Logic gates were fabricated from an array of configurable switches, each consisting of a monolayer of redox-active rotaxanes sandwiched between metal electrodes. The switches were read by monitoring current flow at reducing voltages. In the "closed" state, current flow was dominated by resonant tunneling through the electronic states of the molecules. The switches were irreversibly opened by applying an oxidizing voltage across the device. Several devices were configured together to produce AND and OR logic gates. The high and low current levels of those gates were separated by factors of 15 and 30, respectively, which is a significant enhancement over that expected for wired-logic gates.

Synthetic approaches to self-assembling [n]rotaxanes incorporating π-electron deficient bipyridinium-based dumbbell-shaped components and π-electron rich hydroquinone-based macrocycles have been developed. In particular, the so-called slippage methodology relies upon the size complementarity of preformed macrocyclic and dumbbell-shaped components. The spontaneous self-assembly of these complementary components into a rotaxane in solution can be achieved under the influence of an appropriate amount of thermal energy. The absorption spectra, luminescence properties, and electrochemical behavior of the rotaxanes and their dumbbell-shaped components have been investigated and discussed on the basis of the behavior of their chromophoric and electroactive units. Charge-transfer and energy-transfer processes between specific chromophoric subunits and unusual correlations between the redox patterns of the various compounds have been evidenced and interpreted.

A synthetic approachsnamely slippagesto self-assembling [n]rotaxanes incorporating π-electron deficient bipyridinium-based dumbbell-shaped components and π-electron-rich hydroquinone-and/or dioxynaphthalene-based macrocyclic polyether components has been developed. The kinetics of rotaxane formation by the slipping procedure were investigated by absorption UV-visible and 1 H-NMR spectroscopies in a range of temperatures and solvents, varying systematically the size of both the stoppers and the macrocyclic components. As expected, the rate constants for these processes are affected by the size complementarity between macrocycles and stoppers. Furthermore, the enthalpic and entropic contributions to the free energies of activation associated with the slippage and the effect of solvent polarity upon the outcome of these processes have been evaluated. In addition, the spectroscopic and electrochemical properties of some of the rotaxanes are presented and discussed with reference to the properties of their chromophoric and electroactive units.

We have prepared and investigated two dendrimers based on a 1,3,5-trisubstituted benzenoid-type core, containing 9 and 21 viologen units in their branches, respectively, and terminated with tetraarylmethane derivatives. We have shown that, in dichloromethane solution, such highly charged cationic species give rise to strong host-guest complexes with the dianionic form of the red dye eosin. Upon complexation, the absorption spectrum of eosin becomes broader and is slightly displaced toward lower energies, whereas the strong fluorescence of eosin is completely quenched. Titration experiments based on fluorescence measurements have shown that each viologen unit in the dendrimers becomes associated with an eosin molecule, so that the number of positions ("seats") available for the guest molecules in the hosting dendrimer is clearly established, e.g., 21 for the larger of the two dendrimers. The host-guest interaction can be destroyed by addition of chloride ions, a procedure which permits eosin to escape from the dendrimer's interior in a controlled way and to regain its intense fluorescence. When chloride anions are precipitated out by addition of silver cations, eosin molecules re-enter the dendrimer's interior and their fluorescence again disappears.