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|Title:||Functionally rigid and degenerate molecular shuttles||Authors:||Stoddart, J. Fraser
Miljanić, Ognjen Š.
Leung, Ken C. F.
Khan, Saeed I.
Goddard III, William A.
Kim, Soo Young
|Keywords:||DRNTU::Science::Chemistry::Organic chemistry||Issue Date:||2009||Source:||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.||Series/Report no.:||Chemistry - a European journal||Abstract:||The preparation and dynamic behavior of two functionally rigid and degenerate 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 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 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 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.||URI:||https://hdl.handle.net/10356/92127
|ISSN:||1521-3765||DOI:||10.1002/chem.200802096||Rights:||© 2009 Wiley-VCH Verlag.||Fulltext Permission:||open||Fulltext Availability:||With Fulltext|
|Appears in Collections:||SPMS Journal Articles|
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