JPH0145893B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electrochromic display element, and an object of the present invention is to improve the basic characteristics of a display, such as responsiveness, repeated operation life, contrast, etc., by configuring a specific combination of reactive media. Electrochromic display elements are made by enclosing a reactive medium between two electrically conductive electrodes, at least one of which is transparent. In such a structure, information is selectively displayed by dividing the electrodes into appropriate segments and applying a potential between the appropriate electrodes to cause coloring in a desired area. As a result of various studies on the above-mentioned reactive medium, the present inventor found that a reactive medium having a styryl-like compound as shown in Structural Formula (1), a supporting electrolyte as shown in Structural Formula (2), and a basic solvent is It has been found that responsiveness, repeated operation life, and contrast are significantly improved over conventional ones. Here, n is an integer of 1 or 2, A is -H,
Lower alkyl group, halogen group, alkoxylalkyl group, -SO ₂ CH ₃ , -SO ₂ C ₂ H ₅ , -SO ₂ C ₄ H ₉ , Z is

Y
represents O or S, and R represents a lower alkyl group. (R ₁ ) ₄ N・X ...(2) Here, R ₁ is an alkyl group having 2 to 8 carbon atoms,
X represents any one of --ClO ₄ , --PF ₆ , --BF ₄ , --SO ₃ CF ₃ . DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the drawings, while comparing them with conventional ones. Pigments of styryl-like compounds are colorless when no voltage is applied, but are oxidized and colored when voltage is applied. In addition, in an acidic solvent, color develops just by mixing. Generally, when moisture is contained, the material develops color or is likely to develop color. This varies depending on the acidity of the solvent.
On the other hand, when a basic solvent is used, the dye does not develop color just by being dissolved in the solvent. Therefore, only by applying a voltage can the phenomenon of decoloring and developing occur. Therefore, the contrast between decolorization and decolorization is good, and it looks beautiful because coloration occurs from a colorless state. Tetraalkylammonium salts exhibit the best properties as supporting electrolytes. Other supporting electrolytes used in non-aqueous solvents, such as LiClO ₄ and CuClO ₄ , develop color only when mixed with a dye, and the responsiveness of color decolorization is slow. In order to dissolve well in nonaqueous solvents, the alkyl group needs to have a larger number of carbon atoms than the ethyl group, which has two carbon atoms. As an anion,
ClO ₄ ^- is the most common, but BF ₄ -, PF ₆ -,
There is SO ₃ CF ₃ -. When halogen ions are used, the electrodes are likely to be corroded and react with dyes, resulting in a shortened repeated operation life. by the way,
The coloring potential of dyes of styryl-like compounds is +0.8 ~
+1.5V, and the decoloring potential is -0.5 to -1.5V (vs. SCE). The responsiveness of decoloring and developing due to voltage application is most easily affected by the viscosity of the solvent. The color density changes over time as shown in the figure. The time _t1 required for the concentration to saturate after applying a voltage is, for example, 5 to 10 when using something like propylene carbonate.
seconds, 4 to 8 seconds for γ-butyrolactone, 0.5 to 1 second for methyl isobutyl ketone, and 0.5 seconds or less for acetonitrile. 0.5 for basic solvents dimethylformamide and dimethylacetamide
~2 seconds. The color density varies depending on the concentration of the dye and the supporting electrolyte in the reactive medium, but when compared at the saturation concentration _A1 in the figure, the color density of propylene carbonate, acetonitrile, dimethylformamide, dimethylacetamide, methyl isobutyl ketone, and γ-butyrolactone is The color density increases in this order. From a practical standpoint as a display device, the most important characteristic is the repeated operation life. As a result of this test, it was confirmed that 2×10 ⁶ or more times when a basic solvent was used. When other solvents were used, it was about 5×10 ⁵ . The dye concentration in the reactive medium is 0.005M/min.
The concentration of the supporting electrolyte is 0.01M/or higher, and it can be used up to saturation concentration. By the way, since the dye has good solubility in a basic solvent, it is easy to obtain a high color density because a large amount of the dye is dissolved. Therefore, even when the number of electrode segments increases, variations in color density between segments can be reduced.
To erase color, reverse the voltage used to develop color, or use +
This is done by shorting the pole and negative pole and leaving it alone, or by just leaving it alone. The decoloring time is shorter in this order. When a basic solvent is used, as described above, the dye tends to become decolored, so decoloring can be carried out in a short time without applying voltage.
For example, when comparing the cases where propylene carbonate and dimethylformamide are used as solvents, dimethylformamide can erase the color in about half the time. It takes about 4 to 5 minutes. In order to continuously obtain a colored state, a direct current voltage is continuously applied or a pulse is applied, but in this case, decomposition of the supporting electrolyte becomes a problem. for example,
Although it is generally said that there is no problem when the supporting electrolyte is used in the range of -1.5 to +1.5V, differences in the supporting electrolyte become apparent when continuous color development is performed for hundreds to thousands of hours. In terms of longevity, NR ₄ ClO ₄ NR ₄ SO ₃ CF ₃ <NR ₄ BF ₄ NR ₄ PF ₆ . Specific examples will be described below. <Example 1> The dye used as the electrochromic material was 3,3-dimethyl-5 shown by the structural formula below.
-Methylsulfonyl-2-(P-dimethylaminostyryl)indolino[2-1-b]oxazoline. The supporting electrolyte is tetrabutylammonium perchlorate, (C ₄ H ₉ ) ₄ N.ClO ₄ . Propylene carbonate was used as the solvent and dimethylformamide was used as the basic solvent. The display properties of the two solvents are shown in Table 1. The distance between the display electrode and the counter electrode of the display element used was 35 μm. The concentrations of the dye and supporting electrolyte are 0.1 mol/0.5 mol/, respectively.

