Anti‐Aromatic versus Induced Paratropicity: Synthesis and Interrogation of a Dihydro‐diazatrioxa[9]circulene with a Proton Placed Directly above the Central Ring

We present a high‐yielding intramolecular oxidative coupling within a diazadioxa[10]helicene to give a dihydro‐diazatrioxa[9]circulene. This is the first [n]circulene containing more than eight ortho‐annulated rings (n>8). The single‐crystal X‐ray structure reveals a tight columnar packing, with a proton from a pendant naphthalene moiety centred directly above the central nine‐membered ring. This distinct environment induces a significant magnetic deshielding effect on that particular proton as determined by ¹H NMR spectroscopy. The origin of the deshielding effect was investigated computationally in terms of the NICS values. It is established that the deshielding effect originates from an induced paratropic ring current from the seven aromatic rings of the [9]circulene structure, and is not due to the nine‐membered ring being antiaromatic. UV/Vis spectroscopy reveals more efficient conjugation in the prepared diazatrioxa[9]circulene compared to the parent helical azaoxa[10]helicenes, and DFT calculations, including energy levels, confirm the experimental observations.     

Anti-Aromatic versus Induced Paratropicity: Synthesis and Interrogation of a Dihydro-diazatrioxa[9]circulene with a Proton Placed Directly above the Central Ring

We present a high-yielding intramolecular oxidative coupling within a diazadioxa[10]helicene to give a dihydro-diazatrioxa[9]circulene. This is the first [n]circulene containing more than eight ortho-annulated rings (n>8). The single-crystal X-ray structure reveals a tight columnar packing, with a proton from a pendant naphthalene moiety centred directly above the central nine-membered ring. This distinct environment induces a significant magnetic deshielding effect on that particular proton as determined by ¹H NMR spectroscopy. The origin of the deshielding effect was investigated computationally in terms of the NICS values. It is established that the deshielding effect originates from an induced paratropic ring current from the seven aromatic rings of the [9]circulene structure, and is not due to the nine-membered ring being antiaromatic. UV/Vis spectroscopy reveals more efficient conjugation in the prepared diazatrioxa[9]circulene compared to the parent helical azaoxa[10]helicenes, and DFT calculations, including energy levels, confirm the experimental observations.     

Compressing a Non-Planar Aromatic Heterocyclic [7]Helicene to a Planar Hetero[8]Circulene

This work describes a synthetic approach where a non-planar aromatic heterocyclic [7]helicene is compressed to yield a hetero[8]circulene containing an inner antiaromatic cyclooctatetraene (COT) core. This [8]circulene consists of four benzene rings and four heterocyclic rings, and it is the first heterocyclic [8]circulene containing three different heteroatoms. The synthetic pathway proceeds via a the flattened dehydro-hetero[7]helicene, which is partially a helicene and partially a circulene: it is non-planar and helically chiral as helicenes, and contains a COT motif like [8]circulenes. The antiaromaticity of the COT core is confirmed by nucleus independent chemical shift (NICS) calculations. The planarization from a helically π-conjugated [7]helicene to a fully planar heterocyclic [8]circulene significantly alters the spectroscopic properties of the molecules. Post-functionalization of the [7]helicenes and the [8]circulenes by oxygenation of the thiophene rings to the corresponding thiophene-sulfones allows an almost complete fluorescence emission coverage of the visible region of the optical spectrum (400–700 nm).     

Synthesis of a Tetrabenzotetraaza[8]circulene by a “Fold‐In” Oxidative Fusion Reaction

Tetrabenzotetraaza[8]circulene ( 1 ) has been synthesized in good yield by a “fold‐in” oxidative fusion reaction of a 1,2‐phenylene‐bridged cyclic tetrapyrrole. X‐ray diffraction analysis of 1 has revealed a planar square structure with a central cyclooctatetraene (COT) core that shows little alternation of the bond lengths. Despite these structural features, 1 shows aromatic‐like character, such as sharp absorption bands, high fluorescence quantum yields (Φ_F=0.55 in THF), and a single exponential fluorescence decay with τ_F=3.8 ns. These observations indicate a dominant contribution of an [8]radialene‐like π conjugation and hence aromatic character of the local aromatic segments in 1 .     

