Thiophene electropolymerization

One also obtains analogous findings with trace-crossing effects for the electropolymerization of thiophene and pyrrole. This cannot be explained by a simple linear reaction sequence, as presented in Scheme I, because it indicates competing homogeneous and heterogeneous electron transfer processes. Measurements carried out in a diluted solution of JV-phenylcarbazole provide a more accurate insight into the reaction mechanism (Fig. 2). 

Fig. 3. Accessible potential ranges for the electropolymerization of substituted pyrroles, thiophenes, indoles, pyrenes and fluorenes...

In the synthesis of l,3-dithiole-2-thione derivatives as intermediates for electropolymerization precursors, the bicyclic 462 was found to be inert to normal cyclization conditions <1999JOC6418>. This is believed to be due to steric hindrance, from the boat conformation of the dithiin ring. Cyclization was achieved, albeit in only moderate yields, by heating with P2S3 to give the thiophene 463a or HBr/AcOH for the furan 463b (Equation 125). 

Conductive polymers have attracted increasing attention because they have wide applications. Recently, very stable poly(thiophenes) with polyfluorinated side chains have been electrochemically synthesized and characterized [81]. Furthermore, notably novel conductive materials have been prepared by cathodic electropolymerization of perfluoro cvclobutene and cyclopentene [82]. 

Electrochemistry is one of the most promising areas in the research of conducting polymers. Thus, the method of choice for preparing conducting polymers, with the exception of PA, is the anodic oxidation of suitable monomeric species such as pyrrole [3], thiophene [4], or aniline [5]. Several aspects of electrosynthesis are of relevance for electrochemists. First, there is the deposition process of the polymers at the electrode surface, which involves nucleation-and-growth steps [6]. Second, to analyze these phenomena correctly, one has to know the mechanism of electropolymerization [7, 8]. And thirdly, there is the problem of the optimization of the mechanical, electrical, and optical material properties produced by the special parameters of electropolymerization. 

All these findings prove that the electropolymerization mechanism of donor-substituted thiophenes and pyrroles does not involve a chain-propagation... 

The histamine [131], adenine [132] and dopamine [133] amines are electroactive in the positive potential range, in which the thiophene is electropolymerized. Therefore, these amines could be oxidized at the electrode surface in the course of deposition of the MIP film. That way, products of these oxidations might be available in the electrode vicinity for imprinting rather than the desired pristine... 

Electrochemical synthesis utilizes the ability of a monomer to be self-coupled upon irreversible oxidation (anodic polymerization) or reduction (cathodic polymerization). While this method does not always produce materials with well-defined structures (as do the three other polymerization methods to be discussed), electropolymerization, nonetheless, is a rather convenient alternative, avoiding the need for polymer isolation and purification. Of these two routes, anodic polymerization is the most widely explored as monomers such as pyrrole and thiophene are relatively electron-rich and prone to oxidation. For this reason the anodic route will be the focus of the remainder of this presentation. 

Polymers obtained from electropolymerization of 3-(benzyloxyethyl) thiophene have been described. They showed an absorption band at ca. 520 nm (90JCS(CC)414). 

In oxidative electropolymerization, monomers such as pyrrole, thiophene, alkylth-iophenes or aniline are dissolved in an appropriate solvent containing an electrolyte that can act as a source for the anions needed to neutralize the cations formed during the oxidation process [33,34]. The nature of this electrolyte is of great importance to the structural features obtained for the electropolymerized layer since the dopants become an intrinsic part of the polymer layer structure. A general outline of a mechanism describing the electropolymerization process is shown in Figure 4.21. 

Guglielmetti et al.21 also reported the synthesis of a series of thiophenes (e.g., 25) and terthiophenes (e.g., 26) substituted with spironaphthoxazine photochromic groups. It has been shown that electropolymerization of the thiophene group in 25 that occurs at 1.7 V [vs. saturated calomel electrode (SCE)] is blocked by the... 

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