Regensburg 2019 – wissenschaftliches Programm
CPP 14.3: Vortrag
Montag, 1. April 2019, 15:30–15:45, H31
Vibronic coupling governs ultrafast intermolecular energy transfer in an oligomer thin film — Ephraim Sommer1, Xuan Trung Nguyen1, Lynn Gross2, Thomas Frauenheim2, Elena Mena-Osteritz3, Peter Bäuerle3, •Antonietta De Sio1, and Christoph Lienau1 — 1Institut für Physik, Universität Oldenburg — 2BCCMS, Universität Bremen — 3Institut für organische Chemie II und neue Materialien, Universität Ulm
Organic photovoltaic(OPV) materials are complex molecular systems with many vibrational degrees of freedom. In such large molecules, vibronic coupling may result in conical intersections(CIs) of potential energy surfaces. Close to CIs, large vibronic couplings induce efficient ultrafast transition between electronic states. Hence CIs may profoundly influence the dynamics and yield of energy and charge transfer processes. So far, however, the importance of CIs for OPV materials has not yet been discussed. Here we use ultrafast two-dimensional electronic spectroscopy to study the light-induced dynamics in an oligomer thin film for OPV. Upon impulsive excitation, we detect a grid-like peak pattern suggesting coherent wavepacket motion in the excited state. After <50fs, the pattern transforms into a broad, featureless single peak. We observe an increase of oscillation period with an abrupt vanishing of the optically excited wavepacket, followed by the emergence of a new wavepacket with different oscillation. These results, together with ab-initio molecular dynamics calculations, show that intermolecular energy transfer in stacked dimers of this oligomer involves passage of the optically excited wavepacket through a CI within <50fs.