The Construction Of Functional Supramolecular Polymeric Materials Via Hierarchical Orthogonal Self-Assembly

The development of supramolecular chemistry makes it possible to utilize low-molecular-weight building blocks to obtain molecular aggregates with complicated architectures and unique functions via noncovalent interactions. Supramolecular materials, dynamic materials by nature, are defined as materials whose components are bridged via reversible noncovalent (or dynamic covalent) connections and undergo spontaneous and continuous assembly/disassembly processes under specific conditions. On account of the dynamic and reversible nature of noncovalent interactions, these noncovalent materials have the ability to adapt to their environment and possess a wide range of intriguing properties, such as degradability, shape-memory, and self-healing, etc. Hierarchical orthogonal self-assembly is a highly efficient and powerful methodology to construct complexed and functional supramolecular materials with facile syntheses. In this thesis, we reported the construction of functional supramolecular polymeric materials via hierarchical orthogonal self-assembly by elegant unification of multiple noncovalent interactions. The main content of the dissertation includes the following six parts:In the first part, we designed and synthesized a B21C7/dialkylammonium-based AB monomer, which can self-assemble into linear supramolecular polymers in chloroform. The flexible long alkyl chain of the monomer favors the formation and entanglement of the linear supramolecular polymer and the good association between B21C7and dialkylammonium salt moieties in chloroform leads to the high viscosity of the linear supramolecular polymer, which facilitates the formation of a stable jet when the supramolecular polymer solution is subjected to an electric field. Therefore, we successfully obtained supramolecular polymer nanofibers via electrospinning of a low-molecular-weight monomer for the first time.In the second part, we used the combination of a heteroditopic monomer with bridging ligand and the metallic cross-linker to orthogonally self-assemble into an extended supramolecular polymer network, resulting in the gelation. The cross-linked supramolecular polymer network gel shows pH-, thermo-, cation-, and metallo-induced reversible gel-sol transitions. SEM characterization of the resultant gel demonstrates that the supramolecular gel pore size can be modulated by the amount of cross-linker added to the system, which facilitates its application as a smart material. More importantly, this supramolecular polymeric material can be molded into shape-persistent, free-standing objects and rebound after a free-falling process, which are all due to the dynamically reversible complexation between B21C7and dialkylammonium salt moieties and the good mechanical properties of the cross-linked supramolecular polymer network.In the third part, two orthogonal processes are exploited:coordination-driven self-assembly and hydrogen bonding. The former relies on the predictable formation of metal-ligand bonds wherein the directionalities of the rigid precursors used determines the structural outcome. The latter uses2-ureido-4-pyrimidinone interfaces which are structurally robust by virtue of the quadruple hydrogen bonding that can occur between subunits. By combining these two processes into a single system it is possible to generate hierarchical materials that preserve the attractive tunability associated with discrete supramolecular coordination complexes. For instance, the synthesis of a one-dimensional chain comprising linked metalla-rhomboids is readily adapted to a two-dimensional cross-linked hexagonal network by simply selecting a different metal acceptor precursor as an assembly component. The specific interactions between subunits, in this case platinum(II)-pyridyl bonds and the quadruple H-bonding of ureidopyrimidinone, are unchanged, establishing a novel strategy to obtain supramolecular polymers with marked topological differences with minimal synthetic redesign. The solvent swelling formation of gels observed for the hexagonal networks lent themselves to the formation of long, macroscopic fibers which possessed enough strength and flexibility to permit the construction of stable knots. The robustness of these fibers is consistent with heightened cross-link densities which occur due to the reversibility of the metal-ligand and hydrogen bonding that form the material. Deformations that can permanently sever polymer strands in other materials can reform in these gel-like soft matters, restoring intermolecular cross-linking and allowing the fibers to adapt to stresses.In the fourth part, we described the efficient preparation of rhomboidal metallacycles that self-assemble upon mixing a donor decorated with2-ureido-4-pyrimidinone (UPy) with acceptors containing pendant [G1]-[G3] dendrons. Once formed, these rhomboids subsequently polymerize into dendronized organoplatinum(Ⅱ) metallacyclic polymers (DOMPs) through H-bonding UPy interfaces, which possess the structural features of conventional dendronized polymers as well as the dynamic reversibility of supramolecular polymers. Preservation of both properties in a single material is achieved by exploiting hierarchical self-assembly, namely the unification of coordination-driven self-assembly with H-bonding, which provides facile routes to dendronized metallacycles and subsequent high-ordering. The supramolecular polymerization defined here represents a novel method to deliver architecturally complex and ordered polymeric materials with adaptive properties.In the fifth part, we unified the spontaneous formation of metal-ligand bonds with the host/guest chemistry of crown ethers to deliver a3D supramolecular polymer network (SPN). Specifically, we have prepared a highly directional dipyridyl donor decorated with a benzo-21-crown-7moiety that undergoes coordination-driven self-assembly with a complementary organoplatinum acceptor to furnish hexagonal metallacycles. These hexagons subsequently polymerize into a supramolecular network upon the addition of a bisammonium salt due to the formation of [2]pseudorotaxane linkages between the crown ether and ammonium moieties. At high concentrations, the resulting3D SPN becomes a gel comprising many cross-linked metallohexagons. Notably, thermo-and cation-induced gel-sol transitions are found to be completely reversible, reflecting the dynamic and tunable nature of such supramolecular materials. As such, these results demonstrate the structural complexity that can be obtained when carefully controlling multiple interactions in a hierarchical fashion, in this case coordination and host/guest chemistry, and the interesting dynamic properties associated with the materials thus obtained.In the last part, metallacyclic cores provide a scaffold upon which pendant functionalities can be organized to direct the formation of dimensionally controllable nanostructures. Due to the modularity of coordination-driven self-assembly, the properties of a given supramolecular core can be readily tuned with a significant effect on the resulting nanostructured material. We reported the efficient preparation of two amphiphilic rhomboids that can subsequently order into OD micelles,1D nanofibers, or2D nanoribbons. This structural diversity is enforced by three parameters:the nature of the hydrophilic moieties decorating the parent rhomboids, the concentration of precursors during self-assembly and the reaction duration. These nanoscopic constructs further interact to generate metallohydrogels at high concentrations, driven by intermolecular hydrophobic and π-π interactions, demonstrating the utility of coordination-driven self-assembly as a first-order structural-element for the hierarchical design of functional soft materials.