Highly conducting iodine derivatives of polyacetylene: Raman, XPS and x-ray diffraction studies

Abstract

Polyacetylene film and bulk samples were prepared by polymerization of acetylene in the presence of a μ- (η1:η5-cyclopentadienyl) -tris (η-cyclopentadienyl) dititanium (Ti–Ti) catalyst in hexane. Conducting films (σR.T.∼25 Ω−1⋅cm−1), or bulk polymer samples (σR.T.∼1 Ω−1⋅ cm−1) were prepared by treatment of the nascent polymer with solutions of iodine in hexane. Raman, x-ray photoelectron, and x-ray diffraction techniques were used to characterize these polyacetylene-iodine derivatives. The measurements are consistent with the presence of iodine in two different forms, I3− and possibly I5−. Although the concentration of the iodine varied in different samples (40%–70% by weight), in all cases the amount of the second species decreases irreversibly upon thermal annealing or the application of high mechanical stresses. X-ray diffraction measurements suggest that iodine species intercalate in sheets parallel to a close packed plane of the polyacetylene. Valence band x-ray photoelectron spectroscopy measurements on an iodinated cis-rich polymer film, show a finite density of states at the Fermi level. This observation suggests metallike conductivity in the sample.