Mechanical Interlocking of 144 Symmetrical F and Tetraphenylethylene for Magnetic Resonance-Fluorescence Dual Imaging.

Single-molecule dual F magnetic resonance imaging (F MRI) and fluorescence imaging (FLI) agents are valuable tools in biomedical research. However, integrating millimolar-sensitivity F MRI and micromolar-sensitivity FLI into a single molecule remains challenging. Here, we report the use of mechanically interlocked [5]rotaxanes to efficiently incorporate 144 symmetrical fluorines (F) for sensitive F MRI and to control the motion of tetraphenylethylene (TPE) for responsive FLI at the molecular level, yielding a dual imaging agent with micromolar sensitivity. The sensitivity gap between F MRI and FLI is bridged by generating an intense singlet F peak from 144 symmetrical F and modulating their motion through mechanical interlocking. Spectroscopic and imaging studies, in conjunction with molecular dynamics simulations, highlight the critical role of [5]rotaxane formation, wheel "stationing-shuttling", and the introduction of fluorous bulky perfluoro--butoxymethyl (PFBM) groups as effective strategies to improve F MRI sensitivity and enable responsive FLI. This work not only advances the development of high-performance dual imaging agents but also provides valuable insights into the structure, dynamics, and potential applications of [5]rotaxanes in materials science.