Macrospirocyclic oligomers based on carbazole and fluorene

Monodisperse macrospirocyclic oligomers were prepared using self-condensation of the Friedel-Crafts reaction. Through the C-9s of the central fluorene units of four surrounding oligofluorenes, four carbazole units are connected in a series to form a macrocyclic core. These rodlike oligofluorenes form a rigid three-dimensional structure, affording the resulting macrocyclics a high steric hindrance for close interchain packing.     

Monodisperse fluorene oligomers exhibiting strong dipolar coupling interactions

Well-defined fluorene oligomers (n = 1 to 6) were prepared step by step using Suzuki and Yamamoto couplings, while absorption and photoluminescence properties evidenced very large dipolar coupling interactions between fluorene moieties.     

Reactivity of aromatic nitrons with alkyl and alkylperoxyl radicals

The catalytic properties of Mn(II)-histidine complexes for the oxidation of indigo carmine by H₂O₂ have been studied. It has been shown that the complex Mn(II) (Histidine)₂ existing in as a dimer is the true catalyst but at high concentration of the reactant the reaction is inhibited because of complex formation between the reactant and the catalyst.

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Mn(II)- . , Mn(II)·()₂ . , .

     

Novel, yellow-emitting anthracene/fluorene oligomers: synthesis and characterization

A novel series of highly soluble and strongly yellow fluorescent with well-controlled, alternative anthracene, and fluorene units were successfully synthesized by a Pd/Cu-catalyzed Sonogashira coupling reaction and characterized. Their thermal stabilities, electrochemical behaviors, and photophysical properties were investigated. These oligomers might be used as models to study structure-property relationship for their corresponding polymers and applied in optoelectronics devices as materials themselves.     

Reaction of aromatic amines with vinyl alkyl ethers

Summary Aromatic amines such as aniline, p-anisidine, and p-bromoaniline in the presence of BF₃ etherate react with vinyl alkyl ethers to form 1-alkoxy-tetrahydroquinaldine derivatives.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12 p. 2221–2222, December, 1964     

Mesogenic aromatic esters with sulphur containing alkyl chains

A new series of aromatic esters, 1 and 2 with a sulphur atom in one of the side chains, is described. They exhibit nematic and/or smectic A/C mesophases as a function of the length of the alkyloxy chain. The presence of sulphur in the 4-position of the alkanoyloxy chain depresses both the clearing and the melting points with respect to the corresponding carbon analogues 3, resulting from the higher conformational mobility of the thiaalkyl chain. In 2, the presence of a methyl group in the 2-position of the alkanoyloxy chain induces a S_A phase below room temperature.     

Fluorescent aromatic polyamides with urea binding sites and fluorene or dansyl signaling units

This work describes six novel fluorescent aromatic polyamides with bulky dansyl or fluorene pendant groups or with the fluorene moiety in the main chain. The fluorescent signaling dansyl or fluorene moieties are chemically connected to, or within, the main polymer chains through a urea group, a well-known binding site in supramolecular chemistry. These polyamides are amorphous and soluble in polar aprotic solvents and demonstrate a film-forming capability. They also show yellowish-green or blue fluorescence in solution and in the solid state depending on the signaling unit, with the former corresponding to the dansyl and the latter to the fluorene residue. The water uptake and the thermal behavior have also been evaluated and related to the chemical structure. The polar amide, urea, and sulfonamide groups give rise to a high water sorption of up to 3.8 water molecules per repeating unit. The thermal behavior has been investigated by means of DSC and TGA. The glass transition temperatures of the polymers are high (up to 331 °C) and the decomposition temperatures (around 300 °C) are due to the moderate thermal stability of the urea group.     

