Electrochromic applications

Electrodeposition on transparent material such as indium tin oxide (ITO) can be used for electrochromic applications [328]. Pb deposition on indium-tin oxide electrode occurs by three-dimensional nucle-ation with a diffusion-controlled growth step for instantaneous nucleation [329], and the electrode process has also been studied using electrochemical impedance spectroscopy [328]. 

Badilescu, S. and P.V. Ashrit (2003). Study of sol-gel prepared nanostructured WO3 thin films and composites for electrochromic applications. Solid State Ionics, 158(1-2), 187-197. 

Fig. 19.10. Schematic diagram of nanostructured-semiconductor-redox chromophore assembly for electrochromic applications.

John P. Lock, Jodie L. Lutkenhaus, Nicole S. Zacharia, Sung Gap Im, Paula T. Hammond, and Karen K. Gleason. Electrochemical investigation of PEDOT films deposited via CVD for electrochromic applications. Synthetic Metals, 157(22-23) 894-898, 2007. 

An important area where technology and heterocyclic chemistry combine is that of electroactive organic materials. The applications of these materials, which extend beyond simple replacements for metals, include use as conductors, superconductors, semiconductors, batteries, transistors, sensors, light emitting diodes (LEDs), and related electrochromic applications. This area is of great commercial importance. 

Electrochromic applications of the PAn and substituted PAn films [307a-h], composite films of PAn or its derivatives with other electrochromic materials [307i-m], silanized PAn films [306o] and photo-induced electrochromic reactions on semiconductor particles [307p]. Again, most other polymers can be used for this purpose as long as their oxidized and reduced states are stable and have different colors from that of neutral polymers. 

Independently of any electrochromic application, optical spectroscopy was extensively used to study the properties of PANl, either ex situ after equilibration in different media, or in situ during polarization [45,46,49,50,52,60-63]. 

Electropolymerization techniques have also been popular for the preparation of electrodes modified by thin films of Schiff-base metallopolymers for prospective electrocatalytic, chemical sensing, and electrochromic applications [79-85]. In... 

Highly hydrophilic polymers derivatized with oligoethers chains have been prepared from 45. These polymers show electroactivity in aqueous medium and present cation recognition properties. Moreover, they constitute a unique example of polymers with solid state ionochromic properties (see Section 13.4.1.1) [146]. The synthesis of 54 bearing perfluoro chains has also been reported starting from 45 and its related polymer has been investigated for electrochromic application [147]. 

Leventis, N. and Y.C. Chung. 1990. Polyaniline—Prussian Blue novel composite material for electrochromic applications. J Electrochem Soc 137 3321—3322. 

Poly (thiophene)s are of particular interest as electfochromic materials owing to their chemical stability, ease of synthesis and processability. For the most part, current research has been focused on composites, blends and copolymer formations of several conjugated polyheterocyclics, polythiophene and its derivatives, especially PEIX)T. In one example, poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS) composite films were prepared by Sonmez et al. for alternative electrochromic applications [50]. Thin composite films comprised of PEDOT/PAMPS were reported to switch rapidly between oxidized and neufial states, in less than 0.4 s, with an initial optical contrast of 76% at A.max. 615 nm. Nanostructured blends of electrochromic polymers such as polypyrrole and poly(3,4-ethylenedioxythiophene) were developed via self-assembly by Inganas etal. for application as an electrochromic window [26]. Uniir etal. developed a graft-type electrochromic copolymer of polythiophene and polytetrahydrofuran for use in elecfiochromic devices [51]. Two EDOT-based copolymers, poly[(3,4-ethylenedioxythiophene)-aZ/-(2,5-dioctyloxyphenylene)] and poly[(3,4-ethylenedioxythiophene)-aft-(9,9 -dioctylfluorene)] were developed by Aubert et al. as other candidates for electrochromic device development [52],... 

Polythiophenes and their derivatives have been intensely studied due to their interesting electronic properties. Owing to the combination of their electronic properties, environmental stability, stmctural versatility, low bandgap, low cost and ease of preparation, polythiophene and its derivatives have been utilized in the development of many new electrochromic devices. Here, we focus on the use of polythiophenes for electrochromic applications in terms of their basic properties bandgap and its relation to stability, chain length of substituted functional groups and optical properties such as electrochromic contrast (with some examples from the literature). 

The property of polythiophenes to change color upon the reversible oxidation/reduction process and the resulting electrochromic applications (e.g. smart windows) are the subject of the review Chapter 20 by Greg Sotzing and co-workers. 

The low oxidation (p-doping) potential of poly(oxythiophene)s along with high conductivity, transparency and stability of doped state make them ideal as a transparent conductor and as a hole-transport layer in various optoelectronic devices. On the other hand, alkyl-substituted EDOT and ProDOT derivatives are suitable for electrochromic applications. However, PEDOT remains one of the most extensively studied polymers in this class due to the easy commercial access of EDOT monomer and processable PEDOT polymers (Clevios-P). 

Fused azole systems with three heteroatoms can be represented by ben-zothiadiazole (BT), benzoselenodiazole (BSe), benzotriazole (BTA)." Among them the heterocycle BT is most widely used in conjugated co-polymers. Derivatives of BT have been widely used in organic electronic devices, especially in terms of electrochromic applications. While incorporated into the conjugated backbone these BT moieties bring to the polymeric material such properties as strong ICT transition dipole, multicolored electrochromism and efficient photoluminescence. 

Infrared Electrochromics. While applications for visible electrochromics are widespread with many commercial possibilities, infrared (3-17 /xm) electrochromics applications are limited. Disordered transition-metal oxides have been pursued because of their broad polaron absorption (318), but slow response times and processing difficulties have limited applications. As with most electrochromics appUcations, EAPs are attractive for IR electrochromics because of their rapid response times and ease of processing. Research to date in EAPs for IR electrochromics has focused on polyaniline-based (319-321) and poly(3,4-alkylenedioxythiophene)-based (322,323) systems. The... 

Star conducting polymers, which have a central core with multiple branching points and linear conjugated polymeric arms radiating outward, are currently being investigated for electrochromic applications (69,70). Examples include star... 

The challenge that remains for conducting polymer electrochromic applications is clearly in the domain of device scale-up. The application of these materials to large area devices, such as windows, requires uniform real-time switching of the polymer oxidation state to access different color regions. Although this has been demonstrated for small-scale devices, it is difficult at larger scales. 

Spectroelectrochemical analyses of the BBB, BBL, and PPTZPQ polymer films were performed to study the electronic structure and to examine the spectral changes that occur during redox switching both are inportant for electrochromic applications. BBL spectra showed an increase in absorbance at 524 nm, a decrease at 583 nm, and two not well-defined isosbestic points at 375 and 550 nm BBB spectra did not show clear isosbestic points. For die reduced form of BBB, the maximum peak was at 503 nm, and as die lied potential passed over the first voltammetric feature, the film exhibited an absorption peak at 576 nm These electrochromic effects were stable and reversible under anaerobic and anhydrous conditions die BBL and BBB films continued to exhibit strong color changes after more dian 500 successive cycles in MeCN (24). 

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