Intercomponent π-stacking stabilised formation of [n]rotaxanes with self-sorting and cargo-conjugation properties

Despite their chemistry being known for several decades, the development of mechanically interlocked molecules as molecular machines is still in its infancy. Focusing on rotaxanes, controlling the position where subcomponents self-assemble to from a macrocycle on a given thread is imperative to develop new materials. Particularly, intercomponent interactions govern the mechanical bonds formed between these components. Making use of π-stacking intercomponent interactions, four novel [n]rotaxanes namely 4O-[2], 5O-[2], 4O-[3] and 5O-[3] have been synthesized by dynamic imine clipping reactions. 2D NMR spectra indicate the phenanthroline containing macrocycles are located on ammonium stations closest to the anthracene stoppers. Whilst the X-ray structures of 4O-[2], 5O-[2] and 4O-[3] reveal π-stacking interactions between the anthracene and phenanthroline units, indicating the thermodynamically stable structures are the major products. Furthermore, unforeseen Michael Addition reactions of the [2]rotaxanes with dimethyl acetylenedicarboxylate afforded two novel rotaxane adducts 4O-[2]-DMAD and 5O-[2]-DMAD, demonstrating these structures may be conjugated for cargo-carrying applications. This work provides an elegant strategy to control site recognition in the template directed synthesis of [n]rotaxanes.