Optically active electrochromism

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. ... 

Chiral disubstituted PEDOTs have recently been prepared for the first time via transetherification of 3,4-dimethoxythiophene monomers with chiral glycols followed by potentiodynamic oxidation.174 An alternative approach to optically active PEDOTs has also been recently described, which involves the electrochemical polymerization of the EDOT monomer in aqueous hydroxypropyl cellulose (HPC) as a polymer lyotropic liquid crystal to give a chiral PEDOT/HPC hybrid.175 The PEDOT prepared in this chiral nematic liquid crystal exhibited optically active electrochromism in that it could be electrochemically switched between a dark blue reduced state and a sky blue oxidized form that exhibited a different CD spectrum. 

Electrochromism is defined as a persistent but reversible optical change in absorption or reflection produced electrochemically in a medium by an applied electric field or current. An electrochromic device in which this process can be realized is schematically shown in Figure 1. Generally such a device contains transparent conductors, an ion storage layer, an ionic conductor and an optically active electrochromic layer. We will focus on properties of the ionic conductor. 

Critical properties of TCO coatings are electrical resistance and transparency [3], but for solar cell applications very often texture and large haze factors, i.e., ratio of diffuse to total transmission, have similar importance. Large haze factors have been shown to influence positively the efficiency of silicon solar cells, because the reflection at the TCO-silicon interface is reduced and the scattering increases the pathway of light inside the active material. The preparation and characteristics of several TCO materials have been reviewed by Chopra et al. [92] and Dawar and Joshi [93]. The optical and electrical properties of ITO and aluminum doped zinc oxide have been studied in detail by Granqvist and coworkers [94, 95], but these films were prepared by sputtering and not by CVD. Very recently they also published an overview of transparent conductive electrodes for electrochromic devices [7]. 

Electrochromism is the reversible change in optical properties that occurs when a material is electrochemically oxidized or reduced [224], This working definition includes a change in optical properties anywhere in the solar (and even in some cases the microwave) range. In addition to the active electrochromic layer, a device consists of an electrolyte and a counter electrode, which may or may not be electrochromic. The electrolyte should be a good ionic conductor and electrically insulating in order to be nonvolatile. 

Functionalized PTs have been investigated in various applications, e.g., their ability to detect, transduce, and amplify various physical or chemical informations into an electrical or an optical signal has led to the development of devices capable of detecting analytes or biomolecules in the field of environment, security, and biotechnology. Currently, functionalized PTs play a key role as active materials in the development of electrochromic devices and electronic devices, such as OLEDs, OFETs, and organic solar cells. 

ECDs are designed to modulate absorbed, transmitted, or reflected incident electromagnetic radiation. This is accomplished through the application of an electric fleld across the electrochromic materials within the device. The device acts as an electrochemical cell where electrochemical reactions occur between two redox-active materials that are separated by an electrolyte. Often, an ECD includes two electrochromic materials that have complementary electronic and optical properties allowing both electrochromes to contribute to the optical response of the device. 

A number of potential applications of conducting polymers are expected because they are organic compounds, have conjugated structure and many subordinating properties and functions, such as electronic conducting properties, electrochemically active properties (electrochemical doping-undoping), electrochromic behaviours, nonlinear optical properties, etc. 

Optical memory (open-circuit memory). Optical memory is defined as the time that an electrochromic material maintains its absorption state once the applied voltage is removed. Solution-based electrochromic systems will bleach (lose their absorptive state) more quickly than their solid-state counterparts [24]. In the solution case, the mobile redox-active species, which are dissolved in an electrolyte, can diffuse to both electrodes when the circuit is open. Therefore, there is no open-circuit memory in these devices and power must be supplied continuously to maintain coloration. 

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. 

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