Yoshi Okamoto

Fabrication and superfluorescence of rare-earth chelate-doped graded index polymer optical fibers

Rare-earth chelate-doped graded index (GI) polymer optical fibers (POF) are proposed and fabricated. The attenuation loss was measured to be 0.4 dB/m at 650 nm for a GI POF doped with 1 wt % of europium (Eu) chelate. Lifetime shortening and spectral narrowing verified the occurrence of superfluorescence at 614 nm in the Eu chelate-doped GI POF pumped with xenon flashlamps. The demonstration of superfluorescence shows that rare-earth chelate-doped GI POFs are appealing as optical amplifiers and superfluorescent sources in a variety of communication and sensor applications.

High-efficiency organic dye-doped polymer optical fiber lasers

A graded-index polymer optical fiber containing rhodamine 6G in poly(methyl methacrylate-co-2-hydroxyethyl methacrylate) has been fabricated. Lasing behavior of the fiber was observed by pumping with a frequency-doubled Q-switched Nd: yttrium–aluminum–garnet laser. A slope efficiency of 43% and a lifetime of 110 000 shots at a repetition rate of 10 Hz have been observed. With a 1.5 mJ pump energy, an output energy of 640 μJ was produced.

Fabrication and properties of polymer optical fibers containing Nd-chelate

Graded-index poly(methyl methacrylate) optical fibers (GI POF) containing a Nd-chelate have been fabricated. The absorption spectrum of the fiber exhibited several strong bands in the visible and infrared regions. We have observed infrared fluorescence (0.90, 1.06, and 1.3 /spl mu/m) of the Nd/sup 3+/ ion of the fiber at room temperature when it was pumped with an Ar/sup +/-pumped dye laser at 580 nm.

Electrical Communication Between Glucose Oxidase and Novel Ferrocene-Containing Siloxane-Ethylene Oxide Copolymers: Biosensor Applications

Abstract Electrical communication between the flavin adenine dinucleotide redox centers of glucose oxidase and a conventional electrode has been achieved using two electron transfer relay systems based on siloxane-ethylene oxide copolymers containing covalently attached ferrocene moieties. The results from stationary potential experiments show that carbon paste electrodes modified with these redox polymers and glucose oxidase respond rapidly to addition of glucose, with larger steady-state response currents than those measured in previous studies of glucose sensors based on ferrocene-modified siloxane polymers. The results also indicate that the mediating ability of the polymers is dependent upon the length of the ethylene oxide side chain onto which the ferrocene molecules are attached.

Tacticity control in the radical polymerization of 2,2,2-trifluoroethyl methacrylate with fluoroalcohol

Abstract The free-radical polymerization of 2,2,2-trifluoroethyl methacrylate (TEMA) was carried out in fluoroalcohols to achieve stereoregulation. The polymerization reactivity at low temperature and syndiotactic specificity were enhanced by the use of fluoroalcohol as a solvent. The polymer having triad syndiotacticity (rr) of 70% was obtained in perfluoro- t -butyl alcohol. It was noted that the stereochemistry was nearly independent of reaction temperature. The stereoeffect of fluoroalcohols seemed to be due to the hydrogen-bonding interaction between the alcohol and the monomer or growing species. The hydrogen-bonding formation was determined by FTIR. The copolymerization of TEMA with methyl methacrylate (MMA) in hexafluoroisopropanol afforded a copolymer with syndiotactic specificity. By this method, a cladding material for an optical fiber based on poly(methyl methacrylate) (PMMA) with high mechanical strength and low refractive index could be obtained.

Organic dye‐doped polymer optical fiber laser

We report on the lasing action of the graded-index polymer optical fibers containing dyes, such as Rhodamine B, Rhodamine 6G, Perylene orange and Pyrromethene 567. These dyes have been incorporated into poly(methyl methacrylate-co-2-hydroxyethyl methacrylate). These fibers were transversely pumped at 532 nm with a frequency-doubled Q-switched Nd–YAG laser. Slope efficiency of 24% and output of 1.2 mJ were obtained with a Rhodamine 6G-doped fiber. Lifetime of 200,000 pulses at 10 Hz was achieved with a Rhodamine B-doped fiber. Copyright

Redox polymer-modified electrodes for the electrocatalytic regeneration of NAD

Abstract A new siloxane polymer containing covalently attached Meldola Blue has been synthesized and shown to mediate the oxidation of the reduced nicotinamide adenine dinucleotide cofactor (NADH). Cyclic voltammetry and stationary potential experiments demonstrate that spectrographic graphite electrodes coated with this polymer can electrocatalytically regenerate NAD+ at a substantially lower overvoltage (e.g., 0 mV vs. SCE) than can unmodified electrodes. These polymer-modified electrodes should be useful as transducers in dehydrogenase-based biosensors.

Glutamate Biosensors Based on Electrical Communication Between L-Glutamate Oxidase and a Flexible Redox Polymer

Abstract Electrical communication between the flavin adenine dinucleotide redox centers of L-glutamate oxidase and a conventional carbon electrode has been achieved using a new electron transfer relay system based on a ferrocene-modified siloxane-ethylene oxide branch copolymer. Using cyclic voltammetry and stationary potential experiments, it was shown that spectrographic graphite electrodes modified with this redox polymer and L-glutamate oxidase respond rapidly to addition of glutamate, with steady-state current responses achieved in less than 1 min. At an applied potential of +400 mV (vs. Ag/AgCl), a lower detection limit of approximately 0.01 mM and an apparent Michaelis-Menten constant, KM app, of 0.20 mM were determined.

Fluorescence, ion binding, and viscosity properties of poly[2‐ and 4‐vinylpyridine]s in methanol and in sulfuric acid

Fluorescence intensities of poly(2-vinylpyridine) (P2VP) and poly(4-vinylpyridine) (P4VP) in H2SO4/H2O solutions were increased with increasing acid concentration. The intensities for P2VP were found to be six times stronger than that of P4VP. These differences were accounted for by the microenvironment of protonated pyridinium group. The ion binding properties of 4-methylpyridine (4MP), P2VP, and P4VP were investigated in methanol using Tb3+ as a fluorescence probe. The increase of fluorescence intensity of Tb3+ in [P2VP–Tb3+] and [P4VP–Tb3+] complexes is due to both the replacement of the inner coordinated methanol molecules and ligand-to-metal energy transfer. The model compound 4MP was inefficient from this point of view, and the results were attributed to the polymer cooperative effect. Reduced viscosities of poly(vinylpyridine)s (PVP) in methanol were similar to nonionic polymers; however, when TbCl3 was added into the solution, the viscosities increased upon dilution. These results also indicated that PVP form complexes with Tb3+ in methanol. When diluted, the counterions Cl− are allowed to dissociate and the charged polymer expands. Consequently, the solutions viscosity increases.

Spectroscopic properties of lanthanide chelates in perfluorinated plastics for optical applications

The absorption spectra of neodymium (Nd), praseodymium (Pr), erbium (Er), and thulium (Tm) ions in perfluorinated (PF) plastic solutions were measured, and the Judd–Ofelt parameters of the Er and Nd ions have been calculated. The radiative properties of the Nd and Er ions in PF plastic solutions were determined from the absorption measurements and the Judd–Ofelt theory. The fluorescence spectrum of Nd3+ in a PF plastic solution from 900 nm to 1350 nm was measured for the first time, to our knowledge. Furthermore, the PF plastic films containing lanthanide chelates were fabricated by spin coating, and the refractive indices of the films were measured.