Halogen Bonding Directed Supramolecular Quadruple and Double Helices from Hydrogen-Bonded Arylamide Foldamers

Benzoselenadiazole-Functionalized H-Bonded Arylamide Foldamers: Solvent-Responsive Properties and Helix Self-Assembly Directed by Chalcogen Bonding in Solid State

In this study, a series of H-bonded arylamide foldamers bearing benzoselenadiazole ends with solvent-responsive properties have been synthesized. In dichloromethane or dimethyl sulfoxide solvents, the molecules exhibit meniscus or linear structures, respectively, which can be attributed to the unique intramolecular hydrogen bonding behavior evidenced by 1D 1H NMR and 2D NOESY spectra. UV-vis spectroscopy experiments show that the absorption wavelength of H-bonded arylamide foldamers are significantly red-shifted due to the presence of benzoselenadiazole group. In addition, the crystal structures reveal that effective intermolecular dual Se ⋅ ⋅ ⋅ N interactions between benzoselenadiazole groups induce further assembly of the monomers. Remarkably, supramolecular linear and double helices structures are constructed under the synergistic induction of intramolecular hydrogen bonding and intermolecular chalcogen bonding. Additionally, 2D DOSY diffusion spectra and theoretical modelling based on density functional theory (DFT) are performed to explore the persistence of intermolecular Se ⋅ ⋅ ⋅ N interactions beyond the crystalline state.

Multiple non-covalent-interaction-directed supramolecular double helices: the orthogonality of hydrogen, halogen and chalcogen bonding

In this study, a benzoselenadiazole- and pyridine-bifunctionalized hydrogen-bonded arylamide foldamer was synthesized. A co-crystallization experiment with 1,4-diiodotetrafluorobenzene showed that a new type of supramolecular double helices, which were induced by three orthogonal interactions, namely, three-center hydrogen bonding (O⋯H⋯O), I⋯N halogen bonding and Se⋯N chalcogen bonding, have been constructed in the solid state. This work presents a novel instance of multiple non-covalent interactions that work together to construct supramolecular architectures.

Correction: Halogen-bonded charge-transfer co-crystal scintillators for high-resolution X-ray imaging

[This corrects the article DOI: 10.1039/D4SC00735B.].

Halogen-bonded charge-transfer co-crystal scintillators for high-resolution X-ray imaging

The development of high-quality organic scintillators encounters challenges primarily associated with the weak X-ray absorption ability resulting from the presence of low atomic number elements. An effective strategy involves the incorporation of halogen-containing molecules into the system through co-crystal engineering. Herein, we synthesized a highly fluorescent dye, 2,5-di(4-pyridyl)thiazolo[5,4-d]thiazole (Py2TTz), with a fluorescence quantum yield of 12.09%. Subsequently, Py2TTz was co-crystallized with 1,4-diiodotetrafluorobenzene (I2F4B) and 1,3,5-trifluoro-2,4,6-triiodobenzene (I3F3B) obtaining Py2TTz-I2F4 and Py2TTz-I3F3. Among them, Py2TTz-I2F4 exhibited exceptional scintillation properties, including an ultrafast decay time (1.426 ns), a significant radiation luminescence intensity (146% higher than Bi3Ge4O12), and a low detection limit (70.49 nGy s-1), equivalent to 1/78th of the detection limit for medical applications (5.5 μGy s-1). This outstanding scintillation performance can be attributed to the formation of halogen-bonding between I2F4B and Py2TTz. Theoretical calculations and single-crystal structures demonstrate the formation of halogen-bond-induced rather than π-π-induced charge-transfer cocrystals, which not only enhances the X-ray absorption ability and material conductivity under X-ray exposure, but also constrains molecular vibration and rotation, and thereby reducing non-radiative transition rate and sharply increasing its fluorescence quantum yields. Based on this, the flexible X-ray film prepared based on Py2TTz-I2F4 achieved an ultrahigh spatial resolution of 26.8 lp per mm, underscoring the superiority of this strategy in developing high-performance organic scintillators.

Supramolecular helix of an oligomeric azapeptide building block containing four β-turn structures

Oligomers of benzoylalanine-based amidothioureas containing four β-turn structures spaced by meta-substituted benzenes were shown to undergo assembly in dilute CH3CN solution into supramolecular helices of enhanced supramolecular helicity, whereas those spaced by para-substituted benzene spacer(s) or those spaced by meta-substituted benzenes but with one or two β-turns exhibit a substantially decreased tendency of assembling.

