JP2000087024A - Photochromic crystal material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material exhibiting photochromic reactivity in a crystalline state and excellent in heat stability, durability, sensitivity and the like by composing it of a molecular crystal of a derivative of bis(2-methyl-1-benzothiophen-3- yl)perfluorocyclopentene. SOLUTION: This material is composed of a molecular crystal of a compound represented by formula I. In formula I, R1-2 are each NO2, CN, amide, sulfonic acid, carboxyl, an acyl, an ester or an alkyl and the number of carbon atoms in the acyl, the ester and the alkyl is desirably 1-4. Preferably, the compound of formula I is bis(2-methyl-6-nitro-1-benzothiophen-3-yl)benzofluorocyclopentene (a compound of formula II). This photochromic material changes its color reversibly in a crystalline state by the action of light. For example, on irradiation of ultraviolet rays on the crystal (colorless) of a compound of formula II, it turns green, and on irradiation of a visible ray, the green color fades to return to the original colorless state.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a novel photochromic material comprising a compound which exhibits photochromic reactivity in a crystalline state.

[0002]

2. Description of the Related Art A photochromic material is a material containing molecules or molecular aggregates that reversibly generate isomers having different colors by the action of light. This photochromic material reversibly changes not only color but also various physical properties such as refractive index, dielectric constant and oxidation / reduction potential by light irradiation.
It is expected to be applied to optical functional materials, particularly optical memories, optical switches, and optical elements.

[0003] Conventional photochromic molecules or molecular aggregates can only function when dissolved in a medium (molecule-dispersed state). Therefore, when used in a solid state, they are dispersed on a polymer film or the like. I needed to. However, when dispersed in a polymer film, the photochromic reactivity is reduced, the durability is poor, and it is difficult to increase the sensitivity by increasing the dispersion concentration because the solubility is limited, such as in use. There was a problem.
When the molecules are dispersed in a polymer, the polarization characteristics of the molecules are lost.

It is expected that these problems will be solved if a material that exhibits photochromic reactivity in a crystalline state can be obtained. However, photochromic crystal materials suitable for this are hardly found. For example, as a molecule that undergoes a photochromic reaction in a crystalline state, a dithienyl perfluorocyclopentene derivative has been reported by the present inventors (Irie et al., Molecular Crystal
Liquid Crystal, Vol. 8, p. 297 (1997
Year) (M. Irie, et. Al, Mol. Cryst. Liq. Cryst. 81
(1997) 297), this dithienyl perfluorocyclopentene derivative is colored red or blue by irradiation with ultraviolet light, and returns to its original state by irradiation with visible light. However, when this coloring was observed using polarized light, no change in the color tone itself was recognized, and only the intensity of the red or blue coloring changed. It is also described that bisbenzothienyl perfluorocyclopentene exhibits photochromic reactivity in a solution and has high repetition durability, but does not exhibit photochromic reactivity in a crystalline state.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and has as its object to exhibit photochromic reactivity in a crystalline state, and to improve heat stability, durability, sensitivity, and the like. An object of the present invention is to provide a photochromic material which is excellent and is suitable for being used as various optical functional devices such as a polarizing element, an optical memory, and an optical switch.

[0006]

According to the present invention, there is provided a photochromic material comprising a molecular crystal of a compound represented by the following general formula (1) to achieve the above object. Is done.

[0007]

Embedded image

Here, in the formula (1), R ¹ and R ² are
Each independently represents a nitro group, a cyano group, an amide group, a sulfonic acid group, a carboxyl group, an acyl group, an ester group or an alkyl group. That is, R ¹ and R
² represents the same or different functional groups selected from these functional groups. The acyl group, ester group or alkyl group generally has 1 to 4 carbon atoms.

A particularly preferred example of the compound of the formula (1) constituting the molecular crystal photochromic material of the present invention is bis (2-methyl-6-nitro-1) represented by the following formula (2).
-Benzothiophen-3-yl) perfluorocyclopentene.

[0010]

Embedded image

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The compound of the above formula (1) used in the present invention has been reported previously (Hanazawa et al., Journal Chemical Society Chemical Communication,
Page 206 (1992): M. Hanazawa et al. J. Ch.
em. Soc. Chem. Commun. (1992) 206)
Methyl-1-benzothiophen-3-yl) perfluorocyclopentene derivative. When this bis (2-methyl-1-benzothiophen-3-yl) perfluorocyclopentene is dispersed in a solution such as hexane or a polymer medium such as polystyrene, the bis (2-methyl-1-benzothiophen-3-yl) turns red by irradiation with ultraviolet light, and becomes visible light. It shows photochromic reactivity to return to the original colorless state by irradiation. This compound has a feature that it has excellent repetition durability as compared with diarylethene having an aryl group having a thiophene ring (Irie et al., Britain Chemical Society Japan, vol. 71, p. 958 (1998): M. Irie, B
ull. Chem. Soc. Jpn, 71 (1998) 985). However, this compound shows no photochromic reactivity in a crystalline state.

