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With the largest cavity in the cucurbituril family, cucurbit[10]uril (CB[10]) has been utilized to make supramolecular assemblies by host – guest ‐ enhanced charge ‐ transfer interactions. Two packed “sandwiches” have been assembled by forming a 1:2:1 or 1:1:1 complex between CB[10] and viologen derivatives and an electron ‐ rich molecule in water. Amazingly, as a known building block for the construction of molecular machines, blue box can be encapsulated within CB[10]. By threading a guest through the cavities of both blue box and CB[10], a supramolecular “Russian doll” architecture has been built up. More information can be found in the Full Paper by L. Isaacs, S. Liu et al. on page 17612 ff. [ABSTRACT FROM AUTHOR]

Flexible porphyrin covalent cages behave as allosteric receptors and control guest encapsulation through large conformational changes. In the closed state, the cage cavity is restricted preventing guest molecules to be captured. Coordination of silver ions to the allosteric sites switches the cage to an open state allowing for the encapsulation of guest molecules. For more details, see the Full Paper by K. Rissanen, V. Heitz and co‐workers on page 1481 ff. [ABSTRACT FROM AUTHOR]

Ternary‐component crystals with guest‐dependent photofunctions, such as crystallization‐induced enhanced emission, intermolecular charge‐transfer emission, and room‐temperature phosphorescence emission under UV‐light irradiation, have been designed. The single‐crystal X‐ray structure determination of eight different guest crystals was performed, and the structure–property relationships at a molecular level were studied. The findings provide important guidelines for the future design of novel optoelectronic organic materials. More information can be found in the Full Paper by T. Ono, Y. Hisaeda et al. on page 17487. [ABSTRACT FROM AUTHOR]

Mimicking the antibacterial activity of polyphenols in synthetic systems is an attractive approach for the development of new active pharmaceutical ingredients. Resorcinarenes represent a class of polyphenols, which have been exploited for decades for their attractive chemical scaffold suitable for forming host–guest complexes with hydrophobic guest molecules. However, the polyphenolic character of resorcinarenes, which could be a potential asset to the pharmaceutical industry, have been least exploited. The present work represents an unprecedented interplay of antimicrobial activity of resorcinarene together with its ability to interact chemically with an antibacterial drug gatifloxacin, improving the overall antibacterial activity. The chemistry and the clinical activities involved in this study were investigated simultaneously by spectroscopic techniques, as well as by in vitro measurement of antibacterial activity toward two human bacterial pathogens, a Gram-positive pathogen Staphylococcus aureus and a Gram-negative lung pathogen Legionella pneumophila. The initial positive result obtained from this study could revolutionize the use of synthetically modifiable resorcinarenes and their analogues in fine tuning the clinical behavior of drugs. [ABSTRACT FROM AUTHOR]

The development of new tuning methods for π-conjugated insulated molecular wires with strictly defined axle lengths as well as positions and degrees of macrocycle coverage would provide unprecedented insight into insulation effects in functionalized materials. Herein, iterative reactions of oligo(phenylene ethynylene) (OPE) linked with permethylated α-cyclodextrins were carried out to fabricate insulated molecular wires with a defined length and insulation in desired areas. Insulated OPEs were elongated in a stepwise manner by performing sequential coupling/deprotection reactions. The insulated areas on the OPE units in each expansion step were selectively controlled by means of programmed solvent conditions (high/low polarity). Moreover, a completely insulated OPE (up to a linked [11]rotaxane) with high structural regularity and high covering ratio was synthesized by appropriate tuning of the Pd catalyst and an extension unit bearing a traceless capping unit based on a tert-butyldimethylsilyl group. This strategy may guide the development of the selective synthesis of fully insulated, partially insulated, and uninsulated molecular wires with well-defined lengths and covered/uncovered areas. [ABSTRACT FROM AUTHOR]

Stepwise growth of fullerene nanoparticles ( nC x; x=60 or 70) was performed through guest exchange of a γ-cyclodextrin (γ-CD) complex. Fullerenes bicapped by γ-CD were mixed with presynthesized nC x in the presence of poly(ethylene glycol) (PEG) in water. Fullerenes expelled from the γ-CD hosts by PEG were piled on the original nC x, resulting in growth of nC x. This process could be repeated and the size of nC x increased according to the number of growth steps. The growth of fullerene nanoparticles was confirmed by UV/Vis absorption spectroscopy, dynamic light scattering measurements, and TEM observations. The stepwise growth method also enabled the preparation of C60/C70 core/shell fullerene nanoparticles, which had the ability to photogenerate active oxygen, 1O2. [ABSTRACT FROM AUTHOR]

Off ‐ charge ‐ stoichiometry assemblage of ionic H ‐ bond donors and acceptors was found to be a straightforward approach to a hydrogen ‐ bonded open framework with pores decorated by basic sites. The supramolecular architecture exhibits 1 ‐ nm ‐ wide channels functionalized by pyridyl groups and high accessible voids (53 %).Remarkable affinity was achieved for acidic organic molecules, including larger drug molecules. Notably, good selectivity of the porous material for the halogenated acids was also observed. More information can be found in the Full Paper by N. Roques, J. ‐ P. Sutter et al. on page 11818. [ABSTRACT FROM AUTHOR]

