Mechanically interlocked molecules based

Mechanically Interlocked Molecules Based on Pillar[n]arenes... 

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... 

Before going on to discuss molecular electronic machines, it will be useful to describe their structural foundation at a molecular level, namely those based on interlocked molecules. Interlocked molecules can take on a variety of forms, the most common being catenanes, rotaxanes, knots [16], and carceplexes [17]. For the purpose of this review, only catenanes, rotaxanes and their geometrically related complexes - pseudorotaxanes [18] - will be discussed. When conferred with the ability to undergo some mechanical motion as a result of an applied stimulus - be it chemical, electrochemical, or photochemical - these interlocked molecular and interpenetrated supramo-lecular systems often take on the characteristics of molecular machines [19]. 

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. 

Polyrotaxanes, in which many cyclic molecules are mechanically interlocked onto a polymeric chain, have been synthesized using macrocyclic compounds such as cyclodextrins, crown ethers and blue boxes. Synthesis of pillar[5]arene-based polyrotaxanes consisting of cationic polymers, such as viologen polymer, is relatively easy because pillar[5]arene forms stable host-guest complexes with cationic molecules (see details in Chapter 9) however, it is difficult to synthesize nonionic polymer-based polyrotaxanes. To synthesize nonionic polymer-based polyrotaxanes, we used a liquid... 

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