JPS584956B2 - Electrochromic display materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a viologen-based electrochromic display material, and more particularly to an electrochromic display material comprising a compound in which viologen groups are introduced into monodisperse polystyrene.

As shown by the following formula (1), viologens are stable ions that are electrochemically reduced in an aqueous solution containing an appropriate electrolyte or a mixed solution of water and alcohol, such as methanol, and exhibit strong reddish-purple to blue coloring. It generates radicals and utilizes this property to be used as an electrochromic display material.

(In the formula, R is an alkyl group or an aralkyl group.

) Philips (Netherlands) says that when a compound having an alkyl group with an appropriate number of carbon atoms, such as a heptyl group, is used as R in the viologens shown in formula (1), ion radicals become insolubilized on the electrode and the voltage is turned off. They also discovered that coloration remains and forms a memory state, which can be erased by applying a reverse voltage, and applied this phenomenon to display elements.

(C, J, 5hootet, al, Applied
Physics Letter, 23°64, (197
3)) However, various studies have been conducted on heptyl viologen dipromide (hereinafter abbreviated as DpHpBr), and it has been found that it has the following drawbacks as a display material.

(1) Due to the application of excessive voltage, 2
A step-by-step reduction reaction occurs, and the products of the second-step reduction reaction are not completely restored to their original state even when a reverse voltage is applied, so that the display element is likely to deteriorate.

(Be-1inko, Applied Physics
Letter, 29° 363 (1976)) When examining the redox potential of these two stages using a polarographic method, it is found that DpHpBr of 2.5X10-3M (molar concentration; viologen group concentration) and KBr (supporting electrolyte) of 0.2M.
In an aqueous solution consisting of saturated calomel electrodes (hereinafter S, C, E
), El and E2 in (■) were -0.35■ and -0.81V, respectively.

Therefore, in DpHpBr, the potential width ΔE in which stable ion radicals can be generated without causing the second stage reaction is extremely narrow at 0.28V.

However, in electrochromic display elements, it is necessary to apply a considerably high voltage in order to obtain uniform coloring of the electrodes for the following reason.

(i) Since the solution in a solution-type electrochromic display element has a low impedance, when the electrode resistance increases, a voltage drop occurs inside the electrode, making it difficult to color the entire electrode.

(11) When a transparent electrode such as Nesa is used as an electrode, uniform coloring cannot be obtained because a voltage drop due to electrode resistance cannot be ignored.

(iii) In a display element with a planar electrode structure [the structure shown in FIG. 2 of the attached drawings in which the cathode, anode, and reference electrode are all arranged on the same plane (substrate)], when the area of the display electrode becomes large in DpHpBr, The entire electrode is colored.
<, uneven coloring occurs.

Therefore, in order to prevent deterioration of the display element, it is necessary to widen the potential width ΔE that allows stable driving.

(2) If the colored film on the electrode is left in a memory state for a long time, the colored state changes and it becomes difficult to erase the color by applying a reverse voltage.

DpHpBr has memory properties because the electrochemically generated ion radicals become insoluble in solvents, and this has been one of the advantages of electrochromic display elements, but recently it has become possible to maintain the memory state for only a few seconds. However, it has been reported that uneven coloring occurs due to structural changes in the ion radical film, and that the colored film cannot be completely erased by applying a reverse voltage (J, J, P
onjee′.

Electro Chemical 5ociety,
Spring Meeting, No. 421.19
76).

To solve the above-mentioned drawbacks, viologen-based materials have been proposed in which structural changes in the ion radical membrane are less likely to occur.For example, the ionene-type viologen polymer represented by the general formula reduces uneven coloring, lowers driving voltage, etc. However, because the molecular weight is large, the time required for coloring and decoloring (hereinafter abbreviated as response) is about 10 times longer than that of DpHpBr, and the molecular weight distribution is also quite wide.
The decoloring process is complicated.

The present invention has been made in view of the above-mentioned current situation, and its purpose is to obtain uniform coloring even when deterioration occurs, to prevent structural changes in the colored film from occurring, and to suppress deterioration of response characteristics. An object of the present invention is to provide a transparent electrochromic display material.

The electrochromink display material of the present invention which achieves the above object has the general formula (1) in which a viologen group is introduced into monodisperse polystyrene (wherein R is an alkyl group or an aralkyl group,
l is chlorine or bromine, X2 is a halogen atom or an atomic group forming a stable anion, X is 0.3 to 1.0, n is 5 to
500).

In the general formula (1), R is an alkyl group, preferably an alkyl group having 2 to 10 carbon atoms, such as ethylpropyl,
Butyl, amyl, heptyl, etc., and in the case of an aralkyl group, an aralkyl group whose aryl group is phenyl or naphthyl, such as a pentyl group.

