Fused Benzene Rings Research Articles

Effects of volatile–char interactions on in-situ destruction of nascent tar during the pyrolysis and gasification of biomass. Part II. Roles of steam

This study aims to investigate the importance of steam to tar destruction during the volatile–char interactions. Steam was supplied in the absence and presence of nascent char during the pyrolysis/gasification of biomass at 850°C. In the absence of char, steam has more significant effects on the reforming of large aromatic ring systems (e.g. >2 fused benzene rings) than small and isolated aromatics. In the presence of char, steam can significantly enhance the reforming of both large and small aromatic ring systems during the volatile–char interactions, especially when the steam–char reactions are also significant. The results indicate that the steam–char reactions are particularly inhibited in a thin char bed by the volatile–char interactions. It is believed that the steam–char reactions can produce additional active sties on the char, such as the radicals/intermediates of char gasification and/or the O-containing groups, to facilitate tar reforming during the volatile–char interactions.

Double [4 + 2] cycloaddition reaction to approach a large acene with even-number linearly fused benzene rings: 6,9,16,19-tetraphenyl-1.20,4.5,10.11,14.15-tetrabenzooctatwistacene.

It is more challenging to synthesize acenes with even-number fused benzene rings (AWEB) than acenes with odd-number fused benzene rings (AWOB) because AWEB are either synthetically asymmetric or the precursors to prepare AWEB are very difficult to obtain or to prepare from commercially available sources. In this work, we employed 2,6-naphthodiyne precursor (2) as an effective synthon to prepare a large AWEB, 6,9,16,19-tetraphenyl-1.20,4.5,10.11,14.15-tetrabenzooctatwistacene (1), through a simple, one-step, double [4 + 2] cycloaddition reaction. The physical properties of as-prepared octatwistacene (1) have been carefully studied, and the OLED performance of compound 1 was also investigated.

Spin transport properties of n-polyacene molecules (n = 1-15) connected to Ni surface electrodes: theoretical analysis.

Using non-equilibrium Green function formalism in conjunction with density functional theory, we explore the spin-polarized transport characteristics of several planar n-acene molecules suspended between two semi-infinite Ni electrodes via the thiol group. We examine the spin-dependence transport on Ni-n-acenes-Ni junctions, while the number of fused benzene rings varies between 1 and 15. Intriguingly, the induced magnetic moments of small acene molecules are higher than that of longer acene rings. The augmentation of fused benzene rings affects both the magnetic and transport features, such as the transmission function and conductance owing to their coupling to the Ni surface contacts via the anchoring group. The interplay between the spin-polarized transport properties, structural configuration and molecular electronic is a fortiori essential in these attractive molecular devices. Thus, this can conduct to the engineering of the electron spin transport in atomistic and molecular junctions. These prominent molecules convincingly infer that the molecular spin valves can conduct to thriving molecular devices.

Unconventional, chemically stable, and soluble two-dimensional angular polycyclic aromatic hydrocarbons: from molecular design to device applications.

