Stimuli pseudorotaxane

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]. 

The first publications describing [33] the controlled unthreading and rethreading of pseudorotaxanes from our laboratories appeared in the early 1990s. The pseudorotaxane machines produced to date fall into two distinct classes - one that relates to switches (basic on-off actions in response to an applied stimulus), and the other to gates (responses to two stimuli that mimic the operation of a logic function). 

One of the earliest pseudorotaxane-based switches to emerge from our laboratories relied [34] upon the electrostatic repulsion between the macro-cyclic component and a signaling stimulus. In this switch (Fig. 18), the thread... 

CBPQT + ring. The major difference to the pseudorotaxane is the presence of a secondary electron-donor station in the form of 1,5-dioxynaphthalene (DNP, colored red). Thus, when the CBPQT + ring is repelled away from the TTF" " station, it has an alternative and favorable location to settle onto. The repulsion from TTF" " as well as the attraction to DNP in the catenane has led to its designation as a push-pull switch.- The added stability conferred when the CBPQT " " encircles the DNP station means that, once the oxidation stimulus is removed, the CBPQT " " takes some time to move back that is, the co-conformation with CBPQT " " at the DNP station is metastable. This feature is explored below when considering the effect of environment on the switching rates. 

Ma X, Sun R, Li W, Tian H (2011) Novel electrochemical and pH stimulus-responsive supramolecular polymer with disparate pseudorotaxanes as relevant unimers. Polym Chem 2 1068-1070... 

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