A Highly Warped Heptagon-Containing sp2 Carbon Scaffold via Vinylnaphthyl π-Extension

Controllable 1,4-Palladium Aryl to Aryl Migration in Fused Systems─Application to the Synthesis of Azaborole Multihelicenes

Herein, we report the first 1,4-Pd aryl to aryl migration/Miyaura borylation tandem reaction in fused systems. The Pd shift occurred in the bay region of the dibenzo[g,p]chrysene building blocks, giving rise to a thermodynamically controlled mixture of 1,8- and 1,9-borylated compounds that allowed the preparation of regioisomeric azaborole multihelicenes from the same starting material. The outcome of this synthesis can be controlled by the choice of reaction conditions, allowing the migration process to be turned off in the absence of an acetate additive and the target multiheterohelicenes to be prepared in a regioselective manner. The target compounds show bright green fluorescence in dichloromethane with emission quantum yields (Φ) of up to 0.29, |glum| values up to 2.7 × 10-3, and green or green-yellow emission in the solid state, reaching Φ of 0.22. Single crystal X-ray diffraction analyses gave insight into their molecular structures and the packing arrangement. Evaluation of aromaticity in these multihelicenes revealed a nonaromatic character of the 2H-1,2-azaborole constituent rings.

A Negatively Curved Nanographene with Four Embedded Heptagons

Negatively curved nanographenes are considered as cutouts of three-dimensional fully sp2-hybridized carbon allotropes such as Schwarzites. Here we present the synthesis of a C76 cut-out of the Schwarzite 8-4-1-p proposed by Lenosky et al. and investigate its optical as well as electrochemical properties. Furthermore, supramolecular interactions with fullerenes C60 and C70 were studied.

Orchestrated Octuple C-H Activation: A Bottom-Up Topology Engineering Approach toward Stimuli-Responsive Double-Heptagon-Embedded Wavy Polycyclic Heteroaromatics

Curiosity-driven innovations on the design and synthesis of nonplanar polycyclic aromatic/heteroaromatic compounds with new molecular topologies unfold exciting opportunities for harnessing their intriguing supramolecular properties and thereby the development of novel functional organic materials. This work presents such an innovative synthetic concept of a bottom-up molecular topology engineering through a unique orchestrated octuple C-H activation reaction, toward the rapid synthesis of a novel class of double heptagon-incorporated nitrogen-doped laterally-fused polycyclic compounds with rarely reported wavy structural configuration. The profound impact of the molecular wavy structures of these compounds on their properties is manifested by weak and tunable solid-state intermolecular interactions controlling the electronic properties of the materials, leading to reversibly switchable fluorochromism in the solid state and thin films with mechanical force and solvent vapors as external stimuli, thereby indicating their potential applicability in rewritable fluorescent optical recording media, security papers, mechanosensors, volatile organic compound (VOC) sensors etc.

Schwarzites and Triply Periodic Minimal Surfaces: From Pure Topology Mathematics to Macroscale Applications

Schwarzites are porous (spongy-like) carbon allotropes with negative Gaussian curvatures. They are proposed by Mackay and Terrones inspired by the works of the German mathematician Hermann Schwarz on Triply-Periodic Minimal Surfaces (TPMS). This review presents and discusses the history of schwarzites and their place among curved carbon nanomaterials. The main works on schwarzites are summarized and are available in the literature. Their unique structural, electronic, thermal, and mechanical properties are discussed. Although the synthesis of carbon-based schwarzites remains elusive, recent advances in the synthesis of zeolite-templates nanomaterials have brought them closer to reality. Atomic-based models of schwarzites are translated into macroscale ones that are 3D-printed. These 3D-printed models are exploited in many real-world applications, including water remediation and biomedical ones.