Noncovalent interaction network of chalcogen, halogen and hydrogen bonds for supramolecular β-sheet organization

An alanine-based bilateral building block, linked by 2,5-thiophenediamide motifs and equipped with C-terminal 4-iodoaniline groups, was designed, allowing a noncovalent interaction network consisting of intramolecular chalcogen bonds and intermolecular halogen/hydrogen bonds, which cooperatively maintain a supramolecular β-sheet organization in the solid state, as well as in dilute CH3CN solution with a high g factor of -0.017.

Design of Chiral β-Double Helices from γ-Peptide Foldamers

Chirality is ubiquitous in nature, and homochirality is manifested in many biomolecules. Although β-double helices are rare in peptides and proteins, they consist of alternating L- and D-amino acids. No peptide double helices with homochiral amino acids have been observed. Here, we report chiral β-double helices constructed from γ-peptides consisting of alternating achiral (E)-α,β-unsaturated 4,4-dimethyl γ-amino acids and chiral (E)-α,β-unsaturated γ-amino acids in both single crystals and in solution. The two independent strands of the same peptide intertwine to form a β-double helix structure, and it is stabilized by inter-strand hydrogen bonds. The peptides with chiral (E)-α,β-unsaturated γ-amino acids derived from α-L-amino acids adopt a (P)-β-double helix, whereas peptides consisting of (E)-α,β-unsaturated γ-amino acids derived from α-D-amino acids adopt an (M)-β-double helix conformation. The circular dichroism (CD) signature of the (P) and (M)-β-double helices and the stability of these peptides at higher temperatures were examined. Furthermore, ion transport studies suggested that these peptides transport ions across membranes. Even though the structural analogy suggests that these new β-double helices are structurally different from those of the α-peptide β-double helices, they retain ion transport activity. The results reported here may open new avenues in the design of functional foldamers.

Two and three-dimensional halogen-bonded frameworks: self-assembly influenced by crystallization solvents

In this paper, two types of solid phase 2D and 3D XBOFs were selectively constructed from identical building blocks of tetraphenylmethane tetrapyridine derivative and 1,4-diiodotetrafluorobenzene by changing the crystallization solvent. This 3D XBOF is a novel hybrid supramolecular organic framework with the synergistic control of hydrogen and halogen bonds.

Principles and Applications of CF2X Moieties as Unconventional Halogen Bond Donors in Medicinal Chemistry, Chemical Biology, and Drug Discovery

As an orthogonal principle to the established (hetero)aryl halides, we herein highlight the usefulness of CF2X (X = Cl, Br, or I) moieties. Using tool compounds bearing CF2X moieties, we study their chemical/metabolic stability and their logP/solubility, as well as the role of XB in their small molecular crystal structures. Employing QM techniques, we analyze the observed interactions, provide insights into the conformational flexibilities and preferences in the potential interaction space. For their application in molecular design, we characterize their XB donor capacities and its interaction strength dependent on geometric parameters. Implementation of CF2X acetamides into our HEFLibs and biophysical evaluation (STD-NMR/ITC), followed by X-ray analysis, reveals a highly interesting binding mode for fragment 23 in JNK3, featuring an XB of CF2Br toward the P-loop, as well as chalcogen bonds. We suggest that underexplored chemical space combined with unconventional binding modes provides excellent opportunities for patentable chemotypes for therapeutic intervention.

Synergistic Covalent-and-Supramolecular Polymers with an Interwoven Topology

Network topologies, especially some high-order topologies, are able to furnish cross-linked polymer materials with enhanced properties without altering their chemical composition. However, the fabrication of such topologically intriguing architectures at the macromolecular level and in-depth insights into their structure-property relationship remain a significant challenge. Herein, we relied on synergistic covalent-and-supramolecular polymers (CSPs) as a platform to prepare a range of polymer networks with an interwoven topology. Specifically, through the sequential supramolecular self-assemblies, the covalent polymers (CPs) and metallosupramolecular polymers (MSPs) could be interwoven in our CSPs by [2]pseudorotaxane cross-links. As a result, the obtained CSPs possessed a topological network that could not only promote the synergistic effect between CPs and MSPs to afford mechanically robust yet dynamic materials but also vest polymers with some functions, as manifested by force-induced hierarchical dissociations of supramolecular interactions and superior thermomechanical stability compared to our previously reported CSP systems. Furthermore, our CSPs exhibited tunable mechanical performance toward multiple stimuli including K⁺ and PPh₃, demonstrating abundant stimuli-responsive properties. We hope that these findings could provide novel opportunities toward achieving topological structures at the macromolecular level and also motivate further explorations of polymeric materials via the way of controlling their topological structures.

