A Peri‐tetracene Diradicaloid: Synthesis and Properties

Peri‐acenes are good model compounds for zigzag graphene nanoribbons, but their synthesis is extremely challenging owing to their intrinsic open‐shell diradical character. Now, the successful synthesis and isolation of a stable peri‐tetracene derivative PT‐2ClPh is reported; four 2,6‐dichlorophenyl groups are attached onto the most reactive sites along the zigzag edges. The structure was confirmed by X‐ray crystallographic analysis and its electronic properties were systematically investigated by both experiments and theoretical calculations. It exhibits an open‐shell singlet ground state with a moderate diradical character (y₀=51.5 % by calculation) and a small singlet–triplet gap (ΔE_S‐T=?2.5 kcal mol^?1 by SQUID measurement). It displays global aromatic character, which is different from the smaller‐size bisanthene analogue BA‐CF3 .     

Heptagon‐Embedded Pentacene: Synthesis,Structures, and Thin‐Film Transistors of Dibenzo[d,d′]benzo[1,2‐a:4,5‐a′]dicycloheptenes

This study presents a new class of conjugated polycyclic molecules that contain seven‐membered rings, detailing their synthesis, crystal structures and semiconductor properties. These molecules have a nearly flat C₆‐C₇‐C₆‐C₇‐C₆ polycyclic framework with a p‐quinodimethane core. With field‐effect mobilities of up to 0.76 cm² V^?1 s^?1 as measured from solution‐processed thin‐film transistors, these molecules are alternatives to the well‐studied pentacene analogues for applications in organic electronic devices.     

Layered Electron Acceptors by Dimerization of Acenes End‐ Capped with 1,2,5‐Thiadiazoles

Layered electron acceptors D1 – 4 equipped with terminal 1,2,5‐thiadiazole groups have been constructed using a one‐pot protocol of acene dimerization. Their molecular structures are determined using single‐crystal X‐ray diffraction analysis. Photophysical and electrochemical properties of these molecules present a marked dependence on conjugation length and molecular geometry. An aggregation‐induced emission peak and an intramolecular excimer emission (IEE) band were observed for D2 and D4 , respectively. This work paves the way for the efficient synthesis of layered heteroacenes.     

Stabilizing Pentacene By Cyclopentannulation

A new class of stabilized pentacene derivatives with externally fused five‐membered rings are prepared by means of a key palladium‐catalyzed cyclopentannulation step. The target compounds are synthesized by chemical manipulation of a partially saturated 6,13‐dibromopentacene precursor that can be fully aromatized in a final step through a DDQ‐mediated dehydrogenation reaction (DDQ=2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone). The new 1,2,8,9‐tetraaryldicyclopenta[fg,qr]pentacene derivatives have narrow energy gaps of circa 1.2 eV and behave as strong electron acceptors with lowest unoccupied molecular orbital energies between ?3.81 and ?3.90 eV. Photodegradation studies reveal the new compounds are more photostable than 6,13‐bis(triisopropylsilylethynyl)pentacene (TIPS‐pentacene).     

En Route to Stimuli‐Responsive Boron‐, Nitrogen‐, and Sulfur‐Doped Polycyclic Aromatic Hydrocarbons

Replacing both meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms creates an efficient blue fluorophore with a strong electron‐accepting character. The corresponding meso‐B,S‐doped bisanthene exhibits a solvent‐dependent green‐to‐orange photoluminescence and undergoes a reversible reduction at E =?2.06 V (vs. FcH/FcH⁺). After oxidation of the sulfur atom, the resulting sulfoxide emits in the blue range of the spectrum, shows only negligible solvatochromism, and a reversible redox transition at E =?1.74 V. Several related B, N‐ and B, S‐containing PAHs have been prepared following the same modular synthetic procedure and are also described herein. In order to systematically compare their optoelectronic properties, all products have been investigated by cyclic voltammetry as well as UV/Vis absorption/emission spectroscopy.     

