(355j) Coarse-Grained Model of Energy Transport in Disordered Conjugated Polymer Network

Conjugated polymers are important components in optoelectronic devices such as light-emitting diodes, field-effect transistors, and photovoltaic cells. A comprehensive understanding of electronic energy transport such as excitons and charge carriers in conjugated polymers is challenging, given the effects of electron-electron interactions, electron-nuclear coupling, and disorder on a wide range length scales—from molecular level up to the device scale. Here we present a novel coarse-grained approach for simulating the dynamics of excitons in long and disordered organic conjugated polymer aggregates. In our model, the polymer is described as a time-dependent array of ring-ring torsion angles of individual monomer units as well as the relative monomer positions to capture the aniosotropic π-stacking and semi-flexible polymer backbone properties. Exciton dynamics arise in direct response to the evolution of ring-ring torsional landscape along its excited state potential energy surface, which includes exciton-induced forces such as those that lead to self-trapping. We show that this model can reproduce transient pump-probe experiments; we remark on the importance of the excited state force field when describing these systems. Then we go on to present molecular-level physical insights into exciton dynamics in these polymer materials, which have been previously speculative, to help better engineer organic optical and electronic devices.