Metallosupramolecular polymers: current status and future prospects

Improving Light-Responsive Efficiency of Type II Porous Liquid by Tailoring the Functionality of Host

Light-responsive porous liquids (LPLs) attract significant attention for their controllable gas uptake under light irradiation, while their preparation has remained a great challenge. Here we report the fabrication of type II LPLs with enhanced light-responsive efficiency by tailoring the host's functionality for the first time. The functionality of light-responsive metal-organic cage (MOC-RL, constructed from dicopper and responsive ligands) is modified by introducing the second long-chain alkyl ligand, producing MOC-RL-AL as a new host. A spatially hindered solvent based on polyethylene glycol, IL-NTf2, is designed and can dissolve MOC-RL-AL due to the suitable interaction, creating a type II LPL (PL-RL-AL). Under light irradiation, the variation in propylene adsorption for PL-RL-AL increases by 58.0 % compared to PL-RL. The enhanced light-responsive efficiency is caused by easier control in accessibility of internal cavities within MOCs and increased number of external cavities between MOCs and IL-NTf2. This makes PL-RL-AL the first LPL with the probability for propylene/propane separation.

Should I stay or should I flow? An exploration of phase-separated metallosupramolecular liquid crystal polymers

Dynamic liquid crystalline polymers (dLCPs) incorporate both liquid crystalline mesogens and dynamic bonds into a single polymeric material. These dual functionalities impart order-dependent thermo-responsive mechano-optical properties and enhanced reprocessability/programmability enabling their use as soft actuators, adaptive adhesives, and damping materials. While many previous works studying dynamic LCPs utilize dynamic covalent bonds, metallosupramolecular bonds provide a modular platform where a series of materials can be accessed from a single polymeric feedstock through the variation of the metal ion used. A series of dLCPs were prepared by the addition of metal salts to a telechelic 2,6-bisbenzimidazolylpyridine (Bip) ligand endcapped LCP to form metallosupramolecular liquid crystal polymers (MSLCPs). The resulting MSLCPs were found to phase separate into hard and soft phases which aids in their mechanical robustness. Variations of the metal salts used to access these materials allowed for control of the thermomechanical, viscoelastic, and adhesive properties with relaxations that can be tailored independently of the mesogenic transition. This work demonstrates that by accessing phase separation through the incorporation of metallosupramolecular moieties, highly processable yet robust MSLCP materials can be realized. This class of materials opens the door to LCPs with bulk flow behavior that can also be utilized as multi-level adhesives.

A multistimuli responsive and self-healing Zn(ii)-inosine supramolecular metal-organic gel: phase selective gelation and application as a light-responsive Schottky barrier diode

Utilization of naturally available biomolecules such as nucleosides with several coordination sites as organic counterparts for the synthesis of multifunctional self-assembled metal-organic gels is important, considering the time and efforts required for the design of organic ligands that can coordinate to metal ions, forming a gel. In the present work, inosine, a simple nucleoside has been utilized as a ligand for the generation of a supramolecular metallo-hydrogel through coordination with Zn2+ ions in the presence of NaOH. Several spectroscopic, microscopic and rheological investigations have been performed to characterize the formed gel. The obtained metallo-hydrogel is transparent, and the transparency can be tuned depending on the amount of NaOH used. The Zn-inosine metal-organic gel exhibits several functional properties such as self-healing, stimuli responsiveness, thixotropy, and injectability. Furthermore, the freeze-dried Zn-inosine xerogel exhibited selective gelation of water, which has been utilized to separate water from mixtures that include organic solvents (or oils) and water. The semiconducting characteristics of the Zn-inosine metallogel have been used for device fabrication based on the Schottky diode interface between a semiconductor and metal. The fabricated device was found to be photo-responsive in nature and exhibited better device parameters when illuminated with light. The present results are anticipated to lead to the development of newer soft materials constructed using simple biomolecules for environmental and electronic applications.

