Akihiko Ouchi

Photoisomerization of the azobenzenes included in Langmuir-Blodgett films of cyclodextrins

A new type of photochemical Langmuir-Blodgett (LB) film containing azobenzenes (p-phenylazobenzoic acid (PAB), methyl red (MR) and methyl orange (MO)) without long alkyl chains was prepared by the host-guest interaction with an amphiphilic cyclodextrin derivative. The azobenzenes in the LB film of the host- guest complex exhibited an excellent cis-trans photoisomerization, while trans-to- cis photoisomerization was restricted for LB films of long chain azobenzene derivatives alone. The cavity of cyclodextrin provides a favourable environment for the photochemical reaction leading to an increase in the molecular area in the rigid LB film. The half-life times of cis isomers of PAB, MR and MO in the host-guest complex LB films were 35 h, 55 s and 13 min respectively at 20°C.

Comparison of the transmission behavior of a triazeno-polymer with a theoretical model

The threshold fluence,FTh, of ablation of a triazeno-polymer was measured in the low fluence range for thin films using conventional UV-spectroscopy. It was found that there is a clearly definedFTh for 308 nm irradiation between 20 and 25 mJ cm−2. In the case of 248 nm irradiation, a “threshold fluence range” between 16 and 32 MJ cm−2 was found. The ablation rate for both irradiation wavelengths depends on film-thickness. For the XeCl excimer-laser, the point at which the rate becomes independent of thickness was observed to lie at a value which did not correspond to the calculated laser penetration depth, whereas for the KrF laser the independence was not reached within the applied thickness range (up to 0.35 μm). Additional transmission measurements have been performed showing that the target transmission at 248 nm increases only slightly, whereas for 308 nm the transmission increases by a factor of approximately 4. This result shows that dynamic target absorption properties are very important for describing the ablation process. The results derived from the transmission studies and etch rates were analyzed theoretically with a two-level model of chromophore absorption. For 248 nm irradiation this model can describe the transmission behavior and the ablation rate. In the case of 308 nm irradiation, it was only possible to match one data set. A good agreement with the experimental transmission ratio does not match the ablation rate and vice versa.

Synthesis of nitrogen-rich B–C–N materials from melamine and boron trichloride

Nitrogen-rich B–C–N materials have been prepared by the reaction between melamine and boron trichloride at different temperatures. The composition of the materials was dependent on the synthesis and annealing temperatures: C6N10.8-11H9.4B1.5-1.7 (for products synthesized and annealed at 673 K), C6N9.3-9.4H3.8-3.9B2.2-2.5 (for those synthesized at 673 K and annealed at 873 K) and C6N9.2H3.6B1.2-1.3 (for those synthesized and annealed at 873 K). Fourier transform infrared spectroscopy and 13C nuclear magnetic resonance showed that the s-triazine rings from the melamine molecules were preserved in materials synthesized and annealed at 673 and 873 K. The sample obtained at 873 K had a graphite-like structure as suggested by X-ray and electron diffraction studies. The s-triazine rings were decomposed in the materials synthesized or annealed at 1223 K and the main product obtained was turbostratic boron nitride.

Chemical vapour deposition of selenium and tellurium films by UV laser photolysis of selenophene and tellurophene

Excimer laser-induced photolysis of gaseous selenophene and tellurophene affords gaseous 1-buten-3-yne and ethyne (as major products) and butadiyne (a very minor product) and results in chemical vapour deposition of selenium and tellurium films. The film properties were characterized by XPS and SEM techniques and by UV spectroscopy. Copyright

Sunlight oxidation of alkyl aryl tellurides to the corresponding carbonyl compounds: a new carbonyl precursor.

Alkyl aryl tellurides were efficiently transformed to the corresponding carbonyl compounds by photo-oxidation with sunlight without affecting various functional groups in the alkyl moiety. The tellurides can be used as a new carbonyl precursor, and the photolysis can be conducted without special equipment for light sources.

Facile photochemical transformation of alkyl aryl selenides to the corresponding carbonyl compounds by molecular oxygen: use of selenides as masked carbonyl groups.

Alkyl aryl selenides with and without functional groups on the alkyl group were transformed efficiently into the corresponding carbonyl compounds, particularly primary alkyl aryl selenides in good yields, by a simple photolysis in the presence of air or oxygen. This transformation can be conducted without protection of functional groups. The yield of carbonyl compounds was much affected by the solvent viscosity, reaction temperature, concentration of dissolved oxygen in the solvents, wavelength of light, and structure of the aryl substituents. The present study indicates that aryl selenides can be considered as a masked carbonyl group that can be easily converted to a carbonyl group by very mild reaction conditions even in the presence of various unprotected functional groups. Therefore, this functional group transformation can be used as an important tool in organic synthesis due to its simplicity and mild reaction condition.

A remarkable wavelength dependence on the laser-induced two-photon CC bond formation

Abstract Two-photon intramolecular C C bond formation of 1,8-bis(bromomethyl)naphthalene and 1,8-bis(chloromethyl)naphthalene by high fluence excimer laser irradiations showed a considerable wavelength dependence on the conversion, the efficiency, and the yield of the product; the results are interpreted by the selective excitation of the substrates.

Wavelength Dependence on the Formation of Electrically Conductive Fine Particles by Excimer Laser-Induced Ablative Photodecomposition of Monomeric Polynuclear Aromatic Solids

The reaction of reactive intermediates generated by excimer laser-induced ablative photodecomposition of solid monomers, namely, 3,4,9,10-perylenetetracarboxylic dianhydride, 3,4,9,10-perylenetetracarboxylic diimide, and 1,4,5,8-naphthalenetetracarboxylic dianhydride, yielded electrically conductive fine particles. The electrical conductivity was largely dependent on the wavelength of the lasers used. The fine particles had polymeric hydrocarbon moieties containing extended aromatic planes.

Deposition of nanostructured Te and Te/C particles by excimer laser-induced photolysis of organotelluriums in the liquid phase

Excimer laser induced photolysis of dialkyltellurides R 2 Te (R=C 2 H 5 , n-C 5 H 11 ) and tellurophene in n-hexane affords nanostructured Te and Te/C particles the surface of which is oxidized in the atmosphere and whose C content depends on the structure of the organotellurium precursor.

Preparation of polykis azobenzene by photolysis of 1,4-diazidobenzene with excimer laser radiation

Abstract The photolysis of 1,4-diazidobenzene (1) with a KrF excimer laser gave a dark-purple precipitate, which was characterized as polykis azobenzenes by UV-visible, IR, Raman and nuclear magnetic resonance spectroscopies. The intermolecular reaction of 1,4-dinitrenobenzene, which was generated from the photolysis of matrix-isolated 1 in argon at 20 K, also gave a similar product. High intensity irradiation with excimer lasers provides a new polymerization method as the result of effective formation of an intermediate having two reactive sites.