Ultrafast Exciton Self-Trapping and Delocalization in Cycloparaphenylenes: The Role of Excited-State Symmetry in Electron-Vibrational Coupling |
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Authors: | Juno Kim Prof?Dr Ryohei Kishi Dr Eiichi Kayahara Dr Woojae Kim Prof?Dr Shigeru Yamago Prof?Dr Masayoshi Nakano Prof?Dr Dongho Kim |
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Institution: | 1. Department of Chemistry, Spectroscopy Laboratory for Functional, π-Electronic Systems, Yonsei University, 03722 Seoul, Korea;2. Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, 560–8531 Japan;3. Institute for Chemical Research, Kyoto University, Uji, 611-0011 Japan |
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Abstract: | Upon photon absorption, π-conjugated organics are apt to undergo ultrafast structural reorganization via electron-vibrational coupling during non-adiabatic transitions. Ultrafast nuclear motions modulate local planarity and quinoid/benzenoid characters within conjugated backbones, which control primary events in the excited states, such as localization, energy transfer, and so on. Femtosecond broadband fluorescence upconversion measurements were conducted to investigate exciton self-trapping and delocalization in cycloparaphenylenes as ultrafast structural reorganizations are achieved via excited-state symmetry-dependent electron-vibrational coupling. By accessing two high-lying excited states, one-photon and two-photon allowed states, a clear discrepancy in the initial time-resolved fluorescence spectra and the temporal dynamics/spectral evolution of fluorescence spectra were monitored. Combined with quantum chemical calculations, a novel insight into the effect of the excited-state symmetry on ultrafast structural reorganization and exciton self-trapping in the emerging class of π-conjugated materials is provided. |
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Keywords: | cycloparaphenylene excited-state symmetry exciton self-trapping fs broadband fluorescence upconversion spectroscopy torsional relaxation |
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