Showing papers by "J. Fraser Stoddart published in 2023"
TL;DR: In this article , an electric molecular motor based on a [3]catenane was described, in which two cyclobis(paraquat-p-phenylene)6 (CBPQT4+) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop.
Abstract: Macroscopic electric motors continue to have a large impact on almost every aspect of modern society. Consequently, the effort towards developing molecular motors1-3 that can be driven by electricity could not be more timely. Here we describe an electric molecular motor based on a [3]catenane4,5, in which two cyclobis(paraquat-p-phenylene)6 (CBPQT4+) rings are powered by electricity in solution to circumrotate unidirectionally around a 50-membered loop. The constitution of the loop ensures that both rings undergo highly (85%) unidirectional movement under the guidance of a flashing energy ratchet7,8, whereas the interactions between the two rings give rise to a two-dimensional potential energy surface (PES) similar to that shown by FOF1 ATP synthase9. The unidirectionality is powered by an oscillating10 voltage11,12 or external modulation of the redox potential13. Initially, we focused our attention on the homologous [2]catenane, only to find that the kinetic asymmetry was insufficient to support unidirectional movement of the sole ring. Accordingly, we incorporated a second CBPQT4+ ring to provide further symmetry breaking by interactions between the two mobile rings. This demonstration of electrically driven continual circumrotatory motion of two rings around a loop in a [3]catenane is free from the production of waste products and represents an important step towards surface-bound14 electric molecular motors.
9 citations
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TL;DR: Porous organic cages (POCs) as mentioned in this paper are a relatively new class of low-density crystalline materials that have emerged as a versatile platform for investigating molecular recognition, gas storage and separation, and proton conduction, with potential applications in the fields of porous liquids, highly permeable membranes, heterogeneous catalysis and microreactors.
Abstract: Porous organic cages (POCs) are a relatively new class of low-density crystalline materials that have emerged as a versatile platform for investigating molecular recognition, gas storage and separation, and proton conduction, with potential applications in the fields of porous liquids, highly permeable membranes, heterogeneous catalysis, and microreactors. In common with highly extended porous structures, such as metal–organic frameworks (MOFs), covalent organic frameworks (COFs), and porous organic polymers (POPs), POCs possess all of the advantages of highly specific surface areas, porosities, open pore channels, and tunable structures. In addition, they have discrete molecular structures and exhibit good to excellent solubilities in common solvents, enabling their solution dispersibility and processability—properties that are not readily available in the case of the well-established, insoluble, extended porous frameworks. Here, we present a critical review summarizing in detail recent progress and breakthroughs—especially during the past five years—of all the POCs while taking a close look at their strategic design, precise synthesis, including both irreversible bond-forming chemistry and dynamic covalent chemistry, advanced characterization, and diverse applications. We highlight representative POC examples in an attempt to gain some understanding of their structure–function relationships. We also discuss future challenges and opportunities in the design, synthesis, characterization, and application of POCs. We anticipate that this review will be useful to researchers working in this field when it comes to designing and developing new POCs with desired functions.
3 citations
TL;DR: In this article , a color-tunable upconversion-emission switch based on the interconversion between two cocrystals is presented, where one red and one yellow-emissive cocrystal, composed of an electron-deficient naphthalenediimide-based triangular macrocycle and different electron donors, have been obtained.
Abstract: 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. One red- and one yellow-emissive cocrystal, composed of an electron-deficient naphthalenediimide-based triangular macrocycle and different electron donors, have been obtained. The red- and yellow-emissive cocrystals undergo reversible transformations on exchanging the electron donors. Benefiting from intermolecular charge transfer interactions, the two cocrystals display superior two-photon excited upconversion emission. Accompanying the interconversion of the two cocrystals, their luminescent color changes between red and yellow, forming a dual-color upconversion-emission switch. This research provides a rare yet critical example involving precise control of cocrystal-to-cocrystal transformation and affords a reference for fabricating color-tunable nonlinear optical materials in the solid state.
2 citations
TL;DR: In this paper , a cage-like molecular container incorporating two porphyrinic sensitizers and encapsulating two perylene emitters inside its cavity was designed to harness photon upconversion.
