Erlangen 2018 – scientific programme

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MO: Fachverband Molekülphysik

MO 13: Posters 1: Ultrafast Spectroscopy

MO 13.9: Poster

Tuesday, March 6, 2018, 16:15–18:15, Orangerie

Disentangling the different time scales in the photodynamics of the molecular rotor molecule Thioflavin T — •Bastian Geissler, Kevin Artmann, and Patrick Nuernberger — Physikalische Chemie II, Ruhr-Universität Bochum, 44780 Bochum

In the dye Thioflavin T (ThT), a benzothiazole (BTA) cation is linked to N,N-dimethylaniline (DMA) via a freely rotatable bond. When excited, this rotation can lead to ultrafast deactivation, while the fluorescence yield strongly increases if this rotation is hindered, which is why ThT is a popular marker for protein aggregation and amyloid fibril formation. Moreover, the fluorescence lifetime of ThT can also vary from ps up to ns depending on the excitation wavelength, as a consequence of the pre-rotation angle between the BTA and DMA moieties in the ground state. An initially planar ThT molecule deactivates within ps because of excited-state twisting, whereas an initially pre-twisted ThT molecule shows no excited-state rotational motion and is thus long-lived. Previous work disclosed that the long-lived fluorescence originates from the BTA moiety of the dye. In this study, we performed ultrafast spectroscopy via fluorescence streaking and transient absorption in the UV spectral range for ThT and its building blocks DMA and BTA in various solvents and with different pH values. While the pre-twisted and planar ThT configurations can be selectively excited below and above 400 nm, respectively, leading to pronounced differences in the photodynamics, deep-UV excitation below 300 nm leads to no selectivity. The long-lived emission of ThT can be associated with the ns lifetime observed for BTA.