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1.
Adv Mater ; : e2001592, 2020 Jun 29.
Artigo em Inglês | MEDLINE | ID: mdl-32602131

RESUMO

Efficient heterogeneous photosensitizing materials require both large accessible surface areas and excitons of suitable energies and with well-defined spin structures. Confinement of the tetracationic cyclophane (ExBox4+ ) within a nonporous anionic polystyrene sulfonate (PSS) matrix leads to a surface area increase of up to 225 m2 g-1 in ExBox•PSS. Efficient intersystem crossing is achieved by combining the spin-orbit coupling associated to Br heavy atoms in 1,3,5,8-tetrabromopyrene (TBP), and the photoinduced electron transfer in a TBP⊂ExBox4+ supramolecular dyad. The TBP⊂ExBox4+ complex displays a charge transfer band at 450 nm and an exciplex emission at 520 nm, indicating the formation of new mixed-electronic states. The lowest triplet state (T1 , 1.89 eV) is localized on the TBP and is close in energy with the charge separated state (CT, 2.14 eV). The homogeneous and heterogeneous photocatalytic activities of the TBP⊂ExBox4+ , for the elimination of a sulfur mustard simulant, has proved to be significantly more efficient than TBP and ExBox+4 , confirming the importance of the newly formed excited-state manifold in TBP⊂ExBox4+ for the population of the low-lying T1 state. The high stability, facile preparation, and high performance of the TBP⊂ExBox•PSS nanocomposites augur well for the future development of new supramolecular heterogeneous photosensitizers using host-guest chemistry.

2.
Science ; 368(6496): 1247-1253, 2020 06 12.
Artigo em Inglês | MEDLINE | ID: mdl-32527831

RESUMO

Mechanically interlocked molecules are likely candidates for the design and synthesis of artificial molecular machines. Although polyrotaxanes have already found niche applications in exotic materials with specialized mechanical properties, efficient synthetic protocols to produce them with precise numbers of rings encircling their polymer dumbbells are still lacking. We report the assembly line-like emergence of poly[n]rotaxanes with increasingly higher energies by harnessing artificial molecular pumps to deliver rings in pairs by cyclical redox-driven processes. This programmable strategy leads to the precise incorporation of two, four, six, eight, and 10 rings carrying 8+, 16+, 24+, 32+, and 40+ charges, respectively, onto hexacationic polymer dumbbells. This strategy depends precisely on the number of redox cycles applied chemically or electrochemically, in both stepwise and one-pot manners.

3.
Artigo em Inglês | MEDLINE | ID: mdl-32571947

RESUMO

Urban mining of precious metals from electronic waste, such as printed circuit boards (PCB), is not yet feasible because of the lengthy isolation process, health risks, and environmental impact. Although porous polymers are particularly effective toward the capture of metal contaminants, those with porphyrin linkers have not yet been considered for precious metal recovery, despite their potential. Here, we report a porous porphyrin polymer that captures precious metals quantitatively from PCB leachate even in the presence of 63 elements from the Periodic Table. The nanoporous polymer is synthesized in two steps from widely available monomers without the need for costly catalysts and can be scaled up without loss of activity. Through a reductive capture mechanism, gold is recovered with 10 times the theoretical limit, reaching a record 1.62 g/g. With 99% uptake taking place in the first 30 min, the metal adsorbed to the porous polymer can be desorbed rapidly and reused for repetitive batches. Density functional theory (DFT) calculations indicate that energetically favorable multinuclear-Au binding enhances adsorption as clusters, leading to rapid capture, while Pt capture remains predominantly at single porphyrin sites.