Asararenes—A Family of Large Aromatic Macrocycles

We announce the establishment of a new family of macrocycles—the asararenes, which are based on para‐methylene linked “asarol methyl ether” (1,2,4,5‐tetramethoxybenzene) units. Macrocycles with 6–12 aromatic units have been synthesized and isolated in a single step from asarol methyl ether and paraformaldehyde. Even larger rings, with up to 15 asarol methyl ether units, have been observed by high‐resolution mass spectrometry. Single‐crystal X‐ray structures of asar[6]‐, asar[7]‐, asar[8]‐, asar[9]‐, asar[10]‐ and asar[11]arene highlight the diverse structural features of this family of macrocycles. While the cavities of the asar[6–8]arene macrocycles are mostly filled with methoxyl groups, the asar[9]‐ and asar[10]arene rings contain accessible cavities and self‐assemble into infinite channels filled with solvent molecules in the solid state. These solid‐state structures highlight the potential of this family of macrocycles for a wide range of potential applications.     

Analysis of polyaddition levels in i-Sc3NC80

Using the density functional method, the stabilities of highly hydrogenated and fluorinated [80]fullerenes, both empty and containing the Sc3N molecule, have been calculated. Addition of 44 atoms to i-Sc3NC80 is predicted to be most favorable due to the formation of six octahedrally located benzenoid rings, while addition of up to 52 atoms (consistent with preliminary fluorination data) gives a structure stabilized by the presence of four benzenoid rings. The most stable isomers at this addition level have been determined and the relative stabilities of a number of C80H52, C80F52, and i-Sc3NC80H52 species calculated. The hydrogenation of the i-Sc3NC80 has been computed to be more difficult than the corresponding partner, C80. From the geometrical point of view, the Sc3N molecule is planar in the parent [80]fullerene but is calculated to be pyramidal in some of the hydrogenated/fluorinated derivatives. Moreover, in these it has fixed locations due to orbital interactions arising from deformation of the cage and the presence of localized double bonds.     

Self‐inclusion structure of 5,11,17,23‐tetrakis(azidomethyl)‐25,26,27,28‐tetrahydroxycalix[4]arene,and 5,11,17,23‐tetra‐tert‐butyl‐25,27‐bis(chloroacetoxy)‐26,28‐bis(2‐pyridylmethoxy)calix[4]arene

In the structures of the two title calix[4]arene derivatives, C₃₂H₂₈N₁₂O₄, (I), and C₆₀H₆₈Cl₂N₂O₆, (II), compound (I) adopts an open‐cone conformation in which there are four intramolecular O—H...O hydrogen bonds, while compound (II) adopts a distorted chalice conformation where the two pendant pyridyl rings, one of which is disordered, are almost mutually perpendicular, with an interplanar angle of 79.2 (2) or 71.4 (2)°. The dihedral angles between the virtual plane defined by the four bridging methylene C atoms and the phenol rings are 120.27 (7), 124.03 (6), 120.14 (8) and 128.25 (7)° for (I), and 95.99 (8), 135.93 (7), 97.21 (8) and 126.10 (8)° for (II). In the supramolecular structure of (I), pairs of molecules associate by self‐inclusion, where one azide group of the molecule is inserted into the cavity of the inversion‐related molecule, and the association is stabilized by weak intermolecular C—H...N hydrogen bonds and π(N₃)–π(aromatic) interactions. The molecular pairs are linked into a two‐dimensional network by a combination of weak intermolecular C—H...N contacts. Each network is further connected to its neighbor to produce a three‐dimensional framework via intersheet C—H...N hydrogen bonds. In the crystal packing of (II), the molecular components are linked into an infinite chain by intermolecular C—H...O hydrogen bonds. This study demonstrates the ability of calix[4]arene derivatives to form self‐inclusion structures.     

