Fused Benzene Rings Research Articles

Clar's Aromatic π‐Sextet Rule for the Construction of Red Multiple Resonance Emitter

AbstractDespite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π‐sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π‐sextets). Theoretical studies indicate that the quantity of π‐sextets ultimately determines the optical band gap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94 % and horizontal dipole ratio of ~90 %, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light‐emitting diode shows a high external quantum efficiency of 27.3 %, with only a slight decrease of 3.7 % at an elevated luminance level of 100,000 cd/m2.

Investigation of cytotoxic indoleninyl-thiobarbiturate zwitterions as DNA targeting agents

A series of indoleninyl-thiobarbiturate zwitterions were synthesized in up to 83 % yields from the Knoevenagel condensation between N-substituted diformyl indolenine and thiobarbiturate. The structures were characterized by spectroscopic methods such as NMR (1H, 13C), FT-IR, high-resolution mass spectrometry (HR-MS) and elemental analysis. However, their physicochemical properties and biological activities remain elusive. Herein, results from in silico ADMET calculations and cytotoxicity predictions suggest that all zwitterions are likely to exhibit a higher bioavailability and more specific cytotoxicity than doxorubicin. The notably high predicted cytotoxicity of 2d and drug-likeness score of 2f may be linked to the position of the fused benzene ring and methoxy groups, respectively. The initial biological assessment of these compounds began with in vitro DNA-binding studies because the treatment of numerous diseases such as cancer and bacterial infections is linked to DNA interactions. Zwitterion 2f demonstrated the most significant spectral change in DNA binding studies, suggesting a possible role of the methoxy group in inducing DNA binding activity. The hypothesis that 2f interacts with DNA through groove binding was confirmed by observations made during salt-back titration and DNA denaturation experiments. It was anticipated that the non-zwitterionic 2f would interact more stably with DNA (PDB code: 453D) at the minor groove than its zwitterionic form based on molecular docking calculations and molecular dynamic (MD) simulations. Additionally, the MTT assay demonstrates that 2f is moderately cytotoxic to the human breast cancer cell line MDA-MD-231, most probably as a result of the previously stated DNA binding mechanisms. Overall, the computational and in vitro data suggest the potential application of 2f as a cytotoxic DNA-targeting agent.

Synthesis of Carbazole-Thiazole Dyes via One-Pot Tricomponent Reaction: Exploring Photophysical Properties, Tyrosinase Inhibition, and Molecular Docking.

Carbazole is an aromatic heterocyclic organic compound consisting of two fused benzene rings and a pyrrole ring and is a very valuable building structure for the design of many compounds for use in various fields of chemistry and medicine. This study presents three new carbazole-based thiazole derivatives that differ in the presence of a different halogen atom: chlorine, bromine, and fluorine. Experimental studies and quantum-chemical simulations show the effect of changing a halogen atom on the physicochemical, biological, and linear and nonlinear optical properties. We have also found that carbazoles C-Cl, C-Br, and C-F exhibit high tyrosinase inhibitory activity, with IC50 values in the range of 68-105 µM with mixed mechanism of action. Finally, molecular docking to the active site of Concanavalin A (ConA) and bioavailability for all compounds were evaluated.

The Journey for the Synthesis of Large Acenes.

Acenes, the group of polycyclic aromatic hydrocarbons (PAHs) with linearly fused benzene rings, possess distinctive electronic properties with potential applicability in material science. Hexacene was the largest acene obtained and characterized in the last century, followed by heptacene in 2006. Since then, a race for obtaining the largest acene resulted in the development of several members of this family as well as diverse innovative synthetic strategies, from solid-state chemistry to the promising on-surface chemistry. This last technique allows the obtention of large acenes, up to tridecacene, the largest acene so far. This review presents the different methodologies employed for the synthesis of acenes, highlighting the newest studies, to provide a much more thorough understanding of the essence of the electronic structure of this captivating group of organic compounds.

Clar's Aromatic π-Sextet Rule for the Construction of Red Multiple Resonance Emitter.

