Benzene Moiety Research Articles

Room temperature tri-alkynyl benzene based discotic nematic mesophase enabling high-efficiency deep blue OLEDs

In the hunt to develop room-temperature nematic discotic materials, we engineered a molecular structure that employs a tri-alkynyl benzene core incompatible with π-π stacking, providing flexibility to the system. Micro-segregation was prohibited due to the direct attachment of the flexible alkoxy chain to the central benzene ring, leading to a discotic nematic phase. The nematic phase was found stable down to room temperature and, on further cooling, transformed into a glassy state. Detailed analysis of differential scanning calorimetry plots, polarized optical microscopic textures, and temperature-dependent X-ray diffraction patterns confirmed the glassy nematic phase at low temperatures. The tri-alkynyl benzene moiety imparts high solid and solution-state blue emission properties to mesogens 1a and 1b. On stimulating the compounds electrically as a solid-state emitter in organic light-emitting diodes, they showed emission in the deep blue (CIEy < 0.08) region at 100 cd m−2 luminance and pure blue (CIEy < 0.11) region at maximum luminance using CBP host. Amongst all the configurations used, the device based on 0.5 wt% 1a displayed the best performance with a maximum external quantum efficiency of 4.1% with a turn-on voltage of 3.5 V and CIExy coordinates of (0.16,0.07).

Bent and Twisted: Synthesis of an Alkoxy-Substituted (1,5)Naphthalene-paracyclophanediene.

This contribution describes the synthesis of [2.2](1,5)naphthalenoparacyclophane-1,13-diene in four steps from 1,5-bis(bromomethyl)naphthalene and 1,4-benzenedimethanethiol. Consisting of 2,6-dioctyloxynaphthalene and benzene moieties, the effects of differing arene size on the structure, strain energy, and chemical reactivity of the cyclophanediene are examined. Despite a strain energy of 24.3 kcal/mol, the naphthalenoparacyclophanediene was unreactive toward a library of olefin metathesis catalysts. This diminished reactivity can be explained by the steric hindrance of the twisted olefin. Incorporation of an electron donor (naphthalene) into the rigid paracyclophanediene structure can allow for applications in optoelectronics, chiral ligands, and planar chiral materials.

Rational Design of Persistent Phosphorus-Centered Singlet Tetraradicals and Their Use in Small-Molecule Activation.

Biradicals are important intermediates in the process of bond formation and breaking. While main-group-element-centered biradicals have been thoroughly studied, much less is known about tetraradicals, as their very low stability has hampered their isolation and use in small-molecule activation. Herein, we describe the search for persistent phosphorus-centered tetraradicals. Starting from an s-hydrindacenyl skeleton, we investigated the introduction of four phosphorus-based radical sites linked by an N-R unit and bridged by a benzene moiety. By varying the size of the substituent R, we finally succeeded in isolating a persistent P-centered singlet tetraradical, 2,6-diaza-1,3,5,7-tetraphospha-s-hydrindacene-1,3,5,7-tetrayl (1), in good yields. Furthermore, it was demonstrated that tetraradical 1 can be utilized for the activation of small molecules such as molecular hydrogen or alkynes. In addition to the synthesis of P-centered tetraradicals, the comparison with other known tetraradicals as well as biradicals is described on the basis of quantum mechanical calculations with respect to its multireference character, coupling of radical electrons, and aromaticity. The strong coupling of radical electrons enables selective discrimination between the first and the second activations of small molecules, which is shown by the example of H2 addition. The mechanism of hydrogen addition is investigated with parahydrogen-induced hyperpolarization NMR studies and DFT calculations.

Heterophenoquinones: Tuning Optoelectronics and Electrochromicity.

