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.     

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.     

Zirconacyclopentadiene‐Annulated Polycyclic Aromatic Hydrocarbons

Syntheses of large polycyclic aromatic hydrocarbons (PAHs) and graphene nanostructures demand methods that are capable of selectively and efficiently fusing large numbers of aromatic rings, yet such methods remain scarce. Herein, we report a new approach that is based on the quantitative intramolecular reductive cyclization of an oligo(diyne) with a low‐valent zirconocene reagent, which gives a PAH with one or more annulated zirconacyclopentadienes (ZrPAHs). The efficiency of this process is demonstrated by a high‐yielding fivefold intramolecular coupling to form a helical ZrPAH with 16 fused rings (from a precursor with no fused rings). Several other PAH topologies are also reported. Protodemetalation of the ZrPAHs allowed full characterization (including by X‐ray crystallography) of PAHs containing one or more appended dienes with the ortho‐quinodimethane (o‐QDM) structure, which are usually too reactive for isolation and are potentially valuable for the fusion of additional rings by Diels–Alder reactions.     

One‐Step Borylation of 1,3‐Diaryloxybenzenes Towards Efficient Materials for Organic Light‐Emitting Diodes

The development of a one‐step borylation of 1,3‐diaryloxybenzenes, yielding novel boron‐containing polycyclic aromatic compounds, is reported. The resulting boron‐containing compounds possess high singlet‐triplet excitation energies as a result of localized frontier molecular orbitals induced by boron and oxygen. Using these compounds as a host material, we successfully prepared phosphorescent organic light‐emitting diodes exhibiting high efficiency and adequate lifetimes. Moreover, using the present one‐step borylation, we succeeded in the synthesis of an efficient, thermally activated delayed fluorescence emitter and boron‐fused benzo[6]helicene.     

β‐Iminoenamine‐BF2 Complexes: Aggregation‐Induced Emission and Pronounced Effects of Aliphatic Rings on Radiationless Deactivation

The synthesis, photophysical, and electrochemical attributes of a novel class of boron difluorides containing an aromatic‐fused alicyclic/hetero‐alicyclic ring built on a β‐iminoenamine chromophoric backbone are reported. The compounds displayed large Stokes shifts (86–121 nm), and were emissive in the solid state. The quantum yields obtained in solution at room temperature were unusually lower by an order of magnitude compared to those in the solid state. Some of the tested compounds displayed aggregation‐induced emission (AIE). Single crystal XRD analyses revealed a lack of interplanar π–π interactions, which are presumed to be absent owing to non‐planarity of the alicyclic component in the molecule. For most of the studied compounds, time‐dependent DFT (TD‐DFT) calculations invariably reveal intramolecular charge transfer (π–π*) characteristics with the frontier orbitals concentrated on the boron–nitrogen heterocycle. The participation of boron and fluorine atoms was found to be negligible.     

Recent Progress in Polycyclic Aromatic Hydrocarbon‐Based Organic Co‐Crystals

Recently, the development of polycyclic aromatic hydrocarbon ( PAH )‐based organic co‐crystals has attracted increasing interest due to their unique packing modes, optic‐electronic properties and various potential applications in electronic, optic‐electronic and magnetic devices. In this account, we mainly discuss the definition, classification, packing patterns, preparation methods, and applications of PAH‐based co‐crystals. Specifically, the main categories of PAH‐based organic co‐crystals, the frequent methods to prepare them, three main packing patterns, their optical and electrical properties, and their potential applications will be presented. Finally, an outlook of this field is provided.     

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.     

Benzodipyrrole‐based Donor–Acceptor‐type Boron Complexes as Tunable Near‐infrared‐Absorbing Materials

Benzodipyrrole‐based donor–acceptor boron complexes were designed and synthesized as near‐infrared‐absorbing materials. The electron‐rich organic framework combined with the Lewis acidic boron co‐ordination enabled us to tune the LUMO energy level and the HOMO–LUMO gap (i.e.,the absorption wavelength) by changing the organic acceptor units, the number of boron atoms, and the substituents on the boron atoms.     

