Mechanically interlocked molecules (MIMs) have been attracting much attention in the past few decades due to their challenging constructions and potential applications as an excellent framework for the fabrication of molecular machines. Functional bistable [2]rotaxanes are representatives of MIMs, in which the shuttling motion of the macrocycle between different recognition sites on the rotaxane thread can be driven by acid/base, ion binding, photochemical, and solvent changes.

Leyong Wang, Juli Jiang, and colleagues from Nanjing University, China, prepared an acid/base and anion-responsive bistable molecular shuttle bearing an anthracene stopper on the thread and a ferrocenyl (Fc) unit on the macrocycle, in which two different states are obtained by using external stimuli. As a result, the fluorescence is reduced or enhanced by the distance-dependent photoinduced electron-transfer effect between the electron-donating Fc moiety and the anthracene stopper.

This kind of molecular shuttle would pave the way for the construction of functional fluorescent switches and further dynamic fluorescent materials with multiple outputs.

• A Ferrocene-Functionalized Bistable [2]Rotaxane with Switchable Fluorescence,
  Li Liu, Qi Wang, Ming Cheng, Xiao-Yu Hu, Juli Jiang, Leyong Wang,
  Asian J. Org. Chem. 2014.
  DOI: 10.1002/ajoc.201402155