Polycyclic aromatic hydrocarbons (PAHs), consisting of laterally fused benzene rings, are among the most widely studied small-molecule organic semiconductors, with potential applications in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). Linear acenes, including tetracene, pentacene, and their derivatives, have received particular attention due to the synthetic flexibility in tuning their chemical structure and properties and to their high device performance. Unfortunately, longer acenes, which could exhibit even better performance, are susceptible to oxidation, photodegradation, and, in solar cells which contain fullerenes, Diels-Alder reactions. This Account highlights recent advances in the molecular design of two-dimensional (2-D) PAHs that combine device performance with environmental stability. New synthetic techniques have been developed to create stable PAHs that extend conjugation in two dimensions. The stability of these novel compounds is consistent with Clar's sextet rule as the 2-D PAHs have greater numbers of sextets in their ground-state configuration than their linear analogues. The ionization potentials (IPs) of nonlinear acenes decrease more slowly with annellation in comparison to their linear counterparts. As a result, 2-D bistetracene derivatives that are composed of eight fused benzene rings are measured to be about 200 times more stable in chlorinated organic solvents than pentacene derivatives with only five fused rings. Single crystals of the bistetracene derivatives have hole mobilities, measured in OFET configuration, up to 6.1 cm(2) V(-1) s(-1), with remarkable Ion/Ioff ratios of 10(7). The density functional theory (DFT) calculations can provide insight into the electronic structures at both molecular and material levels and to evaluate the main charge-transport parameters. The 2-D acenes with large aspect ratios and appropriate substituents have the potential to provide favorable interstack electronic interactions, and correspondingly high carrier mobilities. In stark contrast to the 1-D acenes that form mono- and bis-adducts with fullerenes, 2-D PAHs show less reactivity with fullerenes. The geometry of 2-D PAHs plays a crucial role in determining both the barrier and the adduct stability. The reactivity and stability of the 2-D PAHs with regard to Diels-Alder reactions at different reactive sites were explained via DFT calculations of the reaction kinetics and of thermodynamics of reactions and simple Hückel molecular orbital considerations. Also, because of their increased stability in the presence of fullerenes, these compounds have been successfully used in OPVs. The small-molecule semiconductors highlighted in this Account exhibit good charge-transport properties, comparable to those of traditional linear acenes, while being much more environmentally stable. These features have made these 2-D PAHs excellent molecules for fundamental research and device applications.

The longest acenes.

For a long time, the largest known member of the acene series was hexacene, consisting of six linearly fused benzene rings. The next higher member, heptacene, is so highly reactive that either stabilization using substituents is required or matrix isolation techniques need to be employed for the detection of the parent hydrocarbon. This Record Review summarizes recent research that culminated in the synthesis of substituted and parent nonacene.

The complex polymorphism and thermodynamic behavior of a seemingly simple system: naphthalene on Cu(111).

Naphthalene, C10H8, is a polycyclic aromatic hydrocarbon (PAH) consisting of two fused benzene rings. From previous studies, it is known to form three different commensurate structures in thin epitaxial films on Cu(111), depending on the preparation conditions. One of these structures even exhibits a chiral motif of molecular rotations within the unit cell. In an attempt to elucidate this polymorphism, we performed in situ low-energy electron diffraction (LEED) as a function of temperature and surface coverage, revealing an unexpected and extraordinarily complex structural and thermodynamic behavior. We present experimental evidence for a phase transition from a two-dimensional gas to a highly ordered molecular solid via an intermediate metastable phase with moderate order (extending over a few lattice constants only) which undergoes a reversible orientational shift upon temperature variation. At monolayer coverage and above, we find that two different point-on-line (POL) coincident epitaxial relations constitute the dominant structures. This is remarkable because, so far, POL structures of naphthalene on Cu(111) and other substrates have either not been recognized or not obtained under the respective experimental conditions. Our results are corroborated by the analysis of characteristic moiré patterns observed in scanning tunneling microscopy (STM), indicative of a noncommensurate epitaxial registry.

Synthesis and characterization of poly(tetramethylsilarylenesiloxane) derivatives bearing benzodithiophene moieties