A hydrogen-bonded open framework with pores decorated by pyridyl groups was constructed by off-charge-stoichiometry assembly of protonated tetrakis(4-pyridyloxymethyl)methane and [Al(oxalate)3]3−, which are the H-bond donor and acceptor of ionic H-bond interactions, respectively. This supramolecular porous architecture ( SPA-2) has 1 nm-large pores interconnected in 3D with large solvent-accessible void (53 %). It demonstrated remarkable affinity for acidic organic molecules in solution, which was investigated by means of various carboxylic acids including larger drug molecules. Competing sorption between acetic acid and its halogenated homologues evidenced good selectivity of the porous material for the halogenated acids. The gathered results, including a series of guest@ SPA-2 crystal structures and HRMAS-NMR spectra, suggest that the efficient sorption exhibited by the material relies not only on an acid-base interaction. The facile release of these guest molecules under neutral conditions makes this SPA a carrier of acidic molecules. [ABSTRACT FROM AUTHOR]

Complexation of racemic 2,6-helic[6]arene 1 and its hexamethyl-substituted derivative 2 with quaternary ammonium salts, N-heterocyclic salts, and tetracyanoquinodimethane have been described in detail. It was found that host 2 could form stable complexes with acetyl choline, thiaacetyl choline, N, N, N-trimethylbenzenammonium salt, pyridinium, and 4,4′-bipyridinium salts in solution and/or in the solid state. The unsubstituted macrocycle 1 showed more significant complexation with the widely tested quaternary ammonium salts and N-heterocyclic salts, and exhibited stronger complexation towards the guests than its derivative 2. Moreover, it was found that macrocycle 1 and its derivative 2 could also complex with neutral electron-deficient tetracyanoquinodimethane (TCNQ), and the association constants were determined to be 2840±94 and 1358±46 m−1, respectively. These results could make this new macrocycle and its derivatives find wide applications in the design and construction of functional supramolecular assemblies. [ABSTRACT FROM AUTHOR]

We synthesized a novel green-light-responsive tetra- ortho-isopropoxy-substituted azobenzene (ipAzo). Cis-ipAzo forms a strong host-guest complex with γ-cyclo dextrin (γ-CD) whereas trans-ipAzo binds weakly. This new photoresponsive host-guest interaction is reverse to the well-known azobenzene (Azo)/α-cyclodextrin (α-CD) complex, which is strong only between trans-Azo and α-CD. By combining the UV-light-responsive Azo/α-CD and green-light-responsive ipAzo/γ-CD host-guest complexes, a photoresponsive orthogonal supramolecular system is developed. [ABSTRACT FROM AUTHOR]

A porous organic salt (POS) composed of 2-sulfophenyl anthracene (2-SPA) and triphenylmetylamine (TPMA) forms five types of porous crystals, POS-a-e, by recognizing subtle differences in the molecular structure of incorporated guest molecules. This structurally variable POS was hierarchically designed on the basis of a supramolecular cluster with a directionally flexible linker formed by the organic salt. X-ray crystallographic analysis reveals that the salt forms six conformers attributable to rocking and rotational motions of the phenylene group in 2-SPA. The clusters form POS crystals through different porous networks according to the conformers. The POS crystals show a wide range of fluorescence spectra that are responsive to differences in the molecular and electronic structure of the guest molecule. This remarkable behavior has potential application in sensitive chemical sensors that are responsive to slight differences in molecular structures. [ABSTRACT FROM AUTHOR]

There is broad interest in molecular encapsulation as such systems can be utilized to stabilize guests, facilitate reactions inside a cavity, or give rise to energy-transfer processes in a confined space. Detailed understanding of encapsulation events is required to facilitate functional molecular encapsulation. In this contribution, it is demonstrated that Ir and Rh-Cp-type metal complexes can be encapsulated inside a self-assembled M6L4 metallocage only in the presence of an aromatic compound as a second guest. The individual guests are not encapsulated, suggesting that only the pair of guests can fill the void of the cage. Hence, selective co-encapsulation is observed. This principle is demonstrated by co-encapsulation of a variety of combinations of metal complexes and aromatic guests, leading to several ternary complexes. These experiments demonstrate that the efficiency of formation of the ternary complexes depends on the individual components. Moreover, selective exchange of the components is possible, leading to formation of the most favorable complex. Besides the obvious size effect, a charge-transfer interaction may also contribute to this effect. Charge-transfer bands are clearly observed by UV/Vis spectrophotometry. A change in the oxidation potential of the encapsulated electron donor also leads to a shift in the charge-transfer energy bands. As expected, metal complexes with a higher oxidation potential give rise to a higher charge-transfer energy and a larger hypsochromic shift in the UV/Vis spectrum. These subtle energy differences may potentially be used to control the binding and reactivity of the complexes bound in a confined space. [ABSTRACT FROM AUTHOR]