Abstract: Triplet-triplet annihilation-based molecular photon upconversion (TTA-UC) is a photophysical phenomenon that can yield high-energy emitting photons from low-energy incident light. TTA-UC is believed to fuse two triplet excitons into a singlet exciton through several consecutive energy-conversion processes. When organic aromatic dyes─i.e., sensitizers and annihilators─are used in TTA-UC, intermolecular distances, as well as relative orientations between the two chromophores, are important in an attempt to attain high upconversion efficiencies. Herein, we demonstrate a host-guest strategy─e.g., a cage-like molecular container incorporating two porphyrinic sensitizers and encapsulating two perylene emitters inside its cavity─to harness photon upconversion. Central to this design is tailoring the cavity size (9.6-10.4 Å) of the molecular container so that it can host two annihilators with a suitable [π···π] distance (3.2-3.5 Å). The formation of a complex with a host:guest ratio of 1:2 between a porphyrinic molecular container and perylene was confirmed by NMR spectroscopy, mass spectrometry, and isothermal titration calorimetry (ITC) as well as by DFT calculations. We have obtained TTA-UC yielding blue emission at 470 nm when the complex is excited with low-energy photons. This proof-of-concept demonstrates that TTA-UC can take place in one supermolecule by bringing together the sensitizers and annihilators. Our investigations open up some new opportunities for addressing several issues associated with supramolecular photon upconversion, such as sample concentrations, molecular aggregation, and penetration depths, which have relevance to biological imaging applications.
1 citations
TL;DR: In this paper , 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 was reported.
Abstract: Abstract 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. The efficiency of gold recovery reaches 99.8% when dibutyl carbitol is deployed as the additive. This cocrystallization is highly selective for square-planar tetrabromoaurate anions. In a laboratory-scale gold-recovery protocol, over 94% of gold in electronic waste was recovered at gold concentrations as low as 9.3 ppm. This simple protocol constitutes a promising paradigm for the sustainable recovery of gold, featuring reduced energy consumption, low cost inputs, and the avoidance of environmental pollution.
1 citations
TL;DR: In this article , a tetracationic cyclophane was used as a probe for live-cell imaging in a breast cancer cell line (MCF-7) using near-infrared (NIR) light.
Abstract: 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. The preparation of NIR-emissive porphyrin-free cyclophanes is, however, still challenging. In an attempt for fluorescence emissions to reach into the NIR spectral region, employing organic tetracationic cyclophanes, we have inserted two 9,10-divinylanthracene units between two of the pyridinium units in cyclobis(paraquat-p-phenylene). Steady-state absorption, fluorescence, and transient-absorption spectroscopies reveal the deep-red and NIR photoluminescence of this cyclophane. This tetracationic cyclophane is highly soluble in water and has been employed successfully as a probe for live-cell imaging in a breast cancer cell line (MCF-7).
TL;DR: A review of the role of sequence isomerism in the synthesis of polyrotaxanes is presented in this article , where several possible synthetic strategies are proposed in an attempt to foretell the future of sequence-controlled synthesis of rotaxanes, including orthogonal templation, active-metal templations, self-sorting and snapping, cooperative-capturing, ring-through-ring-shuttling and molecular pumping.
Abstract: Rotaxanes with well-defined ring sequences are attractive synthetic goals in the construction of functional materials associated with molecular shuttles and switches, molecular electronics, and information storage. Sequence-controlled synthesis of oligo- and polyrotaxanes is important in the context of the development of both sequence-defined polymers and dynamic functional materials. To date, examples of sequence-controlled rotaxanes are limited to oligorotaxanes on account of the synthetic challenges they pose. This Review sheds light on the pivotal role that sequence isomerism plays in rotaxanes. Synthetic approaches, including orthogonal templation, active-metal templation, self-sorting and snapping, cooperative-capturing, ring-through-ring-shuttling, and molecular pumping, for the construction of sequence-controlled rotaxanes are all discussed in this Review. By comparing the advantages and disadvantages of these different approaches, several possible synthetic strategies are proposed in an attempt to foretell the future of sequence-controlled synthesis of polyrotaxanes.
