Electropolymerization azulenes

A strategy to enable multifold switching in macromolecular systems is briefly described below. On the basis of previous work, which showed that switchable and conducting films can be obtained by electropolymerization of 1,3-unsubstituted azu-lenes (Figure 31),[3S] investigations were carried out on DHA/azulene derivatives.1361... 

Perchlorate salts are used as electrolytes in - electropolymerization reactions involving monomers such as aniline, benzidine, azulene, biphenyl, di-vinylbenzene, and indole. 

A number of investigators have reported the detection of protons released from the de-prontonation step of coupled products during the electropolymerization. Bruckenstein and Sharkey [76] observed protons released during the polymerization reaction of PyH and azulene using rotating ring-disk electrodes. A similar observation was made by Beck and Oberst [77], who monitored the proton/electron stoichiometry, the accuracy of which was found to be limited by the occlusion of acid in the pores of a growing polymer film. 

Infrared spectra confirm the loss of two protons after radical cation coupling [377]. Bruckenstein and Sharkey [378] provide a theoretical analysis of the electropolymerization of azulene at a rotating ring-disk electrode. Hydrogen ion has been identified and quantified as a product of the electrochemical polymerization. 

A variety of other aromatic compounds have been successfully electropolymerized and found to have the general electroactive properties described for the polyaniline, polypyrrole and polythiophene films. Films have been prepared from azulene furan, indole , carbazolepyrenetriphenylene and phenylene (see Scheme 1). In principle, all of these films could be used as electrodes in energy... 

Figures shows the potential range where some heterocycles polymerizeThe cathodic cutoff for the polymerization (around 1.2 V) occurs when the stability of the radical cation is enhanced (intrinsically or via a substituent). When becomes greater than kp - - k ([S] + PC ]) diffusion of R+ from the electrode results in the production of soluble products. The anodic cutoff (around 2.1 V) occurs when k,([S] -t- [X ]) > (kp -t- k ). Then R" becomes unstable and reacts with the solvent or anions. Between around 1.2 and 2.1 V good conditions for the electropolymerization of such monomers exists where kp > k q- k ([S] -f- [X ]). The influence of substituents in pyrroles, thiophenes, indoles, azulenes, fluorenes, and pyrenes on whether electropolymerization of the monomers or other reactions can occur has been discussed in detail including consideration of electronic or steric effects...

Many other aromatic systems can be similarly electropolymerized, including thiophene, furan, carbazole, azulene, indole, aniline, phenol and thiophenol among others. 

During a typical electropolymerization, it is nearly always noted that the net charge transfer is a little in excess of that indicated stoichiometrically, due to the additional oxidation (and doping) that occurs during electrochemical preparation of CPs. For example, while P(Py) and poly(azulene) both stoichiometrically require 2 electrons per monomer for electropolymerization, experimentally a charge of the order of 2.3 electrons per monomer is foimd to be consumed. The excess 0.3 is used to effect a 30% doping of the polymer. 

---