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Published September 13, 2017 | Supplemental Material
Journal Article Open

Mechanical Bond-Protected Air-Stable Radicals


Radical templation centered around a heterotrisradical tricationic inclusion complex DB^(•+)⊂DAPQT^(2(•+)), assembled from an equimolar mixture of a disubstituted 4,4′-bipyridinium radical cation (DB^(•+)) and an asymmetric cyclophane bisradical dication (DAPQT^(2(•+))), affords a symmetric [2]catenane (SC·7PF_6) and an asymmetric [2]catenane (AC·7PF_6) 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 (BIPY^(2+)) units forming a mixed-valence (BIPY_2)^(•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 BIPY^(2+) 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 (DAP^(2+)) units, respectively, a consecutive series of five, six, and seven redox states can be accessed in the resulting SC·7PF_6 (0, 4+, 6+, 7+, and 8+), HC·7PF_6 (0, 2+, 4+, 6+, 7+, and 8+), and AC·7PF_6 (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.

Additional Information

© 2017 American Chemical Society. Received: July 5, 2017; Published: August 14, 2017. This research is part of the Joint Center of Excellence in Integrated Nano-Systems (JCIN) at King Abdulaziz City for Science and Technology (KACST) and Northwestern University (NU). The authors thank both KACST and NU for their continued support of this research. The computational studies at Caltech were supported by NSF EFRI-1332411 (ODISSEI). This work was also supported by National Science Foundation grant no. CHE-1565925 (M.R.W.) The authors declare no competing financial interest.

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August 19, 2023
October 17, 2023