TL;DR: Xu et al. as mentioned in this paper reviewed the recent advances in heterogeneous catalytic hydrogenation of CO2 to higher alcohols, in terms of catalyst families, reaction mechanisms, and the rational design of ideal catalysts.
Abstract: The challenges faced in controlling the monodispersity of synthetic nanotubes have hampered the exploration and development of chemistry in confined spaces. Recently in Nature Synthesis, Sue and co-workers have reported an elegant approach to prepare a family of chiral organic nanotubes with well-defined diameters and lengths by dimerizing rim-differentiated pillar[5]arenes. The challenges faced in controlling the monodispersity of synthetic nanotubes have hampered the exploration and development of chemistry in confined spaces. Recently in Nature Synthesis, Sue and co-workers have reported an elegant approach to prepare a family of chiral organic nanotubes with well-defined diameters and lengths by dimerizing rim-differentiated pillar[5]arenes. Advances in higher alcohol synthesis from CO2 hydrogenationXu et al.ChemNovember 13, 2020In BriefHigher alcohol synthesis from CO2 hydrogenation is a promising and challenging way to realize the efficient utilization of CO2 resources. Despite recent progress, there is still a lack of deeper understanding in this field. This review focuses on the recent advances in heterogeneous catalytic hydrogenation of CO2 to higher alcohols, in terms of catalyst families, reaction mechanisms, and the rational design of ideal catalysts. This will providea new prospect for future research on catalytic CO2 hydrogenation to higher alcohols. Full-Text PDF Open Archive
TL;DR: In this article , photoinduced charge transfer and relaxation dynamics in three host-guest complexes, where a perylene (Per) electron donor guest is incorporated into two symmetric and one asymmetric extended viologen cyclophane acceptor hosts, are presented.
Abstract: Designing and controlling charge transfer (CT) pathways in organic semiconductors are important for solar energy applications. To be useful, a photogenerated, Coulombically bound CT exciton must further separate into free charge carriers; direct observations of the detailed CT relaxation pathways, however, are lacking. Here, photoinduced CT and relaxation dynamics in three host-guest complexes, where a perylene (Per) electron donor guest is incorporated into two symmetric and one asymmetric extended viologen cyclophane acceptor hosts, are presented. The central ring in the extended viologen is either p-phenylene (ExV2+) or electron-rich 2,5-dimethoxy-p-phenylene (ExMeOV2+), resulting in two symmetric cyclophanes with unsubstituted or methoxy-substituted central rings, ExBox4+ and ExMeOBox4+, respectively, and an asymmetric cyclophane with one of the central viologen rings being methoxylated ExMeOVBox4+. Upon photoexcitation, the asymmetric host-guest ExMeOVBox4+ ⊃ Per complex exhibits directional CT toward the energetically unfavorable methoxylated side due to structural restrictions that facilitate strong interactions between the Per donor and the ExMeOV2+ side. The CT state relaxation pathways are probed using ultrafast optical spectroscopy by focusing on coherent vibronic wavepackets, which are used to identify CT relaxations along charge localization and vibronic decoherence coordinates. Specific low- and high-frequency nuclear motions are direct indicators of a delocalized CT state and the degree of CT character. Our results show that the CT pathway can be controlled by subtle chemical modifications of the acceptor host in addition to illustrating how coherent vibronic wavepackets can be used to probe the nature and time evolution of the CT states.
TL;DR: In this paper , the problem of poor solubility of single-crystal polymeric polymers with rigid polycationic backbones was addressed by using an ultraviolet-induced topochemical polymerization from an elaborately designed monomer that results in a multitude of photoinduced cycloadditions.
