Electro‐Optic (E‐O) Molecular Glasses

This Focus Review describes molecular glasses as a new class of materials for nonlinear optical (NLO) applications, especially for electro‐optic (E‐O) devices. Examples of E‐O molecular glasses are reviewed with a focus on the molecular design of NLO chromophores and solid‐state engineering of molecular glasses. Molecular glasses based on dendrimers of multiple chromophores, molecular glass blends of chromophores, and molecular glasses based on reversible self‐assembly of chromophores are introduced as promising architectures to prepare morphologically stable molecular glasses with large E‐O activities and improved material properties for device applications. Future directions to fully exploit the potential of molecular glasses for NLO materials are presented.     

Self‐Assembling Proteins for Design of Anticancer Nanodrugs

Inspired by the diverse protein‐based structures and materials in organisms, proteins have been expected as promising biological components for constructing nanomaterials toward various applications. In numerous studies protein‐based nanomaterials have been constructed with the merits of abundant bioactivity and good biocompatibility. However, self‐assembly of proteins as a dominant approach in constructing anticancer nanodrugs has not been reviewed. Here, we provide a comprehensive account of the role of protein self‐assembly in fabrication, regulation, and application of anticancer nanodrugs. The supramolecular strategies, building blocks, and molecular interactions of protein self‐assembly as well as the properties, functions, and applications of the resulting nanodrugs are discussed. The applications in chemotherapy, radiotherapy, photodynamic therapy, photothermal therapy, gene therapy, and combination therapy are included. Especially, manipulation of molecular interactions for realizing cancer‐specific response and cancer theranostics are emphasized. By expounding the impact of molecular interactions on therapeutic activity, rational design of highly efficient protein‐based nanodrugs for precision anticancer therapy can be envisioned. Also, the challenges and perspectives in constructing nanodrugs based on protein self‐assembly are presented to advance clinical translation of protein‐based nanodrugs and next‐generation nanomedicine.     

Micro‐/Nanostructured Multicomponent Molecular Materials: Design,Assembly, and Functionality

Molecule‐based micro‐/nanomaterials have attracted considerable attention because their properties can vary greatly from the corresponding macro‐sized bulk systems. Recently, the construction of multicomponent molecular solids based on crystal engineering principles has emerged as a promising alternative way to develop micro‐/nanomaterials. Unlike single‐component materials, the resulting multicomponent systems offer the advantages of tunable composition, and adjustable molecular arrangement, and intermolecular interactions within their solid states. The study of these materials also supplies insight into how the crystal structure, molecular components, and micro‐/nanoscale effects can influence the performance of molecular materials. In this review, we describe recent advances and current directions in the assembly and applications of crystalline multicomponent micro‐/nanostructures. Firstly, the design strategies for multicomponent systems based on molecular recognition and crystal engineering principles are introduced. Attention is then focused on the methods of fabrication of low‐dimensional multicomponent micro‐/nanostructures. Their new applications are also outlined. Finally, we briefly discuss perspectives for the further development of these molecular crystalline micro‐/nanomaterials.     

Supramolecular Organogels Based on Dendrons and Dendrimers

Dendrons and dendrimers have well‐defined, discrete structures that can be precisely controlled at the molecular lever. Owing to their unique architectures and multiple functionalities, dendritic molecules have shown intensive self‐assembly behavior and functional performance. In particular, they have been shown to be promising candidates for applications in the assembly of gel‐phase materials. Furthermore, the introduction of suitable functional moieties into the core, the branches, and/or the periphery of the dendritic gelators enables the construction of smart and functional supramolecular gel materials. Over the past decade, a number of dendritic organogelators that are based on poly(amino acid), poly(amide), and poly(aryl ether) dendrons, or together with multiple alkyl chains on the periphery, have been reported. This review describes the important developments in dendritic organogelators, with an emphasis on new strategies for the molecular design of dendritic gelators, understanding of driving forces for gel formation, and their evolution for potential applications in smart soft materials.     

