Two catenane ‘molecular flasks’ have been designed to create stabilized, redox-controlled tetrathiafulvalene (TTF) dimers, enabling their spectrophotometric and structural properties to be probed in detail. The mechanically interlocked framework of the catenanes creates the ideal arrangement and ultrahigh local concentration for the encircled TTF units to form stable dimers associated with their discrete oxidation states. These dimerization events represent an affinity umpolung, wherein the inversion in electronic affinity replaces the traditional TTF-bipyridinium interaction, which is over-ridden by stabilizing mixed-valence (TTF)2•+ and radical-cation (TTF•+)2 states inside the ‘molecular flasks.’ The experimental data, collected in the solid state as well as in solution under ambient conditions, together with supporting quantum mechanical calculations, are consistent with the formation of stabilized paramagnetic mixed-valence dimers, and then diamagnetic radical-cation dimers following subsequent one-electron oxidations of the catenanes.
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The authors acknowledge support from the Air Force Office of Scientific Research under the Multidisciplinary Research Program of the University Research Initiative (award number FA9550-07-1-0534, “Bioinspired Supramolecular Enzymatic Systems”) and the National Science Foundation under CHE-0924620. M.R.W. was supported by the National Science Foundation under Grant No. CHE-0718928. Proteomics and Informatic services were provided by the CBC-UIC Research Resources Center Proteomics and Informatics Services Facility, which was established by a grant from The Searle Funds at the Chicago Community Trust to the Chicago Biomedical Consortium. Use of the Advanced Photon Source was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. Use of the LS-CAT Sector 21 was supported by the Michigan Economic Development Corporation and the Michigan Technology Tri-Corridor (Grant 085P1000817). J.M.S. acknowledges the National Science Foundation for a Graduate Research Fellowship and Northwestern University for a Presidential Fellowship. M.T.C. thanks the Link Foundation for a fellowship. G.C. thanks the EPSRC for support (GR/M32702, EP/E018211). G.C. thanks R. C. Hartley for his help regarding preliminary EPR measurements and Patrice Woisel for advice regarding the preliminary synthesis of cyclobis(paraquat-4,4′-biphenylene) and its complexation with TTF.
The authors declare no competing financial interests.
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Spruell, J., Coskun, A., Friedman, D. et al. Highly stable tetrathiafulvalene radical dimers in catenanes. Nature Chem 2, 870–879 (2010). https://doi.org/10.1038/nchem.749
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