Electron spin resonance of polyacetylene and AsF5-doped polyacetylene

The results of an electron spin resonance (ESR) study of trans-polyacetylene, before and after doping with AsF5, are reported. The undoped polymer exhibits a Lorentzian line (g=2.00263) indicative of motional narrowing from a mobile unpaired electron species. Measurement of the intensity indicates a Curie law susceptibility with approximately one unpaired electron per 3×103 carbon atoms in agreement with earlier studies. From these results and comparison with earlier data on the cis polymer, it is suggested that the ESR signal arises from a mobile defect in the π system. Utilizing an apparatus which allows in situ AsF5 doping of a polyacetylene sample in the microwave cavity, we have monitored the ESR signal during the doping process. The spin resonance line narrows and increases in intensity, with no detectable g shift, as the doping proceeds. At high doping levels the line becomes asymmetric with a characteristic Dysonian line shape consistent with metallic behavior.