Aromatic Subunits Research Articles

Hydroquinone-pyrrole dyads with varied linkers.

A series of pyrroles functionalized in the 3-position with p-dimethoxybenzene via various linkers (CH2, CH2CH2, CH=CH, C≡C) has been synthesized. Their electronic properties have been deduced from 1H NMR, 13C NMR, and UV–vis spectra to detect possible interactions between the two aromatic subunits. The extent of conjugation between the subunits is largely controlled by the nature of the linker, with the largest conjugation found with the trans-ethene linker and the weakest with the aliphatic linkers. DFT calculations revealed substantial changes in the HOMO–LUMO gap that correlated with the extent of conjugation found experimentally. The results of this work are expected to open up for use of the investigated compounds as components of redox-active materials in sustainable, organic electrical energy storage devices.

Fullerene and corannulene derivatives acting as insulators of Cl(-) and BeH2.

The capacity of corannulene and its benzo-derivatives CxH10 (x = 20-60) as prototypes of non-planar π-aromatic systems which mimic the end of carbon nanotubes to act as insulators between BeH2 and Cl(-) chemical entities has been explored by means of M06-2x/cc-pVDZ and M06-2x/6-311+G(d) calculations. For the sake of completeness, the set investigated includes also fullerene, C60. All these aromatic derivatives lead to stable binary complexes either with BeH2 or halogen (Cl(-)) anions. For BeH2, however, only the complexes in which the interaction involves the convex face of the aromatic system are stable. No significant changes are observed when the binding energies (BEs) of the BeH2 complexes are compared to those involving planar aromatic compounds, but the ones involving Cl(-) with the concave face of the aromatic moiety can be very large, because its curvature favors many contacts of the anion with the carbon atoms of the π-aromatic system. The formation of these binary complexes changes to a large extent the electrostatic potential on the free face of the aromatic system leading to a mutual reinforcement of both interactions, the beryllium bond and the interaction with Cl(-), when the ternary complexes are formed. As a result, the BEs for the triads are larger than the sum of the BEs of the corresponding binary complexes and the distances between the aromatic subunit and BeH2 or Cl(-) become shorter in the triads than in the binary complexes. A MBIE analysis also indicates that the enhanced stability of ternary complexes arises mainly from the reinforcement of the beryllium bonds as well as from the three-body terms. An exploration of all the minima for BeH2:C60H10:Cl(-) shows that BeH2 binds preferentially to the peripheral aromatic rings than those in the more curved region.

Synthesis and Computational Bandgap Engineering of New 3,4-Alkylenedioxypyrrole (ADOP) Derivatives and Investigation of Their Electrochromic Properties

This research highlights the degree of conformity between our electrochemical and theoretical studies conducted on the newly designed electropolymerizable monomers (BuDOP, BenDOP and BenzoDOP) possessing 3,4-alkylenedioxypyrrole (ADOP) backbone (BuDOP). We tried to select logical enhancing of the structures in a stepwise in order to discuss the effects of benzene (BenDOP) and benzodioxane (BenzoDOP) like aromatic subunits to the electrochromic properties of the target monomers. Following to the completion of the synthetic steps, appropriate structural analyses of monomers were performed (FT-IR, GC-MS, 1H-NMR, 13C-NMR). Subsequently, their corresponding polymers were prepared by electrochemical oxidation and characterized. Afterwards, our consecutive efforts have been contributed to theoretical studies in order to obtain information about their structural properties. To this aim, geometry optimizations were carried out using hybrid density functional theory (DFT/B3LYP/LANL2DZ) and HOMO, LUMO energy levels, HOMO-LUMO energy gaps (ΔE), electron affinity (EA) as well as ionization potential (IP) values were calculated. Theoretical data were then used for identifying the structure-electronic properties relationship and we aimed to determine the electrochromic properties of the studied monomers. Our results from the B3LYP/LANL2DZ calculations indicated that P(BenDOP) has the lowest HOMO-LUMO gap and we predicted that theoretical data were in good agreement with the experimental studies.

Synthesis of inherently chiral calixarenes via direct mercuration of the partial cone conformation.

Direct mercuration of calix[4]arene immobilized in the partial cone conformation led to the meta-substituted isomer which was subsequently subjected to Pd-catalysed coupling (C-H activation) with the neighbouring aromatic subunit. Regioselective mercuration thus enabled access to a novel type of inherently chiral calixarenes with a highly distorted cavity potentially applicable to the design of new chiral receptors.