Despite the proliferation of multiple resonance (MR) materials in the blue to green spectral ranges, red MR emitters remain scarce in the literature, an area that certainly warrants attention for future applications. Here, through a clever application of classic Clar's aromatic π-sextet rule, we triumphantly constructed the first red MR emitter by substituting the conventional benzene ring core with anthracene (fewer π-sextets). Theoretical studies indicate that the quantity of π-sextets ultimately determines the optical bandgap of a molecule, rather than the number of fused benzene rings. Benefiting from the high photoluminescence quantum yield of ~94% and horizontal dipole ratio of ~90%, the corresponding narrowband red (luminescence wavelength: 608 nm) organic light-emitting diode shows a high external quantum efficiency of 27.3%, with only a slight decrease of 3.7% at an elevated luminance level of 100,000 cd/m2.

Effect of Oriented External Electric Fields on the Electronic Properties of Linear Acenes: A Thermally Assisted Occupation DFT Study.

Recently, oriented external electric fields (OEEFs) have earned much attention due to the possibility of tuning the properties of electronic systems. From a theoretical perspective, one can resort to electronic structure calculations to understand how the direction and strength of OEEFs affect the properties of electronic systems. However, for multi-reference (MR) systems, calculations employing the popular Kohn-Sham density functional theory with the traditional semilocal and hybrid exchange-correlation energy functionals can yield erroneous results. Owing to its decent compromise between accuracy and efficiency for MR systems at the nanoscale (i.e., MR nanosystems), in this study, thermally assisted occupation density functional theory (TAO-DFT) is adopted to explore the electronic properties of n-acenes (n = 2-10), containing n linearly fused benzene rings, in OEEFs, where the OEEFs of various electric field strengths are applied along the long axes of n-acenes. According to our TAO-DFT calculations, the ground states of n-acenes in OEEFs are singlets for all the cases examined. The effect of OEEFs is shown to be significant on the vertical ionization potentials and vertical electron affinities of ground-state n-acenes with odd-number fused benzene rings. Moreover, the MR character of ground-state n-acenes in OEEFs increases with the increase in the acene length and/or the electric field strength.

Comparative study of Sombor index and its various versions using regression models for top priority polycyclic aromatic hydrocarbons

The aromatic compounds having structural configurations with two or more fused benzene rings are the polycyclic aromatic hydrocarbons (PAHs). Topological indices are valuable tools for studying the structure property relationships of PAHs and also helps in predicting various properties and activities. They find applications widely in computational chemistry, drug design and QSPR studies. This article focuses on analysing the potential predictive index for Sombor index (SO), elliptic Sombor index (ESO), Euler Sombor index (EU), reverse Sombor index (RSO), reverse elliptic Sombor index (RESO) and reverse Euler Sombor index (REU) using regression models for top priority 38 PAHs. From the study it is evident that, SO and RSO have proved to be potential predictive indices among the considered degree-based and reverse degree-based indices. The variation of best predictive index with minimal RMSE are plotted for linear, quadratic and cubic regression models for better understanding.

Computational Studies of Dimerization of [n]-Cyclacenes.

Cyclacenes, C4nH2n, consist of n linearly fused benzene rings that are arranged to result in a closed nanohoop structure. Cyclacenes are thus the cyclic versions of acenes and have so far escaped synthesis. In order to estimate the tendency of [n]-cyclacenes (6 ≤ n ≤ 20) to undergo dimerization, which is assumed to be a major pathway of degradation under oxygen-free conditions, we here report the energy of dimerization as computed by density functional theory using spin-restricted, spin-unrestricted, and thermally assisted-occupation (TAO) formalisms. It is found that the energy of dimerization increases with increasing size of n but that this increase is not monotonic for the smaller members of the series. This is due to the combination of the cryptoannulenic effect and the inherent strain of the cyclacenes. The energy of dimerization of the largest member inspected, [20]-cyclacene, is -59.3 kcal/mol, while we expect it to converge to -46 kcal/mol for n → ∞ based on comparison with data obtained for acenes.

Bowl-Shaped Kekulene Analogues: Cycloarenes with two Five-Membered Rings.

Kekulene, a cycloarene composed of 12 fused benzene rings in a circular arrangement, exhibits a highly planar and robust structure. Kekulene has been the subject of investigation into its aromaticity and electronic structure, particularly in relation to the cyclic benzenoid. We have successfully synthesized novel bowl-shaped kekulene analogues with five-membered rings incorporated into the kekulene structure. The results of DFT calculations and VT-NMR spectra indicate that inversion of their concave-convex structures occurs at room temperature. The NICS and AICD plots predict that the Clar's type resonance structure is found in a manner analogous to the pristine kekulene, albeit with the interruption of the π-conjugation on the sp3 carbons at the five-membered rings. Despite the presence of the Clar's resonance structure, the Diels-Alder reaction proceeded smoothly with a dienophile, in contrast to the behavior of planar kekulene derivatives. This study will lead to the creation of novel bowl-shaped compounds and development of reactivity in aromatic compounds.