We report the synthesis and optoelectronic properties of 16 thiophene-based heterophenoquinones. These compounds were accessed in a convergent and modular approach, allowing for their efficient synthesis. Tuning of the optical band gap was achieved through π-extension by annulation of a benzene or tropone moiety to the thiophene, oxidation, change of the heteroatom or by attachment of a donor substituent to the thiophene core. The resulting compounds display intense colors covering the entire visible spectrum. We identified structure-property relationships and their impact on the HOMO and LUMO levels. Additionally, these materials change color upon reduction and according to in situ ultraviolet-visible-near infrared (UV-vis-NIR) and electron paramagnetic resonance (EPR) spectro-electrochemistry, they are promising electrochromes with cathodic color changes. Seven different electrochromic devices were constructed which all displayed a change in color upon reduction, demonstrating the potential of these new dyes in for example tintable glass.

Strengthening spillover hydrogenation of quinoline compounds over platinum-encapsulated amorphized HA zeolite catalyst

Hydrogen spillover has been widely used in heterogeneous catalysis, yet how to explore the potential of catalyst support to further promote catalytic function of hydrogen spillover has rarely been investigated. Herein, platinum encapsulated into amorphized HA zeolite (denoted as Pt@HA) with generated hydroxyl groups was used as model catalyst to study the role of HA zeolite support on the promotion of catalytic performance in hydrogenation of quinolines to tetrahydroquinolines. Benefiting from small pore size of amorphized HA zeolite to prevent direct interaction of quinoline with encapsulated platinum, Pt@HA showed good catalytic selectivity in this transformation through hydrogen spillover. This remarkable catalytic selectivity was resulted from the interaction of hydroxyl groups at surface of HA zeolite with pyridine moiety through the formation NH bond to facilitate adsorption to make much lower apparent activation energy of Pt@HA for hydrogenation of pyridine moiety than that of benzene moiety, thus exhibiting enhanced catalytic selectivity.

Bromination of quinolin-2(1H)-ones fluorinated on the benzene moiety

Bromination of ten known fluorinated quinolin-2(1H)-ones by the KBrO3/HBr system is investigated. If there is no F atom in the position 6 of substrate, the Br atom is introduced into position 3 or 6 to form monobromo derivative, the second Br atom is introduced into the same positions leading to 3,6-dibromo product. If a F atom is in position 6, the 3-bromo product is initially obtained, which gives a 3,5-dibromo or 3,8-dibromo derivatives upon further bromination depending on the F atoms positions. In this case, when both positions 5 and 8 of 3-bromoquinolin-2(1H)-one are unsubstituted, the second Br atom is introduced into position 8. If there are more than two F atoms in the benzene moiety, the sole 3-bromo product is obtained. Relative (ΔE) energies of the considered σ−complexes estimated by DFT calculations for the reactions in question are consistent with the experimentally observed regioselectivity.

Growth of single-crystals and microstructures using benzothiadiazole derivatives for efficient optical waveguide and nonlinearity

Organic nanomaterials have been extensively studied for the applications of the electronic and photonic fields. The bottom-up fabrication through self-assembly provides a powerful strategy to construct the nanostructures. In this work, we synthesized a conjugated molecule, namely, 4-(1-phenyl-1H-1,2,3-triazol-4-yl)benzo[c][1,2,5]thiadiazole (BT-SC), based on benzothiadiazole and benzene moieties bridged by a triazole. Then, a simple solvent-vapor annealing technique was presented to drive the self-assembly of BT-SC into highly uniform microrods or microfibers. The morphology of the self-assembly could be controlled by simply changing the solution concentration. The compound also could be assembled into aligned nanowires by wetting into hard templates of anodic aluminum oxide (AAO). The fabricated microrods showed strong emitter and excellent optical waveguide behaviors excited with a UV laser. Moreover, the microrods displayed nonlinear optical responses of two-photon excited fluorescence and could therefore become building blocks for actual photonic devices.

In silico approach to explore anti-chikungunya potential of Schiff’s bases with benzene and pyrimidine moieties

In silico approach to explore anti-chikungunya potential of Schiff’s bases with benzene and pyrimidine moieties

Quinoid-Thiophene-Based Covalent Organic Polymers for High Iodine Uptake: When Rational Chemical Design Counterbalances the Low Surface Area and Pore Volume.