V-shaped organic dyes with triphenylamine core for dye-sensitized solar cells: Simple synthesis with enhanced open-circuit voltage

A new series V-shaped organic dyes featured with triphenylamine as core/π-linker has been synthesized for the application of dye-sensitized solar cells. Four different polycyclic aromatic subunits have been introduced as donor group in this series of dyes (named DH-6 to DH-9). These dyes have been systematically characterized and employed in DSSC devices. Among the fabricated devices, DH-6-based cell exhibits the highest power conversion efficiency of 4.04% with a short-circuit current density of 8.02mAcm−2, an open-circuit photo voltage of 0.73V and a fill factor of 0.69 under AM 1.5 illumination without coadsorbent that reaches 83% of the reference dye N719-based cell. This result indicates that other than electron-donor, triphenylamine could also be a promising π-linker to construct high-performance metal-free organic sensitizer.

1,2,3-Triazole pharmacophore-based benzofused nitrogen/sulfur heterocycles with potential anti-Moraxella catarrhalis activity

Versatile 1,2,3-triazole pharmacophore-based benzofused heterocycles containing halogen-substituted aromatic (9–17 and 25–28), 7-substituted coumarin (18–23 and 29–30) or penciclovir-like subunit (31a,b–38a) were designed and synthesized to evaluate their antibacterial activities against selected Gram-positive and Gram-negative bacteria. Hybridization approach using environmentally friendly Cu(I)-catalyzed click reaction under microwave irradiation was adopted in the synthesis of regioselective 1,4-disubstituted 1,2,3-triazole tethered heterocycles (9–23 and 25–30), while post-N-alkylation of NH-1,2,3-triazoles afforded both 2,4- (31a–38a) and 1,4-disubstituted (31b–33b, 35b–37b) 1,2,3-triazole regioisomers. The compounds 18–23 and 25–30 revealed fluorescence in the violet region of the visible spectrum with a strong influence of phenyl spacer in 25–30 on both wavelength and emission intensity. Fusion of selected subunits led to new hybrid architecture, benzothiazole–1,2,3-triazole–coumarin 29 that demonstrated extremely narrow spectrum activity towards fastidious Gram-negative bacteria Moraxella catarrhalis. Selected hybrid showed the potency against Moraxella catarrhalis (MIC⩽0.25μg/mL) comparable to that of reference antibiotic azithromycin, which suggested that further investigations are necessary to optimize this potential hit compound as a new anti-Moraxella catarrhalis agent.

Concise Synthesis of Broussonone A.

A concise and expeditious approach to the total synthesis of broussonone A, a p-quinol natural compound, has been developed. The key features of the synthesis include the Grubbs II catalyst mediated cross metathesis of two aromatic subunits, and a chemoselective oxidative dearomatizationin the presence of two phenol moieties. Especially, optimization associated with the CM reaction of ortho-alkoxystyrenes was also studied, which are known to be ineffective for Ru-catalyzed metathesis reactions under conventional reaction conditions because ortho-alkoxy group could coordinate to the ruthenium center, resulting in the potential complication of catalyst inhibition.

Selective Formylation of Azacalixpyridine Macrocycles and Their Transformation to Molecular Semicages.

The aromatic electrophilic formylation reaction of azacalix[2]arene[2]pyridine and azacalix[4]pyridine were systematically studied. By simply controlling the ratio of reactants and the reaction temperature, the Vilsmeier-Haack reaction selectively afforded mono-, di-, and tetra-formylated azacalix[2]arene[2]pyridines and azacalix[4]pyridines. The preferential and selective functionalization reactions of macrocycles were discussed in terms of their conformational structure and conjugation effect between aromatic subunits and bridging nitrogen atoms. All resulting functionalized azacalix[2]arene[2]pyridines and azacalix[4]pyridines adopted a 1,3-alternate conformation both in the crystalline state and in solution. Taking advantage of the close proximity of aldehyde groups in 1,3-alternate di- and tetra-formylated azacalixpyridine macrocycles, the McMurry reductive coupling reaction of carbonyls was accomplished to yield unique semicage molecules.

