Tateo Nomoto

Photophysical properties of diphenylacetylene derivatives in the solution phase: Comparison with the dynamical properties of diphenylbutadiyne

Abstract Using femtosecond and picosecond transient absorption measurement techniques, we have investigated the dynamic behavior of the S 2 state of diphenylbutadiyne (DPB) and its methoxy derivatives in solution. The observed much larger rate constants at room temperature and the smaller temperature-dependence of the S 2 →S 1 internal conversion of the DPB derivatives compared to those of diphenylacetylene should be due to the large S 2 –S 1 energy gap of DPBs.

Photoinduced intramolecular charge separation ofp-N,N-dimethylamino-p′-cyano-diphenylacetylene in polar solvents

Abstract By using picosecond transient absorption measurement techniques, we have investigated the intramolecular charge separation process and the dynamic spectral shift of p -N,N-dimethylamino- p ′-cyano-diphenylacetylene in various polar solvents. In alcohols the spectral shift of the intramolecular charge-separated state was observed in the tens of picosecond time scale, while in aprotic polar solvents the spectral shift was too fast to measure with our time resolution. The dipole moment of the intramolecular charge-separated state, which gives a transient absorption spectrum in the red region, is about 36 D.

Higher excited singlet state of diphenylacetylene in solution phase

Abstract By using picosecond transient absorption spectral measurement techniques, we have investigated photophysical properties of several mono-substituted diphenylacetylenes (DPA). The strongly temperature dependent S 2 →S 1 internal conversion which was reported for DPA previously was observed for methoxy-DPA, hydroxy-DPA, and chloro-DPA. In these compounds the S 2 and S 1 states are fluorescent 1 B 1u and nonfluorescent 1 A g or 1 B 2u , respectively, while the S 1 state of cyano-DPA and CH 3 COO-DPA should be fluorescent 1 B 1u . The probable mechanism of the S 2 →S 1 internal conversion, where the promoting vibrational mode was excited in the S 2 state, was proposed on the basis of the results that the former group has a similar activation energy of the internal conversion.

Effective hydrogenation of carbon-carbon triple bonds by NaBH4/PdCl2 in polyethylene glycol/CH2Cl2: usefulness of PEG in synthetic reactions

The NaBH4-PdCl2-polyethylene glycol-CH2Cl2 system has been found to be effective for the hydrogenation of carbon-carbon triple bonds to the corresponding cis-alkenes.

Synthetic reactions in polyethylene glycol. Diazotization and sandmeyer reactions of anilines in polyethylene glycol–methylene dichloride

Diazotization and the Sandmeyer reactions of representative arylamines proceed smoothly in polyethylene glycol–CH2Cl2 and have been found to be effective for the preparation of aryl halides and cyanides.

Antioxidative Activity of Amino Acids and Sulfur-containing Compounds to Superoxide : Measurement by Quenching the Chemiluminescence of a Cypridina Luciferin Analogue

Reaction rate constants between superoxide (O2(-)) and natural anti-oxidants, amino acids and some related sulfur-containing compounds were determined by quenching the chemiluminescence of a Cypridina luciferin analogue, 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-a]pyrazin-3-one (CLA) in pH 7.0 buffer solutions at 25°C as described in our previous report. The results are discussed in comparison with the literature data. We found that the present method can be applied to measured antioxidative activity of even a fairly unstable sample.

Dehydroannulenes. V. Synthesis and properties of 1,6,12,17-tetra-t-butyl-2,4,13,15-tetrakisdehydro(22)annulene.

1,6,12,17-Tetraphenyl-2,4,13,15-tetrakisdehydro[22]annulene has been synthesized. The sparlingly soluble tetrakisdehydro[22]annulene was found to be conformationally stable and strongly diatropic.

Photophysical properties of diphenylacetylene derivatives in solution phase. IV. N,N-dimethylanilino(phenyl)acetylene in n-hexane

Abstract By using picosecond transient absorption and fluorescence lifetime measurement techniques, we have investigated the photophysical properties of N,N-dimethylanilino(phenyl)-acetylene in n -hexane solution. The lifetime of the second excited singlet state was determined to be about 20 ps at room temperature and a strong delayed S 2 fluorescence excited from S 1 was observed. The characteristic features we observed seem to result from the accidental degeneracy of S 2 and S 1 . Introduction of the dimethylamino group makes the vibrational level density high and results in a large rate constant of internal conversion from S 2 to S 1 without excess vibrational energy.

Selective reactions in polyethylene glycol. Hydrogenation of acetylenes by NaBH4–PdCl2 in polyethylene glycol–methylene dichloride

The NaBH4–PdCl2–polyethylene glycol–CH2Cl2 system has been found to be effective for the hydrogenation of acetylenic triple bonds to the corresponding cis-alkenes.

Diazotization and Sandmeyer reactions of arylamines in poly(ethylene glycol)–methylene dichloride: usefulness of PEG in synthetic reactions

Diazotization and Sandmeyer reactions of representative arylamines (la–h) proceed smoothly in PEG–CH2Cl2 and were found to be effective for the preparations of halogenoarenes (X = Cl, Br, and I) and cyanoarenes (X = CN).