Highly Contorted 1,2,5‐Thiadiazole‐Fused Aromatics for Solution‐Processed Field‐Effect Transistors: Synthesis and Properties

A straightforward strategy has been used to construct 1,2,5‐thiadiazole‐fused 12‐ring π systems through twofold Stille coupling and subsequent cyclodehydrogenation by utilizing the building blocks of naphthodithiophene and 5,6‐substituted benzo[b]‐2,1,3‐thiadidazole. Molecules 1 a and 1 b , which exhibit highly contorted π surfaces, show a butterfly‐shaped conformation according to DFT calculations. Within the molecules, a plane‐to‐plane angle of 44.8° was found. UV/Vis absorption, thermogravimetric analysis, differential scanning calorimetry, and cyclic voltammetry (CV) were used to study their physical properties. Strong intermolecular interactions of the nonplanar molecules were also observed by concentration‐dependent ¹H NMR spectroscopy measurements and thin‐film XRD characterization. The low‐lying LUMO and high‐lying HOMO levels of the molecules are ?3.73 and ?5.48 eV, respectively, as estimated from CV measurements; this indicates their potential as semiconducting materials for solution‐processed organic field‐effect transistors (OFETS). A field‐effect hole mobility of up to 0.035 cm² V^?1 s^?1, a threshold voltage of 6.98 V, and a current on/off ratio of 8.65×10⁵ in air for 1 a have been demonstrated with the top‐contact bottom‐gate field‐effect transistor device structures; this represents an important step toward the solution‐processed OFET application of contorted aromatics.     

A Soluble Dynamic Complex Strategy for the Solution‐Processed Fabrication of Organic Thin‐Film Transistors of a Boron‐Containing Polycyclic Aromatic Hydrocarbon

The solution‐processed fabrication of thin films of organic semiconductors enables the production of cost‐effective, large‐area organic electronic devices under mild conditions. The formation/dissociation of a dynamic B?N coordination bond can be used for the solution‐processed fabrication of semiconducting films of polycyclic aromatic hydrocarbon (PAH) materials. The poor solubility of a boron‐containing PAH in chloroform, toluene, and chlorobenzene was significantly improved by addition of minor amounts (1 wt % of solvent) of pyridine derivatives, as their coordination to the boron atom suppresses the inherent propensity of the PAHs to form π‐stacks. Spin‐coating solutions of the thus formed Lewis acid–base complexes resulted in the formation of amorphous thin films, which could be converted into polycrystalline films of the boron‐containing PAH upon thermal annealing. Organic thin‐film transistors prepared by this solution process displayed typical p‐type characteristics.     

Synthesis,Properties, and Packing Structures of Corannulene‐Based π‐Systems Containing Heptagons

Introduction of heptagons into hexagonal carbon lattices can generate negatively curved polycyclic aromatic hydrocarbons, which are of significant interest in the field of exotic molecular nanocarbons. We have successfully synthesized and characterized corannulene‐based π‐systems containing heptagons ( 4 and 5 ) as new negatively curved polycyclic aromatic hydrocarbons as well as possible intermediates in the synthesis of warped nanographene 1 . The formation of 4 and 5 represents the first example for which a heptagon is formed under Scholl reaction conditions before all hexagons are formed. Even more interestingly, we discovered that the mode and degree of solid‐phase intermolecular π–π interaction can be altered significantly by the degree of ring closure.     

Boron‐Containing Polycyclic Aromatic Hydrocarbons: Facile Synthesis of Stable,Redox‐Active Luminophores

Herein we show that replacing the two meso carbon atoms of the polycyclic aromatic hydrocarbon (PAH) bisanthene by boron atoms transforms a near‐infrared dye into an efficient blue luminophore. This observation impressively illustrates the impact of boron doping on the frontier orbitals of PAHs. To take full advantage of this tool for the targeted design of organic electronic materials, the underlying structure–property relationships need to be further elucidated. We therefore developed a modular synthesis sequence based on a Peterson olefination, a stilbene‐type photocyclization, and an Si–B exchange reaction to substantially broaden the palette of accessible polycyclic aromatic organoboranes and to permit a direct comparison with their PAH congeners.     

Synthesis of Nitrogen‐Doped ZigZag‐Edge Peripheries: Dibenzo‐9a‐azaphenalene as Repeating Unit

A bottom‐up approach toward stable and monodisperse segments of graphenes with a nitrogen‐doped zigzag edge is introduced. Exemplified by the so far unprecedented dibenzo‐9a‐azaphenalene (DBAPhen) as the core unit, a versatile synthetic concept is introduced that leads to nitrogen‐doped zigzag nanographenes and graphene nanoribbons.     