【table】

[Table] <Example 2> The dye used was the same as in Example 1. There are two types of supporting electrolytes: (C ₄ H ₉ ) ₄ N·ClO ₄ and (C ₄ H ₉ ) ₄ N·PF ₆ . The solvent is dimethylformamide. The concentrations of the dye and supporting electrolyte are 0.1 mol/0.5 mol/, respectively. Table 2 shows display characteristics when two types of supporting electrolytes are used.

[Table] The point at which the temperature decreased was defined as the service life.
In addition to the above examples, as the basic solvent, any one of N-methylformamide, N-methylacetamide, and pyridine may be used, or two or more of these including dimethylformamide and dimethylacetamide may be mixed. The same results as in each of the Examples were obtained even when using the same method. Furthermore, as a supporting electrolyte, (C ₄ H ₉ ) ₄ N・BF ₄
The same results as in each example were obtained using the following. As described above, the present invention uses a styryl-based analog compound as an electrochromic material and has improved display characteristics by using a specific combination of a basic solvent and a supporting electrolyte of a tetraalkylammonium salt. In particular, the repeated operation life, which is a practically important property, is improved.

[Brief explanation of drawings]

The figure shows the change in color density over time when a voltage is applied to an electrochromic display element.

Claims (1)

[Scope of Claims] 1 A reactive medium containing a styryl-like compound represented by the structural formula (), a supporting electrolyte represented by the structural formula (), and a basic solvent is mixed into two liquids, at least one of which is transparent. An electrochromic display element characterized by being arranged between conductive electrodes. Here, n is an integer of 1 or 2, and A is -
H, lower alkyl group, halogen group, alkoxyalkyl group, -SO ₂ CH ₃ , -SO ₂ C ₂ H ₅ , -SO ₂ C ₄ H ₉
Z is an alkylene group having 2 to 4 carbon atoms with or without an alkyl substituent necessary to form a cyclic structure together with [Formula], Y is O or S, and R is a lower Each represents an alkyl group. (R ₁ ) ₄ N・X ...() R ₁ is an alkyl group having 2 to 8 carbon atoms, and X is
Each represents one of ClO ₄ , -PF ₆ , -BF ₄ , -SO ₃ CF ₃ . 2 The basic solvent is dimethylformamide, N-
Methylformamide, dimethylacetamide, N
The electrochromic display element according to claim 1, characterized in that it contains at least one member selected from the group consisting of -methylacetamide and pyridine. 3. _{A patent claim characterized in that the supporting electrolyte consists of (C4H9)4N.PF6 or (C4H9)4N.BF4 , and the basic solvent consists} of dimethylformamide or dimethylacetamide _. Electrochromic display element according to scope 1.