Chemical and electrochemical isomerization of polyacetylene: In situ optical studies

In situ optical studies during electrochemical doping demonstrate that doping cis-(CH)_x to a fixed dilute concentration induces partial cis-trans isomerization. "Undoping" back to neutral (CH)_x converts that portion of the sample which was doped, back into undoped trans-(CH)_x. Subsequent doping to the same level (or to lower levels) redopes only that portion which is already trans. Although doping to a higher level induces additional isomerization, complete isomerization is not achieved until dopant levels are obtained which are characteristic of the metallic state. The results indicate that at dilute doping levels cis-(CH)_x consists of isolated segments of doped trans-(CH)_x in the predominantly cis-(CH)_x chains. Since the dopant uniformity in cis-rich samples is determined by the history of partial isomerization and by the simultaneous isomerization induced during doping, care should be taken in drawing fundamental conclusions from studies of doped cis-(CH)_x material at all but the highest doping levels.