Chirality Amplification Over the Morphology Control of the Rod-Coil Molecules with Lateral Methyl Groups

In the context of sustainable development, research regarding chirality has aroused enormous attention. Concurrently, chiral self-assembly is one of the most important subjects in supramolecular research, which can broaden the applications of chiral materials. This study focuses on the morphology control of amphiphilic rod-coil molecules composed of the rigid hexaphenyl unit and flexible oligoethylene and butoxy groups containing lateral methyl groups, carried out using an enantioseparation application. The methyl side chain being located on different blocks influences the driving force through steric hindrance, which determines the direction and degree of tilted packing during the π-π stacking of the self-assembly process. Interestingly, the amphiphilic rod-coil molecules aggregated into long helical nano-fibers, which further hierarchically aggregated into nano-sheets or nano-tubes upon increasing the concentration of the THF/H₂O solution. In particular, the hierarchical-chiral assembly effectively amplified the chirality and was validated by the strong Cotton signals; playing a vital role in the enantioselective nucleophilic substitution reaction. These results provide new insights into the applications of chiral self-assemblies and soft chiral materials.

Supramolecular hybrids of chiral Waugh polyoxometalate with cyclodextrins

The development of novel systems for chiral polyoxometalates (POMs) is an attractive research field because of their fascinating topological structures and well-defined functions. Herein, we have developed a new reaction route for the synthesis of two unprecedented chiral Waugh POM-based supramolecular architectures. Single-crystal X-ray diffraction reveals that the architectures exhibit a wavy three-dimensional framework and bamboo-rod-connected framework upon regulating the size of the cyclodextrin and the stacking pattern of the D₃ symmetric Waugh {MnMo₉}. Solution studies using NMR, circular dichroism and isothermal titration calorimetry corroborate nicely the very weak interactions between the components. The intricate chiral microenvironment originating from the hybrid frameworks may be responsible for the selective recognition of the Λ-{MnMo₉} enantiomer. This study highlights the importance of the asymmetric configuration of the POM for designing CD/POM assemblies and understanding their chirality.

Hyaluronic Acid-Enwrapped Polyoxometalate Complex for Synergistic Near Infrared-II Photothermal/Chemo-Therapy and Chemodynamic Therapy

To enhance the efficacy of tumor therapy, the collection of functional components into a targeting system shows advantages over most homogeneous materials in inducing apoptosis of cancer cells. The security and targeting of therapeutic agents also require the effect combination of additional components. However, the construction of multifunctional composites in a simple system with intelligent cooperative responsiveness remains a challenge. Herein, a reduced polyanionic cluster (rP₂W₁₈) bearing the absorption at the near infrared (NIR) II region is used as a core carrier to bind the positively charged doxorubicin hydrochloride (DOX) through ionic interaction. To reduce the physiological toxicity, hyaluronic acid grafting β-cyclodextrin side chains is used to cover the ionic complex through host-guest inclusion to DOX. When the nanocomposite is activated by local laser exposure, the final three-component therapeutic agent is demonstrated to present targeted photothermal conversion capability and chemodynamic activity together with chemotherapy. With the controlled release of DOX under the stimulation of mild acidity in the tumor region and photothermal effect, the exposed rP₂W₁₈ is aroused by hydrogen peroxide overexpressed in a tumor microenvironment to produce toxic reactive oxygen species, ¹O₂. This work presents an opportunity for the development of a nanocomposite in NIR-II photothermal/chemo-therapy and chemodynamic synergistic therapy.

Chiral hexamers of organically modified polyoxometalates via ionic complexation

Anderson-Evans type polyoxometalates (POMs) that are modified on double sides with anthracene groups through the linking of β-amino acid enantiomers covalently are synthesized. The modified Anderson-Evans POMs are successfully used...

A self-assembly solvothermal synthesis of SiMoVn@[Cu6O(TZI)3(H2O)6]4·nH2O for the efficient selective oxidation of various alkylbenzenes

A series of SiMoVn@rht-MOF-1 were isolated via a one-pot self-assembly solvothermal synthesis, exhibiting effective catalytic activity and excellent recyclability.

