Other Organic Electrochromes

Several other organic systems have been stndied as potential electrochromes because of their redox behaviour. These include carbazoles, methoxybiphenyls, fluorenones, benzoquinones, naphthaquinones and anthraqninones, tetracyanoquinodimethane, tetrathiafnlvalene and pyrazolines. ° Of particnlar interest are the 1,4-phenylenedi-amines, which form highly colonred species on oxidation. These, known as Wurster s salts, exemplified by Wnrster s Bine (1.97), are anodically colouring and this type of material has found nse in composite electrochromic systems for car rearview mirrors (see 1.5.4.1). 

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In bacterial chromatophores the RC and the b/c, complex are arranged to form a cyclic electron transfer system possibly mediated by the diffusion of ubiquinone and cyt. Cj these carriers are, however, also coupled to other multienzyme complexes forming the respiratory chain and perform the aerobic metabolism of these facultative photosynthetic organisms [254]. The electrogenic steps of the photosynthetic cycle take place both within the RC and the 6/cj complexes and can be monitored by the electrochromic spectral shift of endogenous carotenoids and on the basis of their response to specific inhibitors and kinetics. When induced by a short laser flash the carotenoid signal displays three distinct kinetic phases (r,/2 10 h/i 5 jas... 

Conjugated polymers, such as polypyrrole, pol3d hiophene, polyaniline (PANl) and its derivatives, are the most promising class of organic-semiconducting materials due to their better electrochemical behavior, electrochromism, ease of doping, and synthesis. But, on the other hand the low processability due to its low solubility is a problem. 

Organic electronics relies on electrically active materials that can be used as conductors, semiconductors, dielectrics, luminescent, electrochromic or electrophoretic materials. The materials have to be carefully chosen since process conditions and the interplay with the other layers will influence the performance of the device. Many approaches are being taken on the material side which have resulted in, as yet, unresolved questions such as organic or inorganic Solntion based or evaporated It is very likely that several approaches will be used in parallel. 

Electrochromic devices (ECDs) consist of a two-electrode electrochemical cell. They include an ion-conducting liquid or solid electfolyte medium sandwiched between two electrode surfaces coated with organic or inorganic electrochromic materials, chosen for their electrical and optical properties. Their purpose is the generation of a variable-color system that can be changed in a controllable fashion for potential applications as displays, smart windows or in other technologies. 

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