Nanohoop Rotaxanes from Active Metal Template Syntheses and Their Potential in Sensing Applications

The unique optoelectronic properties and smooth, rigid pores of macrocycles with radially oriented π systems render them fascinating candidates for the design of novel mechanically interlocked molecules with new properties. Two high-yielding strategies are used to prepare nanohoop [2]rotaxanes, which owing to the π-rich macrocycle are highly emissive. Then, metal coordination, an intrinsic property afforded by the resulting mechanical bond, can lead to molecular shuttling as well as modulate the observed fluorescence in both organic and aqueous conditions. Inspired by these findings, a self-immolative [2]rotaxane was then designed that self-destructs in the presence of an analyte, eliciting a strong fluorescent turn-on response, serving as proof-of-concept for a new type of molecular sensing material. More broadly, this work highlights the conceptual advantages of combining compact π-rich macrocyclic frameworks with mechanical bonds formed via active-template syntheses.