Crystalline Porous Materials for Nonlinear Optics

Crystalline porous materials have been extensively explored for wide applications in many fields including nonlinear optics (NLO) for frequency doubling, two-photon absorption/emission, optical limiting effect, photoelectric conversion, and biological imaging. The structural diversity and flexibility of the crystalline porous materials such as the metal-organic frameworks, covalent organic frameworks, and polyoxometalates provide numerous opportunities to orderly organize the dipolar chromophores and to systemically modify the type and concentration of these dipolar chromophores in the confined spaces, which are highly desirable for NLO. Here, the recent advances in the crystalline porous NLO materials are discussed. The second-order NLO of crystalline porous materials have been mainly devoted to the chiral and achiral structures, while the third-order NLO crystalline porous materials have been categorized into pure organic and hybrid organic/inorganic materials. Some representative properties and applications of these crystalline porous materials in the NLO regime are highlighted. The future perspective of challenges as well as the potential research directions of crystalline porous materials have been also proposed.

Constructing chiral polyoxometalate assemblies via supramolecular approaches

Polyoxometalates (POMs), as a typical class of discrete metal oxide clusters that are known in inorganic and structural chemistry since long, have displayed more and more interesting applications over recent years. However, in comparison to the chemical synthesis, the photochemical, electrochemical, and magnetic properties, the structural asymmetry, and relative characteristic investigations arising therefrom are far behind even if they are very important for functional materials, especially in solution systems. One of the main reasons is that it is hard to control and maintain a stable chiral state of POMs to carry out further corresponding performances. Aiming to overcome these disadvantages, the main concerns of this review are to discuss the generation of the chirality for discrete metal oxide clusters, chirality transfer via a supramolecular approach, chirality amplification in self-assemblies, and the related functional properties such as photochromism, catalysis, and bioactivities in solutions. Considering that some previous reviews dealt with chiral structures and packing architectures in the crystalline solids of POMs, this article only concentrates on the induced chirality and material properties in solution systems, which have been more active recently but no review article has been involved in this interesting area.

An inorganic Co-containing heteropolyoxoniobate: reversible chemochromism and H2O-dependent proton conductivity properties

A novel pure inorganic cobalt-containing heteropolyoxoniobate is constructed from crescent-shaped [SiNb18O54]14− units. It exhibits reversible chemochromism, H2O-dependent proton conductivity, water vapor adsorption and magnetic properties.

Two-Dimensional Supramolecular Ionic Frameworks for Precise Membrane Separation of Small Nanoparticles

Supramolecular frameworks driven by intermolecular interactions represent a new type of porous materials differing from those driven by covalent or coordination bonding. The intermolecular interaction-induced flexible assembly structures display unique advantages in material processing, structure stimuli response, and recycling. In this work, a two-dimensional (2D) supramolecular ionic framework (SIF) was constructed through the initial ionic interaction between the host cation and polyoxometalate polyanion and then the host-guest inclusion of the formed host ionic complex with a four-arm porphyrin guest molecule following a [2+4] type reaction. Several prepared framework monolayers bearing an orthometric grid structure constituted a nanosheet-like assembly with flexibility and exhibited processability, which provided feasibility for the further preparation of separation membranes via a simple suction procedure of their dispersed suspensions in mixed solvents. The nanofiltration based on the uniform square pores under a slightly reduced pressure successfully achieved precise separation of several types of nanoparticles and molecular clusters in wide distribution at a cutting off value as small as 2.2 nm. These results also implied the potential of the present strategy for more separations at a molecular level and very fine nanoscale.

Processing supramolecular framework for free interconvertible liquid separation

Nanoporous structures constructed by small molecular components exhibited vigorous materials potentials. While maintianing uniform porosity and functional properties, more applicable processing methods for the solid powders need to be considered and the improvement of binding interactions represents a preferable approach for structural flexibility. Here, by combining ionic interaction and host-guest inclusion, we constructed flexible supramolecular frameworks composing of inorganic polyanionic clusters, cationic organic hosts, and a bridging guest. The formed layer framework structure assemblies grew into nano-fibers and then supramolecular gels, donating highly convenient processability to porous materials. A simple spin-coating generated a new type of liquid separation membranes which showed structural stability for many liquids. The surface properties can be facilely modulated via filling a joystick liquid and then a hydrophilic/hydrophobic liquid into the porous frameworks, providing in-situ consecutive switchings for cutting liquids. This strategy extends the potential of flexible supramolecular frameworks for responsive materials in the laboratory and in industry.

Porous materials show potential in various technological fields but processing of these materials remains challenging which hampers their application. Here the authors demonstrate an organic/inorganic framework composed of a supramolecular gel as processable porous material.

Supramolecular chiroptical switches

Recent progress in chiroptical switches including on/off, amplification, and inversion of the chiral signals such as ECD and CPL in supramolecular assemblies is shown.

