Photophysical and electrochemical properties of π-extended molecular 2,1,3-benzothiadiazoles

The reaction of 4,7-dibromo-2,1,3-benzothiadiazole with arylboronic acids (phenyl, 1-naphthyl, 4-methoxyphenyl, 4-chlorophenyl and 4-trifluoromethylphenyl) in the presence of catalytic amounts of a NCP-pincer palladacycle affords photoluminescent π-extended 4,7-diaryl-2,1,3-benzothiadiazoles 4a-e in high yields. These 4,7-diaryl-2,1,3-benzothiadiazoles exhibit high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-bis-naphthyl-2,1,3-benzothiadiazole 4b presents two different lifetimes (bi-exponential decay) due to the presence of two atropisomers. The Sonogashira coupling reaction of 4,7-diethynyl-2,1,3-benzothiadiazole 6 with the corresponding halo-aryl compounds (iodobenzene, 1-bromonaphthalene, 4-iodoanisole, 4-bromo-N,N-dimethylaniline and 2-bromopyridine) afforded the photoluminescent π-extended 4,7-bis-alkynylaryl-2,1,3-benzothiadiazoles 7a-e, also in high yields. These 4,7-diethynyl-2,1,3-benzothiadiazoles also present high fluorescent quantum yields, high electron affinities and adequate band gap values for testing as OLEDs. The 4,7-disubstituted-2,1,3-benzothiadiazoles 4a-e and 7a-e exhibit different electrochemical behavior. The presence of two ethynyl spacers in 2,1,3-benzothiadiazoles 7a-e shifts the reduction potentials to less cathodic values and also results in two well-defined and distinct reduction processes.     

Reductive sulfur extrusion reaction of 2,1,3-benzothiadiazole compounds: a new methodology using NaBH4/CoCl2·6H2O(cat) as the reducing system

A new simple and efficient methodology for reductive sulfur extrusion from 2,1,3-benzothiadiazole compounds has been developed using NaBH₄ in the presence of catalytic amounts of CoCl₂·6H₂O (1 mol %). This method is an efficient alternative for the generation of various 1,4-disubstituted-2,3-diaminobenzene derivatives from 4,7-disubstituted-2,1,3-benzothiadiazoles. The diamines can be easily converted into 4,7-disubstituted-quinoxaline compounds by simple reaction with glyoxal-sodium bisulfite.     

Synthesis and characterization of new linear pi-conjugated molecules containing bis(ethynylpyridine) units with a benzothiadiazole spacer

Three novel 4,7-bis(n-pyridylethynyl)-2,1,3-benzothiadiazoles (n = 2, 3, and 4) were synthesized by using the Sonogashira cross-coupling reaction of 4,7-dibromo-2,1,3-benzothiadiazole with the corresponding ethynylpyridines in the presence of a Pd(II) catalyst. The viologen analogues were also prepared by methylation of pyridyl nitrogen atoms. X-ray structure analysis of these compounds revealed the linear molecular structures with unusual columnar crystal structures. Insertion of a benzothiadiazole moiety into the acetylene-pyridine skeleton brings about a large increase in electron affinity and the bispyridyl compounds obtained here show high fluorescence quantum yields.     

Synthesis of 2,1,3-benzothiadiazolecarbonitriles

2,1,3-Benzothiadiazolecarbonitriles, 2 , have been prepared by two different methods. Reaction of bromo-2,1,3-benzothiadiazoles, 1 , with cuprous cyanide occurs advantageously in refluxing dimethylformamide to give 2 , complexed with curpous bromide. Hydrogen peroxide in hydrochloric acid at 30–40° is shown to be an effective reagent for efficient decomposition of these reactions complexes, 2 CuBr, and subsequent isolation of 2. Yields in the Sandmeyer method for preparing nitriles 2 were improved by diazotizing amino-2,1,3-benzothiadiazoles, 3 , with nitrosyl-sulfuric acid prior to reaction with the cuprous-sodium cyanide complex.     

Reactivity of 4-nitro- and 4-nitro-7-halogeno-2,1,3-benzothiadiazoles toward methoxide ion

4-Nitro-2,1,3-benzothiadiazole reacted with sodium methoxide (0.1-1 M) in methanol yielding 2,1,3-benzothiadiazole-4, 7-dione monoxime (syn+anti). Methoxy-dehalogenation of 4-nitro-7-halogeno-derivatives yielded 4-nitro-7-methoxy-2,1,3-benzothadiazole under similar conditions. In both eases transitions attributable to the formation of Meisenheimer complexes were detected.     

