The electronic structure at organic/organic interfaces plays a key role, among others, in defining the quantum efficiency of organics-based photovoltaic cells. Here, we perform quantum-chemical and microelectrostatic calculations on molecular aggregates of various sizes and shapes to characterize the interfacial dipole moment at pentacene/C 60 heterojunctions. The results show that the interfacial dipole mostly originates in polarization effects due to the asymmetry in the multipolar expansion of the electronic density distribution between the interacting molecules, rather than in a charge transfer from donor to acceptor. The local dipole is found to fluctuate in sign and magnitude over the interface and appears as a sensitive probe of the relative arrangements of the pentacene and C 60 molecules (and of the resulting local electrical fields sensed by the molecular units).

Normal mode sampling and molecular dynamics simulations are coupled to a valence-bond/Hartree-Fock approach to evaluate the impact of the lattice and molecular vibrations on site energies in anthracene single crystals. The calculations are conducted in the temperature range 0-400 K and show substantial contributions from high-frequency modes, which calls for a quantum-mechanical model even at room temperature. External reorganization energies are also obtained from these modeling studies and found to be much smaller than their internal counterparts. Implications for charge transport in organic single crystals are discussed.