Optical properties of potassium-doped polyacetylene

Abstract

The optical reflectance of polyacetylene doped with high concentrations of potassium has been measured, and the optical properties estimated by Kramers–Kronig analysis. The samples, doped by a vapor-phase technique to y≈0.08 and 0.18, showed strong doping-induced infrared absorption at ∼900, 1270, and 1390 cm −1. These experiments were motivated by calculations of the infrared absorption which showed that whereas there are only small differences in the infrared spectra for isolated solitons and isolated polarons, there is a dramatic difference between the high-concentration polaron and soliton lattices. The shapes of the absorption spectra are rather similar but the absorption for the polaron lattice is 13 orders of magnitude weaker than that of the soliton lattice. The observation of these features at high doping levels is inconsistent with both the polaronic metal and strongly disordered Peierls insulator models for highly doped polyacetylene and furthermore suggests that solitonic defects maintain their integrity to very high doping levels.