A functionalized ethylenedioxythiophene (EDOT) derivative bearing a highly nucleophilic thiolate group has been synthesized. The efficiency of this new building block as a precursor to a wide range of EDOT-based monomers is demonstrated by reaction with different electrophilic species or by oxidation to a disulfide dimer. The corresponding electropolymerized PEDOT-based films, incorporating various side arms, have been prepared. In addition, the possibility to functionalize preformed PEDOT films obtained from these monomers, by nucleophilic substitution under heterogeneous conditions, was also checked thanks to the introduction of a tetrathiafulvalene redox probe.