Tetsuo Okutsu

Synthesis, structure, and photochemical reaction of 9,10-dihydro-9-silaanthracene derivatives carrying bulky substituents

Abstract Some of 9-aryl-9,10-dihydro-9-silaanthracenes (1) were prepared and the alkylation of the compounds gave trans-9-aryl-10-alkyl-9,10-dihydro-9-silaanthracenes exclusively. Upon photolysis of a 9-phenyl derivative, 9-phenyl-9-silaanthracene was confirmed by spectroscopic analysis. Also, structural studies of the dihydro compounds were performed by NMR and X-ray.

Photochemical processes of benzyltrimethylsilane at 77 K remarkable solvent effects and reaction mechanism

Photophysical and photochemical processes of benzyltrimethylsilane have been studied in 3-methylpentane and ethanol glass at 77 K. Remarkable solvent effects were observed in the UV photolysis: in ethanol glass, benzyl radicals were produced, while in 3-methylpentane glass α-trimethylsilylbenzyl radicals and benzyltrimethylsilane radical cations were produced. It was confirmed that the α-trimethylsilylbenzyl radicals and benzyltrimethylsilane radical cations were formed via the lowest triplet state and the benzyl radicals via the excited singlet state or higher triplet state. The molecular structure of the excited-state benzyl-trimethylsilane has been studied by MNDO-PM3 calculations. Based on the results, a possible mechanism involving the excited state of radical pair character has been proposed for the photochemical process of benzyltrimethylsilane.

Excited state dynamics of p-chlorotoluene in rigid glass matrices

Abstract Excited state dynamics of dual phosphorescent p-chlorotoluene (PCT) was investigated in 3-methylpentane (3MP), methylcyclohexane (MCH), ethanol/methanol (EtOH/MeOH) and EPA rigid matrices in the temperature range of 77-110 K. Dual phosphorescence was ascribed to two low-lying triplet states, 3 ππ * and 3 πσ * . The rate of intersystem crossing (ISC) from S 1 to 3 ππ * and 3 πσ * states depends both on the temperature and solvent. Mutual conversion process between 3 ππ * and 3 πσ * states was observed above 87 K in 3MP, 92 K in MCH and 105 K in EtOH/MeOH matrices. Non-radiative decay rate constants strongly depend on the viscosity of the solvent; in the more viscous solvent, non-radiative decay rates become smaller. The activation energies depend on the solvent viscosity and it was ascertained that the mutual conversion process between 3 ππ * and 3 πσ * requires conformational change.

Photochemical reaction intermediates of benzyl chloride in condensed phase

Reaction intermediates produced upon the photolysis of benzyl chloride have been studied in glassy matrix and in solution. In the steady-state photolysis both benzyl radicals and structural isomers of benzyl chloride were formed in ethanol, while in 3-methylpentane the structural isomers were predominantly formed. The nanosecond laser photolyses of benzyl chloride in ethanol and in cyclohexane also generated benzyl radicals and structural isomers at room temperature. In acetonitrile, in addition to these species, benzyl cations were observed in the early stage after the photolysis.

Phosphorescence spectra of bromobenzene in highly viscous glassy matrices

Abstract Phosphorescence spectra of bromobenzene have been observed in glycerol, 3-methyloctane and 4-methylheptane glassy matrices. The phosphorescence quantum yield has been determined to be ca. 0.03 in glycerol at 77 K. The phosphorescence is composed of two emissions, from 3 π π ∗ and 3 π σ ∗ to the ground state. The phosphorescence radiative lifetime is 14 times shorter than that of chlorobenzene and this shortening has been explained by the internal heavy atom effect. The non-radiative rate constants were independent of the solvent species but depended only on the solvent viscosity. The non-radiative decay rate constant was 10 2 times larger than that of chlorobenzene.

First observation of the triplet state of fluorobenzene

Abstract A triplet–triplet (T–T) absorption spectrum of fluorobenzene was observed for the first time. The broad absorption in the region of 330–550 nm with lifetime of τ=0.7 μs was ascribed to the T–T absorption spectrum by the T–T energy transfer experiment using naphthalene as an acceptor. The spectrum reported previously as the T–T absorption was elucidated to be the spectrum of radical. Quantum yield of the intersystem crossing φISC was determined to be 0.27 by use of the time-resolved thermal lensing (TRTL) experiment.

Photochemical formation of 9-silaanthracenes in rigid glass

UV photolysis of 9,10-dihydro-9-silaanthracenes in 3-methylpentane glass at 77 K results in the formation of 9-silaanthracenes and diphenylmethyl-type radicals; by use of a triplet quencher, it was confirmed that these were produced via the lowest triplet state.

Verification of Photochemically Induced Crystallization Mechanism of Proteins by Dimer Addition

We investigated the light-induced crystallization mechanism of proteins. The photochemically produced protein dimer was thought to grow to a crystal size. This was proven experimentally in this study.

Evidence for the specific species of benzyltriethoxysilane derivatives with a high-coordination silicon atom.

Evidence for the specific species of benzyltriethoxysilane derivatives with a high-coordination silicon atom is presented. Nanosecond laser flash photolyses of benzyltriethoxysilane and triethoxysilyldiphenylmethane have been studied in polar and nonpolar solvents. For the transient absorption spectra of benzyltriethoxysilane and triethoxysilyldiphenylmethane in methanol, a characteristic band attributed to the benzyl radical or diphenylmethyl radical was observed at around 317 and 330 nm, with a second-order decay rate constant of 5.7 × 10(9) and 4.2 × 10(9) M(-1) s(-1), respectively. While in cyclohexane, an absorption band attributable to the specific species with a high-coordination silicon atom was observed at around 330 nm with a first-order decay rate constant of 5.7 × 10(4) and 1.2 × 10(4) s(-1) for benzyltriethoxysilane and triethoxysilyldiphenylmethane, respectively. A two-step laser-induced fluorescence study of triethoxysilyldiphenylmethane supports the assignment that the transient absorption bands observed at around 330 nm in methanol and in cyclohexane are ascribed to the diphenylmethyl radical and the specific species of triethoxysilyldiphenylmethane with a high-coordination silicon atom, respectively. The candidates for this specific species with a high-coordination silicon atom have been calculated by means of the TD-DFT method and SAC-CI method, and their molecular structures were discussed.

Photochemically Induced Crystallization of Proteins Accelerated on Two-Dimensional Gold Gratings

The photochemically induced crystallization of lysozyme was studied on a two-dimensional surface relief grating coated with a thin gold film (2D-plasmonic chip), a flat thin gold film, and a flat UV-curable resin. The lysozyme solution prepared in a metastable compositional region was dropped on each surface. After an exposure to visible light from a filtered Hg lamp (500 and 800 nm in wavelength, 1.5 W/cm2) for 30 min followed by 18 h keeping in the dark, the crystal particles were observed in the droplets. Under a microscope, the numbers of crystalline particles were counted to be 1280, 258, and 180 on the 2D-plasmonic chip, the flat gold film, and the flat UV-curable resin, respectively. It was suggested that the crystallization tendency of lysozyme was effectively accelerated by the enhanced electric field caused by the coupling of incident light with surface plasmon polaritons on the 2D-plasmonic chip.