DEPARTMENT OF
PHYSICAL CHEMISTRY
Physikalische Chemie - Direktor: Prof. Dr. Martin Wolf
PC Online Talk
Chair: Julian Maklar

Thursday, October 1, 2020, 11:00 am
Seminar Link
Dr. Hélène Seiler
FHI Department PC
Structural dynamics of singlet fission in pentacene single crystals
Singlet fission in organic molecular semiconductors has attracted significant attention for its relevance in opto-electronic applications. It is known that molecular packing strongly impacts singlet fission properties, and the structural dynamics are thought to play an essential role as well. Yet to this day, a direct probe of the molecular motions involved in the singlet fission process has been lacking. Here we directly observe the structural dynamics accompanying the singlet fission process in single crystal pentacene using femtosecond electron diffraction. Our data reveal the presence of coherent atomic motions at 1 THz, incoherent motions, as well as a long-lived structural distortion (> 1 ns). Molecular dynamics simulations allow us to attribute the coherent motions to collective intermolecular motions involving several molecules. These motions transiently modify the excitonic coupling between different molecules by moving entire molecules against each other. Our findings imply that both long-range coherent and incoherent vibrational dynamics participate in the singlet fission process in pentacene on the picosecond timescale by facilitating the destruction of the electronically correlated triplet pairs.

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