Lithium Ion Responsive [2]Catenane Molecular Spring

Abstract

Catenanes, which can be designed as stimulus-responsive molecular machines with controlled motion, hold significant potential for biomimetic and molecular switching applications. However, the synthesis of structurally intricate and multifunctional catenanes remains challenging. Herein, we report the construction of an elaborate molecular machine that integrates a supramolecular macrocycle, pillararene, into a catenane framework. This system exhibits both intramolecular charge transfer (CT) and photoinduced electron transfer (PET), both of which can generate naphthalenediimide radical anions (NDI•–). In terms of ion recognition, the supramolecular system exhibits high specificity toward lithium ions. Coordination with Li+ induces a contracted conformational state of the catenane, whereas subsequent extraction of Li+ by the chelator 12-crown-4 restores its relaxed conformational state. Through alternating cycles of adding Li+ and 12-crown-4, reversible contraction–relaxation motion of this so-called “molecular spring” (in a metaphorical sense) is achieved, demonstrating a switchable conformational transition.