Quadruply BN-Fused Tetrathia[8]circulenes with Flexible Frameworks: Synthesis,Structures and Properties

Quadruply BN-fused tetrathia[8]circulenes were synthesized through four-fold electrophilic borylation. The single-crystal X-ray diffraction analysis revealed that the BN-fused tetrathia[8]circulene with peripheral phenyl groups exhibits crystal polymorphism, in which the circulene core adopts both planar and saddle conformations in the solid state. The experimental and theoretical studies revealed that the weaker aromaticity of azaborine compared with benzene renders the flexibility of the BN-fused tetrathia[8]circulenes.     

From Fenestrindane towards Saddle‐Shaped Nanographenes Bearing a Tetracoordinate Carbon Atom

Two saddle‐shaped polycyclic aromatic compounds ( 8 a and 8 b ) bearing an all‐cis‐[5.5.5.5]fenestrane core surrounded by an o,p,o,p,o,p,o,p‐cyclooctaphenylene belt were synthesized and characterized by NMR spectroscopy and mass spectrometry. The key step of this synthesis involves the formation of four cycloheptatriene rings from the corresponding electron‐rich 1,4,9,12‐tetraarylfenestrindane derivatives 7 a and 7 b in Scholl‐type cyclizations. The structural details of the D_2d‐symmetric saddle compound 8 a were determined by X‐ray crystallography, and the properties of 8 a and 8 b were studied by UV/Vis and fluorescence spectroscopy and cyclic voltammetry.     

Highly Stable Radical Cations of N,N’-Diarylated Tetrabenzotetraaza[8]circulene

N,N’-Diarylated tetrabenzotetraaza[8]circulenes 3 a and 3 b were synthesized in good yields by a reaction sequence involving oxidation of tetrabenzodiazadithia[8]circulene 5-Oct and S_NAr reaction with aniline derivatives. The obtained aza[8]circulenes 3 a and 3 b were easily oxidized to give their radical cations 3 a⁺ and 3 b⁺ , which are highly stable under ambient conditions. X-ray diffraction analysis of radical cation 3 a⁺ showed a face-to-face dimer arrangement with an interplanar separation of 3.320 Å. The spin density of 3 a⁺ was calculated to be delocalized over the whole circulene π-systems with spin–spin exchange integral (J=−144 cm⁻¹) in the dimeric part. These radical cations displayed far red-shifted absorption bands reaching to 2000 nm. Thus this study has proved the hetero[8]circulene scaffold to be a new entry of promising electronics and spin materials.     

Shedding light on octathio[8]circulene and some of its plate-like derivatives

A quantum chemical investigation is made on the recently synthesized octathio[8]circulene (C16S8), an exotic molecule, the first fully heterocyclic circulene, from the structural and electronic properties and some charge-transport parameters viewpoints. Since the molecule consists of eight thiophene rings fused together, we have chosen to compare it with the acyclic (octathienoacene) analogue and to some relatives thereof, in which the sulfur atoms are substituted by Se, NH, CH2 and O. C16S8, C16Se8 and C16S4Se4 are found to show a low reorganization energy comparable or lower than that for already well known field-effect transistor (FET) materials, a promising property which, combined to some others revealed by this study, makes these compounds potential candidates for FET use. In addition, the twist angle is found to be tightly linked to the peripheral bonds lengths, the least twisted structures showing the most interesting properties for organic FET use.     