Photodegradation of aromatic amines by Ag-TiO2 photocatalyst

The photocatalytic degradation of ortho, para and meta-nitroanilines (ONA, PNA and MNA) was investigated by Ag-TiO₂ suspension. The effect of some parameters such as the amount of photocatalyst, irradiation time of UV light, flow rate of O₂, pH, and temperature for the Ag-TiO₂ photocatalyst was also examined. Degradation of amines was small when the reaction was carried out in the absence of photocatalyst, and negligible in the absence of the UV light. Degradation rate of aniline derivatives decreases with increasing O₂ in the system. The effect of pH indicated that effective degradation occurred in alkaline conditions. Degradation kinetics of these aromatic amines can be described by Langmuir-Hinshelwood equation and shows pseudo-first order law.     

Synthesis and properties of wholly aromatic polymers bearing cardo fluorene moieties

Three series of aromatic polyamides, polyesters, and poly(1,3,4‐oxadiazole)s containing bulky fluorene structures were prepared from 9,9‐bis(4‐carboxyphenyl) fluorene. All of the polymers were readily soluble in many organic solvents and showed useful thermal stability associated with high glass‐transition temperatures in the range of 220–366 °C. These wholly aromatic polymer films were colorless, with high optical transparency, and exhibited UV‐vis absorption bands at 266–348 nm and photoluminescence maximum bands at 368–457 nm within the purple to green region in N,N‐dimethylacetamide (DMAc) solutions. The poly(amine‐amide) Ic exhibited excellent electrochromic contrast and coloration efficiency, changing color from the colorless neutral form to green and then to the dark blue oxidized forms with good stability of electrochromic characteristics. Almost all of these wholly aromatic polymer films were colorless and showed high optical transparency. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4352–4363, 2007     

Challenges in distinguishing superexchange and hopping mechanisms of intramolecular charge transfer through fluorene oligomers

The temperature dependence of intramolecular charge separation in a series of donor-bridge-acceptor molecules having phenothiazine (PTZ) donors, 2,7-oligofluorene FL(n) (n = 1-4) bridges, and perylene-3,4:9,10-bis(dicarboximide) (PDI) acceptors was studied. Photoexcitation of PDI to its lowest excited singlet state results in oxidation of PTZ via the FL(n) bridge. In toluene, the temperature dependence of the charge separation rate constants for PTZ-FL(n)-PDI, (n = 1-4) is relatively weak and is successfully described by the semiclassical Marcus equation. The activation energies for charge separation suggest that bridge charge carrier injection is not the rate limiting step. The difficulty of using temperature and length dependence to differentiate hopping and superexchange is discussed, with difficulties in the latter topic explored via an extension of a kinetic model proposed by Bixon and Jortner.     

N-heterocyclic carbene-catalyzed cross-coupling of aromatic aldehydes with activated alkyl halides

N-Heterocyclic carbene-catalyzed umpolung of aldehydes followed by their interception with diarylbromomethanes has been reported. This conceptually novel transition-metal-free cross-coupling of aldehydes with alkyl halides works well at low catalyst loadings and under mild reaction conditions leading to the formation of diaryl acetophenone derivatives in good yields. In addition, α-halo ketones and esters can also be used as aldehyde reaction partners.     

Amphipathic helices from aromatic amino acid oligomers

Synthetic helical foldamers are of significant interest for mimicking the conformations of naturally occurring molecules while at the same time introducing new structures and properties. In particular, oligoamides of aromatic amino acids are attractive targets, as their folding is highly predictable and stable. Here the design and synthesis of new amphipathic helical oligoamides based on quinoline-derived amino acids having either hydrophobic or cationic side chains are described. Their structures were characterized in the solid state by single-crystal X-ray diffraction and in solution by NMR. Results of these studies suggest that an oligomer as short as a pentamer folds into a stable helical conformation in protic solvents, including MeOH and H(2)O. The introduction of polar proteinogenic side chains to these foldamers, as described here for the first time, promises to provide possibilities for the biological applications of these molecules. In particular, amphipathic helices are versatile targets to explore due to their importance in a variety of biological processes, and the unique structure and properties of the quinoline-derived oligoamides may allow new structure-activity relationships to be developed.     