We investigate the gas-phase chemistry of noncovalent complexes of [10]cycloparaphenylene ([10]CPP) with C60 and C70 by means of atmospheric pressure photoionization and electrospray ionization mass spectrometry. The literature-known [1: 1] complexes, namely [10]CPP⊃C60 and [10]CPP⊃C70, are observed as radical cations and anions. Their stability and charge distribution are studied using energy-resolved collision-induced dissociation (ER-CID). These measurements reveal that complexes with a C70 core exhibit a greater stability and, on the other hand, that the radical cations are more stable than the respective radical anions. Regarding the charge distribution, in anionic complexes charges are exclusively located on C60 or C70, while the charges reside on [10]CPP in the case of cationic complexes. [2: 1] complexes of the ([10]CPP2 ⊃C60/70)+ ⋅/- ⋅ type are observed for the first time as isolated solitary gas-phase species. Here, C60 -based [2: 1] complexes are less stable than the respective C70 analogues. By virtue of the high stability of cationic [1: 1] complexes, [2: 1] complexes show a strongly reduced stability of the radical cations. DFT analyses of the minimum geometries as well as molecular dynamics calculations support the experimental data. Furthermore, our novel gas-phase [2: 1] complexes are also found in 1,2-dichlorobenzene. Insights into the thermodynamic parameters of the binding process as well as the species distribution are derived from isothermal titration calorimetry (ITC) measurements. [ABSTRACT FROM AUTHOR]

The β ‐ cyclodextrin/azobenzene host – guest binding site has a pronounced effect on the morphology, size, dynamic self ‐ assembly process, and controlled release function of two thermo ‐ and photoresponsive Y ‐ shaped supramolecular polymer self ‐ assemblies. The binding ‐ site ‐ tunable self ‐ assembly can be attributed to the positive cooperativity generated amongst adjacent binding sites on the surfaces of supramolecular polymer self ‐ assemblies. More information can be found in the Full Paper by W. Tian et al. on page 8508 ff. [ABSTRACT FROM AUTHOR]

Host – Guest Systems After extensive work toward the creation of molecular capsules in which two cavitands self ‐ assemble to produce a constricted space amenable to guest encapsulation, a water ‐ soluble version of Rebek’s capsules was recently introduced. By combining EPR and NMR spectroscopy and ESI ‐ MS, O. Ouari and co ‐ workers have investigated the inner space metrics (width and height) of these supramolecular objects in water, as well as their binding constants and guest rotational dynamics. Nitroxides have been shown to be powerful probes affording a wealth of information. Read more in the Full Paper on page 16404 ff. [ABSTRACT FROM AUTHOR]

The ability to use bio‐inspired building blocks in the assembly of novel supramolecular frameworks is at the forefront of an exciting research field. Herein, we present the first polyproline helix to self‐assemble into a reversibly porous, crystalline, supramolecular peptide framework (SPF). This framework is assembled from a short oligoproline, adopting the polyproline II conformation, driven by hydrogen‐bonding and dispersion interactions. Thermal activation, guest‐induced dynamic porosity and enantioselective guest inclusion have been demonstrated for this novel system. The principles of the self‐assembly associated with this SPF will be used as a blueprint allowing for the further development of helical peptide linkers in the rational design of SPFs and metal‐peptide frameworks. [ABSTRACT FROM AUTHOR]

Five isostructural microporous supramolecular architectures prepared by H‐bonded assembly between the hexa‐anionic complex [Zr2(Ox)7]6− (Ox=oxalate, (C2O4)2−) and tripodal cations (H3‐TripCH2‐R)3+ with R=H, CH3, OH and OBn (Bn=CH2Ph) are reported. The possibility to obtain the same structure using a mixture of tripodal cations with different R group (R=OH and R=CH3) has also been successfully explored, providing a unique example of three‐component H‐bonded porous framework. The resulting SPA‐1(R) materials feature 1D pores decorated by R groups, with apparent pore diameters ranging from 3.0 to 8.5 Å. Influence of R groups on the sorption properties of these materials is evidenced through CO2 and H2O vapor sorption/desorption experiments, as well as with I2 capture/release experiments in liquid media. This study is one of the first to demonstrate the possibility of tuning the porosity and exerting precise control over the chemical functionalization of the pores in a given H‐bonded structure, without modifying the topology of the reference structure, and thus finely adjusting the sorption characteristics of the material. [ABSTRACT FROM AUTHOR]

We describe a new concept for rotaxane synthesis through intramolecular slippage using π-conjugated molecules as rigid axles linked with organic soluble and flexible permethylated α-cyclodextrins (PM α-CDs) as macrocycles. Through hydrophilic-hydrophobic interactions and flipping of PM α-CDs, successful quantitative conversion into rotaxanes was achieved without covalent bond formation. The rotaxanes had high activation barrier for their de-threading, so that they were kinetically isolated and derivatized even under conditions unfavorable for maintaining the rotaxane structures. 1H NMR spectroscopy experiments clearly revealed that the restricted motion of the linked macrocycle with the rigid axle made it possible to control the kinetic stability by adjusting the length of the rigid axle in the precursor structure rather than the steric bulkiness of the stopper unit. [ABSTRACT FROM AUTHOR]

A cyclic zinc(II) bisporphyrin with flexible linker was employed as a dynamic molecular switch under the regulation of π-acceptors (tetracyanoquinodimethane, trinitrofluorenone, 9-dicyanomethylenefluorene) and bidentate N-donor ligands (1,4-diazabicyclo[2.2.2]octane, pyrazine, 4,4′-bipyridine). The cyclic bisporphyrin host can efficiently encapsulate the π-acceptor guests through the strong π-π interaction, which can be replaced again by using a bidentate N-donor ligand, which coordinates strongly with the metal centers. The open conformation of the bisporphyrin can be efficiently recovered by removing the bidentate ligands using Cu+ ion. During the process, two porphyrin rings also reversibly change their relative orientation between perpendicular and parallel. The behavior of the cyclic bisporphyrin was followed by using UV/Vis, 1H NMR, fluorescence, and electrochemical analyses along with X-ray structure determination of the complexes. Moreover, control of photoinduced electron transfer (PET 'ON-OFF') is also achieved by the use of guest exchange. Association constants for the host-guest binding were very high, which further explains the robust nature of such assemblies in solution. The experimental evidence is supported by DFT calculations. Such controllable dynamic features can constitute a new step towards "smart" adaptive molecular devices and the emergence of such systems is of significant interest in supramolecular chemistry. [ABSTRACT FROM AUTHOR]

