MECHANISM OF CIS-TRANS THERMAL-ISOMERIZATION OF POLYACETYLENE

Isothermal cis-trans isomerization of polyacetylene (PA) films proceed s according to a stretched-exponential function of time with an expone nt alpha (0 < alpha < 1). A mechanism is proposed for the cis-trans is omerization. Cis-trans isomerization of PA occurs under the condition that the molecular axis is almost fixed. The interspace-diffusion mode l is effective in simply describing the intermolecular cooperative mot ions of neighboring chains to avoid the intermolecular constraints for cis-trans isomerization motion. If an interspace appears in the neigh borhood of a cis bond (or moving unit of cis state), this cis unit is assumed to change to the trans state instantaneously. Using the contin uous-time random walk model, the decay of survival probability of a ci s unit can be expressed by the stretched-exponential function under th e assumption of the distribution of activation energy for cis-trans is omerization. The relationship between the two-state model and the inte rspace-diffusion model is discussed.