4.
J Am Chem Soc ; 2020 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-32470290

RESUMO

We report how the nanoconfined environment, introduced by the mechanical bonds within an electrochemically switchable bistable [2]rotaxane, controls the rotation of a fluorescent molecular rotor, namely, an 8-phenyl-substituted boron dipyrromethene (BODIPY). The electrochemical switching of the bistable [2]rotaxane induces changes in the ground-state coconformation and in the corresponding excited-state properties of the BODIPY rotor. In the starting redox state, when no external potential is applied, the cyclobis(paraquat-p-phenylene) (CBPQT4+) ring component encircles the tetrathiafulvalene (TTF) unit on the dumbbell component, leaving the BODIPY rotor unhindered and exhibiting low fluorescence. Upon oxidation of the TTF unit to a TTF2+ dication, the CBPQT4+ ring is forced toward the molecular rotor, leading to an increased energy barrier for the excited state to rotate the rotor into the state with a high nonradiative rate constant, resulting in an overall 3.4-fold fluorescence enhancement. On the other hand, when the solvent polarity is high enough to stabilize the excited charge-transfer state between the BODIPY rotor and the CBPQT4+ ring, movement of the ring toward the BODIPY rotor produces an unexpectedly strong fluorescence signal decrease as the result of photoinduced electron transfer from the BODIPY rotor to the CBPQT4+ ring. The nanoconfinement effect introduced by mechanical bonding can effectively lead to modulation of the physicochemical properties as observed in this bistable [2]rotaxane. On account of the straightforward synthetic strategy and the facile modulation of switchable electrochromic behavior, our approach could pave the way for the development of new stimuli-responsive materials based on mechanically interlocked molecules for future electro-optical applications, such as sensors, molecular memories, and molecular logic gates.

5.
J Am Chem Soc ; 142(23): 10273-10278, 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32422050

RESUMO

Suitanes are two-component mechanically interlocked molecules in which one (torso) of the components, with several protruding limbs, is encompassed by another (suit) all-in-one component. This kind of molecular ship-in-a-bottle architecture remains a challenging one to make. Herein, we report a porphyrin-based suit[4]ane, which is composed of a porphyrin with four protruding ligands (two phenyl groups and two bromine atoms) called the limbs that are encompassed by a tricyclic octacationic cyclophane. The suit[4]ane can be obtained by slippage, a mechanism by which the cyclophane is able to open up two of its entrances in order to take up the porphyrin at high temperature and close them down at low temperature, locking the porphyrin inside its binding cavity. Dynamic 1H NMR spectroscopy reveals that the trapped porphyrin inside the cyclophane rocks back and forth in the suit[4]ane about 1000 times a second.

6.
J Am Chem Soc ; 142(23): 10308-10313, 2020 Jun 10.
Artigo em Inglês | MEDLINE | ID: mdl-32463231

RESUMO

The assembly of a kinetically trapped daisy chain polymer under redox control has been achieved with a self-complementary monomer using an energy ratchet mechanism. The monomer is composed of a molecular pump at one end and a cyclobis(paraquat-p-phenylene) (CBPQT4+) ring at the other end. The pump and ring are linked together by a long collecting chain. When the monomer is reduced to its radical state, it self-assembles into a supramolecular daisy chain polymer on account of radical-pairing interactions. When all of the bipyridinium radical cations are quickly oxidized to dications, the CBPQT4+ rings are forced to thread onto the collecting chains, forming an out-of-equilibrium, kinetically trapped daisy chain polymer. This polymer can be switched reversibly back to the supramolecular polymer by reduction, followed by depolymerization to afford the monomer as a result of slow oxidation. This proof-of-concept investigation opens up opportunities for synthesizing mechanically interlocked polymers using molecular machines.

