SKM 2021 – wissenschaftliches Programm
CPP 5.18: Poster
Dienstag, 28. September 2021, 17:30–19:30, P
Charge-transfer excitons in pentacene:perfluoropentacene co-crystal — •Ana M. Valencia Garcia1,2, Darius Günder3, Michele Guerrini1,2, Tobias Breuer3, Gregor Witte3, and Caterina Cocchi1,2 — 1Institut für Physik, Carl von Ossietzky Universität Oldenburg — 2Physics Dept., Humboldt-Universität zu Berlin & IRIS Adlershof — 3Philipps-Universität Marburg, Molekulare Festkörperphysik, Marburg
Disclosing the nature of optical excitations in organic co-crystals is a challenge due to the complex interplay between the structural arrangement of the molecules and long-range electronic interactions in these systems. For these reasons, the application of isolated cluster models is highly questionable. By means of density functional theory and many-body perturbation theory, we investigate the electronic and optical properties of the triclinic pentacene:perfluoropentacene co-crystal. The band-structure analysis indicates that the highest-occupied and the lowest-unoccupied states are mainly localized on different molecules, suggesting the presence of a charge-transfer exciton at the lowest energy, which is indeed revealed in the dielectric tensor computed from the solution of the Bethe-Salpeter equation. We demonstrate that this feature cannot be reproduced by a molecular cluster model where the first excitation is unambiguously polarized along the short molecular axis. Comparison with corresponding measurements clarifies the importance of adequate periodic treatment of molecular co-crystals to correctly reproduce the character of their excitations .  Günder, Valencia, et al., in preparation.