X2 is a halogen atom such as Cl, Br, I or BF4. C
It is an atomic group that forms stable anions such as 7O4.

According to the synthesis method shown below, Xl and X2 in general formula (1) are generally not the same, and Xl is CI
or Br, but after synthesis, it can be exchanged with other counter anions by performing counter anion exchange as desired
, and X2 are the same, and Xl is not limited to C4 or Br.

However, the synthesis procedure becomes complicated, and even if Cl or Br of Xl is ion-exchanged with other counter anions, no significant effect is observed.

X is 0.3 to 1.0, and although it depends on the degree of polymerization n, 0.3 or more is appropriate based on the coloring density when a voltage is applied.

The degree of polymerization n is determined from the response characteristics and the solubility in water and a mixed solvent of water and an alcohol such as methanol, and is suitably between 5 and 500.

The compound represented by the general formula (1) is produced by introducing viologen groups into the flanks of a monodisperse styrene oligomer according to the steps shown in the following formula.

However, X1=Cl, Br or n, R and X2 are of the general formula (
It has the same meaning as n, R and X2 in 1).

Here, the styrene oligomer of general formula (2) is polystyrene with an extremely narrow molecular weight distribution and a relatively low degree of polymerization obtained by anionic polymerization etc., where n is 5 to 500, and Mw/M
Desirably, n=1.02 to 1.2 (Mw is weight average molecular weight, Mn is number average molecular weight).

For halomethylation of the styrene oligomer, chloromethyl methyl ether or bromomethyl methyl ether of the general formula (3) is used to perform chloromethylation and bromomethylation, respectively, to produce a halomethylated styrene oligomer of the general formula (4).

In this reaction, stannic chloride or anhydrous aluminum chloride is used as a Friedel-Crafts catalyst.

Table 1 shows the properties of the styrene oligomer and the halomethylated styrene oligomer obtained therefrom.

From Table 1, changes in molecular weight distribution due to halomethylation can be almost ignored.

The obtained halomethylated styrene oligomer has the general formula (5)
N-alkyl-4-(4-pyridyl)-pyridinium halide or N-aralkyl-4-(4-pyridyl)
- Pyridinium halide is reacted with a polar organic solvent such as dimethyl sulfoxide (hereinafter abbreviated as DMSO) to obtain a compound of general formula (1).

The reaction conditions are N-alkyl-4-(4-pyridyl) per mole of halomethyl group of the halomethylated styrene oligomer.
-pyridinium halide or N-aralkyl-4-(
4-pyridyl)-pyridinium halide 1.2-2.5
Mol, reaction time 30 minutes to 4 hours, reaction temperature 80℃ to 12
It is 0°C.

The generated compound of general formula (1) is tetrahydrofuran (
It was purified by repeating reprecipitation several times with a solvent such as THF (hereinafter abbreviated as THF) and acetone.

The product was confirmed by infrared absorption spectrum and elemental analysis.

Figure 1 shows chloromethylated styrene oligomer C8-28 (
(see Production Example 3 below) and 28-AmB synthesized from it
The infrared absorption spectrum of r (see Production Example 3 below) is shown.

As shown in Figure 1, after the reaction, the strong absorption of the chloromethyl group at 1260 cm-1 disappeared completely, and the chloromethyl group at 1640 cm-1
The absorption of the quaternary pyridinium salt of 1 is shown.

Next, some production examples will be shown regarding the synthesis of the compound of general formula (1), but the present invention is not limited thereto.

Production Example 1 Styrene oligomer 5-55.0g (0.04g) shown in Table 1
8 monomer moles) to 5.0 c of crylemethyl methyl ether
c (0,065 mol), 10 CC of carbon tetrachloride was added, and stannic chloride Ice was diluted with 5ee of carbon tetrachloride.
(0,009 mol) was added dropwise at 0° C. over about 10 minutes, followed by reaction for 30 minutes.

The reaction solution is reprecipitated with an excess amount of methanol, and then reprecipitation is repeated two more times in a benzene-methanol system for purification.

Thus obtained chloromethylated styrene oligomer C8-5
0.5g (2.0X10-3 moles of chloromethyl group) and N
-n-heptyl-4-(4-pyridyl)-pyridinium bromide 0.8 g (2,35XI0-3 mol) and 1
Dissolved in 5 cc of DMSO and incubated at 120°C under nitrogen stream for 3 hours.
Let it react for 0 minutes.

The reaction solution was reprecipitated into 100 cc of cold THF and sent to each house.