A novel 2D covalent organic polymer (COP), based on conjugated quinoid-oligothiophene (QOT) and tris(aminophenyl) benzene (TAPB) moieties, is designed and synthesized (TAPB-QOT COP). Some DFT calculations are made to clarify the equilibrium between different QOT isomers and how they could affect the COP formation. Once synthetized, the polymer has been thoroughly characterized by spectroscopic (i.e., Raman, UV-vis), SSNMR and surface (e.g., SEM, BET) techniques, showing a modest surface area (113 m2 g-1) and micropore volume (0.014 cm3 g-1 with an averaged pore size of 5.6-8 Å). Notwithstanding this, TAPB-QOT COP shows a remarkably high iodine (I2) uptake capacity (464 %wt) comparable to or even higher than state-of-the-art porous organic polymers (POPs). These auspicious values are due to the thoughtful design of the polymer with embedded sulfur sites and a conjugated scaffold with the ability to counterbalance the relatively low pore volumes. Indeed, both morphological and Raman data, supported by computational analyses, prove the very high affinity between the S atom in our COP and the I2. As a result, TAPB-QOT COP shows the highest volumetric I2 uptake (i.e., the amount of I2 uptaken per volume unit) up to 331 g cm-3 coupled with a remarkably high reversibility (>80% after five cycles).

Antioxidative Indenone and Benzophenone Derivatives from the Mangrove-Derived Fungus Cytospora heveae NSHSJ-2.

Seven new polyketides, including four indenone derivatives, cytoindenones A-C (1, 3-4), 3'-methoxycytoindenone A (2), a benzophenone derivative, cytorhizophin J (6), and a pair of tetralone enantiomers, (±)-4,6-dihydroxy-5-methoxy-α-tetralone (7), together with a known compound (5) were obtained from the endophytic fungus Cytospora heveae NSHSJ-2 isolated from the fresh stem of the mangrove plant Sonneratia caseolaris. Compound 3 represented the first natural indenone monomer substituted by two benzene moieties at C-2 and C-3. Their structures were determined by the analysis of 1D and 2D NMR, as well as mass spectroscopic data, and the absolute configurations of (±)-7 were determined on the basis of the observed specific rotation value compared with those of the tetralone derivatives previously reported. In bioactivity assays, compounds 1, 4-6 showed potent DPPH· scavenging activities, with EC50 values ranging from 9.5 to 16.6 µM, better than the positive control ascorbic acid (21.9 µM); compounds 2-3 also exhibited DPPH· scavenging activities comparable to ascorbic acid.

Amino-Terephthalonitrile-Based Single Benzene Fluorophores with Large Stokes Shifts and Solvatochromic Behavior.

We have synthesized a small library of blue-to-green emissive single benzene-based fluorophores (SBFs) in a short synthetic sequence. The molecules exhibit good Stokes shift in the range of 60-110 nm and select examples also possess very high fluorescence quantum yields of up to 87%. Theoretical investigations into the ground state and excited state geometries of many of these compounds reveal that good degree of planarization between the electron donor secondary amines and electron accepting benzodinitrile units can be achieved under certain solvatochromic conditions, giving rise to the strongly fluorescent behavior. On the other hand, the excited state geometry which lacks co-planarity of the donor amine and the single benzene moiety can open up a non-fluorescent channel. Additionally, in molecules with a dinitrobenzene acceptor, the perpendicular nitro moieties render the molecules completely non-emissive.

