodiment, from the viewpoint of further exhibiting the effects of the present invention, _R3 is a substituted or unsubstituted alkyl group having 1 to 20 carbon atoms, more preferably a substituted or unsubstituted alkyl group having 1 to 4 carbon atoms, still more preferably a methyl group, ethyl group, n-propyl group, n-butyl group, isopropyl group, isobutyl group, sec-butyl group or tert-butyl group, and particularly preferably a methyl group.

In a preferred embodiment, from the viewpoint of red-shifting the absorption spectrum, _R3 is a substituted or unsubstituted aromatic hydrocarbon group having 6 to 20 carbon atoms, more preferably a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, still more preferably a phenyl group, 1-naphthyl group, 2-naphthyl group, anthryl group, phenanthryl group, pyrenyl group, naphthacenyl group, indenyl group, azulenyl group, anthracenyl group, triphenylenyl group, or chrysenyl group, and particularly preferably a phenyl group.

By red-shifting the absorption spectrum, coloring and decoloring can be controlled not only by ultraviolet light but also by infrared light.

In formulas (I) and (I)′, R ₄ is preferably a hydrogen atom, a substituted or unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms, or an electron-withdrawing group, from the viewpoint of being able to more effectively exhibit the effects of the present invention.

In a preferred embodiment, _R4 is an electron-withdrawing group, more preferably a dicyanoethylene group, from the viewpoint of red-shifting the absorption spectrum.

In a preferred embodiment, from the viewpoint of further exhibiting the effects of the present invention, _R4 is a phenyl group or an aldehyde group substituted with an alkoxy group having 1 to 4 carbon atoms, more preferably a methoxyphenyl group or an aldehyde group, and even more preferably an aldehyde group.

In a more preferred embodiment, _R1 and _R2 are each independently a methyl group, a methylphenyl group, or a tert-butylphenyl group, _R3 is a methyl group or a phenyl group, and _R4 is a hydrogen atom, a methoxyphenyl group, a dicyanoethylene group, or an aldehyde group. In this case, _R1 and _R2 are preferably the same substituent.

In formulae (I) and (I)′, X ₁ is a heteroatom, preferably a nitrogen atom.

In formulas (I) and (I)', A is a group derived from a heterocyclic compound. Examples of the heterocyclic compound include heterocyclic compounds having 5 to 14 ring atoms, such as thiophene, thiazole, oxazole, furan, benzothiophene, and benzofuran.

In a preferred embodiment, the compound according to the present invention is a compound represented by either one of the following formulas (I-1) and (I-1)', from the viewpoint of further exhibiting the effects of the present invention.

In each of formulas (I-1) and (I-1)′, R ₁ to R ₄ and X ₁ are as defined above, and X ₂ is a heteroatom.

In a preferred embodiment, _X2 is an oxygen atom, a nitrogen atom or a sulfur atom, more preferably a sulfur atom.

In a more preferred embodiment, the compound according to the present invention is a compound represented by either one of the following formulas (I-2) and (I-2)', from the viewpoint of being able to further exert the effects of the present invention.

In each of formulas (I-2) and (I-2)′, R ₁ to R ₄ are as defined above.

The method for synthesizing the compound according to the present invention is not particularly limited, and any conventionally known synthesis method can be applied. For example, taking Compound 1 of Formula (I), in which _R1 and _R2 are 4-tert-butylphenyl groups, _R3 is a phenyl group, _R4 is a 4-methoxyphenyl group, _X1 is a nitrogen atom, and A is a group derived from thiophene, as an example, Compound 1 can be synthesized according to Scheme 1 below.

In the above Scheme 1, compound 3 and compound 4 can be synthesized according to the method described in S. Lee et al., Org. Lett., 2012, 14, 2238-2241.

In the above Scheme 1, compound 5 can be synthesized according to the method described in F. Sun et al., Tetrahedron, 2003, 59, 7615-7621.