Nitroxide free radicals have been used to study the inner space of one of Rebek's water-soluble capsules. EPR and 1H NMR spectroscopy, ESI-MS, and DFT calculations showed a preference for the formation of 1:2 complexes. EPR titrations allowed us to determine binding constants ( Ka) in the order of 107 M−2. EPR spectral-shape analysis provided information on the guest rotational dynamics within the capsule. The interplay between optimum hydrogen bonding upon capsule formation and steric strain for guest accommodation highlights some degree of flexibility for guest inclusion, particularly at the center of the capsule where the hydrogen bond seam can be barely distorted or slightly disturbed. [ABSTRACT FROM AUTHOR]

Rotaxanes Bisimidazolium salts with one central biphenyl binding site and two terminal adamantyl binding sites form water ‐ soluble binary or ternary aggregates with macrocyclic host molecules cucurbit[7]uril and β ‐ cyclodextrin with rotaxane and pseudorotaxane architectures, as described by R. Vicha et al. in their Full Paper on page 11712 ff. The resultant arrangements are attributed to the binding strength of the supramolecular stopper and steric barriers against free slippage of the macrocyclic host molecules over the bisimidazolium guest axle. [ABSTRACT FROM AUTHOR]

The intriguing dual-emission behavior of p- dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule- specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water-soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation. Heating of the CB8 ⋅(DMABN)2 complex from 0 to 100 °C results in the dissociation of the ternary complex and restoration of the dual-emission properties of the monomer. Alternatively, monomer emission can be obtained by selecting cucurbit[7]uril (CB7), a host homologue that is too small to accommodate two DMABN molecules, or by introducing ethyl instead of methyl groups at the amino terminus of the aminobenzonitrile guest. [ABSTRACT FROM AUTHOR]

Switchable Anion Receptor The conformation of bispyrrolylbenzene anion receptor can be controlled by a proper anionic stimuli. Addition of fluoride anion gradually changes the conformation of this receptor. It was demonstrated that switchability of this building block allowed it to act as INHIBIT and NAND molecular logic gates using fluoride and dihydrogenphosphate anions as inputs and UV/Vis or fluorescence readout, respectively. For more information, see the Full Paper by J. Jurczak et al. on page 12790 ff. [ABSTRACT FROM AUTHOR]

The shortest possible C70 peapods were formed in a size‐ and orientation‐selective manner from C70 and either [10]cycloparaphenylene (CPP) or [11]CPP as 1:1 complexes. C70 exists in two distinct orientations inside the CPP cavity, namely “lying” and “standing”, depending on the size of the CPP. The interaction between [10]CPP and the short axis of C70 is isotropic, but that between [11]CPP and C70 is anisotropic, involving the radial deformation of [11]CPP to an ellipsoidal shape. This “induced‐fit” occurred due to the radically elastic character of the CPPs and maximized the van der Waals interactions with the long axis of C70. For more details, see the Full Paper by S. Yamago et al. on page 14061 ff. [ABSTRACT FROM AUTHOR]

Urea, which has both hydrogen bond acceptor and donor moieties, is an ideal structure for a supramolecular synthon. Various supramolecules having ureido group(s) have been widely developed. This article summarizes recent developments of urea derivatives that exhibit various functions: i) supramolecular capsules that form discrete urea–urea intermolecular hydrogen bonds, ii) supramolecular polymers that form continuous urea–urea intermolecular hydrogen bonds, iii) supramolecular gels that form continuous urea–urea intermolecular hydrogen bonds, iv) artificial host molecules based on the molecular recognition ability of the ureido group, and v) catalytic reactions developed by utilizing the molecular recognition ability of the ureido group. [ABSTRACT FROM AUTHOR]

A new supramolecular paradigm is presented for reliable capture and co‐precipitation of haloauric acids (HAuX4) from organic solvents or water. Two classes of acyclic organic compounds act as complementary receptors (tectons) by forming two sets of directional non‐covalent interactions, (a) hydrogen bonding between amide (or amidinium) NH residues and the electronegative X ligands on the AuX4−, and (b) electrostatic stacking of the electron deficient Au center against the face of an aromatic surface. X‐ray diffraction analysis of four co‐crystal structures reveals the additional common feature of proton bridged carbonyls as a new and predictable supramolecular design element that creates one‐dimensional polymers linked by very short hydrogen bonds (CO⋅⋅⋅OC distance <2.5 Å). Two other co‐crystal structures show that the amidinium‐π⋅⋅⋅XAu interaction will reliably engage AuX4− with high directionality. These acyclic compounds are very attractive as co‐precipitation agents within new "green" gold recovery processes. They also have high potential as tectons for controlled self‐assembly or co‐crystal engineering of haloaurate composites. More generally, the supramolecular paradigm will facilitate the design of next‐generation receptors or tectons with high affinity for precious metal square planar coordination complexes for use in advanced materials, nanotechnology, or medicine. [ABSTRACT FROM AUTHOR]

