Rotaxanes molecular string

The synthesis of [3]- (figuratively shown as 7) and a [5]rotaxane (8) with one central and two terminal porphyrins in the open configuration has been reported <96AG(E)906> also a rotaxane with two Ru(terpy>2 stoppers has appeared <96CC1915>. A pseudorotaxane comprised of a macroring of 2,9-diphenyl-1,10-phenanthroline unit and a molecular string... 

Stoddart and co-workers have developed molecular switch tunnel junctions [172] based on a [2]rotaxane, sandwiched between silicon and metallic electrodes. The rotaxane bears a cyclophane that shuttles along the molecular string toward the electrode and back again driven by an electrochemical translation. They used electrochemical measurements at various temperatures [173] to quantify the switching process of molecules not only in solution, but also in self-assembled monolayers and in a polymer electrolyte gel. Independent of the environment (solution, self-assembled monolayer or solid-state polymer gel), but also of the molecular structure - rotaxane or catenane - a single and generic switching mechanism is observed for all bistable molecules [173]. 

Willner et al. developed a redox-active rotaxane (Figure 50) as a monolayer assembly on an Au electrode. The rotaxane comprises a CBPQT + cyclophane threaded onto a molecular string, which includes a rr-donor diiminobenzene unit stoppered by an adamantane unit. The cyclophane localizes on the diiminobenzene unit initially, and shuttling can be induced by the reduction or oxidation of the cyclophane, which can be characterized... 

Molecular motion based on the electrochemical-induced ligand substitution reaction has been reported in a copper(I) rotaxane (Figure 37). This rotaxane is composed of a 2,9-diphenyl-l,10-phenanthroline-containing cyclic poly ether ring, a tetraphenylmethane-stoppered molecular string that contains another 2,9-disubstitnted phenanthroline chelate... 

Cucurbit [6] uril and increasingly its higher homologues have been used extensively in a variety of host-guest chemistry and nanostructure assemblies. Of particular appeal are rotaxanes and molecular necklaces, mechanically interlocked assemblies of molecules based on CB [6]. Efficient synthesis of ID, 2D and 3D polyrotaxanes and molecular necklaces (cucurbituril beads linked by a macrocyclic molecule string ) has been achieved by a combination of self-assembly and coordination chemistry. We discuss rotaxanes and molecular necklaces in Section 10.7, and cucurbil-based systems are summarised in a recent review.23... 

Figure 2.35. Diagram of the molecular motions in copper(I)-complexed [2]-rotaxane 101 controlled by the redox state dependence of the stereoelectronic requirements of Cu. Cu(I) and Cu(II) are represented by black and white circles, respectively. Chelating sites are represented by thick lines. Initially, the string coordinates Cu(I) together with the bidentate site of the macrocycle in a tetrahedral geometry, affording the state 101(4). Electrochemical oxidation of Cu(I) to Cu(II) produces the state 101+(4), which slowly converts into the state 101+(5) after rotation of the Cu(II)-complexed macrocycle. The cycle is completed by reduction of Cu(II), which produces the state 101(5), converting to the initial state by back motion of the Cu(I)-complexed macrocycle.

Rotaxanes are molecular assemblies in which a linear component is mechanically threaded through one or more cyclic molecules - much like beads on a string -with the ends of the linear component terminated with bulky groups to prevent unthreading of the structure. The concept of a rotaxane (Latin rota, wheel axis, axle) is not new, with the idea of a rotaxane being put forward as early as 1961. Following this, several early syntheses were reported in which the rotaxane was typically obtained in very low yield. ... 

ACRONYM, ALTERNATIVE NAME Inclusion complex, molecular necklace (MN), string of pearls, rotaxane-type polymer, polymeric rotaxane. 

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