Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 134, Issue 28, Pages 11709-11720Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja3037355
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Funding
- U.S. by the National Science Foundation [CHE-0924620]
- Engineering and Physical Sciences Research Council [EP/H003517/1]
- WCU Program [NRFR-31-2008-000-10055-0]
- Ministry of Education, Science and Technology, Korea
- NSF Graduate Research Fellowship
- National Science Foundation [CHE-1012378]
- ANSER Center
- Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0001059]
- Engineering and Physical Sciences Research Council [EP/H003517/1] Funding Source: researchfish
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [0924620] Funding Source: National Science Foundation
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [1012378] Funding Source: National Science Foundation
- EPSRC [EP/H003517/1] Funding Source: UKRI
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Two redox-active bistable [2]catenanes composed of macrocyclic polyethers of different sizes incorporating both electron-rich 1,5-dioxynaphthalene (DNP) and electron-deficient 4,4'-bipyridinium (BIPY2+) units, interlocked mechanically with the tetracationic cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(4+)), were obtained by donor acceptor template-directed syntheses in a threading-followed-by-cyclization protocol employing Cu(I)-catalyzed azide-alkyne 1,3-dipolar cycloadditions in the final mechanical-bond forming steps. These bistable [2]catenanes exemplify a design strategy for achieving redox-active switching between two translational isomers, which are driven (i) by donor-acceptor interactions between the CBPQT(4+) ring and DNP, or (ii) radical-radical interactions between CBPQT(2)((center dot+)) and BIPY center dot+, respectively. The switching processes, as well as the nature of the donor-acceptor interactions in the ground states and i:he radical-radical interactions in the reduced states, were investigated by single-crystal X-ray crystallography, dynamic H-1 NMR spectroscopy, cyclic voltammetry, UV/vis spectroelectrochemistry, and electron paramagnetic resonance (EPR) spectroscopy. The crystal structure of one of the [2]catenanes in its trisradical tricationic redox state provides direct evidence for the radical radical interactions which drive the switching processes for these types of mechanically interlocked molecules (MIMs). Variable-temperature H-1 NMR spectroscopy reveals a degenerate rotational motion of the BIPY2+ units in the CBPQT(4+) ring for both of the two [2]catenanes, that is governed by a free energy barrier of 14.4 kcal mol(-1) for the larger catenane and 17.0 kcal mol(-1) for the smaller one. Cyclic voltammetry provides evidence for the reversibility of the switching processes which occurs following a three-electron reduction of the three BIPY2+ units to their radical cationic forms. UV/vis spectroscopy confirms that the processes driving the switching are (i) of the donor-acceptor type, by the observation of a 530 nm charge-transfer band in the ground state, and (ii) of the radical-radical ilk in the switched state as indicated by an intense visible absorption (ca. 530 nm) and near-infrared (ca. 1100 nm) bands. EPR spectroscopic data reveal that, in the switched state, the interacting BIPY center dot+ radical cations are in a fast exchange regime. In general, the findings lay the foundations for future investigations where this radical-radical recognition motif is harnessed in bistable redox-active MIMs in order to achieve close to homogeneous populations of co-conformations in both the ground and switched states.
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