Beyond External Dopants: Functional Group Design in Self-Doped Conducting Polymers

Self-doped conducting polymers represent a distinct class of conjugated materials in which covalently tethered ionic functionalities enable intrinsic charge generation and stabilization. Unlike conventional externally doped systems, where weakly bound dopants often induce phase separation, diffusion, and long-term instability, self-doping establishes built-in charge compensation that enhances thermodynamic robustness and environmental tolerance. This review systematically examines how functional group engineering governs the electronic structure, charge transport, and interfacial properties of conducting polymers. Focusing on representative systems─polyaniline (PANI), poly(3,4-ethylenedioxythiophene) (PEDOT), and polypyrrole (PPy)─we elucidate the roles of sulfonate, carboxylate, quaternary ammonium, and phosphonate groups in modulating doping mechanisms, redox activity, and ion–electron coupling. By correlating molecular design with macroscopic performance across bioelectronics, energy storage, and optoelectronic applications, we establish a unified structure–property–function framework. Finally, we highlight unresolved challenges in doping efficiency, structural regulation, and device integration, providing design principles for next-generation stable and multifunctional conducting polymers.