Polaron mobility intrans-polyacetylene

We present a calculation of the phonon-limited mobility and diffusion coefficient of polarons drifting along a chain in ItransR-polyacetylene for the temperature range 25–300 K. Only scattering by acoustic phonons has been included because the energies of both optical phonons and the polaron’s internal degrees of freedom are large compared to $k_B$T in the range considered. Because the wavelengths of the phonons that dominate the scattering are much longer than the length of the polaron, we treat the scattering by the deformation-potential method. The mobility has been calculated with the effective mass taken as (1) constant and (2) variable, such that there exists a maximum velocity of propagation c. We take c∼2.7$v_s$, where $v_s$ is the velocity of sound, a value obtained from computer simulations for the case of solitons. The constant-mass case is found to become unphysical for T≳75 K because the thermal velocity of the polaron becomes larger than c. The room-temperature mobility of polarons in the model incorporating a maximum velocity is found to be ∼3 ${\mathrm{cm}}^2$/V s corresponding to a diffusion coefficient of ∼0.08 ${\mathrm{cm}}^2$/s. The predicted drift mobilities might be observed in photoconductivity measurements at short enough times after creation that the polaron remains on the same chain.