Self-assembled supramolecular materials for photocatalytic H_(2)production and CO_(2)reduction

Photosynthetic organisms harness solar radiation to produce energy-rich compounds from water and atmospheric CO_(2)via exquisite supramolecular assemblies,which offers a design principle for highly efficient artificial photocatalytic systems.As an emerging research field,significant effort has been devoted to self-assembled supramolecular materials for photocatalytic H_(2)production and CO_(2)reduction.In this review,we introduce the basic concepts of supramolecular photocatalytic materials.After that,we will discuss recent advances in the preparation of supramolecular photocatalytic materials from zero-dimension to three-dimension which include molecular assemblies,micelles,hybrid nanoparticles,nanofibers,nanosheets,microcrystals,lipid bilayers,supramolecular organic frameworks,supramolecular metal-organic frameworks,gels,and host-guest metal-organic frameworks,etc.Furthermore,we show the recent progress in the photocatalytic properties of supramolecular photocatalytic materials,i.e.photocatalytic proton reduction,water splitting,CO_(2)to HCOOH,CO_(2)to CO,CO_(2)to CH4 conversions,etc.Finally,we provide our perspective for the future research,with a focus on the development of new structures and highly efficient photocatalysis.

Intercalation Assembly, Characterization and Luminescent Properties of Novel Supramolecular Composite Materials, Tb(Ⅲ) Complex with Tetrapodal Ligand-Montmorillonite

Two kinds of Tb（ Ⅲ ） complexes with tetrapodal ligand, [TbL（NO3）]^3＋ and [TbL]^3＋ （L： 1,1, 1＇, 1＇-tera （ 2-pyridinecarboxylester ）-di （ trimethylpropane）） were intercalated into the interlayer space of montmorillonite （MT） by ion exchange and coordination reaction of L with the Tb^3＋ ion existing in the interlayer space of Tb-MT respectively. The obtained luminescent supramolecular composite materials, [ TbL （NO3） ]^2＋-MT and [TbL]^3＋-MT were characterized by elemental analysis, XRD, FT-IR, UV-vis and thermal analysis. At the same time, the luminescent properties of the materials were also studied. The results show that the intercalated materials with regular layered structure, good thermal stability and the interlayer spacing （d001） approximates to the size of the complex ions which are located in the interlayer space of MT in the form of a monolayer.

Synthesis of stimuli-responsive pillararene-based supramolecular polymer materials for the detection and separation of metal ions

A stimuli-responsive supramolecular polymer network(G-(CN)_(2)⊂BXDSP5)with aggregation-induced emission(AIE)properties has been efficiently constructed by host-guest interactions between pillar[5]arene derivative BXDSP5 and a homoditopic guest G-(CN)_(2),which shows not only excellent fluorescence properties due to the AIE effect but also desirable ion-sensing abilities in both solution and solid states,holding great potential in the applicable fluorescence detection for Fe^(3+).The resultant G-(CN)_(2)⊂BXDSP5 can be transformed into supramolecular polymer gel at high concentration via multiple noncovalent interactions,showing multi-stimuli-responsiveness in response to temperature change,mechanical force,and competitive agent.Meanwhile,the xerogel of supramolecular polymer material has been successfully used to remove Fe^(3+)from water with high adsorption efficiency.In addition,an ionresponsive film based on supramolecular polymer has also been developed,which can serve as a practical and convenient fluorescence test kit for detecting Fe^(3+).

