Reversible Mechanical Interlocking via Stimuli-Triggered Nonhomeomorphic Topology Transformation Enables Highly Efficient Rotaxane Synthesis.

Rotaxanes, as one of the most fundamental mechanically interlocked molecules (MIMs), have attracted considerable attention in many fields. However, a method that reconciles convenient, efficient, and "high-value-added" (such as reversibility, higher-order structures, and diverse topologies) synthesis of rotaxanes, remains challenging. Here, we report a threading-and-shrinking strategy to quantitatively prepare [2]rotaxane and bis[2]rotaxane (higher than 99% conversion and 92% isolated yield for [2]rotaxane; 96% conversion, 80% isolated yield for bis[2]rotaxane). The rotaxanes with a chair-like and an orthogonal geometry were synthesized in one pot by 365 nm UV light irradiation via shrinkage of macrocycle driven by reversible topology transformation between nonhomeomorphic structures, requiring no extra addition of reagents like stoppers and catalysts. The heat-triggered reverse topology transformation quantitatively converts the chair-like rotaxanes into pseudo-rotaxanes to achieve mechanical unlocking. In contrast, rotaxanes with an orthogonal geometry exhibit thermal stability and remain mechanically interlocked upon heating.