7.
J Am Chem Soc ; 142(15): 7190-7197, 2020 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-32223154

RESUMO

Two new highly charged [2]catenanes-namely, mHe[2]C·6PF6 and mHo[2]C·6PF6-were synthesized by exploiting radical host-guest templation between derivatives containing BIPY•+ radical cations and the meta analogue of cyclobis(paraquat-p-phenylene). In contrast to related [2]catenanes that have been isolated as air-stable monoradicals, both mHe[2]C·6PF6 and mHo[2]C·6PF6 exist as air-stable singlet bisradicals, as evidenced by both X-ray crystallography in the solid state and EPR spectroscopy in solution. Electrochemical studies indicate that the first two reduction peaks of these two [2]catenanes are shifted significantly to more positive potentials, a feature which is responsible for their extraordinary stability in air. The mixed-valence nature of the mono- and bisradical states endows them with unique NIR absorption properties, e.g., NIR absorption bands for the mono- and bisradical states observed at ∼1800 and ∼1450 nm, respectively. These [2]catenanes are potentially useful in applications that include NIR photothermal conversion, UV-vis-NIR multiple-state electrochromic materials, and multiple-state memory devices. Our findings highlight the principle of "mechanical-bond-induced stabilization" as an efficient strategy for designing persistent organic radicals.

8.
Science ; 368(6488): 297-303, 2020 04 17.
Artigo em Inglês | MEDLINE | ID: mdl-32299950

RESUMO

A huge challenge facing scientists is the development of adsorbent materials that exhibit ultrahigh porosity but maintain balance between gravimetric and volumetric surface areas for the onboard storage of hydrogen and methane gas-alternatives to conventional fossil fuels. Here we report the simulation-motivated synthesis of ultraporous metal-organic frameworks (MOFs) based on metal trinuclear clusters, namely, NU-1501-M (M = Al or Fe). Relative to other ultraporous MOFs, NU-1501-Al exhibits concurrently a high gravimetric Brunauer-Emmett-Teller (BET) area of 7310 m2 g-1 and a volumetric BET area of 2060 m2 cm-3 while satisfying the four BET consistency criteria. The high porosity and surface area of this MOF yielded impressive gravimetric and volumetric storage performances for hydrogen and methane: NU-1501-Al surpasses the gravimetric methane storage U.S. Department of Energy target (0.5 g g-1) with an uptake of 0.66 g g-1 [262 cm3 (standard temperature and pressure, STP) cm-3] at 100 bar/270 K and a 5- to 100-bar working capacity of 0.60 g g-1 [238 cm3 (STP) cm-3] at 270 K; it also shows one of the best deliverable hydrogen capacities (14.0 weight %, 46.2 g liter-1) under a combined temperature and pressure swing (77 K/100 bar → 160 K/5 bar).

9.
J Am Chem Soc ; 142(17): 7956-7967, 2020 Apr 29.
Artigo em Inglês | MEDLINE | ID: mdl-32233402

RESUMO

Collisional intermolecular interactions between excited states form short-lived dimers and complexes that lead to the emergence of excimer/exciplex emission of lower energy, a phenomenon which must be differentiated from the photoluminescence (PL) arising from the monomeric molecules. Although the utilization of noncovalent bonding interactions, leading to the generation of excimer/exciplex PL, has been investigated extensively, precise control of the aggregates and their persistence at very low concentrations remains a rare phenomenon. In the search for a fresh approach, we sought to obtain exciplex PL from permanent structures by incorporating anthracene moieties into pyridinium-containing mechanically interlocked molecules. Beyond the optical properties of the anthracene moieties, their π-extended nature enforces [π···π] stacking that can overcome the Coulombic repulsion between the pyridinium units, affording an efficient synthesis of an octacationic homo[2]catenane. Notably, upon increasing the ionic strength by adding tetrabutylammonium hexafluorophosphate, the catenane yield increases significantly as a result of the decrease in Coulombic repulsions between the pyridinium units. Although the ground-state photophysical properties of the free cyclophane and the catenane are similar and show a charge-transfer band at ∼455 nm, their PL characters are distinct, denoting different excited states. The cyclophane emits at ∼562 nm (quantum yield ϕF = 3.6%, emission lifetime τs = 3 ns in MeCN), which is characteristic of a disubstituted anthracene-pyridinium linker. By contrast, the catenane displays an exciplex PL at low concentration (10-8 M) with an emission band centered on 650 nm (ϕF = 0.5%, τs = 14 ns) in MeCN and at 675 nm in aqueous solution. Live-cell imaging performed in MIAPaCa-2 prostate cancer cells confirmed that the catenane exciplex emission can be detected at micromolar concentrations.

