Probing the molecular conformations and dynamics of rotaxanes using 19F NMR/MRI

Motivation: Rotaxanes, with cyclic wheels threaded onto axles, exhibit complex molecular conformations and dynamics driven by mechanical bonds and steric hindrance. Traditional techniques like 1H NMR face limitations due to multiple congested peaks, impeding clear analysis of their dynamics. Goal(s): Our goal was to leverage 19F NMR/MRI to analyze the stable conformations and dynamic motion of rotaxanes. Approach: We employed a comprehensive approach using 1D/2D NMR, molecular dynamic simulations, and 19F MRI to reveal the factors affecting rotaxane conformations and molecular dynamics. Results: Our findings demonstrated that the wheel motion in rotaxanes is predominantly governed by mechanical bonds and further modulated by steric hindrance. Impact: This study established 19F NMR/MRI as a powerful tool for probing the molecular conformations and dynamics of rotaxanes, offering valuable insights for designing next-generation molecular devices with enhanced functionality and precise control over molecular motion.