Hannover 2020 – scientific programme

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MO: Fachverband Molekülphysik

MO 9: Femtosecond Spectroscopy I

MO 9.2: Talk

Wednesday, March 11, 2020, 11:15–11:30, f102

Ultrafast excitation energy localization dynamics following delocalized excitation — •Yang Li, Pavel Malý, Julian Lüttig, Stefan Müller, and Tobias Brixner — Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg

The efficiency of organic photovoltaic materials, such as conjugated polymers, aggregates and dendrimers, depends on the interplay between molecular architecture and light-induced electronic energy redistribution. The spatial localization of the excitation energy is relevant for conversion efficiency and has been a point of intense research for artificial systems that are designed and synthesized to produce solar fuels. While the delocalized excitation followed by localized emission universally appears in a variety of dendrimers [1], the localization process itself has not yet been probed in real time. In this work, polarization-controlled two-dimensional electronic spectroscopy is applied to track the excitation-wavelength-dependent anisotropy evolution of a molecular heterodimer upon broadband excitation with 11 fs pulses. 2D anisotropy reveals a transient delocalization of the excited -state wave function with Frenkel-exciton character at the moment of excitation. The spatial localization of electronic excitation gives rise to 2D anisotropy depolarization within 200 fs.

[1] D. Aulimer et al., J. Am. Chem. Soc. 16, 5742-5743 (2009).