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To investigate the dynamic stereochemical inversion behavior of pillar[5]arenes (P[5]s) in more detail, we synthesized a series of novel rim-differentiated P[5]s with various substituents and examined their rapid rotations by variable-temperature NMR (203–298 K). These studies revealed for the first time the barrier of “methyl-through-the-annulus” rotation (ΔG‡ = 47.4 kJ·mol–1 in acetone) and indicated that for rim-differentiated P[5]s with two types of alkyl substituents, the smaller rim typically determines the rate of rotation. However, substituents with terminal C=C or C≡C bonds give rise to lower inversion barriers, presumably as a result of attractive π–π interactions in the transition state. Finally, data on a rim-differentiated penta-methyl-penta-propargyl P[5] exhibited the complexity of the overall inversion dynamics.

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

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.

Pillar[5]arenes, a type of novel macrocycles containing di-substituted hydroquinone units linked by methylene bridges in para-positions, have attracted extensive attention in supramolecular chemistry as interesting candidates to be used in the preparation of host-guest complexes. Functionalization by means of rim substitution and sustaining an ordered substituent arrangement on both sides of the rim is important for the development of new pillararene-based materials. In order to achieve this, the rim inversion process of rotating the hydroquinone units through the pillar[5]arenes has to be controlled. In this context we have studied the effect of different types of hydroquinone substituents on the rotational energy profile using density functional theory combined with the hybrid M06-2X functional. The influence of polar ([sbnd]CH2F, [sbnd]CH2Cl, [sbnd]CH2OH, [sbnd]CH2SH, [sbnd]CH2NH2) and nonpolar alkyl ([sbnd]CH3, [sbnd]CH2CH3, [sbnd]CH2CH2CH3, [sbnd]CH(CH3)2 and [sbnd]CH2CH2CH2CH3) substituents on the on the energy barriers of the rotation mechanism, and different local minima was investigated. The stabilization of the intermediate structures by non-covalent van der Waals and interactions and also by hydrogen bonds constitute a major factor affecting barrier heights. In case of polar substituents, the largest barriers were found for [sbnd]CH2OH and [sbnd]CH3 substitutions and the lowest ones for [sbnd]CH2SH and [sbnd]CH2NH2. For the alkyl series, the barrier decreased significantly up to propyl due to increasing stabilizing dispersion interactions while it increased again for n-butyl since the chain did not fit in well the cavity to rotate through.

[Image: see text] The development of an efficient synthetic route toward rim-differentiated C(5)-symmetric pillar[5]arenes (P[5]s), whose two rims are decorated with different chemical functionalities, opens up successive transformations of this macrocyclic scaffold. This paper describes a gram-scale synthesis of a C(5)-symmetric penta-hydroxy P[5] precursor, and a range of highly efficient reactions that allow functionalizing either rim at will via, e.g., sulfur(VI) fluoride exchange (SuFEx) reactions, esterifications, or Suzuki–Miyaura coupling. Afterward, BBr(3) demethylation activates another rim for similar functionalizations.

Stereolabile pillar[5]arene (P[5]) derivatives, which are dynamic racemic mixtures in solution on account of their low inversion barriers, were employed as platforms to study chiral symmetry breaking during crystallisation. In the solid state, we showed that crystal enantiomeric excess of a conglomerate-forming P[5] derivative can be obtained by handpicking and Viedma ripening without the intervention of external chiral entities. On the other hand, in the presence of ethyl d/l-lactate as both optically-active solvents and chiral guests, the handedness of P[5] derivative crystals, either forming racemic compounds or conglomerates upon condensation, can be directed and subsequently inverted in a highly controllable manner., Stereolabile pillar[5]arene derivatives, which are dynamic racemic mixtures in solution on account of their low inversion barriers, were employed as platforms to study chiral symmetry breaking during crystallisation.

A bistable [2]catenane composed of a tetracationic cyclophane, namely cyclobis(paraquat-p-phenylene) (CBPQT4+) that is mechanically interlocked by a neutral macrocylic component containing both a 1,5-dioxynaphthalene (DNP) and a naphthalene-1,4,5,8-bis(dicarboximide) (NDI) unit, was obtained by using template-directed synthesis via click chemistry. In the fully oxidized state, the CBPQT4+ component encircles the DNP unit, driven by donor-acceptor interactions. Upon reduction of both the CBPQT4+ ring and the NDI unit, the CBPQT2(˙+) ring undergoes shuttling and resides on the NDI˙- station, driven by coulombic-enhanced spin-pairing interactions between different aromatic radicals.