Conducting Polymer/Redox Biopolymer High-Energy Density Supercapacitors

Recently, there has been an increase in the need for high energy and high power devices to supply the demand in areas as renewable energy generation systems, electric transportation and power leveling systems; traditional capacitors and batteries are not able to meet the current needs. However, new technologies face many challenges, such as material availability, charge efficiency, capacity, cycle stability and scalable manufacturing. Supercapacitors have emerged as promising devices to bridge the gap between conventional high-power capacitors and traditional batteries. Various materials can be use as supercapacitor electrodes, ranging from highly porous, inert carbon micro/nanomaterials to Faradaic metal oxides and conducting polymers. Carbon materials rely upon electrical double layer capacitance (EDLC), which store charge by the physical separation of charges within the interface electrode-electrolyte, leading to fast discharge rates (high power) while limited by low energy densities. On the other hand, Faradaic materials, such as metal oxides and electroactive conducting polymers (EPCs), are more attractive since they store charge base on electron transfer mechanisms, which leads to higher energy densities. Recent studies [1] have shown that redox polymers can be added to ECPs during polymerization to increase the electrodes’s Faradaic redox capacitance. Lignin represents an abundant biorenewbable polymer, which possesses little value aside from its heat content. The complex structure of lignin contains aromatic and aliphatic carbon subunits along with various forms of oxygen with phenolic groups that can undergo redox processes. While the sulfonated form of lignin (sodium lignosulfonate) has been used to enhance the redox capacitance in polymer electrodes, it makes up a small percentage of the available lignin. The widely available form of lignin (alkali lignin, AL) has limited solubility in aqueous acidic solutions thereby limiting the scope and cost advantages of lignin-polymer supercapacitors. In this work, we enable the use of alkali lignin to increase the capacitance of composite electrodes by utilizing acetic acid (AA) as synthesis media. We describe how redox polymer properties and process conditions can be utilized to increase the performance of composite electrodes comprising ECPs and redox materials, for the development of high power and energy density hybrid capacitors, through electrochemical and chemical synthesis methods. Figure 1a shows the solubility (g/mL) of AL in AA solutions along with the peak current from cyclic voltammetry measurements for polymerization solutions with varying AA molarity. For all other conditions equal, we found that electrodes synthesized in 15.3 M AA exhibited the highest redox activity. Furthermore, when varying the pyrrole to lignin ratio we found that the peak current increases with the increases in AL concentration as more lignin is integrated within the polymer network (figure 1b) providing additional redox activity from the phenolic groups present in lignin. Although ratios above 1:2 pyrrole to lignin resulted in a decrease in the electrochemical activity, since the insulated nature of lignin inhibits the electrochemistry in the polymer network. Electrodes of PPy/AL in AA were prepared and compared to the electrochemical properties of PPy/SLS synthesized in either AA or H2SO4. The cyclic voltammetry profiles are presented as of specific capacitance (F/g) vs voltage (figure 2a). PPy/SLS electrodes synthesized in AA and H2SO4 exhibited similar redox activity, indicating similar film chemistry. PPy/AL electrodes, however, show between 20-30% higher capacitance than the films with SLS. We have also shown that PPy/SLS and PPy/AL composites synthesized in solution using oxidative polymerization can be used to make thick electrodes using the doctor blade method. Device-scale electrodes comprising PPy/AL exhibited similar electrochemical characteristics as electrochemically synthesized films (figure 2b). Asymmetric hybrid supercapacitors were fabricated using PPy/AL cathodes with activated carbon anodes to demonstrate low-cost, high energy density supercapacitors containing abundant biorenewable polymers.

Crystal structure of ethyl 2-(1H-benzimidazol-2-yl)-2-[2-(4-nitro-phen-yl)hydrazinyl-idene]acetate.

The title compound, C17H15N5O4, was obtained via the condensation of 3-eth­oxy-2-[2-(4-nitro­phen­yl)hydrazono]-3-oxo­propanoic acid with 1,2-di­amino­benzene. In the mol­ecule, the dihedral angles between the acetate group and the two aromatic subunits (benzimidazole and nitro­phenyl­hydrazone) are 7.35 (9) and 18.23 (9)°, respectively. Intra­molecular N—H⋯O and N—H⋯N contacts occur. In the crystal, C—H⋯O and N—H⋯O hydrogen bonds link the mol­ecules into chains along the b-axis direction.

Donor-acceptor conjugated polymers based on multifused ladder-type arenes for organic solar cells.

