Functionally rigid and degenerate molecular shuttles

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Functionally rigid and degenerate molecular shuttles

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dc.contributor.author Yoon, Il.
dc.contributor.author Benítez, Diego
dc.contributor.author Zhao, Yanli
dc.contributor.author Miljanić, Ognjen Š.
dc.contributor.author Kim, Soo Young
dc.contributor.author Tkatchouk, Ekaterina
dc.contributor.author Leung, Ken C. F.
dc.contributor.author Khan, Saeed I.
dc.contributor.author Goddard III, William A.
dc.contributor.author Stoddart, J. Fraser
dc.date.accessioned 2011-07-29T03:04:28Z
dc.date.available 2011-07-29T03:04:28Z
dc.date.copyright 2009
dc.date.issued 2011-07-29
dc.identifier.citation Yoon, II, Benítez, D., Zhao, Y. L., Miljanić, O. Š., Kim, S. Y., Tkatchouk, E., et al. (2009). Functionally Rigid and Degenerate Molecular Shuttles. Chemistry - a European Journal, 15, 1115-1122.
dc.identifier.issn 1521-3765
dc.identifier.uri http://hdl.handle.net/10220/6949
dc.description.abstract The preparation and dynamic behavior of two functionally rigid and degenerate [2]rotaxanes (1⋅4 PF6 and 2⋅4 PF6) in which a π-electron deficient tetracationic cyclophane, cyclobis(paraquat-p-phenylene) (CBPQT4+) ring, shuttles back and forth between two π-electron-rich naphthalene (NP) stations by making the passage along an ethynyl-phenylene-(PH)-ethynyl or butadiyne rod, are described. The [2]rotaxanes were synthesized by using the clipping approach to template-directed synthesis, and were characterized by NMR spectroscopic and mass spectrometric analyses. 1H NMR spectra of both [2]rotaxanes show evidence for the formation of mechanically interlocked structures, resulting in the upfield shifts of the resonances for key protons on the dumbbell-shaped components. In particular, the signals for the peri protons on the NP units in the dumbbell-shaped components experienced significant upfield shifts at low temperatures, just as has been observed in the flexible [2]rotaxanes. Interestingly, the resonances for the same protons did not exhibit a significant upfield shift at 298 K, but rather only a modest shift. This phenomenon arises from the much reduced binding of the ethynyl-NP unit compared to the 1,5-dioxy-NP unit. This effect, in turn, increases the shuttling rate when compared to the 1,5-dioxy-NP-based rotaxane systems investigated previously. The kinetic and thermodynamic data of the shuttling behavior of the CBPQT4+ ring between the NP units were obtained by variable-temperature NMR spectroscopy and using the coalescence method to calculate the free energies of activation (ΔGc≠) of 9.6 and 10.3 kcal mol−1 for 1⋅4 PF6 and 2⋅4 PF6, respectively, probed by using the rotaxane's α-bipyridinium protons.
dc.format.extent 8 p.
dc.language.iso en
dc.relation.ispartofseries Chemistry - a European journal
dc.rights © 2009 Wiley-VCH Verlag.
dc.subject DRNTU::Science::Chemistry::Organic chemistry.
dc.title Functionally rigid and degenerate molecular shuttles
dc.type Journal Article
dc.contributor.school School of Physical and Mathematical Sciences
dc.identifier.doi http://dx.doi.org/10.1002/chem.200802096
dc.description.version Accepted version
dc.identifier.rims 159745

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