Radically enhanced molecular switches

Albert C. Fahrenbach, Zhixue Zhu, Dennis Cao, Wei Guang Liu, Hao Li, Sanjeev K. Dey, Subhadeep Basu, Ali Trabolsi, Youssry Y. Botros, William A. Goddard, J. Fraser Stoddart

Research output: Contribution to journalArticlepeer-review

65 Scopus citations

Abstract

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 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 BIPY 2+ 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 BIPY 2+ 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.

Original languageEnglish (US)
Pages (from-to)16275-16288
Number of pages14
JournalJournal of the American Chemical Society
Volume134
Issue number39
DOIs
StatePublished - Oct 3 2012

Fingerprint Dive into the research topics of 'Radically enhanced molecular switches'. Together they form a unique fingerprint.

Cite this