Carbonyl compounds and inorganic Brønsted acids as catalysts for electropolymerization of conductive polymers

Abstract

For the electropolymerization of various conductive polymers, boron trifluoride diethyl etherate is commonly used as solvent to grant mild polymerization conditions – although it easily decomposes and leads to film qualities with low reproducibility. By using an appropriate catalyst, films with improved properties can be deposited at lower potentials from stable solvents in a reproducible manner. In this communication, various carbonyl compounds and inorganic Brønsted acids were investigated as catalysts for thiophene and pyrrole electropolymerization in acetonitrile and water. In a series of cyclic voltammetry experiments, catalysts were found to dramatically reduce the initial oxidation potential of the monomers. Hereby, the catalytic effect depended on the electrophilic nature of the catalyst centre, which is majorly influenced by the nature of the ligands. A Raman spectroscopy study demonstrated a decreased aromaticity of the monomers in contact with appropriate catalysts. By exemplarily investigating the catalysing effect of butyric acid on pyrrole polymerization in acetonitrile, conductive films with a lower charge transfer resistance resulted, as well as greater homogeneity and smoothness. Films were characterized by electrochemical impedance spectroscopy, white light interferometry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, as well as surface-enhanced Raman spectroscopy. The catalysts presented in this communication convince with low prices and high solubility in acetonitrile and water, are already available in most labs, and can therefore serve as universal tools for the mild electropolymerization of well-known as well as novel monomers for innovative applications.