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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]

Exciton delocalization in organic semiconducting polymers, affected by structures at a molecular level, plays a crucial role in modulating relaxation pathways, such as charge generation and singlet fission, which can boost device efficiency. However, the structural diversity of polymers and broad signals from typical electronic spectroscopy have their limits when it comes to revealing the interplay between local structures and exciton delocalization. To tackle these problems, we apply femtosecond stimulated Raman spectroscopy in archetypical conjugated oligothiophenes with different chain lengths. We observed Raman frequency dispersions of symmetric bond stretching modes and mode‐specific kinetics in the S1 Raman spectra, which underpins the subtle and complex interplay between exciton delocalization and bond length alternation along the conjugation coordinate. Our results provide a more general picture of exciton delocalization in the context of molecular structures for conjugated materials. [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]

Bond length alternation, exciton delocalization, femtosecond stimulated Raman, torsional relaxation Keywords: bond length alternation; exciton delocalization; femtosecond stimulated Raman; torsional relaxation EN bond length alternation exciton delocalization femtosecond stimulated Raman torsional relaxation 1 1 1 08/07/21 20210726 NES 210726 B Organic Semiconductors b In their Research Article on page 16999, Tahei Tahara, Dongho Kim et al. report the mode-specific vibrational analysis of exciton delocalization and structural dynamics in conjugated oligomers. Frontispiece: Mode-Specific Vibrational Analysis of Exciton Delocalization and Structural Dynamics in Conjugated Oligomers. [Extracted from the article]