Synthesis of Highly Thermostable and Transparent Colorless Polyimides Based on a Semi‐aromatic Tetracarboxylic Anhydride

AbstractA semi‐aromatic tetracarboxylic dianhydide, 1,2,3,4,5,6,7,8‐octahydroanthracene‐2,3,6,7‐tetracarboxylic dianhydride (OHADA), was successfully synthesized via a Diels Alder reaction. Two polyimides (OHADA‐TFDB and OHADA‐BAFL) were obtained via one‐step polycondensation of OHADA with 2,2′‐Bis(trifluoromethyl)benzidine (TFDB) and 9,9‐bis(4‐aminophenyl)fluorene (BAFL) in m‐cresol, respectively. OHADA‐TFDB has better solubility and processibilty than OHADA‐BAFL, but colorless OHADA‐BAFL exhibits higher thermal stability and lighter color. OHADA‐TFDB and OHADA‐BAFL display high glass transition temperatures (Tgs) of 339 °C/385 °C from DSC curves and 335 °C/395 °C from TMA trances, respectively. Their decomposition temperatures at 5 % weight loss (Td5) are above 537 °C/546 °C under nitrogen. These results are much better than those from wholly alicyclic tetracarboxylic dianhydride‐based polyimides (PIs), which can be attributed to the benzene moiety in OHADA. Furthermore, OHADA‐TFDB and OHADA‐BAFL exhibit good optical transparency with the cutoff wavelength of 315 nm/305 nm, light transmittance over 74 %/72 % at 400 nm and 84 %/80 % at 500 nm, which indicates it is an effectively way to suppress the formation of charge transfer complex (CTC) by introducing alicyclic moieties in OHADA. Their mechanical properties are also characterized in this study.

Tailoring the Interfacial Termination via Dipole Interlayer for High‐Efficiency Perovskite Solar Cells

AbstractThe ionic nature of the organic‐inorganic hybrid perovskite material is prone to react with different functional groups. Here, a series of polar molecules with permanent dipole moments are designed to modify the perovskite surface termination. It is observed that proper interfacial design can significantly reduce trap state density for effective charge transfer. The energy level of the substrate can be adjusted by the magnitude and direction of the dipole moment. As a result, a high 24.54% photo‐electric conversion efficiency is reached by introducing pentafluoride benzene moieties with carboxylic functional groups. In addition, the humidity and heat stability of the perovskite device is obviously improved. This work demonstrates the importance of chemical interactions at perovskite termination and paves the way for further enhancing the performance of perovskite solar cells.

Linear, Electron-Rich, Homoleptic Rare Earth Metallocene and Its Redox Activity

The first homoleptic sandwich complex of dibenzocyclooctatetraene (dbCOT), representing a large cyclooctatetraene (COT) ligand with two fused benzene moieties, for any metal was accessed through salt metathesis of YCl3 with K2dbCOT in the presence of 2.2.2-cryptand. Single-crystal X-ray diffraction analysis on red-brown [K(crypt-222)][Y(dbCOT)2], 1, revealed a remarkably linear anionic yttrocene complex featuring a centroid-yttrium-centroid angle of 180.0°. The anionic moiety adopts a pseudo D2d geometry, where the carbon atoms of the central COT ring exhibit a staggered geometry. In total, 36 π-electrons are stored on both dbCOT anions, rendering it the largest isolated sandwich complex containing only fused aromatic rings. The solution-state structure of 1 was probed through a series of techniques involving cyclic voltammetry, UV-vis, and 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, including 89Y NMR. The density functional theory (DFT) and natural bond orbital (NBO) analysis uncovered an ionic bonding interaction between the (dbCOT)2- ligands and YIII ion. NICS calculations support the experimentally observed aromatic character of 1, despite the deviation from planarity found in the dbCOT moieties. The cyclic voltammograms allude to the accessibility of a radical oxidation state, dbCOT3-•, based on a quasi-reversible feature. Excitingly, the chemical one-electron reduction of 1 through exposure to potassium graphite yielded a paramagnetic molecule, which was detected by electron paramagnetic resonance (EPR) techniques. Notably, this EPR spectrum is the first one for any sandwich complex containing a COT radical. Remarkably, 1 is thermally stable, and its isolation may provide access to mono- and multinuclear complexes comprising heavier metals with applications in small-molecule activation, single-molecule magnetism, and molecular nanowires.

