Regensburg 2025 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 11: Ultra-fast Phenomena I
HL 11.8: Talk
Monday, March 17, 2025, 18:00–18:15, H14
Excited-state symmetry breaking and antisymmetric mode brightening in quadrupolar dye — •Somayeh Souri1, Katrin WInte1, Daniel Lünemann1, Fulu Zheng2, Mohamed Madjet2, Teresa Kraus3, Elena Mena-Osteritz3, Peter Bäuerle3, Sergei Tretiak4, Antonietta De Sio1, and Christoph Lienau1 — 1Oldenburg University, Germany — 2Bremen University, Germany — 3Ulm University, Germany — 4Los Alamos National Laboratory, USA
Quadrupolar acceptor-donor-acceptor (A-D-A) dyes are chemically tunable materials displaying a rapid photo-induced charge transfer of interest for applications in solution-processed photovoltaics. The origin of the ultrafast charge transfer is unknown. Using sub-10-fs ultrafast spectroscopy, we investigate the excited-state dynamics of a prototypical A-D-A with comparable electronic and vibronic coupling strengths. Our results reveal that vibronic couplings to high-frequency C-C-stretching vibrations on each arm of the quadrupolar dye induce a double-minimum potential energy surface (PES) in the excited-state S1 driving symmetry breaking along the antisymmetric vibrational coordinate (Q-). Upon excitation, this induces periodic splitting of the optically launched coherent wavepacket along Q- with 20-fs period, rapidly relaxing into local minima of the symmetry-broken PES within less than 100 fs. Our results demonstrate highly nonadiabatic vibronic quantum dynamics, theoretically predicted for this class of dyes [1], and unravel their role for the ultrafast charge transfer in this class of molecules. [1] J. Chem. Phys. 141, 164317 (2014).
Keywords: Quadrupolar dyes; Excited-state symmetry-breaking; Ultrafast spectroscopy