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MO: Fachverband Molekülphysik

MO 16: Femtosecond Spectroscopy II

MO 16.1: Vortrag

Donnerstag, 12. März 2020, 14:00–14:15, f102

Sensitized photoswitching by ultrafast electronic energy transfer in a benzimidazole-naphthopyran donor-acceptor dyad — Shuangqing Wang, Sebastian Megow, Mats Bohnsack, •Falk Renth, and Friedrich Temps — Institut für Physikalische Chemie, Christian-Albrechts-Universität zu Kiel, Olshausenstr. 40, 24098 Kiel, Deutschland

The excited-state dynamics of a molecular dyad with a benzimidazole (PPBI) donor and a naphthopyrane (DPNP) photochromic switch as acceptor was studied by static and femtosecond time-resolved spectroscopies and quantum chemical calculations. The static absorption spectrum of the dyad and calculations indicate that the electronic coupling between the donor and acceptor in the electronic ground state is weak. Selective photoexcitation of the PPBI subunit at 310 nm shows a strong quenching of the PPBI fluorescence in the dyad compared to free PPBI. The corresponding transient absorption maps for the dyad and its constituents and measurements of the transient absorption anisotropy decay reveal a quantitative electronic energy transfer (EET) from the PPBI^∗-DPNP donor-excited state to the PPBI-DPNP^∗ acceptor-excited state with a time constant of 2.90 ± 0.60 ps. This reduces the excited-state lifetime of PPBI from 1.4 ns to a few ps and enables ultrafast ring-opening of the DPNP to the merocyanine form. Quantitative modeling assuming Förster resonance energy transfer (FRET) provided an EET time estimate of 1.2 − 4.2 ps and confirmed FRET as EET mechanism. Our results highlight the feasibility of functional devices utilizing FRET for sensitized photoswitching.