Rotaxanes dumbbell-shaped component

Rotaxanes are made of dumbbell-shaped and ring components which exhibit some kind of interaction originating from complementary chemical properties. In rotaxanes containing two different recognition sites in the dumbbell-shaped component it is possible to switch the position of the ring between the two stations by an external stimu-... 

Figure 13.10 Cyclic voltammetric behavior on reduction of the protonated 9H3+ and deprotonated 92+ rotaxane shown in Fig. 13.9 and of its protonated and deprotonated dumbbell-shaped component (argon-purged MeCN/EtrNPFe 0.05 M, 298 K, glassy carbon electrode, scan rate 50mV/s). The current intensity has been corrected to account for the differences in diffusion coefficients.

Figure 13.26 Structure formula of rotaxane 294+ and the electrochemically induced shuttling of the cyclophane along the dumbbell-shaped component (CH3CN, 298 K).

In dumbbell-shaped component 326+, all the redox processes of the incorporated units are present at almost the same potentials as in the separated units (Fig. 13.30) this finding shows that there are no substantial intercomponent electronic interactions. On going from the dumbbell component to rotaxane 316+, some processes are affected while others are not (Fig. 13.30). 

Figure 13.29 Structure formulas of rotaxane 316+, its dumbbell-shaped component 326+,...

Figure 13.31 Potential shifts caused by the donor/acceptor interaction between ring 2 and dumbbell-shaped component 326+ when they are assembled in rotaxane 316+. Circles, squares,...

The redox-controlled mechanical switching in SAMs of disulfide-functionalized bistable TTF-DMN rotaxanes consisting of cyclophane 124+ and a dumbbell-shaped component containing TTF and DMN stations was also extensively investigated.49... 

Figure 1. Threading (a and b) and slipping (c) approaches to [2]iotaxanes. Clipping (not shown) is another synthetic approach to rotaxanes. It involves the macrocyclization of the ring component around the preformed dumbbell-shaped component.

Figure 10. The self-assembly of the [2]rotaxane 12 3PF6 incorporating two different recognition sites within its dumbbell-shaped component.

A rotaxane is a supramolecular system composed of a macrocyclic and a dumbbellshaped component. The macrocycle encircles the linear rod-like portion of the dumbbell-shaped component and is trapped mechanically around it by two bulky stoppers. Thus, the two components cannot dissociate, but the ring component can shuttle along the axis component (Fig. 15). 

Because of their wheel and axle structure, much of the interest in rotaxane chemistry is focused on the mechanical movements of the ring around and along the dumbbell-shaped component. Of particularly interest is the possibility to control... 

Figure 13. The two spatial arrangements (co-conformations) associated with a [2]rotaxane, incorporating two different recognitions sites within its dumbbell-shaped component, can be interchanged by appropriate stimuli.

Figure 14 shows [2]rotaxane 13 + which contains two recognition sites in its dumbbell-shaped component. In this compound, the stable structure is that with the macrocyclic component surrounding the benzidine recognition site, but shuttling of the macrocycle between the two sites can be controlled electrochemically [43]. The... 

Figure 14. Shuttling of the macrocyclic component of [2]rotaxane 13 along its dumbbell-shaped component can be controlled electrochemically by oxidizing/reducing the benzidine unit [43]. Shuttling of the macrocycle component can also be controlled by protonating/deprotonating the benzidine unit (see text).

---