期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 135, 期 1, 页码 456-467出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja310060n
关键词
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资金
- Non-Equilibrium Energy Center (NERC), an Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences [DE-SC0000989]
- NSF MRSEC program at the Materials Research Center of Northwestern University [DMR-1121262]
- NSF Graduate Research Fellowship
- DoD National Defense Science and Engineering Graduate Fellowship
- Ryan Fellowship
- Royal Society in the UK
- Direct For Mathematical & Physical Scien
- Division Of Materials Research [1121262] Funding Source: National Science Foundation
A homologous series of [2]rotaxanes, in which cyclobis(paraquat-p-phenylene) (CBPQT(4+)) serves as the ring component, while the dumbbell components all contain single 4,4'-bipyridinium (BIPY2+) units centrally located in the midst of oligomethylene chains of varying lengths, have been synthesized by taking advantage of radical templation and copper-free azide-alkyne 1,3-dipolar cycloadditions in the formation of their stoppers. Cyclic voltammetry, UV/vis spectroscopy, and mass spectrometry reveal that the BIPY center dot+ radical cations in this series of [2]rotaxanes are stabilized against oxidation, both electrochemically and by atmospheric oxygen. The enforced proximity between the BIPY2+ units in the ring and dumbbell components gives rise to enhanced Coulombic repulsion, destabilizing the ground-state co-conformations of the fully oxidized forms of these [2]rotaxanes. The smallest [2]rotaxane, with only three methylene groups on each side of its dumbbell component, is found to exist under ambient conditions in a monoradical state, a situation which does not persist in acetonitrile solution, at least in the case of its longer analogues. H-1 NMR spectroscopy reveals that the activation energy barriers to the shuttling of the CBPQT(4+) rings over the BIPY2+ units in the dumbbells increase linearly with increasing oligomethylene chain lengths across the series of [2] rotaxanes. These findings provide a new way of producing highly stabilized BIPY center dot+ radical cations and open up more opportunities to use stable organic radicals as building blocks for the construction of paramagnetic materials and conductive molecular electronic devices.
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