Thermally stable polymers based on 1,3,4-oxadiazole rings

<正>In the present work,new thermally stable polymers containing 1,3,4-oxadiazole units have been synthesized through Huisgen reaction of the aromatic bis-tetrazole compounds with the aromatic/aliphatic bis-acid chlorides in pyridine as solvent.The obtained polymers are insoluble or slightly soluble in polar aprotic solvents such as DMSO and DMF. Thermal analyses of the polymers using DSC and TGA techniques showed that the polymers had improved thermal stabilities.The model reaction was also investigated and the resulting bis-l,3,4-oxadiazole compounds were characterized by conventional spectroscopic methods.     

Polyamides with pendant 1,3,4-oxadiazole and pyridine moieties

A novel aromatic diamine,2-（5-（3,5-diaminophenyl）-l,3,4-oxadiazole-2-yl）pyridine（POBD）,containing a pyridine ring and a 1,3,4-oxadiazole moiety,was synthesized.It was used in a polycondensation with various aromatic and aliphatic diacid chlorides to generate a series of new aromatic polyamides with pendant 1,3,4-oxadiazole groups.The prepared polyamides were characterized by IR,elemental analysis and through the synthesis of model compounds.Thermophysical properties of the synthesized polyamides have been studied by DSC,TGA and inherent viscosity measurements. Relatively high inherent viscosity values（0.76-1.62 dL/g,in 0.125%H₂SO₄ at 25℃） were observed for these compounds. Number average molecular weight（M_n） of the polymers was measured by vapor phase osmometry（VPO）.The introduction of bulky side chains in the structure of aromatic polyamides led to increased solubility of these polymers in common polar and aprotic solvents,such as DMF,DMSO,NMP and DMAc,which allowed thin films to be cast from polymer solutions. The highest molecular weight（M_n = 51190） was observed for polymer（DC）,which was prepared from pyridine-2,6-dichlorocarbonyl.     

Columnar liquid crystalline benzenetrisamides with pendant 1,3,4-oxadiazole groups

Novel liquid crystal materials based on 1,3,5-benzenetrisamide derivatives with three pendant 2-phenyl-5-(mono-, di-, and/or tri-n-alkoxyphenyl)-1,3,4-oxadiazole arms (Ia–c, IIa–c) were prepared. The mesomorphic properties of these compounds were characterised and studied by differential scanning calorimetry, polarising optical microscopy and X-ray diffraction. The formation of a columnar mesophase was found to be dependent on the number of alkoxy side chains. The compounds Ib and IIb, with a total of six alkoxy chains, and compounds Ic and IIc, with nine alkoxy chains, exhibited an enantiotropic hexagonal columnar (Col_h ) phase with high isotropisation temperatures; however, compounds Ia and IIa with a total of three alkoxy chains formed a crystalline phase. Compounds IIb and c were room temperature liquid crystals.     

对称双-1,3,4-噁二唑化合物的合成及性质

首先以苯氧乙酰肼和二酰氯为原料反应得到对称双酰肼化合物,再以POCl3合环得到系列对称双-1,3,4-噁二唑化合物。考察了该系列化合物的紫外-可见吸收光谱,其中,间苯双-1,3,4-噁二唑化合物在250nm附近有明显的最大吸收峰,对苯双-1,3,4-噁二唑化合物的最大吸收峰则红移至290nm附近;而脂肪族双-1,3,4-噁二唑化合物没有明显的最大吸收峰,说明没有大的共轭体系,与结构相符合。所有化合物的结构均经元素分析、IR、1H NMR和MS确证。     

