JP2009062477A - Photoresponsive ionic liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a novel ionic liquid, in which a photochromic compound is introduced into a molecular structure. <P>SOLUTION: The ionic liquid, in which the photochromic compound is introduced into the molecular structure, has physical properties varied by photoirradiation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an ionic liquid in which a predetermined compound is introduced into a molecular structure.

An ionic liquid is a salt that exhibits a liquid state near room temperature, and is expected to be applied as a liquid having non-volatility, incombustibility, high thermal stability, high ionic conductivity, and electrolysis resistance. For example, the present inventors have proposed to use an ionic liquid having high proton conductivity as a proton exchanger for a fuel cell (see, for example, Patent Document 1).
On the other hand, photochromic compounds in which the absorption band is reversibly changed by light and isomerized are conventionally known. For example, in the case of a photochromic compound whose absorption spectrum changes in the visible light band, the color changes depending on the light, so that it is used for various optical materials.

International Patent Publication No. 03/83981 Pamphlet

However, most of the photochromic compounds are solids, and in order to cause a photochromic reaction, it is necessary to form a solution or dilute in a medium such as a polymer, and there is a problem that applications and use conditions are limited.
On the other hand, as a method for imparting new characteristics to the ionic liquid, it is conceivable to introduce another compound into the molecular structure of the ionic liquid.
Accordingly, an object of the present invention is to provide a novel ionic liquid in which a compound is introduced into a molecular structure.

The present inventors have found that physical properties are changed by light irradiation by introducing a photochromic compound into the molecular structure of an ionic liquid. This is presumably because the physical properties of the introduced photochromic compound were changed by light irradiation.
That is, the photoresponsive ionic liquid of the present invention is an ionic liquid in which a photochromic compound is introduced into a molecular structure, and its physical properties are changed by light irradiation.

When the photoresponsive ionic liquid is used as an ionic conductor of an electric double layer capacitor, the amount of charge charged in the capacitor by light irradiation may change.
This is considered because the photoresponsive ionic liquid was photoisomerized by light irradiation.

  According to the present invention, physical properties can be changed by light irradiation by introducing a photochromic compound into the molecular structure of an ionic liquid.

  Hereinafter, embodiments of the present invention will be described. The photoresponsive ionic liquid according to the present invention is obtained by introducing a photochromic compound into the molecular structure of the ionic liquid.

<Ionic liquid>
An ionic liquid (ionic liquid) is composed only of ions, is a liquid, has no vapor pressure (nonvolatile), has high heat resistance, has nonflammability, and nonvolatility. In the present invention, the melting point of the ionic liquid is preferably 100 ° C. or lower, more preferably room temperature or lower.
Although an ionic liquid is not specifically limited, For example, what is shown in Table 1 described in the said patent document 1 can be used. In Table 1, B ⁺ is a cation, X ⁻ is an anion, and an ionic liquid is composed of B ⁺ and X ⁻ . As shown in Table 1, the ionic liquid mainly includes imidazolium, pyridinium, quaternary ammonium, and phosphonium.
Moreover, EMITFSI (name) described in the international publication 2006/117997 pamphlet can be used as an ionic liquid.

<Photochromic compound>
A photochromic compound is a compound that reversibly changes its absorption band by light and isomerizes. When the absorption spectrum changes in the visible light band, the color tone changes depending on the light.
The photochromic compound is not particularly limited. Chromenes can be used.
Specific examples of the photochromic compound are described in, for example, JP-A-2-28154, JP-A-62-288830, WO94 / 22850, WO96 / 14596, and the like. The thing that is.
Moreover, the thing of the international publication 2006/95705 pamphlet can be used as a photochromic compound.

FIG. 1 shows an example of a structural change caused by light of a photochromic compound that can be used in the present invention. Since photochromic compounds are isomerized by light and the molecular structure changes, not only the above-mentioned change in color tone but also the dielectric properties (dipole moment, dielectric constant) change. For example, in the case of azobenzene, the trans-type dipole moment is 0.5 D (Debye; 0.5D = 1.668 × 10 ⁻³⁰ C · m), and the cis-type dipole moment is 3.1 D (= 1.034 × 10 ⁻²⁹ C).・ Change to m).

