34 research outputs found
Vers des nanorubans aromatiques : approches par formation de céramidonines et par réaction de Perkin
No full textLes nanorubans de graphène (NRGs) sont des matériaux prometteurs pour l'organique électronique, à mi chemin entre polymères conjugués et nanotubes de carbone. Deux approches différentes pour la synthèse de nanorubans aromatiques sont développées et évaluées. La première est fondée sur la formation de céramidonines par cyclisation d'arylamino-anthraquinones en milieu acide. Plusieurs tétraaza-arènes incorporant deux de ces unités sont obtenus, mais l'approche s'est uniquement avérée appropriée dans le cas de courts substrats. La seconde approche repose sur la condensation d'acides aryle-acétiques avec des formylarènes ou acides aryle-glyoxyliques, suivie soit de cyclo-deshydrogénations en présence de quinone, soit de deshydrodebromation catalysée par le palladium, pour donner des arenes carboxy-substitués allongés. La méthode impliquant la quinone s'avère limitée à des substrats suffisamment réactifs tels que des thiophènes et laisse envisager des poly(arènodithiophènes) en partie rigidifiés et carboxy-substitués. La catalyse au palladium s'avère plus générale, ouvrant des perspectives d'obtention d'une grande variété de rubans aux propriétés électroniques ajustables.Graphene nanoribbons (GNRs) are promising materials for organic electronics, as they bridge the gap betweensingle-stranded conjugated polymers and carbon nanotubes. Two different synthetic approaches to GNRs aredeveloped and evaluated. The first approach is based on the acid-promoted cyclisation of arylaminoanthraquinonesto ceramidonines. Tetraazaarenes with two ceramidonine units are obtained, but the approachis found to be appropriate only to such small systems. The second approach is based on the condensation ofarylacetic acids with arenecarboxaldehydes or arylglyoxylic acids, followed either by quinone-assistedoxidative cyclodehydrogenation or palladium-catalysed dehydrodebromination to yield carboxy-substitutedelongated arenes. The quinone-based variant is found to be limited to reactive substrates such as thiophenederivatives and offers the perspective of partially rigidified carboxy-substituted poly(arenodithiophenes). Thepalladium-based variant is found to be more general, opening the prospect of obtaining a variety of ribbontypestructures with tunable electronic properties
The ceramidonine and perkin approaches to aromatic nanoribbons
No full textLes nanorubans de graphène (NRGs) sont des matériaux prometteurs pour l'organique électronique, à mi chemin entre polymères conjugués et nanotubes de carbone. Deux approches différentes pour la synthèse de nanorubans aromatiques sont développées et évaluées. La première est fondée sur la formation de céramidonines par cyclisation d'arylamino-anthraquinones en milieu acide. Plusieurs tétraaza-arènes incorporant deux de ces unités sont obtenus, mais l'approche s'est uniquement avérée appropriée dans le cas de courts substrats. La seconde approche repose sur la condensation d'acides aryle-acétiques avec des formylarènes ou acides aryle-glyoxyliques, suivie soit de cyclo-deshydrogénations en présence de quinone, soit de deshydrodebromation catalysée par le palladium, pour donner des arenes carboxy-substitués allongés. La méthode impliquant la quinone s'avère limitée à des substrats suffisamment réactifs tels que des thiophènes et laisse envisager des poly(arènodithiophènes) en partie rigidifiés et carboxy-substitués. La catalyse au palladium s'avère plus générale, ouvrant des perspectives d'obtention d'une grande variété de rubans aux propriétés électroniques ajustables.Graphene nanoribbons (GNRs) are promising materials for organic electronics, as they bridge the gap betweensingle-stranded conjugated polymers and carbon nanotubes. Two different synthetic approaches to GNRs aredeveloped and evaluated. The first approach is based on the acid-promoted cyclisation of arylaminoanthraquinonesto ceramidonines. Tetraazaarenes with two ceramidonine units are obtained, but the approachis found to be appropriate only to such small systems. The second approach is based on the condensation ofarylacetic acids with arenecarboxaldehydes or arylglyoxylic acids, followed either by quinone-assistedoxidative cyclodehydrogenation or palladium-catalysed dehydrodebromination to yield carboxy-substitutedelongated arenes. The quinone-based variant is found to be limited to reactive substrates such as thiophenederivatives and offers the perspective of partially rigidified carboxy-substituted poly(arenodithiophenes). Thepalladium-based variant is found to be more general, opening the prospect of obtaining a variety of ribbontypestructures with tunable electronic properties
