Modular Synthesis of Structurally Diverse Azulene-Embedded Polycyclic Aromatic Hydrocarbons by Knoevenagel-Type Condensation

The research interest in azulene-embedded polycyclic aromatic hydrocarbons (PAHs) has significantly increased recently, but the lack of efficient synthetic strategies impedes the investigation of their structure-property relationships and further opto-electronic applications. Here we report a modular synthetic strategy towards diverse azulene-embedded PAHs by a tandem Suzuki coupling and base-promoted Knoevenagel-type condensation with good yields and great structural versatility, including non-alternant thiophene-rich PAHs, butterfly- or Z-shaped PAHs bearing two azulene units, and the first example of a two-azulene-embedded double [5]helicene. The structural topology, aromaticity and photophysical properties were investigated by NMR, X-ray crystallography analysis and UV/Vis absorption spectroscopy assisted by DFT calculations. This strategy provides a new platform for rapidly synthesizing unexplored non-alternant PAHs or even graphene nanoribbons with multiple azulene units.     

Laser Desorption and Ionization of Solid Polycyclic Aromatic Hydrocarbons in Air With Analysis by Ion Mobility Spectrometry

Abstract

Solid polycyclic aromatic hydrocarbons with 4–7 rings on metal, glass, ceramic, and plastic substrates were desorbed and ionized in air with a quadrupled Nd-YAG laser. Gaseous product ions were analyzed at ambient conditions in air directly using ion mobility spectrometry. Ablation rates for perylene on borosilicate glass were estimated as 0.01 ng/mm2 per pulse and standard deviation for peak heights with roughly 1 ug/mm² was 34 %. Substrate interference was avoided by using an unfocused laser beam at 0.5–1 mJ/pulse although gaseous ions also could be generated from substrates with a focused beam at 1 mJ/pulse.     

Cascade Synthesis of Benzotriazulene with Three Embedded Azulene Units and Large Stokes Shifts

We report here the one-pot synthesis of benzo[1,2-a : 3,4-a′ : 5,6-a′′]triazulene ( BTA ), wherein three azulene units are embedded through a tandem reaction comprising two steps, Suzuki coupling and Knoevenagel condensation, between a readily available triborylated truxene precursor and 8-bromo-1-naphthaldehyde. Its nitration leads to a regioselective trinitrated product, namely, BTA - NO₂ . Single-crystal X-ray crystallography revealed that the superstructure of BTA consists of a dimer stacked by two enantiomeric helicene conformers, while that of BTA - NO₂ consists of an unprecedented π-tetramer stacked from two enantiomeric dimers, that is, four distinct helicene conformers. Both compounds show excellent stability and fluorescence with large Stokes shifts of up to 5100 cm⁻¹. In addition, BTA - NO₂ exhibits a unique solvatochromic effect in different solvents and hydrogen-bonding-induced emission transfer in different ratios of THF/H₂O solutions.     

Synthesis of triphenylene derivatives by Pd-catalyzed Suzuki coupling/intramolecular CH activation between arylboronic acids and dibromobiphenyls

An efficient and regioselective synthesis of functionalized triphenylenes via palladium-catalyzed Suzuki-Miyaura coupling and subsequent intramolecular CH activation between arylboronic acids and dibromobiphenyls was developed. This methodology showed excellent atomic economy and regiospecificity as well as synthetic feasibility of unsymmetrical triphenylenes.     

Synthesis of 5-heteroarylazulenes: first selective electrophilic substitution at the 5-position of azulene

1,3-Di-tert-butylazulene reacted with highly electrophilic trifluoromethanesulfonate of N-containing heterocycles to give 5-(dihydroheteroaryl)azulene derivatives in good yield and treatment of the 5-(dihydroheteroaryl)azulene derivatives with KOH afforded 5-(heteroaryl)azulenes in excellent yield.     