In the above Scheme 1, compound 7 can be synthesized according to the method described in C. L. Dong et al., Org. Lett., 2020, 22, 1076-1080.

In the above Scheme 1, compound 8 can be synthesized according to the method described in P. Ni et al., Org. Lett., 2019, 21, 3518-3522.

In the above Scheme 1, compound 9 can be synthesized, for example, by the following method.

To a reaction solution prepared by dissolving compound 8 in dehydrated toluene, bis(4-tert-butylphenyl)amine, sodium tert-butoxide, tri-tert-butylphosphonium tetrafluoroborate, and tris(dibenzylideneacetone)dipalladium(0) are added and the mixture is refluxed overnight under an argon atmosphere. The reaction solution is extracted with ethyl acetate, and the organic layer is washed, dried, concentrated, and purified to obtain compound 9.

In the above Scheme 1, compound 10 can be synthesized, for example, by the following method.

Compound 9 is dissolved in a dichloromethane/methanol (volume ratio: 5/2) mixed solution, to which calcium carbonate and benzyltrimethylammonium tribromide ( _BTMABr3 ) are added and stirred at room temperature for 30 minutes. The reaction solution is extracted with dichloromethane, and the organic layer is washed, dried, concentrated, and purified to obtain compound 10.

In the above Scheme 1, compound 1 can be synthesized, for example, by the following method.

Under an argon atmosphere, a 1.6 M n-butyllithium hexane solution is slowly added dropwise at -78°C to a reaction solution prepared by dissolving compound 10 in anhydrous tetrahydrofuran. After stirring at that temperature for 30 minutes, a solution of compound 5 dissolved in anhydrous tetrahydrofuran is slowly added dropwise at -78°C. After stirring at that temperature for 1 hour, the temperature is slowly raised to room temperature. Water is added to the reaction solution to quench the reaction. The reaction solution is extracted with ethyl acetate, and the organic layer is washed, dried, concentrated, and purified to obtain compound 1.

Furthermore, taking as an example a compound 1′ of formula (I) in which R ₁ and R ₂ are 4-tert-butylphenyl groups, R ₃ is a methyl group, R ₄ is a 4-methoxyphenyl group, X ₁ is a nitrogen atom, and A is a group derived from thiophene, the compound can be synthesized according to the following scheme 2.

In Scheme 2 above, compounds 3-5, 9, 10, and 1' can be synthesized in the same manner as in Scheme 1 above.

In the above Scheme 2, compound 7 can be synthesized according to the method described in X. Song et al., Org. Lett., 2017, 19, 6542-6545.

The compounds according to the present invention are suitable as light-controlling materials because they can absorb light more uniformly across the entire visible spectrum. They can be used in particular in applications where absorption across the entire visible spectrum is required, such as anti-glare applications, and in applications where black color development is required.

Accordingly, one embodiment of the present invention is a photochromic material containing the compound of the present invention. The photochromic material may be in liquid or solid form.

When the light-modulating material is in a liquid form, it can be a solution in which the compound of the present invention is dissolved in a solvent. There are no particular restrictions on the solvent, as long as it is colorless and can dissolve the compound of the present invention. Examples of solvents include organic solvents, supercritical solvents, ionic liquids, and mixtures thereof.

When the light-modulating material is solid, the compound according to the present invention is dispersed in a solid matrix. Examples of solid matrices include crystalline solids or glassy (amorphous) solids, liquid crystals, and gels. Components of the solid matrix include organic or inorganic low-molecular-weight compounds and organic or inorganic polymer compounds. For example, when providing anti-glare protection against light incident from a light source located outside (in front of) a moving body (vehicle), examples of the matrix include glassy (amorphous) solids and polymer matrices containing organic polymers. Solid light-modulating materials can be used as glass, films, etc.

The present invention will be described in more detail below using examples. However, the technical scope of the present invention is not limited to the following examples.