Theoretical perspective on properties of DNA‐functionalized surfaces

The molecular recognition properties of DNA gave rise to many novel materials and applications such as DNA biosensors, DNA‐functionalized colloidal materials, DNA origami and DNA‐based directed surface assembly. The DNA‐functionalized surfaces are used in biosensors and for programmed self‐assembly of biological, organic and inorganic moieties into novel materials. However, surface density, length, and linker design of the surface functionalized DNAs significantly influence the properties of DNA‐driven assemblies and materials. This perspective discusses the understanding of structure and dynamics of DNA immobilized on the surfaces from the theoretical point of view including recent progress in analytical theories, atomistic simulations, and coarse‐grained models. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1563–1568, 2011     

Supramolecular Photothermal Effects: A Promising Mechanism for Efficient Thermal Conversion

Supramolecular assemblies have been very successful in regulating the photothermal conversion efficiency of organic photothermal materials in a simple and flexible way, compared with conventional molecular synthesis. In these assemblies, it is the inherent physiochemical mechanism that determines the photothermal conversion, rather than the assembly strategy. This Minireview summarizes supramolecular photothermal effects, which refer to the unique features of supramolecular chemistry for regulating the photothermal conversion efficiency. Emphasis is placed on the mechanisms of how self‐assembly affects the photothermal performance. The supramolecular photothermal effects on various types of light‐harvesting species are discussed in detail. The timely interpretation of supramolecular photothermal effects is promising for the future design of the photothermal materials with high efficiency, precision, and multiple functionalities for a wide array of applications.     

Intermolecular Charge‐Transfer Interactions Facilitate Two‐Photon Absorption in Styrylpyridine–Tetracyanobenzene Cocrystals

Cocrystals of 4‐styrylpyridine and 1,2,4,5‐tetracyanobenzene were successfully prepared by supramolecular self‐assembly. Donor–acceptor interactions between the molecular components are the main driving force for self‐assembly and contribute to intermolecular charge transfer. The cocrystals possess two‐photon absorption properties that are not observed in the individual components; suggesting that two‐photon absorption originates from intermolecular charge‐transfer interactions in the donor–acceptor system. The origin of two‐photon absorption in multichromophore systems remains under‐researched; thus, the system offers a rare demonstration of two‐photon absorption by cocrystallization. Cocrystal engineering may facilitate further design and development of novel materials for nonlinear optical and optoelectronic applications.     

Beyond Charge Balance: Counter‐Cations in Polyoxometalate Chemistry

Polyoxometalates (POMs) are molecular metal‐oxide anions applied in energy conversion and storage, manipulation of biomolecules, catalysis, as well as materials design and assembly. Although often overlooked, the interplay of intrinsically anionic POMs with organic and inorganic cations is crucial to control POM self‐assembly, stabilization, solubility, and function. Beyond simple alkali metals and ammonium, chemically diverse cations including dendrimers, polyvalent metals, metal complexes, amphiphiles, and alkaloids allow tailoring properties for known applications, and those yet to be discovered. This review provides an overview of fundamental POM–cation interactions in solution, the resulting solid‐state compounds, and behavior and properties that emerge from these POM–cation interactions. We will explore how application‐inspired research has exploited cation‐controlled design to discover new POM materials, which in turn has led to the quest for fundamental understanding of POM–cation interactions.     

Advanced Materials Based on Polymers and Ionic Liquids

Ionic liquids (ILs) are ambient temperature molten salts, which have attracted considerable attention owing to their unique properties. In this contribution, we review advanced materials composed of ILs and polymers for the basis of a new design protocol to fabricate novel materials. As electrolytes for electrochemical devices, cross‐linked polymers containing ILs (ion gels) are endowed with functional properties inherited from ILs and mechanical consistency derived from polymers. To create such materials, micro‐phase separation of block copolymers and colloidal arrays in the ILs are utilized. Based on the molecular design of task‐specific ILs, the resultant ion gels are applicable as electrolytes for actuator, fuel cell, and secondary battery applications. Thermo‐ and photo‐responsive polymers in ILs are also highlighted, whereby such stimuli elicit changes in the solubility of the self‐assembly of block copolymers and colloidal arrays in the ILs. Further, thermo‐ and photo‐reversible changes in the self‐assembled structure can be exploited to demonstrate sol‐gel transitions and fabricate photo‐healable materials.     

