Polarization-dependent EXAFS in bromine-doped polyacetylene

Polyacetylene, (CH)x, is often considered as the simplest prototype of conjugated polymers. It can be synthesized in form of thin films with fibrillar morphology by Shirakawa’s method [1]. Doping with electron acceptors like halogen molecules has been found to cause an increase in electrical conductivity by many orders of magnitude from the insulating to the metallic regime [2]. While there are detailed models for the crystalline structure of pristine (CH)x very little structural information on the microscopic level is available for its doped forms [3,4,5]. This is due to the poor crystalinity of doped (CH)x, which complicates the use of diffraction methods. It is the purpose of this paper to show that detailed information on the local structure of the dopant molecules can be obtained from EXAFS measurements exploiting the linear polarization of synchrotron radiation (SR).