Electroactive conducting polymers electrochromism

The electrochemical polymerization of Ti-electron-rich aromatics, such as aniline, pyrrole and thiophene, to obtain electrically conducting polymers is well-known. Some reports describe the polymerization of amino-, pyrrolyl- and hydroxy-substituted tetraphenylporphyrins and suitable substituted phthalocyanines (for reviews see [230,231]) (anodic electropolymerization of 2,9,16,23-tetraaminophthalocyanine (M = Co(II), Ni(II)) [231,232] and 2,9,16,23-tetra(l-pyrrolylalkyleneoxy)phthalocyanines (M = 2H, Zn(II), Co(II) [232])) under formation of polymers 53 and 54 shown as idealized structures. Depending on the reaction conditions the film thicknesses are between around 50 nm and several pm. The films remain electroactive at the electrochemical potential so that oxidation or reduction current envelope grows with each successive potential cycle. Electrochromism, redox mediation and electrocatalysis of the electrically conducting films are summarized in [230,231]. 

In the most important series of polymers of this type, the metallotetraphenylporphyrins, a metalloporphyrin ring bears four substituted phenylene groups X, as is shown in 7.19. The metals M in the structure are typically iron, cobalt, or nickel cations, and the substituents on the phenylene groups include -NH2, -NR2, and -OH. These polymers are generally insoluble. Some have been prepared by electro-oxidative polymerizations in the form of electroactive films on electrode surfaces.79 The cobalt-metallated polymer is of particular interest since it is an electrocatalyst for the reduction of dioxygen. Films of poly(trisbipyridine)-metal complexes also have interesting electrochemical properties, in particular electrochromism and electrical conductivity.78 The closely related polymer, poly(2-vinylpyridine), also forms metal complexes, for example with copper(II) chloride.80... 

A number of conjugated heterocyclic polymers, viz., poly(pyrrole) [9], poly(p-phenylene) [10], poly(thiophene) [11], and poly(aniline) [12] are also electrically conducting and continue to be developed and studied for electrochromic devices [13-14 see also the companion chapter in this volume] and ion switching devices [15-16], among others. Polymer films with high electrical conductivity have been generated by electrochemical polymerization of benzenoid, nonbenzenoid and heterocyclic aromatics, in particular from the derivatives of pyrrole, thiophene, carbazole, azulene, pyrene, triphenylene and aniline. The electrochemical approach for making these films is very versatile and it provides a facile way to vary the properties of the films. The realization of the applications for each electroactive polymer depends on the control and particularly the enhancement of the... 

Many typical electrochromic devices are composed of seven layers, as shown in Figure 20.4 [37]. One alternative to this classical model is a simplified five-layer electrochromic device, where transparent conducting layers were eliminated by Mecerreyes et al. (Figure 20.5) [37]. This type of configuration was successfully tested by using a solution of poly(ethylene oxide-lithium triflate) (PEO -I- CEsSOsLi) in tetrahydrofuran (THF) as a polymer electrolyte, while PEDOT was used as an electroactive polymer by Carpi and De Rossi [29]. 

An electroactive polymeric laminate suitable for an electrochromic display device comprises a conductive substrate, a first layer of an electroactive polymer, and a second layer of another electroactive polymer prepared from a monomer with a higher oxidation potential than that of the first monomer and adhering to the first layer [174]. 

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