Fast electrochemical studies of the polymerization mechanisms of pyrroles and thiophenes. Identification of the first steps. Existence of π-dimers in solution

The content of several works effected on the electrochemical polymerization of several pyrroles and thiophenes is given and exemplified. It is shown that the polymerization of pyrroles proceeds via a cation-radical coupling. In the case of thiophenes, the electrochemistry of end-capped oligomers giving stable cation radicals has been first examined. The existence of associated forms of the cation radicals, the π-dimers, has been demonstrated, and the formation parameters of these π-dimers have been determined using only the electrochemical analysis of the reversible voltammograms in solution. On the other hand, the σ-polymerization of some polymerizable thiophene oligomers (quinquethiophenes and trimethylsilylterthiophenes) has been examined, and it is also shown that the preferred process in acetonitrile or dichloromethane is a cation-radical/cation-radical coupling.