Bowl-shaped Polycyclic Aromatic Hydrocarbons Research Articles

Formation of five-membered ring structures via reactions of o-benzyne

The formation of five-membered ring structures is important for the generation of curved and bowl-shaped polycyclic aromatic hydrocarbons (PAHs) under combustion conditions. Here, we report the identification of the indenyl (C9H7) radical – the simplest aromatic hydrocarbon radical carrying an adjacent five- and six-membered ring, as the major product of the o-benzyne (o-C6H4) reaction with propargyl (C3H3). Because real flames exhibit a complex chemistry, elucidation of a specific reaction is very challenging. Instead, we studied the o-C6H4 + C3H3 reaction in a resistively heated microtubular SiC reactor at controlled conditions of 1150 K and a pressure near 10–20 Torr. To this end, the reactants o-benzyne and propargyl were pyrolytically generated from benzoyl chloride and propargyl bromide. We identified the reactants and the indenyl radical isomer-selectively utilizing photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). The experimentally observed predominant formation of indenyl radicals finally confirms the theoretical predictions of Matsugi and Miyoshi [Phys. Chem. Chem. Phys. 14 (2012), 9722–9728] and highlights a versatile route for the formation of five-membered rings and curved PAHs via reactions of o-benzyne that favor the formation of multiring species over aliphatically substituted aromatic species.

Electronic excited states of planar vs bowl-shaped polycyclic aromatic hydrocarbons in interaction with water clusters: a TD-DFT study

Electronic excited states of planar vs bowl-shaped polycyclic aromatic hydrocarbons in interaction with water clusters: a TD-DFT study

Macromolecular Architectures of Corannulene: Synthesis, Properties, and Applications of Polymers Containing a Molecular Bowl of Carbon

Corannulene (C20H10) is a bowl-shaped polycyclic aromatic hydrocarbon. The molecular curvature endows corannulene with a dipole moment, affinity for electrons, and the capacity to host fullerenes. Corannulene can also act as a guest in the cavity of gamma cyclodextrin. Corannulene is thus an appealing building block for polymer synthesis. It is envisaged that the multifaceted properties of corannulene can be combined with the modularity of synthetic polymers to access functional soft materials. Indeed, these efforts are now a decade old and some corannulene polymers have already been tested in real-life devices. In this perspective, we will contemplate the motivation behind these efforts, progress made within the past decade, and future prospects of the field.

Infrared and Laser-Induced Fluorescence Spectra of Sumanene Isolated in Solid para-Hydrogen.

The para-hydrogen (p-H2) matrix-isolation technique has been scarcely used to record electronic absorption and emission spectra. It is expected that its small matrix shifts due to diminished molecular interactions and the softness of the lattice might be advantageous to help identify the carriers of the diffuse interstellar bands. In this article, we present infrared, fluorescence excitation, and dispersed fluorescence spectra of sumanene (C21H12), a bowl-shaped polycyclic aromatic hydrocarbon and a fragment of C60, isolated in solid p-H2. The recorded vibrational wavenumbers from infrared and dispersed fluorescence agree with the scaled harmonic vibrational wavenumbers calculated with the B3PW91/6-311++G(2d,2p) and B3LYP/6-311++G(2d,2p) methods. The recorded fluorescence excitation spectra are consistent with the spectra of jet-cooled gas-phase C21H12 reported previously by Kunishige et al. We found a rather small matrix shift of 55 cm-1 for the S1-S0 electronic transition origin located at 27 888 cm-1. Vibrational wavenumbers associated with the S1 state of C21H12 inferred from the experimental spectrum can be assigned mostly to fundamental normal modes; they are in satisfactory agreement with scaled harmonic vibrational wavenumbers calculated at the TD-B3PW91/6-311++G(2d,2p) level of theory. Significantly more vibrational modes of the S1 state were identified as compared with those in the reported gas-phase work. The potential of p-H2 matrix-isolation spectroscopy to provide electronic excitation spectra suitable for comparison to astronomical observations is discussed by comparing the spectra of C21H12 isolated in solid p-H2 and in solid Ne, a matrix host commonly employed in astrochemistry.