10.
J Am Chem Soc ; 142(19): 8938-8945, 2020 May 13.
Artigo em Inglês | MEDLINE | ID: mdl-32243141

RESUMO

We report the encapsulation of free-base and zinc porphyrins by a tricyclic cyclophane receptor with subnanomolar binding affinities in water. The high affinities are sustained by the hydrophobic effect and multiple [CH···π] interactions covering large [π···π] stacking surfaces between the substrate porphyrins and the receptor. We discovered two co-conformational isomers of the 1:1 complex, where the porphyrin is orientated differently inside the binding cavity of the receptor on account of its tricyclic nature. The photophysical properties and chemical reactivities of the encapsulated porphyrins are modulated to a considerable extent by the receptor. Improved fluorescence quantum yields, red-shifted absorptions and emissions, and nearly quantitative energy transfer processes highlight the emergent photophysical enhancements. The encapsulated porphyrins enjoy unprecedented chemical stabilities, where their D/H exchange, protonation, and solvolysis under extremely acidic conditions are completely blocked. We anticipate that the ultrahigh stabilities and improved optical properties of these encapsulated porphyrins will find applications in single-molecule materials, artificial photodevices, and biomedical appliances.

11.
Acc Chem Res ; 2020 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-32181637

RESUMO

ConspectusCyclodextrin-based metal-organic frameworks (CD-MOFs), derived from γ-cyclodextrin (γ-CD) and potassium ions, constitute a new class of porous, renewable, and edible MOFs that can be synthesized wholly from naturally occurring starting materials on a large scale. γ-CD is a C8 symmetrical cyclic oligosaccharide, composed of eight asymmetric α-1,4-linked d-glucopyranosyl residues, which possesses a bucket-shaped cavity with an inner diameter of ∼1 nm and a depth of ∼0.8 nm. Upon combining 1 equiv of γ-CD with 8 equiv of potassium hydroxide in aqueous solution, followed by vapor-diffusion of MeOH (or EtOH) into the solution during several days, CD-MOF-1 is obtained as cubic crystals. It was discovered serendipitously in 2010 as the first CD-MOF with a cubic cell of space group I432 and unit cell dimensions of approximately 31 × 31 × 31 Å3. Other CD-MOFs, namely, CD-MOF-2 and CD-MOF-3, can be obtained, respectively, wherein potassium is replaced with rubidium and cesium ions. CD-MOFs comprise infinite body-centered frameworks of (γ-CD)6 cubic units linked by alkali metal cations with spherical pores which reside at the center of the cubes interconnected by both cylindrical and triangular channels.During the past decade, CD-MOFs have emerged as a new class of multifunctional materials based on a porous framework with an extended structure displaying robust crystallinity, permanent porosity, and biocompatibility. The family of CD-MOFs has been enlarged by a growing collection of metal nodes involving alkali metal cations (Li+, Na+, K+, Rb+, Cs+) and γ-CD as well as its derivatives. As a result of the ability of their porous extended frameworks to absorb guest molecules, including gases, drug molecules, metal-based nanoclusters, and nanoparticles, CD-MOFs have potential applications in areas as disparate as adsorption and separation, sensing, template syntheses of metal-based nanoparticles and gels, electrical memory, drug delivery, and catalyst stabilization.In this Account, we tell the story of CD-MOFs, a scientific discovery that was made in our research laboratory at the Northwestern University, and the subsequent commercialization of CD-MOF technology on the part of a spinoff company, which developed a line of successful skin care products. This Account includes representative synthetic methods for the preparation of CD-MOFs, along with a brief overview of their structural features and a general summary of their state-of-the-art applications. The examples, however, are only illustrative, and a significant body of additional findings is emanating from our own laboratory and others, especially in the development of new synthetic strategies, tuning the framework stabilities, and exploring the guest-inclusion properties of CD-MOFs. We refer readers to communications, papers, and reviews on CD-MOFs and to references therein. We also put on record how CD-MOFs have been rebranded as organic molecular vessels (OMVs), a smart, functional, environmentally friendly delivery platform for commercial skin care applications. We hope that, in the telling and retelling of the story of CD-MOFs, this Account may encourage the commercialization of discoveries that have been made in other research laboratories.

