Mechanistic studies of the electrochemical polymerization of C60 in the presence of dioxygen or C60O

Abstract

Electropolymerization of C60 in the presence of dioxygen, in a mixture of acetonitrile and toluene (1 : 4, v : v) containing tetra(alkyl)ammonium perchlorate, was investigated by multi-scan cyclic voltammetry and piezoelectric microgravimetry with the use of an electrochemical quartz crystal microbalance. The fullerene was readily electropolymerized if the O2 to C60 concentration ratio in solution exceeded 1 : 10 and the applied potential reached values where electro-reduction of dioxygen to superoxide, O2˙−, and C60 to C602− occurred. The redox activity of the polymer was determined by cyclic voltammetry for solutions with different tetra-(alkyl)ammonium perchlorates used as supporting electrolytes. The film conductivity was higher the smaller the size of the cation in the supporting electrolyte. The C60 electropolymerization in the presence of dioxygen was suppressed when a spin trapping agent, N-tert-butyl-α-(4-nitrophenyl)nitrone that could intercept superoxide, was present. The fullerene was also electropolymerized in the presence of small amounts of the epoxide, C60O, in the absence of dioxygen. We postulate that the C60 electropolymerization in the presence of O2 proceeds via the initial nucleophilic attack of superoxide on C60 to form a C60O2˙− radical anion, which then interacts with another molecule of C60 to produce C60O and C60O˙−. Under further electro-reduction, these intermediates serve to initiate polymerization of C60 through the formation of C60O2−, as determined earlier in studies of the electropolymerization of C60O itself.