The effect of a highly twisted CC double bond on the electronic structures of 9,9′-bifluorenylidene derivatives in the ground and excited states

Atsuro Takai, Dylan J. Freas, Toshikane Suzuki, Manabu Sugimoto, Jan Labuta, Rie Haruki, Reiji Kumai, Shin Ichi Adachi, Hayato Sakai, Taku Hasobe, Yoshitaka Matsushita, Masayuki Takeuchi

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Abstract

We synthesized methyl-substituted 9,9′-bifluorenylidene (9,9′-BF) derivatives in which two planar fluorene units are connected through a CC double bond. The CC double bond is twisted owing to the steric crowding between the fluorene units, and by introducing substituents at 1,1′-positions (inner space of 9,9′-BF) it becomes more twisted. Indeed, single crystal X-ray structural analysis and theoretical calculation reveal that the dihedral angle between two fluorene π-planes of a 1,1′-dimethyl-substituted 9,9′-BF is 56°, which is clearly larger than those of pristine 9,9′-BF (42°) and 1-methyl-substituted 9,9′-BF (50°). The twisted conformation of 1,1′-dimethyl-substituted 9,9′-BF facilitates the cis-trans isomerization process which we assessed quantitatively by variable-temperature NMR measurements. The 9,9′-BF derivatives with different numbers of methyl groups also exhibit remarkable changes in optoelectronic properties, primarily because of the change in the twisting angle of the central CC double bond. Theoretical calculation further indicates that the electronic structures of methyl-substituted 9,9′-BF derivatives in the excited states are considerably different from those of pristine 9,9′-BF.

Original languageEnglish
Pages (from-to)650-657
Number of pages8
JournalOrganic Chemistry Frontiers
Volume4
Issue number5
DOIs
Publication statusPublished - 2017 May 1

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ASJC Scopus subject areas

  • Organic Chemistry

Cite this

Takai, A., Freas, D. J., Suzuki, T., Sugimoto, M., Labuta, J., Haruki, R., Kumai, R., Adachi, S. I., Sakai, H., Hasobe, T., Matsushita, Y., & Takeuchi, M. (2017). The effect of a highly twisted CC double bond on the electronic structures of 9,9′-bifluorenylidene derivatives in the ground and excited states. Organic Chemistry Frontiers, 4(5), 650-657. https://doi.org/10.1039/c7qo00125h