Redox-switchable rotaxanes

Other interesting and recent contributions have shown (i) the utilization of self-complexing molecules as a Brownian ratchet, (ii) the use of reductive electrochemistry to turn on attractive axle-wheel interactions in a rotaxane, (iii) the use of CDs as wheels in redox-switchable rotaxanes,and (iv) redox control on the movements of two... 

Figure 11.38 A [2] rotaxane-based, pH- and redox-switchable molecular shuttle.

Figure 17.7 A molecular valve based on redox switchable bistable rotaxane 84 1 77 (Adapted with permission from V. Balzani et al., ChemPhysChem 2008, 9, 202-220. Copyright Wiley-VCH Verlag GmbH Co. KGaA.)...

Yasuda T, Tanabe K, TsujiTet al (2010) A redox-switchable 2 rotaxane in a Hquid-crystalline state. Chem Commun 46 1224-1226... 

Fig. 16A-D. Mechanical switching in rotaxanes. A Rotaxanes may exist in isomeric states by the movement of the ring component between dissymmetric sites on the string component. B A redox- or pH-switchable [2]rotaxane. While the cyclophane complexes the native benzidine site (spectrum, curve a), the reduced or protonated benzidine repels the cyclophane, causing it to move to the dioxybiphenylene site (spectrum, curve b). C An azobenzene-based switchable [2]rotaxane. The cyclodextrin ring complexes the azobenzene site in the trans-state, but it is repelled from the ds-azobenzene. The state of the system is measurable by circular dichroism (plot). D A pH-switchable rotaxane. When the amine on the string component is protonated, it complexes the crown ether ring by hydrogen-bonding interactions (40a). When the amine is deprotonated, however, the ring component moves to the bipyridinium unit, where it is complexed by n donor-acceptor interactions (40b). The plots in B and C are adapted from [67] and [69], respectively, with permission...

Stoddart et al reported a redox-switchable a-CD-based [2]rotaxane R16 (Figure 16) via cycloaddition Click reaction, wherein an a-CD first incorporates a TTF unit of the dumbbell to form pseudorotaxane, and then employs a threading-followed-by-stopping approach via the copper(l)-actalyzed azide-alkyne cycloaddition (yield 23%). The host O -CD ring is preferred to rest on the TTF station. After the oxidation of TTF to its radical cation or to its dication, a-CD moves onto the 1,2,3-triazole ring unit. The redox-switchable process of rotaxane R16 is reversible as reported. This is the first example of redox-switchable CD-based [2]rotaxanes. 

Figure 16 A redox-switchable a-cyclodextrin-based [2]rotaxane R16 prepared by Click reaction.

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