Electrostatically Dominated Pre-Organization in Cyclodextrin Metal-Organic Frameworks.

Electrostatic interactions between oppositely charged entities play a key role in pre-organizing substrates and stabilizing transition states of reactions in enzymes. The use of electrostatic interactions to pre-organize ions in nanoconfined pores, however, has not been investigated to its full potential. Herein, we describe how carboxylate anions can be pre-organized at the behest of their electrostatic interactions with K cations in nanoconfined tunnels present in γ-cyclodextrin metal-organic frameworks, i.

Balancing volumetric and gravimetric capacity for hydrogen in supramolecular crystals.

The storage of hydrogen is key to its applications. Developing adsorbent materials with high volumetric and gravimetric storage capacities, both of which are essential for the efficient use of hydrogen as a fuel, is challenging. Here we report a controlled catenation strategy in hydrogen-bonded organic frameworks (RP-H100 and RP-H101) that depends on multiple hydrogen bonds to guide catenation in a point-contact manner, resulting in high volumetric and gravimetric surface areas, robustness and ideal pore diameters (~1.

A Geometrically Flexible Three-Dimensional Nanocarbon.

The development of architecturally unique molecular nanocarbons by bottom-up organic synthesis is essential for accessing functional organic materials awaiting technological developments in fields such as energy, electronics, and biomedicine. Herein, we describe the design and synthesis of a triptycene-based three-dimensional (3D) nanocarbon, , with geometrical flexibility on account of its three peripheral π-panels being capable of interconverting between two curved conformations. An effective through-space electronic communication among the three π-panels of has been observed in its monocationic radical form, which exhibits an extensively delocalized spin density over the entire 3D π-system as revealed by electron paramagnetic resonance and UV-vis-NIR spectroscopies.

Metal-Assisted Carbohydrate Assembly.

The sequence-controlled assembly of nucleic acids and amino acids into well-defined superstructures constitutes one of the most revolutionary technologies in modern science. The elaboration of such superstructures from carbohydrates, however, remains elusive and largely unexplored on account of their intrinsic constitutional and configurational complexity, not to mention their inherent conformational flexibility. Here, we report the bottom-up assembly of two classes of hierarchical superstructures that are formed from a highly flexible cyclo-oligosaccharide─namely, cyclofructan-6 (CF-6).

Tailoring Dynamic Hydrogels by Controlling Associative Exchange Rates.

Dithioalkylidenes are a newly-developed class of conjugate acceptors that undergo thiol exchange via an associative mechanism, enabling decoupling of key material properties for sustainability, biomedical, and sensing applications. Here, we show that the exchange rate is highly sensitive to the structure of the acceptor and tunable over four orders of magnitude in aqueous environments. Cyclic acceptors exchange rapidly, from 0.

Photosalience and Thermal Phase Transitions of Azobenzene- and Crown Ether-Based Complexes in Polymorphic Crystals.

Stimuli-responsive molecular crystals have attracted considerable attention as promising smart materials with applications in various fields such as sensing, actuation, and optoelectronics. Understanding the structure-mechanical property relationships, however, remains largely unexplored when it comes to functionalizing these organic crystals. Here, we report three polymorphic crystals (, , and ) formed by the non-threaded complexation of a dibenzo[18]crown-6 (DB18C6) ether ring and an azobenzene-based ammonium cation, each exhibiting distinct thermal phase transitions, photoinduced deformations, and mechanical behavior.

Spin-Frustrated Trisradical Trication of PrismCage.

Organic trisradicals featuring threefold symmetry have attracted significant interest because of their unique magnetic properties associated with spin frustration. Herein, we describe the synthesis and characterization of a triangular prism-shaped organic cage for which we have coined the name and its trisradical trication─. is composed of three 4,4'-bipyridinium dications and two 1,3,5-phenylene units bridged by six methylene groups.

Exciplex Emission and Förster Resonance Energy Transfer in Polycyclic Aromatic Hydrocarbon-Based Bischromophoric Cyclophanes and Homo[2]catenanes.

Energy transfer and exciplex emission are not only crucial photophysical processes in many living organisms but also important for the development of smart photonic materials. We report, herein, the rationally designed synthesis and characterization of two highly charged bischromophoric homo[2]catenanes and one cyclophane incorporating a combination of polycyclic aromatic hydrocarbons, i.e.

