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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. [ABSTRACT FROM AUTHOR]

Elucidating structural roles in photoinduced charge transfer is indispensable, as nuclear rearrangements are simultaneously usually involved in the dynamics. However, it is hard to evaluate whether the structural changes occur or not by using conventional time‐resolved electronic spectroscopy. Here, time‐resolved impulsive stimulated Raman spectroscopy is applied to record the evolution of vibrational snapshots during charge‐separation dynamics of donor–acceptor–donor‐type quadrupolar perylene bisimide in real time. Drastic frequency shifts were observed for several Raman bands with their population kinetics, thus symmetry‐breaking charge separation accompanies significant structural changes, as supported by (TD)‐DFT calculations. A comparison between time‐resolved Raman spectra of the neutral S1 state and the radical anion species shows that the spectral signatures, especially in high‐frequency regions, provide important clues to bond length alternation patterns in the PBI core. [ABSTRACT FROM AUTHOR]

Inside Cover: Real-time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda-dimer by Ultrafast Time-Domain Raman Spectroscopy (Angew. In their Research Article (202114474), Hyungjun Kim, Frank Würthner, Dongho Kim and co-workers have captured the vibrational snapshots triggering the excimer formation and relaxation processes of the perylene bisimide folda-dimer using the ultrafast time-domain Raman spectroscopy. Keywords: Excimer; Perylene Bisimide; Structural Dynamics; Time-Resolved Impulsive Stimulated Raman Spectroscopy; Vibrational Coherence EN Excimer Perylene Bisimide Structural Dynamics Time-Resolved Impulsive Stimulated Raman Spectroscopy Vibrational Coherence 1 1 1 03/16/22 20220321 NES 220321 B The excimer b (a contraction of the excited-state dimer) is the most classical photoproduct which has been generally regarded as a trap site. [Extracted from the article]

Keywords: Excimer; Perylene Bisimide; Structural Dynamics; Time-Resolved Impulsive Stimulated Raman Spectroscopy; Vibrational Coherence EN Excimer Perylene Bisimide Structural Dynamics Time-Resolved Impulsive Stimulated Raman Spectroscopy Vibrational Coherence 1 1 1 03/16/22 20220321 NES 220321 B Das Excimer b (eine Kontraktion des Dimers im angeregten Zustand) ist ein klassisches Photoprodukt, das allgemein als Fallenzentrum angesehen wurde. Innentitelbild: Real-time Observation of Structural Dynamics Triggering Excimer Formation in a Perylene Bisimide Folda-dimer by Ultrafast Time-Domain Raman Spectroscopy (Angew. Excimer, Perylene Bisimide, Structural Dynamics, Time-Resolved Impulsive Stimulated Raman Spectroscopy, Vibrational Coherence. [Extracted from the article]

Zeitaufgelöste impulsive stimulierte Raman‐Spektroskopie, eine ultraschnelle Raman‐Technik, ermöglicht es, Momentaufnahmen von Molekülen im angeregten Zustand mit hoher Empfindlichkeit und Zeitauflösung zu gewinnen. Durch Anwendung dieser Technik demonstrieren D. Kim et al. in ihrem Forschungsartikel auf S. 8649, dass struktureller Symmetriebruch eine wichtige Voraussetzung für eine Ladungstrennungsreaktion in einem Donor‐Akzeptor‐Donor‐Perylenbisimid ist. [ABSTRACT FROM AUTHOR]

Time‐resolved impulsive stimulated Raman spectroscopy, which is an ultrafast time‐domain Raman technique, facilitates capturing vibrational snapshots of excited‐state molecules with high sensitivity and time resolution. By using this technique, D. Kim and co‐workers demonstrate in their Research Article on page 8571 that structural symmetry breaking is an important prerequisite for a charge separation reaction in a donor–acceptor–donor perylene bisimide. [ABSTRACT FROM AUTHOR]