JPH04359922A - Production of electrochromic material - Google Patents

Abstract

PURPOSE:To obtain the title material which can give a thin film having good oxidation/reduction stability and excellent durabiliting and being capable of giving a large area, easily moldable in any desired shape and nonproblematic in transparency by electrolytically polymerizing a specified triphenylamine monomer mixture as a starting monomer. CONSTITUTION:An electrochromic material is obtained by polymerizing through electrolytic oxidation a mixture, as a starting monomer, prepared by mixing a compound of formula I (wherein X is alkyl, alkoxy or halogen which is ortho, meta or para to the nitrogen atom) with 5-50mol% compound of formula II. This material can give at good efficiency an electrochromic thin film containing a triphenylamine moiety, having good oxidation/reduction stability and excellent durability and being capable of giving a large area, easily moldable in any desired shape and nonproblematic in transparency.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] This invention is based on the following formula

[Chemical formula 3] (wherein X represents a hydrogen atom or a substituent selected from an alkyl group, an alkoxy group, and a halogen atom at the ortho, meta, and para positions) is added to a compound represented by the following formula:

[C4
The present invention relates to a method for producing an electrochromic material by electrolytic oxidation polymerization using a mixture containing 5 to 50 mol % of the compound represented by the formula as a raw material monomer.

0002

[Prior Art] Until now, electrochromic (E
C) Various organic and inorganic materials have been proposed as materials, but problems with driving stability and durability have prevented them from being put into practical use. Among EC materials, so-called conductive polymers are attractive because of their wide range of material variations, good processability, wide variety of colors, possibility of multicolorization, and good responsiveness. However, durability was still an issue. The applicant has so far developed a series of conductive polymers called polytriphenylamines, which have fairly high conductivity (on the order of 1S cm-1 due to doping) and have particularly excellent drive stability and durability. [
JP-A No. 61-28524]. A polytriphenylamine EC thin film is prepared as follows. Poly (4
, 4'-triphenylamine) in a solvent such as chloroform and coated with I by spin coating.
After forming a film on a transparent conductive glass such as T0 (indium-doped tin oxide), it is heated to dope with iodine and cross-link to make it insoluble to form an electrochromic thin film. The electrochromic thin film produced in this way has excellent redox stability, driving stability, and durability, and has good moldability as described above, so it is extremely practical.

0003

[Problems to be Solved by the Invention] However, polytriphenylamines such as the above-mentioned poly(4,4'-triphenylamine) are insufficient for practical use when constructing large-area EC elements. It is difficult to produce an EC thin film that is uniform and free from unevenness, and there is also a problem in that there is no simple and appropriate processing method to accurately remove unnecessary parts after film formation when configuring EC elements that include complex patterns such as letters. Met. Therefore, if an EC thin film of polytriphenylamine could be produced using electrolytic polymerization, this problem could be solved.
As shown in Comparative Example 1 below, it was found that an EC thin film could not be obtained by direct electrolytic polymerization of triphenylamine due to the stability of the triphenylamine dimer. Therefore, the inventors have been studying how to somehow obtain a conductive polymer thin film containing triphenylamine units, which are extremely excellent reactive sites, in the main chain by electrolytic polymerization. As a result, we came to the conclusion that the problem could be solved by synthesizing a raw material monomer that had good electrolytic polymerizability and stability against Grignard reagents, combining thiophene and triphenylamine, and electropolymerizing it. 4
,4',4''-tris(2-thienyl)triphenylamine (Japanese Patent Application No. 137194/1994) and 4,
4'-bis(2-thienyl) triphenylamine (
(Japanese Patent Application No. 115872/1999) were synthesized and subjected to electrolytic oxidation polymerization using each as a raw material monomer to obtain a desired electrochromic material. At that time, 4, 4',
The coulometric efficiency of 4″-tris(2-thienyl)triphenylamine was very good, virtually 100%. This is probably due to the covalent bonding ability of this monomer in three directions, resulting in high yields. The molecules were thought to have a network structure.Perhaps because of this, the transparency of this film was slightly impaired.On the other hand, when only 4,4'-bis(2-thienyl)triphenylamine was used, Although there was no problem with the transparency of the membrane, there was a problem because the efficiency of the amount of electricity in electrolytic polymerization was not good.

