Development and advancement of rotaxane dendrimers as switchable macromolecular machines

Rotaxane dendrimers are a newly emerging large family of mechanically interlocked molecules (MIMs), which combine the concept of molecular switching properties into hyperbranched dendrimers to render new macromolecular machines. Basically, rotaxane dendrimers are divided into three types and each type represents a special connection between the mechanical bonds, macrocycles and rods. In the past few years, with the methodology development of rotaxane synthesis, more complex and high molecular weight rotaxane dendrimers have been designed and synthesized, especially the most complicated Type III rotaxane dendrimers. In particular, higher generation sophisticated rotaxane dendrimers bring advancements from 1-dimensional to 3-dimensional molecular switching, and have been applied in advanced functional materials for various applications towards drug delivery. This review surveys the development and advancement of each type of rotaxane dendrimer, from the simple dendron-grafted Type I to intricate Type III dendritic polyrotaxane dendrimers with future perspectives.