FORCED RAYLEIGH-SCATTERING ON A SOLUBLE CONDUCTING POLYMER

Forced Rayleigh scattering (FRS) is used to probe the dynamics of a conducting polymer, poly- (3-octylthiophene), in solution. The optical labels employed are photoexcited states on the chains themselves; chemical addition of a photochromic labeling attachment is not required. The main feature of the time dependence of the diffracted intensity is an exponential time decay; from the quadratic dependence of the decay time on the grating wave vector, we find a translational diffusion coeffícient in the dilute regime of (8 ± 1) X 10-8 cm2/s, corresponding to a hydrodynamic radius of Rh = 130 ± 15 Å. It is shown that the mean value measured in the experiments is the z-average diffusion coefficient, in contrast with FRS experiments in which photochromic labels are chemically attached to the ends of the chains. We propose that bipolarons are the excited states responsible for chain labeling, based in part on the photoinduced absorption spectra for poly(3-alkylthiophenes). © 1990, American Chemical Society. All rights reserved.