E.S.R. of BF₄^--doped polythiophene

We have studied poly(3-methylthiophene) doped electrochemically with BF4- by electron spin resonance. The spin concentration increases linearly by about one spin per injected charge up to quite high doping levels (≈ 10 mol% at room temperature). The magnetic susceptibility χm(T) gradually changes from a Curie- to a Pauli-type behaviour with increasing doping concentration. Simultaneously, an increasing degree of delocalization of the corresponding spin centres is inferred from linewidths, line shape analysis and spin-lattice relaxation rates. The metallic behaviour observed by e.s.r. at high doping levels is attributed to a microscopic electrical conductivity, which is higher than the macroscopic one observed by transport measurements by a factor of about 50. The present results demonstrate that polarons are the dominant charge states in poly(3-methylthiophene) doped with BF4-. © 1988.