Energy Flow in a Purpose‐Built Cascade Molecule Bearing Three Distinct Chromophores Attached to the Terminal Acceptor

A multicomponent cluster has been synthesised in which four disparate chromophores have been covalently linked through a logical arrangement that favours efficient photon collection and migration to a terminal emitter. The primary energy acceptor is a boron dipyrromethene (Bodipy) dye and different polycyclic aryl hydrocarbons have been substituted in place of the regular fluorine atoms attached to the boron centre. The first such unit is perylene, linked to boron through a 1,4‐diethynylphenyl unit, which collects photons in the 320–490 nm region. The other photon collector is pyrene, also connected to the boron centre by a 1,4‐diethynylphenyl spacer and absorbing strongly in the 280–420 nm region, which itself is equipped with an ethynylfluorene residue that absorbs in the UV region. Illumination into any of the polycyclic aryl hydrocarbons results in emission from the Bodipy unit. The rates of intramolecular electronic energy transfer have been determined from time‐correlated, single‐photon counting studies and compared with the rates for Coulombic interactions computed from the Förster expression. It has been necessary to allow for i) a more complex screening potential, ii) multipole–multipole coupling, iii) an extended transition dipole moment vector and iv) bridge‐mediated energy transfer. The bridge‐mediated energy transfer includes both modulation of the donor transition dipole vector by bridge states and Dexter‐type electron exchange. The latter is a consequence of the excellent electronic coupling properties of the 1,4‐diethynylphenyl spacer unit. The net result is a large antenna effect that localises the photon density at the primary acceptor without detracting from its highly favourable photophysical properties.     

Dearomatization Approach Toward a Superbenzoquinone‐Based Diradicaloid,Tetraradicaloid, and Hexaradicaloid

Reported here is the step‐by‐step dearomatization of a highly aromatic polycyclic aromatic hydrocarbon (PAH), the hexa‐peri‐hexabenzocoronene (also called as “superbenzene”), to give a series of superbenzoquinones containing two, four, and six ketone groups. Different from traditional PAH‐based quinones, these superbenzoquinones show open‐shell multiradical character by rearomatization in the open‐shell forms as experimentally validated by X‐ray crystallographic analysis, NMR and ESR spectroscopy, and FT‐IR measurements, as well as theoretically supported by restricted active space spin‐flip calculations. These compounds exhibit structure‐ and molecular‐symmetry‐dependent optical, electrochemical, and magnetic properties.     

Dearomatization Approach Toward a Superbenzoquinone‐Based Diradicaloid,Tetraradicaloid, and Hexaradicaloid

Reported here is the step‐by‐step dearomatization of a highly aromatic polycyclic aromatic hydrocarbon (PAH), the hexa‐peri‐hexabenzocoronene (also called as “superbenzene”), to give a series of superbenzoquinones containing two, four, and six ketone groups. Different from traditional PAH‐based quinones, these superbenzoquinones show open‐shell multiradical character by rearomatization in the open‐shell forms as experimentally validated by X‐ray crystallographic analysis, NMR and ESR spectroscopy, and FT‐IR measurements, as well as theoretically supported by restricted active space spin‐flip calculations. These compounds exhibit structure‐ and molecular‐symmetry‐dependent optical, electrochemical, and magnetic properties.     

BN‐Embedded Polycyclic Aromatic Hydrocarbon Oligomers: Synthesis,Aromaticity, and Reactivity

BN‐embedded oligomers with different pairs of BN units were synthesized by electrophilic borylation. Up to four pairs of BN units were incorporated in the large polycyclic aromatic hydrocarbons (PAHs). Their geometric, photophysical, electrochemical, and Lewis acidic properties were investigated by X‐ray crystallography, optical spectroscopy, and cyclic voltammetry. The B?N bonds show delocalized double‐bond characteristics and the conjugation can be extended through the trans‐orientated aromatic azaborine units. Calculations reveal the relatively lower aromaticity for the inner azaborine rings in the BN‐embedded PAH oligomers. The frontier orbitals of the longer oligomers are delocalized over the inner aromatic rings. Consequently, the inner moieties of the BN‐embedded PAH oligomers are more active than the outer parts. This is confirmed by a simple oxidation reaction, which has significant effects on the aromaticity and the intramolecular charge‐transfer interactions.     