Oxidationsreaktionen methyl-substituierter 2,1,3-Benzothiadiazole und 2,1,3-Benzoselenadiazole mit Selen-dioxid

Oxidation Reactions of Methyl Substituted 2,1,3-Benzothiadiazoles and 2,1,3-Benzoselenadiazoles with Selenium Dioxide The synthesis 5–8 by oxidation of 4-methyl-( 1 ),5-methyl( 2 ), 5,6-dimethyl-2,1,3-benzoselenadiazole ( 3 ), and 5,6-dimethyl-2,1,3-benzothiadiazole ( 4 ), respectively, with selenium dioxide as well as their spectroscopic properties are described.     

Site-selective formation of N-arylmethylimidazoles and C-arylimines in the reaction of 4,5-diamino-2,1,3-benzothiadiazole with aromatic aldehydes

Regioselective formation of N-arylmethylimidazoles and C-arylimines was found in the reaction of 4,5-diamino-2,1,3-benzothiadiazole with selected aromatic aldehydes. The regiochemistry of the reaction products was confirmed by single crystal X-ray analysis. Gibbs free energy calculation using DFT method at the B3LYP/6-31G(d) level supports the regio-selectivity observed. The 4-imine obtained in the reaction of 4,5-diamino-2,1,3-benzothiadiazole with pyrene-1-carboxaldehyde showed an unusually low magnetic field shift of the imine proton that was reproduced by molecular calculations.     

Nitro derivatives of 2,1,3-benzothiadiazole 1-oxides: synthesis,structural study,and NO release

A convenient one-pot synthesis of nitro derivatives of 2,1,3-benzothiadiazole 1-oxides by the reaction of o-nitroanilines with sulfur monochloride was developed. The structural features of 4-nitrobenzothiadiazole and its N-oxide were considered. High in vitro release of nitric oxide (69%) was found for a 6-nitro-2,1,3-benzothiadiazole sample by the Griess assay, which indicated good prospects for this class of compounds.     

Benzo[c]fused isothiazoles. II. Synthesis of some angular isothiazolo[c]benzothiadiazoles. An anomalous amination reaction

The syntheses and pmr properties of the angular isothiazolo[c]-2,1,3-benzothiadiazoles ( 1 and 2 ) are described. An unusual electrophilic amination reaction with N-sulfinylmethanesulfonamide is discussed.     

Transformations of some 6- and 7-substituted 1,2,3-benzothiadiazoles

The preparation of some 6- and/or 7-substituted derivatives of 1,2,3-benzothiadiazole is described. The reactivity of some compounds was investigated in view of the possibility that 1,2,3-benzothiadiazoles may behave as masked diazo compounds. 7-Diazo or diazonium compounds were prepared but no interaction with the thiadiazole part could be observed.     

Efficient palladium-catalyzed C-S cross-coupling reaction of benzo-2,1,3-thiadiazole at C-5-position: A potential class of AChE inhibitors

Functionalization of 2,1,3-benzothiadiazole (BTD) with thiols at C-5 position remains low explored. Moreover, the arylthiol-substitutions at this position are also unexplored and can not be found by a S_N2 or S_N1 reaction. In this sense, herein we present a new palladium-catalyzed methodology for a wide variety of unpublished 5-arylsulfanyl-benzo-2,1,3-thiadiazole derivatives synthesis with moderate to high yields using a low catalytic loading of Pd(L-Pro)₂ as low-coast, and efficient catalyst in low reaction time. Besides, we concluded that the pKa of thiol species has an important role in this catalysis, mainly in the CMD like catalytic cyclo process, which strongly interferes in the reaction yields. Furthermore, arylsulfanyl-benzo-2,1,3-thiadiazoles derivatives have been assessed (in vitro) as potential acetylcholinesterase inhibitors.     

Cyclic aryleneazachalcogenenes. Part III [1] synthesis of polyfluorinated 2,1,3-benzothia-(selena) diazoles

1-(4-X-Tetrafluorophenyl)-3-trimethylsilyl-1,3-diaza-2- thiaallenes (X = H, CH₃, Br, F, CF₃) treated with CsF in acetonitrile or THF cyclized to 6-X-4,5,7-trifluoro-2,1,3-benzothiadiazoles whose reduction led to the corresponding 1,2-diamino- benzenes. Cyclization of the latter with SeCl₄ gave 6-X-4,5,7- trifluoro-2,1,3-benzoselenadiazoles.     