Ultra-low hydrogen content bowl-shaped polycyclic aromatic hydrocarbons in petroleum

In the ultra-high resolution mass spectrometric analysis of processed petroleums (fossil materials), we observed species with ultra-low hydrogen content (e.g. H/C ratio from 0.1 to 0.4). Some of the observed chemical formula (C20-40H10) can be rationalized by the known corannulene-based peri-condensed Polycyclic Aromatic Hydrocarbons (PAHs). Other formulas (such as C20-40H8, C20-40H6 and C20-40H4) cannot be rationalized with any known structures. We proposed highly curved non-planar PAHs involving multiple connected five member aromatic rings. These structures do not obey the isolated pentagon rule (IPR). The stabilities of the proposed structures were evaluated by density functional theory. Strain energies were calculated based on hypothetical isodesmic conversion of planar structures to the curved non-planar structures. Results showed that the strain energies of the proposed structures are lower than that of fullerenes of the same carbon number, confirming stabilities of the non-IPR structures. The low hydrogen content species are likely formed in the thermal and/or catalytic cracking of the petroleums. They are possible intermediate molecules on the path toward the formation of fullerenes (buckyballs) and other nano-carbon materials

Heteroatoms in Bowl-shaped Polycyclic Aromatic Hydrocarbons: Synthesis and Structures

Nowadays, exploring the chemistry of curved π-conjugated molecules is one of the big trends in organic chemistry. Recently, research interests have been shifted to heteroatom containing analogs. Among these, bowl-shaped π-conjugated molecules with heteroatoms included within their skeletons have gained interest due to their synthetic difficulty and have been developed dramatically as a motif for heteroatom-doped carbon materials. Here, this review highlights analogs based on polycyclic aromatic hydrocarbons, represented by triangulenes, sumanenes and corannulenes, with heteroatoms. These studies have disclosed the effect of heteroatoms in curved π-surfaces.

Graphene Grown from Flat and Bowl Shaped Polycyclic Aromatic Hydrocarbons on Cu(111).

The growth of carbon layers, defective graphene, and graphene by deposition of polycyclic aromatic hydrocarbons (PAHs) on Cu(111) is studied by scanning tunneling microscopy and X-ray photoelectron spectroscopy. Two different PAHs are used as starting materials: the buckybowl pentaindenocorannulene (PIC) which contains pentagonal rings and planar coronene (CR). For both precursors, with increasing sample temperature during deposition, porous carbon aggregates (350 °C), dense carbon layers (400-450 °C), disordered defective graphene (500 °C-550 °C), and extended graphene (≥600 °C) are obtained. No significant differences for defective graphene grown from PIC and CR are observed. C 1s X-ray photoelectron spectra of PIC and CR derived samples grown at 350-550 °C exhibit a characteristic C-Cu low binding energy component. Preparation at ≥600 °C eliminates this C-Cu species and only C-C bonded carbon remains.

Tailoring Diindenochrysene through Intramolecular Multi-Assemblies by C-F Bond Activation on Aluminum Oxide.

The unique nature of the alumina-mediated cyclodehydrofluorination gives the opportunity to execute the preprogrammed algorithm of the C-C couplings rationally built into a precursor. Such multi-assemblies facilitate the construction of the carbon-skeleton, superseding the conventional step-by-step by the one-pot intramolecular assembly. In this work, the feasibility of the alumina-mediated C-F bond activation approach for multi-assembly is demonstrated on the example of a fundamental bowl-shaped polycyclic aromatic hydrocarbon (diindenochrysene) through the formation of all "missing" C-C bonds at the last step. Beside valuable insights into the reaction mechanism and the design of the precursors, a facile pathway enabling the two-step synthesis of diindenochrysene was elaborated, in which five C-C bonds form in a single synthetic step. It is shown that the relative positions of fluorine atoms play a crucial role in the outcome of the assembly and that governing the substituent positions enables the design of effective precursor molecules "programmed" for the consecutive C-C bond formations. In general, these findings push the state of the field towards the facile synthesis of sophisticated bowl-shaped carbon-based nanostructures through multi-assembly of fluoroarenes.

Record Alkali Metal Intercalation by Highly Charged Corannulene.

