Benzene Oligomers Research Articles

Solid-Phase Synthesis of Sequence-Defined Informational Oligomers.

Genetic biopolymers utilize defined sequences and monomer-specific molecular recognition to store and transfer information. Synthetic polymers that mimic these attributes using reversible covalent chemistry for base-pairing pose unique synthetic challenges. Here, we describe a solid-phase synthesis methodology for the efficient construction of ethynyl benzene oligomers with specific sequences of aniline and benzaldehyde subunits. Handling these oligomers is complicated by the fact that they often exhibit multiple conformations because of intra- or intermolecular pairing. We describe conditions that allow the dynamic behavior of these oligomers to be controlled so that they may be manipulated and characterized without needing to mask the recognition units with protecting groups.

The predictive power of aromaticity: quantitative correlation between aromaticity and ionization potentials and HOMO-LUMO gaps in oligomers of benzene, pyrrole, furan, and thiophene.

Aromaticity is a central and ubiquitous concept in organic chemistry, and is used extensively to explain various phenomena. Yet, aromaticity cannot be observed or measured as a property in its own right and, to date, only qualitative and semi-quantitative relationships have been described between aromaticity and an observable property. We now demonstrate for the first time a robust quantitative relationship between the HOMO-LUMO gap and adiabatic ionization potential of a polycyclic aromatic hydrocarbon oligomer - both measurable physical quantities - and its aromaticity, as quantified by the Nucleus Independent Chemical Shift (NICS) index. The agreement found for a range of structurally and electronically diverse oligomeric systems of varying lengths is so well-behaved as to enable accurate prediction of the properties of longer members of the respective oligomer family. The established correlation allows for preliminary screening of compounds geared towards functional use.

Extended Detailed Chemical Kinetic Model for Benzene Pyrolysis with New Reaction Pathways Including Oligomer Formation

The detailed chemical kinetic model based on elementary reactions was developed by adding reactions associated with the formations of benzene oligomers such as quaterphenyl (C24H18) and quinquephenyl (C30H22) and the overall reactions on coke formation to the available model reported previously [Norinaga, K.; J. Anal. Appl. Pyro., 2009]. This extended model was critically evaluated by comparisons of the computed results with experimental data on the benzene pyrolysis performed with an atmospheric flow reactor at temperature ranging from 1123 to 1223 K, residence time up to 4 s, and benzene partial pressure of 10.1 kPa [Kousoku, A.; J. Chem. Eng. Jpn.; accepted for publication]. The extended model showed improved capabilities in predicting product distribution in the benzene pyrolysis, including the yields of unreacted benzene as well as primary products such as benzene oligomers, low molecular weight gaseous products such as hydrogen and methane, and soot/coke. In contrast, the original model significantly underpredicted the conversion of benzene and could not predict the formations of benzene oligomers larger than terphenyl and coke. Acceptable agreements in oligomer yields obtained theoretically and experimentally indicate that the higher oligomer formations that had been ignored in the previous research are important reaction pathways leading to polycyclic aromatic hydrocarbons in the primary stage of benzene pyrolysis.

Two-Dimensional Crystallization of Carboxylated Benzene Oligomers

Various carboxylic acid substitution patterns on the 1,3,5-triphenylbenzene nucleus were explored, and their influence on the symmetry of the resulting two-dimensional (2D) crystal structures was assessed. The symmetry of 1,3,5-benzenetribenzoic acid (H(3)BTB) was reduced by modifying the substitution pattern of the arene and/or adding an additional carboxylic acid. Four analogues belonging to various point groups were studied. Comparison of the monolayers of the analogues to that of H(3)BTB shows that plane group symmetry and molecular symmetry are not correlated: H(3)BTB and its analogues exhibit the same plane group p2 at the heptanoic acid/graphite interface. The 2D crystal structure of the H(3)BTB analogues is more strongly controlled by the geometry of hydrogen-bonding interactions rather than molecular symmetry. Other significant observations in this study include porosity, uncommon hydrogen-bonding motifs, and an unusually high number of inquivalent molecules (Z' = 3) present in the 2D crystal of the lowest symmetry analogue. This research demonstrates that reduction of molecular symmetry based on geometric modification of noncovalent interactions allows for control over porosity of the 2D crystals (close-packed structures to nanoporous networks) without changing the core shape of the molecule.

Synthesis of Carbon Dendron Nano‐Chains with π‐Extended Conjugation Based on Linear 1,4‐Phenylethynyl and 1,5‐Naphthylethynyl Subunits.

Abstract A convenient and efficient synthesis of 3,5-di(trimethylsilylethynyl)phenylacetylene and p-[3,5-di(trimethylsilylethynyl)-1-phenylethynyl]phenylacetylene and the naphthylethynyl homologues terminal acetylenes of 5-(N,N-dimethylamino)naphthylethyne have been carried out. These terminal acetylene compounds serve to prepare nanometer-sized conjugated 1,3,5-tri(ethynylphenyl)benzene and 1,3,5-tri(ethynylnaphthyl)benzene oligomers, by means of heterocoupling with 1,3,5-triiodobenzene, catalysed by palladium, in excellent yields. Both the ethynylphenyl or ethynylnaphthyl homologues chains show fluorescence emission radiation, with important quantum yield.