Cover Feature: A Regulable Internal Cavity inside a Resorcinarene-Based Hemicarcerand (Chem. Eur. J. 26/2020) Keywords: hemicarcerands; host-guest systems; molecular recognition; resorcinarenes; supramolecular chemistry EN hemicarcerands host-guest systems molecular recognition resorcinarenes supramolecular chemistry 5725 5725 1 05/09/20 20200507 NES 200507 B A covalently-linked resorcinarene-based capsule b was synthesized by means of a ring-closing olefin metathesis reaction. The cover artwork illustrates that the reversible shape changes of the internal cavity tune the guest selectivity in shape. [Extracted from the article]

Cover Feature: Computational NMR Spectra of o-Benzyne and Stable Guests and Their Hemicarceplexes (Chem. Eur. J. 12/2020) Keywords: density functional calculations; host-guest systems; NMR chemical shift calculations; o-benzyne; supramolecular chemistry Density functional calculations, host-guest systems, NMR chemical shift calculations, o-benzyne, supramolecular chemistry. [Extracted from the article]

Cover Feature: Dual Responsive Regulation of Host-Guest Complexation in Aqueous Media to Control Partial Release of the Host (Chem. Eur. J. 6/2020) The cover artwork illustrates the opportunity to tune a host concentration in aqueous media in an orchestrated manner by controlling the partial collapse of a colored host-guest synthetic polymeric system featuring both thermo- and pH responsiveness. Host-guest systems, molecular recognition, polymers, supramolecular chemistry. [Extracted from the article]

The flexible host framework of a perfluorinated mononuclear copper complex, [Cu(L1)2] (1, HL1=3‐hydroxy‐1,3‐bis(pentafluorophenyl)‐2‐propen‐1‐one), with a CuO4 core reversibly encapsulated several organic guest molecules through electrostatic interactions in its crystals. Hence, the corresponding dinuclear complex, [Cu2(L2)2] (2, H2L2=1,5‐dihydroxy‐1,5‐bis(pentafluorophenyl)‐1,4‐pentadien‐3‐one), was prepared to enhance guest recognition and the ability to separate molecular mixtures. Complex 2 comprises a Cu2O6 core and four pentafluorophenyl groups. In crystal 2, cavities are formed on the axial sites of the metal core that are surrounded by pentafluorophenyl groups. The crystal of 2 encapsulates various guest molecules, that is, benzene (3), toluene (4), xylene (5), mesitylene (6), durene (7), and anisole (8). X‐ray crystallographic and thermogravimetric (TG) studies show that three guest molecules are present in the crystal cavities. The number of guest molecules found in complex 2 was higher than that in complex 1, for example, (2)3⋅(6)10>1⋅(6)2, (2)2⋅(7)7>1⋅7, or 2⋅(8)3>1⋅(8)2. Naphthalene (9), was encapsulated in 2 to give 2⋅(9)3, but not in 1. In the crystal of complex 2, heteromolecular guest encapsulation was confirmed, designated as 2⋅(3)2⋅9. TG analysis indicates that the thermal stability of the guest‐included crystals of 2 is higher than that of 1. [ABSTRACT FROM AUTHOR]

The use of the electrostatic stoppers concept in the field of mechanically interlocked molecules is reported; these stoppers are chemically sensitive end groups on a linear guest molecule that allows for the conversion of a pseudo‐rotaxane species into a rotaxane complex by a change in the medium acidity. The chemical stimulus causes the appearance of negative charges on both ends of the linear component, passing from cationic to anionic, and causing a significant ring‐to‐axle electrostatic repulsion. This phenomenon has two different and simultaneous effects: 1) destabilizes the complex as a consequence of confining an anionic ring into an anionic axle, and 2) increases the dissociation energy barrier, thus impeding ring extrusion. This newly formed metastable rotaxane species is resistant to solvent and temperature effects and performs as a two‐state degenerated molecular shuttle in solution. [ABSTRACT FROM AUTHOR]

Molecular or supramolecular level photoluminescence (PL) modulation combining chemical and photonic input/output signals together in an integrated system can provide potential high‐density data memorizing and process functions intended for miniaturized devices and machines. Herein, a PL‐responsive supramolecular coordination cage has been demonstrated for complex interactions with redox‐active guests. PL signals of the cage can be switched and modulated by adding or retracting Fc derivatives or converting TTF into different oxidation states through chemical or photochemical pathways. As a result, reversible or stepwise PL responses are displayed by these host–guest systems because of the occurrence of photoinduced electron‐transfer (PET) or fluorescence resonance energy transfer (FREnT) processes, providing unique nanodevice models bearing off/on logic gates or memristor‐like sequential memory and Boolean operation functions. [ABSTRACT FROM AUTHOR]

Saturn‐like systems consisting of nanoscale rings and spheres are fascinating motifs in supramolecular chemistry. Several ring molecules are known to include spherical molecules at the center of the cavity via noncovalent attractive interactions. In this Minireview, we generalize the molecular design, the structural features, and the supramolecular chemistry of such "nano‐Saturns", which consist of monocyclic rings and fullerene spheres (mainly C60), on the basis of previous experimental and theoretical studies. Ring molecules are classified into three types (loop, belt, and disk) according to their shapes and possible interactions. Whereas typical belt‐shaped rings tend to form tight complexes due to the wide contact area via π–π interactions, flat disk‐shaped rings generally form weak complexes due to the narrow contact area mainly via CH–π interactions. In spite of the small association energies, disk‐shaped rings are attractive because such rings can mimic the planet Saturn precisely as exemplified by an anthracene cyclic hexamer–C60 complex. [ABSTRACT FROM AUTHOR]