Recent Progress in Azobenzene-Based Supramolecular Materials and Applications

Azobenzene-containing small molecules and polymers are functional photoswitchable molecules to form supramolecular nanomaterials for various applications. Recently, supramolecular nanomaterials have received enormous attention in material science because of their simple bottom-up synthesis approach, understandable mechanisms and structural features, and batch-to-batch reproducibility. Azobenzene is a light-responsive functional moiety in the molecular design of small molecules and polymers and is used to switch the photophysical properties of supramolecular nanomaterials. Herein, we review the latest literature on supramolecular nano- and micro-materials formed from azobenzene-containing small molecules and polymers through the combinatorial effect of weak molecular interactions. Different classes including complex coacervates, host-guest systems, co-assembled, and self-assembled supramolecular materials, where azobenzene is an essential moiety in small molecules, and photophysical properties are discussed. Afterward, azobenzene-containing polymers-based supramolecular photoresponsive materials formed through the host-guest approach, polymerization-induced self-assembly, and post-polymerization assembly techniques are highlighted. In addition to this, the applications of photoswitchable supramolecular materials in pH sensing, and CO₂ capture are presented. In the end, the conclusion and future perspective of azobenzene-based supramolecular materials for molecular assembly design, and applications are given.     

Oligo(ethylene glycol)/alkyl‐modified Chromophore Assemblies for Photon Upconversion in Water

Molecular self‐assembly is a powerful means to construct nanoscale materials with advanced photophysical properties. Although the protection of the photo‐excited states from oxygen quenching is a critical issue, it still has been in an early phase of development. In this work, we demonstrate that a simple and typical molecular design for aqueous supramolecular assembly, modification of the chromophoric unit with hydrophilic oligo(ethylene glycol) chains and hydrophobic alkyl chains, is effective to avoid oxygen quenching of triplet–triplet annihilation‐based photon upconversion (TTA‐UC). While a TTA‐UC emission is completely quenched when the donor and acceptor are molecularly dispersed in chloroform, their aqueous co‐assemblies exhibit a clear upconverted emission in air‐saturated water even under extremely low chromophore concentrations down to 40 μm . The generalization of this nano‐encapsulation approach offers new functions and applications using oxygen‐sensitive species for supramolecular chemistry.     

Peptides as New Smart Bionanomaterials: Molecular‐Recognition and Self‐Assembly Capabilities

Biomolecules express exquisite properties that are required for molecular recognition and self‐assembly on the nanoscale. These smart capabilities have developed through evolution and such biomolecules operate based on smart functions in natural systems. Recently, these remarkable smart capabilities have been utilized in not only biologically related fields, but also in materials science and engineering. A peptide‐screening technology that uses phage‐display systems has been developed based on this natural smart evolution for the generation of new functional peptide bionanomaterials. We focused on peptides that specifically bound to synthetic polymers. These polymer‐binding peptides were screened by using a phage‐display peptide library to recognize nanostructures that were derived from polymeric structural features and were utilized for possible applications as new bionanomaterials. We also focused on self‐assembling peptides with β‐sheet structures that formed nanoscale, fibrous structures for applications in new bottom‐up nanomaterials. Moreover, nanofiber‐binding peptides were also screened to introduce the desired functionalities into nanofibers without the need for additional molecular design. Our approach to construct new bionanomaterials that employ peptides will open up excellent opportunities for the next generation of materials science and technology.     