Incorporation of Vanadium and Molybdenum into Yttrium-Arsenotungstates Supported by Amino Acid Ligands

The preference for incorporation of molybdenum over tungsten into specific sites of a family of yttrium-arsenotungstates with amino acid ligands prompted exploration of the incorporation of other metals, affording three new vanadium-containing (V/W and V/Mo/W) analogues: K2(GlyH)10[As4(V2W2)W44Y4O160(Gly)8(H2O)12]·11Gly (1), (MBAH)9(L-NleH)3[As4(V2W2)W44Y4O160(L-Nle)8(H2O)12] (2), and (MBAH)9(L-NleH)3[As4(V2W2)Mo2W42Y4O160(L-Nle)8(H2O)12] (3) (Gly=glycine and L-Nle=l-norleucine, MBAH=4-methylbenzylammonium). These hybrid polyoxometalates all possess a tetrametallic oxo-bridged {VIV2WVI2} central core surrounded by an amino acid-ligated cyclic metal-oxo framework. X-Ray photoelectron, UV-visible reflectance, and electron paramagnetic resonance spectroscopy, together with metal analysis, confirm the incorporation of vanadium into the polyoxometalates, while single crystal X-ray diffraction analysis supports the location of the vanadium atoms in the central core.

Polyoxometalate-based room-temperature phosphorescent materials induced by anion–π interactions

A series of polyoxometalate-based host–guest materials emit strong red room-temperature phosphorescence attributed to intermolecular charge-transfer states which was caused by unorthodox anion–π interactions.

Reunderstanding the photoinduced charge transfer process of ammonium polyoxomolybdate

Protonation of 4-phenylpyridine can realize photoinduced electron transfer from the carboxyl group to 4-phenylpyridine and photochromism of ammonium polyoxomolybdate without proton transfer.

Multi-stimuli-responsive induced chirality of polyoxometalates in natural polysaccharide hydrogels

Multi-stimuli-responsive induced circular dichroism of polyoxometalates was realized in natural polysaccharide hydrogels. The extrinsic chiral factors rather than the intrinsic chirality of the polyoxometalates were dominant in κ-carrageenan hydrogel hybrids.

Co-assemblies of polydiacetylenes and metal ions for solvent sensing

We demonstrate an easy and low-cost approach for the colorimetric differentiation of organic solvents using co-assemblies of polydiacetylenes (PDAs) and metal ions. The co-assemblies were prepared by the self-assembly of amphiphilic 10,12-tricosa diynoic acid with different metal ions (Zn²⁺, Cu²⁺, Ni²⁺, Ca²⁺) and subsequent photopolymerization. Different metal ions underwent different interactions with the carboxyl groups on the side chains of poly(10,12-tricosa diynoic acid), which influenced the stimuli-responsiveness of the PDA/metal ion co-assemblies. As a result, the PDA/metal ion co-assemblies with different metal ions showed different solvatochromism. Based on this property, the co-assemblies were used as sensors to differentiate organic solvents.

Induced chirality and reversal of phosphomolybdate cluster via modulating its interaction with cyclodextrins

Direct-induced chirality of a metal–oxide cluster by cyclodextrins was realized and the reversals of the induced Cotton signals were modulated by introducing a competitive guest and/or substituting by different cyclodextrins.

Solvent Dielectricity-Modulated Helical Assembly and Morphologic Transformation of Achiral Surfactant-Inorganic Cluster Ionic Complexes

Ionic complexes comprising single/double chain cationic surfactant and Lindqvist-type polyoxomolybdate anionic cluster were used for controlled self-assembly in organic solutions. In the solvent with low dielectric constant the complexes self-assembled into flat ribbon like lamellar aggregations with an inverse bilayer substructure where the cluster located at the middle. Under the condition of increased dielectric constant, the solvent triggered the formation of helical self-assemblies, which finally transformed from helical ribbons to the flower-like assemblies due to the bilayer becoming excessively twisted. The self-assembled morphology and the substructure were characterized by SEM, TEM, and XRD. The solvent dielectricity-controlled morphologic transformations modulated by the variation of electrostatic interactions between organic cations and inorganic polyanions were demonstrated by ¹H NMR and IR spectra. The strategy in this work represents an effective route in targeting the chirality-directed functionalization of inorganic clusters by combining controllable and helical assemblies of achiral polyoxometalate complexes in one system.

