Electrochromism polymeric electrochromes

The added electron is delocalized on the monovalent radical ion to which it is reduced (3). There is no general agreement on the molecular representation of the reduced stmcture. Various other viologen compounds have been mentioned (9,12). Even a polymeric electrochromic device (15) has been made, though the penalty for polymerization is a loss in device speed. Methylviologen dichloride [1910-42-5] was dissolved in hydrated... 

In general, those properties of industrial interest that are related to the electrochemical rates change several orders of magnitude when the conditions of synthesis are improved and when a solvent suitable for the specific application is used to produce the polymeric gel. We found this to be the case in our laboratory between the first and second generation of artificial muscles, with electrochromic films, or with specific energies. 

A surface-modified polymeric system can be obtained by spin coating or heating [Ru(L6)3]21 as its / -tosylate salt.16 The resulting film shows seven-color electrochromism whose colors cover the spectral range, which can be scanned in 250 ms. 

Metallopolymer films have also been prepared by oxidative polymerization of complexes of the type [M(phen)2(4,4 -bipy)2]2+ (M = Fe, Ru, or Os phen= 1,10-phenanthroline, 4,4 -bipy = 4,4 -bipyridine).23 Such films are both oxidatively and reductively electrochromic reversible film-based reduction at potentials below —IV lead to dark purple films,23 the color and potential region being consistent with the viologen dication/radical cation electrochromic response. A purple state at high negative potentials has also been observed for polymeric films prepared from [Ru(L13)3]2+.24 Electropolymerized films prepared from the complexes [Ru(L16)-(bipy)2][PF6]22 and [Ru(L17)3][PF6]226,27 exhibit reversible orange/transparent electrochromic behavior associated with the Run/Ruin interconversion. 

Kashiwazaki67 has fabricated a complementary ECD using plasma-polymerized ytterbium bis(phthalocyanine) (pp—Yb(Pc)2) and PB films on ITO with an aqueous solution of 4M KC1 as electrolyte. Blue-to-green electrochromicity was achieved in a two-electrode cell by complementing the green-to-blue color transition (on reduction) of the pp—Yb(Pc)2 film with the blue (PB)-to-colorless (PW) transition (oxidation) of the PB. A three-color display (blue, green, and red) was fabricated in a three-electrode cell in which a third electrode (ITO) was electrically connected to the PB electrode. A reduction reaction at the third electrode, as an additional counter electrode, provides adequate oxidation of the pp Yb(Pc)2 electrode, resulting in the red coloration of the pp—Yb(Pc)2 film. 

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

Not surprisingly, the research field of electrochromic compounds is very broad and includes inorganic, organic, and polymeric as well as several hybrid materials. We shall therefore attempt to give a brief overview of past and current achievements before we present our own contributions. Due to its scope, this chapter cannot be considered comprehensive, and the reader is referred to recent review articles for a more detailed description. [26,27,33]. 

Photochemical polymerization of dithiophene 325 in acetonitrile in the presence of CC14 and TBABr leads to a thin film with electrochromic properties in the visible region (94JCS(CC)1911 95SM(69)309). Laser flash photolysis in the presence of CC14 showed absorption at 417 nm due to the radical cation. 

In the most important series of polymers of this type, the metallotetraphenylporphyrins, a metalloporphyrin ring bears four substituted phenylene groups X, as is shown in 7.19. The metals M in the structure are typically iron, cobalt, or nickel cations, and the substituents on the phenylene groups include -NH2, -NR2, and -OH. These polymers are generally insoluble. Some have been prepared by electro-oxidative polymerizations in the form of electroactive films on electrode surfaces.79 The cobalt-metallated polymer is of particular interest since it is an electrocatalyst for the reduction of dioxygen. Films of poly(trisbipyridine)-metal complexes also have interesting electrochemical properties, in particular electrochromism and electrical conductivity.78 The closely related polymer, poly(2-vinylpyridine), also forms metal complexes, for example with copper(II) chloride.80... 

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. 

Table 1. Comparison between inorganic and polymeric electrochromic materials...

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