Palladium-catalyzed double cross-coupling reaction of 1,2-bis(pinacolatoboryl)alkenes and -arenes with 2,2′-dibromobiaryls: annulative approach to functionalized polycyclic aromatic hydrocarbons

This study demonstrates that the double cross-coupling reaction of 1,2-bis(pinacolatoboryl)alkenes and -arenes with 2,2′-dibromobiaryls proceeds smoothly with the aid of a catalytic amount of Pd(PPh₃)₄ in the presence of excess base to give a variety of polycyclic aromatic hydrocarbons, such as phenanthrenes, [5]helicene, dithienobenzenes, triphenylenes, dibenzo[g,p]chrysenes, and triphenyleno[1,2-b:4,3-b′]dithiophenes in good to high yields. It is noteworthy that the annulations using 2,2′-dibromooctafluorobiphenyl as an electrophile furnish the otherwise difficult to synthesize octafluorophenanthrenes and semi-fluorinated dibenzo[g,p]chrysenes in high yields.     

1,3-Imidazole-Based Mesoionic Carbenes and Anionic Dicarbenes: Pushing the Limit of Classical N-Heterocyclic Carbenes

Classical N-heterocyclic carbenes (NHCs) featuring the carbene center at the C2-position of 1,3-imidazole framework (i.e. C2-carbenes) are well acknowledged as very versatile neutral ligands in molecular as well as in materials sciences. The efficiency and success of NHCs in diverse areas is essentially attributed to their persuasive stereoelectronics, in particular the potent σ-donor property. The NHCs with the carbene center at the unusual C4 (or C5) position, the so-called abnormal NHCs (aNHCs) or mesoionic carbenes (iMICs), are however superior σ-donors than C2-carbenes. Hence, iMICs have substantial potential in sustainable synthesis and catalysis. The main obstacle in this direction is rather demanding synthetic accessibility of iMICs. The aim of this review article is to highlight recent advances, particularly by the author's research group, in accessing stable iMICs, quantifying their properties, and exploring their applications in synthesis and catalysis. In addition, the synthetic viability and use of vicinal C4,C5-anionic dicarbenes (ADCs), also based on an 1,3-imidazole framework, are presented. As will be apparent on following pages, iMICs and ADCs hold potentials in pushing the limit of classical NHCs by enabling access to conceptually new main-group heterocycles, radicals, molecular catalysts, ligands sets, and more.     

Ordering the relative power of electrophilic fluorinating,trifluoromethylating, and trifluoromethylthiolating reagents: A summary of recent efforts

Electrophilic fluorination and fluoroalkylation are one of the most promising and efficient strategies in the synthesis of organofluorine compounds. The rapid progress of this field has been made possible by the emergence of a wide variety of power-variable, readily prepared, and easy-to-handle electrophilic fluorinating and fluoroalkylating reagents. Understanding the relative power of these reagents is thus vital for their use in synthetic transformations. This digest will outline some recent efforts to quantitatively ordering the relative power of electrophilic fluorinating, trifluoromethylating, and trifluoromethylthiolating reagents.     

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.     

Uncertainty evaluation for the quantification of low masses of benzo[a]pyrene: Comparison between the Law of Propagation of Uncertainty and the Monte Carlo method

A proper evaluation of the uncertainty associated to the quantification of micropollutants in the environment, like Polycyclic Aromatic Hydrocarbons (PAHs), is crucial for the reliability of the measurement results. The present work describes a comparison between the uncertainty evaluation carried out according to the GUM uncertainty framework and the Monte Carlo (MC) method. This comparison was carried out starting from real data sets obtained from the quantification of benzo[a]pyrene (BaP), spiked on filters commonly used for airborne particulate matter sampling. BaP was chosen as target analyte as it is listed in the current European legislation as marker of the carcinogenic risk for the whole class of PAHs.     

芳醚砜二胺、芳醚砜双马来酰亚胺的合成及共聚树脂的性能研究

通过在三种不同的溶剂一碱体系中合成芳醚砜二胺的研究，确定了最佳的合成路线。用酸碱法对产物进行了纯化，进而合成了芳醚砜双马来酰亚胺。热重分析表明，芳醚砜双马来酰亚胺／芳醚砜二胺共聚树脂具有较高的热和热氧稳定性。     

Synthesis,characterization and catalytic evaluation of ZrCl4:Mg(ClO4)2 for the synthesis of 1,3-diaryl-3-(phenylthio)propan-1-one

