HERACLES : a multidetector for heavy-ion collisions at TRIUMF

HERACLES is a multidetector that has been modified to study heavy-ion collisions, using an ion beam with an energy range between 8 to 15 MeV per nucleon. It has 78 detectors axially distributed around the beam axis in 6 rings allowing detection of multiple charged fragments from nuclear reactions. HERACLES has 4 different types of detectors, BC408/BaF₂ phoswich, Si/CsI(Tl) telescope, BC408/BC444 phoswich and CsI(Tl) detectors. ²⁵ Na?+?¹² C, ²⁵ Na?+?²⁷ Al, ²⁵ Mg?+?¹² C and ²⁵ Mg?+?²⁷ Al reactions have been used to characterize the multidetector. Element identification up to Z = 12 is achieved with the BC408/BaF₂ phoswich detectors, up to Z = 15 with the Si/CsI(Tl) telescopes and up to Z = 12 with the BC408/BC444 phoswich detectors. Isotopic identification is reached with the CsI(Tl) detector up to Z = 2.     

Direct laser printing for high efficiency silicon solar cells fabrication

Silicon solar cells still require cost reduction and improved efficiency to become more competitive. New architectures can provide a significant increase in efficiency, but today most of the approaches need additional fabrication steps. In this context, laser processing offers a unique way to replace technological steps like photolithography that is not compatible with the requirements of the photovoltaic industry. In particular laser induced thermal effects can be used to activate or re-organise dopants at the silicon surface to design new emitter geometries. In this paper dopant diffusion using a nanosecond UV laser on phosphorous-doped silicon emitters is studied. The presence of a phosphosilicate glass underneath a silicon nitride layer leads to a local decrease of the emitter sheet resistance from 100 Ω/sq to 20 Ω/sq. Laser induced damage, phosphorus diffusion profile and electrical shunt are assessed in the perspective of selective emitter silicon solar cells fabrication compatible with electrochemical metal contacts deposition.     

An Enantiopure Cyclometallated Iridium Complex Displaying Long‐Lived Phosphorescence both in Solution and in the Solid State

A new enantiopure cyclometallated iridium complex bearing a [4]helicenic ‐coordinating and two ‐coordinating dfppy (2‐(2,4‐difluorophenyl)‐pyridyl) ligands was prepared. This complex displayed long‐lived phosphorescence both in solution and in the solid state. Its chiroptical properties, namely electronic circular dichroism and circularly polarized luminescence, were also examined. Comparison with former chiral complexes enabled assignment of the Δ_Ir‐(?) and Λ_Ir‐(+) absolute configurations.     

Synthesis and Properties of Partially Saturated Fluorenyl-Derived [n]Helicenes Featuring an Overcrowded Alkene

The straightforward, multigram-scale synthesis of the partially saturated H₆-fluoreno[n]helicenes (n=5 or 7) featuring a central, overcrowded alkene is described. The key cyclization step was based on an intramolecular McMurry reaction from the corresponding 1,5-diketones. Chiral stationary phase HPLC analysis and isomer separation indicate that each helicenic compound is constituted of three diastereoisomers at room temperature, i. e. the configurationally stable (R,R,P)/(S,S,M) pair of enantiomers and an apparently achiral compound resulting from the rapid interconversion between the (R,S,P) and (S,R,M) enantiomers. The partially saturated H₆-fluoreno[n]helicenes are oxidatively aromatized to give an efficient access to the corresponding fluoreno[n]helicenes. The chiroptical properties (vibrational and electronic circular dichroism) of the chiral, enantiopure compounds have been measured and analyzed by quantum-chemical calculations, confirming their helicoidal nature.     

Weinreb Amide,Ketone and Amine as Potential and Competitive Secondary Molecular Stations for Dibenzo-[24]Crown-8 in [2]Rotaxane Molecular Shuttles

This paper reports the synthesis and study of new pH-sensitive DB24C8-based [2]rotaxane molecular shuttles that contain within their axle four potential sites of interaction for the DB24C8: ammonium, amine, Weinreb amide, and ketone. In the protonated state, the DB24C8 lay around the best ammonium site. After either deprotonation or deprotonation-then-carbamoylation of the ammonium, different localizations of the DB24C8 were seen, depending on both the number and nature of the secondary stations and steric restriction. Unexpectedly, the results indicated that the Weinreb amide was not a proper secondary molecular station for the DB24C8. Nevertheless, through its methoxy side chain, it slowed down the shuttling of the macrocycle along the threaded axle, thereby partitioning the [2]rotaxane into two translational isomers on the NMR timescale. The ketone was successfully used as a secondary molecular station, and its weak affinity for the DB24C8 was similar to that of a secondary amine.     

Intramolecular cyclisation of isosorbide by dimethylcarbonate chemistry

In this work the synthesis of a tricyclic isosorbide derivative in moderate yield directly from the dicarboxymethyl isosorbide in a continuous-flow apparatus is reported. The tricyclic structure has been isolated as pure and fully characterized. This product confirms the potentiality of dimethylcarbonate (DMC) as dehydrating agent also for complicated structure and opens up further investigation and application of DMC chemistry on renewable starting materials.     

The Chemoselective Cleavage of Acylthioaryltioacetals with Tributyltin Hydride

Acylthioarylthioacetals are cleaved selectively by tributyltin hydride/AIBN affording thioacyls radicals, which can react with tethered carbon-carbon double or triple bond to form functionalized cyclopentanes.     

New ethyl cellulose/acrylic hybrid latexes and coatings via miniemulsion polymerization

Ethyl cellulose (EC) was incorporated into copolymer latexes via miniemulsion polymerization. The effects of EC viscosity and EC content on droplet size, particle size, and polymerization kinetics were investigated. The higher the EC content and viscosity, the larger the droplet size and the less stable the latex suspension. Small droplets that could be efficiently nucleated were formed for the lower‐viscosity EC but the latex still showed limited colloidal stability. This was attributed to some phase‐incompatibility between EC and the acrylic polymer. These stability issues were overcome by using an oil‐soluble initiator and a crosslinker. The later enabled to physically entrap EC inside the polymer particles, whereas the former allowed in situ grafting of the growing acrylic radicals to the EC backbone decreasing thereby the extent of phase separation. Thermal‐mechanical analyses evidenced that the films obtained from the hybrid latexes displayed better properties than the EC‐free latex films or the physical blends. This supports the hypothesis of formation of hybrid latexes that synergistically combine the properties of the acrylic matrix and the EC polymer. Interestingly, a significant increase of the elastic modulus was observed between 50 and 90 °C. This mechanical reinforcement was tentatively attributed to the formation of a percolating EC‐based hybrid phase. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2329–2339, 2010