In π-conjugated organic photovoltaic materials, an excimer state has been generally regarded as a trap state which hinders efficient excitation energy transport. But despite wide investigations of the excimer for overcoming the undesirable energy loss, the understanding of the relationship between the structure of the excimer in stacked organic compounds and its properties remains elusive. Here, we present the landscape of structural dynamics from the excimer formation to its relaxation in a co-facially stacked archetypical perylene bisimide folda-dimer using ultrafast time-domain Raman spectroscopy. We directly captured vibrational snapshots illustrating the ultrafast structural evolution triggering the excimer formation along the interchromophore coordinate on the complex excited-state potential surfaces and following evolution into a relaxed excimer state. Not only does this work showcase the ultrafast structural dynamics necessary for the excimer formation and control of excimer characteristics but also provides important criteria for designing the π-conjugated organic molecules.
Bibliographical noteFunding Information:
The work was supported by the National Research Foundation of Korea (NRF) through a grant funded by the South Korean government (MEST) (No. 2021R1A2C300630811) and by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (No. 2020R1A5A1019141). The work at Incheon National University was financially supported by the National Research Foundation of Korea(NRF-2019R1G1A1099961) and Basic Science Research Program through the National Research Foundation of Korea funded by the Ministry of Education (NRF-2017R1A6A1A06015181. The quantum mechanical calculations were supported by the National Institute of Supercomputing and Network (NISN)/Korea Institute of Science and Technology Information (KISTI) with needed supercomputing resources, including technical support (KSC-2019-CRE-0201). This work has been supported by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) within the research unit FOR 1809 and the research program Solar Technology Go Hybrid of the Bavarian Ministry of Science and the Arts. Open Access funding enabled and organized by Projekt DEAL.
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