Supramolecular Polymers Driven By Electron Donor-Acceptor Interactions

Supramolecular polymers represent a novel class of macromolecules, in which self-assembly serves as a powerful tool and holds the monomeric units together via reversible noncovalent bonds. As a result, a variety of intriguing behaviors such as stimuli-responsive and self-healing properties assign for the resulting supramolecular polymeric assemblies. For the efficient construction of the desired supramolecular polymers, the non-covalent driving forces should fulfill the basic requirements such as high complexation directionality, strong binding affinity and inherent responsiveness towards the specific external stimuli. Based on this consideration, currently hydrogen bonding, metal-ligand coordination and macrocyclic host-guest interactions have been widely utilized to drive the supramolecular polymerization process. This dissertation, consisting of five parts, focuses on the construction of novel supramolecular polymers based on the donor-acceptor charge-transfer interactions. Moreover, complex and multi-stimuli responsive supramolecular polymers via the concurrent embedment of multiple non-covalent interactions are also fabricated in an effective manner.In the first part, supramolecular polymer networks have been fabricated using a heterometallic coordination-driven self-assembly strategy. Specifically, the terpyridine ligands are attached on both sides of the homoditopic monomer. Upon addition of metal ions such as Fe2+, it is expected to form the linear supramolecular polymer. Subsequently, the1,2,3-triazole unit, embedded in the middle site of the monomer, allows for the efficient complexation with Pd2+, resulting in the formation of the desired supramolecular polymer networks. Moreover, triggered by a variety of competitive ligands such as PPh3or HEDTA, the supramolecular networks could be reversibly assembled/disassembled and thereby demonstrates dynamic properties. Notably, the addition sequence of the metal ions exerts crucial effects on the formation of ordered supramolecular polymeric assemblies.In the second part, we have successfully utilized "one-pot" self-assembly approach to from linear supramolecular polymers, via the combination of orthogonal B21C7/secondary ammonium salt and terpyridine/metal ions (Fe2+or Zn2+) recognition motifs. Based on1H NMR, DOSY, and viscosity measurements, it is evident that both of the orthogonal self-assembling motifs are of significant importance for the construction of the desired supramolecular polymers. Meanwhile, different metal ions (Fe2+or Zn2+) demonstrate significant effects on the size of the resulting assemblies. The resulting supramolecular polymers could be reversibly triggered by a variety of external stimuli such as temperature, potassium cation, and chelating ligands (HEDTA or cyclen).In the third part, with the introduce of "tweezering-directed self-assembly" strategy, linear supramolecular polymers smoothly form based on the novel bis[alkynylplatinum(Ⅱ)] terpyridine molecular tweezer/pyrene recognition motif. The head-to-tail supramolecular polymerization process conforms to a ring-chain equilibrium mechanism. Moreover, addition of the anthracene derivatives, which served as the chain stoppers, could result in the disassembly of the resulting supramolecular polymers. Subsequently, the introduction of bis(2-methoxyethyl) dicyanofumarate, which been proven to undergo Diels-Alder reactions with anthracene derivatives, could trigger the re-assembly processes. Hence, the novel supramolecular polymeric systems driven by donor-acceptor interactions could be regulated in a facile and controlled manner by successive addition of the anthracene derivatives and bis(2-methoxyethyl) dicyanofumarate.In the fourth part, we have investigated the compatibility of tweezer/guest recognition with other non-covalent recognition motifs. It is demonstrated that, for the bisalkynylplatinum(II) terpyridine tweezer-alkynylgold(III) diphenylpyridine recognition motif, although the binding strength is influenced by the microenvironment changes, highly specific complexation capability still maintains in the presence of the B21C7-based host-guest recognition motif. With the implementation of these two non-covalent recognition motifs, dynamic supramolecular hyperbranched polymers were successfully achieved. Therefore, the study expands the scope of the "tweezering directed self-assembly" strategy, benefiting for the further manipulation and application of such hierarchical supramolecular assemblies.Considering that the above tweezering system suffers from the relatively low binding affinity, which is detrimental for the achievement of an appreciable degree of polymerization for the resulting supramolecular polymers, in the last part we have sought to enhance the complexation stability via the elaborate manipulation of the non-covalent interactions involved in the molecular tweezer/guest recognition system. Hence, a novel type of tweezering system (DADA-type) has been developed, which demonstrates significantly reinforced complexation behavior (Ka=(2.23±0.27)×106M-1), primarily attributing to the effective combination of multivalent donor-acceptor and hydrogen-bonding interactions. Moreover, the novel recognition motif exhibits ultra-sensitive responseness towards HFIP solvent as well as pH value. On this basis, linear supramolecular polymers with relatively high degree of polymerization are fabricated via the self-assembly of the two homoditopic monomers derived from such DADA-type tweezering systems. Therefore, it represents an unprecedented example for the formation of reversible supramolecular polymers which are driven by the efficient arrangement of the donor and acceptor moieties in a multivalent and alternating manner.