Harvesting solar energy from sunlight to generate electricity is considered as one of the most important technologies to address the future sustainability of humans. Polymer solar cells (PSCs) have attracted tremendous interest and attention over the past two decades due to their potential advantage to be fabricated onto large area and light-weight flexible substrates by solution processing at a lower cost. PSCs based on the concept of bulk heterojunction (BHJ) configuration where an active layer comprises a composite of a p-type (donor) and an n-type (acceptor) material represents the most useful strategy to maximize the internal donor-acceptor interfacial area allowing for efficient charge separation. Fullerene derivatives such as [6,6]-phenyl-C61 or 71-butyric acid methyl ester (PCBM) are the ideal n-type materials ubiquitously used for BHJ solar cells. The major effort to develop photoactive materials is numerously focused on the p-type conjugated polymers which are generally synthesized by polymerization of electron-rich donor and electron-deficient acceptor monomers. Compared to the development of electron-deficient comonomers (acceptor segments), the development of electron-rich donor materials is considerably flourishing. Forced planarization by covalently fastening adjacent aromatic and heteroaromatic subunits leads to the formation of ladder-type conjugated structures which are capable of elongating effective conjugation, reducing the optical bandgap, promoting intermolecular π-π interactions and enhancing intrinsic charge mobility. In this review, we will summarize the recent progress on the development of various well-defined new ladder-type conjugated materials. These materials serve as the superb donor monomers to prepare a range of donor-acceptor semi-ladder copolymers with sufficient solution-processability for solar cell applications.

Probing the role of π interactions in the reactivity of oxygen species: a case of ethylzinc aryloxides with different dispositions of aromatic rings toward the metal center.

Ethylzinc derivatives of ortho-hydroxybiphenyl and 2,6-diphenylphenol that bear different nuclearity and dispositions of aromatic rings toward the metal center were synthesized and structurally characterized in the solid state and solution. This family of well-defined compounds was examined as a model system for the activation of dioxygen mediated by using complexes that feature lack of a redox-active metal center. Experimental and theoretical studies indicate an essential role in the oxygenation process of intramolecular interactions that involve aromatic subunits. Additionally, novel results for the oxygenation chemistry of alkylzinc compounds, including the isolation and structural characterization of the unique octanuclear aryloxide (hydroxide) compound Zn8 (OAr)8 (OH)6 (O2 ) with an encapsulated peroxide species, are presented.

ChemInform Abstract: Liquid‐Crystalline Ordering as a Concept in Materials Science: From Semiconductors to Stimuli‐Responsive Devices

AbstractReview: <160 refs.

Liquid‐Crystalline Ordering as a Concept in Materials Science: From Semiconductors to Stimuli‐Responsive Devices

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat-panel displays, their intrinsic ability to self-organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid-crystalline materials as organic semiconductors, which are solvent-processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli-responsive macroscopic shape change of cross-linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid-crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.

β-pyrrole substituted porphyrin–pyrene dyads using vinylene spacer: Synthesis, characterization and photophysical properties

We have designed and synthesized donor–acceptor conjugates having donor pyrene at the pyrrole-β position of either free-base porphyrin or Zn(II) porphyrin using vinylene spacer. Both the dyads have been completely characterized by elemental analysis, MALDI-MS, UV-Vis., and fluorescence (steady state and time-resolved) spectroscopies as well as cyclic voltammetry. The absorption maxima of both dyads are red-shifted by 8–12 nm. The ground state properties showed that there exist minimum π–π interaction between the aromatic subunits of these D–A systems. Quenched emission was observed in both the dyads when excited at 290 nm. The quenched emission explained in terms of intramolecular excitation energy transfer competes with the photo-induced electron transfer reaction in these D–A system.

Calix[4]arenes with intramolecularly bridged meta positions prepared via Pd-catalysed double C–H activation

The introduction of a 2-pyridylsulfoxide moiety into the upper rim of calix[4]arenes enabled the synthesis of unprecedented derivatives with intramolecularly bridged meta positions of two neighbouring aromatic subunits. Palladium-catalysed double C-H activation thus represents a straightforward way to a completely novel type of calixarenes.

Use of Organic Precursors and Graphenes in the Controlled Synthesis of Carbon-Containing Nanomaterials for Energy Storage and Conversion