Supramolecular adhesive materials from small‐molecule self‐assembly

Developing high‐performance adhesive materials not only aims at industrial and social requirements but also bears the fundamental importance of understanding the chemical factors of biological adhesion to develop biomimetic adhesive materials.Owing to the wide development of supramolecular chemistry,numerous supramolecular tools are exploited and proved to be reliable in the replacement of traditional covalent materials by reversible noncovalent or dynamic covalent materials.Taking advantage of these readyto‐use supramolecular toolboxes,supramolecular adhesive materials are rising and promising toward“smart”adhesives,that is,enabling responsiveness,reversibility,and recyclability.Compared with polymeric adhesive materials,low‐molecular‐weight adhesives feature chemically precise structure,easier engineering by molecular design,and hence higher reproducibility.However,it remains highly challenging to make high‐performance adhesive materials by low‐molecular‐weight feedstocks.This review will focus on the recent advancement in the construction of supramolecular adhesive materials by smallmolecule self‐assembly.The design guidelines and consideration on the molecular scale will be discussed and summarized on how to enhance the strength of adhesives.Meanwhile,owing to the dynamic nature of supramolecular self‐assembly,several“smart”functions of such materials will be presented,such as stimuli–responsiveness and adaptiveness.Finally,current challenges and future perspectives of this emerging field will be proposed.

Supramolecular Adhesive Materials from Natural Acids and Sugars with Tough and Organic Solvent-Resistant Adhesion

Natural adhesives have been widely replaced by industrial adhesives made from petroleum-based products.Compared with that of traditional natural adhesives,modern industrial adhesives show improved adhesion performance.However,the drawbacks of modern adhesives,including toxicity and nonbiodegradability,drive the need for new and high-performance adhesive materials from renewable and biocompatible natural feedstock.In this study,a new family of acid-sugar adhesive materials exhibiting excellent and long-term adhesion effects was developed inspired by the concept of deep eutectic solvents(DESs).The supramolecular polymerization between natural sugars and acids gave rise to both strong cohesion and adhesion properties.Moreover,high resistance to organic solvents is an advantage of acid-sugar supramolecular adhesive materials.This study not only dramatically expands the applications of DESs but also sheds light on the development of supramolecular adhesive materials as promising alternatives to polymeric adhesives.

Out-of-Equilibrium Assembly Based on Host-Guest Interactions

The field of supramolecular chemistry is rapidly progressing,transitioning from the creation of thermodynamically stable systems found in local or global minima on the free energy landscape to the development of out-of-equilibrium systems that rely on chemical reactions to establish and maintain their structures.Over the past decade,numerous artificial out-of-equilibrium systems have been devised in various domains of supramolecular chemistry,many of which have been extensively reviewed.However,one area that has received limited attention thus far is the use of out-of-equilibrium processes to regulate host-guest interactions.This minireview aims to address this gap by exploring the construction of out-ofequilibrium systems based on host-guest complexation,which likely employs similar strategies to those employed in analogous noncovalent interactions.The review begins with a summary of these shared strategies.Subsequently,it discusses representative publications that exemplify these strategies and classifies thembased onwhich component is being modulated-host,guest,or competitive molecules.Through this examination,our objective is to shed light on the design of out-of-equilibrium systems relying on host-guest interactions and provide valuable insights into the preparation strategies for various transient materials.

Macroscopic Supramolecular Assembly and Its Applications

Macroscopic supramolecular assembly(MSA)has been a recent progress in supramolecular chemistry.MSA mainly focuses on studies of the building blocks with a size beyond ten micrometers and the non-covalent interactions between these interactive building blocks to form ordered structures.MSA is essential to realize the concept of"self-assembly at all scales"by bridging most supramolecular researches at molecular level and at macroscopic scale.This review summaries the development of MSA,the basic design principle and related strategies to achieve MSA and potential applications.Correspondingly,we try to elucidate the correlations and differences between"macroscopic assembly"and MSA based on intermolecular interactions;the design principle and the underlying assembly mechanism of MSA are proposed to understand the reported MSA behaviors;to demonstrate further applications of MSA,we introduce some methods to improve the ordered degree of the assembled structures from the point of precise assembly and thus envision some possible fields for the use of MSA.

