Discrete Dimers of Redox-Active and Fluorescent Perylene Diimide-Based Rigid Isosceles Triangles in the Solid State.

The development of rigid covalent chiroptical organic materials, with multiple, readily available redox states, which exhibit high photoluminescence, is of particular importance in relation to both organic electronics and photonics. The chemically stable, thermally robust, and redox-active perylene diimide (PDI) fluorophores have received ever-increasing attention owing to their excellent fluorescence quantum yields in solution. Planar PDI derivatives, however, generally suffer from aggregation-caused emission quenching in the solid state.

Proton Conduction in Tröger's Base-Linked Poly(crown ether)s.

Exactly 50 years ago, the ground-breaking discovery of dibenzo[18]crown-6 (DB18C6) by Charles Pedersen led to the use of DB18C6 as a receptor in supramolecular chemistry and a host in host-guest chemistry. We have demonstrated proton conductivity in Tröger's base-linked polymers through hydrogen-bonded networks formed from adsorbed water molecules on the oxygen atoms of DB18C6 under humid conditions. Tröger's base-linked polymers-poly(TBL-DB18C6)- t and poly(TBL-DB18C6)- c-synthesized by the in situ alkylation and cyclization of either trans- or cis-di(aminobenzo) [18]crown-6 at room temperature have been isolated as high-molecular-weight polymers.

ExTzBox: A Glowing Cyclophane for Live-Cell Imaging.

The ideal fluorescent probe for live-cell imaging is bright and non-cytotoxic and can be delivered easily into the living cells in an efficient manner. The design of synthetic fluorophores having all three of these properties, however, has proved to be challenging. Here, we introduce a simple, yet effective, strategy based on well-established chemistry for designing a new class of fluorescent probes for live-cell imaging.

Noninvasive Substitution of K Sites in Cyclodextrin Metal-Organic Frameworks by Li Ions.

Co-crystallization of K and Li ions with γ-cyclodextrin (γ-CD) has been shown to substitute the K ion sites partially by Li ions, while retaining the structural integrity and accessible porosity of CD-MOF-1 (MOF, metal-organic framework). A series of experiments, in which the K/Li ratio was varied with respect to that of γ-CD, have been conducted in order to achieve the highest possible proportion of Li ions in the framework. Attempts to obtain a CD-MOF containing only Li ions resulted in nonporous materials.

Surveying macrocyclic chemistry: from flexible crown ethers to rigid cyclophanes.

Macrocycles are molecular entities that display a combination of molecular recognition and complexation properties with vital implications for host-guest/supramolecular chemistry. Since the accidental discovery of the crown ethers by Pedersen half a century ago, the chemistry of wholly synthetic macrocycles for structure-specific, highly selective, host-guest complexation has experienced rapid development. While the structural diversity and host-guest chemistry of the original macrocycles are well-known, new derivatives of them are being investigated continuously and reported on today in order to improve their recognition properties as well as to unleash new opportunities in supramolecular chemistry.

Supramolecular Double-Helix Formation by Diastereoisomeric Conformations of Configurationally Enantiomeric Macrocycles.

Solid-state superstructures, resulting from assemblies programmed by homochirality, are attracting considerable attention. In addition, artificial double-helical architectures are being investigated, especially in relation to the ways in which homochiral small molecules can be induced to yield helical forms as a result of chiral induction. Herein, we report the highly specific self-assembly upon crystallization of a double-helical superstructure from an enantiopure macrocyclic dimer which adopts two diastereoisomeric conformations in a molar ratio of 1.

Chiral Redox-Active Isosceles Triangles.

Designing small-molecule organic redox-active materials, with potential applications in energy storage, has received considerable interest of late. Herein, we report on the synthesis, characterization, and application of two rigid chiral triangles, each of which consist of non-identical pyromellitic diimide (PMDI) and naphthalene diimide (NDI)-based redox-active units. (1)H and (13)C NMR spectroscopic investigations in solution confirm the lower symmetry (C2 point group) associated with these two isosceles triangles.

Supramolecular Gelation of Rigid Triangular Macrocycles through Rings of Multiple C-H···O Interactions Acting Cooperatively.

When equimolar solutions of the enantiomeric naphthalenediimide-based highly rigid triangles R-Δ and S-Δ in ClCH2CH2Cl are mixed, the racemate rac-Δ forms an organogel that is composed of interwoven fibers, resulting from the columnar stacking of the triangles in an alternating R-Δ/S-Δ fashion. Under identical conditions, the pure enantiomers do not form organogels. Density functional theory calculations reveal that the racemic RS dimer is more stable than the RR dimer as a result of the enantiomeric relationship between R-Δ and S-Δ, allowing them to act as two complementary rings comprised of 12 [C-H···O] interactions with an unprecedented and uninterrupted circular ADDAADDAADDA·DAADDAADDAAD alignment of hydrogen bond donors (D) and acceptors (A), in contrast with the square-wave manner in which the RR dimer forms a complementary yet interrupted ADADAD·DADADA circular sequence of six longer [C-H···O] hydrogen bonds.

