Showing papers by "J. Fraser Stoddart published in 2019"
TL;DR: A conductive 2D metal-organic framework involving intercalation pseudocapacitance mechanism for enhanced rate capability and key insights into high-performance, 2D conductive MOF designs for battery electrodes are provided.
Abstract: Currently, there is considerable interest in developing advanced rechargeable batteries that boast efficient distribution of electricity and economic feasibility for use in large-scale energy storage systems. Rechargeable aqueous zinc batteries are promising alternatives to lithium-ion batteries in terms of rate performance, cost, and safety. In this investigation, we employ Cu3(HHTP)2, a two-dimensional (2D) conductive metal-organic framework (MOF) with large one-dimensional channels, as a zinc battery cathode. Owing to its unique structure, hydrated Zn2+ ions which are inserted directly into the host structure, Cu3(HHTP)2, allow high diffusion rate and low interfacial resistance which enable the Cu3(HHTP)2 cathode to follow the intercalation pseudocapacitance mechanism. Cu3(HHTP)2 exhibits a high reversible capacity of 228 mAh g−1 at 50 mA g−1. At a high current density of 4000 mA g−1 (~18 C), 75.0% of the initial capacity is maintained after 500 cycles. These results provide key insights into high-performance, 2D conductive MOF designs for battery electrodes. Aqueous zinc batteries are promising candidates for large scale energy storage systems but development of the cathode material remains a challenge. Here, the authors show a conductive 2D metal-organic framework involving intercalation pseudocapacitance mechanism for enhanced rate capability.
305 citations
01 Mar 2019
TL;DR: In this article, the authors present the principles that have been developed for fabricating reliable molecular junctions and tuning their intrinsic properties from an engineering perspective, along with the open challenges in the field.
Abstract: Over the past two decades, various techniques for fabricating nano-gapped electrodes have emerged, promoting rapid development in the field of single-molecule electronics, on both the experimental and theoretical sides. To investigate intrinsic quantum phenomena and achieve desired functionalities, it is important to fully understand the charge transport characteristics of single-molecule devices. In this Review, we present the principles that have been developed for fabricating reliable molecular junctions and tuning their intrinsic properties from an engineering perspective. Through holistic consideration of the device structure, we divide single-molecule junctions into three intercorrelated components: the electrode, the contact (spacer–linker) interface and the molecular backbone or functional centre. We systematically discuss the selection of the electrode material and the design of the molecular components from the point of view of the materials, the interface and molecular engineering. The influence of the properties of these elements on the molecule–electrode interface coupling and on the relative energy gap between the Fermi level of the electrode and the orbital energy levels of the molecule, which directly influence the charge transport behaviour of single-molecule devices, is also a focus of our analysis. On the basis of these considerations, we examine various functionalities demonstrated in molecular junctions through molecular design and engineering. In this Review, the principles developed for fabricating reliable molecular junctions and tuning their intrinsic properties are examined from the point of view of the electrode, the interface and molecular engineering. The various functionalities demonstrated in molecular junctions through molecular design are discussed, along with the open challenges in the field.
299 citations
TL;DR: In this article, the authors demonstrate a strategy for designing active materials for rechargeable aluminium batteries, which involves the use of redox-active triangular phenanthrenequinone-based macrocycles, which form layered superstructures resulting in the reversible insertion and extraction of a cationic aluminium complex.
Abstract: Since aluminium is one of the most widely available elements in Earth’s crust, developing rechargeable aluminium batteries offers an ideal opportunity to deliver cells with high energy-to-price ratios. Nevertheless, finding appropriate host electrodes for insertion of aluminium (complex) ions remains a fundamental challenge. Here, we demonstrate a strategy for designing active materials for rechargeable aluminium batteries. This strategy entails the use of redox-active triangular phenanthrenequinone-based macrocycles, which form layered superstructures resulting in the reversible insertion and extraction of a cationic aluminium complex. This architecture exhibits an outstanding electrochemical performance with a reversible capacity of 110 mA h g–1 along with a superior cyclability of up to 5,000 cycles. Furthermore, electrodes composed of these macrocycles blended with graphite flakes result in higher specific capacity, electronic conductivity and areal loading. These findings constitute a major advance in the design of rechargeable aluminium batteries and represent a good starting point for addressing affordable large-scale energy storage. The development of aluminium batteries relies heavily on the discovery of cathode materials that can reversibly insert Al-containing ions. Here the authors show that phenanthrenequinone-based compounds can take up the cationic aluminium complex, leading to promising aluminium batteries.