Hierarchical porous photosensitizers with efficient photooxidation

Photosensitizers (PSs) with nano- or micro-sized pore provide a great promise in the conversion of light energy into chemical fuel due to the excellent promotion for transporting singlet oxygen (¹O₂) into active sites. Despite such hollow PSs can be achieved by introducing molecular-level PSs into porous skeleton, however, the catalytic efficiency is far away from imagination because of the problems with pore deformation and blocking. Here, very ordered porous PSs with excellent ¹O₂ generation are presented from cross-linking of hierarchical porous laminates originated by co-assembly of hydrogen donative PSs and functionalized acceptor. The catalytic performance strongly depends on the preformed porous architectures, which is regulated by special recognition of hydrogen binding. As the increasing of hydrogen acceptor quantities, 2D-organized PSs laminates gradually transform into uniformly perforated porous layers with highly dispersed molecular PSs. The premature termination by porous assembly endows superior activity as well as specific selectivity for the photo-oxidative degradation, which contributes to efficient purification in aryl-bromination without any postprocessing.

Boat and Chair Shaped Hexahalogen Synthons

Non-covalent halogen bonding interactions are quintessential in crystal engineering for the construction of distinctive supramolecular synthons. Here, we report the first crystalline evidences of unique boat and chair shaped cyclic hexahalogen synthons in the crystal structures of α,α,α',α',4-pentabromo-o-xylene (PBX) and α,α,α',α',4,5-hexabromo-o-xylene (HBX) respectively. Nature and stability of constituent interactions in the supramolecular synthons are scrutinized with the help of quantum-chemical calculations. Pendás' interacting quantum atoms approach confirmed the stability of Br⋅⋅⋅Br interactions leading to boat and chair shaped synthons with major contribution from exchange-correlation. Although both the molecules are achiral in nature, the packing forces guide PBX to crystallize in the chiral space group P2₁ with a helix-like orientation while HBX packs in a centrosymmetric P2₁ /n space group. The extended furcations in the pentabromo derivative construct a molecular framework consisting of macrocycles realized through halogen bonding.

Hydrogen Bonded Foldamers with Axial Chirality: Chiroptical Properties and Applications

Folding phenomenon refers to the formation of a specific conformation widely featured by the intramolecular interactions, which broadly exist in biomacromolecules, and are closely related to their structures and functions. A variety of oligomeric folded molecules have been designed and synthesized, namely "foldamer", exhibiting potentials in pharmaceutical and catalysis. Molecular folding is a promising strategy to transfer chirality from substituents to the whole skeleton, when chirality transfer, amplification, evolution, and other behaviors could be achieved. Investigating chirality using foldamer model deepens the understanding of the structure-function correlation in biomacromolecules and expands the molecular toolbox towards chiroptical and asymmetrical chemistry. Substitutes with abundant hydrogen bonding sites conjugated to a rotatable aryl group afford a parallel β-sheet-like conformation, which enables the emergence and manipulation of axial chirality. This concept aims to give a brief introduction and summary of the hydrogen bonded foldamers with anchored axial chirality, by taking some recent cases as examples. Design principles, control over axial chirality and applications are also reviewed.

Directing the Self-Assembly of Aromatic Foldamer Helices using Acridine Appendages and Metal Coordination

Folded molecules provide complex interaction interfaces amenable to sophisticated self-assembly motifs. Because of their high conformational stability, aromatic foldamers constitute suitable candidates for the rational elaboration of self-assembled architectures. Several multiturn helical aromatic oligoamides have been synthesized that possess arrays of acridine appendages pointing in one or two directions. The acridine units were shown to direct self-assembly in the solid state via aromatic stacking leading to recurrent helix-helix association patterns under the form of discrete dimers or extended arrays. In the presence of Pd(II), metal coordination of the acridine units overwhelms other forces and generates new metal-mediated multihelical self-assemblies, including macrocycles. These observations demonstrate simple access to different types of foldamer-containing architectures, ranging from discrete objects to 1D and, by extension, 2D and 3D arrays.

Cavity-containing aromatic oligoamide foldamers and macrocycles: progress and future perspectives

As a major class of foldamers, aromatic oligoamide foldamers have attracted intense interest. The rigidity of aromatic residues and amide linkages allows the development of foldamers with readily predictable, stable conformations. Aromatic oligoamide foldamers having backbones fully constrained by intramolecular hydrogen bonds have attracted wide attention. Depending on their lengths, such foldamers adopt crescent or helical conformations with highly negative inner cavities. Cyclizing the backbone of the aromatic oligoamides affords the corresponding macrocycles which are characterised by persistent shapes and non-deformable inner cavities. With their defined, inner cavities, such aromatic oligoamide foldamers and macrocycles have served as hosts for cationic and polar guests, and as transmembrane channels for transporting ions and molecules. Recent synthetic progress resulted in the construction of multi-turn hollow helices that offer three-dimensional inner pores with adjustable depth. Reducing the number of backbone-constraining hydrogen bonds leads to oligoamides which, with their partially constrained backbones, undergo either solvent- or guest-dependent folding. One class of such aromatic olgioamide foldamders, which offer multiple backbone amide NH groups as hydrogen-bond donors, are designed to bind anions with adjustable affinities.

