# Observation of shuttling on the one-second timescale in a [10]cycloparaphenylene/C60 [2]catenane

## TL;DR

This study observes slow molecular shuttling in a [10]cycloparaphenylene/C60 [2]catenane, revealing new insights into π–π interaction kinetics.

## Contribution

The paper reports the slowest π–π and dispersion-based shuttling rates observed in [2]catenanes with identical binding sites.

## Key findings

- Shuttling rates of 1–5 s−1 were observed at room temperature in the [10]CPP/C60 [2]catenane.
- Molecular dynamics simulations matched the experimental activation barrier of approximately 70 kJ mol−1.
- Thermodynamic studies showed regioisomer-dependent binding between [10]CPP and fullerene bis-adducts.

## Abstract

[2]Catenanes comprising two identical binding sites are an excellent platform to study the kinetics of non-covalent interactions. In this work, we show that the “shuttling” of the [10]CPP nanohoop between two identical fullerene bis-adduct binding sites occurs with regioisomer-dependent rates of 1–5 s−1 at room temperature, placing these among the slowest π–π and dispersion-based shuttling processes reported to date. The catenanes were accessed via Glaser–Eglinton macrocyclization from fullerene bis-adduct precursors, which were purified by extensive recycling chromatography, and characterized by variable-temperature 1H NMR spectroscopy. Molecular dynamic simulations employing well-tempered metadynamics closely reproduce the experimental activation barrier (ΔG‡ca. 70 kJ mol−1), offering insight into the nanohoop's motion and metastable states along the shuttling pathway. The kinetic data were further complemented by thermodynamic binding studies between [10]CPP and different fullerene bis-adduct regioisomers. These findings expand our understanding of the kinetics and thermodynamics of concave/convex π–π interactions and will inform the design of future mechanically interlocked machines and 2D materials with slow response to external stimuli.

[2]Catenanes comprising identical binding sites are an excellent platform to study the unusually slow kinetics of concave–convex π–π interactions.