C O M M U N I C A T I O N S
Scheme 2. Graphical Representation Depicting Synthesis of Linear
“Click” Polymer 7-H2n ·2nPF6, Decoordinated Polymer 8a, and
Extended Acylated Polymer 9a
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a Deprotonation of 7-H2n ·2nPF6 (Rg ) 14.8 nm) to generate 8 did not
induce lengthening (Rg ) 13.5 nm), likely due to poor solubility and π-π
slipped-stacking interactions, but acylated polymer 9 showed a 48% increase
in size (Rg ) 21.4 nm).
be placed under an external load, readily inducing a lengthening of
the dimeric units. To mimic the effect of such a force and demonstrate
the extension ability of the DCD polymer, we employed acylation of
7-H2n ·2nPF6 to increase the steric bulk of the amines and force slippage
of the crown-type rings to give extended analogue 9 (Scheme 2).
MALLS showed 9 had an Rg of 21.4 nm, which indicated a size
increase of 48% compared to the contracted analogue. This value
closely matched the anticipated dimer extension percent and showed
that the polymer dimensions were dramatically impacted by the
switchable DCD units.
In conclusion, utilization of olefin metathesis has enabled the
synthesis of a [c2]daisy-chain dimer with the ammonium binding site
near the cap of the dimer. A deprotonated DCD possessing such a
structural attribute will more forcefully seek to restore coordinating
interactions upon reprotonation, enhancing its utility as a synthetic
molecular actuator. Dimer functionalization facilitated incorporation
into linear polymers, with a 48% size increase of an unbound, extended
analogue of the polymer demonstrating slippage of the dimer units.
Ongoing work is directed at further materials studies, with particular
focus on ascertaining the effects of the switchable dimer linkages when
the polymer is under mechanical load. Additionally, we are exploring
the synthesis of macroscopic networks containing the DCD units and
analyzing the correlation between molecular-scale extension-
contraction manipulations and resulting macroscale changes.
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Acknowledgment. We thank Dr. Erin Guidry and Prof. J. Fraser
Stoddart for useful discussions. The ruthenium metathesis catalyst
was received as a generous gift from Materia, Inc. We thank
Lawrence M. Henling for X-ray crystallographic data. The work
was supported by the Office of Naval Research through its MURI
program and the NSF (NSF CHE-0809418).
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(15) See the Supporting Information for complete details.
(16) Crystallographic data have been deposited at the CCDC: deposition number
734570. See Supporting Information for complete details.
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R. H. Angew. Chem., Int. Ed. 1997, 36, 248–251.
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Tseng, H.-R.; Jeppesen, J. O.; Huang, T. J.; Brough, B.; Baller, M.;
Magonov, S.; Solares, S. D.; Goddard, W. A.; Ho, C.-M.; Stoddart, J. F.
J. Am. Chem. Soc. 2005, 127, 9745–97.
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2182–2184.
Supporting Information Available: Complete experimental pro-
cedures as well as full characterization. This material is available free
(20) All GPC/MALLS measurements were performed using 0.2 M LiBr in DMF
in an effort to minimize the effects of charge on the polymers in solution
and prevent aggregation of charged species on the columns.
References
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