Electrochromic properties

Tetrathiafulvalene (TTE) has also been used in electrochromic devices. TTE-based polymers spin-coated onto transparent electrode surfaces form stable thin films with reproducible electrochromic properties (100). The slow response of these devices has been attributed to the rate of ion movement through the polymer matrix. 

A large number of materials show electrochromic properties however, only a few of them are interesting for practical applications since for this purpose, additional requirements must be fulfilled (1) as discussed above, for most applications the materials need to have a colorless (bleached) state (2) the electrochromic transformations should occur without parasitic reactions, such as gas evolution or material degradation (3) to be considered practical, the electrochromic materials should survive at least 10 coloring-bleaching cycles (4) the rate of electrochromic transformation needs to be sufficiently fast (1 s for most applications) and (5) due to problems with leaking and diffusion in iiquids, it is preferabie to have insoiubie soiid efec-trochromic materiais. 

The electrochromism of the phthalocyanine ring-based redox processes of vacuum-sublimed thin films of [Lu(Pc)2] was first reported in 1970,32 and since that time this complex has received most attention, although many other (mainly lanthanide) metallophthalocyanines have been investigated for their electrochromic properties.1 Lu(Pc)2 has been studied extensively by Collins and Schiffrin33,34 and by... 

The structures and redox properties of these complexes have been extensively reviewed 170,171 of interest here is the presence of an intense NIR transition in the neutral and mono-anionic forms, but not the dianionic forms, i.e., the complexes are polyelectrochromic. The positions of the NIR absorptions are highly sensitive to the substituents on the dithiolene ligands. A large number of substituted dithiolene ligands has been prepared and used to prepare complexes of Ni, Pd, and Pt which show comparable electrochromic properties with absorption maxima at wavelengths up to ca. 1,400 nm and extinction coefficients up to ca. 40,000 dm3 mol-1 cm-1 (see refs. 170,171 for an extensive listing). 

As in the case of [3]radialenes, the individual redox stages of [4]radialenes may have different colors. Based on these electrochromic properties, the application of 77 as a component in liquid crystal display devices was patented85. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

Synthesis and electrochromic properties of nanocarbon-metal oxide hybrids... 

Xiong, S. Wei, J. Jia, P. Yang, L. Ma, ]. Lu, X., Water-processable polyaniline with covalently bonded single-walled carbon nanotubes Enhanced electrochromic properties and impedance analysis. Acs. Appl. Mater. Interfaces 2011, 3, 782-788. 

The first demonstration of a PEM with electrochromic properties was disclosed by SchlenofFand coworkers [66], using poly(butanylviologen)/ PSS films. While this film exhibited strong electrochromic response, it still required the use of an outer electrolyte solution. DeLongchamp and Hammond disclosed for the first time a solid-state device comprised of two electrochromic PEM-modified ITO electrodes separated by a 200-p,m thick poly(2-acrylamido-methane-2-propanesulfonic acid), proton-conducting PAMPS membrane (see Eigure 2.30) [196]. Both PEMs used in... 

One of the big drawbacks associated with the use of many conducting polymers as electrochromic materials is their low cycle life stability. To overcome this, and other electrochromic properties, many composite materials have been studied. These composites include mixtures with other optically complementary, conducting polymers and inorganic electrochromes, such as tungsten trioxide and Prussian Blue, and colour enhancing agents or redox indicators, exemplified by the inherently electrochromic indigo carmine (1.96). °... 

Several such polymers have shown electrochromic behavior, among them poly(n-vinylcarbazole) [73] which switches from colorless in the neutral state to green in the doped state (Scheme 10) and poly(Ar-phenyl-2-(2 -thienyl)-5-(5"-vinyl-2"-thienyl)pyrrole) [74], which changes from yellow to reddish brown upon oxidation (Scheme 11). A study of the electrochromic properties of blends consist-... 

Dicationic systems in which two diarylmethyl cations are linked by an 1,2-diphenylethyl,414 biphenyl,415 binaphthyl,415 or naphthalene-1,8-diyl416 417 backbone have attracted great interest recently because of their unique electrochromic properties. The dications 200 were prepared from the corresponding diols416,417 [Eq. (3.50)]... 

Intercalation of cations into a framework of titanium dioxide is a process of wide interest. This is due to the electrochromic properties associated with the process (a clear blue coloration results from the intercalation) and to the system s charge storage capabilities (facilitated by the reversibility of the process) and thus the potential application in rocking-chair batteries. We have studied alkali-metal intercalation and ion diffusion in the Ti02 anatase and spinel crystals by theoretical methods ranging from condensed-phase ab initio to semiempirical computations [65, 66]. Structure relaxation, electron-density distribution, electron transfer, diffusion paths and activation energies of the ion intercalation process were modeled. 

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. 

Other 1,8-naphthalene or acenaphthene dication systems have been described and some have been shown to have useful electrochromic properties.2013 ... 

Sherman, B. C., W. B. Euler, and R. R. Force. 1994. Polyaniline—A conducting polymer electrochemical synthesis and electrochromic properties. Journal of Chemical Education 71 (4) A94-A95. 

Baeck, S.H., K.S. Choi, T.F. Jaramillo, G.D. Stucky and E.W. McFarland (2003). Enhancement of photocatalytic and electrochromic properties of electrochemically fabricated mesoporous WO3 thin films. Advanced Materials, 15(15), 1269-1273. 

S. H. Kawai, S. L. Gilat, R. Ponsient, and J.-M. Lehn, A Dual-mode molecular switching device bis-phenolic diarylethenes with integrated photochromic and electrochromic properties, Chem. Eur. J. 1, 285-293 (1995). 

Hydrous oxides films, many of them with electrochromic properties, have been grown on a number of other metals using potential cycling methods, for example Rh [126] and Ni [159] in alkaline solution. Film formation seems to occur via a similar mechanism to Ir on the various metals under potential cycling conditions. Further, the films exhibit the same type of potential-pH response [150,160] as that described above in the case of Ir. 

The electrical and electrochromic properties of PANi depend not only on its oxidation state but also on its protonation state, and hence the pH value of the electrolyte used. As shown in Figure 1 PANi exhibits electrochromic behavior. Electrochromic behavior of PANi is shown in Figure 9. As demonstrated, small change in the pH of the solution and/or potential could create color and conductivity changes. PANi is green in the oxidized state and is transparent yellow in the reduced states. It has violet color in very acidic and yellow brownish in very basic media [14-16]. 

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