A flexible bipyridinium‐linker‐based porous host framework with electron‐accepting pore surface, namely, [Zn2(L)(pmc)1.5]⋅12 H2O (1; L⋅Cl2=1,1′‐[1,4‐phenylene‐bis(methylene)]bis(4,4′‐bipyridinium) dichloride, H4pmc=pyromellitic acid) exhibits recognition of phenol and aromatic amine guests based on adsorbent–adsorbate charge‐transfer interactions. Significantly, the resultant guest‐encapsulated complexes 1@Guests can all be characterized by single‐crystal X‐ray diffraction. The host framework undergoes a reversible single crystal‐to‐single crystal transformation in response to the inclusion of different guests with flexible torsional motions of the hexagonal ring and the trapezoid‐shaped bipyridinium groups. Such recognition can be visibly monitored and detected by obvious color changes. The host framework could also be recovered, and this suggested that guest sorption/desorption is reversible and that the host framework could be reused in potential applications. This work may provide an effective way to develop porous materials with special emphasis on applications involving guest recognition. Accommodating host: Flexible bipyridinium‐based porous host framework 1 with electron‐accepting pore surface exhibits selective recognition of phenol and aromatic amine guests based on adsorbent–adsorbate charge‐transfer interactions (see figure). Since guest accommodation occurs in a reversible single crystal‐to‐single crystal fashion, all 1@Guests complexes could be fully characterized by single‐crystal XRD. [ABSTRACT FROM AUTHOR]

Cryptophanes with flexible linkers derived from (±)‐tris‐(4‐formyl‐phenyl)‐cyclotriguaiacylene with either bisoxydi(ethylamine) or bis(aminopropyl)ether were isolated as single crystals, the crystal structures of which showed the proposed, but previously uncharacterised, out‐in conformation, in which both cyclotriguaiacylene fragments adopt a crown conformation with one crown sitting inside the other. The usual cage‐like out‐out conformation of the cryptophanes was observed when crystals were dissolved upon heating, and the molecules collapsed back to the out‐in isomers over time. In contrast, a cryptophane also derived from (±)‐tris‐(4‐formyl‐phenyl)‐cyclotriguaiacylene but with rigid dibenzalhydrazine linkers was isolated as the more usual out‐out isomer. Out‐in! Two cryptophanes have been shown to adopt the completely collapsed out‐in conformation with all cyclotribenzylenes groups in the bowl‐like crown conformation. Remarkably, the more common cage‐like out‐out conformation is initially observed upon dissolution at high temperature, and the cage implodes even in the presence of potential guest molecules. [ABSTRACT FROM AUTHOR]

Smart supramolecular vesicles constructed by host–guest interactions between "acid‐degradable" acyclic cucurbit[n]uril (CB[n]) and a doxorubicin prodrug are reported. "Acid‐degradable" acyclic CB[n] is a high‐affinity host for several common antitumor drugs, and its degradation leads to a more dramatic decrease in binding affinity than that observed for "acid‐sensitive" hosts. Supramolecular complexation between acid‐degradable acyclic CB[n] and a doxorubicin prodrug resulted in the formation of negatively charged supramolecular vesicles. The prodrug strategy allowed doxorubicin to be conjugated to vesicles in a stable manner with a high drug‐loading ratio of 20 %. The resulting supramolecular vesicles were responsive to tumor acidity (pH 6.5). Induced by mildly acidic conditions (pH 6.5–5.5), acid‐degradable acyclic CB[n] could be degraded, and this led to a vesicle‐to‐micelle transition to form positively charged micelles. This transition resulted in a pH‐dependent change in size and surface charge, which improved tumoral‐cell uptake for doxorubicin. Improved uptake: Smart supramolecular vesicles were constructed by host–guest interactions between "acid‐degradable" acyclic cucurbit[n]uril (CB[n]) and a doxorubicin prodrug. Under mildly acidic conditions (pH 6.5–5.5), CB[n] degraded, which led to a vesicle‐to‐micelle transition. This transition resulted in a pH‐dependent change in size and surface charge, which improved the uptake of doxorubicin by tumor cells (see figure). [ABSTRACT FROM AUTHOR]

Crystal engineering of three‐component crystals with guest‐dependent photoluminescence switching, including (i) crystallization‐induced emission enhancement, (ii) intermolecular charge‐transfer emission, and (iii) room‐temperature phosphorescence under ultraviolet irradiation, was demonstrated. This strategy was based on the confinement of aromatic guests in a supramolecular host (denoted as EBPDI‐TPFB) composed of 5,5′‐(ethyne‐1,2‐diyl)bis(2‐pyridin‐3‐yl‐isoindoline‐1,3‐dione (EBPDI) with two tris(pentafluorophenyl)borane (TPFB) molecules linked by B−N dative bonds that acted as Lewis pairs. The single‐crystal X‐ray structures of complexes with eight different guests were collected, revealing that the size and/or shape of the supramolecular host EBPDI‐TPFB was modulated by the included guest molecules. The excellent guest inclusion ability of EBPDI‐TPFB allowed systematic photoluminescence regulation of the complexes, which exhibited multicolor emissions in the crystalline state. Photoluminescence switching characteristics of the complexes were observed upon removing the guests or mechanical grinding of the crystals. These results indicated that using the host–guest chemistry of multicomponent crystals not only facilitates crystallization, but also can reveal hidden optical functions by combining molecules of interest, which should contribute to the fields of physical chemistry and materials science. Ternary‐component crystals with guest‐dependent photofunctions, such as (i) crystallization‐induced enhanced emission, (ii) intermolecular charge‐transfer emission, and (iii) room‐temperature phosphorescence emission under UV‐light irradiation, are designed. Single‐crystal X‐ray structure determination of eight different guest crystals is performed, and the structure–property relationships at a molecular level are discussed. [ABSTRACT FROM AUTHOR]

