Finally, a series of 100 ns MD simulations at 50, 100, 200, 300, and 400 K were performed to compare the thermodynamic stability of complex 2C 18 @OPP at different temperatures. Before formal analysis, a short pre-simulation of 10 ns is carried out to make the system reach its equilibrium state. The superposition diagrams of 2C 18 @OPP in MD trajectory at several temperatures show that with the increase of the simulation temperature, the thermal motion of the supramolecular complex 2C 18 @OPP intensifies, and the thermodynamic fluctuation of its structure is obvious (Figure ). Specifically, at very low temperature (50 K), the geometry fluctuations of C 18 and OPP are quite insignificant, and the position and orientation of the two C 18 rings are very stable in the corresponding loop. As the temperature increases to 200 K, the thermal motion of atoms enhances, and the structural fluctuations of C 18 and OPP increase gradually; when the temperature reaches room temperature (about 300 K), the disorder of the system further increases, which not only shows that the structural fluctuations of the host and guest molecules intensifies, but also the individual C 18 ring leaves the center of the loop occasionally and tilts towards the phenyl ring. At the maximum simulated temperature (400 K), the dual-motor nanorotator character of the 2C 18 @OPP is essentially lost, that is, the position and orientation of C 18 in OPP are largely disordered. Notably, C 18 can be temporarily perpendicular to the loop at temperature of 300 K or higher, suggesting that C 18 can undergo ring flipping in the loop and may even break free from the OPP if the kinetic energy is high enough. The statistical distribution of the angle between the plane of C 18 and that of the loop it inhabits shows that the angle distribution is closely related to temperature, that is, the higher the simulated temperature, the wider the angle distribution range, and the stronger the out-of-plane motion trend of C 18 (Figure (b)). For example, at the simulated temperature of 50 K, the deviation of the C 18 plane from the loop plane is small throughout the process, and the dihedral angles are mostly distributed in a small range of 0-10°; while at 400 K, the orientation of the C 18 ring in OPP is highly uncertain and the angle between C 18 and OPP is widely distributed. The statistical distribution of the distance between the C 18 center and the corresponding loop center shows that the temperature-dependence of the distance distribution is very similar to that of the angle distribution, that is, the position of C 18 in the loop fluctuates greater due to the stronger thermal motion of atoms at higher temperatures (Figure ).