Pressure induced modification of the electronic properties of stilbene by two-photon spectroscopy.

Carbon nanothreads are the most exciting carbon based nanomaterials recently discovered. Obtained by compressing aromatics around 20GPa, they are characterized by potentially exceptional mechanical properties. The reaction mechanisms have been partly elucidated through computational studies and x-ray diffraction experiments. However, in all these studies, the electronic modifications to which the molecule is subjected with increasing pressure are neglected as also if, and to which extent, the electronic excited states are involved in the high-pressure reactivity. In fact, the pressure increase induces remarkable changes in the electronic properties of molecular crystals, which are often directly related to the reaction's onset and path. We report the pressure evolution of the two-photon induced emission spectrum of crystalline stilbene, the archetype of a class of molecules from which double-core nanothreads are obtained, with the twofold purpose of gaining insight into the reaction mechanism and monitoring if the structural changes observed in x-ray diffraction studies have a detectable counterpart in the electronic properties of the system. The freezing of the spectral diffusion observed on rising pressure is ascribed to a hampered conformational rearrangement because of the larger stiffness of the local environment. The transition to the high pressure phase where the nanothreads form is revealed by the slope change of the pressure shift of all spectral components, while the progressive intensification with pressure of the 0-0 transition suggests a strengthening of the ethylenic bond favoring the charge delocalization on the benzene moieties, which is likely the trigger of the chemical instability.

Synthesis of precision poly(1,3‐bicyclo[1.1.1]pentane alkylene)s via acyclic diene metathesis polymerization

Abstract1,3‐Disubstituted bicyclo[1.1.1]pentane (BCP) is a rigid, linear, non‐conjugated hydrocarbon unit that is usually transformed from [1.1.1]propellane. This unit has been introduced into drugs as mimics of 1,4‐disubstituted benzene moieties and used as rigid linkers in small‐molecule materials. However, the influence of this unique structure on the polymer properties has only been scarcely investigated. In this work, three symmetrical α,ω‐diene monomers containing one and two BCP units were synthesized for the first time from [1.1.1]propellane. Three types of precise poly(1,3‐bicyclo[1.1.1]pentane alkylene)s with BCPs located on every 11th and 21st chain carbons were obtained via acyclic diene metathesis (ADMET) polymerization and subsequent hydrogenation. All these polymers show higher thermal stability than linear polyethylene. For polymers containing one BCP moiety in their repeating unit, BCP acts as a defect to distort the PE crystals and decrease the melting temperature of PE. However, the polymer that containing a [2]staffane moiety (two jointed BCP units) in the polymer backbone forms a new crystalline morphology. This work elucidates the impact of BCP units on the thermal and crystallization behavior of PE, providing new insights of utilizing BCP unit to construct new polymer backbone, regulate the packing order of polymers and their properties.

Synthesis, crystal structures and semiconductor properties of 2-(thiopyran-4-ylidene)-1,3-benzodithioles with an aryl substituent

We report the synthesis of aryl-substituted TP-BT derivatives and their OFET properties. 4-Pyridyl substituted TP-BT shows switching characteristics by photo-irradiation.

Selective Low-Level Detection of a Perilous Nitroaromatic Compound Using Tailor-Made Cd(II)-Based Coordination Polymers: Study of Photophysical Properties and Effect of Functional Groups.