Poly(tetramethylsilarylenesiloxane) derivatives bearing benzo[1,2-b;4,5-b′]dithiophene (P1) and benzo[2,1-b;3,4-b′]dithiophene (P2) moieties were prepared via polycondensation of the corresponding disilanol monomers, that is, 2,6-bis(dimethylhydroxysilyl)benzo[1,2-b;4,5-b′]dithiophene (M1) and 2,7-bis(dimethylhydroxysilyl)benzo[2,1-b;3,4-b′]dithiophene (M2), respectively. It was deduced that P1 is a crystalline polymer while P2 is an amorphous one from the results of differential scanning calorimetry (DSC). Bathochromic and hyperchromic effects were observed in the absorption and fluorescence spectra when dimethylsilyl substituents were introduced on the benzo[1,2-b;4,5-b′]dithiophene and benzo[2,1-b;3,4-b′]dithiophene skeletons. The fluorescence quantum yields (ΦFs) were not improved by the introduction of dimethylsilyl groups onto the benzo[1,2-b;4,5-b′]dithiophene and benzo[2,1-b;3,4-b′]dithiophene skeletons, whereas the improvement in the ΦFs was remarkable in the case of poly(tetramethylsilarylenesiloxane) derivatives that possessed the corresponding fused benzene ring systems, i.e., poly(tetramethyl-2,6-silanthrylenesiloxane) and poly(tetramethyl-1,8-silphenanthrylenesiloxane).

Polycyclic aromatic hydrocarbons (PAHs) in the aquatic ecosystems of Soweto and Lenasia

Polycyclic aromatic hydrocarbons (PAHs) in the aquatic ecosystems of Soweto and Lenasia Polycyclic aromatic hydrocarbons (PAHs) are fused benzene rings containing only hydrogen and carbon atoms. The aim of the study is to determine the concentrations and origins of the 16 priority PAHs, and the ecotoxicological effects they may have on the aquatic ecosystem and possible risk to the human population.

Photo- and Thermochromic Spiropyrans 42.* The Effect of Structural Factors on the Photochromic Properties of Indolinospiro-Pyrans Containing a Condensed Furan Fragment

Syntheses are reported for a series of N-substituted indolinospiropyrans containing a fused furan fragment in the benzopyran part of the molecule. The structure of these compounds was established by IR and multinuclear NMR spectroscopy. A study was carried out on the effect of the fused benzene ring and bulky N-benzyl substituent on the photochromic properties of these compounds in solution and in a polymer matrix. Dynamic NMR spectroscopy was used to study the thermally induced isomerization of the N-benzyl derivative.

(4bS,8aS)-1-Isopropyl-4b,8,8-trimethyl-4b,5,6,7,8,8a,9,10-octa-hydro-phenan-thren-2-yl benzoate.

The title compound, C27H34O2, was hemisynthesized through direct benzoyl­ation of the naturally occurring meroterpene totarol. The central fused six-membered ring has a half-chair conformation, whereas the terminal six-membered ring displays a chair conformation. The dihedral angle between the fused benzene ring and the benzoyl benzene ring is 73.05 (14)°. The S,S chirality of the mol­ecule is consistent with the synthetic pathway, and confirmed by the refinement of the Flack parameter.

Evolution of graphene molecules: structural and functional complexity as driving forces behind nanoscience.

The evolution of nanoscience is based on the ability of the fields of chemistry and physics to share competencies through mutually beneficial collaborations. With this in mind, in this Perspective, I describe three classes of compounds: rylene dyes, polyphenylene dendrimers, as well as nanographene molecules and graphene nanoribbons, which have provided a superb platform to nurture these relationships. The synthesis of these complex structures is demanding but also rewarding because they stimulate unique investigations at the single-molecule level by scanning tunneling microscopy and single-molecule spectroscopy. There are close functional and structural relationships between the molecules chosen. In particular, rylenes and nanographenes can be regarded as honeycomb-type, discoid species composed of fused benzene rings. The benzene ring can thus be regarded as a universal modular building block. Polyphenylene dendrimers serve, first, as a scaffold for dyes en route to multichromophoric systems and, second, as chemical precursors for graphene synthesis. Through chemical design, it is possible to tune the properties of these systems at the single-molecule level and to achieve nanoscale control over their self-assembly to form multifunctional (nano)materials.

From Perylene to a 22‐Ring Aromatic Hydrocarbon in One‐Pot

AbstractThe successful synthesis of a threefold symmetric C78H36 molecule with 22 fused benzene rings is reported. This clover‐shaped nanographene was characterized on an ultrathin insulating film with atomic resolution by scanning probe microscopy.

