Polymeric electrochromic devices

The added electron is delocalized on the monovalent radical ion to which it is reduced (3). There is no general agreement on the molecular representation of the reduced stmcture. Various other viologen compounds have been mentioned (9,12). Even a polymeric electrochromic device (15) has been made, though the penalty for polymerization is a loss in device speed. Methylviologen dichloride [1910-42-5] was dissolved in hydrated... 

Sonmez, G., Shen, C.K.E, Rubin, Y.,Wudl, E, 2004a. A red, green, and blue (RGB) polymeric electrochromic device (PECD) the dawning of the PECD era. Angewa. Chem. Int. Ed. 43,1498-1502. 

Sonmez, G., H. Meng, and F. Wudl. 2004. Organic polymeric electrochromic devices Polychro-mism with very high coloration efficiency. Chem Mater 16 (4) 574-580. 

Hu, H., L. Hechavarria, and J. Campos. 2003. Optical and electrical responses of polymeric electrochromic devices Effect of polyacid incorporation in polyaniline film. Solid State Ionics 161 165-172. 

Construction of a dual-polymer electrochromic device (type iii memory device) that has two face-to-face polymer layers in each cell producing 400 (20 x 20) different combinations of absorptions was shown by Sonmez and Sonmez [84], In this study, several examples of this 3x3 pixel dual polymeric electrochromic device composed of red poly(3-alkylthiophene), green poly(2,3-di(thien-3-yl)-5, 7-di(thien-2-yl)thieno[3,4-fc]pyrazine] and blue PEDOT polymers, which switch at different wavelengths, were presented. These distinct absorption states have led to speculation that electrochromic polymers could be used for memory storage devices and computing functionalities. 

A further chemical which could be made is duroquinone. Uses which have been proposed for this include the use of the monoxime as a fungicide, particularly to protect seeds prior to planting(53). Duroquinone also forms a complex with Ni(0)(54) and with Ni(0) and cyclooctadiene(55), either of these complexes being claimed as catalysts for polymerizing unsaturated compounds such as acrylonitrile or phenylacetylene. Duroquinone may also have value in electrochromic devices(56,57) however, the requirements for this use are relatively stringent, namely it must have an oxidation/reduction potential within an acceptable range and it must be able to be cycled tens of thousands of times. The advantage of duroquinone is its lack of available reaction sites. Clearly the tetrachloro derivative would also be a possibility. Duroquinone may have a similar potential in electrical accumulators. 

Other materials being investigated include ferrocene with a bipyridinium salt,234 niobium oxide,235 nickel oxo-hydroxide,236 and cobalt oxohydroxide.237 The last is pale yellow in the reduced state and dark gray in the oxidized state. A typical electrolyte is lithium perchlorate in propylene carbonate. Solid electrolytes, such as a lithium salt (perchlorate, tetrafluoroborate, or triflate), in a polyepoxide238 or in a polyvinyl chloride gel in ethylene carbonate-propylene carbonate,239 lithium iodide in polyvinyl bu-tyral,240 and Naflon H (a polymeric perfluorocarbon-sulfonic acid),241 have also been tested. Some other systems use suspended particles between two panes of glass.242 When the particles are aligned by an electric field, the window becomes transparent. Combination photo-voltaic-electrochromic devices are under study.243... 

Among the conjugated polymers, polypyrrole (PPy) is the most representative one for its easy polymerization and wide application in gas sensors, electrochromic devices and batteries. Polypyrrole can be produced in the form of powders, coatings, or films. It is intrinsically conductive, stable and can be quite easily produced also continuously. The preparation of polypyrrole by oxidation of pyrrole dates back to 1888 and by electrochemical polymerization to 1957. However, this organic p>-system attracted general interest and was foimd to be electrically conductive in 1963. Polypyrrole has a high mechanical and chemical stability and can be produced continuously as flexible film (thickness 80 mm trade name Lutamer, BASF) by electrochemical techniques. Conductive polypyrrole films are obtained directly by anodic polymerization of pyrrole in aqueous or organic electrolytes. 

