Hannover 2020 – scientific programme

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MO: Fachverband Molekülphysik

MO 4: Electronic Spectroscopy I

MO 4.3: Talk

Monday, March 9, 2020, 14:45–15:00, f142

From wavelike dynamics to anomalous diffusion: Exciton transport in polymers of varying length, observed by EEI2D spectroscopy — •Pavel Malý¹, Julian Lüttig¹, Arthur Turkin¹, Jakub Dostál^1,2, Christoph Lambert¹, and Tobias Brixner¹ — ¹Institut für Physikalische und TheoretischeChemie, Universität Würzburg, Am Hubland, 97074 Würzburg — ²Faculty of Mathematics and Physics, Charles University, Ke Karlovu 3, 12116 Prague, Czech Republic

Exciton transport and interaction in molecular aggregates and polymers are key processes in solar light harvesting and organic electronics. While the initial dynamics following photoexcitation proceeds in a delocalized, wavelike fashion, the subsequent exciton transport has diffusive character. In this work we use our newly-developed exciton-exciton interaction two-dimensional (EEI2D) spectroscopy [1], in combination with microscopic theoretical modelling, to study exciton dynamics and annihilation in squaraine copolymers of varying length [2]. By directly probing interacting exciton pairs, we observe the transition from wavelike to diffusive exciton motion, dependent on the exciton delocalization length relative to the polymer size. Contrary to the common assumption, we find that the exciton diffusion has anomalous, sub-diffusive character, indicating trapped excitons. Our results demonstrate the potential of high-order spectroscopy, such as EEI2D, to provide new insights into exciton transport and interaction.
[1] J. Dostál et al., Nat. Commun. 2018, 9, 2466-2473
[2] P. Malý et al., Chem. Sci. 2020, DOI:10.1039/C9SC04367E