Effect of dopant-molecule size on the electrical conductivity of polyacetylene

We have measured the temperature dependence of the conductivity of cis-polyacetylene doped with iodine and with ${\mathrm{H}}_2$Ir${\mathrm{Cl}}_6$·6${\mathrm{H}}_2$O. The iodine dopant was introduced from the vapor phase under various vapor pressures and also from solution. The Ir${\mathrm{Cl}}_6$ was introduced from solution. We find $log\rho \propto T^{\frac{-1\mathrm{}}{4}}$ for $\left(\mathrm{CH}\right){\mathrm{I}}_y$ and $log\rho \propto T^{\frac{-1\mathrm{}}{2}}$ for ${\left(\mathrm{CH}\right)}_x$ doped with Ir${\mathrm{Cl}}_6$. We attribute the difference to separate transport mechanisms. We suggest that the size and shape of the dopant molecule is the controlling variable rather than the doping conditions.