Yoshihisa Matsushita

Recent progress on photoreactions in microreactors

A microreaction system for organic photoreactions was developed, and the processes of diastereo-differentiating photosensitized reaction, photocatalytic oxidation and reduction of organic compounds, and amine N-alkylation were examined in microspace. These model reactions proceeded very rapidly with considerably large photonic efficiencies because of some distinct properties of microreactors for photoreactions, such as higher spatial illumination homogeneity and better light penetration through the entire reactor depth, and large surface-to-volume ratio in comparison with large-scale batch reactors. These results suggest feasibility of microreaction systems on organic photoreactions.

The cavity size effect on the fluorescence properties of 4′-dimethylaminoacetophenone complexed with cyclodextrins

Abstract Fluorescence properties of excited 4 ′ -dimethylaminoacetophenone (DMAAP) complexed with α-, β-, and γ-cyclodextrins (CDs) were studied by means of steady state and time-resolved laser spectroscopy. The 1:2 DMAAP–α-CD and 1:1 DMAAP–β-CD complexes exhibited dual fluorescence in neutral aqueous solutions while only the fluorescence from the locally excited state was observed in the case of DMAAP complexed with γ-CD. The CD cavity size effect on the excited state dynamics of DMAAP–CD complexes was further discussed. It revealed that polarity effect introduced by the hydrophobic cavity is more important in controlling of the photochemistry of DMAAP than the restriction of molecular motion inside the CD cavity.

Photochemical reaction in the molecular clusters of benzophenone with hydrogen donors formed in a supersonic free jet expansion

Abstract Photochemical reactions in neutral molecular clusters of benzophenone with hydrogen donors formed in a supersonic free jet expansion have been studied. It has been found that intracluster hydrogen abstraction reaction takes place to form benzophenone ketyl radical in the benzophenone—1,4-cyclohexadiene mixed cluster. On the contrary, no ketyl radical has been detected when ethanol, 2-propanol, or several kinds of amine are used as a hydrogen donor. Excitation and emission spectra of the benzophenone— N , N -dimethylaniline cluster have suggested that benzophenone and N , N -dimethylaniline form a ground state charge transfer complex. The excitation of the benzophenone-tri- n -butylamine cluster promotes the transformation of the van der Waals complex to an exciplex. The reactivity of the clusters on hydrogen abstraction and charge transfer reactions has been discussed on the basis of the nature of hydrogen donors.

Photochemical and photophysical processes in the molecular cluster of fluorenone

Abstract Fluorescence properties of fluorenone and fluorenone molecular clusters with solvent molecules formed in a supersonic free jet expansion were studied. It revealed that fluorenone in the molecular cluster with acetonitrile emits strong fluorescence from its ππ * singlet state while fluorescence from bare fluorenone is very weak. Furthermore, no evidence of intracluster hydrogen abstraction to form ketyl radical in the cluster with 1,4-cyclohexadiene was observed. The fluorenone–ethanol cluster has considerably short lifetime of the S 1 state. It could be attributed to the fact that the hydrogen bond in the molecular clusters should accelerate the nonradiative process.

The photochemical reaction of excited acetophenone and benzaldehyde in the gas phase

Abstract The photochemistry of acetophenone and benzaldehyde with hydrogen donors has been studied in the gas phase. The quenching rate constants of the triplet acetophenone and benzaldehyde can be well correlated with the ionization potentials of hydrogen donors. The results suggested that the charge-transfer interaction plays an important role in the gas-phase reaction as in the case of condensed phase reaction. The slopes of Rehm-Weller plot are more stiff in the gas-phase reaction than condensed phase reaction, which indicates higher degree of charge transfer. Secondary amines were consistently better quencher of carbonyl triplet than tertiary amines, and steric effects are probably to be of importance.

Rotational conformers of m-methoxybenzyl radical in a supersonic jet

The laser induced fluorescence (LIF) excitation spectrum of m-methoxybenzyl radical generated by ArF laser photolysis in a supersonic jet has been observed for the first time. The origin bands in the D1 ← D0 transition are found to be 19 993.0 cm−1 and 19 648.3 cm−1 for the cis and trans conformers, respectively, arising from the orientation of the methoxy group with respect to the methylene group at the meta position. The existence of the rotational conformers was ensured by analyzing the single vibronic level (SVL) dispersed fluorescence spectra with the aid of ab initio calculation. The prominent vibronic bands observed in the LIF excitation and SVL dispersed fluorescence spectra for each conformer were successfully assigned. A significant difference between the conformers was found for their band intensities and frequencies in the observed spectra. The difference will be discussed in terms of intramolecular interaction between the ring carbon atom and the hydrogen atom of the methoxy group.

Photocatalytic Oxidation and Alkylation Processes in Microreactors

A microflow reaction system with immobilized a photocatalytic TiO2 layer was developed and the processes of oxidation of aromatic compounds and amine N-alkylation in microspace were examined. The photocatalytic microreactor has a remarkably large surface-to-volume ratio in comparison to conventional batch reactors and these model reactions proceeded very rapidly with considerably large efficiencies. The results suggest the feasibility of a photocatalytic microreaction system on organic reactions.