Modular synthesis of oligoacetylacetones via site-selective silylation of acetylacetone derivatives
No full textOligoacetylacetones consisting of 3,3-disubstituted pentane-2,4-diones were synthesized through a terminal silylation and oxidative coupling protocol. Highly selective formation of mono-enol silyl ethers of 3,3-disubstituted acetylacetones was achieved using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as a base. Subsequent silver(i) oxide mediated coupling reactions provided tetraketones. Unique substituent dependence was found for the terminal-selective silylation of tetraketones. Finally, octaketones (tetramers of acetylacetone derivatives) with three types of monomer sequences were prepared in their discrete forms. Single crystal X-ray analysis revealed that the solid-state conformations of oligoketone chains were predominantly governed by the ketone sequence rather than substituents. However, differences in the packing structures induced by alkyl substituents led to significant differences in melting points for the structural isomers of octaketones
FAILURE IN SOMATIC PAIRING OF 4TH CHROMOSOME IN CHIRONOMUS STRIATIPENNIS KIEFFER (DIPTERA: CHIRONOMIDAE)
No full textPolytene chromosomes of Chironomus striatipennis Kieffer were studied in terms of pollution in natural habitats and the polytene chromosomes of the species appeared as paired homologous chromosomes of the flies in the somatic cells at interphase stage. The polytene chromosomes obtained from the flies, collected from polluted environment, exhibited asynapsis along the polytene chromosome arms. Asynapsis along the fourth polytene chromosome in this species was most prominent. The larvae grown in artificially developed polluted condition in the laboratory with addition of Cu as heavy metal in the culture medium also exhibited asynapsis of the fourth polytene chromosome and at higher dose i.e., 15 mg/kg of soil in the substratum of the culture tray the larvae showed almost complete asynapis of the fourth chromosomes. Hence, the organization of the polytene chromosome may be an index for assessing the polluting condition of the environment where the Chironomid larvae grow
Dipyreno- and diperyleno-anthracenes from glyoxylic Perkin reactions
No full textTwofold Perkin condensation of 2,5-dibromophenylene-1,4-diacetic acid with arylglyoxylic acids followed by cyclo-dehydrobromination leads to dipyreno- and diperyleno-anthracene tetraesters and diimides. The imides show surprisingly large absorption shifts versus the esters, illustrating that electron-withdrawing substituents at the anthracene unit efficiently impart long wavelength absorption in such electrondeficient graphene nanoribbon fragments
Luminescent Coordination Polymers Constructed from a Flexible, Tetradentate Diisopyrazole Ligand and Copper(I) Halides
No full textOne- and two-dimensional coordination polymers composed of a structurally flexible, tetradentate diisopyrazole ligand and copper(I) halides were synthesized as crystalline solids. Complexation with copper(I) chloride or bromide resulted in the formation of infinite coordination chains through connecting each diisopyrazole ligand with two copper(I) ions in a trigonal planar coordination geometry. Contrarily, the combination of a diisopyrazole ligand and copper(I) iodide gave a two-dimensional coordination network comprising Cu4I4 units with stair-step type geometry and diisopyrazoles that acted as both tetradentate and bidentate bridging ligands. All the coordination polymers exhibited visible photo-emission upon UV irradiation, and the Cu4I4 complex showed thermochromic behavior
Does Foreign Direct Investment Promote Growth? Panel Data and Time Series Evidence from Less Developed Countries, 1970-2002
No full textThe present study casts some doubt on the growth-promoting effect of foreign direct investment (FDI), which is widely supported by the proponents of financial globalization. The panel data analysis of 51 less developed countries shows a rising relationship between growth and FDI (relative to gross capital formation) only for the group of 11 relatively rich and open-economy countries. The time-series analysis observes meaningful positive relationships between FDI and growth only for 3 countries belonging to this group and some other countries. But by and large no long-term positive relationship exists between the two irrespective of income levels, openness and FDI-dependence.Foreign Direct Investment; Financial Globalization; Liberalization
Modular synthesis of oligoacetylacetones via site-selective silylation of acetylacetone derivatives
No full text