12.
Chem Sci ; 11(1): 107-112, 2020 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-32110362

RESUMO

Although host-guest pairing interactions between bisradical dicationic cyclobis(paraquat-p-phenylene) (BB2(˙+) ) and the bipyridinium radical cation (BIPY˙+ ) have been studied extensively, host molecules other than BB2(˙+) are few and far between. Herein, four bisradical dicationic cyclophanes with tunable cavity sizes are investigated as new bisradical dicationic hosts for accommodating the methyl viologen radical cation (MV˙+ ) to form trisradical tricationic complexes. The structure-property relationships between cavity sizes and binding affinities have been established by comprehensive solution and solid-state characterizations as well as DFT calculations. The association constants of the four new trisradical tricationic complexes are found to range between 7400 and 170 000 M-1, with the strongest one being 4.3 times higher than that for [MV⊂BB]3(˙+) . The facile accessibility and tunable stability of these new trisradical tricationic complexes make them attractive redox-controlled recognition motifs for further use in supramolecular chemistry and mechanostereochemistry.

13.
J Am Chem Soc ; 2020 Feb 19.
Artigo em Inglês | MEDLINE | ID: mdl-32017550

RESUMO

The efficient preparation of single-crystalline ionic polymers and fundamental understanding of their structure-property relationships at the molecular level remains a challenge in chemistry and materials science. Here, we describe the single-crystal structure of a highly ordered polycationic polymer (polyelectrolyte) and its proton conductivity. The polyelectrolyte single crystals can be prepared on a gram-scale in quantitative yield, by taking advantage of an ultraviolet/sunlight-induced topochemical polymerization, from a tricationic monomer-a self-complementary building block possessing a preorganized conformation. A single-crystal-to-single-crystal photopolymerization was revealed unambiguously by in situ single-crystal X-ray diffraction analysis, which was also employed to follow the progression of molecular structure from the monomer, to a partially polymerized intermediate, and, finally, to the polymer itself. Collinear polymer chains are held together tightly by multiple Coulombic interactions involving counterions to form two-dimensional lamellar sheets (1 nm in height) with sub-nanometer pores (5 Å). The polymer is extremely stable under 254 nm light irradiation and high temperature (above 500 K). The extraordinary mechanical strength and environmental stability-in combination with its impressive proton conductivity (∼3 × 10-4 S cm-1)-endow the polymer with potential applications as a robust proton-conducting material. By marrying supramolecular chemistry with macromolecular science, the outcome represents a major step toward the controlled synthesis of single-crystalline polyelectrolyte materials with perfect tacticity.

14.
J Am Chem Soc ; 142(11): 5419-5428, 2020 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-32083871

RESUMO

Synthetic macrocycles capable of undergoing allosteric regulation by responding to versatile external stimuli are the subject of increasing attention in supramolecular science. Herein, we report a structurally transformative tetracationic cyclophane containing two 3,6-bis(4-pyridyl)-l,2,4,5-tetrazine (4-bptz) units, which are linked together by two p-xylylene bridges. The cyclophane, which possesses modular redox states and structural post-modifications, can undergo two reversibly consecutive two-electron reductions, affording first its bisradical dicationic counterpart, and then subsequently the fully reduced species. Furthermore, one single-parent cyclophane can afford effectively three other new analogs through box-to-box cascade transformations, taking advantage of either reductions or an inverse electron-demand Diels-Alder (IEDDA) reaction. While all four new tetracationic cyclophanes adopt rigid and symmetric box-like conformations, their geometries in relation to size, shape, electronic properties, and binding affinities toward polycyclic aromatic hydrocarbons can be readily regulated. This structurally transformative tetracationic cyclophane performs a variety of new tasks as a result of structural post-modifications, thus serving as a toolbox for probing the radical properties and generating rapidly a range of structurally diverse cyclophanes by efficient divergent syntheses. This research lays a solid foundation for the introduction of the structurally transformative tetracationic cyclophane into the realm of mechanically interlocked molecules and will provide a toolbox to construct and operate intelligent molecular machines.

