Theoretical Investigation Into The Factors Controlling The Speed Of Switching In Mechanically Interlocked Molecules

In the past decade, the study of mechanically interlocked molecules (MIMs) has beenrisen dramatically as their synthesis has become more controlled and more potentialapplications have been devised. This molecules’ configuration can be altered accordingto an external stimulus, making them to be the ideal candidates for molecular switchesand machines. However, as with all novel materials, several obstacles are still remainedbefore their potential being realized. These obstacles include switching mechanisms-how the interlocked molecules move relative to one another; switching time–the timethat ring switches from one station to another; switching speed–the speed that ringswitches from one station to another; switching barrier-the energy required to switchMIMs.This research investigate the factors controlling the switch of MIMs by classicalmolecular dynamics simulations and semi-empirical quantum mechanics simulation.Firstly, we select three representative rotaxane (the most common mechanical interlockedmolecules), these three groups of rotaxane are switched by acid, chemical interactions,temperature. Rotaxane1switched by PH, there are two recognition station on its linearmolecule-carboxylate station and tertiary station. Rotaxane2switched by chemicalinteractions, there are two recognition station on its linear molecule-1,4,5,8-naphthalenetetracarboxylic acid diimide station and pyromellitic imide station. Rotaxane3switchedby temperature, there are two recognition on its linear molecule-succinamide station andfumaramide station. Ring of the rotaxane will combine different station of the linearmolecule under different condition, so as to make the structure of molecule be the moststable. Conducting molecule mechanics simulations of the molecule configuration thatring combined with different station. Conducting quantum mechanics simulation of themolecules of the former step, so as to estimation of the energy of the system. Conductingvacuum molecular dynamics simulations of the shuttling mechanism. From the result ofthe molecular dynamics simulation, we can obtain the change of the distance betweenring and the station of the rotaxane in the process of switching, as well as the change ofenergy of the rotaxane in the process of switching. According to the change of the distance between ring and the station of the rotaxanein the process of switching, we can get the time and speed of the rotaxane in the processof switching. The switch time and speed suggest their capability for fast responseapplications. According to the change of the rotaxane and the angle change of the ringrotate in the process of switching, we can know whether the rotaxane switch easily underdifferent conditions. The results showed that only2rotaxane switch difficultly underneutral environment, however, other rotaxanes are more easily to switch.