Optical spectra (UV/ViyNIR) of electrochemically polymerized PEDT in both its reduced and fully oxidized state have been published as early as 1994 [10,103], demonstrating the nearly colorless, sky-blue conductive doped state. In addition, optical spectra of the PEDT PSS complex have been measured in the same maimer, exhibiting a value of about 600 run for the reduced form [26]. The exact chemical nature of the deep blue, reduced state of PEDT and PEDT PSS used in electrochromic devices has long been under discussion. As previously discussed in this review, fiilly undoped, reduced PEDT is not blue, but is reddish purple, and it cannot be readily obtained by electrochemical means [27,28]. Some recent... 

De Paoli, M.-A., G. Casalbore-Miceli, E.M. Girotto, and W.A. Gazotti. 1999. All polymeric solid state electrochromic devices. Electrochim Acta 44 2983-2991. 

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... 

Recently, polymers based on 2,3-di(3-thienyl)thieno[3,4- >]pyrazine 3.25 have attracted much attention due to their green color and application prospects in electrochromic devices (Chart 1.47) [339]. Electrochemical polymerization of 3.25a performed at a low potential yielded polymer P3.25a, reflecting a very saturated green color in the neutral state. In the oxidized form, these absorptions were depleted and resulted in a transmissive pale-brown polymer. Terthiophene P3.25b had a better solubility and could be polymerized by chemical oxidants such as FeCls and CuC. Whereas the mild oxidant CuCb gave better polymers P3.25b, the strong oxidant FeCls overoxidized the monomer and gave a purple, insoluble polymer [340-343]. 

These examples of electrochromic devices serve to display the breadth of their applicability to any number of systems. Polymeric electrochromics, particularly those based on thiophene and its derivatives, show promise for use in display technologies. The processability of many of these systems makes them specifically suited for large-area applications, such as smart windows, billboards or organic photovoltaic cells (solar cells), which currently suffer from large environmental and practical costs when fabricating large-area devices. 

Varaprasad, D. V. Agrawal, A. Zhao, M. Allemand, P. Doman, C. A. Lynam, N. R. Electrochromic polymeric solid films, manufacturing electrochromic devices using such solid films, and processing for making such solid films and devices. Eur. Pat. Appl. EP 612826,1994 Chem. Abstr. 1995,122,326083. 

The first example is the work of Lu et al. [124] who fabricated polypyrrole (PPy)ATi02 coaxial nanocables, where the conductivity of PPy was integrated with the photocatalytic activity of Ti02 for applications in electrochromic devices, nonlinear optical systems, and photoelectrochemical devices. The synthetic approach consisted in (1) preparation of Ti02 fibers by sol-gel electrospinning and calcination of the polymer (PVP in the specific case), (2) physical adsorption of Fe " oxidant on the surface of Ti02 nanofibers, and (3) polymerization of pyrrole (from vapor) on the surface of Ti02 nanofibers. 

Other successful electrochromic devices have been realized by Kelly et al. using polyaniline-impregnated fibres [79]. In situ electrochemical polymerization of polyaniline is used to bind poly aniline to a PET or viscose spacer fabric. The fabric is then impregnated with an electrolyte and sandwiched between two electrodes. For the bottom electrode, carbon black or silver ink can be printed directly on the fabric. Polyaniline colour changes from green to blue through oxidation—reduction processes. However, the lifetime of this structure is also short and does not exceed dozens of oxidation—reduction cycles. 

Ethylenedioxythiophene (EDOT) (34) is now commercially available. Hey-wang and Jonas [234-236] first polymerized EDOT and found that the relevant polymer could be useful for antistatic coatings. Heinze and co-workers [237] subsequently studied the spectroscopic and electrochemical properties of poly(EDOT) the optical band gap of the polymer is about 16 eV (760-780 nm). Inganas and colleagues [238] showed the usefulness of poly(EDOT) as a potential material for electrochromic devices because of its ability to cycle between an opaque blue-black in the reduced (undoped) state and a transparent sky blue in the oxidized (doped) state. Recently, poly(EDOT) has been used for the construction of rapidly switching solid-state electrochromic devices based on complementary conducting polymer films [239]. 

Electrochemical polymerization is a major method to synthesize conducting polymer for potential application in energy storage devices, electrochromic devices. 

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