From perylene to a 22-ring aromatic hydrocarbon in one-pot.

The successful synthesis of a threefold symmetric C78H36 molecule with 22 fused benzene rings is reported. This clover-shaped nanographene was characterized on an ultrathin insulating film with atomic resolution by scanning probe microscopy.

Occurrence of polycyclic aromatic hydrocarbons (PAHs) in beached plastic pellets from Mumbai coast, India

PAHs are a class of ubiquitous pollutants which consist of two or more fused benzene rings in various arrangements. A number of PAH compounds are known carcinogens and bioaccumulate and biomagnify. These compounds originate naturally as well as anthropogenically through oil spills, incineration of waste and combustion of fossil fuels and wood. The environmental consequence of Plastic pellets is the sorption organic pollutants on their surface from the sea surface microlayer (SML) where the hydrophobic contaminants are known to be enriched. The plastic pellets were collected along the recent high tide line from four beaches of Mumbai coast bimonthly during May 2011 - March 2012. A total of 72 pools of plastic pellets were extracted, fractionated and analysed by Gas Chromatograph coupled to a mass spectrometer to evaluate the extent and sources of 16 PAHs. The mean ΣPAH concentration in pellets was 9202.30±114.89 ng g-1 with a wide range (35.4-46191.58 ng g-1). The concentration of fluorene was found to be the highest (1606.30±251.54 ng g-1) followed by anthracene, chrysene and phenanthrene. The ΣPAH concentration was significantly varied among months and there was no significant difference among sites at p=0.05. The 2-3 aromatic ring compounds accounted for 60% of the total PAHs in pellets of Mumbai coast while 4 rings and 5-6 rings compounds accounted for 26 and 14%, respectively. The ratio of low and high molecular weight PAHs indicated that the contamination by petrogenic sources was predominant over the pyrogenic ones in plastic pellets suggesting oil pollution in coastal area of Mumbai.Keywords: plastic pellets, PAHs, Mumbai, sources

An extended phenacene-type molecule, [8]phenacene: synthesis and transistor application.

A new phenacene-type molecule, [8]phenacene, which is an extended zigzag chain of coplanar fused benzene rings, has been synthesised for use in an organic field-effect transistor (FET). The molecule consists of a phenacene core of eight benzene rings, which has a lengthy π-conjugated system. The structure was verified by elemental analysis, solid-state NMR, X-ray diffraction (XRD) pattern, absorption spectrum and photoelectron yield spectroscopy (PYS). This type of molecule is quite interesting, not only as pure chemistry but also for its potential electronics applications. Here we report the physical properties of [8]phenacene and its FET application. An [8]phenacene thin-film FET fabricated with an SiO2 gate dielectric showed clear p-channel characteristics. The highest μ achieved in an [8]phenacene thin-film FET with an SiO2 gate dielectric is 1.74 cm2 V−1 s−1, demonstrating excellent FET characteristics; the average μ was evaluated as 1.2(3) cm2 V−1 s−1. The μ value in the [8]phenacene electric-double-layer FET reached 16.4 cm2 V−1 s−1, which is the highest reported in EDL FETs based on phenacene-type molecules; the average μ was evaluated as 8(5) cm2 V−1 s−1. The μ values recorded in this study show that [8]phenacene is a promising molecule for transistor applications.

DNA Mismatch Recognition by a Hexacoordinate Silicon Sandwich–Ruthenium Hybrid Complex

The diastereoselective synthesis of two dinuclear Ru–Si complexes is reported, in which silicon(IV) is coordinated in an octahedral fashion by two 1,10-phenanthrolines and one 4,5-pyrenediolato ligand and additionally η6-coordinated to a (η5-pentamethylcyclopentadienyl)ruthenium(II) moiety through one fused benzene ring of the pyrene ligand. One of these Ru–Si hybrid complexes was found to selectively stabilize DNA duplexes that contain cytosine–cytosine or cytosine–thymine mismatches, and it is proposed that this occurs by a novel dual insertion/intercalation binding mode in which the entire ruthenium sandwich unit is introduced into the DNA π-stacking at the site of the DNA mismatch.