A Stable All‐Thiophene‐Based Core‐Modified [38]Octaphyrin Diradicaloid: Conformation and Aromaticity Switch at Different Oxidation States

A soluble and stable core‐modified [38]octaphyrin, MC‐T8 , containing eight thiophene rings was synthesized by Yamamoto coupling followed by oxidative dehydrogenation. X‐ray crystallographic analysis revealed a nearly planar backbone, and the molecule is globally aromatic with a dominant 38π conjugation pathway. The dication MC‐T8²⁺ is antiaromatic, and the backbone is distorted, with a different orientation of the thiophene rings. The tetracation MC‐T8⁴⁺ becomes aromatic again, with a shallow‐bowl‐shaped geometry. Both the neutral compound and the dication demonstrated open‐shell diradical character with a small singlet–triplet energy gap (?2.70 kcal mol^?1 for MC‐T8 and ?3.78 kcal mol^?1 for MC‐T8²⁺ ), and they are stable owing to effective spin delocalization.     

Synthesis,structure, and aromaticity of a hoop-shaped cyclic benzenoid [10]cyclophenacene

The first hoop-shaped cyclic benzenoid compounds, [10]cyclophenacene derivatives that contain 40 pi electrons, have been synthesized in three or four steps from [60]fullerene by rationally designed chemical modification. The compounds thus synthesized are chemically stable, yellow-colored, luminescent, and EPR-silent. X-ray crystallographic analysis provided high precision structural data sets. On the basis of these results and theoretical investigations, the new cyclic benzenoid molecules were proven to be aromatic.     

Dibenzothienopyrrolo[3,2‐b]pyrrole: The Missing Member of the Thienoacene Family

Dibenzothienopyrrolo[3,2‐b]pyrrole and the corresponding bis(S,S‐dioxide) were synthesized by using a concise synthetic strategy. Despite the presence of six fused aromatic rings, π‐expanded pyrrolo[3,2‐b]pyrroles of this type absorb and emit at relatively short wavelengths, which reflects inefficient π conjugation due to the angular arrangement of the aromatic rings. They exhibit interesting and complex electrochemical behavior, which highlights their potential in organic electronics. Both heteroacenes undergo two‐stage oxidation while retaining the independence of each 1‐phenyl‐1H‐[1]benzothieno[3,2‐b]pyrrole, which was proved by in situ electron spin resonance measurements. Interestingly, electrochemically generated dicationdiradicals are not only distributed over the pyrrolo[3,2‐b]pyrrole scaffold, but also over the phenyl substituents located on nitrogen atoms.     

Synthesis,Structure, and Properties of O6‐Corona[3]arene[3]tetrazines

O₆‐Corona[3]arene[3]tetraazines, a new class of macrocyclic compounds, were synthesized efficiently in a one‐pot reaction from the nucleophilic aromatic substitution reaction between 1,4‐dihydroxybenzene derivatives and 3,6‐dichlorotetrazine in warm acetonitrile. In the crystalline structure, the resulting macrocycles adopt highly symmetric structures of a regular hexagonal cavity with all bridging oxygen atoms and tetrazine rings located on the same plane with phenylene units orthogonally orientated. The constitutional aromatic rings are able to rotate around the macrocyclic annulus, depending on the steric effect of the substituents and temperature, in solution. The electron‐deficient nature revealed by cyclic voltammetry, differential pulse voltammetry, and characteristic absorbances at a visible region show the O₆‐corona[3]arene[3]tetrazines to be suitable macrocyclic receptors for electron‐rich guests.     

Synthesis,Structure, and Properties of O6‐Corona[3]arene[3]tetrazines

O₆‐Corona[3]arene[3]tetraazines, a new class of macrocyclic compounds, were synthesized efficiently in a one‐pot reaction from the nucleophilic aromatic substitution reaction between 1,4‐dihydroxybenzene derivatives and 3,6‐dichlorotetrazine in warm acetonitrile. In the crystalline structure, the resulting macrocycles adopt highly symmetric structures of a regular hexagonal cavity with all bridging oxygen atoms and tetrazine rings located on the same plane with phenylene units orthogonally orientated. The constitutional aromatic rings are able to rotate around the macrocyclic annulus, depending on the steric effect of the substituents and temperature, in solution. The electron‐deficient nature revealed by cyclic voltammetry, differential pulse voltammetry, and characteristic absorbances at a visible region show the O₆‐corona[3]arene[3]tetrazines to be suitable macrocyclic receptors for electron‐rich guests.     