Axially Chiral Nonbenzenoid Nanographene with Second Harmonic Generation Property

Chiral nanographenes (NGs) have garnered significant interest as optoelectronic materials in recent years. While helically chiral NGs have been extensively studied, axially chiral NGs have only witnessed limited examples, with no prior reports of axially chiral nonbenzenoid NGs. Herein we report an axially chiral nonbenzenoid nanographene featuring six pentagons and four heptagons. This compound, denoted as 2, was efficiently synthesized via an efficient Pd-catalyzed aryl silane homocoupling reaction. The presence of two bulky 3,5-di-tert-butylphenyl groups around the axis connecting the two nonbenzenoid PAH (AHR) segments endows 2 with atropisomeric chirality and high racemization energy barrier, effectively preventing racemization of both R- and S-enantiomers at room temperature. Optically pure R-2 and S-2 were obtained by chiral HPLC separation, and they exhibit circular dichroism (CD) activity at wavelengths up to 660 nm, one of the longest wavelengths with CD responses reported for the chiral NGs. Interestingly, racemic 2 forms a homoconfiguration π-dimer in the crystal lattice, belonging to the I222 chiral space group. Consequently, this unique structure renders crystals of 2 with a second harmonic generation (SHG) response, distinguishing it from all the reported axially chiral benzenoid NGs. Moreover, R-2 and S-2 also exhibit SHG-CD properties.

Synthesis of Heptagon-Containing Polyarenes by Catalytic C-H Activation

Nanocarbons incorporating non-hexagonal aromatic rings - such as five-, seven-, and eight-membered rings - have various intriguing physical properties such as curved structures, unique one-dimensional packing, and promising magnetic, optical, and conductivity properties. Herein, we report an efficient synthetic approach to polycyclic aromatics containing seven-membered rings via a palladium-catalyzed intramolecular Ar-H/Ar-Br coupling. In addition to all-hydrocarbon scaffolds, heteroatom-embedded heptagon-containing polyarenes can be efficiently constructed with this method. Rhodium- and palladium-catalyzed sequential six- and seven-membered ring formations also afford complex heptagon-containing molecular nanocarbons from readily available arylacetylenes and biphenyl boronic acids. Detailed mechanistic analysis by DFT calculations showed the feasibility of seven-membered ring formation by a concerted metalation-deprotonation mechanism. This reaction can serve as a template for the synthesis of a wide range of seven-membered ring-containing molecular nanocarbons.

Post-Installation of Fused Benzoheptagons at the Periphery of NiII Porphyrins: Helical Structures and Conformation-Adjustable Fullerenes Binding

Fused-benzoheptagon-installed NiII porphyrins were synthesized by a protocol consisting of (2-formyl)arylation at the meso-position(s) of NiII porphyrins, conversion of formyl group to methoxyethene group by Wittig reaction, and final Bi(OTf)3 -catalyzed cyclization. The structures of these porphyrins have been revealed by X-ray analysis. Owing to the installed heptagon ring(s), these porphyrins show curved structures with conformational flexibility. Dimer has been shown to have a small activation barrier for inversion and to capture C60 and C70 with large association constants with adjustable conformational changes.

Functionalization of Pentacene: A Facile and Versatile Approach to Contorted Polycyclic Aromatic Hydrocarbons

In this work, a facile and versatile strategy for the synthesis of contorted polycyclic aromatic hydrocarbons (PAHs) starting from the functionalized pentacene was established. A series of novel PAHs 1-4 and their derivatives were synthesized through a simple two-step synthesis procedure involving an intramolecular reductive Friedel-Crafts cyclization of four newly synthesized pentacene aldehydes 5-8 as a key step. All the molecules were confirmed by single-crystal X-ray diffraction and their photophysical and electrochemical properties were studied in detail. Interestingly, the most striking feature of 1-4 is their highly contorted carbon structures and the accompanying helical chirality. In particular, the optical resolution of 2 was successfully achieved by chiral-phase HPLC, and the enantiomers were characterized by circular dichroism and circularly polarized luminescence spectroscopy. Despite the highly nonplanar conformations, these contorted PAHs exhibited emissive properties with moderate-to-good fluorescence quantum yields, implying the potential utility of this series PAHs as high-quality organic laser dyes. By using a self-assembly method with the help of epoxy resin, a bottle microlaser based on 3 a was successfully illustrated with a lasing wavelength of 567.8 nm at a threshold of 0.3 mJ/cm2 . We believe that this work will shed light on the chemical versatility of pentacene and its derivatives in the construction of novel functionalized PAHs.