226 citations
TL;DR: A photoluminescent supramolecular assembly, prepared in two stages, is described that displays in situ photo-tuning broad-spectrum output and provides an opportunity to design and construct more advanced anti-counterfeiting materials as well as visual display instruments.
Abstract: Constructing multicolor photoluminescence materials that allow for the integration of suitable external stimuli in order to control luminescence color conversions is a challenging objective. Multicolor luminescent output that is regulated in an in situ photo-controlled manner is not a common phenomenon. Herein, a photoluminescent supramolecular assembly, prepared in two stages, is described that displays in situ photo-tuning broad-spectrum output. Benefiting from the reversible photo-switched constitutional interconversion of diarylethenes, the fluorescence of a guest molecule, styrylpyridinium-modified diarylethene, can be switched on/off by alternating ultraviolet and visible light irradiation. Upon complexation of this guest with a host, cucurbit[8]uril, the fluorescence intensity of the resulting binary supramolecular nanofiber shows a drastic enhancement when compared with that of the free guest, which can also be quenched and recovered reversibly by light irradiation. Significantly, such cationic su...
144 citations
TL;DR: A series of acs-MOFs (NU-1500) based on trivalent trinuclear metal clusters and a rigid trigonal prismatic ligand courtesy of reticular chemistry are reported, which can be activated directly from water and displays an impressive water vapor uptake with small hysteresis.
Abstract: Metal–organic frameworks (MOFs) based on edge-transitive 6-c acs nets are well-developed and can be synthesized from trinuclear metal clusters and ditopic ligands, i.e., MOF-235 and MIL-88. The rational design of noncatenated acs-MOFs by symmetry-matching between trigonal prismatic organic ligands and trinuclear clusters, however, remains a great challenge. Herein, we report a series of acs-MOFs (NU-1500) based on trivalent trinuclear metal (Fe3+, Cr3+, and Sc3+) clusters and a rigid trigonal prismatic ligand courtesy of reticular chemistry. The highly porous and hydrolytically stable NU-1500-Cr can be activated directly from water and displays an impressive water vapor uptake with small hysteresis.
123 citations
TL;DR: Synthetic control over the framework interpenetration could serve as a new strategy to construct complex supramolecular architectures from simple organic building blocks.
Abstract: We describe an example of "interpenetration isomerism" in three-dimensional hydrogen-bonded organic frameworks. By exploiting the crystallization conditions for a peripherally extended triptycene H6 PET, we can modulate the interpenetration of the assembled frameworks, yielding a two-fold interpenetrated structure PETHOF-1 and a five-fold interpenetrated structure PETHOF-2 as interpenetration isomers. In PETHOF-1, two individual nets are related by inversion symmetry and form an interwoven topology with a large guest-accessible volume of about 80 %. In PETHOF-2, five individual nets are related by translational symmetry and are stacked in an alternating fashion. The activated materials show permanent porosity with Brunauer-Emmett-Teller surface areas exceeding 1100 m2 g-1 . Synthetic control over the framework interpenetration could serve as a new strategy to construct complex supramolecular architectures from simple organic building blocks.
82 citations
01 May 2019
TL;DR: This review covers some of the most recent studies demonstrating the widespread interest in MIMs by scientists pursuing the ultimate goal of designing functional molecular machines that surpass their natural analogs or exhibit unprecedented properties.
Abstract: Mechanically interlocked molecules (MIMs), such as rotaxanes, catenanes, and molecular knots, have attracted significant interest because of their unique properties originating from their mechanically bonded components. Recently, MIMs have been employed in increasingly diverse architectures thanks to the tools of rational molecular design and the ability to incorporate functions in a precise manner. Here, we discuss advances in MIM synthesis, the fundamental understanding of their working processes, and applications exploiting their singular behavior. This review covers some of the most recent studies demonstrating the widespread interest in MIMs by scientists pursuing the ultimate goal of designing functional molecular machines that surpass their natural analogs or exhibit unprecedented properties.
