Bowl-shaped Molecules Research Articles

Formation of Nitrogen-Doped Positively Curved Molecules by π-Extension.

Two nitrogen-doped positively curved aromatic molecules bearing doubly fused pentagonal rings were synthesized and characterized. Crystallographic analysis confirms the formation of a bowl-shaped structure, which is induced by the fusion of adjacent pentagons to the rigid aromatic planes. Both compounds demonstrate good photoluminescence. These electron-rich bowl-shaped molecules can associate with C60 to form complexes in 2:1 ratio in toluene with different association constants depending on the molecular dimension of the hosts.

Resistive switching memory using buckybowl sumanene-inserted bilayer graphene

The bowl-shaped molecules of the nanocarbon material called sumanene have structural flexibility (bowl inversion). In the case of the sumanene molecule used as an intercalant between graphene layers, it has been predicted that holes and electrons are unevenly distributed according to the bowl inversion. Using the property of sumanene molecules, we expected that resistive switching for the nonvolatile memory applications could be achieved by the sumanene-inserted bilayer graphene. In this study, metal–insulator–metal devices with sumanene-inserted bilayer graphene are fabricated. As a result, it is observed that the resistance of the sumanene-inserted bilayer graphene changes by applying voltage, demonstrating resistive switching characteristics. This result implies the possibility of realizing a novel ultra-thin resistive memory device using nanocarbon technologies.

A molecular container providing supramolecular protection against acetylcholine hydrolysis.

Alzheimer's disease (AD) is characterized by cognitive decline, often attributed to the deficiency of acetylcholine, which can undergo hydrolysis by acetylcholinesterase (AChE) within the biological milieu. Here, we report a supramolecular strategy that takes advantage of confinement effects to inhibit such a hydrolysis process, shedding some light on AD therapy. A water-soluble and bowl-shaped molecule, hexacarboxylated tribenzotriquinacene (TBTQ-C6), was employed to shield acetylcholine (G1) from enzymatic degradation through host-guest binding interactions. Our study revealed highly efficient host-guest interactions with a binding ratio of 1 : 3, resulting in a significant reduction in acetylcholine hydrolysis from 91.1% to 7.4% in the presence of AChE under otherwise identical conditions. Furthermore, TBTQ-C6 showed potential for attenuating the degradation of butyrylcholine (G2) by butyrylcholinesterase (BChE). The broader implications of this study extend to the potential use of molecular containers in various biochemical and pharmacological applications, opening new avenues for research in the field of neurodegenerative diseases.

A nitrogen-doped bowl-shaped molecule containing a central heptagonal ring

A nitrogen-doped heptagon-centered molecular bowl that can be viewed as a fragment mapped from a fullerene violating the isolated pentagon rule was synthesized and characterized.

Novel organic semiconductor materials combined by sumanene and corannulene: Rational functionalization based on the electronic structures of highly curved buckybowl

Due to the unique optoelectronic properties of bowl-shaped structural materials such as the fullerene fragments corannulene and sumanene, which are widely used in electronic devices, it is important to study their electronic structures in more detail. To this end, we have carried out detailed modeling and computational studies of the electronic structures of highly curved bowl-shaped molecules containing corannulene and sumanene fragments via DFT calculations. Our aim was to investigate whether topological recombination of different buckybowl fragments could multiply their advantages and improve our understanding of these materials at the genetic level. This work has mainly expanded the study from single-molecule photoelectric properties to the crystal transport properties. First, the structural and optoelectronic properties of C- and S-series monomer molecules by theoretical calculations from several aspects, such as bowl depths, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, the absorption spectra in vacuum and the energy difference between the singlet and triplet state were described in detail, furthering the understanding of individual fragments. Then, the investigation of the potential charge transport properties of the crystals according to the quantum nuclear tunneling model using the dimer model is to be carried out in order to provide a deeper understanding of the application of molecule whole in organic semiconductor materials. Monte Carlo simulation was used to obtain the diffusion constant, and the Einstein equation was applied to obtain the carrier mobility. This study provides a deep understanding of the intrinsic properties of the highly curved bowl-shape polycyclic aromatic hydrocarbons. What's more, it reveals that perpendicular columnar stacking crystals can be excellent candidate used for novel organic semiconductor materials. © 2023 Elsevier Science. All rights reserved.