Novel Quinoline‐Based RAF Inhibitors: A Comprehensive Review on Synthesis, SAR and Molecular Docking Studies

AbstractThe RAF (rapidly accelerated fibrosarcoma) kinases play critical roles in a variety of different cellular processes, including the advancement of the cell cycle, the proliferation of cells, the metabolism of cells, cell migration, and the differentiation of cells. RAF kinase was thus established as an important target for the management of cancer disease. RAF inhibitors have elicited remarkable responses and enhanced survival rates in patients with BRAF‐V600E/K melanoma, but their efficacy is restricted by resistance as a result of mutations in RAF, presenting challenges in the identification of novel RAF inhibitors. This has resulted in the development of two generations of RAF inhibitors. In the past years, a variety of heterocyclic scaffolds that are capable of inhibiting RAF activity have been discovered. Quinoline, a molecule with a fused benzene ring and N‐heterocyclic pyridine, is a prime template for designing a variety of new anticancer drugs. In the last few years, quinoline derivative has been studied for their capability to inhibit RAF kinases. In this review, we have summarized synthesis, biological study, and molecular docking studies of substituted quinoline derivatives, which have shown potent anticancer activity by inhibiting the RAF kinases. The present review would help medicinal chemists streamline and guide their efforts toward developing novel quinoline‐based RAF inhibitors, which will be beneficial for drug development.

Skeletal Formation of Carbocycles with CO2: Selective Synthesis of Indolo[3,2-b]carbazoles or Cyclophanes from Indoles, CO2, and Phenylsilane.

The catalytic reactions of indoles with CO2 and phenylsilane afforded indolo[3,2-b]carbazoles, where the fused benzene ring was constructed by forming two C-H bonds and four C-C bonds with two CO2 molecules via deoxygenative conversions. Nine-membered cyclophanes made up of three indoles and three CO2 molecules were also obtained, where the cyclophane framework was constructed by forming six C-H bonds and six C-C bonds. These multicomponent cascade reactions giving completely different carbocycles were switched simply by choosing the solvent, acetonitrile or ethyl acetate.

Computational screening of PCP-type pincer ligands for Mo-catalyzed nitrogen fixation

Abstract Computational screening of N-heterocyclic carbene-based PCP-type pincer ligands (PCP = 1,3-bis(di-tert-buthylphosphinomethyl)benzimidazole-2-ylidene) has been performed for the design of molybdenum-based molecular catalysts for nitrogen fixation. Previously, we theoretically and experimentally demonstrated that the introduction of electron-donating/withdrawing substituents to the original PCP ligand is a promising way to control the catalytic activity. Here, we investigate electronic and energetic properties of nitrogenous Mo intermediates bearing 40 substituted PCP ligands [MoI(NHx)(R-PCP)] (x = 1 to 3) that are involved in the rate-determining step in our proposed catalytic mechanism. Electron-withdrawing substituents enhance the π-accepting ability of R-PCP and effectively stabilize the lowest unoccupied molecular orbital (LUMO) of the corresponding Mo–nitride (Mo≡N) complexes, which is expected to be advantageous for the transformation of the nitride N atom via proton-coupled electron transfer. The introduction of strong electron-withdrawing substituents to the PCP ligand also increases the N–H bond energy of [MoI(NHx)(R-PCP)] evaluated using the bond dissociation free energy and the bond dissociation enthalpy. As a result of the computational screening, we newly propose an alternative strategy for designing PCP ligands with high π-accepting ability: the extension of the π-conjugated system of the PCP ligand by introducing fused benzene rings.

Immunosuppressive steroids quadrilisteroids A−C and derivatives from the terrestrial fungus Aspergillus quadrilineatus

Seven undescribed compounds (1−7) along with six known compounds (8−13) were isolated from Eurotiaceae Aspergillus quadrilineatus. Their structures and absolute configurations were elucidated by NMR, HRESIMS, and ECD calculations. Quadrilisteroids A (1) and B (2) possessed an unprecedented 6/5/6/6/6/5 hexacyclic ring system in conjugation with a highly fused benzene ring, while quadrilisteroid C (3) featured a surprising 6/6/6/5/5-fused carbocyclic skeleton. Quadrilisteroid C (3) exhibited potent inhibitory activity against LPS-induced proliferation of B lymphocyte cells with an IC50 value of 1.03 μM. Compound 4, demonstrated inhibitory activity against Con A-induced proliferation of T lymphocyte cells with IC50 values of 6.42 μM.