(Synthesis of Compound 1)
Compound 1 was synthesized according to Scheme 1 shown below.

Compound 2 (2-methylthiophene) and compound 6 (5-bromoindole) were purchased from Tokyo Chemical Industry Co., Ltd. Compounds 3 to 5, 7, and 8 were synthesized according to the following literature:
Compounds 3 and 4: S. Lee, Y. You, K. Ohkubo, S. Fukuzumi and W. Nam, Org. Lett., 2012, 14, 2238-2241;
Compound 5: F. Sun, F. Zhang, H. Guo, X. Zhou, R. Wang and F. Zhao, Tetrahedron, 2003, 59, 7615-7621;
Compound 7: CL Dong, X. Ding, L.-Q. Huang, Y.-H. He and Z. Guan, Org. Lett., 2020, 22, 1076-1080;
Compound 8: P. Ni, J. Tan, W. Zhao, H. Huang, F. Xiao and G.-J. Deng, Org. Lett., 2019, 21, 3518-3522.

Synthesis of Compound 9

To a reaction solution prepared by dissolving compound 8 (2.0 g, 7.0 mmol) in dehydrated toluene (36 mL), bis(4-tert-butylphenyl)amine (3.04 g, 10.8 mmol), sodium tert-butoxide (1.35 g, 14.0 mmol), tri-tert-butylphosphonium tetrafluoroborate (202 mg, 10 mol%), and tris(dibenzylideneacetone)dipalladium(0) (81 mg, 88 μmol) were added, and the mixture was refluxed overnight under an argon atmosphere. The reaction solution was returned to room temperature, and the progress of the reaction was confirmed by TLC. The solution was extracted with ethyl acetate, and the organic layer was washed with brine. The organic layer was dried over anhydrous sodium sulfate, concentrated under reduced pressure, and then purified by silica gel column chromatography (hexane:dichloromethane = 4:1 (volume ratio)) to obtain compound 9 as a white solid (yield: 2.1 g, 62%).
¹ H NMR (400 MHz, CD ₂ Cl ₂ )δ: 7.42-7.52 (m, 4H), 7.36-7.41 (m, 1H), 7.27-7.35 (m, 2H), 7.20 (d, J = 8 Hz, 2H), 7.02 (d, J = 8 Hz, 1H), 6.93 (d, J = 8 Hz, 2H), 6.42 (s, 1H), 3.71 (s, 3H), 1.27 (s, 18H); MS (MALDI) m/z = 487.42 [M+H] ⁺ (Exact Mass: 486.30).

NMR measurements were performed by dissolving 3-5 mg of the synthesized compound in 1 mL of a deuterated solvent (deuterated chloroform or deuterated dichloromethane) using a JNMEX400 NMR spectrometer (manufactured by JEOL Ltd., magnetic field: 400 MHz).

Synthesis of Compound 10

Compound 9 (1.7 g, 3.5 mmol) was dissolved in a dichloromethane/methanol (volume ratio: 5/2) mixed solution (17.5 mL) to prepare a reaction solution. Calcium carbonate (1.0 g, 10.0 mmol) and benzyltrimethylammonium tribromide (BTMABr ₃ ) (1.5 g, 3.85 mmol) were added and the mixture was stirred at room temperature for 30 minutes. After confirming the progress of the reaction by TLC, the solution was extracted with dichloromethane, and the organic layer was washed with a 2N aqueous hydrochloric acid solution. The organic layer was dried over anhydrous sodium sulfate, concentrated under reduced pressure, and then purified by silica gel column chromatography (hexane:dichloromethane=4:1 (volume ratio)) to obtain compound 10 as a white solid (yield: 2.0 g, quantitative yield).
¹ H NMR (400 MHz, DMSO-d6)δ: 7.48-7.56 (m, 6H), 7.23 (d, J = 8 Hz, 4H), 7.06 (s, 1H), 6.98 (d, J = 8 Hz, 1H), 6.85 (d, J = 8 Hz, 4H), 3.62 (s, 3H), 1.22 (s, 18H); MS (MALDI) m/z = 564.67 [M] ⁺ (Exact Mass: 564.21).