The need for advanced energy storage technologies demands the development of new functional materials. Novel carbon-rich and carbon-based materials of different structural topologies attract significant attention in this regard. Attractive systems include a unique class of bowl-shaped polycyclic aromatic hydrocarbons that map onto fullerene surfaces and are thus often referred to as fullerene fragments, buckybowls, or π-bowls. Importantly, carbon bowls are able to acquire multiple electrons in stepwise reduction reactions producing sets of successively reduced carbanions. The resulting negatively charged π-bowls exhibit unique supramolecular assembly and metal intercalation patterns that only recently have begun to be uncovered. First, we have resolved the long-standing mystery behind the supramolecular structure formed by a highly reduced fullerene fragment called corannulene (C20H104-) with multiple lithium ions, using X-ray crystallography coupled with NMR spectroscopy and theoretical calculations. This work provided a new paradigm for lithium ion intercalation between the curved carbon π-surfaces and facilitated understanding of the lithium ion storage mechanism in carbonaceous matrices. Next, we have initiated a new research direction, an investigation of the mixed alkali metal reduction reactions using bowl-shaped corannulene as a remarkable multielectron reservoir and unique ligand with open convex and concave π-surfaces. As a result, we have revealed the cooperative effect of lithium with heavier Group 1 metals in reduction and self-assembly processes of corannulene. Moreover, we have discovered a new class of organometallic supramolecules having heterometallic cores with high nuclearity and charge such as Li3M36+ and LiM56+ (M = K, Rb, and Cs) sandwiched between two tetrareduced corannulene decks. The resulting triple-decker supramolecular assemblies, fully characterized by X-ray diffraction and spectroscopic methods, were found to exhibit a record ability of the highly charged corannulene π-surfaces to be fully engaged in intercalation of multiple metal ions. Based on this unique ability, curved π-ligands with extended carbon frameworks are expected to show remarkable potential for alkali metal storage compared to flat polycyclic arenes. Notably, a previously unseen mode of internal lithium binding revealed in the heterobimetallic sandwiches is accompanied by unprecedented negative shifts (up to -25 ppm) in 7Li NMR spectra. Based on in-depth analysis of NMR data, augmented by DFT calculations, we have rationalized the observed experimental trends and proposed the mechanism of stepwise alkali metal substitution reactions. Furthermore, we have correlated the origin of the record 7Li NMR shifts with unique electronic structures of these novel supramolecular aggregates. Herein we present comprehensive analysis of unusual structural and electronic features of remarkable heterometallic self-assemblies formed by tetrareduced corannulene, using a wealth of our recent experimental and computational results. This work uncovers unique potential of highly negatively charged bowl-shaped π-ligands for new supramolecular chemistry and materials chemistry applications.

Self-Assembly of Aligned Hybrid One-Dimensional Stacks from Two Complementary π-Bowls

Designed synthesis of a new crystalline donor–acceptor organic hybrid has been accomplished by using two bowl-shaped polycyclic aromatic hydrocarbons (PAHs) having complementary structures and properties, namely, C20H10 and C5-C20H5(CF3)5. The X-ray structural characterization of the product, [(C20H10)·(C20H5(CF3)5)]·C6H4Cl2, revealed the formation of aligned columnar stacks of alternating C20H10 and C20H5(CF3)5 molecules with centroid-to-centroid distances of 3.658(8) and 3.787(8) A and a small bowl slip of 0.086(6) A. The tight bowl packing is accompanied by notable molecular geometry adjustments of the individual PAHs. The bowl depth increased for corannulene (Δ = +0.019 A) and decreased for sym-pentakis(trifluoromethyl)corannulene (Δ = −0.011 A), facilitating enhancement of concave–convex interactions along the stacks. The parallel alignment of one-dimensional columns is supported by multiple intermolecular interactions involving C6H4Cl2 used as the crystallization solvent, forming an infinite two-dim...

Electron-Poor Bowl-Shaped Polycyclic Aromatic Dicarboximides: Synthesis, Crystal Structures, and Optical and Redox Properties.

Two new bowl-shaped polycyclic aromatic hydrocarbons, based on corannulene and naphthalene dicarboximide, are synthesized by an improved Suzuki-Miyaura cross-coupling and C-H arylation cascade reaction. Crystallographic analyses confirm structural assignments and provide insight into molecular interactions in the solid state. The new bowl-shaped molecules show reversible oxidation and reduction, intense visible range absorption, and high fluorescence quantum yields. These molecules can be considered bowl-shaped congeners of planar perylene dicarboximides.

Synthesis of Rationally Halogenated Buckybowls by Chemoselective Aromatic C−F Bond Activation

AbstractHalogenated buckybowls or bowl‐shaped polycyclic aromatic hydrocarbons (BS‐PAHs) are key building blocks for the “bottom‐up” synthesis of various carbon‐based nanomaterials with outstanding potential in different fields of technology. The current state of the art provides quite a limited number of synthetic pathways to BS‐PAHs; moreover, none of these approaches show high selectivity and tolerance of functional groups. Herein we demonstrate an effective route to BS‐PAHs that includes directed intramolecular aryl–aryl coupling through C−F bond activation. The coupling conditions were found to be completely tolerant toward aromatic C−Br and C−Cl bonds, thus allowing the facile synthesis of rationally halogenated buckybowls with an unprecedented level of selectivity. This finding opens the way to functionalized BS‐PAH systems that cannot be obtained by alternative methods.

Synthesis of Rationally Halogenated Buckybowls by Chemoselective Aromatic C-F Bond Activation.

Halogenated buckybowls or bowl-shaped polycyclic aromatic hydrocarbons (BS-PAHs) are key building blocks for the "bottom-up" synthesis of various carbon-based nanomaterials with outstanding potential in different fields of technology. The current state of the art provides quite a limited number of synthetic pathways to BS-PAHs; moreover, none of these approaches show high selectivity and tolerance of functional groups. Herein we demonstrate an effective route to BS-PAHs that includes directed intramolecular aryl-aryl coupling through C-F bond activation. The coupling conditions were found to be completely tolerant toward aromatic C-Br and C-Cl bonds, thus allowing the facile synthesis of rationally halogenated buckybowls with an unprecedented level of selectivity. This finding opens the way to functionalized BS-PAH systems that cannot be obtained by alternative methods.

