Freiburg 2019 – wissenschaftliches Programm
FM 38.9: Talk
Dienstag, 24. September 2019, 16:00–16:15, 3043
Tracking wavepacket dynamics through a conical intersection in an organic photovoltaic oligomer aggregate — Ephraim Sommer1, Xuan Trung Nguyen1, Lynn Groß2, Thomas Frauenheim2, Elena Mena-Osteritz3, Peter Bäuerle3, •Christoph Lienau1, and Antonietta De Sio1 — 1Institut für Physik, Universität Oldenburg — 2BCCMS, Universität Bremen — 3Institut für organische Chemie II und neue Materialien, Universität Ulm
Conical intersections(CoIns) of potential energy surfaces may profoundly influence the dynamics and yield of energy and charge transfer processes. So far, however, their importance for the dynamics in organic photovoltaics (OPV) materials has not yet been discussed. Here we use two-dimensional electronic spectroscopy, with sub-10-fs time resolution, to probe the light-induced dynamics in an acceptor-donor-acceptor oligomer aggregate used in efficient OPV devices. Upon impulsive optical excitation, we detect a grid-like peak pattern suggesting coherent wavepacket motion in the excited state. After <50 fs, this pattern completely transforms into a broader and nearly featureless single peak. Concurrently, we observe an increase of oscillation period and an abrupt vanishing of the optically excited wavepacket, followed by the emergence of a new one with different oscillatory components. Our experimental results, supported by nonadiabatic excited state molecular dynamics simulations, show that ultrafast energy transfer in stacked dimers of this oligomer thin film involves passage of the optically excited wavepacket through an intermolecular CoIn within <50 fs.