Synthesis of Compound 1

To a reaction solution prepared by dissolving compound 10 (1.0 g, 1.77 mmol) in anhydrous tetrahydrofuran (17 mL), a 1.6 M n-butyllithium hexane solution (1.3 mL, 2.1 mmol) was slowly added dropwise at −78°C under an argon atmosphere. After stirring at that temperature for 30 minutes, a solution of compound 5 (860 mg, 2.2 mmol) in anhydrous tetrahydrofuran (5 mL) was slowly added dropwise at −78°C. After stirring at that temperature for 1 hour, the temperature was slowly raised to room temperature. After confirming the progress of the reaction by TLC, water was added to the solution to quench the reaction. The solution was extracted with ethyl acetate, and the organic layer was washed with 2N aqueous hydrochloric acid and brine. The organic layer was dried over anhydrous sodium sulfate, concentrated under reduced pressure, and then purified by silica gel column chromatography (hexane:dichloromethane = 4:1 (volume ratio)) to obtain compound 1 as a pale yellow solid (yield: 1.0 g, 66%).
¹ H NMR (400 MHz, CD ₂ Cl ₂ )δ: 7.29 (t, J = 8 Hz, 2H), 7.15-7.26 (m, 10H), 6.91-6.97 (m, 5H), 6.87 (d, J = 8 Hz, 2H), 6.02 (s, 1H), 3.81 (s, 3H), 3.52 (s, 3H), 1.67 (s, 3H), 1.29 (s, 18H); MS (MALDI) m/z = 863.59 [M+H] ⁺ (Exact Mass: 862.34).

(Synthesis of Compound 1′)
Compound 1' was synthesized according to Scheme 2 shown below.

Compound 2 (2-methylthiophene) and compound 6 (2-methyl-5-chloroindole) were purchased from Tokyo Chemical Industry Co., Ltd. Compounds 3 to 5 and 7 were synthesized according to the following literature:
Compounds 3 and 4: S. Lee, Y. You, K. Ohkubo, S. Fukuzumi and W. Nam, Org. Lett., 2012, 14, 2238-2241;
Compound 5: F. Sun, F. Zhang, H. Guo, X. Zhou, R. Wang and F. Zhao, Tetrahedron, 2003, 59, 7615-7621;
Compound 7: X. Song, C. Xu, D. Du, Z. Zhao, D. Zhu and M. Wang, Org. Lett., 2017, 19, 6542-6545.

Synthesis of Compound 8

To a reaction solution prepared by dissolving compound 7 (1.0 g, 5.6 mmol) in dehydrated toluene (28 mL), bis(4-tert-butylphenyl)amine (2.4 g, 8.5 mmol), sodium tert-butoxide (1.07 g, 11.1 mmol), tri-tert-butylphosphonium tetrafluoroborate (161 mg, 10 mol%), and tris(dibenzylideneacetone)dipalladium(0) (64 mg, 2 mol%) were added, and the mixture was refluxed overnight under an argon atmosphere. The reaction solution was returned to room temperature, and the progress of the reaction was confirmed by TLC. The solution was extracted with ethyl acetate, and the organic layer was washed with brine. The organic layer was dried over anhydrous sodium sulfate, concentrated under reduced pressure, and then purified by silica gel column chromatography (hexane:dichloromethane = 4:1 (volume ratio)) to obtain compound 8 as a white solid (yield: 1.6 g, 68%).
¹ H NMR (400 MHz, CDCl ₃ )δ: 7.18-7. 21 (d, J = 8 Hz, 1H), 7.13-7.18 (m, 5H), 6.86-6.92 (m, 5H), 6.12 (brs, 1H), 3.60 (s, 3H), 2.36 (s, 3H), 1.25 (s, 18H); MS (MALDI) m/z = 425.64 [M+H] ⁺ (Exact Mass: 424.29).

