Selective Positioning of CB[8] on Two Linked Viologens and Electrochemically Driven Movement of the Host Molecule

The binding interactions between cucurbit[8]uril (CB[8]) and a dicationic guest N,N‐dimethyl‐3,3′‐dimethyl‐4,4′‐bipyridinium (DMV2+) have been investigated by various experimental techniques including NMR, ESI‐MS, and UV/Vis and fluorescence spectroscopy. In a three‐component system consisting of CB[8], N,N‐dimethyl‐4,4′‐bipyridinium (MV2+) and DMV2+, CB[8] was found to exhibit a higher binding affinity to DMV2+ than to MV2+. When DMV2+ was connected to MV2+ by an alkyl chain, the first equiv. of CB[8] could be selectively positioned on the DMV2+ moiety, and then a second equiv. of CB[8] was positioned on the MV2+ moiety. Spectroelectrochemical studies showed that upon the reduction of this system at –0.6 V vs. AgCl, the CB[8] could move from the DMV2+ moiety to the MV+· radical, which formed a dimer inside the CB[8] cavity. Molecular oxygen quenched the dimer, and the CB[8] moved back to the DMV2+ moiety, indicating a molecular movement driven by electrochemistry. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) The host CB[8] was selectively positioned on the DMV moiety of a DMV‐MV molecular dyad and subsequently moved to the MV moiety through an electrochemical reduction. The host was moved back to theDMV moiety by oxidation. The ability to reversible move the host from one guest to another contributes to the fundamental understanding required for the design of more advanced molecular devices.