15.
J Am Chem Soc ; 142(5): 2541-2548, 2020 Feb 05.
Artigo em Inglês | MEDLINE | ID: mdl-31895548

RESUMO

Aqueous rechargeable zinc batteries (ZBs) have received considerable attention recently for large-scale energy storage systems in terms of rate performance, cost, and safety. Nevertheless, these ZBs still remain a subject for investigation, as researchers search for cathode materials enabling high performance. Among the various candidate cathode materials for ZBs, quinone compounds stand out as candidates because of their high specific capacity, sustainability, and low cost. Quinone-based cathodes, however, suffer from the critical limitation of undergoing dissolution during battery cycling, leading to a deterioration in battery life. To address this problem, we have introduced a redox-active triangular phenanthrenequinone-based macrocycle (PQ-Δ) with a rigid geometry and layered superstructure. Notably, we have confirmed that Zn2+ ions, together with H2O molecules, can be inserted into the PQ-Δ organic cathode, and, as a consequence, the interfacial resistance between the cathode and electrolytes is decreased effectively. Density functional theory calculations have revealed that the low interfacial resistance can be attributed mainly to decreasing the desolvation energy penalty as a result of the insertion of hydrated Zn2+ ions in the PQ-Δ cathode. The combined effects of the insertion of hydrated Zn2+ ions and the robust triangular structure of PQ-Δ serve to achieve a large reversible capacity of 210 mAh g-1 at a high current density of 150 mA g-1, along with an excellent cycle-life, that is, 99.9% retention after 500 cycles. These findings suggest that the utilization of electron-active organic macrocycles, combined with the low interfacial resistance associated with the solvation of divalent carrier ions, is essential for the overall performance of divalent battery systems.

16.
J Am Chem Soc ; 142(4): 1768-1773, 2020 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-31927881

RESUMO

Protection of enzymes with synthetic materials is a viable strategy to stabilize, and hence to retain, the reactivity of these highly active biomolecules in non-native environments. Active synthetic supports, coupled to encapsulated enzymes, can enable efficient cascade reactions which are necessary for processes like light-driven CO2 reduction, providing a promising pathway for alternative energy generation. Herein, a semi-artificial system-containing an immobilized enzyme, formate dehydrogenase, in a light harvesting scaffold-is reported for the conversion of CO2 to formic acid using white light. The electron-mediator Cp*Rh(2,2'-bipyridyl-5,5'-dicarboxylic acid)Cl was anchored to the nodes of the metal-organic framework NU-1006 to facilitate ultrafast photo-induced electron transfer when irradiated, leading to the reduction of the coenzyme nicotinamide adenine dinucleotide at a rate of about 28 mM·h-1. Most importantly, the immobilized enzyme utilizes the reduced coenzyme to generate formic acid selectively from CO2 at a high turnover frequency of about 865 h-1 in 24 h. The outcome of this research is the demonstration of a feasible pathway for solar-driven carbon fixation.

