A Fullerene‐Based Molecular Torsion Balance for Investigating Noncovalent Interactions at the C60 Surface

• Published in: Angewandte Chemie International Edition 2020-09, Vol.59 (37), p.16133-16140
• Main Authors: Yamada, Michio, Narita, Haruna, Maeda, Yutaka
• Format: Article
• Language: English
• Subjects: Balances (scales); Biphenyl; Buckminsterfullerene; Chemical bonds; Computer applications; conformational analysis; electrostatic interactions; Electrostatic properties; Fullerenes; London dispersion force; NMR; Nuclear magnetic resonance; π interactions
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.202005888

To investigate the nature and strength of noncovalent interactions at the fullerene surface, molecular torsion balances consisting of C60 and organic moieties connected through a biphenyl linkage were synthesized. NMR and computational studies show that the unimolecular system remains in equilibrium between well‐defined folded and unfolded conformers owing to restricted rotation around the biphenyl C−C bond. The energy differences between the two conformers depend on the substituents and is ascribed to differences in the intramolecular noncovalent interactions between the organic moieties and the fullerene surface. Fullerenes favor interacting with the π‐faces of benzenes bearing electron‐donating substituents. The correlation between the folding free energies and corresponding Hammett constants of the substituents in the arene‐containing torsion balances reflects the contributions of the electrostatic interactions and dispersion force to face‐to‐face arene–fullerene interactions. Well balanced: A fullerene‐based molecular torsion balance is constructed to investigate noncovalent arene–fullerene interactions. The interactions are weak but measurable. The linear correlation between the difference in the free energies of two well‐defined conformers and the Hammett constants of the substituents on the arene moieties indicate that the electrostatic interactions are a significant contribution.