79 citations
TL;DR: The design and synthesis of two chiral isosceles triangles, wherein one PDI fluorophore and two pyromellitic diimide or naphthalene diimides units are arranged in a rigid cyclic triangular geometry are reported on.
Abstract: The development of rigid covalent chiroptical organic materials, with multiple, readily available redox states, which exhibit high photoluminescence, is of particular importance in relation to both organic electronics and photonics. The chemically stable, thermally robust, and redox-active perylene diimide (PDI) fluorophores have received ever-increasing attention owing to their excellent fluorescence quantum yields in solution. Planar PDI derivatives, however, generally suffer from aggregation-caused emission quenching in the solid state. Herein, we report on the design and synthesis of two chiral isosceles triangles, wherein one PDI fluorophore and two pyromellitic diimide (PMDI) or naphthalene diimide (NDI) units are arranged in a rigid cyclic triangular geometry. The optical, electronic, and magnetic properties of the rigid isosceles triangles are fully characterized by a combination of optical spectroscopies, X-ray diffraction (XRD), cyclic voltammetry, and computational modeling techniques. Single-c...
78 citations
TL;DR: It transpires that when the photoactive oligo( p-phenylenevinylene) pyridinium unit is incorporated in a macrocyclic scaffold, its reversibility is dramatically improved, and the configurations of the cyclophane can go back and forth between ( EE)- and ( EZ)-isomers upon alternating blue light irradiation and heating.
Abstract: Designing macrocycles with appropriate molecular recognition features that allow for the integration of suitable external stimuli to control host-guest processes is a challenging endeavor which enables molecular containers to solubilize, stabilize, and separate chemical entities in an externally controllable manner. Herein, we introduce photo- and thermal-responsive elements into a semi-rigid tetracationic cyclophane, OPVEx2Box4+, that is composed of oligo( p-phenylenevinylene) pyridinium units and the biphenylene-bridged 4,4-bipyridinium extended viologens and adopts a rectangle-like geometry. It transpires that when the photoactive oligo( p-phenylenevinylene) pyridinium unit is incorporated in a macrocyclic scaffold, its reversibility is dramatically improved, and the configurations of the cyclophane can go back and forth between ( EE)- and ( EZ)-isomers upon alternating blue light irradiation and heating. When the macrocycle is found in its ( EE)-configuration, it is capable of binding various π-electron-rich guests-e.g., anthracene and perylene-as well as π-electron-deficient guests-e.g., 9,10-anthraquinone and 5,12-tetracenequinone-through charge-transfer and van der Waals interactions. When irradiated with blue light, the ( EE)-isomer of the cyclophane can be transformed successfully to the ( EZ)-isomer, resulting in the switching off of the binding affinity for guest molecules, which are bound once again upon heating. The use of light and heat as external stimuli to control host-guest interactions involving a multi-responsive host and various guests provides us with a new opportunity to design and construct more-advanced molecular switches and machines.
55 citations
TL;DR: This work reports the ligand-directed reticular syntheses and isoreticular expansion of a series of Zr-MOFs with the edge-transitive alb net from 12-connected hexagonal-prismatic Zr6 nodes and 6-connected trigonal- prismatic linkers that exhibit remarkable activities toward the destruction of a nerve agent and a nerveAgent simulant.
Abstract: Zirconium-based metal–organic frameworks (Zr-MOFs) based on edge-transitive nets such as fcu, spn, she, csq, and ftw with diverse potential applications have been widely reported. Zr-MOFs based on ...
52 citations
TL;DR: The approach of exploring the 3D topology of 2D tessellations of a naphthalene diimide-based molecular triangle (NDI-Δ) reveals that the 2D molecular arrangement is sensitive to the identity of the solvent and solute concentrations.
