Erlangen 2022 – scientific programme

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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy II

MO 9.3: Talk

Wednesday, March 16, 2022, 11:00–11:15, MO-H5

Tracking Ultrafast Exciton–Exciton Annihilation in a Squaraine Dimer by Sixth-Order Fluorescence-Detected Two-Dimensional Spectroscopy — •Stefan Müller¹, Pavel Malý¹, Julian Lüttig¹, Christoph Lambert², and Tobias Brixner¹ — ¹Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany — ²Institut für Organische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany

Exciton–exciton annihilation (EEA), that is, the loss of one exciton through the interaction with another exciton, is an integral part of the excitation dynamics in molecular aggregates under high light irradiation. Through recent developments, the dynamics of EEA can be measured directly by coherently detected fifth-order two-dimensional (2D) spectroscopy, whereby the properties of exciton diffusion can also be determined [1]. Nonetheless, it is challenging to isolate ultrafast annihilation events as they may be obscured by coherent artifacts and nonresonant response. Here we introduce a novel 2D spectroscopic method to temporally resolve ultrafast EEA by detecting fluorescence and using only a single excitation beam. This is achieved by isolating specific sixth-order signals via 125-fold phase cycling of a collinear four-pulse excitation sequence [2]. We verify our approach on a squaraine heterodimer with aid of fifth-order 2D spectroscopy [3].

[1] J. Dostál et al., Nat. Commun. 9, 2466 (2018).

[2] S. Mueller et al., Nat. Commun. 10, 4735 (2019).

[3] P. Malý et al., J. Chem. Phys. 153, 144204 (2020).