Electronic states studied by ESR in polythiophenes and poly(3methyl)thiophenes

Summary form only given. ESR line width was studied as functions of temperature from 4.2 to 300 K and frequency from 30 to 24,000 MHz mainly in ClO/sub 4/-doped polythiophene and poly(3-methyl)thiophene. These materials are found to be interesting systems in the sense that ESR line is broadened by two different relaxation mechanisms, which yields ample of the information on the electronic states. The observed characteristic behaviors were as follows; (a) with increasing the temperature :he line width increased monotonically, that is, T-square in polythiophene but almost T-linear in poly(3-methyl)thiophene, and (b) the frequency dependence of the line width in polythiophene showed a typical quasi-one-dimensional behavior, in spite of local structure of two-dimensional sheet of chains expected from X-ray analysis in the similar materials as poly(3-alkyl)thiophene and polypyrrole. The (a) can be understood by Elliott mechanism which comes from the electron scattering accompanied with electron spin flip by virtue of the spin-orbit interaction. The Elliott mechanism gives a relaxation time of a resistivity through ESR g-shift. The (b) suggests low crystallinity in polythiophene, which is consistent with the observed amorphouss X-ray pattern. The combined analysis of the two mechanism gives us many parameters; anisotropic diffusion rates, Fermi velocity, effective mass, mean free path, and microscopic electrical conductivity.