Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1982-01-15
1984-09-25
Rotman, Alan L.
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
350357, C07D21322
Patent
active
044736959
DESCRIPTION:
BRIEF SUMMARY
This application is based upon and claims the priority of International Patent Application No. PCT/US81/00949 filed July 14, 1981.
TECHNICAL FIELD
The field of this invention is chemical compounds and, particularly, chemical compounds suitable for use in electrochromic systems.
BACKGROUND ART
Recently there has been considerable interest in reduction-oxidation (redox) active compounds for use in electronic displays. Such electrochromic materials are suitable for use whenever a light absorbing, rather than a light emitting, display can be employed. Electochromic materials are often preferred because of their low power consumption and their ability to operate without a constantly applied power source.
A number of compounds which change color as a result of electrochemical reactions are known. For example, polyvinylferrocene, polynitrostyrene or polymers from hydrolytically unstable ferrocene monomers have been confined to the surface of electrode materials. All of these materials are electrochromic. Polynitrostyrene, a pale yellow solid, is claimed to give an electrode a red appearance upon reduction whereas ferrocene-centered polymers turn from yellow/orange to blue upon oxidation. These results are encouraging, but the ferrocenes are too weakly colored and the reduction of polynitrostyrene is not readily reversible in the presence of moisture.
Compounds formed from 4,4'-bipyridinium, known as viologens, also exhibit electrochromic behavior. For example, dialkyl-4,4'-bipyridinium di-cations and their associated anions (dichloride, dibromide or di-iodide) form contrasting colors. These viologen di-cations range from colorless, yellow, and to red, while mono-cations are a striking blue-purple. Two basic problems with viologens are their long term stability as coatings and their sluggish switching speeds (rates of color change) at typical coating or solution concentrations.
There exists a need for electrochromic materials which can be immobilized, and preferably covalently bonded, upon electrode surfaces and which can be repeatedly subjected to redox actions in display systems. Moreover there is a need for electrochromic materials that can respond rapidly to an applied potential and yield a strong color (i.e. high molar absorbivity).
DISCLOSURE OF THE INVENTION
We have discovered a novel class of dialkyl and dialkyl-aromatic viologens (4,4'-bipyridinium compounds) which may be polymerized and covalently bonded, or otherwise confined, to the surfaces of electrodes. These surface confined compounds exhibit the colors of viologen dications, colorless when oxidized, purple when reduced, while having the ability to avoid dissolution into the electrolyte in their oxidized or reduced, radical cationic, state. Further the surface confined compounds can be reduced and reoxidized rapidly and without degradation.
In one embodiment, our reagents include silicon groups which provide sites for attachment to surfaces bearing OH groups and, in the presence of H.sub.2 O, also promote polymerization. In particular, silicon alkoxides, Si(OR).sub.3, such as Si(OMe).sub.3 ; Si(OEt).sub.3 ; Si(OPr).sub.3 ; Si(OBu).sub.3 ; and silicon halogens such as SiCl.sub.3 may be used. When the silicon alkoxide reagents are applied to the OH bearing surface, the alkoxyls leave the compound and combine with hydrogen from the OH bearing surface to form alcohols while the silicon is thus free to bind to the surface oxide and also polymerize with neighboring silicon atoms. In a similar fashion silicon halogens may also be employed with the halogen being displaced to permit silicon oxide covalent bonding. The resulting coating is a polysiloxane polymeric structure with viologens as a functional group on each silicon atom. Although silicon groups are suitable binding agents other agents, such as boron dihalides and, in particular, BCl.sub.2, may also be used.
We have also found that a wide range of alkyl and aromatic groups can be used to link the viologen center of our compounds to the binding groups. Alkyl chains of one or more carbon ato
REFERENCES:
Bookbinder & Wrighton, Journal of the American Chemical Society, vol. 102, No. 15, pp. 5123-5125, Jul. 16, 1980.
Bookbinder Dana C.
Wrighton Mark S.
Engellenner Thomas J.
Massachusetts Institute of Technology
Rotman Alan L.
Smith, Jr. Arthur A.
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