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Published October 3, 2012 | Supplemental Material + Published
Journal Article Open

Radically Enhanced Molecular Switches


The mechanism governing the redox-stimulated switching behavior of a tristable [2]rotaxane consisting of a cyclobis(paraquat-p-phenylene) (CBPQT^4+) ring encircling a dumbbell, containing tetrathiafulvalene (TTF) and 1,5-dioxynaphthalene (DNP) recognition units which are separated from each other along a polyether chain carrying 2,6-diisopropylphenyl stoppers by a 4,4′-bipyridinium (BIPY^2+) unit, is described. The BIPY^2+ unit acts to increase the lifetime of the metastable state coconformation (MSCC) significantly by restricting the shuttling motion of the CBPQTT^4+ ring to such an extent that the MSCC can be isolated in the solid state and is stable for weeks on end. As controls, the redox-induced mechanism of switching of two bistable [2]rotaxanes and one bistable [2]catenane composed of CBPQT^4+ rings encircling dumbbells or macrocyclic polyethers, respectively, that contain a BIPY2+ unit with either a TTF or DNP unit, is investigated. Variable scan-rate cyclic voltammetry and digital simulations of the tristable and bistable [2]rotaxanes and [2]catenane reveal a mechanism which involves a bisradical state coconformation (BRCC) in which only one of the BIPY^•+ units in the CBPQT^2(•+) ring is oxidized to the BIPY2+ dication. This observation of the BRCC was further confirmed by theoretical calculations as well as by X-ray crystallography of the [2]catenane in its bisradical tetracationic redox state. It is evident that the incorporation of a kinetic barrier between the donor recognition units in the tristable [2]rotaxane can prolong the lifetime and stability of the MSCC, an observation which augurs well for the development of nonvolatile molecular flash memory devices.

Additional Information

© 2012 American Chemical Society. Received: June 20, 2012; Published: September 24, 2012. We acknowledge the multidisciplinary Research Program of the University Research Initiative (MURI) award FA9550-07-1- 0534 on "Bioinspired Supramolecular Enzymatic Systems" as well as the National Science Foundation (NSF) for their award CHE-0924620. We also acknowledge support from the Microelectronics Advanced Research Corporation (MARCO) and its Focus Center Research Program (FCRP) on Functional Engineered NanoArchitectonics (FENA) as well as from the Non-Equilibrium Energy Research Centre (NERC), which is an Energy Frontier Research Centre (EFRC) funded by the U.S. Department of Energy, Office of Basic Sciences (DOEBES) under award DE-SC0000989. The research at Northwestern University (NU) was enabled by the National Center for Nano Technology Research at the King Abdulaziz City for Science and Technology (KACST) in Saudi Arabia. The authors thank Dr. Turki S. Al-Saud and Dr. Mohamed B. Alfageeh at KACST for their generous support of this research. A.C.F, D.C., W.A.G., and J.F.S. were all beneficiaries of the WCU Program (NRF R-31-2008-000-10055-0) funded by the Ministry of Education, Science and Technology, Korea. A.C.F. and D.C. acknowledge support from NSF Graduate Research Fellowships.

Attached Files

Published - ja306044r.pdf

Supplemental Material - ja306044r_si_001.pdf

Supplemental Material - ja306044r_si_002.cif


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August 19, 2023
October 19, 2023