Photochemistry and photocuring properties of thiol‐substituted α‐aminoalkylphenone as radical photoinitiator

Thiol‐substituted α‐aminoalkylphenone was newly developed as a radical photoinitiator. Introduction of the thiol group drastically improved photosensitivity in an alkaline developable resist formulation composed of a prepolymer and a multifunctional acrylate monomer. The improvement in the photocuring speed was explained by a mechanism based on chain transfer reaction of the thiol group. Time‐resolved electron spin resonance (ESR) spectroscopy indicated that the thiol group attached to the chromophore does not influence the photochemical process to generate primary radicals. The photoinitiation of α‐aminoalkylphenone can be spectrally sensitized by 2,4‐diethylthioxanthone (DETX). However, thiol‐substituted α‐aminoalkylphenone showed smaller spectral sensitization than the corresponding compound without a thiol group. Time resolved laser flash photolysis indicated that the rate constant of the quenching of the triplet state of DETX by thiol‐substituted α‐aminoalkylphenone is twice as large as that by the corresponding one without a thiol group. This suggests that, besides energy transfer from DETX in the excited triplet state to the α‐aminoalkylphenone, the thiol group quenches the excited triplet state of DETX via charge transfer and/or hydrogen transfer, as supported by the ESR analysis using a spin trapping technique, and lowers the efficiency of the spectral sensitization effect. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1684–1695, 2005     

Composite structure of liquid crystal/polymer nanotubes revealed by high-angle annular dark-field scanning transmission electron microscopy.

We have applied high-angle annular dark-field microscopy to the characterization of the structure of template-grown nanotubes composed of a polymer and a discotic liquid crystalline material. Selective staining of the liquid crystal phase with ruthenium tetroxide was used to develop adequate Z-contrast that allows us to distinguish between the two phases. At appropriate staining conditions, we could clearly visualize, in the annular dark-field mode, a 5-15-nm thin liquid crystalline layer precipitated on the inner surface of the polymer tubes. Cryo-electron diffraction has shown high alignment of the discotic columns within the layer parallel to the tube axis. However, although the polymer/liquid crystal phase separation is almost complete, the wetting behavior of the polymer in relation to the template appears to be sensitively influenced by kinetic factors.     

Topological degeneracy of non-Abelian states for dummies

We present a physical construction of degenerate groundstates of the Moore-Read Pfaffian states, which exhibits non-Abelian statistics, on general Riemann surface with genus g. The construction is given by a generalization of the recent argument [M.O., T. Senthil, Phys. Rev. Lett. 96 (2006) 060601] which relates fractionalization and topological order. The nontrivial groundstate degeneracy obtained by Read and Green [Phys. Rev. B 61 (2000) 10267] based on differential geometry is reproduced exactly. Some restrictions on the statistics, due to the fractional charge of the quasiparticle are also discussed. Furthermore, the groundstate degeneracy of the p + ip superconductor in two dimensions, which is closely related to the Pfaffian states, is discussed with a similar construction.     

Carbon felt-based bioelectrocatalytic flow detectors: highly sensitive amperometric determination of hydrogen peroxide using adsorbed peroxidase and thionine.

Horseradish peroxidase (HRP) and thionine (TN) were co-adsorbed onto a porous carbon felt (CF), and the resulting HRP and TN-adsorbed CF (HRP-TN-CF) was successfully used as a working electrode unit of a novel bioelectrocatalytic flow detector for a highly sensitive amperometric determination of hydrogen peroxide (H(2)O(2)). Co-adsorbed TN was essential to enhance the cathodic peak current of H(2)O(2), and the current responses of the HRP-TN-CF-based detector were much larger than those of the HRP-CF-based detector (without TN). When air-saturated 0.1 M phosphate buffer (pH 7.0) was used as a carrier at a flow rate of 3.9 ml/min, cathodic peak currents of H(2)O(2) (sample injection volume, 200 microl) obtained at an applied potential of 0 V (vs. Ag/AgCl) increased linearly up to 50 microM with a detection limit of 0.1 microM. Repetitive 100 sample injection of 100 microM H(2)O(2) induced no serious current decrease, and RSD was 0.41 to 1.21% (n = 100). The HRP-TN-CF retained 42% of its original activity after 8 days of storage in 0.1 M phosphate buffer at 4 degrees C.     

Development of 170 GHz/500 kW gyrotron

A development of 170GHz/500kW level gyrotron was carried out as R&D work of ITER. The oscillation mode is TE_31,8. In a short pulse experiment, the maximum power of 750kW was achieved at 85kV/40A. The efficiency was 22%. In the depressed collector operation, 500kW/36%/50ms was obtained. The maximum efficiency of 40% was obtained at P_RF=470kW whereas the power decrease by the electron trapping was observed. Pulse extension was done up to 10s at P_RF=170kW with the depressed collector operation. The power was limited by the temperature increase of the output window.     

Synthesis and characterization of anthracene-clustering dendrimers: observation of fluorescence resonance energy transfer in the multichromophoric system

A series of anthracene-clustering dendrimers bearing various aliphatic substituents at the terminal positions were synthesized using a direct coupling strategy. A remarkable effect of the side chains was imparted to chemical properties of the dendrimers such as drastically increased solubility. Although the multibranched anthracene arrays in the dendritic architectures exhibited no cooperativity in terms of the absorption feature and behaved as single chromophoric systems, investigations focusing on fluorescence properties revealed that a type of cooperativity was present as expressed in the reduced quantum yields of fluorescence. An alternative approach utilizing time-resolved fluorescence decay measurements clearly demonstrated that the most reasonable mechanism of the cooperative action should involve two discernible channels of intramolecular fluorescence resonance energy transfer (FRET) occurring from one chromophore to the others within and across junctions of the branching units.     

Field determination of trace iron in fresh water samples by visual and spectrophotometric methods.

Sensitive visual and micro spectrophotometric methods have been developed for field determination of trace iron in fresh water samples. For the visual method, a water sample (0.45-microm filtrate acidified to 0.1 M HCl) was placed in a glass vial and mixed with a reagent solution containing 1,10-phenanthroline, sodium thiocyanate and 0.1 M HCl. Iron was extracted as pink ferroin thiocyanate with 1 ml of 4-methy-2-pentanone. The sample up to 20 ml was added step-by-step, until the color of the extract was detected visually. Without any special instrument or color standard, iron down to 0.001 mg 1(-1) (0.025 microg) in a sample can be determined with an error of 20% in the field. For the micro spectrophotometric method, the extract for 20 ml of sample was separated by capillary suction in a column (micro pipette chip) with acrylic fibers. A part of the extract was pushed out into a micro cell for the absorbance measurement at 525 nm. The column was re-usable after washing with ethanol. This method had a detection limit of 0.001 mg 1(-1) and allowed determinations within an error of 5%. The proposed methods were applied to deionized-, tap-, river-, lake- and reservoir-water samples.