Abstract: Tessellation of organic polygons though [π···π] and charge-transfer (CT) interactions offers a unique opportunity to construct supramolecular organic electronic materials with 2D topologies. Our approach to exploring the 3D topology of 2D tessellations of a naphthalene diimide-based molecular triangle (NDI-Δ) reveals that the 2D molecular arrangement is sensitive to the identity of the solvent and solute concentrations. Utilization of nonhalogenated solvents, combined with careful tailoring of the concentrations, results in NDI-Δ self-assembling though [π···π] interactions into 2D honeycomb triangular and hexagonal tiling patterns. Cocrystallization of NDI-Δ with tetrathiafulvalene (TTF) leads systematically to the formation of 2D tessellations as a result of superstructure-directing CT interactions. Different solvents lead to different packing arrangements. Using MeCN, CHCl3, and CH2Cl2, we identified three sets of cocrystals, namely CT-A, CT-B, and CT-C, respectively. Solvent modulation plays a critical role in controlling not only the NDI-Δ:TTF stoichiometric ratios and the molecular arrangements in the crystal superstructures, but also prevents the inclusion of TTF guests inside the cavities of NDI-Δ. Confinement of TTF inside the NDI-Δ cavities in the CT-A superstructure enhances the CT character with the observation of a broad absorption band in the NIR region. In the CT-B superstructure, the CHCl3 lattice molecules establish a set of [Cl···Cl] and [Cl···S] intermolecular interactions, leading to the formation of a hexagonal grid of solvent in which NDI-Δ forms a triangular grid. In the CT-C superstructure, three TTF molecules self-assemble, forming a supramolecular isosceles triangle TTF-Δ, which tiles in a plane alongside the NDI-Δ, producing a 3 + 3 honeycomb tiling pattern of the two different polygons. Solid-state spectroscopic investigations on CT-C revealed the existence of an absorption band at 2500 nm, which on the basis of TDDFT calculations, was attributed to the mixed-valence character between two TTF•+ radical cations and one neutral TTF molecule.
TL;DR: A box-like synthetic receptor is appealed to which binds a photosensitizer, 5,15-diphenylporphyrin (DPP) to provide photoprotection by regulating light energy and modulates the phototoxicity of DPP by trapping it in its cavity and releasing it when required.
Abstract: Prompted by a knowledge of the photoprotective mechanism operating in photosystem supercomplexes and bacterial antenna complexes by pigment binding proteins, we have appealed to a boxlike synthetic receptor (ExBox·4Cl) that binds a photosensitizer, 5,15-diphenylporphyrin (DPP), to provide photoprotection by regulating light energy. The hydrophilic ExBox4+ renders DPP soluble in water and modulates the phototoxicity of DPP by trapping it in its cavity and releasing it when required. While trapping removes access to the DPP triplet state, a pH-dependent release of diprotonated DPP (DPPH22+) restores the triplet deactivation pathway, thereby activating its ability to generate reactive oxygen species. We have employed the ExBox4+-bound DPP complex (ExBox4+⊃DPP) for the safe delivery of DPP into the lysosomes of cancer cells, imaging the cells by utilizing the fluorescence of the released DPPH22+ and regulating photodynamic therapy to kill cancer cells with high efficiency.
TL;DR: The preparation and characterization of artificial allomelanin nanoparticles (AMNPs) are reported via oxidative oligomerization of 1,8-dihydroxynaphthalene (1-8-DHN) and it is demonstrated that they are radical scavengers.
Abstract: Allomelanin is a type of nitrogen-free melanin most commonly found in fungi. Its existence enhances resistance of the organisms to environmental damage and helps fungi survive harsh radiation conditions such as those found on spacecraft and inside contaminated nuclear power plants. We report the preparation and characterization of artificial allomelanin nanoparticles (AMNPs) via oxidative oligomerization of 1,8-dihydroxynaphthalene (1,8-DHN). We describe the resulting morphological and size control of AMNPs and demonstrate that they are radical scavengers. Finally, we show that AMNPs are taken up by neonatal human epidermal keratinocytes and packaged into perinuclear caps where they quench reactive oxygen species generated following UV exposure.
TL;DR: A molecular dual pump consisting of two individual AMPs linked in a head-to-tail fashion, wherein a single ring is pumped, in a linear manner, on and off a dumbbell involving a [2]rotaxane intermediate by exploiting the redox properties of the two pumps.