Dynamic Peptide Library for the Discovery of Charge Transfer Hydrogels.

Coupling of peptide self-assembly to dynamic sequence exchange provides a useful approach for the discovery of self-assembling materials. In here, we demonstrate the discovery and optimization of aqueous, gel-phase nanostructures based on dynamically exchanging peptide sequences that self-select to maximize charge transfer of n-type semiconducting naphthalenediimide (NDI)-dipeptide bioconjugates with various π-electron-rich donors (dialkoxy/hydroxy/amino-naphthalene or pyrene derivatives). These gel-phase peptide libraries are characterized by spectroscopy (UV-vis and fluorescence), microscopy (TEM), HPLC, and oscillatory rheology and it is found that, of the various peptide sequences explored (tyrosine Y-NDI with tyrosine Y, phenylalanine F, leucine L, valine V, alanine A or glycine G-NH2), the optimum sequence is tyrosine-phenylalanine in each case; however, both its absolute and relative yield amplification is dictated by the properties of the donor component, indicating cooperativity of peptide sequence and donor/acceptor pairs in assembly.

Charge and spin transport in an organic molecular square.

Understanding electronic communication among multiple chromophoric and redox units requires construction of well-defined molecular architectures. Herein, we report the modular synthesis of a shape-persistent chiral organic square composed of four naphthalene-1,8:4,5-bis(dicarboximide) (NDI) sides and four trans-1,2-cyclohexanediamine corners. Single crystal X-ray diffraction reveals some distortion of the cyclohexane chair conformation in the solid state.

Light-triggered capture and release of DNA and proteins by host-guest binding and electrostatic interaction.

The development of an effective and general delivery method that can be applied to a large variety of structurally diverse biomolecules remains a bottleneck in modern drug therapy. Herein, we present a supramolecular system for the dynamic trapping and light-stimulated release of both DNA and proteins. Self-assembled ternary complexes act as nanoscale carriers, comprising vesicles of amphiphilic cyclodextrin, the target biomolecules and linker molecules with an azobenzene unit and a charged functionality.

Conducting nanofibers and organogels derived from the self-assembly of tetrathiafulvalene-appended dipeptides.

We demonstrate the nonaqueous self-assembly of a low-molecular-mass organic gelator based on an electroactive p-type tetrathiafulvalene (TTF)-dipeptide bioconjugate. We show that a TTF moiety appended with diphenylalanine amide derivative (TTF-FF-NH2) self-assembles into one-dimensional nanofibers that further lead to the formation of self-supporting organogels in chloroform and ethyl acetate. Upon doping of the gels with electron acceptors (TCNQ/iodine vapor), stable two-component charge transfer gels are produced in chloroform and ethyl acetate.

Biocatalytic self-assembly of supramolecular charge-transfer nanostructures based on n-type semiconductor-appended peptides.

The reversible in situ formation of a self-assembly building block (naphthalenediimide (NDI)-dipeptide conjugate) by enzymatic condensation of NDI-functionalized tyrosine (NDI-Y) and phenylalanine-amide (F-NH2) to form NDI-YF-NH2 is described. This coupled biocatalytic condensation/assembly approach is thermodynamically driven and gives rise to nanostructures with optimized supramolecular interactions as evidenced by substantial aggregation induced emission upon assembly. Furthermore, in the presence of di-hydroxy/alkoxy naphthalene donors, efficient charge-transfer complexes are produced.

Biocatalytic amide condensation and gelation controlled by light.

We report on a supramolecular self-assembly system that displays coupled light switching, biocatalytic condensation/hydrolysis and gelation. The equilibrium state of this system can be regulated by light, favouring in situ formation, by protease catalysed peptide synthesis, of self-assembling trans- in ambient light; however, irradiation with UV light gives rise to the cis-isomer, which readily hydrolyzes to its amino acid derivatives (cis- + ) with consequent gel dissolution.

Photoresponsive molecular recognition and adhesion of vesicles in a competitive ternary supramolecular system.

A competitive photoresponsive supramolecular system is formed in a dilute aqueous solution of three components: vesicles of amphiphilic α-cyclodextrin host 1a, divalent p-methylphenyl guest 2 or divalent p-methylbenzamide guest 3, and photoresponsive azobenzene monovalent guest 5. Guests 2 and 3 form weak inclusion complexes with 1a (K(a)≈10(2) M(-1)), whereas azobenzene guest 5 forms a strong inclusion complex (K(a)≈10(4) M(-1)), provided it is in the trans state. The aggregation and adhesion of vesicles of host 1a is mediated by guest 2 (or 3) due to the formation of multiple intervesicular noncovalent links, as confirmed by using isothermal titration calorimetry (ITC), optical density measurements at 600 nm (OD600), dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM).