Electrochromic polymers structures

This section focuses on the influence of structure of the repeat unit on the colors available in the neutral, oxidized, and in some instances the reduced forms for the various families of electrochromic polymers. The section also covers the electrochromism of parent polymers and the result that the addition of substituents with a variety of functionalities has on the electrochromism. 

Figure 20.9 ECD device of PEDOT and PBEDOT-Cz on an interdigitated, line-patterned electrode, switching between (a) bleached state and (b) colored state. Reprinted with permission from A. A. Argun, P. Aubert, B. C. Thompson, I. Schwendeman, C. L. Caupp,J. Hwang, N.J. Pinto, D. B. Tanner, A. G. MacDiarmid, J. R. Reynolds, Multicolored electrochromism in polymers structures and devices, Chem. Mater. 76, 4401 (2004). Copyright 2004 American Chemical Society...

Most recently Beaupre et al. developed a flexible electrochromic device using textile in 2006 [71]. The structure is made with a transparent electrode, covered with spray-coated electrochromic polymer, a gel electrolyte and finally with a conductive textile. The textile electrode is made with a textile fabric coated with copper and nickel. The other electrode is made of glass or polyester (PET) coated with ITO. Two electrochromic conductive polymers have been tested. Similar colours and colour changes are obtained for structures using two PET-ITO electrodes, or two glass-ITO electrodes, or one textile electrode with one PET-ITO electrode. The colour change is visible but slow. When a plastic electrode and a textile electrode are used, the structure is flexible. A similar structure, using a copper-coated textile cathode, was described by Zhan et al. in 2013 [72]. 

Argun AA, et al. Multicoloured electrochromism in polymers structures and devices. Chem Mater 2004 16(23) 4401-12. 

Further developments in the field of electrochromic polymers seem limited only by the skills, resources, and imagination of synthetic organic chemists, polymer chemists, and material scientists. However, the ultimate usefulness of such fascinating materials hinges on a detailed understanding of their fiindamental redox operation and the accompanying physicochemical-structural changes, and therefore the field is truly interdisciplinary. 

A better understanding of intrinsic properties of electrochromic polymer films (such as the electrical, optical and structural properties) and of the tehavior of these films at different interfaces (such as electrode surface and electrolyte solution) will permit in rovement in the design (electrode materials, conq)osition of siq>port electrolyte, contacts, etc.) and performance of ECDs. Usefol information t is needed includes ... 

The photochemical polymerization of 243 in the presence of an appropriate electron acceptor such as p-dinitrobenzene (DNB) and CCI4 involves photoinduced electron transfer from the singlet excited state of 243 to the electron acceptor causing the formation of radical cation of 243 and radical anion of DNB. Electropolymerization of 243 gave a polymer with strong electrochromic properties. Structure 304 is considered to be the most probable of the four possible structures (304-307) [121-124]. 

As a result of the tremendous scientific work that has been published, a set of electrochromic polymers and copolymers is now available besides the blue PEDOT that gain access to the colors green (copolymers with EDOT structures, ProDOT structures, and benzothiazole structures), (polymers with ProDOT structures) as well as high band gap polypyrroles with transparent oxidized and transparent reduced states that serve as optical neutral ion storage layers. ... 

For smart windows structuring is not an issue, but in electrochromic displays either the electrode material or the electrochromic polymer needs to be structured to obtain suitable patterns. In addition to classical subtractive methods of removing material from undesired areas, PEDOTrPSS may be structured by printing methods. 

At present, intercalation compounds are used widely in various electrochemical devices (batteries, fuel cells, electrochromic devices, etc.). At the same time, many fundamental problems in this field do not yet have an explanation (e.g., the influence of ion solvation, the influence of defects in the host structure and/or in the host stoichiometry on the kinetic and thermodynamic properties of intercalation compounds). Optimization of the host stoichiometry of high-voltage intercalation compounds into oxide host materials is of prime importance for their practical application. Intercalation processes into organic polymer host materials are discussed in Chapter 26. 

The conformational mobility of a chromophoric main-chain polymer is often connected to its electronic structure. Therefore, changes in the UV-visible absorption spectra and/or chiroptical properties are spectroscopically observable as thermo-, solvato-, piezo-, or electrochromisms. It is widely reported that o-conjugating polysilanes exhibit these phenomena remarkably clearly.34 However, their structural origins were controversial until recently, since limited information was available on the correlation between the conformational properties of the main chain, electronic state, and (chir)optical characteristics. In 1996, we reported that in various polysilanes in tetrahydrofuran (THF) at 30°C, the main-chain peak intensity per silicon repeat unit, e (Si repeat unit)-1 dm3 cm-1, increases exponentially as the viscosity index, a, increases.41 Although conventional viscometric measurements often requires a wide range of low-dispersity molecular-weight polymer samples, a size exclusion chromatography (SEC) machine equipped with a viscometric detector can afford... 

Nanocarbon hybrids have recently been introduced as a new class of multifunctional composite materials [18]. In these hybrids, the nanocarbon is coated by a polymer or by the inorganic material in the form of a thin amorphous, polycrystalline or single-crystalline film. The close proximity and similar size domain/volume fraction of the two phases within a nanocarbon hybrid introduce the interface as a powerful new parameter. Interfacial processes such as charge and energy transfer create synergistic effects that improve the properties of the individual components and even create new properties [19]. We recently developed a simple dry wrapping method to fabricate a special class of nanocarbon hybrid, W03 /carbon nanotube (CNT) coaxial cable structure (Fig. 17.2), in which W03 layers act as an electrochromic component while aligned... 

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