Electrochromism, reversible redox

Polynuclear transition metal cyanides such as the well-known Prussian blue and its analogues with osmium and ruthenium have been intensely studied Prussian blue films on electrodes are formed as microcrystalline materials by the electrochemical reduction of FeFe(CN)g in aqueous solutionThey show two reversible redox reactions, and due to the intense color of the single oxidation states, they appear to be candidates for electrochromic displays Ion exchange properties in the reduced state are limited to certain ions having similar ionic radii. Thus, the reversible... 

Electrochromism is observed in reversible redox systems, which exhibit significant color changes in different oxidation states. Violenes, whose general structure is represented in Figure 1, are typical examples that exhibit electrochromism (1). 

The Donnelly Corporation have also devised a rear-view mirror using an hybrid system. A metal oxide electrochromic layer is used in conjunction with a non-elec-trochromic reversible redox complex in the contacting solution. ... 

The reaction of thioxanthone with various 3-thienyllithium compounds is the initial step in the synthesis of the diols such as 602 from which the bis(thioxanthylium) dication 603 is obtained. This species functions as a reversible redox pair with its reduction product, the hexaarylethane, creating an electrochromic system in which electron transfer brings about bond making and bond breaking. These oligomers 604 may be considered to be a new class of molecular wires (Scheme 238) <2004OL2523>. 

For better redox stability, Kim et al. [285] electrochemically synthesized the sodium salt of poly(n-anilino-l-alkanesulphonic acid) XVllI from modified aniline monomers. These polymers were evaluated for electrochromic reversibility by in situ spectroelectro-chemical and cyclic voltammetric techniques. High redox stability (>100000 scans) was observed in acetonitrile solution of 0.1 M NaC104 containing 5% (0.3 M) aqueous HC104. 

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. 

Poly(isothianaphthene) (PITN) can be reversibly cation- and anion-doped without decomposition of the material. PITN with these two reversible and stable redox states of different colors is a potential candidate for electrochromic displays. The reversible redox reaction of PITN and the existence of a relatively stable residual charge can be used in electronic devices, such as memories with learning effect (reading-writing device) [253]. 

In the last few years McCleverty, Ward, and co-workers have reported the NIR electrochromic behavior of a series of mononuclear and dinuclear complexes containing the oxo-Mo(iv) v core unit [Mo(Tp )(0)Cl(OAr)], where Ar denotes a phenyl or naphthyl ring system [Tp = hydro-hydrotris(3,5-dimethylpyrazolyl)borate].184-189 Mononuclear complexes of this type undergo reversible MoIV/Mov and Mov/MoVI redox processes with all three oxidation states accessible at modest potentials. Whilst reduction to the MoIV state results in unremarkable changes in the electronic spectrum, oxidation to MoVI results in the appearance of a low-energy phenolate- (or naphtholate)-to-MoVI LMCT process.184,185... 

Electrochromic materials are electroactive compounds whose visible spectra depend on the oxidation state. Possible applications are smart windows, displays, mirrors, and so on. Among the most important performance aspects in electrochromic materials, the reversibility and lifetime of the material to repeated cycles, the time of response (usually in order of seconds), the colors of the oxidized/reduced forms and the change in absorbance upon redox switching (contrast) are of interest. 

The rationale for preparing this hybrid copolymer was to combine the desirable properties of polyaniline with those of polythiophene. For example, polythiophene has demonstrated thermo- and electrochromism, solvatochromism, luminescence, and photoconductivity while polyaniline has demonstrated reversible protonic dupability, excellent redox re-cyclability, and chemical stability. 

Redox series of metal-polypyridines still await their practical exploration. The existence of multistep, reversible, sequential reduction processes, each step occurring at a defined potential and being localized at a specific molecular site, is very promising for possible applications in molecular electronics. This would require to organize the active complexes in films, polymers or supermolecules. Up to now, only the electrochromic behavior of some [Ru(N,N)a] + complexes has been explored with potential applications in electrochromic glasses, displays and redox sensors [206, 262, 264]. 

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