Supramolecular cages/vesicles in biology display sophisticated structures and functions by utilizing a few types of protein subunit quasi-equivalently at distinct geometrical locations. However, synthetic supramolecular cages still lack comparable complexity to reach the high levels of functionality found in natural systems. Herein we report the self-assembly of giant pentagonal supramolecular prisms (molecular weight >50 kDa) with tetratopic pyridinyl subunits serving different geometrical roles within the structures, and their packing into a novel superstructure with unexpected three-fold rotational symmetry in a single two-dimensional layer of crystalline state. The formation of these complicated structures is controlled by both the predetermined angles of the ligands and the mismatched structural tensions created from the multi-layered geometry of the building blocks. Such a self-assembly strategy is extensively used by viruses to increase the volume and complexity of capsids and would provide a new approach to construct highly sophisticated supramolecular architectures.

Atmospheric moisture uptake by materials of varying hygroscopicity can substantially alter their physicochemical properties and thus has long been a point of interest in the development and manufacture of various commodities. In particular, hydrochromic materials have achieved much commercial success as sensors and for their applications in the paint and coatings industry. It is essential that these materials are scalable, easily processed from their raw materials, exhibit point-of-use versatility, and are sufficiently sensitive to changes in water content. Herein, we report the design, synthesis, and material processing of two integrated fluorophore-receptor systems that undergo reversible fluorescence hydrochromism in the solid state in response to changes in atmospheric relative humidity. The systems are comprised of a 1,8-naphthalimide fluorophore coupled to an amphiphilic pyridinium acceptor and its bromide counterion, which serves as a water-sensitive receptor capable of engaging the emissive unit by way of excited state charge transfer. Dynamic vapor sorption isotherms revealed that the pristine raw material experiences a blue-to-green 27 nm bathochromic shift in its emission upon 3.8 weight% water uptake. Processing of the materials into hydrochromic ultra-light agar-based hygroscopic aerogels significantly enhanced their hydrochromic sensitivity, effectively decreasing their critical relative humidity from ≈75% to less than 20% with bathochromic shifts up to 93 nm. Fluorescent hydrochromic silica gel/carboxymethyl cellulose films and inkjet printer compatible inks were developed and demonstrated increased point-of-use versatility.

A class of metal-organic frameworks (MOFs)-namely CD-MOFs-obtained from natural products has been grown in an epitaxial fashion as films on the surfaces of glass substrates, which are modified with self-assembled monolayers (SAMs) of γ-cyclodextrin (γ-CD) molecules. The SAMs are created by host-guest complexation of γ-CD molecules with surface-functionalized pyrene units. The CD-MOF films have continuous polycrystalline morphology with a structurally out-of-plane ( c-axial) orientation, covering an area of several square millimeters, with a thickness of ∼2 μm. Furthermore, this versatile host-guest strategy has been applied successfully in the growth of CD-MOFs as the shell on the curved surface of microparticles as well as in the integration of CD-MOF films into electrochemical devices for sensing carbon dioxide. In striking contrast to the control devices prepared from CD-MOF crystalline powders, these CD-MOF film-based devices display an enhancement in proton conductance of up to 300-fold. In addition, the CD-MOF film-based device exhibits more rapid and highly reversible CO2-sensing cycles under ambient conditions, with a 50-fold decrease in conductivity upon exposure to CO2 for 3 s which is recovered within 10 s upon re-exposure to air.

The synthesis of "rim-differentiated" C5-symmetric pillar[5]arenes, whose two rims are decorated with different chemical functionalities, has remained a challenging task. This is due to the inherent statistical nature of the cyclization of 1,4-disubstituted alkoxybenzenes with different substituents, which leads to four constitutional isomers with only 1/16th being rim-differentiated. Herein, we report a "preoriented" synthetic protocol based on FeCl3-catalyzed cyclization of asymmetrically substituted 2,5-dialkoxybenzyl alcohols. This yields an unprecedented 55% selectivity of the C5-symmetric tiara-like pillar[5]arene isomer among four constitutional isomers. Based on this new method, a series of functionalizable tiara-pillar[5]arene derivatives with C5-symmetry was successfully synthesized, isolated, and fully characterized in the solid state.

