ESR and conductivity studies of doped polyacetylene

Low temperature ESR spectra of cis-rich and trans-rich polyacetylene, lightly doped with pentafluorides (AsF₅, SbF₅) exhibit two clearly distinguishable ESR lines. Detailed studies of these two lines as a function of temperature, doping concentration and microwave power indicate that one of these lines originates from localized spins, the other from conduction electrons. The concentration of the "localized spins", generally speaking, decreases with doping. The Pauli-like susceptibility associated with the conduction electrons changes from 1.5×10^-7 to 15×10^-7 emu·cm³/mole for various doping levels and correlates with the conductivity of the same samples. The longitudinal relaxation time of the localized spins in doped trans-rich was found to be T₁≅100 μs at low temperatures, consistent with values of others in undoped trans rich. The temperature dependence of the homogeneous transverse relaxation T₂ of the localized spins in doped trans-rich polyacetylene is similar to that of undoped trans polyacetylene. These facts show that the localized spins originate from undoped regions of the doped polyacetylene, perhaps due to inhomogenous doping. Our results are consistent with either formation of metallic islands, or, probably more, with impurity band conduction in strongly disordered semiconductors.