Highly active zinc alkyl cations for the controlled and immortal ring-opening polymerization of ε-caprolactone

Zinc alkyl cations supported by N,N-BIAN-type bidentate ligands were found to be highly active in the immortal ROP of ε-caprolactone to yield narrowly disperse and chain length-controlled poly(ε-caprolactone), whether in solution or bulk polymerization conditions.     

Microbead dynamics in optical trap assisted nanopatterning

An optically pumped ZnO nanowire laser with a 10-period SiO₂/SiN _x distributed Bragg reflector (DBR) was demonstrated. Stimulated emissions with equally distributed Fabry–Pérot lasing modes were observed at pumping powers larger than 121 kW/cm². This result, when compared to nanowires of the same length and without a DBR structure, shows that a lower threshold of pumping power, higher quality factor, and larger cavity finesse can be achieved due to the high reflectivity of the DBR in the designed wavelength range. A coexistence of stimulated and spontaneous emissions was also observed above threshold and was attributed to partially confined waveguide modes in nanowires with diameters smaller than 100 nm.     

Adsorption of phenylacetylene on Si(100)-2 x 1: kinetics and structure of the adlayer

Direct adsorption of phenylacetylene on clean silicon surface Si(100)-2 x 1 is studied in ultrahigh vacuum (UHV). The combination of scanning tunnel microscopy (STM) and surface differential reflectance spectroscopy (SDRS) with Monte Carlo calculations are put together to draw a realistic kinetic model of the evolution of the surface coverage as a function of the molecular exposure. STM images of weakly covered surfaces provide evidence of two very distinct adsorption geometries for phenylacetylene, with slightly different initial sticking probabilities. One configuration is detected with STM as a bright spot that occupies two dangling bonds of a single dimer, whereas the other configuration occupies three dangling bonds of adjacent dimers. These data are used to implement a Monte Carlo model which further serves to design an accurate kinetic model. The resulting evolution toward saturation is compared to the optical data from surface differential reflectance spectroscopy (SDRS). SDRS is an in situ technique that monitors the exact proportion of affected adsorption sites and therefore gives access to the surface coverage which is evaluated at 0.65. We investigate the effect of surface temperature on this adsorption mechanism and show that it has no major effect either on kinetics or on structure, unless it passes the threshold of dissociation measured at ca. 200 degrees C. This offers a comprehensive image of the whole adsorption process of phenylacetylene from initial up to complete saturation.     

Grignard reagent-promoted 6-endo-dig cyclization: instantaneous synthesis of original dipyrido[1,2-a:3′,4′-d]imidazole

Dipyrido[1,2-a:3′,4′-d]imidazole derivatives can be readily synthetized from various 3-alkyne-2-cyanoimidazo[1,2-a]pyridines via an efficient Grignard reagent-promoted 6-endo-dig cyclization of nitrile to alkynes. A previous optimization of the Sonogashira coupling reaction at C(3) of the 2-cyanoimidazo[1,2-a]pyridine was necessary as this coupling reaction is known to be largely influenced by the nature of the 2-substituent.     

Raman Study of Aluminum Chloride-Dimethylsulfone Solutions

The Raman spectra of AlCl(3)-LiCl-dimethylsulfone mixtures with different molar compositions have been recorded as a solid (300 K) and as a melt (400 K). In any case, only AlCl(4)(-) ion lines at 120, 179, and 347 cm(-)(1) were observed; we were unable to detect any other chloroaluminate species. Furthermore, some bands assigned to the Al[(CH(3))(2)SO(2)](3)(3+) octahedral coordination compound are evidence for a high AlCl(3) content.     

Undulator beamline optimization with integrated chicanes for X‐ray free‐electron‐laser facilities

An optimization of the undulator layout of X‐ray free‐electron‐laser (FEL) facilities based on placing small chicanes between the undulator modules is presented. The installation of magnetic chicanes offers the following benefits with respect to state‐of‐the‐art FEL facilities: reduction of the required undulator length to achieve FEL saturation, improvement of the longitudinal coherence of the FEL pulses, and the ability to produce shorter FEL pulses with higher power levels. Numerical simulations performed for the soft X‐ray beamline of the SwissFEL facility show that optimizing the advantages of the layout requires shorter undulator modules than the standard ones. This proposal allows a very compact undulator beamline that produces fully coherent FEL pulses and it makes possible new kinds of experiments that require very short and high‐power FEL pulses.     

Selective internal manipulation of a single molecule by scanning tunneling microscopy

We have studied the adsorption of the polyaromatic molecule 1,4"-paratriphenyldimethylacetone, which we have nicknamed Trima. The originality of this linear molecule is that it was designed and synthesized to have two functionalities. First, chemisorb itself to the surface by its two ends rather like a bridge. Second, the central part of the molecule could then be rotated by injecting electrons with the tip of the scanning tunneling microscope (STM). The length of the molecule corresponds exactly to the spacing between five dimers in a row on the Si(100)-2 x 1 surface. We found that the molecule adsorbs as expected on the clean silicon surface by using complementary STM and synchrotron radiation studies. Manipulation of individual molecules with the STM tip showed selective internal modifications that were highly voltage dependent. These manipulations were found to be compatible with an electronic excitation of the pi-pi* transition of the molecule.     

Optical chemical sensors based on hybrid organic-inorganic sol-gel nanoreactors

Sol-gel porous materials with tailored or nanostructured cavities have been increasingly used as nanoreactors for the enhancement of reactions between entrapped chemical reactants. The domains of applications issued from these designs and engineering are extremely wide. This tutorial review will focus on one of these domains, in particular on optical chemical sensors, which are the subject of extensive research and development in environment, industry and health.     

Tabular electrical conductivity for aluminium

A new Sesame-type table for the electrical conductivity of aluminium is described. The table is based on density functional theory calculations and ranges from 10⁻³ to 1 times solid density (2.7 g/cm³), and from 10⁻² to 10³ eV in temperature. The table is compared with other those of simulations and to experiments and is generally in good agreement. The high-temperature, classical limit of the conductivity is recovered for the highest temperatures and lowest densities. The table is critically evaluated, and directions for improvements are discussed.     

α-Amino-iso-Butyric Acid Foldamers Terminated with Rhodium(I) N-Heterocyclic Carbene Catalysts

To investigate how remotely induced changes in ligand folding might affect catalysis by organometallic complexes, dynamic α-amino-iso-butyric acid (Aib) peptide foldamers bearing rhodium(I) N-heterocyclic carbene (NHC) complexes have been synthesized and studied. X-ray crystallography of a foldamer with an N-terminal azide and a C-terminal Rh(NHC)(Cl)(diene) complex showed a racemate with a chiral axis in the Rh(NHC) complex and a distorted 3₁₀ helical body. Replacing the azide with either one or two chiral L-α-methylvaline (L-αMeVal) residues gave diastereoisomeric foldamers that each possessed point, helical and axial chirality. NMR spectroscopy revealed an unequal ratio of diastereoisomers for some foldamers, indicating that the chiral conformational preference of the N-terminal residue(s) was relayed down the 1 nm helical body to the axially chiral Rh(NHC) complex. Although the remote chiral residue(s) did not affect the stereoselectivity of hydrosilylation reactions catalysed by these foldamers, these studies suggest a potential pathway towards remote conformational control of organometallic catalysts.