Collective bending motion of a two-dimensionally correlated bowl-stacked columnar liquid crystalline assembly under a shear force.

Stacked teacups inspired the idea that columnar assemblies of stacked bowl-shaped molecules may exhibit a unique dynamic behavior, unlike usual assemblies of planar disc- and rod-shaped molecules. On the basis of the molecular design concept for creating higher-order discotic liquid crystals, found in our group, we synthesized a sumanene derivative with octyloxycarbonyl side chains. This molecule forms an ordered hexagonal columnar mesophase, but unexpectedly, the columnar assembly is very soft, similar to sugar syrup. It displays, upon application of a shear force on solid substrates, a flexible bending motion with continuous angle variations of bowl-stacked columns while preserving the two-dimensional hexagonal order. In general, alignment control of higher-order liquid crystals is difficult to achieve due to their high viscosity. The present system that brings together higher structural order and mechanical softness will spark interest in bowl-shaped molecules as a component for developing higher-order liquid crystals with unique mechanical and stimuli-responsive properties.

Self-Assembly of a Purely Organic Bowl in Water via Acylhydrazone Formation.

A bowl-shaped molecule can be self-assembled by condensing a triscationic hexaaldehyde compound and three equiv. of a dihydrazide linkers in pure water. The molecular bowl is thus composed of a triscationic π-electron deficient platform, as well as a hexagonal rim that contains six acylhydrazone functions. When the counteranions are chloride, the solid-state structure reveals that this molecular bowl undergoes dimerization via N-H···Cl hydrogen bonds, forming a cage-like dimer with a huge inner cavity. This molecular bowl can employ its cavity to accommodate a hydrophobic guest, namely 1-adamantanecarboxylic acid in aqueous media.

Planarization of a bowl-shaped molecule by triple-decker stacking

A bowl-shaped π-conjugated molecule typically undergoes bowl-inversion motion via a planarized transition state (TS), the highest-energy state along the reaction coordinate between two minimum bowl structures. Isolation of such planarized state has been challenging. Here, we report that a platinum(II) complex of antiaromatic porphyrin, norcorrole, adopts bowl-shaped conformation in solution but can become planar in solid. In the crystalline state, the norcorrole Pt(II) complex forms triple-decker stacking structures, in which the planarized norcorrole is stabilized and sandwiched between two bowl-shaped norcorroles. The planar conformation corresponds to the TS structure in the dynamic bowl-to-bowl inversion motion of the bowl-shaped molecule. Detailed theoretical studies have revealed that the intrinsically unstable planar conformation is stabilized by the dispersion force among the substituents and enhanced Pt–Pt interactions created by the antiaromatic macrocyclic ligand. • A planar structure of an intrinsically bowl-shaped molecule is observed in the solid state • Triple-decker stacking is stabilized by dispersion interactions • Pt–Pt interaction is enhanced by the antiaromaticity of the ligand A bowl-shaped π-conjugated molecule often flips via a planarized conformation. Here, Kawashima et al. describe the synthesis and properties of an antiaromatic Pt(II) norcorrole complex, which forms a triple-decker stacking structure in which one planarized molecule is sandwiched between two bowl-shaped molecules in the solid state.

Periphery-Core Strategy to Access a Bowl-Shaped Molecule Bearing Multiple Heteroatoms.

Most of the bowl-shaped molecules are synthesized via a core-periphery strategy with the bowl rim closed at the final stage. However, the construction of heteroatom-doped buckybowls by the periphery-core method with the bowl bottom sealed by inserting new atoms in the last step is quite limited. Herein we report the synthesis of a bowl-shaped compound containing four sulfur atoms and two embedded N-B bonds with the ratio of carbon atom and heteroatom as low as four through a periphery-core strategy. Crystallographic analysis confirms the formation of a bowl-shaped structure. The multiple heteroatoms alter the molecular electronic structure, thus resulting in the distinct aromaticity when compared with its all-carbon congener. The electron-rich buckybowl shows a strong interaction with the electron-deficient fullerene C60 by forming a 1 : 1 complex in toluene.

Planarization of a Bowl-Shaped Molecule by Triple-Decker Stacking

Planarization of a Bowl-Shaped Molecule by Triple-Decker Stacking

Metal-Templated Oligomeric Macrocyclization via Coupling for Metal-Doped π-Systems.