Using the Conditional Process Analysis Model to Characterize the Evolution of Carbon Structure in Taxodium ascendens Biochar with Varied Pyrolysis Temperature and Holding Time

Temperature determines biochar structure during pyrolysis. However, differences in holding time and feedstock types may affect this relationship. The conditional process analysis model was used in this paper to investigate the potential to affect this mechanism. The branch and leaf parts of Taxodium ascendens were separately pyrolyzed at 350, 450, 650, and 750 °C, and kept for 0.5, 1, and 2 h at each target temperature. We measured the fixed carbon and ash contents and the elemental composition (C, H, O and N) of the raw materials and their char samples. After plotting a Van Krevelen (VK) diagram to determine the aromatization of chars, the changes in the functional groups were analyzed using Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS). The results revealed that pyrolysis at temperatures between 450 and 750 °C accounted for the aromatization of biochar because the atomic H/C ratio of branch-based chars (BC) decreased from 0.53–0.59 to 0.15–0.18, and the ratio of leaf-based chars (LC) decreased from 0.56–0.68 to 0.20–0.22; the atomic O/C ratio of BC decreased from 0.22–0.27 to 0.08–0.11, while that of LC decreased from 0.26–0.28 to 0.18–0.21. Moreover, the average contents of N (1.89%) and ash (13%) in LC were evidently greater than that in BC (N:0.62%; Ash: 4%). Therefore, BC was superior to LC in terms of the stability of biochar. In addition, the increasing ID/IG and ID/I(DR+GL) ratios in BC and LC indicated an increasing amount of the amorphous aromatic carbon structure with medium-sized (2~6 rings) fused benzene rings. According to the CPA analysis, an extension of the holding time significantly enhanced the increase in aromatic structures of LC with temperature. But this extension slightly reduced the growth in aromatic structures of BC. All indicate that holding time and feedstock types (branch or leaf feedstock) could significantly affect the variation in biochar aromatic structure with respect to temperature.

Infrared Emission of Specific Polycyclic Aromatic Hydrocarbon Molecules: Cyanonaphthalenes

The unidentified infrared emission features at 3.3, 6.2, 7.7, 8.6, 11.3, and 12.7 μm are ubiquitously seen in a wide variety of astrophysical regions and commonly attributed to polycyclic aromatic hydrocarbon (PAH) molecules. However, the unambiguous identification of any individual, specific PAH molecules has proven elusive until very recently, when two isomers of cyanonapthalene, which consists of two fused benzene rings and substitutes a nitrile (–CN) group for a hydrogen atom, were discovered in the Taurus Molecular Cloud, based on their rotational transitions at radio frequencies. To facilitate the James Webb Space Telescope (JWST) to search for cyanonapthalenes in astrophysical regions, we model the vibrational excitation of cyanonapthalenes and calculate their infrared emission spectra in a number of representative astrophysical regions. The model emission spectra and intensities will allow JWST to quantitatively determine or place an upper limit on the abundances of cyanonapthalenes.

Elucidating metal composition–coking relationships and coke formation pathways during gas-phase oxydehydration of glycerol over clay mineral-supported Mo-V-O catalysts

Catalyst deactivation by carbon deposition (coking) remains a major obstacle in many important industrial processes, such as catalytic gas-phase oxydehydration of glycerol. Understanding the chemical nature and development of coke species during the time-on-stream (TOS) of the catalytic solids is therefore crucial for mitigating the extent of coking and in the design of regeneration process of the coked catalysts. In this study, multiple analytical techniques, including SEM, XRD, FTIR, Raman, GC-MS, XPS, and 13C solid-state MAS NMR were employed to gain insights into the coking behavior of acid-activated montmorillonite (HMMT) supported Mo-V-O catalysts with modulated metal ratios, along with soluble and insoluble coke compositions and their evolution over time. Insoluble coke was comprised of polycyclic aromatic compounds with 5 or more fused-benzene rings containing different types of oxygen-bonded groups, such as −OCH3, −COOH, −CHO, and −OH. The major chemical constituents of soluble coke were mononuclear aromatic derivatives (i.e., xylenes, 2,4-di-tert-butylphenol, and 1-hydroxycyclohexyl phenyl ketone) and paraffinic hydrocarbons with 12–18 carbon atoms. The latter coke species is thought to be formed via the deoxygenation of linear oligoglycerols. The insights presented in this study may aid in understanding the carbon deposition process during gas-phase oxydehydration of glycerol for improved design of supported Mo-V-O catalyst materials with high coking resistance.

