On the Role of Nuclear Motion in Singlet Exciton Fission: The Case of Single‐Crystal Pentacene.

Singlet exciton fission (SF), the formation of two triplet excitons from one singlet exciton, involves electronic, nuclear, and spin degrees of freedom as well as their couplings. Despite almost 60 years of research on this process, a complete microscopic understanding is still missing. One important open question concerns the role of nuclear motion in SF. In this perspective, recent results on the exciton dynamics are related to the structural dynamics of single‐crystal pentacene and how they provide insights into that open question is shown. To probe the electronic dynamics, orbital‐resolved measurements of the electronic structure are carried out using time‐ and angle‐resolved photoemission spectroscopy. With femtosecond electron diffraction and with ab initio computations, the complementary nuclear dynamics is tracked. The results from both techniques are summarized, and how they relate to each other is discussed. Then, remaining open questions are outlined and potential routes are identified to tackle them, hopefully guiding future studies. [ABSTRACT FROM AUTHOR]