Fig. 1: Design and working mechanism of the [3]catenane molecular motor [3]CMM.
a, Graphical representations with key structural fragments for the oxidized state of the [3]catenane molecular motor [3]CMM13+. The cyclobis(paraquat-p-phenylene) rings, the bisradical dicationic states of cyclobis(paraquat-p-phenylene), the viologens, the radical cationic states of the viologens, the bis(4-methylenephenyl)methane, the isopropylphenylene, the triazole and the 2,6-dimethypyridinium units are labelled as CBPQT4+, CBPQT2(+•), V2+, V+•, BPM, IPP, T and PY+, respectively. b, Graphical representations for the reduced state of the [3]catenane molecular motor [3]CMM7+6• with key superstructural formulas showing the radical-pairing interactions between the CBPQT2(+•) rings and the V+• units. Positive charges are balanced by PF6− counterions, which are omitted for the sake of clarity. c, The redox operation of [3]CMM13+/7+6• demonstrating the unidirectional rotary motion of the two CBPQT4+/CBPQT2+• rings. In state I, [CBPQT-A]4+ and [CBPQT-B]4+ are positioned around the T and BPM units, respectively. Reduction of the V2+ units and the CBPQT4+ rings by the injection (step 1) of six electrons in total triggers both rings to undergo a clockwise rotation, leading to the formation (state II) of the reduced state [3]CMM7+6•. Subsequent oxidation by the removal (step 2) of six electrons restores the Coulombic repulsion between the two rings and the loop, obliging [CBPQT-B]4+ to thread over (state III) the steric barrier (IPP) under thermal activation and eventually encircle T, whereas [CBPQT-A]4+ finds itself threaded around BPM, thus completing a 180° positional exchange between the two rings shown in state I′. A second redox cycle (steps 3 and 4) resets the system back to state I after the accomplishment of another 180° positional exchange between the two rings.
