Thermodynamics of Supramolecular Naphthalenediimide Nanotube Formation: The Influence of Solvents, Side Chains, and Guest Templates

Shape and size directed self-selection in organic cage formation

The selective formation of a single isomer of a [3+2] self-assembled organic cage from a reaction mixture of an unsymmetrical aldehyde and a flexible amine is discussed. The experimental and theoretical findings suggest that in such a process, the geometric features of the aldehyde play a key role.

Charge-transfer complexation between naphthalene diimides and aromatic solvents

Naphthalene diimides (NDIs) form emissive ground-state charge-transfer (CT) complexes with various electron rich aromatic solvents like benzene, o-xylene and mesitylene. TD-DFT calculation of the complexes suggests CT interaction and accounts for the observed ground-state changes.

Sugar based nanotube assembly for the construction of sonication triggered hydrogel: an application of the entrapment of tetracycline hydrochloride

The tube assembly comprised of naphthalimide and glucose segments could undergo direct suspension-to-hydrogel transformation accelerated by ultrasound.

Assembly modulation of PDI derivative as a supramolecular fluorescence switching probe for detection of cationic surfactant and metal ions in aqueous media

We report an amphiphilic perylene diimide (1), a bimolecular analog of l-3,4-dihydroxyphenylalanine (L-DOPA), as a reversible fluorescence switching probe for the detection and sensing of cationic surfactants and Fe(3+)/Cu(2+) in an aqueous media respectively by means of host-guest interactions driven assembly and disassembly of 1. Photophysical studies of 1, going from dimethyl sulfoxide (DMSO) (State-I) to pure aqueous medium (State-II), suggested the formation of self-assembled aggregates by displaying very weak fluorescence emission along with red shifted broad absorption bands. Interestingly, the cationic surfactant cetyltrimethylammonium bromide (CTAB) could disassemble 1 in miceller conditions by restoring bright yellow fluorescence and vibronically well-defined (Franck-Condon progressions A0-0/A0-1 ≈ 1.6) absorption bands of 1 over other neutral and anionic surfactants (State-III). Owing to the metal chelating nature of L-DOPA, 1 was able to sense Fe(3+) and Cu(2+) among a pool of other metal ions by means of fluorescence switching off state, attributed to metal interaction driven assembly of 1 (State-IV). Such metallosupramolecular assemblies were found to reverse back to the fluorescence switching on state using a metal ion chelator, diethylenetriaminepentaacetic acid (DTPA, State-III), further signifying the role of metal ions toward assembly of 1. Formation of assembly and disassembly could be visualized by the diminished and increased yellow emission under green laser light. Further, the assembly-disassembly modulation of 1 has been extensively characterized using infrared (IR), mass spectrometry, microscopy and dynamic light scattering (DLS) techniques. Therefore, modulation of the molecular self-assembly of PDI derivative 1 in aqueous media (assembled state, State-II) by means of host-guest interactions provided by micellar structures of CTAB (disassembled state, State-III), metal ion (Fe(3+) and Cu(2+)) interactions (assembled state, State-IV) and metal ion sequestration using DTPA (disassembled state, State-III) is viewed as a supramolecular reversible fluorescence switching off-on probe for cationic surfactant CTAB and Fe(3+)/Cu(2+).

Disulfide exchange: exposing supramolecular reactivity through dynamic covalent chemistry

A Tutorial Review of the subtle supramolecular interactions influencing the outcomes of equilibrating systems, focusing on the dynamic covalent chemistry (DCC) of disulfide exchange reactions, is presented. We discuss the topics of cation-π interactions (2.1), hydrophobic effects (2.2), hydrogen bonding interactions (2.3) aromatic donor-acceptor interactions (2.4), and metal-ligand interactions (2.5) in the context of dynamic disulfide chemistry.