Thermally stable silarylene-1,3,4-oxadiazole polymers

The effects of incorporating a p-phenylene- (or m-phenylene)-1,3,4-oxadiazole fragment into the backbone of poly[1,4-phenylene(diphenylsilyl)-1,4-phenylene-2,5-(1,3,4-oxadiazole)], which was developed by the authors, was investigated. Bis[(p-carbohydrazidophenyl)]diphenylsilane was copolymerized with dipentachlorophenyl terephthalate or isophthalate to produce the prepolymers poly[N-(p-diphenylsilylbenzoyl)-N′N″-(terephthaloyl)-N″′-(p-benzoyl)dihydrazide] and poly[N-(p-diphenylsilylbenzoyl)-N′,-N″-(isophthaloyl)-N″′-p-(benzoyl) dihydrazide], respectively. The polyhydrazides were converted by thermal dehydration into poly[1,4-phenylene(diphenylsilyl)-1,4-phenylene-(1,3,4-oxadiazole-2,5-diyl)-1,4-phenylene-2,5-(1,3,4-oxadiazole)] and poly[1,4-phenyl-ene(diphenylsilyl)-1,4-phenylene-(1,3,4-oxadiazole-2,5-diyl)-1,3,4-(oxadiazole)]. The new polymers were soluble in organic solvents. Films cast from these solutions exhibited good adhesion to glass and metal surfaces. Thermal analysis showed that the heat stability of all these polymers was about the same and that they were resistant to decomposition when heated in air to about 400°C. The results also indicated that these polymers were somewhat less heat-resistant than samples of poly-[1,4-phenylene(diphenylsilyl)-1,4-phenylene-2,5-]1,3,4-(oxadiazole) synthesized from bis(p-carbohydrazidophenyl)diphenylsilane and bis-(p-carbopentachlorophenoxy-phenyl)diphenylsilane.     

Vinyl copolymers containing pendant 1,3,4-oxadiazole chromophores: Preparation and electrochemical and electroluminescent properties

Three vinyl copolymers (P1–P3) containing pendant aromatic 1,3,4-oxadiazole derivatives were prepared from their precursor poly(styrene-ran-4-vinylbenzyl chloride) (weight-average molecular weight = 11,400, polydispersity index = 1.18), which had been synthesized by controlled radical polymerization (reversible addition–fragmentation chain transfer). The copolymers were readily soluble in common organic solvents and were basically amorphous materials with 5% weight loss temperatures higher than 360°C. The photoluminescence spectroscopy results revealed that the architectures of P2 and P3 suppressed aggregate formation in the solid state. The LUMO levels of P2 (−3.10 eV) and P3 (−3.09 eV), estimated from cyclic voltammetry data, were much higher than that of P1 (−3.81 eV). The HOMO levels were in the order of P3 (−5.37 eV) > P2 (−5.77 eV) > P1 (−5.96 eV). However, both the HOMO and LUMO levels of P1–P3 were much lower than that of poly[2-methoxy-5-(2′-ethylhexoxy)-p-phenylenevinylene] (MEH-PPV) because of the electron-withdrawing characteristics of the pendant aromatic 1,3,4-oxadiazole groups. The luminance (5860 cd/m²) and current efficiency (1.45 cd/A) of an electroluminescence device [indium tin oxide/poly(3,4-ethylene dioxythiophene)/MEH-PPV/Al] were improved significantly to 16,261 cd/m² and 4.79 cd/A, respectively, through blending with P2 (50/50). This study suggests that copolymers P1–P3 are versatile materials for electron-transport/injection applications. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2259–2272, 2007     

Synthesis and photophysical properties of new carbon-chain copolymers with europium-containing and carbazole fragments in pendant chains

Functionalized polynorbornenes with terpyridine and carbazole groups in pendant chains were prepared by metathesis copolymerization. The polymeric products prepared react with europium thenoyltrifluoroacetonate to form new carbon-chain copolymers with different ratios of organic and europium-containing units. The polymeric materials prepared were characterized by IR and NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and elemental analysis. All the europium-containing copolymers exhibit strong metal-centered photoluminescence in solution and in thin film.     

Synthesis and properties of naphthalene trimers linked by 1,3,4-oxadiazole spacers

Two types of naphthalene trimers linked by 1,3,4-oxadiazole spacers were synthesized and investigated for their physical and electronic properties. 2,6- and 2,7-isomers on central naphthalene moieties were obtained in the forms of pale yellow solids and colorless crystals, respectively. The melting point of the 2,6-isomer was higher than that of the 2,7-isomer. An X-ray crystallographic analysis revealed a π-stacked column with a short intermolecular distance in the crystals of the 2,6-isomer. The absorption maximum of the 2,6-isomer was red-shifted as compared to that of the 2,7-isomer, indicating a π-conjugation between di-2-naphthyloxadiazole moieties in the 2,6-isomer. The quantum yields of the 2,6- and 2,7-isomers were measured to be 0.97 and 0.74, relative to that of 2,5-di-2-naphthyl-1,3,4-oxadiazole (0.85). Molecular orbital (MO) calculations demonstrated that the 2,6-isomer had a higher electron affinity than the 2,7-isomer. Thus, the crosslinking of building blocks is important for the design of functional materials.     