The present inventors have surprisingly found that by introducing a somewhat bulky (bulky) substituent into such a benzothiophene ring of the bisbenzothienyl perfluorocyclopentene structure, the photochromic reactivity can be improved even in a crystalline state. Was found to be expressed.

Although the reason why a photochromic phenomenon is observed in a crystalline state by introducing a specific substituent into a bisbenzothienyl perfluorocyclopentene structure according to the present invention has not yet been completely elucidated, one possibility is as follows. Since the presence of the substituent provides free space in which the benzothiophene ring can rotate, it is considered that an isomer capable of exhibiting photochromic properties is reversibly generated.

That is, bisbenzothienyl perfluorocyclopentene as the object of the present invention is packed with two benzothiophene rings standing before light irradiation (left side in FIG. 1). When irradiated (usually with ultraviolet light), the benzophenone ring rotates to form an isomer having a planar structure (right side in FIG. 1), causing a color change, and light of another wavelength (usually visible light). ) Will return to the original state, but at this time, if there is no substituent on the benzophenone ring, there will be no free space for rotation and no photochromic phenomenon will occur (solution state or polymer medium). When dispersed at a low concentration, it is understood that rotation of the benzophenone ring becomes possible even without a substituent and photochromic reactivity occurs). It is presumed that each of the substituents as defined above in formula (1) representing the compound of the present invention has a size that provides such a free space that allows such rotation of the benzophenone ring.

The photochromic material of the present invention reversibly changes color in the crystalline state by the action of light. For example, a crystal (colorless) of bis (2-methyl-6-nitro-1-benzothiophen-3-yl) perfluorocyclopentene of the formula (2) is colored green when irradiated with ultraviolet light, and is colored when irradiated with visible light. This shows a photochromic behavior in which the green color disappears and returns to the original colorless state. Thus,
The photoromic material of the present invention can be applied to an optical memory, an optical switch, and the like based on such photochromic reactivity.

Further, it has been found that the photochromic material of the present invention has a very specific property of exhibiting polychromaticity under the observation of polarized light. For example, when observing a green crystal obtained by irradiating bis (2-methyl-6-nitro-1-benzothiophen-3-yl) perfluorocyclopentene of the formula (2) with ultraviolet light under polarized light (linearly polarized light),
It has been recognized that when the angle between the polarized light and the crystal axis becomes a specific angle, the color becomes yellow, and when the light is further turned 90 degrees from that position, the color becomes blue. Based on the fact that a plurality of distinctly different color tones can be obtained from a single crystal, the photochromic material of the present invention can be applied as an image element of a display, in addition to an optical memory and an optical switch.

Further, it should be noted that a reversible polarizer (polarizing element) can be obtained from the photochromic material of the present invention based on this phenomenon. For example, bis (2-methyl-6-nitro-1-benzothiophene-3)
-Il) Perfluorocyclopentene crystals do not have polarization characteristics in the wavelength region of 550 to 650 nm (do not convert natural light into polarized light) before ultraviolet irradiation, but become a polarizing element in this wavelength region when irradiated with ultraviolet light. That is, the photochromic material of the present invention has a function as a reversible polarizer that becomes a polarizer only when necessary.

The photochromic material of the present invention has a high sensitivity because it causes a photochromic reaction in a crystalline state, and is the only compound known to exhibit crystal photochromic reactivity in durability and thermal stability due to repeated light irradiation. Than diarylperfluorocyclopentene having a thiophene ring as an aryl group.
This is presumably because the photochromic material of the present invention has a diolylethene structure having a benzothiophene ring as an aryl group.

The compound of the above formula (1) constituting the photochromic material of the present invention can be synthesized relatively easily by devising a known reaction, and generally, bis (2-methyl-1) -Benzothiophen-3-yl) perfluorocyclopentene by nitration, cyanation, sulfonation, formylation, or acetylation to introduce a desired substituent. The position at which the substituent is introduced is generally at position 6 because of high reactivity, but is not limited thereto. In addition, bis (2-methyl-1-benzothiophen-3-yl) perfluorocyclopentene can be prepared by brominating and lithiating the 3-position of 2-methylbenzothiophene, and performing a coupling reaction with perfluorocyclopentene. .

The compound of the formula (1) synthesized as described above is dissolved in a suitable solvent (for example, hexane, benzene, toluene or a mixed solvent thereof), and the solvent is gradually evaporated to obtain the desired molecule. A crystal (single crystal) is obtained. It has been confirmed by microscope observation that the crystals constituting the photochromic material of the present invention are generally colorless thin plate-like crystals (for example, rhombic crystals).