Electron delocalization in a rigid cofacial naphthalene-1,8:4,5-bis(dicarboximide) dimer

Investigating through-space electronic communication between discrete cofacially oriented aromatic π-systems is fundamental to understanding assemblies as diverse as double-stranded DNA, organic photovoltaics and thin-film transistors. A detailed understanding of the electronic interactions involved rests on making the appropriate molecular compounds with rigid covalent scaffolds and π-π distances in the range of ca. 3.5 Å. Reported herein is an enantiomeric pair of doubly-bridged naphthalene-1,8:4,5-bis(dicarboximide) (NDI) cyclophanes and the characterization of four of their electronic states, namely 1) the ground state, 2) the exciton coupled singlet excited state, 3) the radical anion with strong through-space interactions between the redox-active NDI molecules, and 4) the diamagnetic diradical dianion using UV/Vis/NIR, EPR and ENDOR spectroscopies in addition to X-ray crystallography. Despite the unfavorable Coulombic repulsion, the singlet diradical dianion dimer of NDI shows a more pronounced intramolecular π-π stacking interaction when compared with its neutral analog.

Strategies for the synthesis of functional naphthalene diimides

Naphthalene diimides, which have for a long time been in the shadow of their higher homologues the perylene diimides, currently belong to the most investigated classes of organic compounds. This is primarily due to the initial synthetic studies on core functionalization that were carried out at the beginning of the last decade, which facilitated diverse structural modifications of the naphthalene scaffold. Compounds with greatly modified optical and electronic properties that can be easily and effectively modulated by appropriate functionalization were made accessible through relatively little synthetic effort. This resulted in diverse interesting applications. The electron-deficient character of these compounds makes them highly valuable, particularly in the field of organic electronics as air-stable n-type semiconductors, while absorption bands over the whole visible spectral range through the introduction of core substituents enabled interesting photosystems and photovoltaic applications. This Review provides an overview on different approaches towards core functionalization as well as on synthetic strategies for the core expansion of naphthalene diimides that have been developed mainly in the last five years.

Direct core functionalisation of naphthalenediimides by iridium catalysed C–H borylation

We report the first boron-substituted naphthalenediimides (NDIs), prepared by iridium catalysed C–H activation. Both mono- and diborylated products are available, which have been further elaborated by Suzuki–Miyaura coupling.

The structure of 3-(diethylborylethynyl)pyridine: a nonplanarly arranged cyclic trimer

The cyclic trimer of 3-(diethylborylethynyl)pyridine is conformationally flexible enough to be affected by the crystal packing.

Biomimetic molecular organization of naphthalene diimide in the solid state: tunable (chiro-) optical, viscoelastic and nanoscale properties

Biomimetic molecular organization of naphthalene diimide in the solid state: tunable (chiro-) optical, viscoelastic and nanoscale properties.

Hydrogen-bond-driven controlled molecular marriage in covalent cages

A supramolecular approach that uses hydrogen-bonding interaction as a driving force to accomplish exceptional self-sorting in the formation of imine-based covalent organic cages is discussed. Utilizing the dynamic covalent chemistry approach from three geometrically similar dialdehydes (A, B, and D) and the flexible triamine tris(2-aminoethyl)amine (X), three new [3+2] self-assembled nanoscopic organic cages have been synthesized and fully characterized by various techniques. When a complex mixture of the dialdehydes and triamine X was subjected to reaction, it was found that only dialdehyde B (which has OH groups for H-bonding) reacted to form the corresponding cage B3X2 selectively. Surprisingly, the same reaction in the absence of aldehyde B yielded a mixture of products. Theoretical and experimental investigations are in complete agreement that the presence of the hydroxyl moiety adjacent to the aldehyde functionality in B is responsible for the selective formation of cage B3X2 from a complex reaction mixture. This spectacular selection was further analyzed by transforming a nonpreferred (non-hydroxy) cage into a preferred (hydroxy) cage B3X2 by treating the former with aldehyde B. The role of the H-bond in partner selection in a mixture of two dialdehydes and two amines has also been established. Moreover, an example of unconventional imine bond metathesis in organic cage-to-cage transformation is reported.