Ferroelectricity in organic materials remains a subject of great interest, given its potential impact as lightweight information storage media. Here we report supramolecular charge-transfer cocrystals formed by electron acceptor and donor molecules that exhibit ferroelectric behavior along two distinct crystallographic axes. The solid-state superstructure of the cocrystals reveals that a 2:1 ratio of acceptor to donor molecules assemble into nearly orthogonal mixed stacks in which the molecules are positioned for charge-transfer in face-to-face and edge-to-face orientations, held together by an extended hydrogen-bonding network. Polarization hysteresis was observed along the face-to-face and edge-to-face axes at room temperature. The noncentrosymmetric nature of the cocrystals, required to observe ferroelectric behavior, is demonstrated using second harmonic generation measurements. This finding suggests the possibility of designing supramolecular arrays in which organic molecules support multidimensional information storage.

A general synthetic route to inherently luminescent and optically active 6-fold substituted C3-symmetric and asymmetric biphenyl-based trianglimines has been developed. The synthesis of these hexa-substituted triangular macrocycles takes advantage of a convenient method for the synthesis of symmetrically and asymmetrically difunctionalized biphenyl dialdehydes through a convergent two-step aromatic nucleophilic substitution-one-pot Suzuki-coupling reaction protocol. A modular [3+3] diamine-dialdehyde cyclocondensation reaction between both the symmetrically and asymmetrically difunctionalized-4,4′-biphenyldialdehydes with enantiomerically pure (1R,2R)-1,2-diaminocyclohexane was employed to construct the hexa-substituted triangular macrocycles. B97-D/6-311G(2d,p) density functional theory determined structures and X-ray crystallographic analysis reveal that the six substituents appended to the biphenyl legs of the trianglimine macrocycles adopt an alternating conformation not unlike the 1,3,5-alternate con...

Tiara[5]arenes (T[5]s), a new class of five‐fold symmetric oligophenolic macrocycles that are not accessible from the addition of formaldehyde to phenol, were synthesized for the first time. These pillar[5]arene‐derived structures display both unique conformational freedom, differing from that of pillararenes, with a rich blend of solid‐state conformations and excellent host–guest interactions in solution. Finally we show how this novel macrocyclic scaffold can be functionalized in a variety of ways and used as functional crystalline materials to distinguish uniquely between benzene and cyclohexane., I have a tiara! Tiara[5]arenes, a class of five‐fold symmetric oligophenol macrocycles, which is not accessible by direct phenol‐formaldehyde condensation, was synthesized through the metamorphosis of pillar[5]arenes.

International audience; Lock-arm supramolecular ordering cocrystals formed by π-stacked materials constitute an interesting class of materials, which exhibits ferroelectric behavior at room temperature. To characterize the charge transfer in excited states, two complexes with π-stacked donors and acceptors, the 1,5-naphthalene diol (NDI) donor and pyromellitic diimide with diethylene glycol arms (PDIA) acceptor, 5-amino-1-naphthol (AMN) donor and PDIA acceptor, were investigated. The electronic excitations were calculated using the scaled opposite-spin variant of ADC(2), time-dependent density functional theory (TD-DFT) using a long-range corrected (LC) functional (ωB97xD), and the TD-LC approach within density-functional-based tight binding (TD-LC-DFTB). Face-to-face mixed stacks and edge-to-face crossed stacks up to hexamers were investigated. The calculations show that the ground state of the complexes does not possess significant CT character. On the other hand, the lowest excited state (S1) shows in all clusters a strong charge transfer. In several cases, the second excited state and also higher excited singlet states possess significant CT character. The orbitals involved in the excitation are mostly well localized and located on adjacent donor/acceptor pairs. Comparing different stacking directions, the vertical excitation energies for the NDI–PDIA crossed stacks are larger than those for the mixed stacks by 0.2–0.4 eV. In the case of the AMN–PDIA system, the energy differences are smaller (∼0.1 eV) with mostly the same energetic ordering as for the NDI–PDIA case. Strong red shifts in vertical fluorescence emission transitions have been computed, which could even lead to intersection between ground and first excited states, resulting in ultrafast radiationless decay and fluorescence quenching.

