Structure-Driven Ion Transport in Conjugated Polymers with Crown Ether Side Chains: From the Nano- to Microscale

In this study, five poly-(3,4-ethylenedioxythiophene) PEDOT derivatives with different 15-crown-5 contents (0-100%) are synthesized. This allows a systematic variation of nanoscale ordering, porosity, and selectivity toward sodium ions. We thus built a polymer platform to investigate the electrolyte and structural dependence of electrochemical doping. We find a trade-off in performance, where adding more crown ether enhances electronic delocalization and nanoscale ordering but suppresses ion transport because of a more compact structure with smaller pores. Spectroelectrochemistry shows that a higher crown ether content narrows the voltage range over which doping takes place (redox window width). The redox onset is shifted by the anion of the electrolyte, while the cation plays a minor role despite the chelation to the crown ether. From this systematic study, we identify PEDOT-C50 with 50% crown ether as the ideal derivative, as it combines the highest volumetric capacitance with fast switching dynamics. In chloride electrolytes, its doping remains thickness-independent, making PEDOT-C50 particularly attractive for up-scaling and bioelectronic applications.