Pseudorotaxanes molecular devices

Keywords Molecular Devices a Molecular Machines a Molecular Wires a Antenna Systems a Molecular Switches a Plug/socket Systems a Pseudorotaxanes a Rotaxanes a Catenanes a Supramolecuiar Chemistry a Photochemistry a Electrochemistry a Luminescence... 

Pseudorotaxane species whose components incorporate units capable of exhibiting specific photochemical and/or redox properties are of particular interest for the purpose of constructing photochemical molecular devices. Some examples are reported in Figure 5, namely, a thread (11H+) with an ammonium function and a photoactive anthracene as a... 

The interest in rotaxanes, pseudorotaxanes, and catenanes (i.e., molecules that contain non-covalently interlocked components) stems from their potential use as building blocks in molecular devices. Their syntheses usually rely on some sort of template assistance, such as the preorganization of the assembly s components around a metal center. While cationic templates have been widely used in this context, only a few examples of anion-directed synthesis of interlocked molecules have been reported. In fact, although rotaxanes and pseudorotaxanes have been prepared in this way (as discussed in this section), to date there is no reported example of anion-directed synthesis of catenanes. 

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... 

Changes in coordination number on redox reactions can be harnessed for designing molecular devices, such as a pseudorotaxane, which behaves as a molecular shuttle. ... 

In the previous section we have described pseudorotaxane systems in which electron transfer inputs govern dethreading/threading processes, opening the way to the control of nuclear movements (molecular machines). In this section, we will see that, in their turn, nuclear movements induced by an appropriate stimulation (e.g., an acid/base reaction) can govern the occurrence of electron transfer processes or CT interactions. This aspect of pseudorotaxane chemistry can be exploited for the construction of electronic devices for information processing at the molecular level. 

Figure 22. The reversible acid/base-driven threading/dethreading motions of pseudorotaxane [30H 21]+ CH2CI2, 298 K) [19]. In the threaded structure, energy transfer can take place from the binaphthyl unit of the crown ether to the anthracenyl group of the dialkylammonium ion. The acid-driven threading of compound 19, incorporating a bulky benzene group, through the macrocyclic cavity of 21 does not occur. Such systems can be viewed as molecular-level plug-socket devices.

Another topic of current chemistry should be addressed here briefly, again with reference to the article on "Rotaxancs and Pseudorotaxanes, where further aspects of molecular machinery are discussed in greater detail. A solid state, electronically addressable, bistable L21catc-nane-based molecular switching device was fabricated from a single monolayer of the [21catenane. - The... 

The remnant molecular signature of an MSTJ fabricated from the [2]pseudorotaxane [837]" is presented in Fig. 1.10(a). This device, which is based on a polysilicon bottom electrode and a Ti/Al top electrode, was fabricated in a manner similar to that already described in Section 1.1.3 for the single-station... 

The above devices inspired scientists to develop solid-state MSTJ devices made from a [2]pseudorotaxane and [2]rotaxane (Figure 76) in which hydrophobic and hydrophilic regions were directly incorporated into the molecular structure to allow self-organization. ° The electrical properties were found to be highly dependent on the supramolecular structure, the presence of bistability within the (super)molecule, and the organization of the Langmuir-Blodgett film. The devices exhibited a... 

---