From Corannulene to Indacenopicene: Effect of Carbon Framework Topology on Aromaticity and Reduction Limits

The electronic structure, reduction limits, and coordination abilities of a bowl-shaped polycyclic aromatic hydrocarbon, indacenopicene (C26H12, 1), have been investigated for the first time using a combination of theoretical and experimental tools. A direct comparison with the prototypical corannulene bowl (C20H10, 2) revealed the effects of carbon framework topology and symmetry change on the electronic properties and aromaticity of indacenopicene. The accessibility of two reduction steps for 1 was predicted theoretically and then confirmed experimentally. Two reversible one-electron reduction processes with the formal reduction potentials at −1.92 and −2.29 V vs Fc+/0 were detected by cyclic voltammetry measurements, demonstrating the stability of the corresponding mono- and dianionic states of 1. The products of the doubly reduced indacenopicene have been isolated as rubidium and cesium salts and fully characterized. Their X-ray diffraction study revealed the formation of tetranuclear organometallic b...

Synthesis and Properties of a Buckybowl/Buckyball Dyad

In this work, we describe the synthesis of a molecule in which fullerene C60 is covalently attached to a bowl-shaped polycyclic aromatic hydrocarbon, corannulene. The developed synthetic route is comprised of four linear steps with isolated yields ranging from 41–91%. The first three steps relate to the preparation of a hydrazone derivative of corannulene carrying a butyric acid methyl ester group. This key compound generates a reactive diazo moiety under base-induced decomposition process. The generated diazoalkane then adds to the C60 molecule to furnish the targeted corannulene-C61-butyric acid methyl ester (CCBM) molecule. This compound is structurally characterized by NMR spectroscopy and mass spectrometry, whereas material properties are determined with the help of optical absorption spectroscopy and cyclic voltammetry. Finally, some preliminary aspects on its application are examined in a poly(3-hexyl thiophene)-based photovoltaic device.

Fused Dibenzo[a,m]rubicene: A New Bowl-Shaped Subunit of C70 Containing Two Pentagons.

Total synthetic approaches of fullerenes are the holy grail for organic chemistry. So far, the main attempts have focused on the synthesis of the buckminsterfullerene C60. In contrast, access to subunits of the homologue C70 remains challenging. Here, we demonstrate an efficient bottom-up strategy toward a novel bowl-shaped polycyclic aromatic hydrocarbons (PAH) C34 with two pentagons. This PAH represents a subunit for C70 and of other higher fullerenes. The bowl-shaped structure was unambiguously determined by X-ray crystallography. A bowl-to-bowl inversion for a C70 fragment in solution was investigated by dynamic NMR analysis, showing a bowl-to-bowl inversion energy (ΔG(⧧)) of 16.7 kcal mol(-1), which is further corroborated by DFT calculations.

Host–guest interaction between corannulene and γ-cyclodextrin: mass spectrometric evidence of a 1 : 1 inclusion complex formation

The toroidal cavity of γ-cyclodextrin is shown to interact with a bowl-shaped polycyclic aromatic hydrocarbon, corannulene, through host–guest interactions.

Reactivity and Selectivity of Bowl-Shaped Polycyclic Aromatic Hydrocarbons: Relationship to C60.

The Diels-Alder reactivity of different bowl-shaped polycyclic aromatic hydrocarbons (namely, corannulene, cyclopentacorannulene, diindenochrysene, hemifullerene, and circumtrindene) has been explored computationally within the DFT framework. To this end, both the increase in reactivity with the size of the buckybowl and complete [6,6]-regioselectivity in the process have been analyzed in detail by using the activation strain model of reactivity in combination with the energy decomposition analysis method. These results have been compared with the parent C60 fullerene, which also produces the corresponding [6,6]-cycloadduct exclusively. The behavior of the buckybowls considered herein resembles, in general, that of C60 . Whereas the interaction energy between the deformed reactants along the reaction coordinate mainly controls the regioselectivity of the process, it is the interplay between the activation strain energy and the transition-state interaction that governs the reactivity of the system.

ChemInform Abstract: Chemistry on a Half‐Shell: Synthesis and Derivatization of Buckybowls

AbstractReview: 76 refs.

Bending contorted hexabenzocoronene into a bowl

This article describes the synthesis of a new type of bowl-shaped polycyclic aromatic hydrocarbon. These bowls are formed by joining the proximal carbons of contorted hexabenzocoronenes. These methods begin to tap a wealth of structural diversity available from these core structures. The bowl-shaped hydrocarbons more easily accept electrons than their contorted hexabenzocoronene precursors and associate strongly with C70.