Rotaxanes molecular switch based

Fig. 7 The pH switched molecular switch based on a two-component rotaxane.

Figure 40 An electrochemically driven molecular switch based on a rigid [2]rotaxane. ...

Figure 63 A photo-driven chiroptical molecular switch based on a peptide rotaxane.

In the previous sections, our main focus was on mechanical molecular switches based on mechanically interlocked structures pseudorotaxanes, rotaxanes, and cate-nanes. Molecular motors, rotors, and propellers based on single rotor molecules, as important molecular machines, have also attracted great attention during the last two decades. Molecular motors can be defined as molecules that are able to convert any energy input into controlled motion. Inspired by the unidirectional rotary motion of Fi-ATPase, much effort has been focused on systems that allow controlled molecular rotation and translation. 

This remarkable molecular memory was preceded by two other related examples of addressable molecular electronics from the Stoddart and Heath groups in collaboration with Hewlett-Packard scientists. First in 1999 a [2] rotaxane based system was configured into molecular AND and OR logic gates,63 then in 2000 a [2] catenane based molecular switch was reported.64 The molecular basis for the operation of this switch is the same as in 11.67, namely reorientation in response to reduction of... 

Balzani, V., Venturi, M., Credi, A. Molecular Devices and Machines. A Jorney into the Nanoworld, Wiley-VCH, Weinheim, 2003 b) Feringa, B.L. (ed.), Molecular Switches, Wiley-VCH, Weinheim, 2001 c) Raehm, L., Sauvage, J.-P. Molecular machines and motors based on transition metal-containing catenanes and rotaxanes, Struct. Bond. 99 (2001), 55-78. 

Two-terminal devices might seem more natural for the molecular-scale systems than three-terminal ones because of the technological difficulties in manipulating small structures. Furthermore, chemical assembly of molecular devices usually results in a periodic structure. This observation resulted in the idea to have a two-terminal switch, electronically reconfigurable, where a relatively high voltage (e.g. —2V or +2V in [62], which uses a 2-catenane-based molecule) (Fig. (7a)) is applied to close or open the switch, but a relatively low voltage to read (M). 1 V) [60]. These molecular switches [62], a mono-layer of rotaxane molecules, are not field-activated but can be described as small electro-chemical cells, which are characterized by... 

A Redox-driven [2]Rotaxane-based Molecular Switch Tunnel Junctions (MSTJs) Device... 

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]. 

We have already seen how rotaxanes have been used for self-assembled molecular devices (see Chapter 3, Section 3.4.4). Another interesting molecular device based on logic operations using pseudorotaxanes has been developed. Logic gates are switches that use binary notation, i.e. the output state is a zero or... 

Another active, connected device, a molecular switch tunnel junction, has been prepared based on the switching of a two-station rotaxane. At a specific voltage, the system switches from a stable state (isomer) to a metastable one with a different conductivity. It then remains in that state until another voltage pulse returns it to its initial form (isomer). 

Kim et al. reported a rotaxane-based molecular switch (Figure 28) with fluorescence signaling." They have... 

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