Three coordination polymers (CPs 1-3) are prepared based on diverse electron-donating properties and coordination arrangements of conjugated ligands. Interestingly, this is also reflected in their photophysical properties. The distinguishable high emissive nature of the luminescent coordination polymer shows its potentiality toward the detection of the perilous substance 2,4,6-trinitrophenol (TNP) or picric acid (PA). TNP has a higher propensity among explosive nitroaromatic compounds (epNACs) due to its significant π···π interaction with the free benzene moieties present in the CPs. Among CPs 1-3, 2 exhibits the highest sensitivity and selectivity toward TNP because of the most favorable π-π stacking with the conjugated organic linker. The calculated limit of detection (LOD) and corresponding quenching constant (KSV) from the Stern-Volmer (SV) plot for 1, 2, and 3 are found to be 0.68 μM and 7.49 × 104 M-1, 0.41 μM and 8.01 × 104 M-1, and 1.18 μM and 8.1 × 104 M-1, respectively. The fluorescence quenching mechanism is also highly influenced by their structure and coordination arrangement.

Accessing the Thiol Toolbox: Synthesis and Structure-Activity Studies on Fluoro-Thiol Conjugated Antimicrobial Peptides.

The para-fluoro-thiol reaction (PFTR) is a modern name for the much older concept of a nucleophilic aromatic substitution reaction in which the para-position fluorine of a perfluorinated benzene moiety is substituted by a thiol. As a rapid and mild reaction, the PFTR is a useful technique for the post-synthetic modification of macromolecules like peptides on the solid phase. This reaction is of great potential since it allows for peptide chemists to access the vast catalogue of commercially available thiols with diverse structures to conjugate to peptides, which may impart favorable biological activity, particularly in antimicrobial sequences. This work covers the generation of a library of antimicrobial peptides by modifying a relatively inactive tetrapeptide with thiols of various structures using the PFTR to grant antimicrobial potency to the core sequence. In general, nucleophilic substitution of the peptide scaffold by hydrophobic thiols like cyclohexanethiol and octanethiol imparted the greatest antimicrobial activity over that of hydrophilic thiols bearing carboxylic acid or sugar moieties, which were ineffectual at improving the antimicrobial activity. The general trend here follows expected structure-activity relationship outcomes like that of changing the acyl group of lipopeptide antibiotics and is encouraging for the use of this reaction for structural modifications of antimicrobial sequences further.

Antibacterial activity evaluation of pleuromutilin derivatives with 4(3H)-quinazolinone scaffold against methicillin-resistant Staphylococcusaureus

Growing antibiotic resistance is causing a health care crisis, leading to an urgent need for new antibiotics to tackle serious hospital and community infections. Pleuromutilin, a naturally occurring product with moderate antibacterial activity, has a unique structure that has attracted great efforts to modify its scaffold to obtain lead compounds. Herein, we report the synthesis of a series of novel pleuromutilin derivatives with a scaffold of 4(3H)-quinazolinone or its analogues at the C-14 side chain and investigated their in vitro activity against Staphylococcus aureus and Staphylococcus epidermidis as well as Gram-negative bacteria (Escherichia coli and Salmonella enterica subsp. enterica serovar pullorum). Structure-activity relationship (SAR) studies showed that the substituents on the benzene ring of 4(3H)-quinazolinone was not as important as the substituted position to improve antibacterial activity while the substituted groups on the N-3 position of 4(3H)-quinazolinone had strong impact on the efficacy. The replacement of the benzene moiety of 4(3H)-quinazolinone with other rings (pyridine, pyrrole, thiophene, or cyclopentyl) also showed high antibacterial efficacy, meaning the benzene ring was dispensable for exerting powerful antibacterial properties. In vitro pharmacokinetics investigations and cytotoxicity assays indicated that 2-mercapto-4(3H)-quinazolinone scaffold was superior to 2-(piperazin-1-yl)quinazolin-4(3H)-one. Among this series of pleuromutilin analogues, compound 23 with a structure of 2-mercapto-3H-pyrrolo[2,3-d]pyrimidin-4(7H)-one displayed the best in vitro antibacterial activity against MRSA (MIC = 0.063 μg/mL) and low cytotoxicity to RAW 264.7 cells (IC50＞100 μM) and was demonstrated to inhibit MRSA effectively in a mouse thigh infection model, outperforming the comparator, tiamulin.