Mother and child play toy trains, they freely arrange the sequences of containers. This image describes a new synthetic method of insulated molecular wires with strictly defined axle lengths and macrocyclic covering positions/degrees. A completely insulated molecular wire (up to a linked‐[11]rotaxane) was afforded through an iterative synthetic technique. Moreover, the insulated areas were selectively controlled using programed solvent conditions. More information can be found in the Full Paper by J. Terao et al. on page 15073. [ABSTRACT FROM AUTHOR]

Abstract: The dimetallic system [CuII2(L)]4+ contains two facing equivalent metallocyclam subunits and incorporates ambidentate anions, mono‐ (halides) and poly‐atomic (sulfate), which bridge the two CuII centres. Isothermal titration calorimetry (ITC) experiments in water showed that the log K values of the inclusion equilibria for halides and sulfate varied over a restricted interval (3.6±0.2), which indicated lack of selectivity and that similarity of ΔG° values resulted from the unbalanced contribution of the ΔH° and TΔS° terms: the more favourable the one, the less favourable the other. In particular, a linear dependence of ΔH° and TΔS° was observed (a typical enthalpy/entropy compensatory diagram), which assigned a major role to hydration terms: 1) a more hydrated anion resulted in a more endothermic dehydration process; and 2) a larger number of water molecules released to the solution resulted in a more positive TΔS°. Limiting cases refer to the complexation 1) of the poorly hydrated iodide (highly exothermic process, entropically disfavoured), and 2) of the highly hydrated sulfate (moderately endothermic process, entropically very favoured). Anion receptors operating in water belong to two main domains: 1) those exhibiting positive ΔH° and positive TΔS° (+/+ signature), and 2) those displaying the opposite behaviour: (−/− signature). The receptor investigated herein connects the two domains, along the ΔH°/TΔS° straight line, thanks to the hidden role of the versatile metal–anion interaction. [ABSTRACT FROM AUTHOR]

Abstract: Mixed valence/metal polyoxometalate (POM) clusters are one of the most interesting host species because they show the ability to incorporate a wide range of heteroatoms of various charges and geometries. We report herein the incorporation of pyramidal EO32− heteroanions (E=PH, S, Se, Te) that are responsible not only for directing the templated assembly of a family of mixed‐metal POMs but also for the symmetry‐breaking of the traditional Dawson architecture and modulation of the electronic characteristics of the cluster's shell. The isolated family of POMs consists of four members: (Me2NH2)5Na2[Mo11V7O52(HPO3)]⋅MeOH⋅5 H2O (1), (NH4)7[Mo11V7O52(SO3)]⋅12 H2O (2), K7[Mo11V7O52(SeO3)] ⋅31 H2O (3), and (Me2NH2)6Na[Mo11V7O52(TeO3)]⋅15 H2O (4), and were characterized by X‐ray structural analysis, electrospray ionization mass spectrometry (ESI‐MS), thermogravimetric analysis (TGA), UV/Vis, FTIR, elemental analysis, flame atomic absorption spectroscopy (FAAS), and inductively coupled plasma optical emission spectroscopy (ICP‐OES). Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) spectroscopic studies in concert with density functional theoretical (DFT) calculations have been used to elucidate the effect of the heteroatom on the electronic properties of the cluster. [ABSTRACT FROM AUTHOR]

Abstract: The cavity of an M8L12 cubic coordination cage can accommodate a cluster of ten water molecules in which the average number of hydrogen bonds per water molecule is 0.5 H‐bonds less than it would be in the bulk solution. The presence of these “hydrogen‐bond frustrated” or “high‐energy” water molecules in the cavity results in the hydrophobic effect associated with guest binding being predominantly enthalpy‐based, as these water molecules can improve their hydrogen‐bonding environment on release. This contrasts with the classical form of the hydrophobic effect in which the favourable entropy change associated with release of ordered molecules from hydrophobic surfaces dominates. For several guests Van't Hoff plots showed that the free energy of binding in water is primarily enthalpy driven. For five homologous pairs of guests related by the presence or absence of a CH2 group, the incremental changes to ΔH and TΔS for guest binding—that is, ΔΔH and TΔΔS, the difference in contributions arising from the CH2 group—are consistently 5(±1) kJ mol−1 for ΔΔH and 0(±1) kJ mol−1 for TΔΔS. This systematic dominance of ΔH in the binding of hydrophobic guests is consistent with the view that guest binding is dominated by release of “high energy” water molecules into a more favourable solvation environment, as has been demonstrated recently for some members of the cucurbituril family. [ABSTRACT FROM AUTHOR]