Synthesis of Compound 9 Compound 8 (300 mg, 0.7 mmol) was dissolved in a dichloromethane/methanol (volume ratio: 5/2) mixed solution (3.5 mL) to prepare a reaction solution. Calcium carbonate (200 mg, 2.0 mmol) and benzyltrimethylammonium tribromide (BTMABr ₃ ) (300 mg, 0.78 mmol) were added and the mixture was stirred at room temperature for 30 minutes. After confirming the progress of the reaction by TLC, the solution was extracted with dichloromethane, and the organic layer was washed with a 2N aqueous hydrochloric acid solution. The organic layer was dried over anhydrous sodium sulfate, concentrated under reduced pressure, and then purified by silica gel column chromatography (hexane:dichloromethane=4:1) to obtain Compound 9 as a white solid (yield: 360 mg, quantitative yield).
¹ H NMR (400 MHz, CDCl ₃ )δ: 7.19 (d, J = 8 Hz, 6H), 6.85-7.02 (m, 4H), 3.64 (brs, 3H), 2.38 (s, 3H), 1.27 (s, 18H); MS (MALDI) m/z = 502.14 [M] ⁺ (Exact Mass: 502.20).

Synthesis of Compound 1'

To a reaction solution prepared by dissolving compound 9 (2.0 g, 4.0 mmol) in anhydrous tetrahydrofuran (35 mL), a 1.6 M n-butyllithium hexane solution (3.0 mL, 4.8 mmol) was slowly added dropwise at −78°C under an argon atmosphere. After stirring at that temperature for 30 minutes, a solution of compound 5 (2.0 g, 5.0 mmol) in anhydrous tetrahydrofuran (5 mL) was slowly added dropwise at −78°C. After stirring at that temperature for 1 hour, the mixture was slowly warmed to room temperature. After confirming the progress of the reaction by TLC, water was added to the solution to quench the reaction. The mixture was extracted with ethyl acetate, and the organic layer was washed with 2N aqueous hydrochloric acid and brine. The organic layer was dried over anhydrous sodium sulfate, concentrated under reduced pressure, and then purified by silica gel column chromatography (hexane:dichloromethane = 3:1 (volume ratio)) to obtain compound 1' as a pale yellow solid (yield: 1.8 g, 54%).
¹ H NMR (400 MHz, CD ₂ Cl ₂ )δ: 7.27-7.33 (m, 3H), 7.04-7.26 (m, 10H), 6.88 (d, J = 8 Hz, 2H), 6.82 (s, 1H), 3.83 (s, 3H), 3.58 (s, 3H), 1.97 (s, 3H), 1.71 (s, 3H), 1.28 (s, 18H); MS (MALDI) m/z = 801.45 [M+H] ⁺ (Exact Mass: 800.32).

(Example 1: Measurement of visible light absorptance)
10 μg of Compound 1′ was dissolved in 3 mL of tetrahydrofuran, and the absorption spectrum was measured using an ultraviolet-visible spectrophotometer (U-3310, manufactured by Hitachi High-Tech Science Co., Ltd.) The results are shown in FIG.

In Figure 1, UV shows the absorption spectrum of the closed-ring form after 30 seconds of irradiation with 365 nm light, and Vis shows the absorption spectrum of the open-ring form after 3 minutes of irradiation with 650 nm light.

As shown in Figure 1, compound 1' is transparent in its open-ring form, and can absorb light across the entire visible range in its closed-ring form.

The visible light absorptance was calculated from the absorption spectrum. Specifically, the maximum absorbance in the visible range (λ = 400 to 700 nm) was defined as A _max , and the area occupied by the horizontal axis and A _max in the visible range was defined as 100%. The visible light absorptance was calculated as the ratio of the area of the absorption spectrum of the closed-ring isomer in the visible range. The results are shown in Table 1.

