Leuco Emeraldine

In this type of doping the number of electrons does not change the energy levels are rearranged, however. The most common example for redox doping is polyanaline that has different appearances or oxidation states, as shown in Scheme 11.3. The average oxidation state of polyanaline (y) can be varied continuously 1> y > 0 leuco-emeraldine (y = 1, fully reduced, insulator), emeraldine (y = 0.5, half-oxidised, semi-conductor) and pernigraniline (y = 0, fully oxidised, insulator). 

FIG. 11.19 Oxidative doping (p-doping) of leuco-emeraldine base and protonic acid doping of emeraldine base, leading to the same final product, emeraldine salt. Reproduced from Fig. 34.3 in Mark (1996). Courtesy Springer Verlag. 

Latent heat of fusion (crystallisation), 118 Layer thickness, 698, 699 Length of folds in crystal lamellae, 727 Lennard-Jones equation, 658 scaling factors, 658 temperature, 658,661, 662,663 Leslie-Ericksen theory, 585, 587, 641 Leuco-emeraldine, 345,346 Lewis... 

Figures 11.63 and 11.64 show that the contact of polyaniline with iron in the presence of water changes the polyaniline from the green to the yellow form, which can be understood as the reduction of polyaniline from the emeraldine salt to the leuco-emeraldine. This requires an equivalent oxidation of iron (to Fe " ). The back reaction shown in Figures 11.65 and 11.66 leads back to the normal polyaniline, although with some bluish component (emeraldine base or nigraniline) in the neutral environment. This back reaction is performed with the help of oxygen, as can be seen from the comparison of the spectra in Figures 11.69 and 11.70 with 11.65/11.66 and 11.71/11.72. In the de-...

A number of problems still exist for the practical use of this material in any solution, it is difficult to obtain a perfect bleaching and a memory effect, since leuco-emeraldine samples after equilibration cannot be kept unpolarized without evolving towards yellow/green polymer. The use of an organic electrolyte could avoid the oxidizing effect of water. 

The most electrically conductive state is the emeraldine salt (ES) that is between pernigraniline salt (Pas) at the high potential side and the leuco-emeraldine salt (LS) at the low potential side. The LS and the Pas are the most reduced and oxidised states, respectively, and have been found to be insulating. In an oxidation process from the LS to the ES, two electrons are withdrawn and two chloride ions are doped for every four benzene units. For the oxidation from the ES to the Pas, two electrons are withdrawn and two protons are released. The LS/ ES reaction is reversible, however, the hydrolysis occurs at the higher oxidised Pas states. 

Figures 3 a, b, c summarize the typical spectral IR and Visible region spectral properties of devices. The large light/dark variation ( dynamic range ) is clearly seen therein as well. An interesting property, discussed at length in conjunction with electrochemical data in one of our earlier communications (4), is that the Visible- and IR-region reflectances vary in tandem between applied potentials of -1.1 V and 0.0 V, but behave in an opposite fashion between 0.0 and +0.8 V. As we discussed earlier (5a), this is due to transitions between die various poly(aniline) states reduced non-conductive leuco-emeraldine, partially oxidized conductive doped-emeraldine, and highly oxidized and again non-conductive pemigraniline.

This is a continuum of oxidation states ranging from completely reduced (leuco emeraldine) to fully oxidized (pemigraniline) species. The situation becomes more... 

Bishop, A. and P. Gouma (2005). Leuco-emeraldine based polyanilme — poly-vinyl-pyrrolidone electrospun composites and bio-composites a preliminary study of sensing behavior. Reviews on Advanced Materials Science 10(3) 209-214. 

Quite evidently, all states except leuco-emeraldine can be protonated. The states with no protonation are denoted as the "base" form, e.g. emeraldine base (which would be non-conductive). The reader may note tlie presence and alternation of "benzenoid" and "quinonoid" segments, as defined in an earlier Chapter, in the structures of Fig. 13-9. Upon protonation, the polymer is denoted as the salt, for example protonation of the emeraldine base form (Fig. 13-9c with HCl would yield emeraldine hydrochloride-. 

For (l-y)= 0, we have die completely reduced polymer, denoted as leuco-erneraldine, as shown in Fig. 13-9b. With (l-y)= 0.5, we have the half-oxidized state of the polymer, denoted as emeraldine, depicted in Fig. 13-9c. 

When two molecular weights of an aromatic monoamine were allowed to condense with one molecular weight of DHDHTA, a -phenylenediamine was produced. Thus, Ph-NH-Ph-NH-Ph-NH-Ph-NH2 ("emeraldine base") afforded "COA blue", a material with an unknown number of Q s which could be reduced to COA (white, leuco) with phenyl hydrazine. 

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