Chemical and Structural Insights into Nonequilibrium Polyrotaxanes Formed by Molecular Pumps.

Mahapatra, Sayantan; Seale, James S W; Rajak, Soumyajit; Zhang, Xu; Jiang, Nan; Stoddart, J Fraser · Nano Lett · 2025

basic_science · Level V

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Abstract

Conventionally, the synthesis of polyrotaxanes (PRs) has been constrained by methods that depend on an inherent affinity between the rings and polymer chains. Recently, we reported nonequilibrium polyrotaxanes (NEQ-PRs), where precise numbers of rings (up to 10) can be stored on polymer chains through the action of artificial molecular pumps (AMPs), despite the rings having little to no inherent affinity for the chains. A complete understanding of the intramolecular interactions in such NEQ-PRs is essential for advancing their practical applications but remains largely unexplored. Herein, we report on a comprehensive experimental and theoretical study of poly(propylene glycol) NEQ-PRs formed by AMPs. In this investigation, Raman spectroscopy, low-temperature scanning tunneling microscopy, and theoretical simulations were employed to achieve direct real-space visualization of PRs at the single-molecule level and to uncover the coconformational changes in the polymer chains that arise because of the pumped rings.