Electron–Hole Separation in Perylene Diimide Based Self-Assembled Nanostructures: Microelectrostatics Analysis and Kinetic Monte Carlo Simulations

Electron-hole separation in self-assembled mesomorphic nanostructures composed of donor-acceptor (DA) co-oligomers is investigated by combined microelectrostatics and kinetic Monte Carlo simulations. The relevant DA dyads are based on perylene diimide (PDI) acceptor moieties covalently bound to fluorene-thiophene-benzothiadiazole donor moieties, which form highly ordered, stacked structural motifs upon self-assembly. These are characterized by efficient electron transport along PDI stacks, whereas hole transport is almost three orders of magnitude slower. On the basis of an atomistic structure obtained by electron diffraction, the energetics of charge separation is characterized by a microelectrostatics analysis. This information is subsequently employed to compute electron-hole (e-h) separation rates and dissociation yields by kinetic Monte Carlo simulations. The latter have been calibrated against recent quantum dynamical studies for a reduced one-dimensional representation of the DA system. It is shown that charge separation of "cold" e-h pairs is characterized by dissociation rates around 10(9) s(-1), which are associated with two-dimensional transport features, where the predominant electron transport in the PDI stacking direction is assisted by a secondary mechanism that involves neighboring stacks.