Rotaxane charged

More recently, Kim et al. synthesized dendritic [n] pseudorotaxane based on the stable charge-transfer complex formation inside cucurbit[8]uril (CB[8j) (Fig. 17) [59]. Reaction of triply branched molecule 47 containing an electron deficient bipyridinium unit on each branch, and three equiv of CB[8] forms branched [4] pseudorotaxane 48 which has been characterized by NMR and ESI mass spectrometry. Addition of three equivalents of electron-rich dihydrox-ynaphthalene 49 produces branched [4]rotaxane 50, which is stabilized by charge-transfer interactions between the bipyridinium unit and dihydroxy-naphthalene inside CB[8]. No dethreading of CB[8] is observed in solution. Reaction of [4] pseudorotaxane 48 with three equiv of triply branched molecule 51 having an electron donor unit on one arm and CB[6] threaded on a diaminobutane unit on each of two remaining arms produced dendritic [ 10] pseudorotaxane 52 which may be considered to be a second generation dendritic pseudorotaxane. 

Figure B. Pictorial representation of the self-assembly of pseudorotaxa-nes based on (a) charge-transfer and C-H—O hydrogen-bonding interactions between 1,1 -diben-zyl-4,4 -bipyridinium dication and 1,5-dinaphtho[38] crown-10 (1/5DN38C10), and (b) hydrogen-bonding interactions between dibenzyl ammonium ion and dibenzo[24]crown-8 (DB24C8). A possible route towards the synthesis of rotaxanes and catenanes is also schematized.

Fujimoto and coworkers used a self-assembled Janus [2]-pseudorotaxane406 to obtain a Janus[2]rotaxane 407 (Figure 8.2.4) [33]. A quadruply stranded alkaline earth metal containing helical catenate, a charge-neutral heterotopic homodinuclear [2]catenane, was reported by Castro et al. [34]. 

When rotaxanes and catenanes contain redox-active units, electrochemical techniques are a very powerful means of characterization. They provide a fingerprint of these systems giving fundamental information on (i) the spatial organization of the redox sites within the molecular and the supramolecular structure, (ii) the entity of the interactions between such sites, and (iii) the kinetic and thermodynamic stabilities of the reduced/oxidized and charge-separated species. 

In this chapter, for space reasons, only a few paradigmatic examples of rotaxanes and catenanes based on donor-acceptor (charge transfer (CT)) and/or hydrogen bonding interactions (systems based on metal-ligand bonding are reviewed in another... 

It can be concluded, as shown in the square scheme reported in Fig. 13.27, that in the deprotonated rotaxane (i) the first reduction of the bipyridinium weakens the charge transfer interactions and promotes the displacement of the ring far from the monoreduced unit, and (ii) the reoxidation of such a unit, restoring its electron acceptor power, causes the back movement of the ring. 

Since caroviologens are rather fragile compounds, they can be protected from the environment by inclusion into polyanionic derivatives of (J-cyclodextrin in a rotaxane fashion 102 [8.156]. Also, in the design of molecular devices, it may be desirable to introduce some extent of redundancy in order to reduce the risk of device failure. This is the case in the tris-carotenoid macrobicycle 103 that represents a sort of triple-threated molecular cable whose crystal structure 104 has been determined. It forms a dinuclear Cu(i) complex 105 in which the bound ions introduce a positive charge at each of the species, a feature of potential interest for transmembrane inclusion [8.157]. 

The rotaxane 16 + (the rotaxane nomenclature used here is 16 "+, where N refers to the coordination number of the metal (4 or 5) and n to its charge) synthesized here is composed of two subunits a macrocycle and a molecular thread (Figure 15). The macrocycle1861 17 (Figure 15 (a) and (b)) possesses two different coordi-... 

Keywords Catenane Ir/Ru Light-driven molecular machine Photoinduced Charge Separation Rotaxane Scorpionate... 

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