Voltammetric characterization of soluble polyacetylene derivatives obtained from the ring-opening metathesis polymerization (ROMP) of substituted cyclooctatetraenes

High molecular weight, amorphous, partially substituted polyacetylenes (poly-RCOT) have been prepared using the ring-opening metathesis polymerization of substituted cyclooctatetraenes. Spin-cast films of these polymers yielded unusually sharp, well-denned, reversible electrochemistry for oxidative and reductive doping processes. As the substituent on the polymer chain was varied (R = alkyl, tert-butoxy, trimethylsilyl, and p-X-phenyl), the potentials for oxidative and reductive doping changed by 0.3 V. In addition, the separation between the oxidative and reductive doping processes varied from 1.66 V to >2.0 V. Coulometry suggested that the reversible doping step represented a transfer of 1 electron for every 13-15 double bonds of the polymer. In contrast, the electrochemistry of predominantlycis poly-RCOT films was irreversible, and indicated the presence of an electrochemical cis-trans isomerization on the first voltammetric sweep through either reductive or oxidative doping. Spectroelectrochemical studies indicated that the electrochemically doped poly-RCOT materials (R = sec-butyl, (CH₃)₃Si) possessed mid-gap transitions at energies of 0.8-0.9 eV. The redox chemistry of the soluble, poly-RCOT (R = sec-butyl, (CH₃)₃Si) species in CH₂Cl₂ solution was also investigated. Voltammetric studies showed that both the reductive and oxidative doping processes were chemically irreversible, and indicated that the dissolved polymers were electroactive over a wide range of potentials.