Understanding of supramolecular solution polymerization and interfacial polymerization via forming multiple hydrogen bonds: a computer simulation study

By employing dissipative particle dynamics (DPD) simulations combined with stochastic polymerization models, we have conducted a detailed simulation study of supramolecular solution polymerization as well as interfacial polymerization employing a coarse-grained model which is closer to the real monomer structure. By adding bending angle potentials to coarse-grained models representing supramolecular reactive monomers, we achieved monomer model simulations for different kinds of multiple hydrogen bonds. Our simulation results indicated that for the interfacial polymerization system, the volume of the monomer caused a strong steric hindrance effect, which in turn led to a low average degree of polymerization of the product. Therefore, by appropriately reducing the volume of the reaction monomer (corresponding to different confinement ascribed to the multiple hydrogen bonds), the average polymerization degree, the degree of reaction and the polymerization rate of the monomer can be effectively improved. For the solution polymerization system and the interfacial polymerization system, a certain proportion of rigid monomers and flexible monomers (60% rigid monomers and 40% flexible monomers) are mixed. High molecular weight products can thus be obtained via the polymerization reaction. The simulation strategy proposed in this study can not only provide theoretical guidance for better design of new supramolecular systems, but also provide ideas for the further synthesis of higher molecular weight supramolecular polymers.

Bifurcated Halogen Bond-Driven Supramolecular Double Helices from 1,2-Dihalotetrafluorobenzene and 2,2′-Bi(1,8-naphthyridine)

The unique enantiomeric pairs of double helices have been found in the structure of the cocrystal between 1,2-diiodotetrafluorobenzene and 2,2′-bi(1,8-naphthyridine). The formation of the supramolecular double helices is driven by the strong bifurcated iodine bonds which can force the herringbone packing arrangement of the molecules 2,2′-bi(1,8-naphthyridine) into a face-to-face π···π stacking pattern. In contrast, the cocrystal between 1,2-dibromotetrafluorobenzene (or 1,2-dichlorotetrafluorobenzene) and 2,2′-bi(1,8-naphthyridine) was not obtained under the same conditions. The interaction energies of the bifurcated halogen bonds and π···π stacking interactions were computed with the reliable dispersion-corrected density functional theory. The computational results show that the bifurcated iodine bond is much stronger than the bifurcated bromine bond and bifurcated chlorine bond, and it is the much stronger bifurcated iodine bond that makes the cocrystal of 1,2-diiodotetrafluorobenzene and 2,2′-bi(1,8-naphthyridine) much easier to be synthesized.

Intramolecular chalcogen bonding to tune molecular conformation of helical building block for supramolecular helix

We propose to employ intramolecular chalcogen bonding to make the helical building block take its otherwise unfavorable cis-conformation. 2,5-Thiophenediamide motif was taken to bridge two β-turn structures to lead to...

Supramolecular helices from helical building blocks via head-to-tail intermolecular interactions

Supramolecular helices from helical building blocks represent an emerging analogue of the α-helix. In cases where the helicity of the helical building block is well propagated, the head-to-tail intermolecular interactions that lead to the helix could be enhanced to promote the formation and the stability of the supramolecular helix, wherein homochiral elongation dominates and functional helical channel structures could also be generated. This feature article outlines the supramolecular helices built from helical building blocks, i.e., helical aromatic foldamers and helical short peptides that are held together by intermolecular π-π stacking, hydrogen/halogen/chalcogen bonding, metal coordination, dynamic covalent bonding and solvophobic interactions, with emphasis on the influence of efficient propagation of helicity during assembly, favouring homochirality and channel functions.

