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.
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