Thereafter, reprecipitation was performed twice in a methanol-THF system for purification, and a heptyl group was added as the terminal group and B as the terminal counter anion.
A styrene oligomer (hereinafter abbreviated as 5-HpBr) containing a viologen group with r- was obtained.

Production Example 2 Styrene oligomer 5-95.0g (0.04g) shown in Table 1
8 monomer mole) to 12ee of bromomethyl methyl ether
(0,147 mol), aluminum chloride 2.9 (0,0
15 mol) and 20 cc of carbon tetrachloride were added, and the mixture was reacted at 0°C for 1 hour.

The subsequent purification was the same as in Production Example 1.

Thus obtained bromomethylated styrene oligomer B5-9
0.5g (bromomethyl group 2.7X10-3 mol),
N-benzyl-4-(4-pyridyl)-pyridinium chloride 1. Og (3,5X10-3 mol) and 200
Dissolve in CODMSO and react at 100°C for 2 hours.

Thereafter, the product was purified in the same manner as in Production Example 1 to obtain a styrene oligomer (hereinafter abbreviated as 9-BzCl) containing a viologen group having a benzyl group as a terminal group and Cl- as a terminal counter anion.

Production Example 3 Using styrene oligomer 5-28 shown in Table 1, chloromethylated styrene oligomer C8-280.5g (chloromethyl group 2.4X10-
3 mol) and N-n-amyl-4-(4-pyridyl)-pyridinium bromide 0.97 g (3,2X10-3 mol) were dissolved in 30 cc of DMSO, reacted at 90°C for 2 hours, and purified to remove the terminal groups. A styrene oligomer (hereinafter abbreviated as 28-AmBr) containing a viologen group having an amyl group as an anion and a Br- as a terminal counter anion was obtained.

Production Example 4 Using styrene oligomer 5-97 shown in Table 1, bromomethylated styrene oligomer B5-970.5g (bromomethyl* group 2.6X10
-3 mol) and N-n-propyl-4-(4-pyridyl)
- 2.1 g of pyridinium iodide (6,5X10-
3 mol) in 40 cc of DMSO and purified by reacting at 80°C for 4 hours to obtain a styrene oligomer containing a viologen group (hereinafter abbreviated as 97-ProI) having a propyl group as the terminal group and ■- as the terminal counter anion. I got it.

The electrochromic display material of the present invention is used as a solution in water or a water-alcohol mixture, such as methanol, together with a supporting electrolyte, and the supporting electrolyte can be appropriately selected from commonly used materials, such as potassium bromide, potassium chloride, Sodium hypophosphite etc. are suitable.

The concentration of viologen groups in the solution is 0.05-0.
3M.

A suitable concentration of the supporting electrolyte is 0.2 to 0.5M.

Regarding the electrochromic display material of the present invention, the value of the redox potential of each viologen group-containing styrene oligomer shown in the above production example was measured.

That is, 5-HpBr obtained in Production Examples 1 to 4.

9-BzCl, 28-AmBr and 97-ProI and as a comparative example DpHpBr were each added at 2.5X10-
3M (viologen group concentration), KBr as supporting electrolyte
When the redox potential of an aqueous solution containing 0.2M (supporting electrolyte concentration) is defined using the Yanagimoto triode polarograph, it is shown in Table 2 below corresponding to the first and second stage reactions for a saturated calomel electrode. The potential shown was obtained.

As is clear from Table 2, the display material of the present invention is DpHpB
Compared to r, IEll is lowered by 0.1V or more, and ΔE is expanded to the same level as normal.

Therefore, there is an advantage that it can be driven at a lower voltage and the voltage margin can be expanded.

The display material of the present invention can be used together with the above-mentioned supporting electrolyte in water or water.
An electrochromic display is constructed by filling the display cell shown in FIG. 2 as a solution of the alcohol mixture and sealing it.

FIG. 2 is a schematic diagram of the structure of the electrochromic display, in which a shows a cross-sectional view and b shows a top view.

In the figure, 1 is a board (double-sided printed wiring board), 2 is a spacer (0.5 mm thick), 3 is a cover glass (1 mm thick),
4 is a circular electrode for display (surface gold plated), 5 is a reference electrode (
6 is a counter electrode (surface gold plated), 7 is a through hole (sealed by solder filling), 8 is a lead wire and drive circuit, 9 is an electrochromic solution, and 10 is an injection port.

A circular display electrode 4, a reference electrode 5, and a counter electrode 6 whose surface was plated with gold were made on a substrate 1, and a sealed cell was made using a cover glass 3 and the substrate 1 via a spacer 2, and the lead wires and drive circuit 8 were The cell was taken out from the back side through a through hole 7, and an electrochromic solution 9 was injected through an injection port 10, and the injection port 10 was sealed.