Carbonized silk fibers for in‐tube solid‐phase microextraction to detect polycyclic aromatic hydrocarbons in water samples

Silk fibers were carbonized to develop a biomass carbon material as an adsorbent for solid‐phase microextraction. The surface structure of the carbonized silk fibers was characterized by scanning electron microscopy, and the graphitization degree was determined by Raman spectrometry. After carbonization under high temperature, the orderliness and structural regularity of carbon atoms on silk fibers were promoted. Extraction tube packed with carbonized silk fibers was prepared for in‐tube solid‐phase microextraction. Coupled with high performance liquid chromatography, it exhibited good extraction performance for hydrophobic polycyclic aromatic hydrocarbons. Main parameters including sampling volume, sampling rate, methanol content in sample, and desorption time were systematically investigated. Under the optimum conditions, the analysis method was established and it exhibited wide linear range (0.016–20 μg/L) with good linearity (correlation coefficient ≥ 0.9947), low limits of detection (0.005–0.050 μg/L), and high enrichment factors (1189–2775). Relative standard deviations (n = 3) for intraday (≤3.3%) and interday (≤9.6%) tests indicated that the extraction material had satisfactory repeatability. Finally, the analytical method was successfully applied to detect trace polycyclic aromatic hydrocarbons in real water samples, demonstrating its satisfactory practicability.     

Boron‐Cluster‐Enhanced Ultralong Organic Phosphorescence

Although carborane‐based luminescent materials have been studied for years, no persistent phosphor has been reported so far. Herein, we describe boron‐cluster‐based persistent phosphors obtained by linking a σ‐aromatic carboranyl cage to the π system of a carbazolyl group. The carboranes were found to promote intersystem crossing from a singlet to a triplet state. The rigid boron cluster was able to stabilize the ultralong triplet excitons through multiple nonclassical hydrogen bonds, such as B?H???π interactions, thus leading to a long lifetime of up to 0.666 s and an absolute phosphorescence quantum yield of 7.1 %, which is outstanding for an organic phosphor without heavy atoms. These phosphors can be excited by visible light and show dynamic emission behavior, including thermochromism and mechanochromism. This study demonstrates that non‐metal/heavy‐atom boron clusters can be used to develop multifunctional high‐performance phosphors for potential applications.     

Nanostructured‐silver‐coated polyetheretherketone tube for online in‐tube solid‐phase microextraction coupled with high‐performance liquid chromatography

Polyetheretherketone tube is a better substrate for in‐tube solid‐phase microextraction than fused‐silica capillary and metal tube because of its resistance to high pressure and good flexibility. It was modified with a nanostructured silver coating, and characterized by scanning electron microscopy and energy dispersive X‐ray spectroscopy. It was connected into high‐performance liquid chromatography equipment to build the online analysis system by replacing the sample loop of a six‐port injection valve. To get the highest extraction capacity, the preparation conditions of the coating was investigated. Important extraction conditions including length of tube, sample volume, and desorption time were optimized using eight polycyclic aromatic hydrocarbons as model analytes. The tube exhibits excellent extraction efficiency toward them, with enrichment factors from 52 to 363. The online analysis method provides good linearity (0.5–100 or 1.0–100 μg/L) and low detection limits (0.15–0.30 μg/L). It has been used to determine polycyclic aromatic hydrocarbons in water samples, with relative recoveries in the range of 92.3–120%. The tube showed highest extraction ability for polycyclic aromatic hydrocarbons, higher extraction ability for hydrophobic phthalates and anilines, and almost no extraction ability for low hydrophobic phenols, due to the possible extraction mechanism including hydrophobic and electron‐rich element‐metal interactions.     

Nano‐MoO3 for highly selective enrichment of polycyclic aromatic hydrocarbons in in‐tube solid‐phase microextraction

Nano‐molybdenum trioxide was prepared from nano‐molybdenum disulfide by simple firing in muffle furnace. Nano‐molybdenum trioxide was used as the extraction coating on the stainless steel wire. Four wires were filled in a polyetheretherketone tube to get an extraction tube. The tube was connected to the six‐port valve of a high performance liquid chromatograph, and the online analysis system was constructed. Extraction selectivity of the tube for different types of compounds, including polycyclic aromatic hydrocarbons, plasticizers, estrogens, anilines and neonicotinoids, was studied. Good enrichment ability for polycyclic aromatic hydrocarbons, but the extraction efficiency of others was not satisfactory. Using eight polycyclic aromatic hydrocarbons as the targets, an analytical method was established after optimizing main factors such as sampling volume, sampling rate, methanol content, and desorption time. The established method exhibited wide linear range to 0.016–20.00 μg/L and low limits of detection to 0.005 μg/L, and the enrichment factors can be up to 2443. The method was applied to the detection of trace polycyclic aromatic hydrocarbons in tap water and river water, and a good recovery was obtained. The tube showed good durability and chemical stability, and it still remained good extraction effect after more than 140 run.     