Covalent Organic Frameworks and Cage Compounds: Design and Applications of Polymeric and Discrete Organic Scaffolds

Porous organic materials are an emerging class of functional nanostructures with unprecedented properties. Dynamic covalent assembly of small organic building blocks under thermodynamic control is utilized for the intriguingly simple formation of complex molecular architectures in one‐pot procedures. In this Review, we aim to analyze the basic design principles that govern the formation of either covalent organic frameworks as crystalline porous polymers or covalent organic cage compounds as shape‐persistent molecular objects. Common synthetic procedures and characterization techniques will be discussed as well as more advanced strategies such as postsynthetic modification or self‐sorting. When appropriate, comparisons are drawn between polymeric frameworks and discrete organic cages in terms of their underlying properties. Furthermore, we highlight the potential of these materials for applications ranging from gas storage to catalysis and organic electronics.     

Triplex DNA Nanostructures: From Basic Properties to Applications

Triplex nucleic acids have recently attracted interest as part of the rich “toolbox” of structures used to develop DNA‐based nanostructures and materials. This Review addresses the use of DNA triplexes to assemble sensing platforms and molecular switches. Furthermore, the pH‐induced, switchable assembly and dissociation of triplex‐DNA‐bridged nanostructures are presented. Specifically, the aggregation/deaggregation of nanoparticles, the reversible oligomerization of origami tiles and DNA circles, and the use of triplex DNA structures as functional units for the assembly of pH‐responsive systems and materials are described. Examples include semiconductor‐loaded DNA‐stabilized microcapsules, DNA‐functionalized dye‐loaded metal–organic frameworks (MOFs), and the pH‐induced release of the loads. Furthermore, the design of stimuli‐responsive DNA‐based hydrogels undergoing reversible pH‐induced hydrogel‐to‐solution transitions using triplex nucleic acids is introduced, and the use of triplex DNA to assemble shape‐memory hydrogels is discussed. An outlook for possible future applications of triplex nucleic acids is also provided.     

Self-assembled free-floating nanomaterials from sequence-defined polymers

Sequence-defined polymers can be programmed to self-assemble into precise nanostructures for applications in biosensing, drug delivery, optics, and molecular computation. Inspired by the natural self-assembly processes present in biological protein and DNA systems, sets of molecular design rules have emerged across materials classes as instructions to build a variety of tunable structures. This review highlights recent advances in self-assembled sequence-defined and sequence-specific polymers across peptides, peptoids, DNA, and non-biological synthetic materials, with a focus on synthesis, assembly processes and overall structure. Specifically, these self-assembled structures are free-floating, as such constructs can potentially serve as a platform for the aforementioned applications. Emphasis is placed on the molecular design of polymers that self-assemble into zero-dimensional, one-dimensional, two-dimensional, or three-dimensional nanostructures. With the development of automated syntheses and increasing control over self-assembly, future work may focus on emerging classes of compatible hybrid materials with exciting directions toward new architectures and applications.     

Molecular and Crystal Magnetic Engineering of Polymetallic Coupling System: From Magnetic Molecules to Molecular Magnets

One of the main challenges in the field of molecular materials is the design of molecular ferromagnets. General design strategy includes two steps, that is molecular magnetic engineering and crystal magnetic engineering. The first step is the synthesis of ferromagnetically coupled polymetallic systems. The second step is the assembly of polymetallic systems with muti‐dimensional structure and exhibiting a ferromagnetic transition. This paper summarized the strategies of molecular design and crystal engineering allowed to obtain such systems and our efforts in the fields of molecular magnetism and molecular‐based magnets.     

Modular Synthesis of Functional Nanoscale Coordination Polymers

The coordination‐directed assembly of metal ions and organic bridging ligands has afforded a variety of bulk‐scale hybrid materials with promising characteristics for a number of practical applications, such as gas storage and heterogeneous catalysis. Recently, so‐called coordination polymers have emerged as a new class of hybrid nanomaterials. Herein, we highlight advances in the syntheses of both amorphous and crystalline nanoscale coordination polymers. We also illustrate how scaling down these materials to the nano‐regime has enabled their use in a broad range of applications including catalysis, spin‐crossover, templating, biosensing, biomedical imaging, and anticancer drug delivery. These results underscore the exciting opportunities of developing next‐generation functional nanomaterials based on molecular components.     