Kekulé-based Valence Bond Model. II. Diels-Alder Reactivity of Polycyclic Aromatic Hydrocarbons

ＩｎｔｒｏｄｕｃｔｉｏｎＩｔｉｓｗｅｌｌｋｎｏｗｎｔｈａｔｍｏｌｅｃｕｌａｒｏｒｂｉｔａｌ (ＭＯ)ｔｈｅｏｒｙｈａｓｐｌａｙｅｄａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｕｎｄｅｒｓｔａｎｄｉｎｇｖａｒｉｏｕｓｃｈｅｍｉｃａｌｒｅａｃｔｉｏｎｓｏｆｐｏｌｙｃｙｃｌｉｃａｒｏｍａｔｉｃｈｙｄｒｏｃａｒｂｏｎｓ .1Ｅｓｐｅｃｉａｌｌｙ ,ｔｈｅＤｉｅｌｓ Ａｌｄｅｒｒｅａｃｔｉｏｎｓｏｆｍａｎｙｐｏｌｙｃｙｃｌｉｃｂｅｎｚｅｎｏｉｄｈｙｄｒｏｃａｒｂｏｎｓｗｉｔｈｍａｌｅｉｃａｎｈｙｄｒｉｄｅｈａｖｅｂｅｅｎｓ…     

Perylene‐Fused,Aggregation‐Free Polycyclic Aromatic Hydrocarbons for Solution‐Processed Distributed Feedback Lasers

Perylene‐fused, aggregation‐free polycyclic aromatic hydrocarbons with partial zigzag periphery ( ZY‐01 , ZY‐02 , and ZY‐03 ) were synthesized. X‐ray crystallographic analysis reveals that there is no intermolecular π–π stacking in any of the three molecules, and as a result, they show moderate‐to‐high photoluminescence quantum yield in both solution and in the solid state. They also display the characteristic absorption and emission spectra of perylene dyes. ZY‐01 and ZY‐02 with a nearly planar π‐conjugated skeleton exhibit amplified spontaneous emission (ASE) when dispersed in polystyrene thin films. Solution‐processed distributed feedback lasers have been fabricated using ZY‐01 and ZY‐02 as active gain materials, both showing narrow emission linewidth (<0.4 nm) at wavelengths around 515 and 570 nm, respectively. In contrast, ZY‐03 did not show ASE and lasing, presumably due to its highly twisted backbone, which facilitates nonradiative internal conversion and intersystem crossing.     

Unexpected Chemistry from the Reaction of Naphthyl and Acetylene at Combustion‐Like Temperatures

The hydrogen abstraction/acetylene addition (HACA) mechanism has long been viewed as a key route to aromatic ring growth of polycyclic aromatic hydrocarbons (PAHs) in combustion systems. However, doubt has been drawn on the ubiquity of the mechanism by recent electronic structure calculations which predict that the HACA mechanism starting from the naphthyl radical preferentially forms acenaphthylene, thereby blocking cyclization to a third six‐membered ring. Here, by probing the products formed in the reaction of 1‐ and 2‐naphthyl radicals in excess acetylene under combustion‐like conditions with the help of photoionization mass spectrometry, we provide experimental evidence that this reaction produces 1‐ and 2‐ethynylnaphthalenes (C₁₂H₈), acenaphthylene (C₁₂H₈) and diethynylnaphthalenes (C₁₄H₈). Importantly, neither phenanthrene nor anthracene (C₁₄H₁₀) was found, which indicates that the HACA mechanism does not lead to cyclization of the third aromatic ring as expected but rather undergoes ethynyl substitution reactions instead.     