Synthetic ion transporters that work with anion-π interactions, halogen bonds, and anion-macrodipole interactions

The transport of ions and molecules across lipid bilayer membranes connects cells and cellular compartments with their environment. This biological process is central to a host of functions including signal transduction in neurons and the olfactory and gustatory sensing systems, the translocation of biosynthetic intermediates and products, and the uptake of nutrients, drugs, and probes. Biological transport systems are highly regulated and selectively respond to a broad range of physical and chemical stimulation. A large percentage of today's drugs and many antimicrobial or antifungal agents take advantage of these systems. Other biological transport systems are highly toxic, such as the anthrax toxin or melittin from bee venom. For more than three decades, organic and supramolecular chemists have been interested in developing new transport systems. Over time, curiosity about the basic design has evolved toward developing of responsive systems with applications in materials sciences and medicine. Our early contributions to this field focused on the introduction of new structural motifs with emphasis on rigid-rod scaffolds, artificial β-barrels, or π-stacks. Using these scaffolds, we have constructed selective systems that respond to voltage, pH, ligands, inhibitors, or light (multifunctional photosystems). We have described sensing applications that cover the three primary principles of sensor development: immunosensors that use aptamers, biosensors (an "artificial" tongue), and differential sensors (an "artificial" nose). In this Account, we focus on our recent interest in applying synthetic transport systems as analytical tools to identify the functional relevance of less common noncovalent interactions, anion-π interactions, halogen bonds, and anion-macrodipole interactions. Anion-π interactions, the poorly explored counterpart of cation-π interactions, occur in aromatic systems with a positive quadrupole moment, such as TNT or hexafluorobenzene. To observe these elusive interactions in action, we synthesized naphthalenediimide transporters of increasing π-acidity up to an unprecedented quadrupole moment of +39 Buckinghams and characterized these systems in comparison with tandem mass spectrometry and computational simulations. With π-acidic calixarenes and calixpyrroles, we have validated our results on anion-π interactions and initiated our studies of halogen bonds. Halogen bonds originate from the σ-hole that appears on top of electron-deficient iodines, bromines, and chlorines. Halogen-bond donors are ideal for anion transport because they are as strong and at least as directional as hydrogen-bond donors, but also hydrophobic. The discovery of the smallest possible organic anion transporter, trifluoroiodomethane, illustrates the power of halogen-bond donors. This molecule contains a single carbon atom and is a gas with a boiling point of -22 °C. Anion-macrodipole interactions, finally, differ significantly from anion-π interactions and halogen bonds because they are important in nature and cannot be studied with small molecules. We have used anion-transporting peptide/urea nanotubes to examine these interactions in synthetic transport systems. To facilitate the understanding of the described results, we also include an in-depth discussion of the meaning of Hill coefficients. The use of synthetic transport systems to catch less common noncovalent interactions at work is important because it helps to expand the collection of interactions available to create functional systems. Progress in this direction furthers fundamental knowledge and invites many different applications. For illustration, we briefly discuss how this knowledge could apply to the development of new catalysts.

Amino acid-bile acid based molecules: extremely narrow surfactant nanotubes formed by a phenylalanine-substituted cholic acid

An amino acid-substituted bile acid forms tubular aggregates with inner and outer diameters of about 3 and 6 nm. The diameters are unusually small for surfactant self-assembled tubes. The results enhance the spectrum of applications of supramolecular tubules and open up possibilities for investigating a novel class of biological amphiphiles.

Extremely Slow Dynamics of an Abiotic Helical Assembly: Unusual Relevance to the Secondary Structure of Proteins

Serendipitously, we found that isoleucine methylester functionalized perylenediimide 1 undergoes an extremely slow supramolecular helical assembly over a day's time. Surprisingly, heating led to irreversible chiral denaturation. However, reversible helical assembly could be achieved only in the presence of nondenatured aggregates of 1, which act as seeds. The intriguing functional relevance deduced from 1 was employed to draw parallels with the secondary structure of proteins, envisaging its plausible implications.

