BPCPPDYSOE21 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 6: Poster Session I - Molecular Electronics and Wetting
CPP 6.10: Poster
Montag, 22. März 2021, 16:30–18:30, CPPp
Observing Singlet Fission in Time-Energy-Momentum Space — •Alexander Neef1, Sebastian Hammer2, Samuel Beaulieu1, Shuo Dong1, Tommaso Pincelli1, Julian Maklar1, Martin Wolf1, Laurenz Rettig1, Jens Pflaum2, and Ralph Ernstorfer1 — 1Fritz Haber Institute of the Max Planck Society, Faradayweg 4-6, 14195 Berlin, Germany — 2Experimental Physics VI, Julius- Maximilian University Wuerzburg, 97074 Wuerzburg, Germany
Under suitable conditions, the optically excited singlet exciton in organic crystals can split into two triplet excitons, a process known as singlet fission (SF) [Michl, 2010]. Though extensively studied, the proposed mechanisms for SF [Berkelbach, 2013] have not yet been unambiguously verified experimentally.
By means of XUV time- and angle-resolved photoemission spectroscopy (trARPES) performed on crystals of the archetypical SF compounds pentacene and tetracene, we are - for the first time - able to directly observe the transient behavior of the excited singlet and triplet states (S1 and T1) in momentum space. This allows us to compare the S1 and T1 energies with respect to the dispersing valence band within one measurement, implying that the T1 energy is significantly smaller than previous estimates. Exploiting the multi-dimensionality of trARPES, we can furthermore decompose the excited states in pentacene by their unique signature in momentum space, thereby suggesting a strong mixing of charge-transfer (CT) states into S1 and hence a CT-mediated superexchange mechanism of SF.