Herein we demonstrate a novel tandem aldol condensation-thia-Michael addition process using a bimetallic catalyst (ZrCl₄:Mg(ClO₄)₂). The novel bimetallic catalyst performs under very mild conditions. The catalyst helps in the efficient synthesis of β-mercapto carbonyl derivatives from chalcones and thiols in one-pot method. We successfully used the zirconium tetrachloride in combination with magnesium perchlorate in a specific ratio which is considered as green catalyst and efficiently worked for the synthesis of β-mercapto carbonyl derivatives at room temperature. This is the first report which presents the use of ZrCl₄:Mg(ClO₄)₂ without calcination. Significant advantages of this method are that the reaction is performed under mild conditions, shows good selectivity and high yield, within short reaction times and easy workup. This method minimizes waste disposal problems as well, which makes present method highly efficient and convenient. The synthesized bimetallic catalyst was characterized by different analytical techniques such as XRD and SEM. Subsequently, the synthesized β-mercapto carbonyl products were identified by using FTIR, NMR, GC–MS and CHN elemental analyzer.     

Catechol reactivity: Synthesis of dopamine derivatives substituted at the 6-position

Dopamine is a ubiquitous neurotransmitter essential in the proper functioning of the human body. In addition to this critical role, the catecholamine core has shown utility as a scaffold for numerous drugs and in other applications, like metal detection and adhesive materials. Substituents at the 6-position of dopamine’s catechol core can modulate its stereoelectronic properties, the acidity of its phenolic hydroxyl groups, and the overall hydrophobicity of the molecule. Herein, we report the synthesis of a series of four novel dopamine analogues substituted at the 6-position of catechol core. The ¹H NMR chemical shift of the aromatic proton meta to the substituent correlated strongly with the Hammett σ_m constant, confirming the electronic properties of substituents.     

Synthesis of diarylmethanes via a Friedel-Crafts benzylation using arenes and benzyl alcohols in the presence of triphenylphosphine ditriflate

Triphenylphosphine ditriflate (TPPD) was found to be an efficient promoter for the Friedel-Crafts benzylation of arenes with benzyl alcohols in CH₂Cl₂ at room temperature. The good yields, the 1:1 molar ratio of arene and benzyl alcohol, the benzylation of chlorobenzene as a nonactivated aromatic compound at room temperature, and no by-product formation are the main advantages of this procedure.     

Synthesis and duplex formation of the reverse amidohelicene tetramer

The reverse amidohelicene (P)-tetramer containing (P)-helicenediamine and m-phenylenedicarboxylate was synthesized. The circular dichroism (CD) and vapor pressure osmometry (VPO) analysis revealed the dimeric aggregate formation in THF. It is notable that the reverse amide tetramer formed a duplex, as well as the original amidohelicene oligomers. In various solutions, mixtures of the reverse (P)-tetramer and amidohelicene (P)/(M)-tetramer formed homoaggregates instead of heteroaggregates.     

Oxidation of Electrodeposited Copper on Boron Doped Diamond in Acidic Solution: Manipulating the Size of Copper Nanoparticles Using Voltammetry

The in situ deposition of copper, in acidic solution onto a Boron Doped Diamond electrode, using cyclic voltammetry is explored and produced surfaces are imaged using Atomic Force Microscopy. A uniformly dense covering of copper nanoparticles is produced when the potential of a freshly polished BDD electrode is swept from 0 V in a negative direction. For example, in 1 M H₂SO₄ with a Cu(II) concentration of 1 mM, nanoparticles of height 10.1 nm, diameter 74.6 nm and a density of 16.1 particles per μm² are created when the potential is swept to ?0.35 V. The higher the concentration of Cu(II) in solution or the larger the magnitude of the end potential the larger the nanoparticles are and the more densely they are spread. When the direction of the scan is reversed and a positive potential sweep carried out evidence from the observed cyclic voltammograms and AFM images shows that copper is being incompletely stripped from the electrode surface. If the potential is then cycled continuously ten times, as would happen when the process is used for electroanalytical purposes, then an irregular and irreproducible deposit is observed. One can infer from this evidence that the incompletely stripped copper is electrochemically active and therefore adversely affecting subsequent deposition processes. Comparison to existing literature shows that the discrete application of particular deposition and stripping potentials is a much better way to produce a deposit of copper nanoparticles than application of potential through cyclic voltammetry.     

