Towards the Design and Synthesis of Organic Cage Rotaxanes

Mechanically interlocked molecules, such as rotaxanes, catenanes, and knots, have been extensively studied for many years. Of these molecules, rotaxanes are one of the most common types - these consist of a macrocycle encompassing a dumbbell-shaped component called the axle, which are held together by a mechanical bond. This allows for the relatively free movement of individual components in the form of rotational (pirouetting) and translational (shuttling) movements. Their popularity has led to the design and synthesis of functional materials such as cage-based rotaxanes, rotacatenanes, polyrotaxanes, and rotaxane dendrimers. Of these materials, very little has been done to exploit the use of cages, both porous and non-porous, as core building blocks in rotaxanes. In contrast, studies on porous organic cages have led to the discovery of several catenated cage structures, commonly formed by the recrystallisation of pre-formed cages. Porous organic cages are shape-persistent, microporous structures that typically form from the self-assembly of two or more discrete multi-topic precursors, resulting in the formation of a permanent, guest-accessible cavity. This project aims to combine the chemistry of porous organic cages and rotaxanes by investigating the synthesis of [n]rotaxanes involving organic cages as building blocks, which would either be used as stoppers and/or core units in the rotaxane structure. The combination of these two species to form organic cage rotaxanes could lead to materials with advanced functionality, such as an increase in the number of sites for catalysis or separation of molecules.