Dual-mode "co-conformational" switching in catenanes incorporating bipyridinium and dialkylammonium recognition sites

Three [2]catenanes and three [3]catenanes incorporating one or two pi -elec tron-rich macrocyclic polyethers and one pi -electron-deficient polycationi c cyclophane have been synthesized in yields ranging from 4 to 38 %. The pi -electron-rich macrocyclic components possess either two 1,4-dioxybenzene or two 1,5-dioxynaphthalene recognition sites. The pi -electron-deficient c yclophane components incorporate two bipyridinium and either one or two dia lkylammonium recognition sites. The template-directed syntheses of these ca tenanes rely on i) pi . . . pi stacking interactions between the dioxyarene and bipyridinium recognition sites, ii) C-H . . .O hydrogen bonds between some of the bipyridinium hydrogen atoms and some of the polyether oxygen at oms, and iii) C-H . . . pi interactions between some of the dioxyarene hydr ogen atoms and the aromatic spacers separating the bipyridinium units. The six catenanes were characterized by mass spectrometry and by both IH and C- 13 NMR spectroscopy. The absorption spectra and the electrochemical propert ies of the catenanes have been investigated and compared with those exhibit ed by the component macrocycles and by related known catenanes. Broad and w eak absorption bands in the visible region, originating from charge-transfe r (CT) interactions between electron-donor and electron-acceptor units, hav e been observed. Such charge-transfer interactions are responsible for the quenching of the potentially fluorescent excited states of the aromatic uni ts of the macrocyclic polyether components. The redox behavior of these nov el compounds has been investigated and correlations among the observed redo x potentials are illustrated and discussed. The catenanes undergo co-confor mational switching upon one-electron reduction of the two bipyridinium unit s. One of them-in its reduced form-can be also switched by acid/base inputs and exhibits AND logic behavior. The co-conformational rearrangements indu ced by the redox and acid/base stimulations lend themselves to exploitation in the development of molecular-level machines and logic gates.