DE2449278A1 - DEVICE FOR CONTROLLING LIGHT TRANSMISSION OR REFLECTION - Google Patents

Description

PATEMENTAL OFFICE O

I IEDTKE - ÜÜHLING - IVlNNE

TEL. (089) 53 96 53-56 TELEX: 524 845 tipat CABLE ADDRESS: Germaniapatent Munich

8000 Munich 2

Bavariaring 4

P.O. Box 20 2403 > October 16, 1974

case Q 26518 - B 6279

IMPERIAL CHEMICAL INDUSTRIES LII-IITED London, Great Britain

Device for controlling light transmission

or reflection

The invention relates to devices for controlling light transmission or reflection such as in particular Viewing devices or display boards.

In the applicant's GB-PS 1 314 049 devices for controlling light transmission or reflection described, which has a working electrode with radiation transmission or reflective properties as well as one in contact with the working electrode surface Located active .Material that has an N- (p-cyanophenyl) -substituted has bicyclic compound with two nitrogen-containing rings and e'a counter electrode, the also in contact with the active material and arranged with respect to the working electrode such that

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the passage of radiation through the device due to reactions occurring at the counter electrode is not significantly affected. In the context of this application, the phrase "through the device" is intended to denote the Include the case where the radiation is partially or fully reflected by the working electrode surface will.

The N- (p-cyanophenyl) compound is in the device reversibly electrolytically reduced to a radical form which differs from the original form is colored.

According to the invention there is now an improved apparatus for controlling light reflection or transmission provided, which has a working electrode with radiation transmission or reflective properties and an active material having an N-aryl substituted bicyclic Connection with a positive half-wave potential (compared to the normal hydrogen electrode) in contact with the Working electrode and a counter electrode, which is also in contact with the active material.

According to a preferred embodiment of the invention a viewing device is provided which comprises a plurality of working electrodes which are arranged in such a way that

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that by deposition of reduced N-aryl compound a pattern such as a number or a letter on a preselected pattern of said electrodes either through increased light absorption through a transparent or translucent working electrode or reduced reflectivity of a radiation-reflecting working electrode becomes visible.

Each of the working electrodes can be provided with a separate counter electrode, although this is not essential is, there is a single counter electrode, for example in the form of a wire surrounding a number of electrodes can be completely sufficient. An increased response speed to the passage of a current results, when the surface area of the counter electrode is larger than that of the working electrodes.

Preferably, the surface of the counter electrode is 1-bis 10 times larger than that of the working electrode and in particular 2 to 5 times larger. With the area or the area is the area of the electrode that is in electrical contact with the active material is.

The electrode surface must of course be conductive, but high degrees of conductivity are not are essential. It's usually two-dimensional

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-M-

i.e. it is a flat surface or a surface curved in one or more planes and can, for example, be a be flat plate or sheet or wire. For a device in which light is transmitted through the electrode it must be transparent or translucent, for which a glass with a coating of conductive oxide or a very thin metal film is required. A metal surface can be used for reflective arrangements or a transparent or translucent electrode may have a reflective surface, for example of metal or other opaque reflective material such as white pigmented thermoplastic film or board or layer.

Active electrodes with gold turned out to be even with a small layer thickness, for example in the area of 100 Å, as they can be deposited on glass to achieve a transparent composite, as special usable and also platinum.

Any electrochemical reaction on the working electrode is of a corresponding reaction on the Accompanying counter electrode. It is therefore important that the products of the counter electrode reaction are the light reflection or - do not interfere with the transmission properties of the working electrodes; this is most conveniently achieved by

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the counter electrode outside the radiation path to or from the working electrode.

The counter electrodes are usually arranged within a shell or capsule, so that electrochemical Changes that occur on their surfaces do not become visible and the only visible changes are those are on the surface of the working electrode. However, it is possible that the counter electrode itself is used as a viewing or display electrode can be used by reversing the electric current, so that in fact the roles of working and Counter electrode are swapped. So it is intended to arrange the counter electrode itself so that it is visible or can be made visible and to provide that the counter electrode by reversing the electric current to the working electrodes to indicate a color change can be used in the same way as the working electrode. In such a device the counter electrode can be arranged at a distance (usually a few millimeters) from the working electrodes or it can be provided closely adjacent thereto, for example between the working electrodes. The counter electrode can thus even be provided in the form of a few different and possibly separately actuated electrodes.

It should be noted that the operation of the counter electrode

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systems can be exploited to transmit two sets of information using two Rows or sets of electrodes capable of acting as a digital display, for example.

The active material is used for this purpose in an inert solvent (i.e. in a solvent which does not react adversely with any components of the device with which it normally interacts). The concentration is determined by the solubility under the operating conditions such as the probable occurring temperature limited, but it is usually between 0.001 and 2 preferably between 0.01 and 1 and in particular between 0.1 and 0.8 molar concentration.

The use of relatively high concentrations of active material, for example 0.01 molar and more, is proposed. preferably accompanied by the presence in the solution of an "alternative" reversibly oxidizable body comprising both iron (II) and iron (III) ions. This system can be introduced by dissolving an appropriate amount of ferric ammonium sulfate in the active material solution.

However, it has now been found that the application of a Mixture of both ferrous and ferric salts equally

5 0 9 8 17, / 084 3

Beginning with a view to increasing the service life or number of cycles of the device can be advantageous. Thus, using a mixture of ferric ammonium sulfate and ferric ammonium sulfate as additives in the following Concentrations preferred: ferroammonium sulfate = 0.1 molar to saturation, preferably 0.1 to 0.7 molar and in particular 0.2 to 0.5 molar; Ferric ammonium sulfate = 0.001 to 0.1 molar, preferably about 0.01 molar. Such "Doping Amount" · Ferris salt has been found to assist in bleaching otherwise permanent deposits of active material that could develop. The application of a neutral pH range is also used preferred when the ferrous / ferric mixture is used.