π-Extended benzo[1,2:4,5]di[7]annulene bis(dicarboximide)s - a new class of non-alternant polycyclic aromatic dicarboximides

Aromatic dicarboximides are a class of molecules represented by the well-known rylene bis(dicarboximide)s, in particular perylene or naphthalene bis(dicarboximide)s, which show pronounced optoelectronic properties and are applied as color pigments, fluorescent dyes and organic semiconductors. Herein we extend the family of aromatic bis(dicarboximide)s and report the synthesis of the first series of non-alternant aromatic dicarboximides by twofold Pd-catalyzed [5 + 2] annulation. Characterization by UV/vis spectroscopy and cyclic voltammetry (CV) measurements give insight into the optoelectronic characteristics of the hitherto unexplored substance class of heptagon-containing imides. Theoretical studies by nucleus independent chemical shift (NICS) XY-scans and anisotropy of the induced current density (ACID) plots demonstrate the influence of both the non-alternant carbon framework and the imide moieties on aromaticity of the synthesized bisimides.

Diazulenorubicene as a Non-benzenoid Isomer of peri-Tetracene with Two Sets of 5/7/5 Membered Rings Showing Good Semiconducting Properties

Non-benzenoid polycyclic aromatic hydrocarbons (PAHs) have received a lot of attention because of their unique optical, electronic, and magnetic properties, but their synthesis remains challenging. Herein, we report a non-benzenoid isomer of peri-tetracene, diazulenorubicene (DAR), with two sets of 5/7/5 membered rings synthesized by a (3+2) annulation reaction. Compared with the precursor containing only 5/7 membered rings, the newly formed five membered rings switch the aromaticity of the original heptagon/pentagon from antiaromatic/aromatic to non-aromatic/antiaromatic respectively, modify the intermolecular packing modes, and lower the LUMO levels. Notably, compound 2 b (DAR-TMS) shows p-type semiconducting properties with a hole mobility up to 1.27 cm2  V-1  s-1 . Moreover, further extension to larger non-benzenoid PAHs with 19 rings was achieved through on-surface chemistry from the DAR derivative with one alkynyl group.

One-Pot Synthesis of Helical Azaheptalene and Chiroptical Switching of an Isolable Radical Cation

A nitrogen-centered heptalene, azaheptalene, was designed as a representative of a new class of redox-responsive molecules with a large steric strain that originates from the adjacent seven-membered rings. The pentabenzo derivative of azaheptalene was efficiently synthesized by a palladium-catalyzed one-pot reaction of commercially available reagents. Bromination led to mono- and dibrominated derivatives, the latter of which is interconvertible with isolable radical cation species exhibiting near-infrared absorption. Since the azaheptalene skeleton shows configurationally stable helicity with a large torsion angle, enantiomers could be successfully separated. Thus, optically pure azaheptalenes with P- or M-helicity showed strong chiroptical properties (|gabs |≥0.01), which could be changed by an electric potential.

A Heptacene Analogue Entailing a Quinoidal Benzodi[7]annulene (7/6/7 Ring) Core with a Tunable Configuration and Multiple Redox Properties

Non-benzenoid acenes containing heptagons have received increasing attention. We herein report a heptacene analogue containing a quinoidal benzodi[7]annulene core. Derivatives of this new non-benzenoid acene were obtained through an efficient synthetic strategy involving an Aldol condensation and a Diels-Alder reaction as key steps. The configuration of this heptacene analogue can be modulated from a wavy to a curved one by just varying the substituents from a (triisopropylsilyl)ethynyl group to a 2,4,6-triisopropylphenyl (Trip) group. When mesityl (Mes) groups are linked to the heptagons, the resulting non-benzenoid acene displays polymorphism with a tunable configuration from a curved to a wavy one upon varying the crystallization conditions. In addition, this new non-benzenoid acene can be oxidized or reduced by NOSbF₆ or KC₈ to the respective radical cation or radical anion. Compared with the neutral acene, the radical anion shows a wavy configuration and the central hexagon becomes aromatic.

