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

Abstract

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.

Synthesis and Conformational Analysis of Fullerene Torsion Balances for Assessing the Contribution of Dispersion and Anionic Character in Non‐Covalent Arene–Fullerene Interactions

“…2‐Iodo‐3‐methylbenzoic acid was prepared by the Sandmeyer‐type reaction of 2‐amino‐3‐methylbenzoic acid with potassium iodide according to a previously reported procedure [20] . 2‐((1,5‐Diethoxy‐1,5‐diethoxy‐1,5‐dioxopentan‐3‐yl)amino)acetic acid ( 3 ) [6a] and tert ‐butyl 2‐iodo‐3‐methylbenzoate ( 4’ ) [21] were synthesized according to the procedure reported in the literature. The NMR data of these known compounds were consistent with the literature values.…”

Unraveling the Nature and Strength of Non‐Covalent Interactions on the Surface of Fullerenes

“…Despite the aforementioned examples providing robust evidence for the significance of various factors such as electrostatic forces and polarizabilities with regard to the interactions on fullerenes, a quantitative evaluation of these components has yet to be realized. To address this challenge, the present authors have devised and synthesized a single molecular model system and studied the non‐covalent interactions between arenes and fullerenes to quantitatively evaluate the various factors impacting the fullerene surface [63,64] . As depicted in Figure 8, the fullerene‐based molecular torsion balance 20 comprises C 60 ‐fulleropyrrolidine as the fundamental skeleton and an arene moiety (or another group whose interaction with C 60 is to be verified) at the terminal with a biphenyl structure and ester bond.…”