Electrochromic, electrochromism optically transparent

Figure 33.1a illustrates the idea of the smart window. In this device a layer of electrochromic material and a layer of a transparent ion-conducting electrolyte are sandwiched between two optically transparent electrodes (OTEs). Indium-doped tin oxide on glass is used most commonly as the OTE. This material has very low... 

In situ UV-visible spectroscopy monitors the energy of electrons within the analyte. While, strictly speaking, all materials change their UV-visible spectrum in accompaniment with electrode reactions (they are said to be electrochromic), the majority of these changes are not discernible by the human eye, and therefore may not be useful to the analyst. Electrodes must be optically transparent for in situ work, with the most commonly used being a thin film of the semiconductor, indium-tin oxide, on glass. 

ECDs operate in the diffuse reflectance mode and the basic requirements for their functionality are (i) a primary electrochromic electrode (e.g. a polymer electrode) deposited on a substrate which is both optically transparent and electrically conducting (generally indium-tin-oxide(ITO)-... 

Interest has developed in electrochromic light transmission modulators, which are called smart windows , for control of temperature and lighting in buildings and automobiles. A cross section of an electrochromic light transmission modulator is shown in Fig. 11.31 (Rauh and Cogan, 1988). The two electrochromic elements of the structure are designated ECl and EC2, and are sandwiched between two thin film, optically transparent, electrodes of ITO and separated by an electrolyte. The ECl layer should colour when a negative potential is applied and the EC2 layer should either colour under positive potentials or remain in a transparent state. This is indicated by the chemical reactions ... 

To assess the electrochromic response of the bipyridinium dications embedded into multilayers of 7, we envisaged the possibility of assembling these films on optically transparent platinum electrodes.27d f Specifically, we deposited an ultrathin platinum him on an indium-tin oxide substrate and then immersed the resulting assembly into a chloroform/methanol (2 1, v/v) solution of 7. As observed with the gold electrodes (Fig. 7.5), the corresponding cyclic voltammograms show waves for the reversible reduction of the bipyridinium dications with a significant increase in 2p with the immersion time. In fact, is 0.8,1.5, and 3.1 nmol/cm2 after immersion times of 1, 6, and 72 h, respectively. Furthermore, the correlation between ip and v is linear after 1 h and deviates from linearity after 6 and 72 h. Thus, the bisthiol 7 can indeed form multiple electroactive layers also on platinum substrates. 

The detection limit for TLV has been improved substantially by using differential pulse and square-wave voltammetry (Chap. 5). For example, detection limits in the 10 8 M range and below have been demonstrated in thin-layer cells requiring less than 100 /xL of sample [61,62]. One practical application of twin-electrode thin-layer cells is in the automatic electrochromic rearview mirror for automobiles. A cell with optically transparent electrodes is placed in front of a mirrored surface. At night, electrolysis in the cell to generate colored material can rapidly reduce glare from following vehicles. 

Deposition of CufFe(CN)6] on to transparent Sn02 gives an optically transparent electrode which undergoes a marked change in the visible spectrum on redox reaction, thus making this material a further candidate for electrochromic devices. 

Sotzing [2] prepared intrinsically conducting water-borne dispersions of poly (thieno[3,4-b]thiophene) homopolymer, (II), and copolymers of thieno[3,4-b] thiophene and 3,4-ethylenedioxythiophene, (111), for electroactive applications including electrochromic displays, optically transparent electrodes, and antistatic coatings. 

The properties of benzothiazolinone azine redox systems have been studied with a view to their practical applications Shelepin and co-workers studied a mixed system involving 3-ethylbenzothiazolin-2-one azine and methyl viologen as an electrochromic system activated by optically transparent electrodes Sharp has described perchlorate-sensitive electrodes also involving 3-ethylbenzothiazolin-2-one azine solid-state electrical properties of salts of the 3-methylbenzothiazolin-2-one azine radical-cation have been reported. ... 

Disordered WO3 films transform from an optically transparent to an absorbing state under ion insertion (intercalation) (cathodic coloration). The octahedral W06 units are favorable for both ion as well as electron transport. The pertinent crystal structure allows long-range diffusion through tunnels or between layers (about WO3 structures, see Section 4.2.7). Thin films show a cluster-type microstructure and a column-type macrostructure. This type of coordination leads to electronic bands, responsible for the electrochromic properties. 

Triphenylamine forms a radical cation on anodic oxidation which dimerizes into tetraphenylbenzidine. The redox potential can be mned by the substituting the aromatic ring. The redox behavior of the PAI can be characterized by cyclic voltametry. Films are cast on an indium tin oxide-coated glass substrate as a working electrode in dry acetonitrile. The electrochromism is examined by an optically transparent thin-layer electrode coupled with a UV-vis spectroscopy. 

The use of PTs as electrochromic materials has been considered in the very early years of development of these polymers [288,289]. However, progress in this area has been hampered by the lack of stability of PTs in their oxidized and most transmissive form. The development of PEDOT, at the beginning of 1990s, has generated a renewal of interest in this field. In fact, PEDOT presents the advantage of a low oxidation potential combined with a stable doped conducting state, which is also the optically transparent state [107,108,290]. 

Doping-undoping cycles of PITN are electrochemically reversible and are accompanied by an electrochromic change in the visible spectmm [ISO]. In the undoped state, thin films of PITN are blue upon doping, the films become optically transparent. 

The properties of sol-gels that are useful in electroanalysis include abrasion and corrosion resistance, ionic conductivity, optical transparency, and electrochromism. These, along with the ease with which sol-gels can be constructed with variable chemical composition have led to their use in electrocatalysis (116), sensing, and as robust reference electrodes (113). Other applications are summarized in references (113,115). Table 1 in (115) includes an in-depth list of useful sol-gel modified electrodes. 

Optics Electrochromic displays, optical filters (windows with adjustable transparency), materials with non-linear optical properties... 

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