Sequence-controlled synthesis of rotaxanes

Rotaxanes with well-defined ring sequences are attractive synthetic goals in the construction of functional materials associated with molecular shuttles and switches, molecular electronics, and information storage. Sequence-controlled synthesis of oligo- and polyrotaxanes is important in the context of the development of both sequence-defined polymers and dynamic functional materials. To date, examples of sequence-controlled rotaxanes are limited to oligorotaxanes on account of the synthetic challenges they pose. This Review sheds light on the pivotal role that sequence isomerism plays in rotaxanes. Synthetic approaches, including orthogonal templation, active-metal templation, self-sorting and snapping, cooperative-capturing, ring-through-ring-shuttling, and molecular pumping, for the construction of sequence-controlled rotaxanes are all discussed in this Review. By comparing the advantages and disadvantages of these different approaches, several possible synthetic strategies are proposed in an attempt to foretell the future of sequence-controlled synthesis of polyrotaxanes.