17.
J Am Chem Soc ; 142(4): 2042-2050, 2020 01 29.
Artigo em Inglês | MEDLINE | ID: mdl-31935077

RESUMO

A class of γ-cyclodextrin-containing hybrid frameworks (CD-HFs) has been synthesized, employing γ-cyclodextrin (γ-CD) as the primary building blocks, along with 4-methoxysalicylate (4-MS-) anions as the secondary building blocks. CD-HFs are constructed through the synergistic exploitation of coordinative, electrostatic, and dispersive forces. The syntheses have been carried out using an organic counteranion co-assembly strategy, which allows for the introduction of 4-MS-, in place of inorganic OH-, into the cationic γ-CD-containing metal-organic frameworks (CD-MOFs). Although the packing arrangement of the γ-CD tori in the solid-state superstructure of CD-HFs is identical to that of the previously reported CD-MOFs, CD-HFs crystallize with lower symmetry and in the cuboid space group P43212-when compared to CD-MOF-1, which has the cubic unit cell of I432 space group-on account of the chiral packing of the 4-MS- anions in the CD-HF superstructures. Importantly, CD-HFs have ultramicroporous apertures associated with the pore channels, a significant deviation from CD-MOF-1, as a consequence of the contribution from the 4-MS- anions, which serve as supramolecular baffles. In gas adsorption-desorption experiments, CD-HF-1 exhibits a Brunauer-Emmett-Teller (BET) surface area of 306 m2 g-1 for CO2 at 195 K, yet does not uptake N2 at 77 K, confirming the difference in porosity between CD-HF-1 and CD-MOF-1. Furthermore, the 4-MS- anions in CD-HF-1 can be exchanged with OH- anions, leading to an irreversible single-crystal to single-crystal transformation, with rearrangement of coordinated metal ions. Reversible transformations were also observed in CD-MOF-1 when OH- ions were exchanged for 4-MS- anions, with the space group changing from I432 to R32. This organic counteranion co-assembly strategy opens up new routes for the construction of hybrid frameworks, which are inaccessible by existing de novo MOF assembly methodologies.

18.
J Am Chem Soc ; 142(6): 3165-3173, 2020 Feb 12.
Artigo em Inglês | MEDLINE | ID: mdl-31944691

RESUMO

The rational design of wholly synthetic receptors that bind active substrates with ultrahigh affinities is a challenging goal, especially in water. Here, we report the synthesis of a tricyclic octacationic cyclophane, which exhibits complementary stereoelectronic binding toward a widely used fluorescent dye, perylene diimide, with picomolar affinity in water. The ultrahigh binding affinity is sustained by a large and rigid hydrophobic binding surface, which provides a highly favorable enthalpy and a slightly positive entropy of complexation. The receptor-substrate complex shows significant improvement in optical properties, including red-shifted absorption and emission, turn-on fluorescence, and efficient energy transfer. An unusual single-excitation, dual-emission, imaging study of living cells was performed by taking advantage of a large pseudo-Stokes shift, produced by the efficient energy transfer.

19.
Nat Commun ; 10(1): 4948, 2019 10 30.
Artigo em Inglês | MEDLINE | ID: mdl-31666515

RESUMO

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.

20.
J Am Chem Soc ; 141(44): 17472-17476, 2019 Nov 06.
Artigo em Inglês | MEDLINE | ID: mdl-31622089

RESUMO

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 ratchets are operated by the alteration of kinetic barriers and thermodynamic wells, which are, in turn, determined by the switching on and off of noncovalent interactions. Previously, we have developed artificial molecular pumps (AMPs) capable of pumping rings consecutively onto a collecting chain as part of a molecular dumbbell, leading to the formation of rotaxanes. Here, we report a molecular dual pump (MDP) 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. This MDP, defined by the finely tuned noncovalent interactions and fueled by either chemicals or electricity, utilizes an energy ratchet mechanism to capture a ring and subsequently release it back into solution. The unidirectional motion and the resulting controlled capture and release of the ring were followed by 1D and 2D 1H NMR spectroscopy and supported by control experiments. This molecular dual pump may be considered to be a forerunner of AMMs that are capable of pumping rings across a membrane in a way similar to how bacteriorhodopsin transports protons from one side of a membrane to the other under the influence of light. Such extensive multicomponent AMMs can lead potentially to molecular transporting platforms with positional and directional control of cargo uptake and release when, and only when, instructed.

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