ESR studies on polarons in long oligothiophenes

We have performed electron spin resonance (ESR) studies on long oligothiophenes (13 and 20 T) doped by iodine vapor. The oligomers gave anisotropic ESR spectra differing from ordinary cases in conjugated polymers. Our analyses by way of the Fourier transform of ESR spectra indicate that the cutoff event between parallel chains occurs at the same degree of frequency as the motion along a chain: 31.8 MHz at 50 K in 13 T. Above 150 K, we observed the signature of the cutoff motion between nonparallel chains (∼5 MHz). We assert that polarons mainly move within aggregates consisting of parallel chains formed in the film.