Crystalline Arrays of Copper Porphyrin Qubits Based on Ion-Paired Frameworks.

Molecular electronic spin qubits have great potential for use in quantum information science applications because their structure can be rationally tuned using synthetic chemistry. Their integration into a new class of materials, ion-paired frameworks, allows for the formation of ordered arrays of these molecular spin qubits. Three ion-paired frameworks with varying densities of paramagnetic Cu(II) porphyrins were isolated as micron-sized crystals suitable for characterization by single-crystal X-ray diffraction.

Divinylanthracene-Containing Tetracationic Organic Cyclophane with Near-Infrared Photoluminescence.

Near-infrared (NIR) light is known to have outstanding optical penetration in biological tissues and to be non-invasive to cells compared with visible light. These characteristics make NIR-specific light optimal for numerous biological applications, such as the sensing of biomolecules or in theranostics. Over the years, significant progress has been achieved in the synthesis of fluorescent cyclophanes for sensing, bioimaging, and making optoelectronic materials.

High-efficiency gold recovery by additive-induced supramolecular polymerization of β-cyclodextrin.

Developing an eco-friendly, efficient, and highly selective gold-recovery technology is urgently needed in order to maintain sustainable environments and improve the utilization of resources. Here we report an additive-induced gold recovery paradigm based on precisely controlling the reciprocal transformation and instantaneous assembly of the second-sphere coordinated adducts formed between β-cyclodextrin and tetrabromoaurate anions. The additives initiate a rapid assembly process by co-occupying the binding cavity of β-cyclodextrin along with the tetrabromoaurate anions, leading to the formation of supramolecular polymers that precipitate from aqueous solutions as cocrystals.

Color-Tunable Upconversion-Emission Switch Based on Cocrystal-to-Cocrystal Transformation.

Cocrystal engineering, involving the assembly of two or more components into a highly ordered solid-state superstructure, has emerged as a popular strategy for tuning the photophysical properties of crystalline materials. The reversible co-assembly and disassembly of multicomponent cocrystals and their reciprocal transformation in the solid state remain challenging objectives. Herein, we report a color-tunable upconversion-emission switch based on the interconversion between two cocrystals.

An electric molecular motor.

Macroscopic electric motors continue to have a large impact on almost every aspect of modern society. Consequently, the effort towards developing molecular motors that can be driven by electricity could not be more timely. Here we describe an electric molecular motor based on a [3]catenane, in which two cyclobis(paraquat-p-phenylene) (CBPQT) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop.

Mechanical Bond-Assisted Full-Spectrum Investigation of Radical Interactions.

Molecular recognition, based on noncovalent bonding interactions, plays a central role in directing supramolecular phenomena in both chemical and biological environments. The identification and investigation of weakly associated recognition motifs, however, remains a major challenge, especially when the motifs are interlinked with and obscured by other robust binding modes in complicated systems. For example, although the host-guest recognition between the radical cations of both cyclobis(paraquat--phenylene) (CBPQT) and 4,4'-bipyridinium (BIPY) salts has been thoroughly investigated, the question of whether other binding modes exist between these two positively charged entities is the subject of some debate because of the complexity and dynamic nature of this supramolecular system.

Alkoxy-Substituted Quadrupolar Fluorescent Dyes.

Polar and polarizable π-conjugated organic molecules containing push-pull chromophores have been investigated extensively in the past. Identifying unique backbones and building blocks for fluorescent dyes is a timely exercise. Here, we report the synthesis and characterization of a series of fluorescent dyes containing quadrupolar A-D-A constitutions (where A = acceptor and D = donor), which exhibit fluorescence emission at a variety of different wavelengths.

Helically Chiral Hybrid Cyclodextrin Metal-Organic Framework Exhibiting Circularly Polarized Luminescence.

Three achiral polycyclic aromatic fluorophores─namely, 1-pyrenecarboxylic acid, 9-anthracenecarboxylic acid, and perylene-3,9-dicarboxylic acid─were chosen based on their desired properties before being incorporated into the construction of a K-carrying gamma-cyclodextrin (γ-CD)-based metal-organic framework (CD-MOF-1) and γ-CD-containing hybrid frameworks (CD-HFs). Among these fluorophores, only the pyrene-carrying one shows significant noncovalent bonding interactions with γ-CD in solution. This fluorophore is encapsulated in a CD-HF with a trigonal superstructure instead of the common cubic CD-MOF-1 found in the case of the other two fluorophores.