Synthesis of substituted 1,3,4-oxadiazole derivatives

Monosubstituted oxadiazoles were synthesized by the reaction of hydrazides with triethyl orthoformate. Their reactions with benzoyl chloride gave benzoylcarbohydrazides, which under the action of thionyl chloride were cyclized to the respective 2,5-disubstituted oxadiazoles. 1-Aryl-4-(5-thioxo-4,5-dihydro-1,3,4-oxadiazol-2-yl)-pyrrolidin-2-ones were synthesized from acid hydrazides using carbon disulfide under basic conditions. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 269-272, February, 2009.     

微波促进下2,5-二取代-1,3,4-(口恶)二唑衍生物的合成

报道了微波促进无溶剂条件下二酰基肼可以良好产率脱水闭环得到2，5-二取代-1，3，4-E二唑衍生物。反应产率受取代基影响较大，苯基取代时产率较高，烷基取代时产率较低；反应产率与所用的无机支持有关，其中以酸性三氧化二铝的效果最佳。此法不仅环境友好且操作安全，避免使用化学脱水剂。     

Synthesis and photophysical properties of conjugated polymers with pendant 9,10-anthraquinone units

We have synthesized and investigated the photophysical properties of a series of electron-donor conjugated copolymers with pendant electron-acceptor units. The copolymers consist of diethynyl-1,4-phenylene, fluorene, or phenylene rings alternating with a phenylene unit bearing a pendant 9,10-anthraquinone moiety. The pendant donor-acceptor polymers were designed to have different optical pi-pi* band gaps, while the oxidation potential of the polymer backbone remains approximately constant in the series. The reduction potential of the donor-acceptor polymers is associated with the pendant acceptor units. This leads to the special situation that the electrochemical gap between oxidation and reduction potentials is constant, while the optical band gap decreases, going from PPP, via PPF, to PPE. This design is used to study the effect of the optical gap on the photoinduced electron-transfer reaction that occurs between the main chain electron donor and the pendant acceptor, while the same polymer architecture and energy of the charge separated state are maintained. Fluorescence and photoinduced absorption spectroscopy are used to study the electron transfer following photoexcitation in relation to solvent polarity and in thin solid films. For the fluorene-phenylene alternating copolymer, intramolecular photoinduced electron transfer occurs in the Marcus optimal region.     

Synthesis of nitrophenyl derivatives of 1,3,4-oxadiazole

Acylation of nitrobenzhydrazides with nitrobenzoyl chlorides and ethyl chlorocarbonate yielded a number of corresponding 1,2-diacylhydrazines, which were converted by the action of phosphorus oxychloride to nitro-substituted 2,5-diphenyl- and 2-phenyl-5-ethoxy-1, 3,4-oxidazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 741–743, June, 1977.     

Synthesis and rare earth metal ion-sensing properties of aza-crown derivative incorporating with diaryl-1,3,4-oxadiazole

A new fluorescent chemosensor (A18C6-Ox) in which a monoaza-18-crown-6 is linked to a diaryl-1,3,4-oxadiazole fluorophore by a methylene spacer has been synthesized to evaluate binding interaction with the rare earth ions by means of absorption and emission spectrophotometry. Absorption spectra of A18C6-Ox showed a broad band at 289nm and there was no significant change in the presence of Sc3+, La3+, Pr3+, Sm3+, Gd3+, Tb3+, Yb3+ and Lu3+ except for Ce3+ and Eu3+. From the emission spectral change of A18C6-Ox, interaction of the rare earth ions with A18C6-Ox is very strong. The formation of A18C6-Ox complexing with Sc3+, La3+, Pr3+, Sm3+, Gd3+, Tb3+, Yb3+ and Lu3+ leads to an increase in fluorescence intensity of A18C6-Ox, while Ce3+ and Eu3+ ions interact strongly causing fluorescence quenching of A18C6-Ox. In addition, the optimal complexation stoichiometry of the rare earth ions with A18C6-Ox was investigated by the fluorescent titration.     

