ELECTROCHEMISTRY AND POLYMERIZATION MECHANISMS OF THIOPHENE-PYRROLE-THIOPHENE OLIGOMERS AND TERTHIOPHENES - EXPERIMENTAL AND THEORETICAL MODELING STUDIES
P. Audebert et al., ELECTROCHEMISTRY AND POLYMERIZATION MECHANISMS OF THIOPHENE-PYRROLE-THIOPHENE OLIGOMERS AND TERTHIOPHENES - EXPERIMENTAL AND THEORETICAL MODELING STUDIES, JOURNAL OF PHYSICAL CHEMISTRY B, 102(44), 1998, pp. 8661-8669
The electrochemical properties of several substituted terheterocycles
thiophene-pyrrole-thiophene oligomers have been studied by cyclic volt
ammetry and double-potential-step chronoamperometry and then compared
with the behavior of the corresponding pure terthiophenes. E degrees a
nd lifetimes of the cation radicals have been measured. Ab initio and
DFT calculations show that the cation radicals of thiophene-pyrrole-th
iophene oligomers (N-alkyl-2,5-bis(thien-2-yl)pyrroles) are twisted in
contrast to the terthiophene case where cation radicals are planar. T
hese geometries explain the variations of the oxidation potentials wit
h the substituents positions. When the alpha-positions are free, the c
ation radical undergoes a fast coupling reaction in solution, leading
to either a dimer or a polymer involving the coupling between two cati
on radicals. The same cation radical-cation radical coupling reaction
is involved when the alpha-terminal positions are substituted by bromi
des. We propose that this reaction involves a hindered alpha-alpha' co
upling followed by a nucleophilic attack of the protonated dimer and n
ot the coupling with one of the beta-positions (or beta' or beta '').
This view is supported by comparison with the electrochemical behavior
of other oligothiophenes and oligopyrroles.