Light-driven molecular shuttle

SCHEME 19 A LIGHT-DRIVEN MOLECULAR SHUTTLE WITH WHICH MOLECULAR MOTIONS CAN BE INDUCED BY... 

As illustrated in Figure 5.23, Willner et al. [49] have developed a light-driven molecular shuttle. This device consists of a ferrocene-functionalized /3-cyclodextrin... 

Willner and coworkers described an exciting light-driven molecular shuttle organized on the eledrode surface [72]. The assembly consists of a ferrocene-... 

Murakami, H, A Kawabuchi, K Kotoo, M Kunitake and N Nakashima (1997). A light-driven molecular shuttle based on a rotaxane. Journal of American Chemical Society, 119(32), 7605-7606. 

Fig. 4 Schematic structure of the first light driven molecular shuttle reproduced with permission from ref. 35. Copyright 1997 American Chemical Society.

Nakashima et al. reported the first light-driven molecular shuttle based on a rotaxane (Figure 55) comprising an a-CD linked mechanically with an axle containing an azobenzene unit located at the center, two paraquat units at each side of the azobenzene unit, and 2,4-dinitrophenyl stoppers. The location of a-CD could be changed between the azobenzene and ethylene moieties by lights of different wavelengths or by the heat both in water and in DMSO. 

In this rotaxane, a-CD exists at the trans-azobenzene part but it moves to the methylene part when the trans-azobenzene unit is converted into cts-azoben-zene. This light-driven locational change was regarded as a molecular shuttle system. 

The earliest light-driven CD-based molecular shuttle consisted of an azobenzene moiety in the axis and a-CD (Fig. 4). NMR spectroscopy supported the formation of a rotaxane complex where a-CD stays at the central trans-azobenzene site. Trans-cis conversion with 360 nm light caused a shift of a-CD to the methylene spacer, due to the exclusion of the cts-azobenzene moiety from the CD cavity. Back photoreaction and repositioning of the macrocycle on the trarzs-azobenzene unit was obtained with irradiation at 430 nm. 

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