Supramolecular Polymers for Drug Delivery

Supramolecular polymers are constructed through highly reversible and directionally specific non-covalent interactions between monomer units. This unique feature enables supramolecular polymers to undergo controlled structural reconfiguration and functional transformation in response to external stimuli, imparting them with high environmental responsiveness and self-healing properties. In particular, supramolecular polymers exhibit several specific advantages compared to conventional polymers, such as inherent degradability, the ease of preparation and the incorporation of functional units, and smart responsiveness to various biological stimuli. These characters make supramolecular polymers promising candidates for intelligent drug delivery systems in complex biological environments. In this review, we comprehensively summarize the latest developments and representative achievements of supramolecular polymers in drug delivery fields, focusing primarily on the design and synthesis, the properties and functionalities, and the practical applications of supramolecular polymers in small molecule drug delivery, gene therapy, and protein delivery. Finally, we highlight future research directions, focusing on multifunctionality, adaptability, and personalized therapy. We focus on recent studies that address key challenges in the field, providing rational polymer design, important properties, functionality, and understanding delivery strategies. These developments are expected to advance supramolecular polymers as new platforms of intelligent drug delivery systems, offering innovative solutions for the treatment of complex diseases.

Electronic Structure Tunable Metallosupramolecular Polymers as Bifunctional Electrocatalysts for Rechargeable Zn-Air Battery

Metallosupramolecular polymers (MSPs) have shown great potential in the area of oxygen electrocatalysis due to their tunable electronic structure, and predictable coordination environment. Further exploration of structure-performance relationships of oxygen electrocatalysts is crucial for designing highly efficient catalysts. Herein, a strategy is proposed to prepare MSP-based bifunctional oxygen electrocatalysts with different oxygen electrocatalytic preferences (Co-AQ and Co-AN) by adjusting the electronic structure of organic linkers. The electronic effects of organic linkers significantly influence the adsorbate evolution mechanism. Co-AQ, with an electron-withdrawing linker, demonstrated superior OER activity among the two with an overpotential of 280 mV at 10 mA cm-2 and 340 mV at 50 mA cm-2. In contrast, Co-AN, with an electron-donating linker, exhibited outstanding ORR activity with a large limiting current density of 6.14 mA cm-2. Furthermore, the Co-AQ-based Zn-air battery showed a high power density (135 mW cm-2) and excellent cycling stability of 100 h. This work presents a novel approach for adjusting bifunctional oxygen electrocatalysis performance and further reveals the structure-performance relationships of oxygen electrocatalysts.

Photoregulated Supramolecular Polymerization through Halogen Bonding

Supramolecular polymers are able to change their structure, morphology and function in response to external stimuli. However, controlling the independence of stimuli-responses in these systems is challenging. Herein, we exploit halogen bonding (XB) as a reversible network element to regulate the photoresponsive and adaptive behavior of supramolecular polymers. To this end, we have designed a two-component system comprising an amphiphilic XB acceptor with the ability to self-assemble in aqueous media (OPE-Py) and a molecule with a dual photoresponsive and XB donor function [(E)-Azo-I]. OPE-Py self-assembles in aqueous media into supramolecular polymers, which transform into nanoparticle assemblies upon co-assembly with (E)-Azo-I. Interestingly, a third type of assembly (2D sheets) is obtained if OPE-Py is treated with (E)-Azo-I and exposed to photoirradiation. At ambient conditions, both nanoparticles and 2D sheets remain invariant over time. However, heating dissociates the XB interactions present in both assemblies, resulting in their transformation to the original fiber-like morphology of OPE-Py. Thus, breaking the communication between self-assembly and the stimuli-responses upon heating restores the original state of the system, drawing parallels to feedback loops in programming language. This work broadens the still limited scope of XB in solution assemblies and paves the way for multifunctional adaptive supramolecular systems.

Spatiotemporal generation of alternating disparate pH domains via audible sound controlled opposing enzymatic reactions

Intracellular spatiotemporal chemical heterogeneities with controlled properties are essential for life. However, creating these heterogeneities artificially is challenging. In this study, we used both acid- and base-producing enzymatic reactions simultaneously and demonstrated that the execution of these reactions in the presence of audible sound can effectively create spatiotemporally ordered pH domains in a solution.

