Hydrogen Bonding Modules for Use in Supramolecular Polymers

Supramolecular organic frameworks: engineering periodicity in water through host-guest chemistry

The development of homogeneous, water-soluble periodic self-assembled structures comprise repeating units that produce porosity in two-dimensional (2D) or three-dimensional (3D) spaces has become a topic of growing interest in the field of supramolecular chemistry. Such novel self-assembled entities, known as supramolecular organic frameworks (SOFs), are the result of programmed host-guest interactions, which allows for the thermodynamically controlled generation of monolayer sheets or a diamondoid architecture with regular internal cavities or pores under mild conditions. This feature article aims at propagating the conceptually novel SOFs as a new entry into conventional supramolecular polymers. In the first section, we will describe the background of porous solid frameworks and supramolecular polymers. We then introduce the self-assembling behaviour of several multitopic flexible molecules, which is closely related to the design of periodic SOFs from rigid multitopic building blocks. This is followed by a brief discussion of cucurbit[8]uril (CB[8])-encapsulation-enhanced aromatic stacking in water. The three-component host-guest pattern based on this stacking motif has been utilized to drive the formation of most of the new SOFs. In the following two sections, we will highlight the main advances in the construction of 2D and 3D SOFs and the related functional aspects. Finally, we will offer our opinions on future directions for both structures and functions. We hope that this article will trigger the interest of researchers in the field of chemistry, physics, biology and materials science, which should help accelerate the applications of this new family of soft self-assembled organic frameworks.

Surprising impact of remote groups on the folding--unfolding and dimer-chain equilibria of bifunctional H-bonding unimers

Oligoamide 1, consisting of two H-bonding units linked by a trimethylene linker, was previously found to form a very stable, folded dimer. In this work, replacing the side chains and end groups of 1 led to derivatives that show the surprising impact of end groups on the folding and dimer-chain equilibria of the resultant molecules.

An asymmetric A-B-A' metallo-supramolecular triblock copolymer linked by Ni(2+)-bis-terpyridine complexes at one junction

A metallo-supramolecular triblock copolymer polystyrene-b-polyisoprene-[Ni(2+)]-polystyrene (SI-[Ni(2+)]-S') has been efficiently prepared using a one-pot, two-step procedure, where the blocks are held by bis-terpyridine complexes at the junction of SI-S'. This specific metallo-supramolecular chemistry is demonstrated to be a robust approach to potentially broaden the diversity of block copolymers. The location of the metal-ligand complexes has a profound influence on the phase separation of the triblock copolymer in the bulk, which results in a distinctive phase segregation between the end blocks and leads to an unexpected asymmetry of the triblock copolymer. The metal-ligand complexes are found to be preferentially located on the adjacent spherical domain and form a core-shell structure. The resulting multiphase material exhibits distinct elastomeric properties with significant toughness and creep recovery behavior. This type of triblock copolymer is anticipated to be a novel class of hybrid thermo-plastic elastomeric material with wide tunability and functionality.

Hydrogen-Bonded Macrocyclic Supramolecular Systems in Solution and on Surfaces

Cyclization into closed assemblies is the most recurrent approach to realize the noncovalent synthesis of discrete, well-defined nanostructures. This review article particularly focuses on the noncovalent synthesis of monocyclic hydrogen-bonded systems that are self-assembled from a single molecule with two binding-sites. Taking advantage of intramolecular binding events, which are favored with respect to intermolecular binding in solution, can afford quantitative amounts of a given supramolecular species under thermodynamic control. The size of the assembly depends on geometric issues such as the monomer structure and the directionality of the binding interaction, whereas the fidelity achieved relies largely on structural preorganization, low degrees of conformational flexibility, and templating effects. Here, we discuss several examples described in the literature in which cycles of different sizes, from dimers to hexamers, are studied by diverse solution or surface characterization techniques.

Polymeric (anion-π)n interactions in crystals of 2-(2,4,6-trioxo-[1,3,5]triazinan-1-yl)ethylammonium iodide

2-(2,4,6-Trioxo-[1,3,5]triazinan-1-yl)ethyammonium halides

Controllable Supramolecular Polymerization through Host-Guest Interaction and Photochemistry

A new method for controllable supramolecular polymerization based on ABBA type monomer and cucurbit[8]uril monomer through host-guest interaction and photochemistry is reported. The molecular weight and polydispersity of supramolecular polymers can be well controlled by tuning the molar ratio of these host and guest monomers or by tuning the isomer ratio of azobenzene groups in the guest monomers upon the competitive irradiation of lights. This research provides a general methodology for the control of supramolecular polymerization and the structure of supramolecular polymers.

Theoretical design and simulation of supramolecular polymer unit based on multiple hydrogen bonds

The heterocyclic urea of deazapterin (DeAPa) and its protomeric conformers (b, c) with different substituents are selected as the building block for a series of dimers in different configurations. The stabilities of all dimers in various conditions have been investigated by density functional theory. Homodimer of b has more stability than other dimers. Topological analyses certify the coexistence of intermolecular with intramolecular H-bonds. Investigations into frequency demonstrate that all H-bonds show an evident red shift in their stretching vibrational frequencies. Electron donating substituents can provide favorable free energies of the dimer. Solvent effect computations suggest that the dimerization can be favored in weakly polar solvents, such as toluene and chloroform. UV-visible spectra exhibit obvious difference of maximum absorption wavelengths between monomers and dimers, thus may have potential applications for identifying intermolecular H-bonds and calculating association constant of DeAP equilibrium systems in experiments.

High-efficiency self-healing materials based on supramolecular polymer networks

A new urea–cytosine-functionalized supramolecular polymer can be rapidly reshaped and reprocessed under mild conditions via rearrangement of the hydrogen bonding network.

The construction of supramolecular polymers through anion bridging: from frustrated hydrogen-bonding networks to well-ordered linear arrays

The construction of supramolecular polymers has been realized by converting random hydrogen-bonding networks into well-ordered linear hydrogen-bonding arrays through an anion-bridging strategy.

Synthesis and complementary self-association of novel lipophilic π-conjugated nucleoside oligomers

A series of lipophilic nucleosides comprising natural and non-natural bases that are π-conjugated to a short oligophenylene–ethynylene fragment has been synthesized and their respective association constants measured.

Topology, assembly, and electronics: three pillars for designing supramolecular polymers with emergent optoelectronic behavior

Supramolecular polymers for solar energy harvesting can be created by considering carefully the relationship between topology, assembly, and photophysics.