De-aggregation of polyfluorene derivative by blending with a series of poly(alkyl methacrylate)s with varying sidegroup sizes

A polyfluorene derivative of the PPV, poly(9,9′-n-dihexyl-2,7-fluorenedilvinylene-alt-1,4-phenylenevinylene), with a strong tendency to aggregation was blended with several members of a series composed by poly(alkyl methacrylate)s with the following substituents in the ester position: methyl, ethyl, isopropyl, isobutyl, n-butyl, and cyclohexyl. The de-aggregation effect in blends was studied by steady-state photoluminescence spectroscopy using several blend compositions. The efficiency of each dispersing phase was discussed in terms of the polymer miscibility, controlled by interaction parameters between the polyfluorene and every poly(alkyl methacrylate)s, here described using Hildebrand solubility parameters.     

Thermal reactivities of polynuclear aromatic hydrocarbons and alkyl derivatives

The HMO free valence, the PMO Dewar reactivity number, and the structure count ratio are correlated with thermal reactivities of polynuclear aromatic hydrocarbons and derivatives. The compounds are classified as thermally reactive if carbonaceous residues are observed upon heating to 750° (Experimental, Ref. 13). Radical intermediates are assumed to mediate the pyrolytic reactivities. The structure count ratio which is the ratio SC (radical intermediate) ÷ SC (reactant) is recommended as a simple working method for correlating and predicting thermal reactivity.     

Two novel oligomers based on fluorene and pyridine: Correlation between the structures and optoelectronic properties

To investigate the fine optoelectronic difference of the target oligomers with or without peripheral fluorene moieties, two dumbbell‐shaped oligomers ( F0 and F1 ) were designed and convergently prepared via Suzuki coupling reaction. The molecular structures of the oligomers were fully characterized by ¹H NMR, ¹³C NMR, and MALDI‐TOF mass spectra, respectively. The absorption, photoluminescent behavior, and energy band gaps of the oligomers were examined through UV–vis, photoluminescent spectra and cyclic voltammetry. The experimental results demonstrate that the absorption and photoluminescent properties are little affected by molecular architecture, while the absolute photoluminescence quantum efficiency of films and energy band gaps derived from cyclic voltammetry in solution are strongly correlated with the molecular frameworks. The observed energy band gaps of oligomers are further validated by the different molecular orbital contours of the HOMO energy levels from theoretical calculations. Preliminary electroluminescent investigations for F1 have also been conducted and discussed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1548–1558, 2008     

Principles of catalytic dehydrogenation of alkyl aromatic hydrocarbons

Russian Chemical Bulletin -     

Recent advances in the chemistry of aromatic cyclic oligomers

Development of an efficient and convenient means for preparation of aromatic cyclic oligomeric carbonates has made these materials available for a wide range of polymerization and processing studies. Building on the workbased on bisphenol A cyclics, recent efforts have concentrated on the preparation of new cyclics which afford polymers with properties substantially different from bisphenol A polycarbonate. Cyclic systems have been developed which lead to polycarbonates with improved solvent resistance, either through cross-linking or via crystallization. Polycarbonates with both high or low glass transition temperatures have also been achieved.     

Figure-eight thermal hysteresis of aminomethylenehelicene oligomers with terminal C16 alkyl groups during hetero-double-helix formation

1 : 1 mixtures of aminomethylenehelicene (P)-tetramer and (M)-pentamer with terminal C₁₆ alkyl groups in fluorobenzene showed structural changes between hetero-double-helices B and C and random-coils 2A. Figure-eight thermal hysteresis appeared when the solution was cooled and heated at a constant rate and involved the crossing of cooling and heating curves in Δε/temperature profiles. This unusual thermal hysteresis emerged in the intermediate state between counterclockwise and clockwise thermal hystereses. This phenomenon arose from the competition between self-catalytic reactions to form B and C from 2A. Significant effects of terminal C₁₆ alkyl groups on the thermodynamic and kinetic phenomena are also described.

1 : 1 mixtures of aminomethylenehelicene (P)-tetramer and (M)-pentamer with terminal C₁₆ alkyl groups in fluorobenzene showed structural changes between hetero-double-helices B and C and random-coils 2A.