condition, the molecular motor stayed at its shuttered state because of the existence
of strong supramolecular complexation interaction between secondary ammonium
salts unit and crown ether group. While upon the addition of base, the acid proton of
the secondary ammonium salt was neutralized resulting with the decreasing of the
host-guest bonding between amine and crown ether, thus further triggering the
sliding out of the axle from the crown ether’s cavity. Then the molecular motor
was switched to a open state. This process is reversible through repeated adding of
acid or base. Finally, through reduplicative exposure, this [1]rotaxane system to
ultraviolet light, a directional rotation of molecular motor, was successfully
constructed.
In 2012, Qu group [21] introduced ferrocene unit into the crown ether-based
bistable [1]rotaxane system. As shown in Fig. 9a, a linear chain was grafted to one of
Fig. 9 Conformation transformation of pseudo[1]rotaxane based on crown ether as host and
ferrocene as linkage upon the addition of acid or base [21, 22]
90
S.-H. Li et al.