A water-soluble fluorescent sensor based on the interaction of twisted cucurbit[14]uril ( tQ[14]) and thiazole orange (TO) in aqueous solution was developed. Formation of the tQ[14]/TO complex gives rise to stronger fluorescence in both neutral and acidic aqueous solutions compared with that of free TO. Further experiments on the interaction of the tQ[14]/TO complex with metal ions revealed that, from a series of nineteen selected common metal ions, 1) only Hg2+ can lead to fluorescence enhancement and then quenching of the tQ[14]/TO (2:1) complex in neutral aqueous solution; 2) only Ba2+ can induce fluorescence quenching of the tQ[14]/TO (2:1) complex in aqueous HCl solution (pH 2); furthermore, the tQ[14]/TO/Ba2+ systems exhibit reversible changes in fluorescent intensity on successively adding SO42− and Ba2+; and 3) only Ba2+ or Pb2+ can induce fluorescence quenching of the tQ[14]/TO (15:1) complex in aqueous HCl solution (pH 2). Thus, the tQ[14]/TO complex can act as a supramolecular fluorescence-based sensor for the determination of Hg2+, Ba2+, and Pb2+ ions. [ABSTRACT FROM AUTHOR]

Selective tuning of arylethynyl urea scaffolds for anionic guests requires an understanding of preferred binding motifs of the host-guest interaction. To investigate the binding preference of receptors without a pre-organized binding pocket, two electron-deficient phenylacetylene receptors with a single urea moiety have been prepared and were found to bind halides as 2:1 host-guest complexes that feature key CH-anion or anion-π interactions. These supporting interactions also appear to influence the mechanism of the 2:1 binding event. [ABSTRACT FROM AUTHOR]

As the host possessing the largest cavity in the cucurbit[ n]uril (CB[ n]) family, CB[10] has previously displayed unusual recognition and assembly properties with guests but much remains to be explored. Herein, we present the recognition properties of CB[10] toward a series of bipyridinium guests including the tetracationic cyclophane known as blue box along with electron-rich guests and detail the influence of encapsulation on the charge-transfer interactions between guests. For the mono-bipyridinium guest (methylviologen, MV2+), CB[10] not only forms 1:1 and 1:2 inclusion complexes, but also enhances the charge-transfer interactions between methylviologen and dihydroxynaphthalene ( HN) by mainly forming the 1:2:1 packed 'sandwich' complex (CB[10] ⋅2 MV2+ ⋅HN). For guest 1 with two bipyridinium units, an interesting conformational switching from linear to 'U' shape is observed by adding catechol to the solution of CB[10] and the guest. For the tetracationic cyclophane-blue box, CB[10] forms a stable 1:1 inclusion complex; the two bipyridinium units tilt inside the cavity of CB[10] according to the X-ray crystal structure. Finally, a supramolecular 'Russian doll' was built up by threading a guest through the cavities of both blue box and CB[10]. [ABSTRACT FROM AUTHOR]

Star-shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa- or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical ( Eg(opt)) as well as electrochemical ( Eg(electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed Eg(opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole-based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host-type light-emitting diodes. They also showed a strong tendency to self-organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X-ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self-assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis-NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes. [ABSTRACT FROM AUTHOR]

Benzene, toluene, ethylbenzene, the isomers of xylene, and trimethylbenzene are harmful volatile organic compounds and pose risks to human health and the environment. However, there are currently no effective chemosensors for vapors of these compounds. A porous supramolecular host for turn-on fluorogenic and chromogenic detection of the vapors of small aromatic hydrocarbons is presented. The host was constructed from a naphthalenediimide derivative that was supramolecularly connected to tris(pentafluorophenyl)borane. The amorphous powder form of the host allowed for effective accommodation of vapors of small aromatic hydrocarbons, resulting in a guest-dependent fluorescence emission. Increases in the fluorescence yield of 76-, 46-, and 37-fold were observed with toluene, benzene, and m-xylene, respectively. Negligible responses were obtained with common organic solvents. This simple supramolecular host could be applied as a useful sensor of small aromatic hydrocarbon vapors. [ABSTRACT FROM AUTHOR]

The Huisgen thermal reaction between an organic azide and an acetylene was employed for the selective monofunctionalization of a X6-azacryptand ligand bearing a tren coordinating unit [X6 stands for calix[6]arene and tren for tris(2-aminoethyl)amine]. Supramolecular assistance, originating from the formation of a host-guest inclusion complex between the reactants, greatly accelerates the reaction while self-inhibition affords a remarkable selectivity. The new ligand possesses a single amino-leg appended at the large rim of the calixarene core and the corresponding Zn2+ complex was characterized both in solution and in the solid state. The coordination of Zn2+ not only involves the tren cap but also the introverted amino-leg, which locks the metal ion in the cavity. Compared with the parent ligand deprived of the amino-leg, the affinity of the new monofunctionalized X6tren ligand 6 for Zn2+ is found to have a 10-fold increase in DMSO, which is a very competitive solvent, and with an enhancement of at least three orders of magnitude in CDCl3/CD3OD (1:1, v/v). In strong contrast with the fast binding kinetics, decoordination of Zn2+ as well as transmetallation appeared to be very slow processes. The monofunctionalized X6tren ligand 6 fully protects the metal ion from the external medium thanks to the combination of a cavity and a closed coordination sphere, leading to greater thermodynamic and kinetic stabilities. [ABSTRACT FROM AUTHOR]