0004

[Means for Solving the Problems] The present invention has been made by focusing on the above-mentioned problems, and is made by adding 5 to 50 mol% of the compound represented by Chemical Formula 4 to the compound represented by Chemical Formula 3 above. The above-mentioned problems have been solved by using the mixture as a raw material monomer and performing electrolytic oxidation polymerization to obtain an electrochromic material.

[0005] Generally, the conditions for electrolytic oxidative polymerization are constant current or constant voltage. In the case of the present invention, it is a necessary condition that oxidation occurs at the potential applied to the second wave in the voltammogram. As the potential at which electrolytic oxidative polymerization occurs, 1
．． The voltage is about 3 to 2.0 V, and if it is too high, it will lead to inactivation of the membrane.

[0006] As the solvent and indicator electrolyte during electrolytic polymerization used in this invention, nitrile solvents and n-tetrabutylammonium hexafluorophosphate are used, but are not limited to these.
Solvents and electrolytes used in non-aqueous electrochemistry can be used as long as they are not oxidatively decomposed at the potential for electrolytic polymerization. Similarly, a propylene carbonate solution of lithium perchlorate is used as the driving solvent for the produced electrochromic thin film, but the solvent is not limited to this.

In the present invention, the product obtained by electrolytic polymerization is reversibly oxidized in propylene carbonate at a voltage of 0.5 V to 1.0 V relative to Ag/AgCl.

[0008]

[Examples] The present invention will be specifically explained below using Examples and Comparative Examples. Comparative Example 1 Direct electrolytic polymerization of triphenylamine It has been shown by Yoshino et al. that a conductive polymer thin film can be produced by electrolytic oxidative polymerization of condensed hydrocarbons such as benzene [J. Electroanal. Chem.
195 (1985) 203 and J. Chem. S
oc. Chem. Commun. , (1986)
[550], electrolytic oxidative polymerization of triphenylamine was attempted using this method as follows. The electrolyte is 0.3
moles/liter triphenylamine, 0.1 moles/liter CuCl2, 0.1 moles/liter LiA
A solution of sF6 in nitrobenzene was used. Nesa glass was used as the working electrode and platinum wire was used as the counter electrode, and 10V was applied between the working electrode and the counter electrode to conduct electrolysis. When benzene was added instead of triphenylamine, a black film was formed, but in this case, the solution turned reddish-brown, but a thin film could not be formed on Nesaglass no matter how much electrolysis was carried out. This is probably due to the oxidative polymerization of triphenylamine to form a dimer.
The cation is stable, and even if dication is oxidized, it is stable to a certain extent, so electrolytic polymerization does not proceed beyond the level of dimer, which is why a film is not formed.

Comparative Example 2 Electropolymerization of 4,4'-bis(2-thienyl)triphenylamine alone Electrolytic polymerization of 4,4'-bis(2-thienyl)triphenylamine was carried out under the following conditions. As the solvent, a mixed solvent of benzonitrile dehydrated with calcium hydride and vacuum distilled and acetonitrile dehydrated in the same manner at a volume ratio of 1:2 was used, and as the supporting electrolyte, 0.1 mol/liter of n-tetrabutyl was used. Ammonium hexafluorophosphate was used, and the reference electrode was a silver/silver chloride electrode in propylene carbonate separated by two glass filters. The concentration of the raw material monomer was 5 mmol/liter. ITO glass (surface resistance: 10 ohms/□) was used for the working electrode. In order to more accurately understand the redox properties of the resulting thin film, a platinum wire (about 2 cm in length) with a diameter of 0.5 mm was also used as a working electrode. A platinum wire was used as the counter electrode. Electrolytic polymerization was carried out in a glove box with a nitrogen atmosphere using a three-chamber electrolytic cell. The working electrode was placed in the central chamber of the cell, the counter electrode was placed in one chamber across the glass filter, and the reference electrode was placed in the other chamber across the glass filter.