[0021]

EXAMPLE 1 Examples will be shown below to further clarify the features of the present invention, but the present invention is not limited by these examples. Example 1 Synthesis of Photochromic Material Compound Bis (2-methyl-6-nitro-1-benzothiophen-3-yl) perfluorocyclopentene represented by the above formula (2) was synthesized as follows. 1,2-bis (2-
Methylbenzothiophen-3-yl) perfluorocyclopentene (3.0 g; 6.4 mmol) was placed in a 200 mL eggplant-shaped flask, and 60 mL of acetic acid and 5 mL of acetic anhydride were added.
And cooled to 10 ° C. While keeping the temperature constant, 3 mL of fuming nitric acid was slowly added, and the mixture was returned to room temperature and stirred overnight. The reaction was stopped by slow addition of cold water and NaOH
The mixture was neutralized with an aqueous solution, extracted with ethyl acetate, washed with water, washed with an aqueous solution of sodium hydrogen carbonate, and dried over anhydrous magnesium sulfate. The solvent was distilled off, and the mixture was developed and separated by silica gel column chromatography (hexane: ethyl acetate = 4: 1). Recrystallization from hexane gave 2.1 g of pale yellow crystals (yield: 58%). Identification data: Melting point: 200-201 ° C. NMR analysis: ¹ H-NMR (200 MHz, CDCl ₃ ,
TMS): δ = 2.32, 2.58 (s, 6H, CH 3), 7.60-8.66
(m, 6H, Ar). Mass spec: m / z 558 (M ⁺ ). Calcd (as _{C 23 H 12 F 6 N 2} O 4 S 2)
C (49.47), H (2.17), N (5.02);
59), H (2.15), N (4.97).

Example 2 Photochromic Reactivity Test Bis (2-methyl-6-nitro-1-benzothiophen-3-yl) perfluorocyclopentene synthesized in Example 1 was converted to hexane / toluene (1/1 vol.).
%) And concentrated by gradually evaporating the solvent to precipitate solid crystals. Microscopic observation of the precipitated colorless crystals revealed that they formed rhombuses with apex angles of 80 ° and 100 °. When this crystal was irradiated with ultraviolet light (350 nm <λ <400 nm), the color of the crystal changed from colorless to green. This green color was stable and did not fade as long as it was stored in a dark place, and did not disappear even when the temperature was raised to 100 ° C. However, visible light (λ
(> 450 nm), fading easily. This coloring / fading by irradiation with ultraviolet / visible light could be repeated 100,000 times (see FIG. 2).

When the (010) plane of the crystal colored green by irradiation with ultraviolet light was observed under polarized light (linearly polarized light), the spectrum shown in FIG. 3 was obtained. That is, it was recognized that the color turned yellow at a specific angle and turned blue when rotated 90 degrees from that angle. The blue orientation coefficient at 600 nm (A ₁ −A ₂ ) / (A ₁ +2)
When A ₂ ) was measured, a very high value of 0.90 was obtained. For this reason, the crystal does not have polarization characteristics before ultraviolet light irradiation in a wavelength region near 600 nm (550 to 650 nm), but when irradiated with ultraviolet light,
It has been found that it functions as a polarizing element in this wavelength region. The orientation coefficient at 460 nm is 0.40.
And it was also recognized that in this wavelength region, it did not substantially function as a reversible polarizer. A ₁ that defines the orientation coefficient indicates the absorbance at the angle at which the blue color was most strongly observed, and A ₂ indicates the absorbance when rotated 90 degrees from that angle.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a state in which a compound constituting a photochromic material of the present invention reversibly generates an isomer by the action of light.

FIG. 2 As an example of a compound constituting the photochromic material of the present invention, bis (2-methyl-6-nitro-1-benzothiophen-3-yl) perfluorocyclopentene isomer isomerically reversible by ultraviolet light and visible light. FIG.

FIG. 3 shows an example of the photochromic material of the present invention, bis (2-methyl-6-nitro-1-benzothiophene-
3 shows an absorption spectrum of 3- (yl) perfluorocyclopentene crystal under polarized light.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // G02B 5/23 G02B 5/23

Claims (2)

[Claims] 1. A photochromic material comprising a molecular crystal of a compound represented by the following general formula (1). Embedded image (In the formula (1), R ¹ and R ² are each independently
Represents a nitro group, a cyano group, an amide group, a sulfonic acid group, a carboxyl group, an acyl group, an ester group or an alkyl group. ) 2. The method according to claim 1, wherein the compound is bis (2-methyl-6-
2. The photochromic material according to claim 1, wherein the photochromic material is nitro-1-benzothiophen-3-yl) benzofluorocyclopentene.