Revisiting the covalent nature of halogen bonding: a polarized three-center four-electron bond

As an important intermolecular interaction, halogen bonding has been studied extensively, but its nature still suffers from controversy without one uniform essence. Electrostatics, charge transfer, polarization and dispersion are emphasized, but the covalent nature is usually overlooked except for the strong halogen bonding species I₃⁻, which is widely accepted as a result of a three-center four-electron (3c-4e) interaction. In our study, the potential energy surface of I₃⁻ has been evaluated to explore the dissociation from I₃⁻ to I₂⋯I⁻. We found that different from an equivalent 3c-4e bond in I₃⁻, I₂⋯I⁻ can be rationalized by a polarized one. In addition, when the orbitals are polarized, it is exactly what traditional charge transfer or the popular σ-hole picture describes. I₃⁻ can be described by the Lewis theory model with the middle I⁺ cation serving as the Lewis acid and two terminal I⁻ anions acting as Lewis base. Therefore, we further extended this model to a series of I-containing species with chemical composition of L–I⁺–L, F⁻–I⁺–L and H₃P–I⁺–L (L = OH⁻, F⁻, Cl⁻, Br⁻, I⁻, PH₃, NH₃, H₂S, HI, H₂O, HBr and HCl) to explore the nature of halogen bonding. When the forces of two bases around I⁺ are the same, it corresponds to an equivalent 3c-4e bond, such as I₃⁻. Otherwise, it is a polarized multicenter bond, such as I₂⋯I⁻. This work gives a new insight into the nature of halogen bonding compounds: besides the well-known I₃⁻, the nature of the other species is also a multicenter bond, existing as equivalent and polarized 3c-4e bonds, respectively.

The halogen bond could be described with a polarized 3c-4e bond.

Chalcogen bonding mediates the formation of supramolecular helices of azapeptides in crystals

To explore whether chalcogen bonding was able to drive the formation of supramolecular helices, alanine-based azapeptides containing a β-turn structure, with a thiophene group, respectively, incorporated in the N- or C-terminus, were employed as helical building blocks. While the former derivative formed a supramolecular M-helix via intermolecular SS chalcogen bonding in crystals, the latter formed P-helix via intermolecular SO chalcogen bonding.

Self-Assembly of Size-Controlled m-Pyridine-Urea Oligomers and Their Biomimetic Chloride Ion Channels

The m-pyridine urea (mPU) oligomer was constructed by using the intramolecular hydrogen bond formed by the pyridine nitrogen atom and the NH of urea and the intermolecular hydrogen bond of the terminal carbonyl group and the NH of urea. Due to the synergistic effect of hydrogen bonds, mPU oligomer folds and exhibits strong self-assembly behaviour. Affected by folding, mPU oligomer generates a twisted plane, and one of its important features is that the carbonyl group of the urea group orientates outwards from the twisted plane, while the NHs tend to direct inward. This feature is beneficial to NH attraction for electron-rich species. Among them, the trimer self-assembles into helical nanotubes, and can efficiently transport chloride ions. This study provides a novel and efficient strategy for constructing self-assembled biomimetic materials for electron-rich species transmission.

Halogen-Bonding-Driven Self-Assembly of Solvates of Tetrabromoterephthalic Acid

Halogen bonding is one of the most interesting noncovalent attractions capable of self-assembly and recognition processes in both solution and solid phase. In this contribution, we report on the formation of two solvates of tetrabromoterephthalic acid (H2Br4tp) with acetonitrile (MeCN) and methanol (MeOH) viz. H2Br4tp·2MeCN (1MeCN) and H2Br4tp·2MeOH (2MeOH). The host structures of both 1MeCN and 2MeOH are assembled via the occurrence of simultaneous Br···Br, Br···O, and Br···π halogen bonding interactions, existing between the H2Br4tp molecular tectons. Among them, the cooperative effect of the dominant halogen bond in combination with hydrogen bonding interactions gave rise to different supramolecular assemblies, whereas the strength of the halogen bond depends on the type of hydrogen bond between the molecules of H2Br4tp and the solvents. These materials show a reversible release/resorption of solvent molecules accompanied by evident crystallographic phase transitions.

Nature of Alkali- and Coinage-Metal Bonds versus Hydrogen Bonds

We have quantum chemically studied the structure and nature of alkali- and coinage-metal bonds (M-bonds) versus that of hydrogen bonds between A-M and B- in archetypal [A-M⋅⋅⋅B]- model systems (A, B=F, Cl and M=H, Li, Na, Cu, Ag, Au), using relativistic density functional theory at ZORA-BP86-D3/TZ2P. We find that coinage-metal bonds are stronger than alkali-metal bonds which are stronger than the corresponding hydrogen bonds. Our main purpose is to understand how and why the structure, stability and nature of such bonds are affected if the monovalent central atom H of hydrogen bonds is replaced by an isoelectronic alkali- or coinage-metal atom. To this end, we have analyzed the bonds between A-M and B- using the activation strain model, quantitative Kohn-Sham molecular orbital (MO) theory, energy decomposition analysis (EDA), and Voronoi deformation density (VDD) analysis of the charge distribution.

Switchable supramolecular ensemble for anion binding with ditopic hydrogen-bonded macrocycles

A novel supramolecular strategy has been proposed by using a ditopic H-bonded amide macrocycle that is capable of controlling the binding process in response to external stimulus due to its assembly-and-disassembly-induced anion binding.

