Rotaxanes with fullerene stoppers

Selected examples of rotaxanes bearing very bulky stoppers include a [2]rotaxane with fullerenes <2003AGE3158>, [2]-, [3]-, and [4]rotaxanes end-capped with dendritic moieties <1996JA12012>, as well as derivatives 142 <2000CC847>, 143 <2001NJC166>, and 144 <2003EJO3744>, which rely on axially coordinated metalloporphyrins as stoppers. 

Rotaxanes endowed with fullerenes are ciurently receiving a lot of attention as a consequence of the bulky nature of the C o molecule, able to act as a stopper, as well as for its unique electrochemical and photochemical properties. Thus, a novel [2]rotaxane has been synthesized in which the Ceo unit behaves as both a stopper and a photoactive unit, as shown in Figure 1. 

By modification of the Leigh protocol,electron donor Fc derivatives were added to a macrocycle in a fullerene-stoppered rotaxane (Figure 2.34). " The distance from the Fc units to the fullerene was important to increase the lifetimes of the radical pair species, which arise from 9 to 26 ns when a triethyleneglycol spacer was added between the 1,4-diamide template and Moreover, the addition of a component (hexafluoroisopropanol) able to distnrb the hydrogen bonds in the solution decreased the relative distance between the electron donors and the fullerene, together with the lifetimes of the radical pairs, reduced at 13 ns. This, together with other photophysical... 

Diederich, F., Dietrich-Buchecker, C., Nierengarten, J.-F. and Sauvage, J.-P. A copper(I)-complexed rotaxane with two fullerene stoppers. J. Chem. Soc., Chem. Commun. 7, 781-782, 1995. 

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