Functionally rigid and degenerate molecular shuttles

DSpace/Manakin Repository


Search DR-NTU

Advanced Search Subject Search


My Account

Functionally rigid and degenerate molecular shuttles

Show full item record

Title: Functionally rigid and degenerate molecular shuttles
Author: Yoon, Il.; Benítez, Diego; Zhao, Yanli; Miljanić, Ognjen Š.; Kim, Soo Young; Tkatchouk, Ekaterina; Leung, Ken C. F.; Khan, Saeed I.; Goddard III, William A.; Stoddart, J. Fraser
Copyright year: 2009
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.
Subject: DRNTU::Science::Chemistry::Organic chemistry
Type: Journal Article
Series/ Journal Title: Chemistry - a European journal
School: School of Physical and Mathematical Sciences
Rights: © 2009 Wiley-VCH Verlag.
Version: Accepted version

Files in this item

Files Size Format View
2009-1115.pdf 775.0Kb PDF View/Open

DOI Query

- Get published version (via Digital Object Identifier)

This item appears in the following Collection(s)

Show full item record


Total views

All Items Views
Functionally rigid and degenerate molecular shuttles 414

Total downloads

All Bitstreams Views
2009-1115.pdf 198

Top country downloads

Country Code Views
United States of America 71
China 31
France 18
Singapore 15
Taiwan 11

Top city downloads

city Views
Mountain View 34
Singapore 15
Scranton 7
Taichung 5
Taipei 5