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 (C-60-calixarene) complexes. The EDOT monomer was added to aqueous sulfonated calixarene solutions with and without C-60 and from these solutions PEDOT(calixarene) and PEDOT(C-60-calixarene) films were electrochemically deposited on GC disk electrodes. The electrochemical properties of GC/PEDOT(C-60-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(C-60-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 C-60 to C-60(-) inside the PEDOT film. This additional reduction peak was, however, not observed when recording the CVs in organic solution, indicating that C-60 was dissolved from the PEDOT film into the organic electrolyte solution, that is a good solvent for C-60. When performing CV measurements in an organic electrolyte solution containing C-60, all GC/PEDOT electrodes with various doping ions and bare GC electrodes showed a reversible reduction peak characteristic for the C-60/C-60(-) redox couple. Interestingly, the peak potential and the shape of the reoxidation peak for the fulleride anion (C-60(-)) on GC/PEDOT in the organic electrolyte solution were found to depend on the PEDOT film thickness. The electrochemical properties of GC/PEDOT(C-60-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.