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Intramolecular Electron Transfer in Multi-Redox Systems Based on Cyclic [3]Spirobifluorenylene Compound.

Authors
  • Imai, Tomoya1
  • Sakamaki, Daisuke2
  • Aoyagi, Shinobu1
  • Amaya, Toru1
  • 1 Department of Information and Basic Science, Graduate School of Science, Nagoya City University, 1 Yamanohata, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8501, Japan. , (Japan)
  • 2 Department of Chemistry, Graduate School of Science, Osaka Metropolitan University Naka-ku, Sakai, Osaka, 599-8531, Japan. , (Japan)
Type
Published Article
Journal
Chemistry - A European Journal
Publisher
Wiley (John Wiley & Sons)
Publication Date
Dec 14, 2023
Volume
29
Issue
70
Identifiers
DOI: 10.1002/chem.202302670
PMID: 37740416
Source
Medline
Keywords
Language
English
License
Unknown

Abstract

Cyclic [3]spirobifluorenylene with bulky alkyl groups at the ends (1) was designed and synthesized to investigate the electron transfer phenomena in a π-conjugated system including orthogonal π-conjugated chains. The three bifluorenyl units in 1 are conjugated to each other via spiro-conjugation, resulting in the splitting of the HOMO levels to a small extent. Therefore, the SOMO-HOMO gap of the radical cation species is small, which is considered to allow the facile intramolecular electron transfer. The electronic properties of 1 and its partial structures were characterized by absorption and fluorescence measurements and electrochemical analysis. From the electrochemical oxidation, the interchain Coulombic repulsion was observed. In the TD-DFT calculations for the radical cation species of 1, the geometry-featured interchain electronic transitions were visualized by NTO calculations. The radical cation species of 1 generated by chemical oxidation with SbCl5 exhibited a broadened and lower-energy NIR absorption band exceeding 2000 nm. Considering the results of the TD-DFT calculations, the NIR band of the radical cation of 1 was attributed to the intramolecular electron transfer processes among the bifluorenyl units in the macrocycle. ESR experiments also indicated the delocalization of a spin of 1⋅+ in the whole molecule via hole hopping in the ESR time scale at room temperature. This work demonstrates the usefulness of spiro-conjugation as a bridging unit in molecular wires to facilitate smooth electron transfer. © 2023 Wiley-VCH GmbH.

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