Abstract: Single-crystal-to-single-crystal (SCSC) polymerization offers an effective protocol for the environmentally friendly preparation of polymer single crystals (PSCs) with extremely high crystallinity and very large molecular weights. Single-crystal X-ray diffraction (SCXRD) serves as a powerful technique for the in-depth characterization of their structures at a molecular level. Hence, a fundamental understanding of the structure-property relationships of PSCs is within our reach. Most of the reported PSCs, however, suffer from poor solubility, a property which hampers their post-functionalization and solution processability when it comes to practical applications. Here, we report soluble and processable PSCs with rigid polycationic backbones by taking advantage of an ultraviolet-induced topochemical polymerization from an elaborately designed monomer that results in a multitude of photoinduced [2 + 2] cycloadditions. The high crystallinity and excellent solubility of the resulting polymeric crystals enable their characterization both in the solid state by X-ray crystallography and electron microscopy and in the solution phase by NMR spectroscopy. The topochemical polymerization follows first-order reaction kinetics to a first approximation. Post-functionalization of the PSCs by anion exchange renders them super-hydrophobic materials for water purification. Solution processability endows PSCs with excellent gel-like rheological properties. This research represents a major step towards the controlled synthesis and full characterization of soluble single-crystalline polymers, which may find application in the fabrication of PSCs with many different functions.
TL;DR: In this article, Zhang et al. showed that the absolute configurations of the D/L-valine residues within the ligands, i.e., (SS)-1 and (RR)-1, determine the helical chirality of the circular helicates.
Abstract: Topological structures [1,2], i.e., knots and links, grace the macroscopic world in the form of biomorphs and artificial tools, all the way down to the molecular scale, such as catenated DNA and phytochromes. Chirality inherently exists in structures in which mirror-image topologies cannot be superimposed upon themselves without disassembling the topological structures. Although the chirality we are most familiar with is based on stereogenic centers, topological chirality can arise inmolecules even in the absence of such centers. The stereospecific synthesis of a molecule with specific topological handedness requires controlling the entropically demanding pathways associated with knotting and linking. From a practical point of view, the stereospecific syntheses ofmoleculeswith topological structures can be controlled by the presence of stereogenic centers. Understanding how the chirality of stereogenic centers can be transferred to topological structures (Fig. 1a) is a matter of fundamental importance. Recently, Zhang et al. [3,4] at East China Normal University have proposed and realized the selective syntheses of an enantiomeric pair of cinquefoil (51) knots and a homochiral Star of David (61) [2]catenane as a result of hierarchical chirality transfer from stereogenic centers to both the knots and the link. The authors demonstrated (Fig. 1b) that the absolute configurations of the D/L-valine residues within the ligands, i.e., (SS)-1 and (RR)-1, determine the helical chirality of the circular helicates -[Zn5((SS)-1)5](OTf)10 and -[Zn5((RR)-1)5](OTf)10. After treatment of the two metallic circular helicates with theHoveyda-Grubbs catalyst to connect the terminal olefins (Fig. 1b), two tight metallic cinquefoil knots, i.e., -[Zn52](OTf)10 and [Zn52](OTf)10, were obtained enantioselectively in the impressively high yield of ∼90%. Demetallation of both knots with Li2S affords the wholly organic enantiomeric cinquefoil knots, i.e., -2 and -2, in ∼30% yields. The syntheses of single-handed knots indicate that the exploitation of stereogenic centers in ligand strands to control the helical chiralities of circular helicates, and dictate the handedness of the corresponding knots, is highly effective. Zhang et al. [4] have also employed their chirality-transfer strategy in the stereospecific synthesis of a Star of David [2]catenane (Fig. 1c). They employed a chiral bipyridine ligand (SS)-3, which was first developed by von Zelewsky and co-workers [5] in the 1990s, to construct a topologically chiral 61 link. They built up the catenated structure in a stepwise fashion (Fig. 1c) by employing the chiral ligand (SS)-3 to afford the hexameric copper(I) circular helicate -[Cu6((SS)-3)6](PF6)6 and converted it into the single-handed star-shaped link by ring-closing olefin metathesis (RCM). The Cu+ ions can be removed by treatment with the chelating agent ethylenediaminetetraacetate to afford the wholly organic homochiral Star of David [2]catenane -3. These breakthroughs are timely and certain to arouse the interest of chemists investigating topological chirality and developing related properties. With the increase in understanding of chirality transfer from stereogenic centers to topologically chiral structures, we can look forward to witnessing the enantioselective syntheses of more complex topologically chiral structures and to developing their applications in chiral separations, information transmissions, asymmetric catalysis, and more into the bargain.