Electrochromism phenomena

In conclusion, in spite of the fact that this technique was not often used until now, it is obviously a preferred technique for studying electrochromism phenomena. 

It is clear that one should take care in interpreting the PSl5 signal. Small changes in the PS 15 signal might be due to non-electrochromic phenomena, like reaction 3. 

Chiroptical luminescence Circular polarized luminescence (CPL) allows obtaining information about excited state structures. Corresponding achiral information can be obtained from electrochromic phenomena of molecules. Serious experimental problems, which often lead to more artifacts than acceptable, have prohibited a broad application of this method. Information can be obtained about S T transitions of enones and ketones. For metal complexes kinetic studies about stereochemical dynamics are available. New experimental developments seem necessary for a broad application of the CPL. 

The test procedures for electrochromic phenomena of these polymers were i) electronic absorption spectra at different values of the injected charge, as in Figure 7.5 ii) data of electrical and optical response (shown by transmittance modulation at the maximum absorption wavelength of the undoped form) following the application of repeated square wave potential steps, as in Figure 7.6 (note that undoping is faster than the doping process) ... 

Compositions of HTSC and ultrathin layers of dyes also exhibit interesting properties [434]. The potentiality of electrosynthesis for fabrication of such structures with specific optical transitions is excellent, particularly as a result of experience gained in studies and applications of the electrochromism phenomenon [435] such as forming films of poorly soluble cyanide complexes [436-441]. These compounds provide the opportunity to carry out electrochemical fabrication of linked and sandwich structures. The region of potential during deposition corresponds to the stability regions of HTSC surfaces. 

Deb SK, Witzke H (1975) The solid state electrochromic phenomenon and its applications to display devices. Proc IEEE Int Electron Devices Mtng 21 393-397... 

PEMs with electrochemical materials change color with an applied potential through a redox process. The LBL-based fabrication technique effectively immobi-hzes electrochromicaUy active polymers or nanoparticles on an electrode to achieve efficiency access of active materials for a maximum response. The first PEM electrochromism phenomenon was reported by Schlenoff and Laurent using PEM... 

The neutral form of polypyrrole is weakly coloured while the oxidised form is a deep blue/black so that switching the state of the film not only changes its conductivity but is also accompanied by a marked colour change, a phenomenon termed electrochromism. 

As shown, optical electron-transfer transitions in polynuclear complexes are certainly not a new phenomenon and have been studied very broadly and thoroughly [119-122]. However, most of the examples are strictly solution based and the attachment to an electrode has not been addressed. As a result, then-applicability to devices has not been investigated. Overall, it is quite obvious that the tremendous potential of the field for the discovery of electrochromic materials has hardly been touched. 

The phenomenon of electrochromism can be defined as the change of the optical properties of a material due to the action of an electric field. The field reversal allows the return to the original state. In practice, when the material is polarized in an electrochemical cell, the change of colour is conelated to the insertion/extrac-tion of small ions H" ", Li" ". This insertion/extraction is monitored by the passage from cathodic to anodic polarization which allows to go from bleached (or coloured) state to coloured (or bleached) one. This property belongs to all (or almost all) transition metal oxides it corresponds to the change of valency of the cation Ni "> Ni " O . .. accompanied... 

Electrochromism is a phenomenon displayed by some materials reversibly changing colors. Various materials can be used to construct electrochromic devices, such as transition metal oxides, liquid crystals, photonic crystals, and polymers (Booth and Casey, 2009 Nicoletta et al., 2005 Arsenault et al., 2007 Gamier et al., 1983). Here, we will focus on the electrochromic materials based on polymers. There are several mechanisms to explain the color changes of polymer electrochromic materials like electro-induced oxidation-reduction and electrothermal chromatic transition and so on. 

Some mixed conductors, i.e. electronic and ionic, into which ions can be rapidly and reversibly inserted can undergo a colour change. This is, for example, the case of the hydrogen bronzes , mentioned earlier in this book. The colour change can be either from transparent to coloured or from one colour to another. This phenomenon, which can be produced electrochemically, is called electrochromism. It is broadly defined as the production of an absorption band in a display material caused by an applied electric field or current. Such a property is currently under intensive study because of its potential use for passive information display glare-free rearview mirrors for automotives " , solar control windows or smart windows " , thermal sensors and projection systems if matrixable. 

Chromatic changes caused by electrochemical processes were originally described in the literature in 1876 for the product of the anodic deposition of aniline [271]. However, the electrochromism was defined as an electrochemically induced phenomenon in 1969, when Deb observed its occurrence in films of some transition metal oxides [272]. Electrochromism in polypyrrole was first reported by Diaz et al. in 1981 [273]. Electrochromism is defined as the persistent change of optical properties of a material induced by reversible redox processes. Electronic conducting polymers have been known and studied as electrochromic materials since the initial systematic studies of their electronic properties. 

Conductive polymers are polyconjugated molecules, with the consequence that the electronic energy levels are close enough to provide transitions in the visible and near-infrared region. The electronic absorption spectra of reduced and oxidized forms of CPs are quite different, and because the redox state can be changed at will by the electrical potential, the phenomenon is often called electrochromism. It is speculated that this phenomenon could be applied in some inexpensive display systems. 

Roger Mortimer graduated from Imperial College London in 1977. Thereafter, he remained at Imperial until 1980, when he completed a PhD on heterogeneous catalysis under the supervision of Dr Michael Spiro. He developed his lifelong interest in the surface modification of electrode surfaces during a postdoctoral fellowship with Professor Fred C Anson at California Institute of Technology in 1981. His scientific horizons were then further broadened at the University of Exeter, where he collaborated with Dr David R Rosseinslq. At Exeter, he carried out important studies on the phenomenon of electrochromism in thin films of... 

Additionally, the film formation properties and outstanding mechanical properties of aramids make these polymers suitable for the production of organic light emitting diodes (OLEDs), and specifically polymer hght emitting diodes (PLEDs). Despite this, classical condensation polymers are rarely studied for these applications. Moreover, some luminescence materials also show electrochromism (EC), a phenomenon in which materials exhibit a reversible change in optical properties when they are oxidized and reduced. Electrochromic materials are now been exploited in diverse applications such as mirrors, displays, windows, and earth-tone chameleon materials [95]. 

Apart from in the materials discussed so far, electrochromism is known to occur in mai binary and ternary mixed oxides and in oxyfluorides. There are also some simple oxides that have been reported to display electrochromism, although this phenomenon has not yet been explored in detail oxides based on Cu, Sr-Ti, Rtt, and Pr belong to this latter class.Finally, among the nonoxides pronounced anodic electrochromism is known in transition metal hexacyanometallates, especially Pmssian Blue (PB). ... 

Electrochromic materials undergo reversible and persistent changes of their optical properties under the action of voltage pulses. The phenomenon is known both in inorganic (oxidic) and organic materials only the former ones have been discussed in this article. Electrochromic... 

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