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In this paper, we describe how we derive the mobility of positive charges (“holes”) along isolated conjugated polymer chains from the results of pulse-radiolysis time-resolved microwave conductivity (PR-TRMC) experiments on dilute polymer solutions. The method is illustrated with results for oxygen-saturated, benzene solutions of the well-known poly(phenylene vinylene) derivative, MEH−PPV with an average chain length of 800 monomer units. Nanosecond pulsed irradiation results initially in ionization of the solvent with the formation of excess electrons and benzene radical cations, Bz+. The former rapidly (<1 ns) undergo attachment to O2 to form O2 - with a rate constant of 1.5 × 1011 M-1 s-1. The Bz+ ions diffuse through the solvent and react with the (lower ionization potential) polymer chains via electron abstraction forming holes on the polymer backbone. This is accompanied by a large increase in the conductivity of the solution after the pulse, demonstrating that the mobility of holes on the polymer chains is very much larger than the mobility, via molecular diffusion, of Bz+ ions in the solvent. To describe the after-pulse growth in conductivity, a large effective reaction radius, R eff, of ca. 400 Å is required for the diffusion-controlled reaction of Bz+ with MEH−PPV chains. This requires taking into account the time-dependent term in the rate coefficient. The value of R eff is compared with theoretical predictions for the reaction of a small entity with a 1-D linear or a 3-D cubic array of 800 reactive moieties. The conclusion that individual polymer chains in solution must have a very open structure with a large persistence length is in agreement with the results of previous static and dynamic light-scattering studies. The conductivity eventually decays because of the recombination of the positively charged polymer chains with negative counterions (O2 -) with a rate coefficient of 1.2 × 1011 M-1 s-1, which is somewhat slower than predicted by the Debije equation. No evidence could be found for first-order trapping of the mobile positive charge on the polymer chains prior to recombination. The pseudo-one-dimensional mobility of holes along the polymer backbone derived from the absolute magnitude of the conductivity transients is 0.46 cm2 V-1 s-1.

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The anisotropic mobility of excess charge carriers in pure and mixed crystals of two polydiacetylene derivatives was determined. The charge carriers were produced by pulsed irradiation and detected by time-resolved measurement of the microwave conductivity. The charge-carrier mobility was measured as a function of the orientation of the polymer backbone in the crystal with respect to the probing electric microwave field. A lower limit in the intrinsic anisotropy in the charge-carrier mobility was found to be 15 in favor of charge transport in the direction of the polymer backbone as compared to the transverse direction for polydiacetylene-(bis p-fluorobenzene sulfonate) (pFBS), while a value of 90 was found for polydiacetylene-(bis p-toluene sulfonate) (pTS) and the 50:50 pTS/FBS copolymer. A lower limit of the charge-carrier mobility along the backbone of 3 cm2/V s was found for both pTS and pFBS. The charge-carrier mobility in the copolymer was found to be one order of magnitude lower than in the pure polymers.