A DC voltage was applied to the display cell filled with an electrochromic solution containing the viologen group-containing styrene oligomer of the present invention, with a viologen group concentration of 0.05 to 0.3M and a supporting electrolyte concentration of 0.2 to 0.5M. Then, 0
．． Uniform and bright coloring was observed at 2 to 0.3V.

When the number of carbon atoms in R in the viologen group-containing styrene oligomer is 2 or more, preferably 3 to 8, this coloration is almost insoluble in water or a water-alcohol mixture used as a solvent and exhibits a memory effect.

With DpHpBr, the coloring state changed and faded when left in the memory state for 30 seconds, and the decoloring time increased to 5 times, but with the viologen group-containing styrene oligomer of the present invention, the coloring state changed after being left in the memory state for 5 to 60 minutes. No deterioration in characteristics was observed.

Moreover, it was possible to repeat coloring and decoloring for a long time.

As the degree of polymerization n increases, the response time increases as DpHpBr
Although it became slightly slower than that of , it did not change much in the low degree of polymerization region.

Next, examples using the electrochromic display material of the present invention will be described.

Example 1 An aqueous solution containing 0.3 M of 5-HpBr obtained in Production Example 1 and 0.5 M of sodium hypophosphite as a supporting electrolyte was prepared, and this was injected into the display cell shown in FIG. The cell was sealed.

All encapsulation operations were performed under nitrogen flow.

When a DC voltage is applied to the display element created in this way, a circular electrode with a diameter of 10 mm can be uniformly colored with a bright blue-purple color at 0.3 V, and the coloring and decoloring can be repeated more than 105 times. did it.

The response characteristics were only 10% lower than that of DpHpBr.

Further, even after being left in the memory state for 5 minutes, no change in the coloring state or deterioration of characteristics such as decoloring speed was observed.

Example 2 A 0.1M aqueous solution of 9-BzCl (supporting electrolyte KC10, 2M) obtained in Production Example 2 was prepared and sealed in the same cell as in Example 1 to create a display element.

When a DC voltage was applied, a circular electrode with a diameter of 10 mm was uniformly colored at 0.3 V, and coloring and decoloring could be repeated 105 times or more.

The response characteristics were only 15% lower than that of DpHpBr.

The memory time to maintain stable coloring even when the voltage is turned off is 1
It took about 0 minutes.

Example 3 0.05M water-methanol solution of 28-AmBr obtained in Production Example 3 (5% by volume of methanol, supporting electrolyte KBr 0
．． 3M) was prepared and sealed in the same cell as in Example 1 to create a display element.

When a DC voltage is applied, uniform coloring occurs at 0.2V,
It was possible to repeat coloring and decoloring more than 105 times.

The response characteristic was 20% lower than that of DpHpBr, and the stable memory time was about 30 minutes.

Example 4 A 0.03M water-methanol solution of 97-ProI obtained in Production Example 4 (methanol 10% by volume, supporting electrolyte sodium hypophosphite 0.15M) was prepared and sealed in the same cell as Example 1. A display element was created.

When a DC voltage is applied, uniform coloring occurs at 0.2V,
I was able to repeat coloring and decoloring.

Although the response characteristics were reduced by 30% compared to DpHpBr, the time during which stable coloring could be maintained was about 60 minutes.

As is clear from the above description, according to the present invention, when electrochromic display is performed using the viologen group-containing styrene oligomer compound represented by the general formula (1), coloring can be achieved without causing a deterioration reaction. There are advantages in that the potential width is increased, a uniform colored film can be obtained on the electrode, the colored film can be completely erased by a reverse voltage, and a decrease in coloring/decoloring speed can be suppressed to a minimum.

[Brief explanation of the drawing]

Figure 1 shows Example 3-2, which is a specific example of the compound of the present invention.
This is an infrared absorption spectrum showing 8-AmBr (bottom diagram) in comparison with cleremethylated styrene oligomer C8-28 (top diagram). FIG. 2 is a schematic diagram of the structure of a display cell used in the present invention, in which a shows a cross-sectional view and b shows a top view. 1...Substrate, 2...Spacer, 3.
... Cover glass, 4 ... Circular electrode for display, 5 ... Reference electrode, 6 ... Counter electrode, 7 ... Through hole, 8... Lead wire and drive circuit, 9... Electrochromic solution, 10... Inlet.

Claims (1)

[Scope of Claims] 1 A general formula in which a viologen group is introduced into monodisperse polystyrene (wherein R is an alkyl group or an aralkyl group,
1' is chlorine or bromine, X2 is a halogen atom or an atomic group forming a stable anion, X is 0.3 to 1.01n is 5
An electrochromic display material comprising a compound represented by: