O

Scheme 6.5.6. A piston-cylinder machine based on light-induced electron-transfer processes within a pseudorotaxane.

cycle. By the Cu(I) ion template effect two of these molecules can be threaded into each other as depicted in Scheme 6.5.8. One of the particular features of copper is that it changes its preferred coordination geometry on oxidation from Cu(I) (tetrahedron) to Cu(II) (trigonal bipyramid). Incorporation of one phenanthroline unit in each of the wheels and both a phenanthroline and a terpyridine in each of the filaments enables switching between an extended and a contracted form. Cu(I) prefers to be bound to two phenanthroline ligands, but oxidation to Cu(II) provokes preferential binding to the terpyridine unit. This change necessarily involves an increase of the distance between the two macrocycles. Reduction of the Cu(II) ion to Cu(I) reverses the process.

The last example is a molecular shuttle with two different states between which one can switch electrochemically and chemically [25]. The more electron-rich part of the axle is the bisaniline moiety and, consequently, the electron-poor wheel tends to bind more strongly to this side (Scheme 6.5.9, center). On oxidation and/ or protonation charge repulsion moves the wheel to the bisphenol part of the axle. Thus, the switching between the two states can be controlled by two different hv hv

0 0

Post a comment