N,N‐Diphenylbenzamide

In the title compound, C₁₉H₁₅NO, the neutral molecules are held together in the crystal structure by very weak C—H...O interactions, giving rise to a linear chain‐like structure. The structure of the molecule has been optimized using density functional theory at the B3LYP/6‐31G(d) level and this is compared with the molecular structure in the solid state. The two structures show significant differences in the relative orientations of the aromatic rings, which is interesting for further supramolecular study. Apart from the crystal structure analysis, powder X‐ray diffraction, UV–visible and thermogravimetric analyses of the compound have been carried out.     

1,2‐Bis(N‐fluoro‐p‐toluene­sulfon­amido)­ethane chloroform solvate

The title compound, N,N′‐difluoro‐N,N′‐ethylenedi‐p‐tolu­enesulfonamide, C₁₆H₁₈F₂N₂O₄S₂·CHCl₃, is a novel stable compound of the N—F class of reagents containing two R₂N—F functionalities. The compound, as the chloro­form solvate, is the first such bis(N—F) compound to be structurally characterized. It adopts a solid‐state structure in which the two aromatic rings are antiperiplanar and a combination of weak C—H?F and C—H?O hydrogen bonds [distances and angles range from 3.265 (4) to 3.439 (4) Å and 150 to 170°, respectively] and π‐stacking between the rings of different mol­ecules (separations of 3.717 and 3.926 Å) results in a solid‐state structure containing well defined channels in which CHCl₃ solvent mol­ecules are located. The N—F distances are 1.428 (3) and 1.433 (3) Å.     

Dianthracenylazatrioxa[8]circulene: Synthesis,Characterization and Application in OLEDs

A soluble, green-blue fluorescent, π-extended azatrioxa[8]circulene was synthesized by oxidative condensation of a 3,6-dihydroxycarbazole and 1,4-anthraquinone by using benzofuran scaffolding. This is the first circulene to incorporate anthracene within its carbon framework. Solvent-dependent fluorescence and bright green electroluminescence accompanied by excimer emission are the key optical properties of this material. The presence of sliding π-stacked columns in the single crystal of dianthracenylazatrioxa[8]circulene is found to cause a very high electron-hopping rate, thus making this material a promising n-type organic semiconductor with an electron mobility predicted to be around 2.26 cm² V⁻¹ s⁻¹. The best organic light-emitting diode (OLED) device based on the dianthracenylazatrioxa[8]circulene fluorescent emitter has a brightness of around 16 000 Cd m⁻² and an external quantum efficiency of 3.3 %. Quantum dot-based OLEDs were fabricated by using dianthracenylazatrioxa[8]circulene as a host matrix material.     

Local aromaticity of [n]acenes, [n]phenacenes, and [n]helicenes (n = 1-9)

The local aromaticity of the six-membered rings in three series of benzenoid compounds, namely, the [n]acenes, [n]phenacenes, and [n]helicenes for n = 1-9, has been assessed by means of three probes of local aromaticity based on structural, magnetic, and electron delocalization properties. For [n]acenes our analysis shows that the more reactive inner rings are more aromatic than the outer rings. For [n]phenacenes, all indicators of aromaticity show that the external rings are the most aromatic. From the external to the central ring, the local aromaticity varies in a damped alternate way. The trends for the [n]helicene series are the same as those found for [n]phenacenes. Despite the departure from planarity in [n]helicenes, only a very slight loss of aromaticity is detected in [n]helicenes as compared to the corresponding [n]phenacenes. Finally, because of magnetic couplings between superimposed six-membered rings in the higher members of the [n]helicenes series, we have demonstrated that the NICS indicator of aromaticity artificially increases the local aromaticity of their most external rings.