Charge-transfer (CT) interactions have recently attracted enhanced interest in creating ordered ferroelectric networks of electron donors (D) and acceptors (A) and in providing the basis of functional photonic devices. In the present work, the CT character of three distinct donor–acceptor (D–A) complex interactions (pyromellitic diimide (PDI)/1,5-diaminonaphthalene (DAN), para-chloranil (pClA)/tetramethyl-para-phenylenediamine (TMPD) and tetracyanobenzene (TCNB)/1,2-di(4-pyridyl)ethylene (Bpe)) has been investigated in their ground and excited states using high-level quantum chemical methods (second-order algebraic diagrammatic construction (ADC(2)) and time-dependent density functional theory (TD-DFT) using a long-range corrected functional (ωB97xD)). The calculations show that the lowest electronic excitation has pronounced CT character in all the three dimers investigated. On the contrary, the ground states possess only smaller amounts of CT degree except for the pClA/TMPD complex, which has a strong amount of CT of 0.4 e. Optimization of the S1 state and calculation of the resulting vertical fluorescence transitions led to the interesting finding of a zero-energy gap for pClA/TMPD. The next smallest energy gap is computed for PDI/DAN (1 eV) followed by TCNB/Bpe (2.6 eV). The analysis of the electronic charge distribution of the D–A complex in the excited state shows a significant variation even though practically a full electron charge has been transferred from D to A.

Reversible template-directed micellar-size and shape modulation by virtue of host-guest reversible docking of molecular templates at the micellar-solvent interface was achieved in water. By combining a π-electron deficient bipyridinium-based gemini amphiphile which is capable of binding and aligning with a π-electron rich tri(ethylene glycol)-disubstituted 1,5-diaminonaphthalene, a switchable detergent system which operates through the pH-responsive formation of bisammonium dications was realised. The binding of the 1,5-diaminonaphthalene guest to the bipyridinium-based micellar aggregate superstructure can be actuated by the addition of acid and base. Upon the addition of acid, protonation of the guest forming the dication deactivates molecular recognition with the charged head groups of the micellar aggregate by Coulombic repulsion. This process is completely reversible upon the addition of base, whereby the guest reintercalates into the superstructure -again forming donor-acceptor π-π stacks at the micellar-solvent interface amongst contiguous surfactant head groups. Synchrotron small angle X-ray scattering and dynamic laser light scattering confirm that this form of reversible directionally-templated micellisation results in an oblate spheroid-to-lamellar micelle morphological transition with a stabilising net decrease in the free energy of micellisation of 1.4 kcal mol(-1) per hydrophobic tail.

The formation dynamics of a host-guest complex is successfully investigated in graphene-based single-molecule electronic devices., Single-molecule electronic devices offer unique opportunities to investigate the properties of individual molecules that are not accessible in conventional ensemble experiments. However, these investigations remain challenging because they require (i) highly precise device fabrication to incorporate single molecules and (ii) sufficient time resolution to be able to make fast molecular dynamic measurements. We demonstrate a graphene-molecule single-molecule junction that is capable of probing the thermodynamic and kinetic parameters of a host-guest complex. By covalently integrating a conjugated molecular wire with a pendent crown ether into graphene point contacts, we can transduce the physical [2]pseudorotaxane (de)formation processes between the electron-rich crown ether and a dicationic guest into real-time electrical signals. The conductance of the single-molecule junction reveals two-level fluctuations that are highly dependent on temperature and solvent environments, affording a nondestructive means of quantitatively determining the binding and rate constants, as well as the activation energies, for host-guest complexes. The thermodynamic processes reveal the host-guest binding to be enthalpy-driven and are consistent with conventional 1H nuclear magnetic resonance titration experiments. This electronic device opens up a new route to developing single-molecule dynamics investigations with microsecond resolution for a broad range of chemical and biochemical applications.

Organic-based molecular switches (OMS) are essential components for the ultimate miniaturization of nanoscale electronics and devices. For practical applications, it is often necessary for OMS to be incorporated into functional solid-state materials. However, the switching characteristics of OMS in solution are usually not transferrable to the solid state, presumably because of spatial confinement or inefficient conversion in densely packed solid phase. A promising way to circumvent this issue is harboring the functional OMS within the robust and porous environment of metal-organic frameworks (MOFs) as their organic components. In this feature article, recent research progress of OMS-based MOFs is briefly summarized. The switching behaviors of OMS under different stimuli (e.g., light, redox, pH, etc.) in the MOF state are first introduced. After that, the technological applications of these OMS-based MOFs in different areas, including CO2 adsorption, gas separation, drug delivery, photodynamic therapy, and sensing, are outlined. Finally, perspectives and future challenges are discussed in the conclusion.