Photochemistry of S-phenacyl xanthates

Various synthetically readily accessible S-phenacyl xanthates are shown to undergo photoinitiated homolytic scission of the C-S bond in the primary step. The resultant fragments, phenacyl and xanthic acid radicals, recombine to form symmetrical 1,4-diketones and xanthogen disulfides, respectively, in high to moderate chemical yields in chemically inert solvents. They can also be efficiently trapped by a hydrogen-atom-donating solvent to give acetophenone and xanthic acid derivatives. The latter compound is in situ thermally converted to the corresponding alcohol in high chemical yields. S-Phenacyl xanthates could thus be utilized as synthetic precursors to the above-mentioned compounds or as photoremovable protecting groups for alcohols in which the xanthate moiety represents a photolabile linker. The photochemically released phenacyl radical fragments efficiently but reversibly add to the thiocarbonyl group of the parent xanthate molecule. The kinetics of this degenerative reversible addition-fragmentation transfer (RAFT)/macromolecular design via the interchange of xanthates (MADIX) mechanism was studied using laser flash photolysis (LFP) and density functional theory (DFT) calculations. The rate constants of the RAFT addition step, k(add) ～ 7 × 10(8) M(-1) s(-1), and phenacyl radical addition to a double bond of 1,1-diphenylethylene, k(add) ～ 10(8) M(-1) s(-1), in acetonitrile were experimentally determined by LFP. In addition, photoinitiation of the methyl methacrylate polymerization by S-phenacyl xanthate is demonstrated. The polydispersity index of the resulting poly(methyl methacrylate) was found to be ～1.4. We conclude that S-phenacyl xanthates can serve simultaneously as photoinitiators as well as RAFT/MADIX agents in polymerization reactions.     

Energy Transfer and Trapping in Rigid Solutions of Aromatic Polymers

Energy transfer by excitons is now well established in films and solutions of aromatic polymers. Excitons in disordered systems can be considered as electronically excited states, which are transferred between the light absorbing groups in a random hopping process (the same is true in molecular crystals if, because of thermal vibrations, the coherence length of the exciton waves approaches the lattice constant and consequently the band model of the excitons breaks down).     

Critical exponents of a multicomponent anisotropict−J model in one dimension

A recently presented anisotropic generalization of the multicomponent supersymmetrict–J model in one dimension is investigated. This model of fermions with general spin-S is solved by Bethe ansatz for the ground state and the low-lying excitations. Due to the anisotropy of the interaction the model possesses 2S massive modes and one single gapless excitation. The physical properties indicate the existence of Cooper-type multiplets of 2S+1 fermions with finite binding energy. The critical behaviour is described by ac=1 conformal field theory with continuously varying exponents depending on the particle density. There are two distinct regimes of the phase diagram with dominating density-density and multiplet-multiplet correlations, respectively. The effective mass of the charge carriers is calculated. In comparison to the limit of isotropic interactions the mass is strongly enhanced in general.Work performed within the research program of the Sonderforschungsbereich 341, Köln-Aachen-Jülich     

Combinatorial synthesis of carbon nanotubes by the catalytic chemical vapor deposition method

Summary Bimetallic (Fe-Co) catalyst samples prepared from different precursors over various supports were tested in carbon nanotube (CNT) production. In order to quicken the evaluation of the performance of the catalysts a combinatorial arrangement was used.</o:p>     

New fluorene‐based copolymers containing oxadiazole pendant groups: Synthesis,characterization, and polymer stability

A series of fluorene‐based copolymers containing hole blocking/electron transporting diphenyloxadiazole units were synthesized by means of Suzuki‐Miyaura coupling of selected aromatic dibromo‐ and diboronato‐ derivatives catalyzed with a Pd(PPh₃)₄ catalyst. All of the copolymers with various composition of main‐chain units were characterized by SEC chromatography, NMR, UV–vis, fluorescence and IR spectroscopy, and DSC. The emission stability of fluorene copolymers was improved by the replacement of alkyl groups on the C‐9 carbon of fluorene with aryl groups or by the incorporation of anthracene units into the copolymer main chain. A comparison of luminescence properties of pristine and annealed thin layers of studied copolymers was performed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4532–4546, 2009     

On the radiation pressure of electromagnetic wave packets in nondispersive fluid dielectrics

Using the classical dipole representation for the gas molecules, an approximate kinetic equation is derived including radiation pressure forces. The energy-momentum tensor for a quasimonochromatic electromagnetic wave packet is constructed. Electrostrictive forces and nonlinear perturbations of the gas rest energy density are taken into account. Certain particle-like properties of the wave packet are demonstrated. Radiation pressure forces are given for some simple models of fluid inhomogeneities.     

Aminosulfonyl-alkan-phosphine

Aminosulphonyl-alkane-phosphines Ph₂PH reacts catalysed by sodium with vinyl- and styrenesulphonamides to form 2-aminosulphonyl-ethane-1-diphenylphosphines or their 1-phenyl-substituted derivatives respectively. Vinylsulphonylfluoride is added to Ph₂PH without catalysis. Allylsulphonamides are isomerised under the influence of Ph₂PNa to α-propenyl-sulphonamides followed by addition of Ph₂PH to give 2-aminosulphonylethane-1-methyl-1-diphenylphosphines. Analogous reactions with dicyclohexyl- and phenylphosphine fail. Aminosulphonyl-alkane-phosphines behave like ordinary tertiary phosphines. Bromo-ethane-sulphonamides react with Ph₂PNa to the mentioned aminosulphonyl-ethane-diphenylphosphines while (RO)₂P(O)Na give aminosulphonyl-ethane-phosphoneesters in a Michaelis-Becker-Reaction beside larger amounts of elimination products. The structure of the prepared compounds is elucidated by investigating their mass, i.r., and n.m.r. spectra.     

Zur Physik und Technik des Kalten Spiegels

Ohne Zusammenfassung     

Determination of the anharmonicity constant of oxygen by raman measurements

The hot band ν = 1 → 2 of O₂, which could not be resolved in previous Raman measurements, has been observed by direct scanning of the purely isotropic part of Raman scattered light. A computer simulation of the spectrum confirmed the set of anharmonicity constants given by Babcock and Herzberg.