Synthesis, structure, and photoelectrochemical properties of new tetrathiafulvalene-diphenyl-1,3,4-oxadiazole dyads

New donor-acceptor dyads containing tetrathiafulvalene (TTF) and 2,5-diphenyl-1,3,4-oxadiazole (PPD) moieties were synthesized to develop new photoconducting materials. Crystal structure analysis indicated the highly planar molecular skeleton of the dyad. Fluorescence from the PPD part was almost quenched by the intramolecular electron transfer from the TTF part to the PPD part. Photoelectrochemical measurements indicate that cathodic photocurrents can be generated from a thin film of the dyad spin-coated on ITO electrode.     

Synthesis of macrocycles containing 1,3,4-oxadiazole and pyridine moieties

A series of peptide-like 25–28 membered macrocycles containing 1,3,4-oxadiazoles and pyridines bearing a chiral center scaffold have been synthesized by using known coupling reagents and common protecting groups. The yield of the purified macrocycles was poor on an average, yet it seems to be independent of amino acid substitution or stereochemistry. These macrocycles represent a new class of structures for further development and for future application in high-throughput screening against a variety of biological targets.     

2,5-双取代-1,3,4-噁二唑类化合物的合成与表征

以3-( 4-氟苯基) -1H-吡唑-5-甲酸乙酯为原料,与H2NNH2?H2O发生肼解生成3-( 4-氟苯基) -1H-吡唑-5-甲酰肼,再与CS2环化生成2-巯基噁二唑中间体,最后在巯基上进行烷基化反应合成了一系列新型的2-硫醚-5-吡唑基-1,3,4-噁二唑类化合物,并利用IR、1H NMR、HRMS等波谱技术对目标化合物结构进行了表征。该合成方法具有原料易得,后处理简便,收率较高的优点。     

Dendrimers with 1,3,4-oxadiazole units, 1. Synthesis and characterization

The synthesis and characterization of two unsymmetrically substituted star-shaped oxadiazoles and of a dendrimer of the first generation are described. The key step in the synthesis is the intramolecular ring transformation of aromatic tetrazoles. The well-defined compounds form stable amorphous glasses with high glass transition temperatures up to 222°C. They are promising candidates for organic light emitting diodes.     

Synthesis and spectral-luminescence properties of hetarylethylene derivatives of 2,5-diphenyloxazole and 2,5-diphenyl-1,3,4-oxadiazole

A number of new organic luminophores was synthesized by PO olefination from 2- (4-bromomethylphenyl)-5-phenyloxazole and -1,3,4-oxadiazole and various heterocyclic aldehydes that contain a furan ring. The absorption and fluorescence spectra of the products in toluene, as well as their scintillation characteristics, were measured. The effect of the electronic nature of the substituents on the spectral-luminescence properties of the luminophores is discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 617–621, May, 1982.     

Synthesis and characterization of mono- and bicyclic heterocyclic derivatives containing 1,2,4-triazole, 1,3,4-thia-, and -oxadiazole rings

A series of new N- and S-substituted 1,3,4-oxadiazole derivatives were synthesized. 5-Pyridin-3-yl-3-[2-(5-thioxo-4,5-dihydro-l,3,4-thiadiazol-2-yl)ethyl]-1,3,4-oxadiazole-2(3H)-thione and 5-[(5-(pyridin-3-yl)-1,3,4-oxadiazol-2-ylthio)methyl]-N-phenyl-1,3,4-thiadiazol-2-amine were formed by cyclization of 3-(5-pyridin-3-yl-2-thioxo-1,3,4-oxadiazol-3(2H)-ylpropanimidohydrazide and 2-[(5-pyridin-3-yl-1,3,4-oxadiazol-2-yl)thio]thiosemicarbazide with CS₂ and H₂SO₄. On the other hand, a number of new bicyclic 1,2,4-triazolo[3,4-b][1,3,4]thiadiazole derivatives were synthesized. 6-Pyridin-3-ylbis[1,2,4]‐triazolo[3,4-b:4′,3′-d][1,3,4]thiadiazole-3(2H)-thione was synthesized by reaction of 6-(hydrazino)-3-pyridine-3-yl[1,2,4]triazolo[3,4-b][1,3,4]thiadiazole with CS₂/KOH/EtOH. The structures of the newly synthesized compounds were elucidated by the spectral and analytical data IR, Mass, and ¹H NMR spectra. Correspondence: Adel A.-H. Abdel-Rahman, Department of Chemistry, Faculty of Science, Menoufia University, Shebin El-Koam, Egypt; Wael A. El-Sayed, National Research Centre, Department of Photochemistry, Cairo, Egypt.