Cubic Polyhedral Oligomeric Silsesquioxane Based Functional Materials: Synthesis,Assembly, and Applications

Organically modified cubic polyhedral oligomeric silsesquioxanes (POSS) have attracted increasing attention in the design of novel functional hybrid materials for applications such as porous materials, liquid crystals, semiconductors, high‐temperature lubricants, fuel cells, and lithium batteries. The nanosized POSS moiety can be conveniently modified on the periphery with a variety of functional groups to lead to hybrid materials with desired functions. In addition, suitable mono‐functionalized POSS derivatives can be incorporated into polymers as side chains via various synthetic strategies to offer a wide class of functional polymeric materials with tunable physical properties for targeted applications. In this Focus Review, we aim to summarize the recent developments on the chemistry and applications of POSS‐based molecules and polymers. Moreover, the properties as well as assembly behavior of the POSS‐based functional hybrid materials will be reviewed, and the relationship of the performance of the hybrid materials with the intrinsic nature of the POSS unit will be addressed.     

Dramatic Specific‐Ion Effect in Supramolecular Hydrogels

We report on a pronounced specific‐ion effect on the intermolecular and chiral organization, supramolecular structure formation, and resulting materials properties for a series of low molecular weight peptide‐based hydrogelators, observed in the presence of simple inorganic salts. This effect was demonstrated using aromatic short peptide amphiphiles, based on fluorenylmethoxycarbonyl (Fmoc). Gel‐phase materials were formed due to molecular self‐assembly, driven by a combination of hydrogen bonding and π‐stacking interactions. Pronounced morphological changes were observed by atomic force microscopy (AFM) for Fmoc‐YL peptide, ranging from dense fibrous networks to spherical aggregates, depending on the type of anions present. The gels formed had variable mechanical properties, with G′ values between 0.8 kPa and 2.4 kPa as determined by rheometry. Spectroscopic analysis provided insights into the differential mode of self‐assembly, which was found to be dictated by the hydrophobic interactions of the fluorenyl component, with comparable H‐bonding patterns observed in each case. The efficiency of the anions in promoting the hydrophobic interactions and thereby self‐assembly was found to be consistent with the Hofmeister anion sequence. Similar effects were observed with other hydrophobic peptides, Fmoc‐VL and Fmoc‐LL. The effect was found to be less pronounced for a less hydrophobic peptide, Fmoc‐AA. To get more insights into the molecular mechanism, the effect of anions on sol–gel equilibrium was investigated, which indicates the observed changes result from the specific‐ion effects on gels structure, rather than on the sol–gel equilibrium. Thus, we demonstrate that, by simply changing the ionic environment, structurally diverse materials can be accessed providing an important design consideration in nanofabrication via molecular self‐assembly.     

Self‐Assembly of Aggregation‐Induced‐Emission Molecules

The last decade has witnessed rapid developments in aggregation‐induced emission (AIE). In contrast to traditional aggregation, which causes luminescence quenching (ACQ), AIE is a reverse phenomenon that allows robust luminescence to be retained in aggregated and solid states. This makes it possible to fabricate various highly efficient luminescent materials, which opens new paradigms in a number of fields, such as imaging, sensing, medical therapy, light harvesting, light‐emitting devices, and organic electronic devices. Of the various important features of AIE molecules, their self‐assembly behavior is very attractive because the formation of a well‐defined emissive nanostructure may lead to advanced applications in diverse fields. However, due to the nonplanar topology of AIEgens, it is not easy for them to self‐assemble into well‐defined structures. To date, some strategies have been proposed to achieve the self‐assembly of AIEgens. Herein, we summarize the most recent approaches for the self‐assembly of AIE molecules. These approaches can be sorted into two classes: 1) covalent molecular design and 2) noncovalent supramolecular interactions. We hope this will inspire more excellent work in the field of AIE.