Reversibility of the doping of polyacetylene with iodine in the gas phase

Abstract

The reversibility of the doping reaction with iodine of Shirakawa polyacetylene (PA) films, carried out in the gas phase, has been studied by means of electrical conductivity, i.r. and ESR measurements. As expected, the level of the doping strongly influences the rate of the back reaction, diffusion processes being involved through the various parts of the film. These processes are characterized by diffusion constants which differ by orders of magnitude. For lightly doped PA samples, it is easily possible to recover the initial characteristics of the electrical conductivity, while the optical i.r. characteristics may be recovered by heating the samples at 50°C, if both cis and trans isomers are present. For lightly doped all trans samples, this heat treatment was not necessary. The heavily doped all trans PA samples also regain their initial characteristics after brief heating, showing that the desorption of I 2 from the interior of the film needs to be thermally activated.