P3mt(1) and P3mt(2) were electrochemically synthesized using two different electrolyte supports H2SO4 and TEABF(4), respectively. First, it was deduced from density functional theory (DFT) calculations that the electronic and steric effects govern polymerization mechanism of the radical monomers. Second, DFT combined with experimental spectroscopic analyses (ESR, Infrared, Raman, and C-13 NMR) demonstrate that H2SO4 or TEABF(4) could generate a homogenous or heterogeneous coupling site, respectively. (c) 2006 Wiley Periodicals, Inc.