Exploration of the Photodegradation of Naphtho[2,3‐g] quinoxalines and Pyrazino[2,3‐b]phenazines

Nitrogen‐containing polycyclic aromatic hydrocarbons are very attractive compounds for organic electronics applications. Their low‐lying LUMO energies points towards a potential use as n‐type semiconductors. Furthermore, they are expected to be more stable under ambient conditions, which is very important for the formation of semiconducting films, where materials with high purity are needed. In this study, the syntheses of naphtho[2,3‐g]quinoxalines and pyrazino[2,3‐b]phenazines is presented by using reaction conditions, that provide the desired products in high yields, high purity and without time‐consuming purification steps. The HOMO and LUMO energies of the compounds are investigated by cyclic voltammetry and UV/Vis spectroscopy and their dependency on the nitrogen content and the terminal substituents are examined. The photostability and the degradation pathways of the naphtho[2,3‐g]quinoxalines and pyrazino[2,3‐b]phenazines are explored by NMR spectroscopy of irradiated samples affirming the large influence of the nitrogen atoms in the acene core on the degradation process during the irradiation. Finally, by identifying the degradations products of 2,3‐dimethylnaphtho[2,3‐g]quinoxaline it is possible to track down the most reactive position in the compound and, by blocking this position with nitrogen, to strongly increase the photostability.     

X‐Shaped Polycyclic Aromatic Hydrocarbons: Optical Properties and Tunable Assembly Ability

Although a number of synthetic methodologies have been developed to prepare stable polycyclic aromatic hydrocarbons (PAHs), much less research has been devoted to functionalizing the peripheries of molecules to tune the self‐assembly ability or introduce functional groups without altering their photophysical properties. Herein, we report twisted “X”‐shaped molecules prepared through annulation of hexacene with benzoanthracene on the zigzag edge, and an investigation of their photophysical properties and self‐assembly properties. The shape‐complementary “X”‐shaped molecules prefer to dimerize, while the π‐extension would lead to one‐dimensional π‐stacking. Our findings give some insights into the design of stable PAHs without disturbing the electronic structures.     

Synthesis,Characterization, and Functionalization of 1‐Boraphenalenes

1‐Boraphenalenes have been synthesized by reaction of BBr₃ with 1‐(aryl‐ethynyl)naphthalenes, 1‐ethynylnaphthalene, and 1‐(pent‐1‐yn‐1‐yl)naphthalene and they can be selectively functionalized at boron or carbon to form bench‐stable products. All of these 1‐boraphenalenes have LUMOs localized on the planar C₁₂B core that are closely comparable in character to isoelectronic phenalenyl cations. In contrast to the comparable LUMOs, the aromatic stabilization of the C₅B ring in 1‐boraphenalenes is dramatically lower than the C₆ rings in phenalenyl cations. This is due to the occupied orbitals of π symmetry being less delocalised in the 1‐boraphenalenes.     

Non‐linear,cata‐Condensed,Polycyclic Aromatic Hydrocarbon Materials: A Generic Approach and Physical Properties

A generic approach to the regiospecific synthesis of halogenated polycyclic aromatics is made possible by the one‐ or two‐directional benzannulation reactions of readily available (ortho‐allylaryl)trichloroacetates (the “BHQ” reaction). Palladium‐catalysed cross‐coupling reactions of the so‐formed haloaromatics enable the synthesis of functionalised polycyclic aromatic hydrocarbons (PAHs) with surgical precision. Overall, this new methodology enables the facile mining of chemical space in search of new electronic functional materials.     

A Highly Sensitive Electrochemical Impedance Spectroscopy Immunosensor for Determination of 1‐Pyrenebutyric Acid Based on the Bifunctionality of Nafion/Gold Nanoparticles Composite Electrode

A simple, highly sensitive and label‐free electrochemical impedance spectroscopy (EIS) immunosensor was developed using Nafion and gold nanoparticles (nano‐Au/Nafion) composites for the determination of 1‐pyrenebutyric acid (PBA). Under the optimal conditions, the amount of immobilized antibody was significantly improved on the nano‐Au/Nafion electrode due to the synergistic effect and biocompatibility of Nafion film and gold nanoparticles composites. The results showed that the sensitivity and stability of nano‐Au/Nafion composite electrode for PBA detection were much better than those of nano‐Au modified glassy carbon electrode (nano‐Au/GCE). The plot of increased electron transfer resistances (R_ets) against the logarithm of PBA concentration is linear over the range from 0.1 to 150 ng·mL^?1 with the detection limit of 0.03 ng·mL^?1. The selectivity and accuracy of the proposed EIS immunosensor were evaluated with satisfactory results.