Electrochromic materials cation

Ladder Polymerization oe Fluoranthene-Based Cation-Radicals AS Route to Electrochromic Materials... 

Bipyridinium dications do not absorb in the visible region of the electromagnetic spectrum.28 After their electrochemical reduction to the corresponding radical cations, however, a broad and intense absorption appears across the visible region. The process is fully reversible and the colorless state is regenerated, after the oxidation of the radical cations back to the original dications. In fact, bipyridinium dications are convenient building blocks for the realization of electrochromic materials, as a result of their spectroscopic response to electrochemical inputs. 

Electrochromic materials are of three basic types [i]. In a given -> electrolyte solution, type I materials are soluble in both the reduced and oxidized (redox) states, an example being l,l -di-methyl-4,4 -bipyridylium ( methyl viologen ), which, on reduction, switches from the colorless di-cation to the blue radical cation. Type II materials are soluble in one redox state, but form a solid film on the surface of an electrode following electron transfer. An example here is l,l -di-heptyl-4,4 -bipyridylium ( heptyl viologen ). In type III materials, such as -> tungsten oxide, - Prussian blue, and electroactive conjugated polymers, both... 

Electrochromic materials are of interest for displays, smart windows, sunroofs, etc., and are characterized by the reversible change in their color upon application of light or electrical inputs. The electrochromic effect is generally associated with the ingress/issue of electrons and metal cations. 

The mechanism is, however, more complicated than simply the anion X entering the polymer during anodic polarization and leaving it upon the cathodic one, as cation motion can also be involved [2]. Conducting polymers are thus a class of ion-insertion electrochromic materials that act during an electrochromic process as mixed electronic and ionic conductors. 

Typical electrochromic materials are bipyridinium salts (viologens). Dyes like viologens often consist of differenf chemical species in an electrolyte which are either oxidized or reduced at the electrodes to form radical cations and anions that recombine charges after diffusion (Figure 10.38 and Figure 10.39). In such systems a small but significant current will be necessary to maintain the colored state. Electrochromism with viologens as electrochromics and liquid electrolytes may be combined with FEDOT as a transparent electrode material. ... 

Spectroelectrochemical analysis of charge-insertion nanostructured materials already offers important insight into these systems. These methods were recently exploited to characterize the electrochemical processes of nanostructured manganese oxide ambi-gel and xerogel films. " 6-229 Spectroelectrochemical measurements were used to corroborate electronic state changes with the observed electrochemical response for the insertion of small cations (Li+, Mg2+) and the unexpected insertion of a bulky organic cation (tetrabutylammonium). Vanadium pentoxide exhibits two distinct electrochromic features that can be assigned to the transition at either sto-... 

The anodic oxidation of spiro[4,9 -fluorenyl]-2,6-diphenyl-4//-thiopyran at high potential leads to deposition on the anode of polymeric material which consists of a polyphenylene framework bearing thiopyran or thiopyrylium substituents depending on the oxidation state. This conducting material is electrochromic, appearing blue, red, or yellow according to its oxidation state. It is proposed that the reaction proceeds via a radical thiopyran cation. 

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