Rocking (and Shuttling) in a Nanosized Metallobox

A pseudo-rotaxane system featuring an naphthalenediimide (NDI)-based guest encapsulated in a nanosized metallorectangle shows redox-modulated stability and reversible chloride-triggered guest release. Combined NMR and computational studies reveal distinct shuttling and rocking motions, highlighting dynamic behavior essential for designing responsive supramolecular devices.

Abstract

Gaining insight into the dynamic behavior of supramolecular systems is essential for understanding selective guest encapsulation and for the rational design of nanodevices capable of precise, controllable motion at the molecular scale. In this work, we report the construction of a pseudo-rotaxane system through the encapsulation of a naphthalenediimide (NDI) derivative bearing long aliphatic chains within the cavity of a nanosized metallorectangle. Electrochemical studies reveal that encapsulation significantly alters the redox properties of the guest. In addition, upon reduction, the NDI-based radical is stably confined within the host cavity, forming a persistent host–guest complex. This encapsulated radical species can be released upon the addition of chloride ions, demonstrating a clear example of reversible, stimuli-responsive guest uptake and release. To elucidate the internal dynamics of the system, we employed variable-temperature ¹H NMR spectroscopy in conjunction with computational modeling. These studies revealed two distinct modes of motion: a) a shuttling motion, in which the guest slides along the axis of the host cavity between central and peripheral positions; and b) a rocking motion, involving partial rotation of the guest enabled by the flexible movement of its aliphatic chains within the host interior.

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