Small-angle X-ray scattering study of self-assembling lipophilic guanines in organic solvents: G-quadruplex formation and cation effects in cyclohexane

Lipophilic guanilic derivatives (lipoGs) dissolved in organic solvents can undergo different self-assembly pathways based on different H-bonded motifs, e.g., the cyclic discrete G-quartet, which forms in the presence of alkali-metal ions, and the "infinite" tape-like G-ribbon observed in the absence of ions. Using in-solution small-angle X-ray scattering, we analyzed a series of lipoGs dissolved in cyclohexane in the presence of different salts. The formation of G-quartet based supramolecular aggregates has been confirmed, evidencing the coexistence equilibrium of octamers and noncovalent molecular nanowires (the so-called G-quadruplexes). By global fitting the scattering data, the concentration of the two kinds of particles as well as the nanowire length have been derived as a function of temperature for the different compounds and salts. The thermodynamic parameters show that the self-assembly aggregation process is enthalpy driven, while the observed enthalpy-entropy compensation suggests that similar stacking interactions control the self-assembly of the different compounds. However, the strength of the stacking interactions, and then the nanowire stability, depends on the nature of templating cations and on their capacity to fill the central cavity of quadruplexes, with the order Sr(+) < Na(+) ≲ K(+).

Molecular marriage through partner preferences in covalent cage formation and cage-to-cage transformation

Unprecedented self-sorting of three-dimensional purely organic cages driven by dynamic covalent bonds is described. Four different cages were first synthesized by condensation of two triamines and two dialdehydes separately. When a mixture of all the components was allowed to react, only two cages were formed, which suggests a high-fidelity self-recognition. The issue of the preference of one triamine for a particular dialdehyde was further probed by transforming a non-preferred combination to either of the two preferred combinations by reacting it with the appropriate triamine or dialdehyde.

Evolution of dynamic combinatorial chemistry

Since its inception in the mid-1990s, dynamic combinatorial chemistry (DCC), the chemistry of complex systems under thermodynamic control, has proved valuable in identifying unexpected molecules with remarkable binding properties and in providing effective synthetic routes to complex species. Essentially, in this approach, one designs the experiment rather than the molecule. DCC has also provided us with insights into how some chemical systems respond to external stimuli. Using examples from the work of our laboratory and others, this Account shows how the concept of DCC, inspired by the evolution of living systems, has found an increasing range of applications in diverse areas and has evolved conceptually and experimentally. A dynamic combinatorial library (DCL) is a thermodynamically controlled mixture of interconverting species that can respond to various stimuli. The Cambridge version of dynamic combinatorial chemistry was initially inspired by the mammalian immune system and was conceived as a way to create and identify new unpredictable receptors. For example, an added template can select and stabilize a strongly binding member of the library which is then amplified at the expense of the unsuccessful library members, minimizing the free energy of the system. But researchers have exploited DCC in a variety of other ways: over the past two decades, this technique has contributed to the evolution of chemistry and to applications in the diverse fields of catalysis, fragrance release, and responsive materials. Among these applications, researchers have built intricate and well-defined architectures such as catenanes or hydrogen-bonded nanotubes, using the ability of complex chemical systems to reach a high level of organization. In addition, DCC has proved a powerful tool for the study of complex molecular networks and systems. The use of DCC is improving our understanding of chemical and biological systems. The study of folding or self-replicating macrocycles in DCLs has served as a model for appreciating how complex organisations such as life can emerge from a pool of simple chemicals. Today, DCC is no longer restricted to thermodynamic control, and new systems have recently appeared in which kinetic and thermodynamic control coexist. Expanding the realm of DCC to unexplored and promising new territories, these hybrid systems show that the concept of dynamic combinatorial chemistry continues to evolve.

Amino acid derivatized arylenediimides: a versatile modular approach for functional molecular materials

Nature's elegant molecular designs and their assemblies with specific structure-property correlations have inspired researchers to design and develop bio-mimics for advanced functional applications. To realize such advanced molecular materials, naturally evolved amino acids are arguably the ideal auxiliaries due to their remarkable molecular/chiral recognition and distinctive sequence specific self-assembling properties. Over the years, this modular approach of derivatizing naphthalenediimides (NDIs) and perylenediimides (PDIs) with amino acids and peptides have resulted in several hitherto unknown molecular assemblies with phenomenal impact on their performance. Derivatization with versatile arylenediimides is especially interesting due to their wide spread applications in fields ranging from biomedicine to electronics. Herein some of these seminal reports of this rapidly emerging field and the design principles embraced are discussed.