Chiral pillar[n]arenes:Conformation inversion,material preparation and applications

Chiral pillar[n]arenes have shown great research value and application prospect in construction of chiral materials and chiral applications,due to their inherent planar chiral configurations,chiral recognition ability,easy modification and highly symmetric hydrophobic cavity.This review systematically summarized the conformation inversion factors of planar chiral pillar[5]arenes(pR/p S),such as solvents,temperature,substituent size,alkyl chains,chiral and achiral guest molecules.We firstly introduced the applications of chiral pillar[n]arenes for constructing chiral materials and pointed out that planar conformation inversion showed a great potential role in constructing chiral materials.Then,we mainly concluded the chiral applications of chiral and planar chiral pillar[n]arenes like chiral enantiomer analysis by circular dichroism,electrochemistry or chiral fluorescence sensing.From this review,we found that the inherent planar chiral conformation of chiral pillar[n]arenes have played a very important role in chiral field in the future.

Polymeric materials reinforced by noncovalent aggregates of polymer chains

Mechanical performances are among the most fundamental properties that dictate the applicability and durability of polymeric materials.Reinforcement of polymeric materials is eternally pursued to broaden the applications of polymers with light-weight,low-cost and easy-processing advantages.Noncovalent aggregates of biomacromolecules have been found to play a significant role in the mechanical properties of many natural materials,such as the spider silk.Increasing numbers of reports have demonstrated that the in situ formed noncovalent aggregates of polymer chains in polymeric systems are highly effective for enhancing the mechanical properties of artificial polymeric materials,in terms of strength,stiffness,toughness,and/or elasticity.The in situ formed noncovalent aggregates act as additional crosslinking domains and well-dispersed“hard”nanofillers in the polymer networks,significantly strengthening,stiffening and/or toughening the polymeric materials.Moreover,the noncovalent crosslinking of polymer chains favors the development of healable and recyclable polymeric materials,thanks to the reversible and dynamic properties of noncovalent bonds.This review provides an overview of the recent advances on the enhancement of the mechanical properties of different polymeric materials by the in situ formed noncovalent aggregates of polymer chains.It is expected to arouse inspirations for the development of novel polymeric materials with extraordinary mechanical performances and functionalities.

Bottom-up construction of mesoporous supramolecular isomers based on a Pd_(3)L_(6) triangular prism as templates for shape specific aggregation of polyiodide

Bottom-up construction of highly complex architecture from simple components remains one of the long-standing challenges in chemistry.Herein two supramolecular isomers based on large trigonal prismatic Pd_(3)L^(1)_(6)building block are reported.Significantly,they can be controllably obtained by adjusting the solute concentration during crystal growth.Specifically,the square shape crystals,α-[Pd_(3)L^(1)_(6)](PF_(6))_(12)in the cubic system with I143 m space group,can be isolated from a high-concentration solution of Pd_(3)L^(1)_(6).Interestingly,a mesoporous cage assembled from eight Pd_(3)L^(1)_(6)units with a diameter of 24Åis observed in the crystal structure.For the low-concentration solution of Pd_(3)L^(1)_(6),the rectangular shape crystalsβ-[Pd_(3)L^(1)_(6)](PF_(6))_(12)are obtained,which crystallize in the hexagonal system with P 63/m space group,and display two-dimension packing pattern and one-dimension mesoporous channels(diameter ca.22Å)along the c axis.Moreover,the two supramolecular isomers were used as nanoporous reactors to induce the specific formation of polyiodides with different compositions and shapes as evidenced from single crystal X-ray diffraction studies.These findings provide a reference in targeting functional crystalline mesoporous supramolecular materials from a single complex building unit.

Effect of spatial configuration on adhesion of 1,2-disubstituted cyclohexane derivatives

Spatial configuration has a significant effect on chemical self-assembly.However,the importance of spatial configuration in supramolecular adhesive materials has been frequently ignored.In this study,the effects of the spatial configuration on cohesion and adhesion were investigated.Owing to the diversities of the chemical structures and assembly patterns,1,2-disubstituted cyclohexane derivatives were used in this combined experimental and theoretical investigation.The self-sorting assembly of enantiopure isomers improved cohesion but had a negative effect on adhesion.In contrast,racemic mixtures displayed stronger adhesion effects.Moreover,it was proven that the cis-configuration was more favorable for supramolecular adhesion than the trans-counterpart.In addition,the influence of the spatial configuration of 1,2-disubstituted cyclohexane derivatives could be effectively mitigated by hydrogen bond donors or acceptors.The addition of natural acids yielded three-dimensional polymeric networks,in which the spatial configuration was not the decisive factor for supramolecular adhesion.