Synthesis and properties of 1-bromo-2,3,5,6-tetrakis(3-pentyl)benzene: a highly sterically hindered aryl bromide

The preparation of 1-bromo-2,3,5,6-tetrakis(3-pentyl)benzene is reported. The ¹H and ¹³C NMR spectra indicate the presence of rotational isomers at room temperature which interconvert on heating. Coalescence of the NMR peaks for the methine and methylene aliphatic protons is observed at 100–120 °C. The conversion of this aryl bromide to the corresponding aryllithium is reported. Similar but less bulky aryl bromides have also been synthesised.     

Rational Design and Facile Synthesis of Dual-State Emission Fluorophores: Expanding Functionality for the Sensitive Detection of Nitroaromatic Compounds

Six novel benzimidazole-based D-π-A compounds 4 a – 4 f were concisely synthesized by attaching different donor/acceptor units to the skeleton of 1,3-bis(1H-benzimidazol-2-yl)benzene on its 5-position through an ethynyl link. Due to the twisted conformation and effective conjugation structure, these dual-state emission (DSE) molecules show intense and multifarious photoluminescence, and their fluorescence quantum yields in solution and solid state can be up to 96.16 and 69.82 %, respectively. Especially, for excellent photostability, obvious solvatofluorochromic and extraordinary wide range of solvent compatibility, DSE molecule 4 a is a multifunctional fluorescent probe for the visual detection of nitroaromatic compounds (NACs) with the limit of detection as low as 10⁻⁷ M. The quenching mechanism has been proved as the results of photoinduced electron transfer and fluorescence resonance energy transfer processes. Importantly, probe 4 a can sensitively detect NACs not only in real water samples, but also on 4 a -coated strips and 4 a @PBAT thin films.     

The First Rare Earth Metal Thioborate: Synthesis and Crystal Structure of EuB2S4

Systematic studies on thio‐ and selenoborates containing heavier metal cations led to the new crystalline phase EuB₂S₄. The crystal structure of the europium metathioborate reveals polymeric [(B₂S₄)^2—]_n anions and divalent Eu‐cations which are connected via ionic interactions. The building blocks of the anions consist of BS₄‐tetrahedra. Condensation of these BS₄‐tetrahedra leads to corner‐ and edge‐sharing 2D‐networks running parallel to (1 0 0). Evacuated carbon coated silica tubes were used as reaction vessels since temperatures up to 990 K were applied. EuB₂S₄ crystallizes in the monoclinic space group P2₁/c (no. 14) with a = 6.4331(6)Å, b = 14.099(1)Å, c = 6.0731(6)Å, β = 110.55(8)° and Z = 4.     

Reactivity of pyrrole pigments,part 15: On the oxidation of bilirubins and biliverdins

Summary Characteristic oxidation reactions of bilin-1,19-diones (biliverdins) and biladien-ac-1,19-diones (bilirubins) were reinvestigated. These include bromine and iodine oxidation of biliverdin IX, bilirubin IX and their Zn(II) complexes, the reaction described by Siedel (1941) of mesobilirubin XIII dimethyl ester with nitric acid (Gmelin reaction) and Smith's oxidation (1977) of etiobiliverdin IV using Tl triacetate and Pb tetra-acetate. For some of these reaction products new structures were assigned on the basis of their spectrometric data. These structures agreed with the expected reactivity pattern of biliverdins and bilirubins.

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Reaktivität von Pyrrolpigmenten, 15 Mitt.: Über die Oxidation von Bilirubinen und Biliverdinen

Zusammenfassung Einige bekannte Oxydationen von Bilin-1,19-dionen (Biliverdinen) und Biladien-ac-dionen (Bilirubinen) wurden neuerlich untersucht, und zwar die Brom- und Jodoxydation von Biliverdin IX und Bilirubin IX sowie der entsprechenden Zn(II)-Komplexe, die Reaktion des Dimethylesters von Mesobilirubin XIII mit HNO₃ (Gmelinreaktion; Siedel 1941) und Smith's Oxydation von Etiobiliverdin IV mit Thaliumtriacetat und Bleitetraacetat. Für einige Reaktionsprodukte wurden aufgrund spektroskopischer Daten neue Strukturen-konsistent mit dem bekannten Reaktionsverhalten von Biliverdinen und Bilirubinen-formuliert.