Regensburg 2025 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 54: Ultra-fast Phenomena II
HL 54.5: Vortrag
Donnerstag, 20. März 2025, 16:15–16:30, H17
Ultrafast Time-Domain Spectroscopy Reveals Coherent Vibronic Couplings Upon Electronic Excitation in Crystalline Organic Thin Films — •Naby Hadilou1, Somayeh Souri1, Daniel Timmer1, Daniel C. Lünemann1, Katrin Winte1, Antonietta De Sio1, Martin Esmann1, Sebastian Anhäuser2, Michele Guerrini1, Ana M. Valencia1, Caterina Cocchi1, Gregor Witte2, and Christoph Lienau1 — 1Oldenburg university, Germany — 2Philipps-Universität Marburg, Germany
Coherent coupling between electronic excitations and molecular vibrations significantly influences the optical and charge transport properties of organic semiconductors and may have profound effect on technologically relevant processes such as excitons fission. Highly ordered crystalline films are ideal for probing such couplings since they enable studies of individual domain. Here, we report first polarization-resolved pump-probe experiments probing the ultrafast dynamics of crystalline perfluoropentacene thin films grown on different substrates with 10-fs time resolution. Coherent oscillations in the spectra reveal vibronic couplings to a high-frequency, 25-fs, in-plane deformation mode that is insensitive to the optical polarization, while the coupling to a lower-frequency, 85-fs, out-of-plane ring bending mode depends significantly on the crystalline and molecular orientation. Raman spectra confirm this interpretation and highlight the dominance of solid-state effects on vibronic couplings. Our results represent a first step toward uncovering the role of anisotropic vibronic couplings for singlet fission processes in crystalline molecular thin films.
Keywords: Ultrafast spectroscopy; time-resolved vibrational spectroscopy; crystalline organic thin films; vibronic coupling; singlet fission