Solvophobic interaction promoted supramolecular helical assembly of building blocks of weak intermolecular halogen bonding

Bromination of β-turn structured bis(N-amidothiourea) facilitates the formation of supramolecular helical polymers in water through halogen bonding and hydrophobic interaction, exhibiting an unusual negative nonlinear CD-ee dependence.

Conformation-Dependent Phosphorescence of Galactose-Decorated Phosphors and Assembling-Induced Phosphorescence Enhancement

Amorphous organic room-temperature phosphorescent (RTP) materials are promising for their facile preparation and processability, while the conformation effects of phosphors at amorphous state are lack of study in comparison with the rigid effects due to the commonly irregular assembling and dispersal of phosphors in rigid systems. Herein, we report a series of phosphorescent molecules modified by polyhydroxy galactose, whose RTP emission at the amorphous state can be regulated by controlling the conformational distortion of the phosphorescent segments. Further, a strong RTP emission is facilely obtained by the co-assembling between polyhydroxy phosphors and polyhydroxy matrices (α-CD, β-CD, and chitosan). Owing to the rigid effect of the enhanced hydrogen bonding cross-linking, the highest RTP quantum yield reaches 19.4%; whereas, the RTP emissions of assemblies become conformation insensitive. The conflicting relationship between the conformation effect and rigid effect is attributed to the differences between aggregated single-component systems and dispersed assembling systems. Besides, the unique and different moisture responsiveness of the co-assembling samples is discovered and further applied in data encryption. The research expands the scope for designing amorphous pure organic RTP materials with supramolecular strategies and shows a modularized approach for assembling-enhanced phosphorescence.

Oligo(5-amino-N-acylanthranilic acids): Amide Bond Formation without Coupling Reagent and Folding upon Binding Anions

Oligomers of 5-amino-N-acylanthranilic acid, previously unknown aromatic oligoamides that cannot be obtained with known amide coupling methods, are synthesized based on a new, highly efficient amide-bond formation strategy that takes advantage of the ring-opening of benzoxazinone derivatives. These oligoamides offer multiple backbone NH groups as H-bond donors which, in the presence of iodide or chloride ion, are convergently arranged and H-bonded, which enforces a folded, crescent conformation. These aromatic oligoamides provide a versatile platform based on which anion-dependent foldamers, or anion binders with tunable affinity and specificity, are being constructed.

Multiturn Hollow Helices: Synthesis and Folding of Long Aromatic Oligoamides

Aromatic oligoamides adopting helical conformations are synthesized by coupling carboxyl-terminated basic units having two, four, and eight residues to amine-terminated oligomer precursors. Coupling yields show no noticeable reduction with the size of the basic units or the final product. One- and two-dimensional NMR spectroscopy and computational studies demonstrate the reliable helical folding of these oligomers. The X-ray structure of 16mer 7 reveals a compact, multiturn helix having a 9 Å inner pore.

Substitution Effects Regulate the Formation of Butterfly-Shaped Tetranuclear Dy(III) Cluster and Dy-Based Hydrogen-Bonded Helix Frameworks: Structure and Magnetic Properties

The generation of two types of complexes with different topological connections and completely different structural types merely via the substitution effect is extremely rare, especially for -CH₃ and -C₂H₅ substituents with similar physical and chemical properties. Herein, we used 3-methoxysalicylaldehyde, 1,2-cyclohexanediamine, and Dy(NO₃)₃·6H₂O to react under solvothermal conditions (CH₃OH:CH₃CN = 1:1) at 80 °C to obtain the butterfly-shaped tetranuclear Dy^III cluster [Dy₄(L¹)₄(μ₃-O)₂(NO₃)₂] (Dy₄, H₂L¹ = 6,6'-((1E,1'E)-(cyclohexane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)). The ligand H₂L¹ was obtained by the Schiff base in situ reaction of 3-methoxysalicylaldehyde and 1,2-cyclohexanediamine. In the Dy₄ structure, (L¹)^2- has two different coordination modes: μ₂-η¹:η²:η¹:η¹ and μ₄-η¹:η²:η¹:η¹:η²:η¹. The four Dy^III ions are in two coordination environments: N₂O₆ (Dy1) and O₉ (Dy2). The magnetic testing of cluster Dy₄ without the addition of an external field revealed that it exhibited a clear frequency-dependent behavior. We changed 3-methoxysalicylaldehyde to 3-ethoxysalicylaldehyde and obtained one case of a hydrogen-bonded helix framework, [DyL²(NO₃)₃]_n·2CH₃CN (Dy-HHFs, H₂L² = 6,6'-((1E,1'E)-(cyclohexane-1,3-diylbis(azanylylidene))bis(methanylylidene))bis(2-ethoxyphenol)), under the same reaction conditions. The ligand H₂L² was formed by the Schiff base in situ reaction of 3-ethoxysalicylaldehyde and 1,2-cyclohexanediamine. All Dy^III ions in the Dy-HHFs structure are in the same coordination environment (O₉). The twisted S-shaped (L²)^2- ligand is linked by a Dy(III) ion to form a spiral chain. The spiral chain is one of the independent units that is interconnected to form Dy-HHFs through three strong hydrogen-bonding interactions. Magnetic studies show that Dy-HHFs exhibits single-ion-magnet behavior (U_eff = 68.59 K and τ₀ = 1.10 × 10^-7 s, 0 Oe DC field; U_eff = 131.5 K and τ₀ = 1.22 × 10^-7 s, 800 Oe DC field). Ab initio calculations were performed to interpret the dynamic magnetic performance of Dy-HHFs, and a satisfactory consistency between theory and experiment exists.