Quantum chemical modeling of the effect of the nature of a μ-SCN-type ligand on the redox properties of iron nitrosyl complexes

The quantum chemical study of the redox potentials of ten iron nitrosyl complexes with functional bridging μ-SCN-type ligands was performed by the DFT method combined with the polarizable continuum model (PCM) in order to clarify the influence of the ligand on the redox properties of the complex. The geometry optimization in terms of the PCM approach gave redox potentials, which are in the best agreement with the experimental values. The redox potential depends on the nature of the heteroatom in the five-membered azole ring, the number of N atoms in the ring, and the presence of the fused benzene ring in the aromatic system of the ligand.

(2Z)-2-Benzyl-idene-4-n-butyl-3,4-di-hydro-2H-1,4-benzo-thia-zin-3-one.

In the title compound, C19H19NOS, the six-membered hetero­cyclic ring of the benzo­thia­zine fragment exhibits a screw boat conformation. The plane of the fused benzene ring makes a dihedral angle of 72.38 (12)° with that of the terminal phenyl ring, and is nearly perpendicular to the mean plane formed by the atoms through the n-butyl chain, as indicated by the dihedral angle of 88.1 (2)°. In the crystal, mol­ecules are linked by C—H⋯O inter­actions to form supra­molecular chains along [110].

Crystal Structure, Spectral Studies, and Hirshfeld Surfaces Analysis of 5-Methyl-5H-dibenzo[b,f]azepine and 5-(4-Methylbenzyl)-5H-dibenzo[b,f]azepine

The compounds, 5-methyl-5H-dibenzo[b,f]azepine (1) and 5-(4-methylbenzyl)-5H-dibenzo[b,f]azepine (2), were synthesized and characterized by spectral studies, and finally confirmed by single crystal X-ray diffraction method. The compound 1 crystallizes in the orthorhombic crystal system in Pca21 space group, having cell parameters a=11.5681 (18) Å, b=11.8958 (18) Å, c=8.0342 (13) Å, and Z=4 and V=1105.6 (3) Å3. And the compound 2 crystallizes in the orthorhombic crystal system and space group Pbca, with cell parameters a=16.5858 (5) Å, b=8.4947 (2) Å, c=23.1733 (7) Å, and Z=8 and V=3264.92 (16) Å3. The azepine ring of both molecules 1 and 2 adopts boat conformation with nitrogen atom showing maximum deviations of 0.483 (2) Å and 0.5025 (10) Å, respectively. The C–H⋯π short contacts were observed. The dihedral angle between fused benzene rings to the azepine motif is 47.1 (2)° for compound 1 and 52.59 (6)° for compound 2, respectively. The short contacts were analyzed and Hirshfeld surfaces computational method for both molecules revealed that the major contribution is from C⋯H and H⋯H intercontacts.

Coupled Cluster Valence Bond Method: Efficient Computer Implementation and Application to Multiple Bond Dissociations and Strong Correlations in the Acenes.

We describe an efficient implementation of the coupled cluster valence bond (CCVB) model. CCVB captures a certain essential part of the description of molecules with strong correlations (SC), which allows it to achieve correct energy profiles when covalent bonds are broken, while maintaining proper spin symmetry and size extensivity. To illustrate treatment of SC in bond breaking, we examine the symmetric dissociation of the sulfur allotropes S6 and S8 into triplet S atoms. To show applicability to larger systems and to explore whether CCVB can capture aspects of SC that arise in extended π systems, we report results for a series of acenes up to 12 fused benzene rings, with active spaces of up to 228 correlated electrons. The lowest-energy CCVB solutions found for two of the largest acenes show signatures consistent with multi-electron SC and partial delocalization.