Isothermal cis—trans isomerization of polyacetylene

Experimental analysis of isothermal cis—trans isomerization behavior of polyacetylene (PA) films suggests that the isomerization ratio changes with time by the stretched (fractional) exponential function, which is different from the previously assumed single exponential decay. s cis—trans isomerization of PA, intramolecular cooperative motions of bonds and also the intermolecular cooperative motions among neighboring chains are needed in order to avoid the steric hindrance in the solid state. Interspace-diffusion model is proposed to simply describe the intermolecular cooperative motions of neighboring chains. Using the continuous time random walk model, the decay of survival probability of cis units can be approximated by the stretched exponential function under the assumption of the distribution of activation energy. The relationship between the two-state model and the interspace-diffusion model was discussed.