Ionic Complexes of Metal Oxide Clusters for Versatile Self-Assemblies

The combination of rational design of building components and suitable utilization of driving force affords spontaneous molecular assemblies with well-defined nanostructure and morphology over multiple length scales. The serious challenges in constructing assemblies with structural advantages for the realization of functions programmed into the building components usually lie ahead since the process that occurs does not always follow the expected roadmap in the absence of external intervention. Thus, prefabricated intermediates that help in governing the target self-assemblies are developed into a type of unique building blocks. Metal oxide cluster polyanions are considered as a type of molecular nanoclusters with size scale and structural morphology similar to those of many known inorganic particles and clusters but possess distinctive characteristics. Following the understanding of these clusters in self-assembly and the rationalization of their most efficient design strategy and approach, the obtained fundamental principles can also be applied in common nanoparticle- and cluster-based systems. On the other hand, the deliberate synergy offered by organic countercations that support the self-assembly of these clusters greatly expands the opportunity for the functionalization of complex building units via control of multiple interactions. The ionic combination of the inorganic clusters with hydrophilicity and the cationic organic component with hydrophobicity leads to discrete properties of the complexes. Significantly, the core-shell structure with rigid-flexible features and amphiphilicity will pave the way for hierarchical self-assemblies of the obtained complexes, while the intrinsic characteristics of the metal oxide clusters can be modulated through external physicochemical stimuli. Within this context, over the past decade we have extensively explored the ionic combination of inorganic polyanionic clusters with cationic organic amphiphiles and devoted our efforts to establishing the general rules and structure-property relationships of the formed complexes for constructing self-assemblies at the interface, in solution, and in solid matrixes. Specific interest has been focused on the functional synergy deriving from the incompatible components in highly organized self-assemblies. In this Account, we describe the recent progress on the ionic complexation of polyoxometalate clusters with cationic amphiphiles and the construction of diverse self-assembled nanostructures. First, the fundamental structural characteristics and molecular geometries of the prepared complexes are analyzed. The construction principle and diversity of the self-assembly based on the complexes and the smart stimuli response are then discussed, subject to the adjustment of various non-covalent interactions occurring in the assemblies. Subsequently, we enumerate the functional applications of the ionic complexes assembling into organic, inorganic, and even biological matrixes. The inspiration from the construction of ionic complexation and self-assembly in this Account provides vivid profiles for the design of hybrid materials involving nanoclusters and/or nanoparticles with rich potentials in addition to polyoxometalate chemistry.

A survey of the different roles of polyoxometalates in their interaction with amino acids, peptides and proteins

This perspective provides a comprehensive description of the different roles of POMs in their interaction with relevant biological molecules.

Switchable Materials for Smart Windows

This article reviews the basic principles of and recent developments in electrochromic, photochromic, and thermochromic materials for applications in smart windows. Compared with current static windows, smart windows can dynamically modulate the transmittance of solar irradiation based on weather conditions and personal preferences, thus simultaneously improving building energy efficiency and indoor human comfort. Although some smart windows are commercially available, their widespread implementation has not yet been realized. Recent advances in nanostructured materials provide new opportunities for next-generation smart window technology owing to their unique structure-property relations. Nanomaterials can provide enhanced coloration efficiency, faster switching kinetics, and longer lifetime. In addition, their compatibility with solution processing enables low-cost and high-throughput fabrication. This review also discusses the importance of dual-band modulation of visible and near-infrared (NIR) light, as nearly 50% of solar energy lies in the NIR region. Some latest results show that solution-processable nanostructured systems can selectively modulate the NIR light without affecting the visible transmittance, thus reducing energy consumption by air conditioning, heating, and artificial lighting.

Supermolecular assembly of polyoxoanion and metal–organic cationic units towards a model for core–shell nanostructures

Two novel core–shell-like molecular composites [NiL₃]₄[HV^IV₁₂V^V₆O₄₂(PO₄)] and [NiL₂]₄[HV^IV₁₂V^V₆O₄₂(PO₄)] were designed and synthesized, which exhibited electrocatalytic activity for the reduction of H₂O₂ and oxidation of NO₂⁻.

Controlled chiral electrochromism of polyoxometalates incorporated in supramolecular complexes

Switchable induced chiral electrochromism of achiral polyoxometalates in a ternary supramolecular system, integrated by host–guest recognition and electrostatic interaction, is realized by controlling the electrochemical redox process in aqueous solution.

Counterion-dominating chirality transfer between chiral and achiral polyoxometalates

The chirality transfer between inorganic polyoxometalate clusters is realized by the suitable mediation of counterions through multi-interactions in aqueous solution.

Chiral polyoxomolybdate-based hybrid compounds obtained by spontaneous resolution: syntheses, structures and non-linear optical properties

By spontaneous resolution, two chiral hybrid 2D architectures [MMo₆O₂₁(glycine)₃]²⁻ (M = Te 1, Se 2) were obtained, which show an SHG efficiency of about 3.5 and 3.7 × KDP.

