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 bis-alkynylplatinum(II) terpyridine tweezer-alkynylgold(III) diphenylpyridine guest is shown to maintain the specific complexation in the presence of a B21C7-secondary ammonium salt recognition motif, which facilitates the formation of supramolecular hyperbranched polymers via the "tweezering directed self-assembly" strategy.

Molecular tweezer/guest recognition has emerged as a novel motif for the construction of supramolecular polymers. However, the overwhelming majority of ADA- or DAD-type (D = donor, A = acceptor) molecular tweezer/guest recognition systems suffer from relatively low binding affinities and inconspicuous variations toward external stimuli. To address this issue, herein a novel heterodimeric DADA-type complex has been designed and constructed. By engineering of donor–acceptor and hydrogen-bonding interactions, it demonstrates 1000 times enhancement for the complexation strength (K a = 2.23 × 106 M–1) than the ADA-type counterpart. Moreover, by modulating the intermolecular hydrogen bonds involved in the system, its binding affinity exhibits significantly large variations toward external stimuli (∼102–103-fold change for K a). The robust yet adaptive heterodimeric complex is employed as a tecton for the fabrication of high-molecular-weight donor–acceptor-type supramolecular polymers, demonstrating the efficiency and versatility to develop self-assembled materials via rational engineering of fundamental noncovalent recognition motifs.

Mechanically linked poly[2]rotaxanes have been successfully constructed via the hierarchical self-assembly strategy. The integration of two noninterfering noncovalent recognition motifs facilitates chain extension of the B21C7-based [2]rotaxane monomer, demonstrating the capabilities to form self-standing films with preferable transparency and softness. P olyrotaxanes have attracted increasing attention due to their unique topological architectures and fascinating properties. 1 Traditionally, polyrotaxanes are fabricated via encircling an already existing polymer with a variety of macrocycles (Scheme 1a). 2 As compared with such mainchain poly[n]rotaxanes, mechanically linked polyrotaxanes, representing the embedment of mechanical bonds as integral parts of the polymer backbone, impart unusual rotational and elongational mobility to the polymeric chain and thereby display unique rheological behaviors. 3 In this respect, poly[c2]-daisy chains (Scheme 1b), which have been elegantly developed by Stoddart and Giuseppone et al., realize the conversion from nanoscale mechanical movement to macroscopic muscle-like function. 4 However, the [c2]daisy chain involved in the structures commonly suffers from tedious preparation and low reaction yield. Additionally, high structural symmetry of the [c2]daisy chain restricts the formation of advanced supramolecular architectures. To solve this issue, an alternative choice is to utilize [2]rotaxane as the basic building block, which is more easily available than the [c2]daisy chain counterpart. Remarkably, different functional groups could be introduced asymmetrically on the axle and wheel sites of the [2]rotaxane scaffold, facilitating the subsequent polymerization steps. 5 For example, Takata et al. have demonstrated the efficient fabrication of linear poly[2]rotaxanes with the utilization of Sonogashira polycondensation reaction. 5aBesides the traditional covalent polymerization methodology, mechanically linked polyrotaxanes could also be achieved via the noncovalent self-assembly strategy. It is worthy of note that such a hierarchical self-assembling protocol could not only inherit the intrinsic viscoelastic properties of the conventional polyrotaxanes, but also possess some novel behaviors. For example, the dynamic features of the implemented noncovalent recognition motifs significantly influence the physical properties of the mechanically linked polyrotaxanes, benefiting for exploring their adaptivity toward external stimuli. 6 Furthermore, various functional elements could be incorporated in a modular way, thus considerably enriching the complexity for the resulting supramolecular assemblies with integrated functionality. 7 In this manuscript, we sought to decorate the [2]rotaxane scaffold with two different supramolecular recognition groups, and furthermore realize the formation of mechanically linked poly[2]rotaxanes via the hierarchical self-assembly strategy. Specifically, the [2]rotaxane 2 (Scheme 1c) is first prepared based on the benzo-21-crown-7 (B21C7)/secondary a...