The electron-impact-induced fragmentation of 1,2,3-benzotriazoles and some related compounds

The mass spectra of 1,2,3-benzotriazole and some derivatives with substituents at the 1-position and in the benzenering have been examined. The loss of N₂from the molecularion is characteristic; loss of N₂ plus the 1-substituent is also common. Structures are proposed for these fragment ions. The relative ease of loss of N₂, NO and NS from the molecular ions of benzotriazole, 2,1,3-benzodiazole, 1,2,3- and 2,1,3-benzothiadiazoles is compared.     

胺烷基侧链取代三苯胺类红光聚合物的合成及性能研究

通过Suzuki偶合反应合成了一系列胺烷基侧链取代的基于三苯胺和芴的共轭聚合物聚[4-(N,N-二甲基胺丙氧基)苯-4,4′-二苯胺-9,9-二辛基芴-4,7-二噻吩-2-基-2,1,3-苯并噻二唑](PFTD), 并对其化学结构和光电性能进行了表征. 末端胺基的存在提高了此类聚合物作为发光层应用于聚合物电致发光器件的性能(采用高功函数的金属铝作为阴极时). 结构为ITO/PVK/PFTD-5(DBT摩尔分数为5%时的聚合物)/Al的器件最大电致发射峰位于647 nm, 最大外量子效率达到了1.24%.     

A New Route to N-Alkyl-o-phenylenediamines Utilising N-Alkyl-2,1,3-benzothiadiazolium Salts and Their Selenium Analogues

The alkyl quaternary salts of 2,1,3-benzothiadiazole and 2,1,3-benzoselenadiazole undergo facile ring-opening to produce the corresponding N-alkyl-o-phenylenediamines.     

1,2,5-Thiadiazole 2-oxides: selective synthesis,structural characterization,and electrochemical properties

A new general procedure for the selective synthesis of 1,2,5-thiadiazole 2-oxides (including fused derivatives) 8a,b,c,g,h from the reaction of vic-glyoximes with S₂Cl₂ and pyridine in acetonitrile was elaborated together with general procedure for the synthesis of 1,2,5-thiadiazoles 7a–i, 10, 12, and 14 from the same starting materials and reagents. Molecular structures of 3,4-dimethyl-1,2,5-thiadiazole 2-oxide 8a and [1,2,5]thiadiazolo[3,4-b]quinoxaline 10 were confirmed by single-crystal X-ray diffraction. Electrochemical properties of 1,2,5-thiadiazole 2-oxides 8 were studied by cyclic voltammetry and different behavior was observed for monocyclic and benzo-fused derivatives. With compounds 8g and 17, previously unknown deoxygenation of 2,1,3-benzothiadiazole 1-oxides was discovered by electrochemical reduction, and resulted 2,1,3-benzothiadiazoles 7g and 19 were detected in the forms of their radical anions by EPR spectroscopy combined with DFT calculations.     

Comparative study on polymer light-emitting devices based on blends of polyfluorene and 4,7-di-2-thienyl-2,1,3-benzothiadiazole with devices based on copolymer of the same composition

The small molecule 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) dye has been synthesized and blended into blue-emitting polyfluorene as a host. The photophysics of the blend films and electroluminescence device performance was compared with that from polyfluorene-co-4,7-di-2-thienyl-2,1,3-benzothiadiazole (PFO-DBT) copolymer of the same molar composition, with DBT incorporated covalently into the polyfluorene backbone. The role of intra- and interpolymer chain interaction and energy transfer in the polymer light-emitting devices are discussed. On the basis of the direct comparison of blend and copolymer from the same molecular composition, we can draw the conclusion that, in conjugated polymers, intrachain energy transfer along the polymer backbone is more efficient than that via interchain interaction and plays a more important role in polymer light-emitting devices.     

An improved synthesis of tetrabromo-2,1,3-benzothiadiazoie

An improved synthesis of tetrabromo-2,1,3-benzothiadiazole using bromine and reduced iron powered is presented.     

EPR measurements of the phosphorescent state of 2,1,3-benzothiadiazole

The spin dipolar interaction and the hyperfine structure of the phosphorescent state of 2,1,3-benzothiadiazole have been measured in a naphthalene host crystal at 77 K. Preliminary transient study indicates the short in-plane spin substate is the active component in the triplet population.     

Applications of proton magnetic resonance spectroscopy to structural problems—XXXIV: Partial bond fixation in bicyclic heteroaromatic compounds

NMR spectral parameters are reported for benzofurazan, 1,2,3- and 2,1,3-benzothiadiazole, and 1-methyl- and 2-methyl-benzotriazole. The coupling constants are discussed in connection with the aromaticity of these compounds and the occurrence of partial bond fixation.