Although the pH of the solution of the active material can and preferably vary between quite wide limits is between 1 and 3, if ferroammonium sulfate is used, it has been found advantageous to use a Use a solution with a roughly neutral pH if ferric salt is also used. The presence of any dissolved components in addition to those already mentioned will therefore preferably not have any "migration" of the pH of neutrality by more than about 2 pH units.

It is particularly desirable to virtually exclude molecular oxygen from within the device

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(which could e.g. be dissolved in a liquid medium), there this has a tendency to favor the formation of iron hydroxides.

The N-aryl-substituted compounds correspond to the general formula

CH = CH

. R-

N _{+ R} 10

1 10
where R to R = H, F, Cl or organic substituents, in particular lower (C ₁ to C ^) alkyl groups or aryl,

Aralkyl, alkaryl or oxyhydrocarbyl (oxygen-bearing

1112 hydrocarbon radicals) are; R and R are organic and at least one aryl group. Examples of suitable groups include substituted phenyls with an alkyl

group with 2 to 12 carbon atoms, CN, COOR ¹⁵ (where

1 3
R ^ is an alkyl group with 1 to 10 carbon atoms, aryl or hydrogen), an amide group, OH,

- 0

N = N-

or halogen; η is equal to 0 or an integer, preferably equal to 1 or 2; X ~ is one of an acid and preferably a strong mineral acid with a pKa value

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■ β.

of less than 2.5 or an anion derived from an organic acid. Examples of inorganic anions are F ", Cl", Br ", SO ^", MeSO ^ (Ni eder alkyl sulfate), chlorate, perchlorate, BF ^ ", SiFg, NO ₃ " and sulfonates. Organic anions include the anions of acetate, citrate, tartrate, formate, maleate, oxalate and other water-soluble mono-, di- and tricarboxylic acids and hydroxy acids.

Anions that tend to reduce the solubility of the in solution depressing existing cations to an undesirably low level are of course avoided, as it should be anions that are irreversibly oxidized.

In the following, the invention is based on the attached * Drawing described; show it

1 shows a plan view of a device with a plurality of working electrodes;

Figure 2 is a section along A-A of Figure 1;

3 shows a plan view of a device with a system

of both working and counter electrodes in a form suitable for the digital display and

FIG. 4 shows a section along B-B of FIG. 3.

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As can be seen, there are opaque gold leaf working electrodes 1 to 7 (each with its own lead 1a to 7a) arranged in a pattern that represent any digit from 0 to 9 by selective deposition on a preselected group of electrodes can. The counter electrode 8 is formed by a wire that is attached to the periphery of the viewing frame or the display board is arranged, which is formed by a frame 9 and glass plates 10 and 11 and also contains a solution 12 of the active compound.

Fig. 3 also shows a counter electrode system 13-19 in a form suitable for a digital display each counter electrode with its own lead to suitable control and electrode selection means is provided.

Figure 4 shows the leads through a back plate 20 to electrode control and selection means are brought out.

example

By immersing 2 platinum electrodes in 100 ml of an aqueous solution with N, N'-di- (p-cyanophenyl) -4,4'-dipyridinium dichloride (0.01 molar) and ferroammonium sulfate (0.5

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, A4 *

molar) a cell was made. Oxygen was vigorously eliminated from all the solutions used and nitrogen gas was continuously passed through them in order to maintain the original Fe ⁺⁺ / Fe ⁺⁺⁺ ratio.

An electrochromic effect was created by applying 0.8 V at 1 Hz to the electrodes. After 20 minutes became a permanent deposition of N, N'-di- (p-cyanophenyl) -4,4'-dipyridinium radical educated. Ferric ions were (in the form of a 0.1 molar aqueous ferric chloride solution) is added to the cell to bring the total ferric ion content to 0.01 molar, whereupon the deposit lightened and the cell continued to work satisfactorily for several days.

The tendency to permanent deposits was completed by increasing the ferric ion content to 0.1 molar eliminated.

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Claims (7)

Claims 1 .J device for controlling light transmission or reflection, characterized by a plurality of working electrodes (1 to 7) with radiation transmission or reflection properties, which are arranged to form a predetermined pattern, an active material (12) which has an N- aryl-substituted bicyclic compound with 2 nitrogen-containing rings in contact with the working electrode and a counter electrode (8) which is also in contact with the active material. 2. Apparatus according to claim 1, characterized in that the one in contact with the active material Surface area of the counter electrode is larger than that of the working electrodes. 3. Device according to claim 2, characterized in that that the surface area of the counter electrode is 1 to 10 times and in particular 1 to 4 times .the surface area of the Working electrode. 4. Device according to one of the preceding claims, characterized in that the counter electrode system is a 5 0 9 8 17/0843 Comprises a plurality of electrodes arranged to form a predetermined pattern. 5. Device according to one of the preceding claims, characterized by an electrolyte, which by an aqueous solution with the active material together with
Ferrous and ferric ions are formed. 6. Device according to one of the preceding claims, characterized in that the active material is a
has positive 1st half-wave potential. 7. Device according to one of the preceding claims, characterized in that the active material is a Is N, N'-di- (p-cyanophenyl) -4,4'-dipyridyl salt. 509817/0843 Blank page