FIG. 1(b) shows a cyclic voltammogram of the above solution using a platinum electrode. potential sweep from 0 to 1
．． When limited to the 1 V range, a very stable one-electron reversible wave is exhibited and electrolytic polymerization does not occur. However, if the potential sweep is 1.5
It can be seen that when the temperature reaches about V, the amount of reaction electricity increases little by little as the number of sweeps increases, and the platinum electrode becomes colored, indicating that an electrolytically polymerized film is being formed. A series of results on well-known polythiophenes (e.g. G. Touril
lon in T. A. Skothheim, (Ed.
), Handbook of Conducting
Polymers, Vol. 1. Dekker
, New York, 1986, p. 293)
2-,5 next to the sulfur of the thiophene skeleton by oxidation from
The proton on the carbon at the - position is removed, and the carbons bond together to form a polymer.

Example 1 Electrolytic polymerization of mixed monomers Electrolyzed in the same manner as in Comparative Example 2 except that 1 mmol/liter of 4,4',4''-tris(2-thienyl)triphenylamine was further added to the solution. Polymerization was carried out.The results are shown in Figure 1(a).Compared to Figure 1(b), as the number of sweeps increased, the amount of reaction electricity (corresponding approximately to the area surrounded by the voltammogram) became constant. It can be seen that the amount increases steadily.In order to investigate the proportion of both monomers contained in the produced polymer, we measured the IR spectrum (Figure 2).Although it was not possible to discuss quantitatively, I
The pattern of the R spectrum was much closer to that of poly(4,4′-bis(2-thienyl)triphenylamine) than to poly(4,4′,4″-tris(2-thienyl)triphenylamine). Therefore, the composition ratio of 4,4'-bis(2-thienyl)triphenylamine is considered to be large.

In order to examine the redox properties of the obtained polymer, cyclic voltammetry was performed in propylene carbonate, a more practical solvent, using 1.0 mol/liter of lithium perchlorate as a supporting electrolyte. The obtained voltammogram is shown in FIG. 3. Redox was repeated more than 100 times in the first wave of oxidation, but no change in waveform was observed and it was very stable. In the same way as for platinum electrodes, ITO
A thin polymer film was fabricated on top. The obtained thin film was made of poly(4,
4'-bis(2-thienyl)triphenylamine), and there was no problem with transparency. Ecretrochromic properties of the obtained thin films were similarly investigated in propylene carbonate, a more practical solvent. An electrochemical cell for measuring absorption spectra was constructed to detect visible -
When we measured changes in the near-infrared absorption spectrum, we found that poly(
4,4'-bis(2-thienyl)triphenylamine)
As in the case of , the color changed reversibly from pale yellow to black with the oxidation in the first wave.

[0013]

As explained above, according to the present invention, it contains a triphenylamine moiety, has good redox stability, is excellent in durability, can be made into a large area, and can be easily formed into any shape. It is possible to efficiently obtain an EC thin film with no problems in film transparency.

[Brief explanation of drawings]

FIG. 1 (a) is a cyclic voltammogram of a solution containing a monomer mixture of 4,4′-bis(2-thienyl)triphenylamine and 4,4′,4″-tris(2-thienyl)triphenylamine. FIG. 3(b) is a cyclic voltammogram of a solution containing 4,4'-bis(2-thienyl)triphenylamine.

FIG. 2 is an IR spectrum diagram of an electrolytically polymerized polymer obtained from a monomer mixture.

FIG. 3 is a cyclic voctamogram diagram of an electrolytically polymerized polymer obtained from a monomer mixture.

Claims (2)

[Claims] Claim 1: A compound represented by the following formula [Formula 1] (wherein X represents a hydrogen atom or a substituent selected from an alkyl group, an alkoxy group, and a halogen atom at ortho, meta, and para positions) The following formula [chemical formula 2
A method for producing an electrochromic material, which comprises carrying out electrolytic oxidation polymerization using a mixture containing 5 to 50 mol % of the compound represented by the following as a raw material monomer. 2. Electrolytic oxidation according to claim 1, characterized in that the produced polymer is reversibly oxidized in the range of 0.5 V to 1.0 V against Ag/AgCl in propylene carbonate. Polymerization method.