Synthesis, characterization, X-ray and electronic structures of diethyl ether and 1,2-dimethoxyethane adducts of molybdenum(IV) chloride and tungsten(IV) chloride.

The bis(diethyl ether) and 1,2-dimethoxyethane (dme) adducts of molybdenum(IV) chloride and tungsten(IV) chloride are valuable starting materials for a variety of synthetic inorganic and organometallic reactions. Despite the broad utility and extensive use of these 6-coordinate complexes, their syntheses remain unoptimized, and their characterization incomplete after more than three decades. While exploring the ligand exchange behaviour of -MoCl(OEt), we obtained single crystals of this red-orange complex and subsequently compared its structural parameters with those of the recently reported -WCl(OEt).

Electron-catalysed molecular recognition.

Molecular recognition and supramolecular assembly cover a broad spectrum of non-covalently orchestrated phenomena between molecules. Catalysis of such processes, however, unlike that for the formation of covalent bonds, is limited to approaches that rely on sophisticated catalyst design. Here we establish a simple and versatile strategy to facilitate molecular recognition by extending electron catalysis, which is widely applied in synthetic covalent chemistry, into the realm of supramolecular non-covalent chemistry.

A contorted nanographene shelter.

Nanographenes have kindled considerable interest in the fields of materials science and supramolecular chemistry as a result of their unique self-assembling and optoelectronic properties. Encapsulating the contorted nanographenes inside artificial receptors, however, remains challenging. Herein, we report the design and synthesis of a trigonal prismatic hexacationic cage, which has a large cavity and adopts a relatively flexible conformation.

Radically Enhanced Dual Recognition.

Complexation between a viologen radical cation (V ) and cyclobis(paraquat-p-phenylene) diradical dication (CBPQT ) has been investigated and utilized extensively in the construction of mechanically interlocked molecules (MIMs) and artificial molecular machines (AMMs). The selective recognition of a pair of V using radical-pairing interactions, however, remains a formidable challenge. Herein, we report the efficient encapsulation of two methyl viologen radical cations (MV ) in a size-matched bisradical dicationic host - namely, cyclobis(paraquat-2,6-naphthalene) , i.

Selective Photodimerization in a Cyclodextrin Metal-Organic Framework.

For the most part, enzymes contain one active site wherein they catalyze in a serial manner chemical reactions between substrates both efficiently and rapidly. Imagine if a situation could be created within a chiral porous crystal containing trillions of active sites where substrates can reside in vast numbers before being converted in parallel into products. Here, we report how it is possible to incorporate 1-anthracenecarboxylate () as a substrate into a γ-cyclodextrin-containing metal-organic framework (), where the metals are K cations, prior to carrying out [4+4] photodimerizations between pairs of substrate molecules, affording selectively one of four possible regioisomers.

Selective Separation of Hexachloroplatinate(IV) Dianions Based on Exo-Binding with Cucurbit[6]uril.

The recognition and separation of anions attracts attention from chemists, materials scientists, and engineers. Employing exo-binding of artificial macrocycles to selectively recognize anions remains a challenge in supramolecular chemistry. We report the instantaneous co-crystallization and concomitant co-precipitation between [PtCl ] dianions and cucurbit[6]uril, which relies on the selective recognition of these dianions through noncovalent bonding interactions on the outer surface of cucurbit[6]uril.

Systematic Merging of Nonfullerene Acceptor π-Extension and Tetrafluorination Strategies Affords Polymer Solar Cells with >16% Efficiency.

The end-capping group (EG) is the essential electron-withdrawing component of nonfullerene acceptors (NFAs) in bulk heterojunction (BHJ) organic solar cells (OSCs). To systematically probe the impact of two frequent EG functionalization strategies, π-extension and halogenation, in A-DAD-A type NFAs, we synthesized and characterized four such NFAs: , , , and . To assess the relative importance of these strategies, we contrast these NFAs with the baseline acceptors, and .