Synthesis of a Dicyclohepta[a,g]heptalene-Containing Polycyclic Conjugated Hydrocarbon and the Impact of Non-Alternant Topologies

Incorporating non-hexagonal rings into polycyclic conjugated hydrocarbons (PCHs) can significantly affect their electronic and optoelectronic properties and chemical reactivities. Here, we report the first bottom-up synthesis of a dicyclohepta[a,g]heptalene-embedded PCH (1) with four continuous heptagons, which are arranged in a "Z" shape. Compared with its structural isomer bischrysene 1 R with only hexagonal rings, compound 1 presents a distinct antiaromatic character, especially the inner heptalene core, which possesses clear antiaromatic nature. In addition, PCH 1 exhibits a narrower highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy gap than its benzenoid contrast 1 R, as verified by experimental measurements and theoretical calculations. Our work reported herein not only provides a new way to synthesize novel PCHs with non-alternant topologies but also offers the possibility to tune their electronic and optical properties.

Enhanced Optical Properties of Azaborole Helicenes by Lateral and Helical Extension

The synthesis and characterization of laterally extended azabora[5]-, -[6]- and -[7]helicenes, assembled from N-heteroaromatic and dibenzo[g,p]chrysene building blocks is described. Formally, the π-conjugated systems of the pristine azaborole helicenes were enlarged with a phenanthrene unit leading to compounds with large Stokes shifts, significantly enhanced luminescence quantum yields (Φ) and dissymmetry factors (g_lum ). The beneficial effect on optical properties was also observed for helical elongation. The combined contributions of lateral and helical extensions resulted in a compound showing green emission with Φ of 0.31 and |g_lum | of 2.2×10^-3 , highest within the series of π-extended azaborahelicenes and superior to emission intensity and chiroptical response of its non-extended congener. This study shows that helical and lateral extensions of π-conjugated systems are viable strategies to improve features of azaborole helicenes. In addition, single crystal X-ray analysis of configurationally stable [6]- and -[7]helicenes was used to provide insight into their packing arrangements.

π-Extended Pleiadienes by [5+2] Annulation of 1-Boraphenalenes and ortho-Dihaloarenes

Palladium-catalyzed [5+2] annulation of 1-boraphenalenes with ortho-dihaloarenes afforded negatively curved π-extended pleiadienes. Two benzo[1,2-i:4,5-i']dipleiadienes (BDPs) featuring a seven-six-seven-membered ring arrangement were synthesized and investigated. Their crystal structure revealed a unique packing arrangement and theoretical calculations were employed to shed light onto the dynamic behavior of the BDP moiety and its aromaticity. Further, a naphthalene-fused pleiadiene was stitched together by oxidative cyclodehydrogenation to yield an additional five-membered ring. This formal azulene moiety led to distinct changes in optical and redox properties and increased perturbation of the aromatic system.

Supramolecular Substructure of C60-Embedded Schwarzite

Herein we present a new concept of carbon allotrope, namely, fullerene-embedded schwarzite. We isolated crystals of fullerene embedded in 4 equiv of a negatively curved polycyclic aromatic hydrocarbon (PAH), 1, which could be viewed as a substructure of the hypothetical fullerene-schwarzite complex. On the basis of crystal structure, the stability of the complex (C₆₀⊂(1)₄) was studied by theoretical methods (ALMO-EDA), showing that the noncovalent interactions driven by dispersion forces is key for stabilizing the complex, which was further supported by noncovalent interactions (NCI) plots and Hirshfeld-surface analyses. Our findings of C₆₀⊂(1)₄ provide a perspective toward the development of novel sp²-carbon allotropes comprising multiple components.