Abstract: Artificial molecular machines (AMMs) built from mechanically interlocked molecules (MIMs) can use energy ratchets to control the unidirectional motion of their component parts. These energy ratchet...
TL;DR: In the solid-state, the TTF-cyclophane co-crystals are paramagnetic and display dual intra- and intermolecular CT behavior at ~470 and ~1000 nm, respectively, offering multi-responsive materials with potential pathways for the electron transport.
Abstract: A series of donor-acceptor (D-A) naphthalene-viologen-based cyclophanes of different shapes, sizes, and symmetries have been synthesized and characterized. Solution optical studies on these cyclophanes reveal the existence of photoinduced intramolecular charge transfer (CT) at 465 nm from naphthalene (D) to viologen (A) units, resulting in a conformational change in the viologen units and the emergence of an emission at 540 nm. The D-A cyclophanes with box-like and hexagon-like shapes offer an opportunity to control the arrangement within 2D layers where D-A interactions direct the superstructures. While a box-like 2,6-disubstituted naphthalene-based tetracationic cyclophane does not form square tiling patterns, a truncated hexagon-like congener self-assembles to form a hexagonal superstructure which, in turn, adopts a hexagonal tiling pattern. Tessellation of the more rigid and highly symmetrical 2,7-disubstituted naphthalene-based cyclophanes leads to the formation of 2D square and honeycomb tiling patterns with the box-like and hexagon-like cyclophanes, respectively. Co-crystallization of the box-like cyclophanes with tetrathiafulvalene (TTF) results in the formation of D-A CT interactions between TTF and viologen units, leading to tubular superstructures. Co-crystallization of the hexagon-like cyclophane with TTF generates well-ordered and uniform tubular superstructures in which the TTF-viologen CT interactions and naphthalene-naphthalene [π···π] interactions propagate with 2D topology. In the solid state, the TTF-cyclophane co-crystals are paramagnetic and display dual intra- and intermolecular CT behavior at ∼470 and ∼1000 nm, respectively, offering multi-responsive materials with potential pathways for electron transport.
TL;DR: The redox-controlled molecular shuttling, which can be likened to the action of a zipper in the macroscopic world, exhibits slow kinetics dampened by the opening and closing of the bifurcated 'tail' of the molecular shuttle.
Abstract: The design and synthesis of artificial molecular switches (AMSs) displaying architectures of increased complexity would constitute significant progress in meeting the challenging task of realizing ...
TL;DR: A hydrogen-bonded three-dimensional porous supramolecular polyknot assembled from a rigid trigonal prismatic triptycene building block with six extended peripheral aryl-carboxyl groups is reported, highlighting the ability of supramolescular systems to form topologically complex architectures using geometrically simple building blocks.
Abstract: Herein we report a hydrogen-bonded three-dimensional porous supramolecular polyknot assembled from a rigid trigonal prismatic triptycene building block with six extended peripheral aryl-carboxyl groups. Within this superstructure, three arrays of undulated 2D rhombic subnets, which display an inclined polycatenation, are interconnected to give an unprecedented uninodal six-connected net with a point symbol of (3.44.610). Such an entanglement results in a trefoil knot motif, which, as the basic repeating unit, is fused and interlocked with itself three-dimensionally to afford a supramolecular polyknot. This example highlights the ability of supramolecular systems to form topologically complex architectures using geometrically simple building blocks.
TL;DR: The strategy of modulating the redox properties of NDI by either host-guest recognition or mechanically interlocking can aid and abet the development of radical-based materials, which could be employed in pursuit of applications in many areas, such as transporting spin and charges.
