Electrochemical synthesis and characterization of poly(3,4-ethylenedioxythiophene) doped with sulfonated calixarenes and sulfonated calixarene-fullerene complexes

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were electrochemically deposited on glassy carbon (GC) disk electrodes using aqueous solutions containing 3,4-ethylenedioxythiophene (EDOT) and sulfonated calixarenes or fullerene-sulfonated calixarene (C60-calixarene) complexes. The EDOT monomer was added to aqueous sulfonated calixarene solutions with and without C60 and from these solutions PEDOT(calixarene) and PEDOT(C60-calixarene) films were electrochemically deposited on GC disk electrodes. The electrochemical properties of GC/PEDOT(C60-calixarene) were compared with those of GC/PEDOT doped with other ions, both in aqueous and organic electrolyte solutions using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). CV measurements carried out on GC/PEDOT(C60-calixarene) in 0.1 M aqueous KCl solution showed a reduction peak at ca. −0.55 V vs. Ag/AgCl/3 M KCl only during the first potential scan. This was attributed to the irreversible reduction of C60 to C60− inside the PEDOT film. This additional reduction peak was, however, not observed when recording the CVs in organic solution, indicating that C60 was dissolved from the PEDOT film into the organic electrolyte solution, that is a good solvent for C60. When performing CV measurements in an organic electrolyte solution containing C60, all GC/PEDOT electrodes with various doping ions and bare GC electrodes showed a reversible reduction peak characteristic for the C60/C60− redox couple. Interestingly, the peak potential and the shape of the reoxidation peak for the fulleride anion (C60−) on GC/PEDOT in the organic electrolyte solution were found to depend on the PEDOT film thickness. The electrochemical properties of GC/PEDOT(C60-calixarene) were compared further to those of GC/PEDOT(calixarene) by fitting EIS data to equivalent electrical circuits and the morphology was studied by scanning electron microscopy.