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The above dynamic materials maintain their constitutions during their metal binding.
When the foldamer chain contains reversible linkages such as imine bonds, a constitu-
tional dynamic polymer library (CDPL) is created which may respond to external stimuli
[94]. Lehn and coworkers combined two amines (
29
and
30
) and two aldehydes (
31
and
32
) to form four possible imine-linked polymers (
33
-
36
). Among the four polymers, only
35
could be stabilized by the CT interactions and the complexation between the oligoether
tethers and alkali metal ions.
When an equimolar mixture of preformed
33
and
34
was allowed to equilibrate at room
temperature, the
33
/
34
/
35
/
36
ratio was found to be 22 : 22 : 28 : 28 by
1
H NMR spectros-
copy, suggesting that there was no preference for any structure under the experimental
conditions. In the presence of NaOTf and LiOTf, the polymeric mixture shifted toward
35
.
1
H NMR spectroscopy showed that the
33
/
34
/
35
/
36
ratio at equilibrium was
8 : 8 : 42 : 42 and 7 : 7 : 43 : 43, respectively, after the addition of the metal ions. The
increased CT complexation also induced a color change of the solution, allowing visual
detection of the changes [94].
Dynamic materials from metallofoldamers are not limited to solution. Lee and
coworkers prepared a bipyridyl-Ag
รพ
complex whose conformation and self-assembly
depended on the counterion in the solid state [95]. With nitrate as the anion (A
),
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