<Introduction of photochromic compound into ionic liquid>
By introducing the photochromic compound into the molecular structure of the ionic liquid, the ionic liquid is imparted with characteristics such as non-volatility, incombustibility, high thermal stability, high ionic conductivity, and electrolysis resistance to the photochromic compound. Depending on the characteristics, completely new characteristics can be imparted to the introduced ionic liquid.
The method for introducing the photochromic compound into the molecular structure of the ionic liquid is not particularly limited, and the photochromic compound can be chemically bonded to any part of the molecular structure of the ionic liquid by a known organic synthesis method. As such a method,
For example, a known organic synthesis method using the nucleophilicity of an ionic liquid, or a salt (ionic liquid) having photoresponsive performance can be synthesized by introducing a photochromic compound into an acid or base and neutralizing it. Can be mentioned.

  When an ionic liquid (photoresponsive ionic liquid) into which a photochromic compound is introduced is used as an ionic conductor of an electric double layer capacitor, the amount of charge charged in the capacitor is changed by light irradiation. This is considered to be caused by the change in molecular properties (shape, dipole moment, ionic conductivity, dielectric constant, etc.) of the photochromic compound due to light irradiation as described above. Conventionally, since a photochromic compound is a solid, in order to cause a photochromic reaction, it is generally necessary to dilute it in a solvent or a polymer, and when the solvent does not have conductivity, the ion conduction of the electric double layer capacitor It could not be used as a body. On the other hand, since the photoresponsive ionic liquid has conductivity which is a characteristic of the ionic liquid, it can be used as an ionic conductor of an electric double layer capacitor, and the molecular characteristics of the introduced photochromic compound portion change by light irradiation, A new characteristic of a change in the charge amount is generated.

  By using the above characteristics, an electric double layer capacitor using the photoresponsive ionic liquid of the present invention can be manufactured. On the other hand, it is known that the displacement of an actuator using an ionic liquid gel is related to the electric double layer capacity. It has been reported that when the applied voltage is changed to change the structure of the ionic liquid, the electric double layer capacity changes and is displaced by the structure change. Therefore, it is considered that by irradiating the photoresponsive ionic liquid of the present invention with light, the structural change of the photochromic compound portion is superimposed and the amount of displacement increases, which is advantageous as an actuator. In addition, it is considered that the amount of displacement can be changed by two methods of voltage application and light irradiation.

According to the photoresponsive ionic liquid of the present invention, in addition to the change in the charge amount of the electric double layer capacitor due to the above-described light irradiation, the characteristics due to the isomerization (change in molecular structure) of the introduced photochromic compound portion are optically reflected. It can be changed by irradiation. Such characteristics include a change in solubility in a solvent, a change in wettability, and a volume change due to light irradiation.
For example, since the photoresponsive ionic liquid of the present invention has both ionic conductivity and photoresponsiveness, the structure changes in response to light and electricity, which may cause a change in wettability.
Further, the photoresponsive ionic liquid of the present invention may be applied to solvent extraction and the like by utilizing the change in polarity due to isomerization of the photochromic compound portion and changing the affinity with various solvents by light irradiation.

<Example of electric double layer capacitor>
The photoresponsive ionic liquid of the present invention can be used as an ionic conductor of an electric double layer capacitor. The electric double layer capacitor has a structure in which an ionic conductor is interposed between two counter electrodes. Among these, at least one electrode is required to be transparent (transmit the irradiation light) to the irradiation light. Typically, an electrode in which ITO (indium tin oxide) is coated on glass or plastic is used. The other electrode may be a transparent electrode or an opaque electrode such as a metal. The ionic liquid, which is an ionic conductor, is filled and held in the space of the spacer separating the electrodes.
The photoresponsive ionic liquid of the present invention can be sealed between electrodes as it is or via a separator, or can be gelled and confined as a solid to prevent liquid leakage. As an example of the gel, it is possible to easily synthesize a gel having ion conductivity by dissolving methyl methacrylate and a crosslinking agent in a photoresponsive ionic liquid and performing radical thermal polymerization.

式（２）で表されるイオン液体のカチオン成分（１−ブチルイミダゾール）とを反応させ、

光応答性イオン液体（[AzoBIm][NTf₂]）を合成し、その特性を評価した。 EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples. In addition, unless otherwise indicated,% shows the mass%.
Azobenzene represented by the following formula (1),

Reacting with the cation component (1-butylimidazole) of the ionic liquid represented by the formula (2),

A photoresponsive ionic liquid ([AzoBIm] [NTf ₂ ]) was synthesized and its properties were evaluated.

