Intrinsic Doping and Electrostatic Complexation of Sulfonated Poly(3,4-ethylenedioxythiophenes) (PEDOTs)

Self-doped conjugated polymers represent a compelling strategy for forming conductive electrostatically complexed polymer blends without the need for additional processing steps for electronic doping. Although self-doped polymers simplify processing, fundamental questions remain about structure-property relationships and the role of doping in electrostatic complexation. A class of sulfonated PEDOT derivatives was investigated to study their self-doping behavior and the ability to form electrostatically mediated complexes with cationic polyelectrolytes. Remarkably, even a subtle change in side chain architecture (differing by only a single carbon) influenced the electrical conductivity, with the shorter side chain exhibiting values up to ≈500 S cm^-1, roughly 1000 times higher than its longer-chain counterpart. Comprehensive spectroscopic and electrochemical analyses were performed to gain insight into the origin of the behavior. These self-doped conjugated polyelectrolytes maintain high electrical conductivity (≈300 S cm^-1), even after complexation with an insulating polyelectrolyte. The phase behavior of complexation revealed the ability to define an effective charge fraction of ionic groups per monomer that can guide the design of electrostatically complex conjugated polyelectrolytes.