The Diverse World of Foldamers: Endless Possibilities of Self-Assembly

Different classes of foldamers, which are synthetic oligomers that adopt well-defined conformations in solution, have been the subject of extensive studies devoted to the elucidation of the forces driving their secondary structures and their potential as bioactive molecules. Regardless of the backbone type (peptidic or abiotic), the most important features of foldamers are the high stability, easy predictability and tunability of their folding, as well as the possibility to endow them with enhanced biological functions, with respect to their natural counterparts, by the correct choice of monomers. Foldamers have also recently started playing a starring role in the self-assembly of higher-order structures. In this review, selected articles will be analyzed to show the striking number of self-assemblies obtained for foldamers with different backbones, which will be analyzed in order of increasing complexity. Starting from the simplest self-associations in solution (e.g., dimers of β-strands or helices, bundles, interpenetrating double and multiple helices), the formation of monolayers, vesicles, fibers, and eventually nanostructured solid tridimensional morphologies will be subsequently described. The experimental techniques used in the structural investigation, and in the determination of the driving forces and mechanisms underlying the self-assemblies, will be systematically reported. Where applicable, examples of biomimetic self-assembled foldamers and their interactions with biological components will be described.

A new soft-matter material with old chemistry: Passerini multicomponent polymerization-induced assembly of AIE-active double-helical polymers with rapid visible-light degradability

Mimicking the superstructures and functions of natural chiral materials is beneficial to understand specific biological activities in living organisms and broaden applications in the fields of chemistry and materials sciences. However, it is still a great challenge to construct water-soluble, double-helical polymers with multiple responsiveness. Herein, we report for the first time a straightforward, general strategy to address this issue by taking advantage of Passerini multicomponent polymerization-induced assembly (PMPIA). The polymerization-induced generation of supramolecular interactions in chiral α-acyloxy amides drives the assembly of polymers and improves their stability in various solvents. This double-helical polymer is sensitive to metal ions, temperature, pH, and solvents, making both the superstructure and the AIE effect reversibly adjustable. Meanwhile, the hydrogen-bonding-assisted cyclization of photolabile α-acyloxy amides accelerates the degradation of helical polymers under visible-light irradiation. It is anticipated that this novel PMPIA strategy opens new horizons to inspire the design of advanced chiral/helical polymers with multiple functions.

Two Orthogonal Halogen-Bonding Interactions Directed 2D Crystalline Supramolecular J-Dimer Lamellae

Dye assemblies exhibit fascinating properties and performances, both of which depend critically on the mutual packing arrangement of dyes and on the supramolecular architecture. Herein, we engineered, for the first time, an intriguing chlorosome-mimetic 2D crystalline J-dimer lamellar structure based on halogenated dyes in aqueous media by employing two distinct orthogonal halogen-bonding (XB) interactions. As the only building motif, antiparallel J-dimer was formed and stabilized by single π-stacking and dual halogen⋅⋅⋅π interactions. With two substituted halogen atoms acting as XB donors and the other two acting as acceptors, the constituent J-dimer units were linked by quadruple highly-directional halogen⋅⋅⋅halogen interactions in a staggered manner, resulting in unique 2D lamellar dye assemblies. This work champions and advances halogen-bonding as a remarkably potent tool for engineering dye aggregates with a controlled molecular packing arrangement and supramolecular architecture.