Pathway-dependent Metallosupramolecular Polymerization Regulated by Ligand Geometry

Understanding structure/property correlations in self-assembly is a key but challenging requirement for developing functional materials. Herein, we explore the importance of ligand geometry to fine-tune photophysical properties (MMLCT vs. MLCT excited states) and self-assembly pathways in metallosupramolecular polymerization. To this end, we have designed two hydrophobic Pt(II) complexes, 1 and 2, containing a π-extended bidentate bipyridine ligand with different substitution pattern, resulting in different molecular geometries (linear vs. V-shaped). Detailed comparative studies revealed significant differences for both complexes in terms of their photophysical properties and self-assembly pathways in non-polar media. The V-shaped topology of 1 enables facile face-to-face molecular stacking with a certain curvature leading to luminescent spherical assemblies exhibiting MMLCT states and short Pt⋅⋅⋅Pt contacts via a single-step cooperative pathway. On the other hand, the higher preorganized linear topology of complex 2 induces a two-step competitive self-assembly process leading to the formation of one-dimensional supramolecular polymers with slipped packing and MLCT-originated emission. Our findings broaden the monomer scope for supramolecular polymerization and provide design guidelines for the realization of luminescent supramolecular assemblies.

Liquid-Liquid and Liquid-Solid Interfacial Nanoarchitectonics

Nanoscale science is becoming increasingly important and prominent, and further development will necessitate integration with other material chemistries. In other words, it involves the construction of a methodology to build up materials based on nanoscale knowledge. This is also the beginning of the concept of post-nanotechnology. This role belongs to nanoarchitectonics, which has been rapidly developing in recent years. However, the scope of application of nanoarchitectonics is wide, and it is somewhat difficult to compile everything. Therefore, this review article will introduce the concepts of liquid and interface, which are the keywords for the organization of functional material systems in biological systems. The target interfaces are liquid-liquid interface, liquid-solid interface, and so on. Recent examples are summarized under the categories of molecular assembly, metal-organic framework and covalent organic framework, and living cell. In addition, the latest research on the liquid interfacial nanoarchitectonics of organic semiconductor film is also discussed. The final conclusive section summarizes these features and discusses the necessary components for the development of liquid interfacial nanoarchitectonics.

Construction of Supramolecular Polymers and Covalent Polymers via the Same Monomers

Nature owns the ability to construct structurally different polymers from the same monomers. While polymers can be classified as covalent polymers (CPs) and supramolecular polymers (SPs), it is still difficult to synthesize CPs and SPs using same monomers like nature do. Herein, M1 with two diazo salts on both the ends was designed. Additionally, hydroquinone was chosen to be M2 for the existence of two hydroxyl groups. When mixing at room temperature, M1 and M2 self-assembled to SPs via N…H hydrogen bonds. In another way, upon the exposure to ultraviolet irradiation when blending M1 with M2, CPs were fabricated in the presence of covalent bonds. The excellent thermal stability of CPs was determined by TGA and DSC, while the great corrosion resistance of covalent polymers was detected by acid or alkali immersion. In this way, constructing two kinds of polymers using the same monomers was successfully achieved. This shows tremendous potential in fields of polymer science, supramolecular chemistry, which would boom the development of polymers.

Confined Space Nanoarchitectonics for Dynamic Functions and Molecular Machines

Nanotechnology has advanced the techniques for elucidating phenomena at the atomic, molecular, and nano-level. As a post nanotechnology concept, nanoarchitectonics has emerged to create functional materials from unit structures. Consider the material function when nanoarchitectonics enables the design of materials whose internal structure is controlled at the nanometer level. Material function is determined by two elements. These are the functional unit that forms the core of the function and the environment (matrix) that surrounds it. This review paper discusses the nanoarchitectonics of confined space, which is a field for controlling functional materials and molecular machines. The first few sections introduce some of the various dynamic functions in confined spaces, considering molecular space, materials space, and biospace. In the latter two sections, examples of research on the behavior of molecular machines, such as molecular motors, in confined spaces are discussed. In particular, surface space and internal nanospace are taken up as typical examples of confined space. What these examples show is that not only the central functional unit, but also the surrounding spatial configuration is necessary for higher functional expression. Nanoarchitectonics will play important roles in the architecture of such a total system.