Fluorosumanenes: unique building blocks for dielectric materials Yumi Yakiyama 1,2 , Minghong Li 1 , Dongyi Zhou 1 , Chisato Sato 3 , Kohei Sambe 3 , Tomoyuki Akutagawa 3,4 , Teppei Matsumura 5 , Nobuyuki Matubayashi 5 , Hidehiro Sakurai 1,2 1 Division of Applied Chemistry, Graduate School of Engineering, Osaka University, Japan, 2 Innovative Catalysis Science Division, Institute for Open and Transdisciplinary Research Initiatives (ICS-OTRI), Osaka University, Japan, 3 Graduate School of Engineering, Tohoku University, Japan, 4 Institute of Multidisciplinary Research for Advanced Materials (IMRAM), Tohoku University, Japan, 5 Division of Chemical Engineering, Graduate School of Engineering Science, Osaka University, Japan Sumanene ( 1 ) is one of the representative buckybowls and is known to show unique properties such as bowl inversion behaviour derived from its unique bowl shape [1]. Especially 1 affords unidirectionally arraigned π-stacking columns in the solid state [2]. However, this nature also makes the bowl inversion behaviour of 1 useless for the induction of dielectric response in the solid state. In this context, we instead focused on the in-plane motion of sumanene skeleton in its columnar structure and attempted to utilize this motion to bring out the dielectric response ( Figure ). In this work, we designed and synthesized new fluorinated sumanene families and investigated their solid state dielectric properties. The representative one, difluorosumanene ( 2 ) possesses two fluorine atoms on the same benzylic carbon of pristine sumanene to have a large dipole moment along the in-plane direction. Thermal analyses, variable temperature X-ray diffraction and IR measurements indicated the presence of in-plane motion of 2 although no clear phase transition was involved [3]-[6]. This thermal property of 2 realized an anisotropic dielectric response with a Debye-type dielectric relaxation in the single crystalline state. In addition, recently synthesized monofluorinated sumanene ( 3 ) was also investigated. Fluorine atom on the benzylic carbon of 3 has two different geometry, the outer ( exo ) and the inner ( endo ) sides of the bowl and therefore the two diastereomers show large difference in their dipole moments. We recently found that these diastereomers were convertible via bowl flipping motion in the solution state and that its exo-endo ratio in the crystalline state was controllable, showing significant difference in their dielectric responses.
References 1. Sakurai, H., Daiko, T., Hirao , T. Science 301 , 1878. 2. Mebs, S., Weber, M., Luger, P., Schmidt, B. M., Sakurai, H., Higashibayashi, S., Onogi, S., Lentz, D. (2012). Org. Biomol. Chem. 10 , 2218. 3. Li, M., Wu, J.-Y., Sambe, K., Yakiyama, Y., Akutagawa, T., Kajitani, T., Fukushima, T., Matsuda, K., Sakurai . H. (2022). Mater Chem Front. 6 , 1752. 4. Li, M., Chen, X., Yakiyama, Y., Wu, J., Akutagawa, T., Sakurai, H . (2022). Chem. Commun. 58 , 8950. 5. Yakiyama, Y., Li, M., Sakurai, H . (2023). Pure Appl. Chem. 95 , 421. 6. Yakiyama, Y., Li, M., Zhou, D., Abe, T., Sato, C., Akutagawa, T., Matsumura, T., Matubayashi, N., Sakurai, H. ChemRxiv 2023 , DOI: 10.26434/chemrxiv-2023-dt8kb
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