Polaron recombination dynamics in linear polyenes

We examine the dynamics of polaron recombination in conjugated polymer syst ems using mixed quantum-classical molecular dynamics. The model treats the particle-hole pair as a two-dimensional quantum mechanical wavefunction int eracting with a classical vibrational lattice. This description allows a na tural evolution of the particle-hole wavefunction from the polaron limit to the exciton limit. We have performed real-time simulations of the coupled nuclear and electronic dynamics associated with the scattering of polarons into exciton states. We use these simulations to calculate cross-sections f or exciton formation as a function of spin state, and explore the variation of these cross-sections with respect to changes in the magnitude of the pa rticle-hole Coulomb interaction and the effective masses of the quasipartic les. Our results indicate that for an optimal choice of parameters, the ele ctroluminescence quantum yields as high as 60% can be achieved, substantial ly greater than the 25% predicted by simple spin statistics.