3 years ago

Mechanical-Bond-Protected, Air-Stable Radicals

Mechanical-Bond-Protected, Air-Stable Radicals
Michael R. Wasielewski, Yuping Wang, J. Fraser Stoddart, Junling Sun, Jonathan C. Barnes, William A. Goddard, Zhichang Liu, Yilei Wu, Wei-Guang Liu, Keith R. Hermann
Radical templation centered around a heterotrisradical tricationic inclusion complex DB•+DAPQT2(•+), assembled from an equimolar mixture of a disubstituted 4,4′-bipyridinium radical cation (DB•+) and an asymmetric cyclophane bisradical dication (DAPQT2(•+)), affords a symmetric [2]catenane (SC·7PF6) and an asymmetric [2]catenane (AC·7PF6) on reaction of the 1:1 complex with diazapyrene and bipyridine, respectively. Both these highly charged [2]catenanes have been isolated as air-stable monoradicals and characterized by EPR spectroscopy. X-ray crystallography suggests that the unpaired electrons are delocalized in each case across two inner 4,4′-bipyridinium (BIPY2+) units forming a mixed-valence (BIPY2)•3+ state inside both [2]catenanes, an observation which is in good agreement with spin-density calculations using density functional theory. Electrochemical studies indicate that by replacing the BIPY2+ units in homo[2]catenane HC•7+—composed of two mechanically interlocked cyclobis(paraquat-p-phenylene) rings—with “zero”, one, and two more highly conjugated diazapyrenium dication (DAP2+) units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC·7PF6 (0, 4+, 6+, 7+, and 8+), HC·7PF6 (0, 2+, 4+, 6+, 7+, and 8+), and AC·7PF6 (0, 1+, 2+, 4+, 6+, 7+, and 8+), respectively. These unique [2]catenanes present a promising prototype for the fabrication of high-density data memories.

Publisher URL: http://dx.doi.org/10.1021/jacs.7b06857

DOI: 10.1021/jacs.7b06857

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