Simultaneous determination of 16 polycyclic aromatic hydrocarbons in reclaimed water using solid‐phase extraction followed by ultra‐performance convergence chromatography with photodiode array detection

A new fast and effective analysis method has been developed to simultaneously determine 16 polycyclic aromatic hydrocarbons in reclaimed water samples by ultra‐performance convergence chromatography with photodiode array detection and solid‐phase extraction. The parameters of ultra‐performance convergence chromatography on the separation behaviors and the crucial condition of solid‐phase extraction were investigated systematically. Under optimal conditions, the 16 polycyclic aromatic hydrocarbons could be separated within 4 min. The limits of detection and quantification were in the range of 0.4–4 and 1–10 μg/L in water, respectively. This approach has been applied to a real industrial wastewater treatment plant successfully. The results showed that polycyclic aromatic hydrocarbons were dramatically decreased after chemical treatment procedure, and the oxidation procedure was effective to remove trace polycyclic aromatic hydrocarbons.     

Evidence of Organic Luminescent Centers in Sol–Gel‐Synthesized Yttrium Aluminum Borate Matrix Leading to Bright Visible Emission

Yttrium aluminum borate (YAB) powders prepared by sol–gel process have been investigated to understand their photoluminescence (PL) mechanism. The amorphous YAB powders exhibit bright visible PL from blue emission for powders calcined at 450 °C to broad white PL for higher calcination temperature. Thanks to ¹³C labelling, NMR and EPR studies show that propionic acid initially used to solubilize the yttrium nitrate is decomposed into aromatic molecules confined within the inorganic matrix. DTA‐TG‐MS analyses show around 2 wt % of carbogenic species. The PL broadening corresponds to the apparition of a new band at 550 nm, associated with the formation of aromatic species. Furthermore, pulsed ENDOR spectroscopy combined with DFT calculations enables us to ascribe EPR spectra to free radicals derived from small (2 to 3 rings) polycyclic aromatic hydrocarbons (PAH). PAH molecules are thus at the origin of the PL as corroborated by slow afterglow decay and thermoluminescence experiments.     

A Macrocycle Based on a Heptagon‐Containing Hexa‐peri‐hexabenzocoronene

A cyclophane is reported incorporating two units of a heptagon‐containing extended polycyclic aromatic hydrocarbon (PAH) analogue of the hexa‐peri‐hexabenzocoronene (HBC) moiety (hept‐HBC). This cyclophane represents a new class of macrocyclic structures that incorporate for the first time seven‐membered rings within extended PAH frameworks. The saddle curvature of the hept‐HBC macrocycle units induced by the presence of the nonhexagonal ring along with the flexible alkyl linkers generate a cavity with shape complementarity and appropriate size to enable π interactions with fullerenes. Therefore, the cyclophane forms host–guest complexes with C₆₀ and C₇₀ with estimated binding constants of K_a=420±2 m ^?1 and K_a=(6.49±0.23)×10³ m ^?1, respectively. As a result, the macrocycle can selectively bind C₇₀ in the presence of an excess of a mixture of C₆₀ and C₇₀.     

Synthesis of 3,4‐Dihalogenated Furan‐2‐(5 H)‐ones by Electrophilic Cyclization of 4‐Hydroxy‐2‐alkynoates

Functionalized 3,4‐dihalogenated furan‐2(5 H)‐ones can be readily prepared in moderate to good yields by treating 4‐hydroxy‐4‐arylbut‐2‐ynoate derivatives with ICl, IBr, and I₂. Both halogen atoms of the electrophile are incorporated in the product. The resulting halides can further afford polycyclic aromatic compounds using known palladium‐catalyzed coupling reactions.