Electrochromicity conjugated polymers

Fundamentals and advances in electrochromic conjugated polymers research has been described in detail in the numerous reviews of Gamier et Wudl and Heeger et Mortimer, Beaujuge and... 

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

Polymers, large molecules made up of smaller molecules in a repeating pattern, are used for many electrochromic materials. Conjugating polymers, which have alternating single and double bonds, are particularly suitable. Figure B shows the electrochemical oxidation of the conjugated polymer, polythiophene. Oxidation (in which electrons are removed) produces a semiconductive polymer. The neutral (unoxidized) polythiophene is red in color, whereas the semiconductive polythiophene (oxidized) is blue. In their neutral... 

Electrochromic materials are of three basic types [i]. In a given -> electrolyte solution, type I materials are soluble in both the reduced and oxidized (redox) states, an example being l,l -di-methyl-4,4 -bipyridylium ( methyl viologen ), which, on reduction, switches from the colorless di-cation to the blue radical cation. Type II materials are soluble in one redox state, but form a solid film on the surface of an electrode following electron transfer. An example here is l,l -di-heptyl-4,4 -bipyridylium ( heptyl viologen ). In type III materials, such as -> tungsten oxide, - Prussian blue, and electroactive conjugated polymers, both... 

Typical functions of substituted poly acetylenes are based on their (i) high gas permeability and (ii) electronic and photonic properties. The former originates from the rigid main chain and bulky substituents. Though electrical insulators, substituted polyacetylenes are more or less conjugated polymers, and this feature has been utilized to develop their electronic and photonic functions such as photoconductivity, electrochromism, optical nonlinearity and ferromagnetism. 

This opened-up a number of strategies for the creation of high-performance functional materials whose morphology is controlled on the 10-nm length scale, which Maik used to create materials with unprecedented electrochromic properties, a world-leading supercapacitor, and 3D 10 nm structured conjugated polymer assemblies that cannot be manufactured in any other fashion. 

Rational Design of Conjugated Polymers for Electrochromic Devices... 

Another rather special strategy to obtain electrochromic polymers with unexpected performance is covalently connecting electrochromic units to the conjugated polymer backbone. Lee and coworkers have reported a new polymer 119 (Fig. 2.7B) thatis aPEDOT derivative containing a pendant viologen (Ko et al, 2004). Electrochemical and spec-troelectrochemical studies showed that this polymer had four colored oxidation states. 

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