Quantum molecular dynamics study of polaron recombination in conjugated polymers

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 fully correlated two-particle quantum mechanical wa ve function interacting with a one-dimensional classical vibrational lattic e. This description allows a natural evolution of the particle-hole wave fu nction from the polaron limit to the exciton limit, and we have performed r eal-time simulations of the coupled nuclear and electronic dynamics associa ted with the scattering of polarons into exciton states. We use these simul ations to calculate cross sections for exciton formation as a function of s pin state, and explore the variation of these cross sections with respect t o changes in the magnitude of the particle-hole Coulomb interaction and the effective masses of the quasiparticles. Our results indicate that for an o ptimal choice of parameters the electroluminescence quantum yield may be as high as 59%, substantially greater than the 25% predicted by simple spin s tatistics. We interpret these results in a diabatic framework, and suggest strategies for the design of organic systems for use in electroluminescent devices.