Self-healing and highly elastic fluorine-free proton exchange membranes comprised of poly(vinyl alcohol) derivative and phytic acid for durable fuel cells

Fluorine-free proton exchange membranes(PEMs)capable of healing from physical damage are important for PEM fuel cells(PEMFCs)with extended service life and enhanced reliability.Herein,highly elastic fluorine-free PEMs with excellent self-healing ability and high proton conductivity are fabricated through complexation of phytic acid(PA)with sulfonated polyvinyl alcohol(SPVA),followed by subsequent grafting of SPVA with positively charged 4-(1H-imidazol-1-yl)benzenecarbaldehyde(IBZ).Compared with recast Nafion membranes,the as-prepared SPVA-IBZ/PA membranes exhibit an enhanced mechanical strength and elasticity and can spontaneously recover from a^50%strain to their initial states within^30 s at room temperature.Meanwhile,the SPVA-IBZ/PA membranes have a proton conductivity of^0.095 S cm-1at^70°C,which is higher than that of recast Nafion membranes.The hydrogen-powered PEMFCs using the SPVA-IBZ/PA membranes,which show an open circuit voltage of^0.98 V and maximum power density of^609 mW cm-2,exhibit a satisfactory cell performance.Importantly,the SPVA-IBZ/PA membranes can spontaneously heal mechanical damage of several tens of micrometers in size and restore their original proton conductivity and cell performance under the working conditions of PEMFCs.

Highly Stretchable,Elastic,Healable,and Ultra-Durable Polyvinyl Alcohol-Based Ionic Conductors Capable of Safe Disposal

Highly durable and stretchable ionic conductors are indispensable components of flexible electronics.However,fabricating such ionic conductors that are also non-toxic and biodegradable remains a challenge.In this study,highly stretchable,elastic,healable,and ultra-durable ionic conductors capable of non-hazardous disposal are conveniently fabricated by complexation of vanillin-grafted polyvinyl alcohol(VPVA)and ionic liquids(ILs)(denoted as VPVA-IL).

Applications of pillarenes, an emerging class of synthetic macrocycles

Synthetic macrocycles, a typical type of building block for molecular recognition and self-assembly, are crucial to supramolecular chemistry and materials science. Since 2008, a new generation of synthetic macrocyclic hosts, pillarenes and their abundant derivatives, which consist of hydroquinone units linked by methylene bridges at 2,5-positions, have been the focus of much research. Numerous studies on their host-guest properties and the fabrication of supramolecular assemblies have demon- strated that pillarenes and their derivatives possess many advantages that facilitate their applications in many research fields. Herein we summarize and classitfy the applications of pillarenes in terms of artificial transmembrane channels, controlled delivery systems, dispersion of carbon hybrid materials, extraction and absorption, liquid crystals, metal-organic frameworks, sensing and detection, stabilization of nanoparticles （Au/Ag/CdTe）, and other typical biological applications. We also provide an overview of future developments in pillarene chemistry.

Dynamic covalent gels assembled from small molecules：from discrete gelators to dynamic covalent polymers

Dynamic covalent chemistry has emerged recently to be a powerful tool to construct functional materials.This article reviews the progress in the research and development of dynamic covalent chemistry in gels assembled from small molecules.First dynamic covalent reactions used in gels are reviewed to understand the dynamic covalent bonding.Afterwards the catalogues of dynamic covalent gels are reviewed according to the nature of gelators and the interactions between gelators.Dynamic covalent bonding can be involved to form low molecular weight gelators.Low molecular weight molecules with multiple functional groups react to form dynamic covalent cross-linked polymers and act as gelators.Two catalogues of gels show different properties arising from their different structures.This review aims to illustrate the structure-property relationships of these dynamic covalent gels.