Enhanced emission and its switching in fluorescent organic nanoparticles

A new class of organic nanoparticles (CN-MBE nanoparticles) with a mean diameter of ca. 30-40 nm, which exhibit a strongly enhanced fluorescence emission, were prepared by a simple reprecipitation method. CN-MBE (1-cyano-trans-1,2-bis-(4'-methylbiphenyl)ethylene) is very weakly fluorescent in solution, but the intensity is increased by almost 700 times in the nanoparticles. Enhanced emission in CN-MBE nanoparticles is attributed to the synergetic effect of intramolecular planarization and J-type aggregate formation (restricted excimer formation) in nanopaticles. On/off fluorescence switching for organic vapor was demonstrated with CN-MBE nanoparticles.     

Tunable phosphinite, phosphite and phosphoramidite ligands for the asymmetric hydrovinylation reactions

Only a limited number of ligands have been successfully employed for the Ni-catalyzed asymmetric hydrovinylation reaction. Diarylphosphinites, carrying β-acylamino groups prepared from readily available carbohydrates, in conjunction with highly dissociated counteranions {[(3,5-(CF₃)₂C₆H₃]₄B⁻ or SbF₆⁻}, effect the hydrovinylation of vinylarenes under ambient pressure of ethylene with high enantioselectivity. Nitrogen substituents such as -COCF₃ and COPh groups lead to isomerization of the primary products (3-arylbutenes) to Z- and E-2-aryl-2-butenes. In a prototypical synthesis of a 2-arylproionic acid, (S)-3-(4-bromophenyl)-1-butene (89% ee) has be transformed into (R)-ibuprofen by Ni-catalyzed cross-coupling with i-BuMgBr, followed by oxidation of the double bond with NaIO₄ and KMnO₄. Asymmetric codimerization of norbonene and ethylene using binaphthol-derived phosphoramidites as ligands gives 1:1, 2:1 or polymeric adducts depending on the relative configurations and nature of the BINAP and amine moieties. With one of the phosphoramidite-Ni complexes, counteranions BAr₄⁻ [Ar=3,5-(CF₃)₂C₆H₃] and SbF₆⁻, which had been used interchangeably in other reactions, give either a 1:1 adduct or a 2:1 adduct, respectively.     

Regioselective synthesis of pentasubstituted benzene derivatives: TBAF as an effective catalyst for the sequential Michael addition-intramolecular aldolization

Polysubstituted benzene derivatives were synthesized starting from the Baylis-Hillman adducts via the sequential introduction of primary nitroalkane at the primary position, Michael addition to β-branched Michael acceptor, aldol condensation, elimination of nitrous acid, and the final aromatization process.     

Isolation of essential oils from tobacco by gas co-distillation/solvent extraction

Summary The essential oils have been isolated from tobacco leaves using a simple gas co-distillation apparatus. The method involves co-distillation with water under the continuous stream of an inert gas with subsequent single solvent extraction of the distillate. The extract is analysed on GC and GC/MS in splitless injection mode without further concentration. The method was evaluated for reproducibility using n-octadecane as an internal standard. The distillation-extraction procedure was reporducible with an average deviation of ±3% for the major constituents. The present method was applied to the analyses of the essential oils of other agricultural products.Dedicated to Dr. L. S. Ettre on the occasion of his 60th birthday.     

Copper coupling of 1-chloro-2-iodo- and 1,2-di-iodo-perfluorocycloalkenes

Reductive coupling of 1-chloro-2-iodoperfluorocyclobutene (I), cyclopentene (III) and cyclohexene (VI) has been carried out with copper powder and a trace amount of dimethylformamide to give the corresponding 2,2′-dichloroperfluoro-(bi-1-cycloalken-1-yl) derivatives in 69%, 36% and 73% yield, respectively. A reduced by-product, 2H,2′H-dodecafluoro-(bi-1-cyclopenten-1-yl) was also obtained in the copper coupling of (III). Coupling of 1,2-di-iodoperfluorocyclobutene (IX) and cyclopentene (XII) under similar conditions gave good yields of cyclic trimers and tetramers. Mass spectra, infrared and ¹⁹F NMR data are discussed.