In Table 1, the visible light absorptance of the comparative compounds was calculated from the absorption spectrum (the absorption spectrum with the highest peak at 583 nm) in Fig. 3(A) of Non-Patent Document 1 (C. Zheng et al., Dyes and Pigments, 2013, vol. 98, pp. 565-574).

As shown in Table 1, the closed-ring form of compound 1' exhibits a broader (more uniform) absorption spectrum in the visible range and a higher visible light absorptance than the comparative compound.

(Example 2: Calculation of visible light absorption rate)

The absorption spectra of Compounds A to C were calculated using Gaussian 16 (Gaussian Corporation) (Compound B has the same structure as the closed ring form of Compound 1):
Geo-opt: TD-DFT
UV-Vis Spectra: CAM-B3LYP
Excited states: 10singlets
Medium: Vacuum.

Furthermore, the visible light absorptance was calculated from the absorption spectrum in the same manner as in Example 1. The results are shown in Figure 2 and Table 2.

As shown in Figure 2 and Table 2, compounds A to C have improved absorption peak intensity on the short wavelength side of visible light and are able to absorb broadly across the entire visible light range.

(Example 3: Measurement of absorption spectrum)
The absorption spectrum of Compound 1 was measured in the same manner as in Example 1. The results are shown in Figure 3 together with the absorption spectrum of Compound 1'.

3, when _R3 of the compound according to the present invention is a phenyl group, it is possible to absorb broadly the entire visible light range and also to red-shift the absorption spectrum, which indicates that the coloring and decoloring of Compound 1 can be controlled not only by ultraviolet light but also by infrared light.

(Example 4: Calculation of absorption spectrum)

The absorption spectra of compounds D and E were calculated using Gaussian 16 (Gaussian) in the same manner as in Example 2. The results are shown in Figure 4.

4, the compound according to the present invention can absorb broadly the entire visible light range and also has a red-shifted absorption spectrum because _R4 of the compound is an electron-withdrawing group (dicyanoethylene). This shows that the coloring and decoloring of compound E can be controlled not only by ultraviolet light but also by infrared light.

(Example 5: Calculation of absorption spectrum)

The absorption spectrum of Compound F was calculated using Gaussian 16 (Gaussian) in the same manner as in Example 2. The results are shown in Figure 4.

Furthermore, in the same manner as in Example 1, the visible light absorptance was calculated from the absorption spectra of compounds E and F. The results are shown in Table 3.

As shown in FIG. 4 and Table 3, when R ₄ of the compound according to the present invention is an aldehyde group, compound F has a broader absorption spectrum in the visible range and exhibits a higher visible light absorptance.

Claims (6)

A compound represented by any one of the following formulas (I-2) and (I-2)′:

In each of formulas (I-2) and (I-2)′,
R ₁ and R ₂ each independently represent a phenyl group substituted with an alkyl group having 1 to 4 carbon atoms or an unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms;
_R3 is an unsubstituted alkyl group having 1 to 4 carbon atoms or an unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms;
_R4 is a phenyl group substituted with an alkoxy group having 1 to 4 carbon atoms . The compound according to claim 1, wherein _R3 is an unsubstituted aromatic hydrocarbon group having 6 to 10 carbon atoms. The compound according to claim 1 or 2, wherein _R3 is a phenyl group, a 1-naphthyl group, a 2-naphthyl group , an indenyl group, or an azulenyl group . The compound according to any one of claims 1 to 3, wherein _R3 is a phenyl group. The compound according to any one of claims 1 to 4, wherein R ₁ and R ₂ are phenyl groups substituted with alkyl groups having 1 to 4 carbon atoms. The compound according to claim 1, wherein R ₁ and R ₂ are tert -butylphenyl groups, R ₃ is a methyl group or a phenyl group, and R ₄ is a methoxyphenyl group .