Rotaxane photoswitchable

As a different type of photoswitchable rotaxane, Murakami et al. reported on the rotaxane, in which a-CD is threaded by an azobenzene-containing chain with two methylenes as the spacer between azobenzene and viologen units (109) [97],... 

Fig. 6 Design of a photoswitchable GOx electrode with electron transfer mediator (a) fer-rocenecarboxylic acid and (b) rotaxane-based molecule, (a) Reproduced from [100, 101] with permission. Copyright The American Chemical Society, 1998. (b) Reproduced from [102] with permission. Copyright Wiley-VCH, 2009...

Figure 17.9 Schematic representation of the surface-bound photoswitchable rotaxane 10.104 Such a device is capable of transducing an optical signal into an electronic signal by means of the photocontrolled ring shuttling in the rotaxane molecules. (Adapted with permission from V. Balzani et al., ChemPhysChem 2008, 9, 202-220. Copyright Wiley-VCH Verlag GmbH Co. KGaA.)...

Fig. 32 Transport of a diiodomethane droplet up a 12° incline on a surface with physisorbed, photoswitchable bistable [2]rotaxanes [228]. (a) Cartoon and photograph of the surface in the ground state. The macrocycle preferentially encircles an unfluorinated recognition site, (b) The same surface in the photostationary state (after UV irradiation). Olefin isomerization in the preferred recognition site causes some macrocycles to shuttle to the fluorinated site, changing the polarophobicity of the surface and moving the droplet several millimeters uphill...

Structural modifications (including introduction of an acetylene unit) of the thread of this type of rotaxane by Schmidt-Schaffer, Grubert, Grummt, Buck, and Abraham [94], allowed preparation of photoswitchable rotaxanes with an unfolded molecular thread. As an alternative to photolysis, treatment of the rotaxane containing the diaryl-methoxy-cycloheptatriene unit with TFA produces the diaryl-tropylium cation, and addition of solid NaHC03 in methanol can then be used to regenerate the diaryl-methoxy-cycloheptatriene station of the rotaxane. 

Abraham, Wlosnewski, Buck, and Jacob [95] invented a new type of photoswitchable rotaxane based on the above principles where the diaryl-methoxy-cycloheptatriene unit is replaced by 9-aryl-9-methoxy-acridanes (Fig. 9b4) that undergo photoheterolysis (313 nm light) with formation of acridinium ions (Fig. 9b5). Duo, Jacob, and Abraham [96] demonstrated that such devices can be deposited and can operate on gold nanoparticles. 

Abraham W, Grubert L, Grummt UW, Buck K (2004) A photoswitchable rotaxane with a folded molecular thread. Chem Eur J 10 3562-3568... 

Abraham W, Wlosnewski A, Buck K, Jacob S (2009) Photoswitchable rotaxanes using the photolysis of alkoxyacridanes. Org Biomol Chem 7 142-154... 

Duo Y, Jacob S, Abraham W (2011) Photoswitchable rotaxanes on gold nanoparticles. Org Biomol Chem 9 3549-3559... 

Supramolecular chemistry typically involves the complexes based on molecular recognition, which include crown ethers, catenates, rotaxanes, etc. Azobenzene derivatives are often used as structural elements in such supramolecular assembly. Already in 1980 (Shinkai et ah, 1980), azobenzene moiety had been introduced into crown ether. Other recent examples include azobenzene-cyclodextrin complexes (Callari et ah, 2006), azobenzene-attached nanotube-cyclodextrin complexes (Descalzo et al., 2006), and molecular recognition complexes with DNA (Haruta et al., 2008). Numerous examples of photoswitch-able azobenzene supramolecular systems in solutions can be found (Yagai et al., 2005 Balzani et al., 2002). But there are no investigations in these systems concerning photoorientation and mass transport. 

Figure 19 Structural formula of the surface-bound photoswitchable rotaxane 31 and schematic representation of its shuttling...

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