Rotaxane bistable

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... 

In order to make the copper central core as easy as possible to rotate, we thought that the bulky stoppers should be located far away from the central complex. We thus prepared and studied a new bistable rotaxane, depicted in Fig. 14.10, whose stoppers are indeed very remote from the copper center.31 This new dynamic system can indeed be set in motion more rapidly than the previously described systems. 

Such controlled motion might become even more important, if one realizes that a bistable, controllable rotaxane might be useful as a nanoscale electronic device. One state would then be the "0", the other would represent the 1" state of one bit of a computer memory. Even if we have a long way to go before using these molecules as reliable functional units in electrical circuits minimized to nanometer dimensions, it seems to be of great promise and such promise demands the intense study of ways to synthesize these molecules and the detailed examination of their properties. 

One rotaxane molecule is shown in Figure 5.9. This molecule is not expected to demonstrate bistable switching, but is a candidate for a molecular switch that can be configured one time. Note that both ends of the molecule are non-polar hydrocarbon moieties while the center of the molecule is polar. Molecules that have both a non-polar and a polar end, for easier formation of Langmuir-Blodgett films, have been synthesized and tested in devices.51... 

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.)...

In the following sections, bistable rotaxanes will be discussed and classified based on the types of the energy inputs utilized to power their mechanical motions. Since many of these compounds have already made their way into the device world, the prospects for their further development in an applied sense will also be addressed. 

A Bistable [2]Rotaxane Driven by Acid-Base Chemistry... 

In one such TTF/DNP-based bistable [2]rotaxane 54+ (Fig. 8.6a), a long, rigid p-ter-phenyl spacer was employed between the TTF and DNP recognition sites and two tetraarylmethane stoppers were employed [22a] on both ends of the dumbbell component for the solution-phase switching studies. UV-Vis spectroscopy (Fig. 8.6b), which reveals the precise location of the CBPQT4+ ring on the dumbbell... 

Fig. 8.7 Chemical switching of an amphiphilic bistable [2]rotaxane 64+ in a condensed phase, monitored by X-ray photoelectron spectroscopy.

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