A method for the synthesis of metal-doped aromatic macrocycles has been developed. The method, i.e., metal-templated oligomeric macrocyclization via coupling, adopts Ni as the template and assembles five pyridine units via a Ni-mediated coupling reaction to form aryl-aryl linkages. A pentameric oligopyridyl macrocycle was selectively obtained in good yield, and the reaction was also applicable to a gram-scale synthesis. The pentameric oligopyridyl macrocycle captured d8-Ni(II) at the center to form a paramagnetic pentagonal-bipyramidal complex. The method was applied to the synthesis of a large π-molecule to afford a nanometer-sized, bowl-shaped molecule having a unique combination of 120π and 8d electrons.

Enantioselective Pd0 -Catalyzed C(sp2 )-H Arylation for the Synthesis of Chiral Warped Molecules.

C-H activation-based ring-forming methods are a powerful approach for the construction of complex molecular architectures, especially those containing a congested stereocenter. Therefore, this strategy seems perfectly suited to address the synthesis of chiral polycyclic aromatic hydrocarbons (PAHs) and bowl-shaped molecules, which are important target molecules in the field of organic electronic materials. Herein, we describe an enantioselective Pd0 -catalyzed C(sp2 )-H arylation protocol for the synthesis of chiral fluoradenes and other warped molecules, which could serve to the bottom-up construction of chiral PAHs. The current approach relies on the use of chiral bifunctional phosphine-carboxylate ligands and delivers diverse polycyclic compounds in high yield and with good to excellent enantioselectivity. The chiroptical properties of the obtained products were investigated, and some of them were found to have a strong ellipticity and an emission band located in the visible region.

Embedding Heteroatoms and Adjacent Pentagons in Concave Molecules

Bowl-shaped molecules, which can be viewed as fragments of fullerenes, have been extensively studied owing to their interesting fundamental properties derived from their unique geometry, and the possibilities for their further functionalization, with potential applications in the field of materials science. Most of the reported concave compounds are based on corannulene or sumanene, the simplest representative fullerene subunits possessing isolated pentagons. Syntheses of concave molecules bearing adjacent pentagons have rarely been reported. Inspired by the structure of N-heterotriangulene, the construction of bowl-shaped compounds containing two fused pentagons and a central nitrogen atom is discussed. Further surface extension of such concave molecules can result in the formation of boat-shaped compounds containing embedded double isolated nitrogen atoms.

A Nanoboat with Fused Concave N-Heterotriangulene.

The surface extension of all-carbon based bowl-shaped molecules, such as corannulene and sumanene, to synthesize even larger buckybowls has been widely studied, leaving other concave compounds with heteroatoms less considered. Herein we present a highly curved molecule synthesized via stepwise cyclization of fjords of a bisacridone derivative. Crystallographic analysis unambiguously confirmed a boat-shaped structure with deformed bottom benzene ring. Theoretical calculation unravels an inversion process with an S-shaped transition structure rather than a planar one. The enlarged boat demonstrates interesting properties, such as red shifts in absorption and emission spectra, enhanced emission intensity, and convergent frontier molecular orbital energy levels, in comparison to the related concave N-heterotriangulene.

Dimensional Matching versus Induced-Fit Distortions: Binding Affinities of Planar and Curved Polyaromatic Hydrocarbons with a Tetragold Metallorectangle.

A tetragold(I) rectangle-like metallocage containing two pyrene-bis-imidazolylidene ligands and two carbazolyl-bis-alkynyl linkers is used for the encapsulation of a series of polycyclic aromatic hydrocarbons (PAHs), including corannulene. The binding affinities obtained for the encapsulation of the planar PAHs guests in CD2 Cl2 are found to exponentially increase with the number of π-electrons of the guest (1.3 > logK >6.6). For the bowl-shaped molecule of corannulene, the association constant is much lower than the expected one according to its number of electrons. The molecular structure of the host-guest complex formed with corannulene shows that the molecule of the guest is compressed, while the host is expanded, thus showing an interesting case of artificial mutual induced-fit arrangement.

Nitrogen-Centered Concave Molecules with Double Fused Pentagons.

