First-Principles Calculation of Triplet Exciton Diffusion in Crystalline Poly

In this article, we present multiscale modeling of triplet exciton energy migrating through the archetypical poly(p-phenylene vinylene) (PPV) polymer in the crystal phase. We combine electronic structure calculations with coupled exciton-nuclear quantum dynamics in order to parameterize exciton evolution in J- and H-aggregate configurations. We then apply this parameterization to a master-equation approach to describe transport at the nanoscale. We find that triplet transport is characterized by two remarkably different components: a fast and coherent intrachain and a slow and incoherent interchain. Energy migration along the polymer backbone is accompanied by coherent superpositions developing between neighboring sites in the first 20 fs; however, no interchain coherence develops. The nonequilibrium exciton density exhibits an initial ultrafast ballistic spread followed by normal diffusive propagation. At room temperature, the diffusion coefficients along the respective interchain axes are found to be Da = 2.48 × 10–2 cm2 s–1, Db = 4.18 × 10–2 cm2 s–1, and Dc = 3.03 cm2 s–1 along the fast axis.