Enhanced Visible Photovoltaic Response of TiO₂ Thin Film with an All-Inorganic Donor-Acceptor Type Polyoxometalate

In the field of material chemistry, it is of great significance to develop abundant and sustainable materials for solar energy harvesting and management. Herein, after evaluating the energy band characteristics of 13 kinds of polyoxometalates (POMs), the trisubstituted POM compound K6H4[α-SiW9O37Co3(H2O)3]·17H2O (SiW9Co3) was first studied due to its relatively smaller band gap (2.23 eV) and higher lowest unoccupied molecular orbital (LUMO) level (-0.63 V vs NHE). Additionally, the preliminary computational modeling indicated that SiW9Co3 exhibited the donor-acceptor (D-A) structure, in which the cobalt oxygen clusters and tungsten skeletons act as the electron donor and electron acceptor, respectively. By employing SiW9Co3 to modify the TiO2 film, the visible photovoltaic and photocurrent response were both enhanced, and the light-induced photocurrent at 420 nm was improved by 7.1 times. Moreover, the highly dispersive and small sized SiW9Co3 nanoclusters loading on TiO2 were successfully achieved by fabricating the nanocomposite film of {TiO2/SiW9Co3}3 with the layer-by-layer method, which can result in the photovoltaic performance enhancement of dye-sensitized solar cells (DSSCs), of which the overall power conversion efficiency was improved by 25.6% from 6.79% to 8.53% through the synergistic effect of POMs and Ru-complex.

Solvent-mediated gel formation, hierarchical structures, and rheological properties of organogels

We report the formation of solvent-mediated gels as well as their hierarchical structures and rheological properties. The gelator used is a hybrid with a molecular structure of cholesterol-polyoxometalate-cholesterol, in which the cholesterol dissolves well in toluene and N,N-dimethylformamide (DMF), whereas the polyoxometalate cluster dissolves only in DMF. These solubility differences enable the gelator to form thermally reversible supramolecular organogels by mixing solvents of toluene and DMF when the volume fraction, ftol, of toluene is larger than 85.7 v/v%. We found a V-shaped correlation between the gelation times, tgel and ftol: tgel decreases from 1300 min to 2 min when ftol increases from 85.7 v/v% to 90.0 v/v%. It then increases from 2 min to 5800 min when ftol further increases from 90.0 v/v% to 100.0 v/v%. We observed ribbon-like self-assembled structures in the gels as well as a structural evolution from rigid and straight ribbons to twistable ones from ftol=85.7 v/v% to ftol=100.0 v/v%. These ribbons constitute two three-dimensional (3D) gel networks: one is constructed via physical connection of the rigid and straight ribbon, and the other is built up from ribbons splitting and intertwining. The latter has a better 3D gel network that offers improved rheological properties. Fundamentally, this solvent-mediated approach regulates the balance between solubility and insolubility of this gelator in the mixing solvents. It also provides a new method for the preparation of organogels.

Temperature-induced racemic compounds and chiral conglomerates based on polyoxometalates and lanthanides: syntheses, structures and catalytic properties

Four new species, originated from [Co₂Mo₁₀H₄O₃₈]⁶⁻ and lanthanides by adjusting the reaction temperature, are reported, which act as Lewis acid–base catalysts toward the cyanosilylation reaction.

Noncovalent fabrication and tunable fusion of block copolymer-giant polyoxometalate hybrid micelles

The block copolymers (BCs), as structure-directing agents, co-assembling with nanoscale inorganic additives is an important route to fabricate nanostructured hybrid materials. In this work, we present a facile approach to fabricate hybrid micelles composed of BCs and polyoxometalates (POMs), in which the POM clusters are premodified with the groups that can specifically interact with a certain BC block. A representative POM (NH4)42[Mo(132)O(372)(CH(3)COO)(30)(H2O)72] (Mo(132)) is chosen as the example and encapsulated with cationic molecules containing carboxyphenyl groups through electrostatic interactions, and then the resulting hybrid complex can further co-assemble with poly(styrene-block-4-vinylpyridine) (PS-b-P4VP) through hydrogen bonding with the pyridine groups, which leads to the formation of hybrid micelles and the localization of Mo(132) in the micelle cores. The micelles exhibit a high stability despite time and dilution. Furthermore, the fusion of the micelles can be readily adjusted by varying the length of PS blocks, which is promising to be used in constructing polymer-POM hybrid materials with discrete or continuous hybrid domains. This work is based on the electrostatic premodification of POMs and thus its concept is generally suitable for the whole anionic POM system, which may create a large class of BC-POM nanocomposites with tunable structures.