Abstract
A homologous series of [2]rotaxanes, in which cyclobis(paraquat-p- phenylene) (CBPQT4+) 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•+ 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. 1H 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•+ 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.
| Original language | English |
|---|---|
| Pages (from-to) | 456-467 |
| Number of pages | 12 |
| Journal | Journal of the American Chemical Society |
| Volume | 135 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - Jan 9 2013 |
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ASJC Scopus subject areas
- Chemistry(all)
- Catalysis
- Biochemistry
- Colloid and Surface Chemistry
Cite this
Mechanical bond-induced radical stabilization. / Li, Hao; Zhu, Zhixue; Fahrenbach, Albert C.; Savoie, Brett M.; Ke, Chenfeng; Barnes, Jonathan C.; Lei, Juying; Zhao, Yan Li; Lilley, Laura M.; Marks, Tobin J; Ratner, Mark A; Stoddart, J. Fraser.
In: Journal of the American Chemical Society, Vol. 135, No. 1, 09.01.2013, p. 456-467.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Mechanical bond-induced radical stabilization
AU - Li, Hao
AU - Zhu, Zhixue
AU - Fahrenbach, Albert C.
AU - Savoie, Brett M.
AU - Ke, Chenfeng
AU - Barnes, Jonathan C.
AU - Lei, Juying
AU - Zhao, Yan Li
AU - Lilley, Laura M.
AU - Marks, Tobin J
AU - Ratner, Mark A
AU - Stoddart, J. Fraser
PY - 2013/1/9
Y1 - 2013/1/9
N2 - A homologous series of [2]rotaxanes, in which cyclobis(paraquat-p- phenylene) (CBPQT4+) 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•+ 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. 1H 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•+ 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.
AB - A homologous series of [2]rotaxanes, in which cyclobis(paraquat-p- phenylene) (CBPQT4+) 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•+ 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. 1H 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•+ 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.
UR - http://www.scopus.com/inward/record.url?scp=84872104877&partnerID=8YFLogxK
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U2 - 10.1021/ja310060n
DO - 10.1021/ja310060n
M3 - Article
C2 - 23163704
AN - SCOPUS:84872104877
VL - 135
SP - 456
EP - 467
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 1
ER -