FUNCTIONAL ROTAXANES - FROM CONTROLLED MOLECULAR MOTIONS TO ELECTRON-TRANSFER BETWEEN CHEMICALLY NONCONNECTED CHROMOPHORES

Rotaxanes are molecules consisting of a cyclic component threaded onto a dumbbell-shaped linear component. Although first synthesized in the late sixties, they were considered as curiosities until they became r elatively easily available through template methods (taking advantage of hydrophobic interactions, or using a transition metal or donor-acce ptor interactions between aromatic stacks). This allowed for the devel opment of functional rotaxanes, that is, rotaxanes responding to exter nal stimuli such as injection or removal of electrons, light irradiati on, and so forth. Examples are rotaxanes displaying electrochemically triggered intramolecular motions like translation of the ring along th e dumbbell axle, or photochemically induced electron transfer from por phyrinic stoppers (electron donors in the excited state) to a gold(III ) porphyrin electron acceptor appended to the ring component.