Color-tunable emissive heptagon-embedded polycyclic aromatic dicarboximides

Heptagon-embedded polycyclic aromatic dicarboximides were developed as new push-pull fluorescent dyes through palladium-catalysed [4+3] annulation followed by nucleophilic substitution. The introduction of a seven-membered ring in these push-pull systems can efficiently modulate the optical properties leading to an enhancement of the fluorescence quantum yields up to 0.93 with color tunable emission covering the visible-NIR spectrum.

Synthesis of Defective Nanographenes Containing Joined Pentagons and Heptagons

Defective nanographenes containing joined pentagons and heptagons exhibit striking physicochemical properties from both experimental and theoretical perspectives compared with their pure hexagonal counterparts. Thus, the synthesis and characterization of these unique polyarenes with well-defined defective topologies have attracted increasing attention. Despite extensive research on nonalternant molecules since the last century, most studies focused on the corresponding mutagenic and carcinogenic activities. Recently, researchers have realized that the defective domain induces geometric bending and causes electronic perturbation, thus leading to significant alteration of the photophysical properties. This review discusses the synthesis and characterization of small nonalternant polycyclic hydrocarbons in the early stage and recent developments in embedding pentagon-heptagon (5-7) pairs into large carbon skeletons through in-solution chemistry.

Nanographene with Multiple Embedded Heptagons: Cascade Radical Photocyclization

Although heptagons are widely found in graphenic materials, the precise synthesis of nanocarbons containing heptagons remains a challenge, especially for the nanocarbons containing multiple-heptagons. Herein, we show that photo-induced radical cyclization (PIRC) can be used to synthesize multi-heptagon-embedded nanocarbons. Notably, a nanographene containing six heptagons (1) was obtained via a six-fold cascade PIRC reaction. The structure of 1 was clearly validated and showed a Monkey-saddle-shaped conformation. Experimental bond analysis and theoretical calculations indicated that the heptagons in 1 were non-aromatic, whereas the peripheral rings were highly aromatic. Compared to planar nanographene with the same number of π electrons, 1 had a similar optical gap due to a compromise between the decreased conjugation in the wrapped structure and enhanced electronic delocalization at the rim. Electrochemical studies showed that 1 had low-lying oxidation potentials, which was attributed to the nitrogen-doping.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

This review surveys recent progress in the chemistry of polycyclic heteroaromatic molecules with a focus on structural diversity and synthetic methodology. The article covers literature published during the period of 2016-2020, providing an update to our first review of this topic (Chem. Rev. 2017, 117 (4), 3479-3716).

Construction of Heptagon-Containing Molecular Nanocarbons

Molecular nanocarbons containing heptagonal rings have attracted increasing interest due to their dynamic behavior, electronic properties, aromaticity, and solid-state packing. Heptagon incorporation can not only induce negative curvature within nanocarbon scaffolds, but also confer significantly altered properties through interaction with adjacent non-hexagonal rings. Despite the disclosure of several beautiful examples in recent years, synthetic strategies toward heptagon-embedded molecular nanocarbons remain relatively limited due to the intrinsic challenges of heptagon formation and incorporation into polyarene frameworks. In this Review, recent advances in solution-mediated and surface-assisted synthesis of heptagon-containing molecular nanocarbons, as well as the intriguing properties of these frameworks, will be discussed.

Multi-Redox Active Carbons and Hydrocarbons: Control of their Redox Properties and Potential Applications

Precise control over redox properties is essential for high-performance organic electronic devices such as organic batteries, electrochromic devices, and information storage devices. In this context, multi-redox active carbons and hydrocarbons, represented as C_x H_y molecules (x≥1, y≥0), are highly sought after, because they can switch between multiple redox states. Herein, we outline the redox properties of C_x H_y molecules as solutes and adsorbed species. Furthermore, the limitations of evaluating their redox properties and the possible solutions are summarized. Additionally, the theoretical capacity (mAh/g) and gravimetric energy density (Wh/kg) of secondary batteries were estimated based on the redox properties of 185 C_x H_y molecules, which have primarily been reported in the last decade. Among them, seven C_x H_y molecules were found to have the potential to surpass the energy density of LiNi_0.6 Mn_0.2 Co_0.2 O₂ /graphite batteries. The use of C_x H_y molecules in multielectrochromic devices and multi-bit memory is also explained. We believe that this review will encourage further utilization of C_x H_y molecules thereby promoting its applications in organic electronic devices.