Synthesis of carbon dendron nano-chains with π-extended conjugation based on linear 1,4-phenylethynyl and 1,5-naphthylethynyl subunits

A convenient and efficient synthesis of 3,5-di(trimethylsilylethynyl)phenylacetylene and p-[3,5-di(trimethylsilylethynyl)-1-phenylethynyl]phenylacetylene and the naphthylethynyl homologues terminal acetylenes of 5-( N, N-dimethylamino)naphthylethyne have been carried out. These terminal acetylene compounds serve to prepare nanometer-sized conjugated 1,3,5-tri(ethynylphenyl)benzene and 1,3,5-tri(ethynylnaphthyl)benzene oligomers, by means of heterocoupling with 1,3,5-triiodobenzene, catalysed by palladium, in excellent yields. Both the ethynylphenyl or ethynylnaphthyl homologues chains show fluorescence emission radiation, with important quantum yield.

Temperature dependence of the growth front roughening of oligomer films

Growth front roughening characteristics of vacuum deposited pentamer 2,5-di-n-octyloxy-1,4-bis[4-(styryl)styryl]-benzene oligomer thin films, onto silicon substrates, strongly depend on the substrate temperature in the range ∼20 °C–100 °C. The measured roughness exponents H increase from H≈0.4 at low substrate temperatures where growth is dominated by vacancy formation, to H≈0.7–0.8 at elevated temperatures where diffusive growth takes place. Moreover, the root-mean-square roughness amplitude and the correlation length evolve with temperature closely as an Arrhenius process with activation barrier comparable to molecule transnational and rotational barriers on oligomer surfaces.

Electrical properties of a phenylene vinylene oligomer

Abstract The electrical properties of 4,4′-bis(4-styryl-styryl) benzene oligomer based diodes were investigated by d.c and a.c measurements. At high field, the charge carriers are injected through potential barriers at the interface and the transport occurs via a field assisted thermal ionization process in the bulk of the oligomer. The influence of the metal electrode revealed in the current-voltage characteristics as well as in the dielectric data suggests that there might be interactions between the metal and the oligomer.

Tetrachloro-p-(o,p)-o-tribenzene: A Building Block for Diels-Alder Oligomers of Benzene and for a Laticyclic Conjugated Hexaene.

Intermolecular cycloaddition of the bifunctional tetrachlorotribenzene 1 results in higher Diels-Alder oligomers of benzene (2), of which the linear and an angular hexamer (n=1) were characterized. The oligomers decompose above 110°C through stepwise extrusion of benzene and tetrachlorobenzene.

Interfacial reactions in oligo(arylene-vinylene)–metal systems

X-ray photoelectron spectra of 4,4′-bis(4 styryl-styryl) benzene oligomer (4PV) films metallized with chromium and aluminum films were used to investigate the nature of 4PV–metal interfacial reactions. The changes in the core level spectra of carbon, metal, and oxygen indicated the formation of a carbide in a chromium covered oligomer and a metal–oxide carbon and/or carbide in aluminum covered films. Yet no apparent reaction was observed in the interfacial layer when depositing the oligomer film on the chromium layer. These reactions are used as a possible explanation for the electrical characteristics of diodes made from these materials.

A coupled anharmonic oscillator model for optical nonlinearities of conjugated organic structures

We present a simple model of coupled locally anharmonic oscillators which can be used to describe the optical nonlinearities in conjugated organic monomeric, oligoneric, and polymeric structures. We show that the method can very readily be used to explain the dependence of the band gap, the polarizability α, and the second hyperpolarizability γ on the number of repeat units of conjugated chain compounds by adjusting two parameters: the local anharmonicity term and the oscillator coupling constant. To illustrate the usefulness of this model, we have calculated the dependence of the band gap, the polarizability α, and the second hyperpolarizability γ, as the function of the number of repeat units for the oligomers of thiophene and benzene. The results predicted by the coupled anharmonic oscillator model are in good agreement with those of the experimental studies on thiophene and benzene oligomers recently reported by our group. In addition, the predicted power dependences of orientationally averaged 〈α〉 and 〈γ〉 on the number of repeat units are compared with those predicted by a free electron model, PPP method, sum-over-states method, and ab initio calculations.

Polymerization of benzene occluded in graphite-alkali metal intercalation compounds

Benzene accommodated within the interlayer space of graphite-alkali metal (potassium and rubidium) intercalation compounds was found to be polymerized not only to biphenyl, but also to terphenyl and quaterphenyl, while only biphenyl was formed by the action of potassium or rubidium metal alone under the same conditions. The formation of higher oligomers of benzene in the interlayer space of graphite intercalation compounds is to be ascribed to the amphoteric nature of the compounds, which are capable of both donating and accepting electrons.