Abstract: Organic radicals are of importance in developing smart materials that have paramagnetic and/or near-infrared optical properties. Their practical applications, however, are limited by the labile nature of the radicals. Here, we demonstrate that by using a tetracationic cyclophane, namely, cyclobis(4,4'-(1,4-phenylene)bispyridine-p-phenylene) (ExBox4+), to encapsulate a naphthalenediimide (NDI) guest, the redox properties of NDI can be modulated. In organic solvents such as MeCN or DMF, ExBox4+ is able to provide the surrounding Coulombic attraction to the NDI•- radical anion and therefore enhance its stability toward oxidation. In water, NDI•- is prone to dimerization, forming its (NDI•-)2 dimer. Under UV-light irradiation, the (NDI•-)2 dimer is observed to disproportionate and yield the dianionic NDI2-. ExBox4+ is able to encapsulate the NDI•- radical anion and prevent its dimerization, and as a consequence, the radical anion is protected from further reduction in a noncovalent manner. We believe that our strategy of modulating the redox properties of NDI by either host-guest recognition or mechanical interlocking can aid and abet the development of radical-based materials, which could be employed in pursuit of applications in many areas, such as transporting spin and charges.
TL;DR: It is reported that calixarenes stabilize UIO-66 nanoparticles effectively by remaining outside the grains through size exclusion, without pores becoming blocked, all the while providing amphiphilicity that permits the formation of stable colloidal dispersions with much narrower size distributions.
Abstract: Making metal–organic frameworks (MOFs) that are stabilized in nonpolar media is not as straightforward as making their inorganic nanoparticle counterparts, since surfactants penetrate through the p...
TL;DR: In this paper, a supramolecular diamond is constructed from the multiple-level self-assembly of a highly symmetrical salt, hexakis[(4,4′-bipyridin-1-ium)methylene]benzene hexafluorophosphate.
TL;DR: In this paper, the π-electron rich macrocycle bis-1,5-dinaphtho(50)crown-14 (1) is shown to form a donor-acceptor ring-in-ring complex with π -electron poor cyclo-phane cyclobis(paraquat-4,4'-biphenylene) (2 4+ ) in solution.
Abstract: The assembly of molecular Borromean Rings from con- stitutionally independent rings in a stepwise manner depends on the preparation of robust "ring-in-ring" complexes. The π-electron rich macrocycle bis-1,5-dinaphtho(50)crown-14 (1) is shown to form a donor-acceptor ring-in-ring complex with the π-electron poor cyclo- phane cyclobis(paraquat-4,4'-biphenylene) (2 4+ ) in solution. In the crystal superstructure of (1⊂2)·4PF6, CH···O interactions between the polyether loops of 1 and the bipyridinium units of 2 4+ could disfavor
TL;DR: In this paper, a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV2+) and dipyridylthiazolothiazole (TTz2+) electron acceptors doubly-linked by means of two p-xylylene linkers was presented.
Abstract: Constructing functional molecular systems for solar energy conversion and quantum information science requires a fundamental understanding of electron transfer in donor–bridge–acceptor (D–B–A) systems as well as competitive reaction pathways in acceptor–donor–acceptor (A–D–A) and acceptor–donor–acceptor′ (A–D–A′) systems. Herein we present a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV2+) and dipyridylthiazolothiazole (TTz2+) electron acceptors doubly-linked by means of two p-xylylene linkers (TTzExVBox4+), which readily incorporates a perylene (Per) guest in its cavity (Per ⊂ TTzExVBox4+) to establish an A–D–A′ system, in which the ExV2+ and TTz2+ units serve as competing electron acceptors with different reduction potentials. Photoexcitation of the Per guest yields both TTz+˙–Per+˙–ExV2+ and TTz2+–Per+˙–ExV+˙ in <1 ps, while back electron transfer in TTz2+–Per+˙–ExV+˙ proceeds via the unusual sequence TTz2+–Per+˙–ExV+˙ → TTz+˙–Per+˙–ExV2+ → TTz2+–Per–ExV2+. In addition, selective chemical reduction of TTz2+ gives Per ⊂ TTzExVBox3+˙, turning the complex into a D–B–A system in which photoexcitation of TTz+˙ results in the reaction sequence 2*TTz+˙–Per–ExV2+ → TTz2+–Per–ExV+˙ → TTz+˙–Per–ExV2+. Both reactions TTz2+–Per+˙–ExV+˙ → TTz+˙–Per+˙–ExV2+ and TTz2+–Per–ExV+˙ → TTz+˙–Per–ExV2+ occur with a (16 ± 1 ps)−1 rate constant irrespective of whether the bridge molecule is Per+˙ or Per. These results are explained using the superexchange mechanism in which the ionic states of the perylene guest serve as virtual states in each case and demonstrate a novel supramolecular platform for studying the effects of bridge energetics within D–B–A systems.