<Synthesis>
In the synthesis of the photoresponsive ionic liquid, as shown in FIG. 2, first, a reactive group was added to azobenzene (FIGS. 2A and 2B). 1-Butylimidazole was added thereto for synthesis, and an anion was added to form an ionic liquid (FIGS. 2 (c) and (d)).
(a) Synthesis of 4-methylazobenzene The reaction shown in Fig. 2 (a) was performed. First, an equimolar amount of p-toluidine ethanol solution (ethanol 12 ml) is added to a solution of nitrosobenzene (0.047 mol) in acetic acid (12 ml acetic acid) immersed in a water bath with light shielding. The solution was added dropwise under a nitrogen atmosphere. 3 hours and stirred at ^45? C After the addition was then reacted for 12 hours at room temperature. The solid was collected by suction filtration and washed with 1 N hydrochloric acid, 1 N aqueous sodium hydroxide solution, and pure water. The product was purified by recrystallization using a mixed solvent of ethanol / water. The yield was about 60%, and the structure of the product was confirmed by ¹ H-NMR. Melting point ^{73? C (Macromolecules 1984, 17} , literature values according to 782-792 are ^72? C) it was.

(b) Synthesis of 4- (Bromomethyl) azobenzene (4- (Bromomethyl) azobenzene) The reaction shown in FIG. 4-Methylazobenzene (6.7 mmol), N-bromosuccinimide (7.2 mmol), and benzoyl peroxide (0.21 mmol) were placed in the flask, and the flask was filled with a nitrogen atmosphere. It was refluxed for 3 hours while irradiated with UV ^85? C after the addition of carbon tetrachloride (Tetrachloromethane) (40 ml). After the UV irradiation was stopped, the mixture was further refluxed for about 12 hours. Succinimide was removed by suction filtration, and carbon tetrachloride was distilled off to obtain the desired product. The product was recrystallized using ethanol. The yield was about 75%, and the structure was confirmed by ¹ H-NMR. The melting point was 115 ~ ^120? C. (The literature values described in Nippon Kagaku Zasshi 1959, 80, 219 are 114-115 ^? C)

(c) 1-Azobenzyl-3-butylimidazolium bromide
Synthesis of (1-Azobenzyl-3-butylimidazolium bromide) The reaction shown in FIG. Was heated to ^70? C was added to the flask with a nitrogen atmosphere 4- (bromomethyl) azobenzene (4- (Bromomethyl) azobenzene) ( 0.011 mol) and dehydrated ethanol (200 ml). 1-Butylimidazole (0.013 mol) was added and refluxed for 12 hours. The target product was obtained by distilling off the solvent. The product was purified by recrystallization using a mixed solvent of 2-propanol and ethyl acetate. The yield was about 65%, and the structure was confirmed by ¹ H-NMR.

(d) 1-azobenzyl-3-methylimidazolium bistrifluoromethanesulfonylamide
Synthesis of (1-Azobenzyl-3-butylimidazolium bis (trifluoromethanesulfonyl) amide) The reaction shown in FIG. 1-Azobenzyl-3-butylimidazolium bromide (6.02 mmol) dissolved in water, and equimolar amount of bistrifluoromethanesulfonylamide lithium salt (Bis (trifluoromethane sulfonyl) amide lithium salt) dissolved in water It was dripped and anion exchange was performed. The water-insoluble red transparent liquid produced at the same time as the dropwise addition was recovered, and LiBr as a byproduct was removed by repeating the liquid separation operation using water. Separation was completed after confirming that no white precipitate was formed even when an aqueous silver nitrate solution was dropped into the aqueous layer. Finally, it was dried under reduced pressure to obtain the desired product. The yield was about 95%, and the structure was confirmed by ¹ H-NMR. FIG. 3 shows the NMR spectrum of the target product. Moreover, when the target product was subjected to elemental analysis (using elemento vario EL III CHNOS Elemental Analyzer), the weight ratio of C to the molecular weight of the product was 44.16 (theoretical value was 44.07), and the weight ratio of N. Was 11.58 (theoretical value was 11.68).
The product was in a red liquid state at room temperature.