A "σ-Hole"-Containing Volatile Solid Additive Enabling 16.5% Efficiency Organic Solar Cells

Here we introduce a σ-hole-containing volatile solid additive, 1, 4-diiodotetrafluorobenzene (A3), in PM6:Y6-based OSCs. Aside from the appropriate volatility of A3 additive, the synergetic halogen interactions between A3 and photoactive matrix contribute to more condensed and ordered molecular arrangement in the favorable interpenetrating donor/acceptor domains. As a result, greatly accelerated charge transport process with suppressed charge recombination possibility is observed and ultimately a champion PCE value of 16.5% is achieved. Notably, the A3 treated OSCs can maintain a high efficiency of over 16.0% in a wide concentration range of A3 additive between 10 and 35 mg/mL. The A3-treated device shows excellent stability with an efficiency of 15.9% after 360-h storage. This work demonstrates that the σ-hole interaction can be applied to enhance the OSC performance and highlights the importance of non-covalent interactions in the optoelectronic materials.

A homochiral 3D framework of mechanically interlocked 1D loops with solvent-dependent spin-state switching behaviors

An atypical homochiral spin-crossover (SCO) framework (1) constructed from mechanically interlocked 1D molecular loops was prepared. Due to the flexibility of the interlocked structure, the guest solvent molecules can be reversibly exchanged. Consequently, its SCO behavior was capable of modulating between one- and two-stepped transitions in response to acetonitrile and methanol.

Determination of association constants and FRET in hydrazide-based molecular duplex strands

The association constants for the hydrazide-based molecular duplex strands can be determined via monitoring the pyrene excimer emission. By mixing pyrene and perylene labelled oligomers, supramolecular substitution reactions induced efficient FRET.

A pH-responsive graftable supramolecular polymer with tailorable surface functionality by orthogonal halogen bonding and hydrogen bonding

Orthogonal halogen (X)-bonding and hydrogen (H)-bonding have been employed for constructing a surface functionalizable supramolecular polymer in water featuring tunable morphology and dual stimuli (pH and temperature) responsive properties.

Absolute handedness control of oligoamide double helices by chiral oxazolylaniline induction

Aromatic oligoamide double helices bearing a chiral oxazolylaniline moiety were synthesized and their helix handedness was completely controlled (de > 99%).

Distinct Crystalline Aromatic Structural Motifs: Identification, Classification, and Implications

Spatial noncovalent helical organization of nucleobases in DNA and radial organization of chromophores in natural light-harvesting systems are fascinating yet enigmatic. Understanding the numerous weak interactions that drive the formation of elegant supramolecular architectures in native natural systems and developing bioinspired design strategies have seen a surge of interest in recent decades. Self-assembly of functional chromophores in the crystalline phase is a definitive strategy to identify novel molecule-molecule interactions, in particular, atom-atom interactions, and to understand the synergistic nature of noncovalent interactions that stabilizes the supramolecular organization. This Account narrates our recent efforts in developing desirable supramolecular motifs employing weak interaction-based strategies and our observation of deviations from the common motifs chartered in aromatic systems. Modulation of long-range aromatic interactions through chemical modifications (acylation, benzoylation, haloacylation, and alkylation of chromophores) to attain a preferred stacking (herringbone, lamellar, or columnar) is presented. Particular attention has been given to attaining lamellar or columnar packing possessing potential interchromophoric electronic coupling mediated high charge mobility. Supramolecular arrangements of noncovalently or covalently associated donor-acceptor systems that open up additional possibilities of packing modes (segregated, mixed etc.) are explored. Our persistent efforts yielded distinct twisted-segregated and alternate distichous stacks for the nonparallel covalently linked donor-acceptor systems that favor a long-lived photoinduced charge-separated state. We further move on to discuss the unconventional packing motifs that were identified recently. The highly sought-after Greek cross (+) stacking of chromophores in crystalline phase and an elegant crystalline radial arrangement of chromophores are examined. The Greek cross (+) stacked architecture exhibits monomer-like emission characteristics owing to the absence of exciton coupling across the orthogonally stacked chromophores. Crystalline helical chromophore assembly is yet another emerging motif with far-reaching applications in domains ranging from asymmetric catalysis to chiral smart materials and has been accounted here by citing certain phenomenal examples from literature. Thus, this Account demonstrates that identifying and classifying new structural motifs based on topological aspects, such as interchromophoric orientation (cross) and extended chromophore arrangement in the crystal lattice (radial, helical, etc.), are crucial since such fundamental characteristics dictate the properties emerging out of the corresponding motifs. Encouraged from ours and others' works, we propose the addition of new aromatic supramolecular structural motifs, namely, cross-stacked, helical, and radial arrangements, in order to expand the classification. We believe that identifying new emergent property-based supramolecular motifs and investigating the methods to achieve the desired motif will eventually have implications in fundamental crystal engineering, supramolecular chemistry, and biomimetic design of functional materials.