SAMOP 2023 – scientific programme

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MO: Fachverband Molekülphysik

MO 14: Ultrafast Dynamics II (joint session MO/A)

MO 14.7: Talk

Thursday, March 9, 2023, 12:30–12:45, F102

Simplifying the Analysis of Transient Absorption Data by Polarization Control — •Yi Xu¹, Lars Mewes¹, Erling Thyrhaug¹, Heinz Langhals², and Jürgen Hauer¹ — ¹Dynamical Spectroscopy, Department of Chemistry, Technical University of Munich, 85748 Garching, Germany — ²Department of Chemistry, Ludwig-Maximilians-Universität München, 81377 Munich, Germany

Ultrafast energy transfer in donor-acceptor (D-A) systems with orthogonal transition dipole moments (TDMs) is of fundamental interest due to its incompatibility with Förster theory. An in-depth theoretical treatment calls for specific experimental tools, which we provide by polarization-controlled transient absorption (TA) spectroscopy with broadband detection. We isolate pure donor and acceptor parts of the total signal. This provides a strategy to greatly reduce spectral congestion in complex systems. The polarization-associated spectra can be isolated to the contributions either parallel (S_z) or orthogonal (S_y) to the excitation TDM. The derived expressions read S_z =3 · S_MA · V_z(r(λ,t),β) and S_y =3 · S_MA · V_y(r(λ,t),β), where S_MA represents the magic angle spectra. The corresponding unit vectors V_z(r(λ,t),β) and V_y(r(λ,t),β) are both functions of the time resolved anisotropy r(λ,t) and the angle β stands for differences between the TDMs defining the first and last light-matter interaction in a TA-sequence. We find that β ≈ 30^∘ is an optimal choice to disentangle the D and A-signals. This proves the non-orthogonality within the “orthogonal” D-A system.