Polaron dynamics of heavily doped regioregular and regiorandom poly(3-alkylthiophenes) revealed by electron spin resonance spectroscopy.
Electron spin resonance (ESR) features in heavily doped conjugated polymers are investigated through the comparison of temperature dependences of ESR spectra between head-to-tail coupled regioregular (RR) and regiorandom (RRa) poly(3-octylthiophenes) (P3OTs). RR-P3OT, used as a model of having crystalline grains in the solid film, is found to exhibit anisotropic ESR spectra, whereas RRa-P3OT gives almost isotropic ESR spectra similar to those of usual heavily doped conjugated polymers. This difference in the degree of spectral anisotropy primarily arises from a difference in their film morphology. Spectral simulations show the anisotropy observed in RR-P3OT to be caused by g-anisotropy. The presence of the g-anisotropy in RR-P3OT indicates that its polarons spend most of the time within a single crystalline grain that has some domains with a common direction of the g-tensor. The g-anisotropy turns out to decrease with increasing temperature. This result is explained by thermally activated hopping motions between crystalline grains. We emphasize that the decrease in the g-anisotropy with temperature should be associated with its activated type of temperature dependence of conductivity. In RRa-P3OT, its isotropic ESR spectra are suggested to be caused by the interchain motion as well as the intrachain one.
Kanemoto
Katsuichi
K
Department of Physics, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto, Sumiyoshi-ku, Osaka 558-8585, Japan. kkane@sci.osaka-cu.ac.jp
Muramatsu
Kazumi
K
Baba
Masaaki
M
Yamauchi
Jun
J
D004578:Electron Spin Resonance Spectroscopy; D011108:Polymers / Q000737:chemistry*; D012015:Reference Standards; D013696:Temperature; D013876:Thiophenes / Q000737:chemistry*
D011108:Polymers; D013876:Thiophenes