Charging a Negatively Curved Nanographene and Its Covalent Network

This study explores a bottom-up approach toward negatively curved carbon allotropes from octabenzo[8]circulene, a negatively curved nanographene. Stepwise chemical reduction reactions of octabenzo[8]circulene with alkali metals lead to a unique highly reduced hydrocarbon pentaanion, which is revealed by X-ray crystallography suggesting a local view for the reduction and alkali metal intercalation processes of negatively curved carbon allotropes. Polymerization of the tetrabromo derivative of octabenzo[8]circulene by the nickel-mediated Yamamoto coupling reaction results in a new type of porous carbon-rich material, which consists of a covalent network of negatively curved nanographenes. It has a specific surface area of 732 m² g^-1 and functions as anode material for lithium ion batteries exhibiting a maximum capacity of 830 mAh·g^-1 at a current density of 100 mA·g^-1. These results indicate that this covalent network presents the key structural and functional features of negatively curved carbon allotropes.

Modular Synthesis of Organoboron Helically Chiral Compounds: Cutouts from Extended Helices

Two types of helically chiral compounds bearing one and two boron atoms were synthesized by a modular approach. Formation of the helical scaffolds was executed by the introduction of boron to flexible biaryl and triaryl derived from small achiral building blocks. All-ortho-fused azabora[7]helicenes feature exceptional configurational stability, blue or green fluorescence with quantum yields (Φfl ) of 18-24 % in solution, green or yellow solid-state emission (Φfl up to 23 %), and strong chiroptical response with large dissymmetry factors of up to 1.12×10-2 . Azabora[9]helicenes consisting of angularly and linearly fused rings are blue emitters exhibiting Φfl of up to 47 % in CH2 Cl2 and 25 % in the solid state. As revealed by the DFT calculations, their P-M interconversion pathway is more complex than that of H1. Single-crystal X-ray analysis shows clear differences in the packing arrangement of methyl and phenyl derivatives. These molecules are proposed as primary structures of extended helices.

Edge-Functionalized Nanographenes

Nanographenes (NGs) have recently emerged as new carbon materials. Their nanoscale size results in a size-dependent quantum confinement effect, opening the band gap by a few eV. This energy gap allows NGs to be applied as optical materials. This property has attracted researchers across multiple scientific fields. The photophysical properties of NGs can be manipulated by introducing organic groups onto their basal planes and/or into their edges. In addition, the integration of organic functional groups into NGs results in NG-based hybrid materials. These features make the post-synthetic modification of NGs an active research area. As obtainable information on chemically functionalized NGs is limited owing to their nonstoichiometry and structural uncertainty, their structural characterization requires a combination of multiple spectroscopic methods. Therefore, information on the characterization procedures of recently published chemically functionalized NGs is of value for advancing the field of NG-based hybrid materials. The present review focuses on the structural characterization of chemically functionalized NGs. It is hoped that this review will help to advance this field.

Dibenzopleiadiene-embeded polyaromatics via [4 + 3] annulative decarbonylation/decarboxylation

A novel and efficient sequential cross-coupling/annulation strategy is developed to construct structurally and optoelectronically diverse class of dibezopleiadiene-embeded polyaromatics.

Conformation and Aromaticity Switching in a Curved Non-Alternant sp2 Carbon Scaffold

A curved sp2 carbon scaffold containing fused pentagon and heptagon units (1) was synthesized by Pd-catalyzed [5+2] annulation from a 3,9-diboraperylene precursor and shows two reversible oxidation processes at low redox potential, accompanied by a butterfly-like motion. Stepwise oxidation produced radical cation 1.+ and dication 12+ . In the crystal structure, 1 exhibits a chiral cisoid conformation and partial π-overlap between the enantiomers. For the radical cation 1.+ , a less curved cisoid conformation is observed with a π-dimer-type arrangement. 12+ adopts a more planar structure with transoid conformation and slip-stacked π-overlap with closest neighbors. We also observed an intermolecular mixed-valence complex of 1⋅(1.+ )3 that has a huge trigonal unit cell [(1)72 (SbF6 )54 ⋅(hexane)101 ] and hexagonal columnar stacks. In addition to the conformational change, the aromaticity of 1 changes from localized to delocalized, as demonstrated by AICD and NICS(1)zz calculations.

