The bottom-up self-assembly of donor-acceptor (D-A) units has received tremendous attention in recent years. Charge-transfer interactions, which are inherently embedded in D-A pairs, have suffered from some disadvantages such as erratic arrangements and weak binding affinity, thus hampering the precise arrangement of D-A units into long-range-ordered supramolecular polymers. To address this issue, a feasible protocol is to incorporate D-A units into molecular tweezers/guest recognition motifs, which concurrently feature high complexation directionality, strong binding affinity and stimuli-responsiveness. In this tutorial review, we have summarized the recent advances on the tweezering directed formation of D-A-type supramolecular polymers, with particular emphasis on the design principles of monomers and macroscopic behaviors of supramolecular polymers, together with future challenges in this research field.
Supramolecular polymers are constructed based on the novel bis[alkynylplatinum(II)] terpyridine molecular tweezer/pyrene recognition motif. Successive addition of anthracene as the diene and cyano-functionalized dienophile triggers the reversible supramolecular polymerization process, thus advancing the concept of utilizing Diels-Alder chemistry to access stimuli-responsive materials in compartmentalized systems.
A facile route is demonstrated to realize the supramolecular
cross-linked
networks based on the benzo-21-crown-7/secondary ammonium salt recognition
motif, which involves the interchain host–guest interactions
between the secondary ammonium salt-functionalized polystyrene and
the complementary homoditopic benzo-21-crown-7 cross-linker. Reversible
addition–fragmentation chain transfer polymerization is utilized
to prepare the well-defined secondary ammonium salt-functionalized
graft polymer. As determined by 1H NMR and GPC, the molecular
weight M
n is 13.3 kDa with polydispersity
value of 1.10, suggesting that 15.9 repeating units of secondary ammonium
salt moieties exist in a single polymer chain. The properties of the
resulting supramolecular cross-linked networks are characterized in
solution by means of 1H NMR titration and viscosity measurements,
which indicate the growth of entangled polymer chains after the efficient
host–guest complexation. At high concentrations of acetonitrile,
the interpenetrating three-dimensional networks could entrap large
amounts of solvent and thereby lead to the formation of supramolecular
gels, which exhibit multistimuli (thermo-, pH-, and chemo-) responsive
sol–gel transition behaviors. Such a strategy will benefit
for the further development of intelligent supramolecular materials
with desired functionalities.
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