<Evaluation>
Various characteristics of the obtained photoresponsive ionic liquid were evaluated.
1. Electrical conductivity In order to evaluate whether the photoresponsive ionic liquid has the same electrical conductivity as a normal ionic liquid, electrical conductivity was measured.
The conductivity was measured by a complex impedance measurement method using a potentiostat (Princeton Applied Research, VMP2 multi potentiostat). The frequency range was 50 Hz to 500 KHz, and the applied voltage was 10 mV. Previously charged cell constant in the cell of the calculated stainless electrode in a standard KCl solution the photoresponsive ionic liquid, ^80? After holding of 1 hour or more at each temperature in the range from C to ^0? C while cooling, It was measured.
Table 4 shows the obtained results. The obtained photoresponsive ionic liquid was found to have the same conductivity as that of a normal ionic liquid.

2. Change in absorbance due to light irradiation In order to evaluate whether the photoresponsive ionic liquid has the characteristics of a photochromic compound, the change in absorbance due to light irradiation was measured. The change in absorbance was measured in the wavelength region from the ultraviolet (UV) region to the visible light region.
The obtained results are shown in FIG. The cis form in the figure is an absorbance spectrum after irradiating light of 366 nm for a certain time, and is a result of photoisomerization of azobenzene into a cis form. The trans form in the figure is the absorbance spectrum after 437 nm light irradiation for a certain period of time, and is the result of azobenzene returning from the cis form to the trans form.
It was found that the photoresponsive ionic liquid reversibly cis-trans isomerizes by irradiation with light as in the case of azobenzene alone.
The measurement was performed by thinly coating the wall surface of the quartz glass cell without diluting the ionic liquid.

3. Change in charge amount of electric double layer capacitor When the obtained photoresponsive ionic liquid was used as an ion conductor of an electric double layer capacitor, the change in charge amount due to light irradiation was measured.
For the measurement, a three-electrode cell shown in FIG. 6 was used. 6A shows a top view and FIG. 6B shows a side view.
The tripolar cell is made by stacking two ITO glasses 2a and 2b, which are conductive glasses, with a slight shift, and sandwiching two spacers 6 and 6 on the overlapping portion of the ITO glasses 2a and 2b. . The spacer 6 is cut into a circular shape having a center of about 0.58 cm ² , and the photoresponsive ionic liquid 8 is accommodated in an internal space surrounded by the ITO glass 2a, 2b and the cut-out portion of the spacer 6.
The ITO glasses 2a and 2b are respectively a working electrode and a counter electrode, and a pseudo reference electrode 4 made of a silver wire having a wire diameter of 0.1 mm is interposed between the spacers 6 and 6, so that current and voltage can be supplied. It comes to measure.

Using an electrochemical measurement device (BAS 100B manufactured by BAS Co., Ltd.), charge is applied from the top surface of the working electrode, the initial potential is set to 0 mV vs. Ag, and the final potential is set to -200 mV vs. Ag. Was measured.
The wavelengths of irradiation light were 366 nm (UV light) and 437 nm (Vis light (visible light)), respectively, and an ultrahigh pressure mercury lamp (USHIO Optical Modulex USH-500SC) was used as a light source. Before the measurement, both UV light irradiation and Vis light irradiation were performed for 10 minutes or more, and the measurement was performed while the light was continuously applied. The obtained results are shown in FIG. From this, it was confirmed that the amount of charge charged to the electrode by light irradiation differs by 10% or more depending on the irradiation wavelength.

It is a figure which shows the example of the structural change by the light of a photochromic compound. It is a figure which shows the synthetic scheme of a photoresponsive ionic liquid. It is a figure which shows the NMR spectrum of the obtained photoresponsive ionic liquid. It is a figure which shows the electrical conductivity of the obtained photoresponsive ionic liquid. It is a figure which shows the light absorbency change by light irradiation of the obtained photoresponsive ionic liquid. It is a figure which shows the structure of the 3 pole-type cell imitating an electric double layer capacitor. It is a figure which shows the change of the charge amount of electric charge by light irradiation when using the obtained photoresponsive ionic liquid.

Claims (2)

  A photoresponsive ionic liquid in which a photochromic compound is introduced into a molecular structure, and the physical properties of the ionic liquid are changed by light irradiation. The photoresponsive ionic liquid according to claim 1, wherein when used as an ionic conductor of an electric double layer capacitor, a charge amount charged in the capacitor by light irradiation changes.

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