Chemically Functionalized Two-Dimensional Carbon Materials

Nanographenes (NGs), also known as graphene quantum dots, have recently been developed as nanoscale graphene fragments. These nanocarbon species can be excited with UV light and emit light from the UV-to-visible region. This photoemission has received great attraction across multiple scientific fields. NGs can be produced by cutting off carbon sources or fusing small organic molecules to grow graphitic structures. Furthermore, the organic synthesis of NGs has been intensely studied. Recently, the number of research papers on postsynthetic modification of NGs has gradually increased. Installed organic groups can tune the properties of NGs and provide new functionalities, opening the door for the development of sophisticated carbon-based functional materials. This review sheds light on recent progress in the postsynthetic modification of NGs and provides a brief summary of their production methods.

The synthesis of brominated-boron-doped PAHs by alkyne 1,1-bromoboration: mechanistic and functionalisation studies

The synthesis of a range of brominated-B n -containing (n = 1, 2) polycyclic aromatic hydrocarbons (PAHs) is achieved simply by reacting BBr3 with appropriately substituted alkynes via a bromoboration/electrophilic C-H borylation sequence. The brominated-B n -PAHs were isolated as either the borinic acids or B-mesityl-protected derivatives, with the latter having extremely deep LUMOs for the B2-doped PAHs (with one example having a reduction potential of E 1/2 = -0.96 V versus Fc+/Fc, Fc = ferrocene). Mechanistic studies revealed the reaction sequence proceeds by initial alkyne 1,1-bromoboration. 1,1-Bromoboration also was applied to access a number of unprecedented 1-bromo-2,2-diaryl substituted vinylboronate esters directly from internal alkynes. Bromoboration/C-H borylation installs useful C-Br units onto the B n -PAHs, which were utilised in Negishi coupling reactions, including for the installation of two triarylamine donor (D) groups onto a B2-PAH. The resultant D-A-D molecule has a low optical gap with an absorption onset at 750 nm and emission centered at 810 nm in the solid state.

A Chiral Polycyclic Aromatic Hydrocarbon Monkey Saddle

A contorted polycyclic aromatic hydrocarbon (PAH) in the shape of a monkey saddle has been synthesized in three steps from a readily available truxene precursor. The monkey saddle PAH is consisting of three five-, seven six-, and three eight-membered rings and has been unambiguously characterized by single-crystal X-ray diffraction. Owing to the three biaryl axes the monkey saddle PAH is inherently chiral. The inversion of the two enantiomeric structures into each other preferably occurs through a twisting of peripheral rings rather than by a fully planar intermediate, as has been calculated by DFT methods. Enantiomers were separated by chiral HPLC and inversion barriers determined by variable temperature circular dichroism spectroscopy, supporting the twisting mechanism.

A Highly Warped Heptagon-Containing sp2 Carbon Scaffold via Vinylnaphthyl π-Extension

A new strategy is demonstrated for the synthesis of warped, negatively curved, all-sp² -carbon π-scaffolds. Multifold C-C coupling reactions are used to transform a polyaromatic borinic acid into a saddle-shaped polyaromatic hydrocarbon (2) bearing two heptagonal rings. Notably, this Schwarzite substructure is synthesized in only two steps from an unfunctionalized alkene. A highly warped structure of 2 was revealed by X-ray crystallographic studies and pronounced flexibility of this π-scaffold was ascertained by experimental and computational studies. Compound 2 exhibits excellent solubility, visible range absorption and fluorescence, and readily undergoes two reversible one-electron oxidations at mild potentials.