Distinctive concave compounds bearing a nitrogen core and double fused pentagons were synthesized with a palladium-catalyzed intramolecular coupling of 1-chloro-8 H-indolo[3,2,1- de]acridine as the key step. Structural analysis confirmed the formation of bowl-shaped molecules. Experimental characterizations and theoretical calculations reveal the incorporation of nitrogen is crucial to alleviate the pentagon fusing strain, as well as in property regulation.

Resorcin[4]arenes: A Convenient Scaffold To Study Supramolecular Self-Assembly and Host:Guest Interactions for the Undergraduate Curriculum

In response to the call for an increased emphasis from the American Chemical Society on including macromolecular studies in the undergraduate curriculum, a supramolecular-themed experiment was designed for undergraduate-level organic laboratory courses that provides a convenient platform to study physical behaviors of supramolecular assemblies. Students synthesize an easily purified resorcin[4]arene and characterize the product of its self-assembly via 1H NMR spectroscopy. These bowl-shaped molecules are noteworthy because of their propensity to self-assemble in organic solution in the presence of trace water or alcohol solvents. Upon self-assembly, the resulting hexamer adopts a well-defined molecular cage structure with a large internal cavity that can be used to explore host:guest chemistry. After completing the experiment, students are expected to gain a better understanding of electrophilic aromatic substitution, 1H NMR spectroscopy, supramolecular chemistry and self-assembly, and molecular recognition.

Self-Assembly and Electronic Structure of Tribenzotriquinacenes on Ag(111)

The structure of two-dimensional layers of organic compounds on metal surfaces is of great interest for the fabrication of devices in the field of organic electronics. To progress in this area, a deeper understanding of intermolecular interactions and charge transfer processes between organic molecules and a metal substrate is required. Here, the two-dimensional self-assembly of tribenzotriquinacenes (TBTQs) on Ag(111) was studied by scanning tunneling microscopy under ultrahigh vacuum conditions. Highly ordered monolayers of tribenzotriquinacene (TBTQ) and centro-methyl tribenzotriquinacene (Me-TBTQ) were observed for the first time. At low to moderate coverage, both of these bowl-shaped molecules adsorb with the bowl opening faced downward, appearing in two orientations that are rotated by 14° from the high-symmetry axis of the Ag(111) surface. At high TBTQ coverage, extended islands with a self-assembled highly ordered windmill nanostructure dominate the surface, interspaced with nanometer-sized openings. This windmill structure is absent in Me-TBTQ, which immediately forms double-layered regions at high coverage. Scanning tunneling spectroscopy measurements, which probe the local density of states, identify a shift of the Ag(111) surface state in the presence of the TBTQ molecules. Investigations such as these into the self-assembly of curved aromatics provide a foundation for further work on the construction of multilayer nanostructures and the production of electronic devices.

Bowl-shaped fluorescent liquid crystals derived from 4-tert butyl calix[4]arene and trans cinnamic acid derivatives

A new family of bowl-shaped molecules with a calix[4]arene rigid core appended by four-side and two-side substitution with trans 4-n-alkoxy cinnamic acid has been synthesized and well characterized.

Columnar self-assembly of bowl-shaped luminscent oxadiazole calix[4]arene derivatives

In the present investigation, we wish to report a new class of blue light emitting liquid crystalline bowl-shaped molecules based on oxadiazole calix[4]arene has been designed and synthesized. These supramolecular compounds were investigated by polarizing optical microscope (POM), differential scanning calorimetry (DSC), thermo gravimetric analysis (TGA), high temperature X-ray diffraction and photophysical studies. We have prepared total six newly supramolecular derivatives having butyl alkyl bridge with oxadiazole ring and variable trisubstituted side alkoxy chain on the lower rim of calix[4]arene. The present synthesized bowl-shaped molecules are promising to stabilize the hexagonal columnar phase over a broad thermal range. Thermal behavior as well as photophysical behaviors of these new bowl-shaped molecules are extremely dependent on the number and types of peripheral tail group present in the lower rim of calix[4]arene inbuilt with schiff-base linking unit. Additionally, these synthesized oxadiazole calix[4]arene based supramolecular compounds showed blue luminescence in solution as well as thin films under long wavelength UV light. These properties of present material suggest that these may have promising applications in organic electronics.