Two novel [2]rotaxanes, comprised of a dibenzo[24]crown-8 (DB24C8) macroring bound mechanically to a chemical 'dumbbell' possessing two different recognition sites - viz., secondary dialkylammonium (NH2+) and 4,4'-bipyridinium (Bpym2+) units - have been synthesized by using the supramolecular assistance to synthesis provided by, inter alia, hydrogen bonding interactions. One of these rotaxanes bears a fluorescent and redox- active anthracene (Anth) stopper unit. NMR spectroscopy and X-ray crystallography have demonstrated that the DB24C8 macroring exhibits complete selectivity for the NH2+ recognition sites, i.e., that the [2]rotaxanes exist as only one of two possible translational isomers. Deprotonation of the rotaxanes' NH2+ centers effects a quantitative displacement of the DB24C8 macroring to the Bpym2+ recognition site, an outcome that can be reversed by acid treatment. The switching processes have been investigated by 1H NMR spectroscopy and, for the Anth-bearing rotaxane, by electrochemical and photophysical measurements. Furthermore, it is possible to drive the DB24C8 macroring from the dumbbell's Bpym2+ unit, in the deprotonated form of the Anth-bearing rotaxane, by destroying the stabilizing DB24C8-Bpym2+ charge- transfer interactions via electrochemical reduction. The photochemical and photophysical properties of this rotaxane (in both its protonated and deprotonated states) have also been investigated.
Ashton, P.R., Ballardini, R., Balzani, V., Baxter, I., Credi, A., Fyfe, M.C.T., et al. (1998). Acid-base controllable molecular shuttles. JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 120(46), 11932-11942 [10.1021/ja982167m].
Acid-base controllable molecular shuttles
Balzani V.;Credi A.;Gandolfi M. T.;Venturi M.;
1998
Abstract
Two novel [2]rotaxanes, comprised of a dibenzo[24]crown-8 (DB24C8) macroring bound mechanically to a chemical 'dumbbell' possessing two different recognition sites - viz., secondary dialkylammonium (NH2+) and 4,4'-bipyridinium (Bpym2+) units - have been synthesized by using the supramolecular assistance to synthesis provided by, inter alia, hydrogen bonding interactions. One of these rotaxanes bears a fluorescent and redox- active anthracene (Anth) stopper unit. NMR spectroscopy and X-ray crystallography have demonstrated that the DB24C8 macroring exhibits complete selectivity for the NH2+ recognition sites, i.e., that the [2]rotaxanes exist as only one of two possible translational isomers. Deprotonation of the rotaxanes' NH2+ centers effects a quantitative displacement of the DB24C8 macroring to the Bpym2+ recognition site, an outcome that can be reversed by acid treatment. The switching processes have been investigated by 1H NMR spectroscopy and, for the Anth-bearing rotaxane, by electrochemical and photophysical measurements. Furthermore, it is possible to drive the DB24C8 macroring from the dumbbell's Bpym2+ unit, in the deprotonated form of the Anth-bearing rotaxane, by destroying the stabilizing DB24C8-Bpym2+ charge- transfer interactions via electrochemical reduction. The photochemical and photophysical properties of this rotaxane (in both its protonated and deprotonated states) have also been investigated.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