The development of high-performance electrochemical energy storage and conversion devices, including supercapacitors, lithium-ion batteries, and fuel cells, is an important step on the road to alternative energy technologies. Carbon-containing nanomaterials (CCNMs), defined here as pure carbon materials and carbon/metal (oxide, hydroxide) hybrids with structural features on the nanometer scale, show potential application in such devices. Because of their pronounced electrochemical activity, high chemical and thermal stability and low cost, researchers are interested in CCNMs to serve as electrodes in energy-related devices. Various all-carbon materials are candidates for electrochemical energy storage and conversion devices. Furthermore, carbon-based hybrid materials, which consist of a carbon component with metal oxide- or metal hydroxide-based nanostructures, offer the opportunity to combine the attractive properties of these two components and tune the behavior of the resulting materials. As such, the design and synthesis of CCNMs provide an attractive route for the construction of high-performance electrode materials. Studies in these areas have revealed that both the composition and the fabrication protocol employed in preparing CCNMs influence the morphology and microstructure of the resulting material and its electrochemical performance. Consequently, researchers have developed several synthesis strategies, including hard-templated, soft-templated, and template-free synthesis of CCNMs. In this Account, we focus on recent advances in the controlled synthesis of such CCNMs and the potential of the resulting materials for energy storage or conversion applications. The Account is divided into four major categories based on the carbon precursor employed in the synthesis: low molecular weight organic or organometallic molecules, hyperbranched or cross-linked polymers consisting of aromatic subunits, self-assembling discotic molecules, and graphenes. In each case, we highlight representative examples of CCNMs with both new nanostructures and electrochemical performance suitable for energy storage or conversion applications. In addition, this Account provides an overall perspective on the current state of efforts aimed at the controlled synthesis of CCNMs and identifies some of the remaining challenges.

Torsional Influences within Disordered Organic Electronic Materials Based upon Non-Benzenoid 1,6-Methano[10]annulene Rings

Conjugated polymers and small molecules containing the nonplanar aromatic 1,6-methano[10]annulene were synthesized in an effort to understand how torsional differences between planar and nonplanar π-electron components influence the electronic properties of π-conjugated materials. The polymers and small molecule model systems contain commonly employed aromatic subunits such as thiophene, diketopyrrolopyrrole, and 2,1,3-benzothiadiazole, leading to electron donor and donor–acceptor polymers. The curved geometry of 1,6-methano[10]annulene can lead to reduced local torsional strain in semiconducting polymers relative to large planar aromatics, potentially increasing intrapolymer conjugation. The relative amount of effective conjugation length increase granted by the annulene in each system of regioisomers was interrogated through the use of UV–vis and photoluminescence spectroscopy and electrochemistry, and it was found that 1,6-methano[10]annulene relieves some torsional strain associated with solubilizing alkyl chains clashing with aromatic rings along the polymer backbone. The polymers were also found to be highly disordered in thin films yet still provided reasonable hole mobilities (ca. 10–4 cm2/(V s)) in OFET devices. These results suggest that methano[10]annulene or other curved aromatics may prove useful in the future development of organic electronics.

One-step template-directed synthesis of acridine-based rigid cyclophanes

Cyclo-bisintercalands are macrocyclic systems containing aromatic subunits, which are commonly used as hosts for aromatic molecules and as DNA intercalators. In this article, a step-by-step synthesis of a series of cyclo-bisintercalands containing 3,6-diaminoacridines as aromatic units, and connected by rigid spacers of different lengths, is reported. In addition, we describe herein a more efficient synthetic alternative, involving single-step template-directed processes. The new routes allow the easy synthetic access to these macrocyclic systems with acceptable yields. The synthesized cyclo-bisintercalands and their precursors have been structurally characterized by UV–visible and NMR methods. Preliminary biological activity assays performed on the bisintercalands and cyclo bisintercalands revealed interesting cytotoxic properties against different tumor cell lines, especially in the case of the bisintercalands, highlighting their potential as cancer chemotherapeutic agents.

Anion-dependent coordinative networking of macrocycle with copper(i) halides

An O2S2-macrocycle L incorporating three aromatic subunits was synthesized and structurally characterized by X-ray analysis. Four coordination polymers of L with copper(I) halides (Cl, Br and I) adopting different topologies and network patterns depending on the anions are reported. Reactions of L with copper(I) chloride and copper(I) bromide yielded a single-stranded one-dimensional (1D) coordination polymer [CuCl2(L)(CH3CN)]n (1) with an oxidized copper(II) centre and a double-stranded 1D coordination polymer [(Cu2Br2)(L)2]·4CH2Cl2]n (2), with each strand linked by a rhomboid-type Cu2Br2 unit. However, the reaction with copper(I) iodide under the same conditions gave an emissive mixture of supramolecular isomers with an identical composition {[Cu4I4(L)2]·CH2Cl2}n, adopting a regular (3a) and a tilted (3b) square-grid-type 2D coordination polymers via cubane-type Cu4I4 linking. The XRPD results also confirmed the binary mixture. The conformational diversity in the ligand leads to a variation in overall structural motifs of the supramolecular isomers.