Biodegradation of pyrene during submerged cultivation of Trametes versicolor

Pyrene is one of the most persistent pollutants belonging to the group of high molecular weight polycyclic aromatic hydrocarbons. Due to the presence of fused benzene rings these compounds are extremely difficult for biodegradation. The white-rot fungi possess remarkably high potential when it comes to the biodegradation of toxic organic substances with aromatic rings due to their unique lignin-degrading enzymatic complex. In the present study, pyrene with concentrations up to 200 ppm was added to the nutrient medium during submerged cultivation of the higher basidiomycete mushroom Trametes versicolor NBIMCC 8939. The experiment continued for 20 days and samples were taken every 5 days. Analysis of the activities of the enzymes laccase and manganese-dependent peroxidase were performed as well as determination of the residual pyrene concertation and identification of the by-products of the degradation process. It was established that the highest pyrene removal was achieved when the lowest initial concentration was introduced to the medium. The strain T. versicolor NBIMCC 8939 was able to biodegrade 12% of the initially introduced 50 ppm pyrene in the medium.

Synthesis of crown-ether-embedded graphene by the solution plasma

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.

Thermal treatment of water-soluble particles formed by compounds composed of carbon nanobelts and C60 molecules

It was previously shown that spherical particles are self-assembled by compounds composed of C60-(6,6)CNB-C60, where CNB stands for “carbon nanobelt”, by mixing two individual solutions of C60 and (6,6)CNB molecules dissolved in 1,2-dichlorobenzene at room temperature. The particles are monodisperse in water thanks to their high absolute value of the zeta potential in water. In this report, we investigate the effect of thermal treatment of the particles on some changes in the physical properties and structures. We find that the particles become electrically conductive after thermal treatment at 600 °C for 1 h. We suppose that the change in the electrical characteristics might have been caused by the structural change of (6,6)CNBs into opened-up ribbons composed of fused benzene rings, which construct networks supported by C60 molecules in the particles, judging by the change in the absorption and mass spectra of the particles after thermal treatment and analysis of a possible change in the structure of C60-(6,6)CNB-C60 based on quantum chemical calculations employing the PM6 method, with which it is known that nanostructures such as carbon nanotubes (CNTs) and (6,6)CNBs can be correctly estimated.

Synthesis and Staphylococcus aureus biofilm inhibitory activity of indolenine-substituted pyrazole and pyrimido[1,2-b]indazole derivatives

Staphylococcus aureus is a highly adaptable opportunistic pathogen that can form biofilms and generate persister cells, leading to life-threatening infections that are difficult to treat with antibiotics alone. Therefore, there is a need for an effective S. aureus biofilm inhibitor to combat this public health threat. In this study, a small library of indolenine-substituted pyrazoles and pyrimido[1,2-b]indazole derivatives were synthesised, of which the hit compound exhibited promising antibiofilm activities against methicillin-susceptible S. aureus (MSSA ATCC 29213) and methicillin-resistant S. aureus (MRSA ATCC 33591) at concentrations significantly lower than the planktonic growth inhibition. The hit compound could prevent biofilm formation and eradicate mature biofilms of MSSA and MRSA, with a minimum biofilm inhibitory concentration (MBIC50) value as low as 1.56 µg/mL and a minimum biofilm eradication concentration (MBEC50) value as low as 6.25 µg/mL. The minimum inhibitory concentration (MIC) values of the hit compound against MSSA and MRSA were 50 µg/mL and 25 µg/mL, respectively, while the minimum bactericidal concentration (MBC) values against MSSA and MRSA were > 100 µg/mL. Preliminary structure–activity relationship analysis reveals that the fused benzene ring and COOH group of the hit compound are crucial for the antibiofilm activity. Additionally, the compound was not cytotoxic to human alveolar A549 cells, thus highlighting its potential as a suitable candidate for further development as a S. aureus biofilm inhibitor.