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.
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We thank Prof. Masahiko Iyoda at Tokyo Metropolitan University for providing us with a series of s investigated in this study. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT; No. 2020R1A5A1019141). The quantum chemical calculations were supported by the National Institute of Supercomputing and Network (NISN)/Korea Institute of Science and Technology Information (KISTI) with supercomputing resources including technical support (TS‐2020‐RE‐004). W.K. acknowledges financial support from the NRF Grant funded by the Korean Government (NRF‐2015H1A2A1033685‐Global Ph.D. Fellowship Program). L‐T n
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