Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 134, Issue 39, Pages 16275-16288Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja306044r
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Funding
- University Research Initiative (MURI) [FA9550-07-1-0534]
- National Science Foundation (NSF) [CHE-0924620]
- Microelectronics Advanced Research Corporation (MARCO)
- Focus Center Research Program (FCRP) on Functional Engineered Nano Architectonics (FENA)
- Non-Equilibrium Energy Research Centre (NERC)
- U.S. Department of Energy, Office of Basic Sciences (DOE-BES) [DE-SC0000989]
- WCU Program [NRF R-31-2008-000-10055-0]
- Ministry of Education, Science and Technology, Korea
- NSF Graduate Research Fellowships
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1040558] Funding Source: National Science Foundation
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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 (BIPY2+) unit, is described. The BIPY2+ unit acts to increase the lifetime of the metastable state coconformation (MSCC) significantly by restricting the shuttling motion of the CBPQT(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 center dot+ units in the CBPQT(2(center dot+)) 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.
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