01 Oct 2019
TL;DR: A recently published article in Matter as mentioned in this paper reports an amphidynamic supramolecular rotor that displays a remarkable thermosalient effect when undergoing a phase transition, concomitant with substantial structural reconfiguration resulting in crystal motility.
Abstract: Amphidynamic crystals have close links to molecular machines, which have considerable potential for developing smart materials. A recently published article in Matter ( Colin-Molina et al .) reports an amphidynamic supramolecular rotor that displays a remarkable thermosalient effect when undergoing a phase transition, concomitant with a substantial structural reconfiguration resulting in crystal motility.
TL;DR: Lateral interactions enhance the guest inclusion and peripheral complexation within a highly charged covalent cage.
Abstract: A hexacationic triangular covalent organic cage, AzaEx2Cage6+, has been synthesized by means of a tetrabutylammonium iodide-catalyzed SN2 reaction. The prismatic cage is composed of two triangular 2,4,6-triphenyl-1,3,5-triazine (TPT) platforms bridged face-to-face by three 4,4′-bipyridinium (BIPY2+) spacers. The rigidity of these building blocks leads to a shape-persistent cage cavity with an inter-platform distance of approximately 11.0 A. This distance allows the cage to accommodate two aromatic guests, each of which is able to undergo π–π interactions with one of the two TPT platform simultaneously, in an A–D–D–A manner. In the previously reported prism-shaped cage, the spacers (pillars) are often considered passive or non-interactive. In the current system, the three BIPY2+ spacers are observed to play an important role in guest recognition. Firstly, the BIPY2+ spacers are able to interact with the carbonyl group in a pyrene-1-carbaldehyde (PCA) guest, by introducing lateral dipole–cation or dipole–dipole interactions. As a consequence, the binding affinity of the cage towards the PCA guest is significantly larger than that of pyrene as the guest, even although the latter is often considered to be a better π-electron donor. Secondly, in the case of the guest 1,5-bis[2-(2-(2-(2-hydroxyethoxy)ethoxy)ethoxy)ethoxy]naphthalene (BH4EN), the pillars can provide higher binding forces compared to the TPT platform. Hence, peripheral complexation occurs when AzaEx2Cage6+ accommodates BH4EN in MeCN. Thirdly, when both PCA and BH4EN are added into a solution of AzaEx2Cage6+, inclusion and peripheral complexation occur simultaneously to PCA and BH4EN respectively, even though the accommodation of the former guest seems to attenuate the external binding of the latter. This discovery of the importance of lateral interactions highlights the relationship between the electrostatic properties of a highly charged host and its complexation behavior, and as such, provides insight into the design of more complex hosts that bind guests in multiple locations and modes.
TL;DR: These redox-active cyclophanes demonstrate that geometry-matching and weak intermolecular interactions are of paramount importance in dictating the formation of their intricate solid-state superstructures.
Abstract: Reported here is the synthesis, solid-state characterization, and redox properties of new triangular, threefold symmetric, viologen-containing macrocycles. Cyclotris(paraquat-p-phenylene) (CTPQT6+ ) and cyclotris(paraquat-p-1,4-dimethoxyphenylene) (MCTPQT6+ ) were prepared and their X-ray single-crystal (super)structures reveal intricate three-dimensional packing. MCTPQT6+ results in nanometer-sized channels, in contrast with its parent counterpart CTPQT6+ which crystallizes as a couple of polymorphs in the form of intercalated assemblies. In the solid state, MCTPQT3(.+) exhibits stacks between the 1,4-dimethoxyphenylene and bipyridinium radical cations, providing new opportunities for the manipulation and control of the recognition motif associated with viologen radical cations. These redox-active cyclophanes demonstrate that geometry-matching and weak intermolecular interactions are of paramount importance in dictating the formation of their intricate solid-state superstructures.