Electrical conductivity and infrared absorption of trans- polyacetylene in the presence of iodine

Abstract

An electronic transition which can be assigned to either a charge-transfer band or to a positively charged soliton has been observed in the near-i.r. (shallow maximum at ca. 1800 nm) for thin films of iodine-doped trans-polyacetylene. From the analysis of this band intensity as a function of the iodine content it is deduced that the complex produced between the (CH)_x polyene units (or the neutral solitons) and I₂ has the average composition (CHI_0.008)_x and obeys a one-to-one stoichiometry with K_eq≈ 64 dm³ mol^–1. On the assumption that charge carriers originate from the production of the spectroscopically observed new species the relationship between the electric conductivity, σ, and the complex concentration has been qualitatively and quantitatively investigated. A logarithmic dependence of σ on the density of carriers has been shown and the experimental data are best accounted for by the three-dimensional variable range-hopping conduction mechanism.