The photocatalytic decomposition of phenol in oxygenated aqueous suspensions of lightly-reduced anatase TiO2, being the most satisfactory among the semiconductors investigated from the standpoint of the photocatalytic activity and stability, has been investigated at the optimum pH 3.5. The products at the initial stage of the reaction were hydroquinone, pyrocatechol, 1,2,4-benzenetriol, pyrogallol, and 2-hydroxy-1,4-benzoquinone. These intermediates underwent further photocatalytic oxidation via acids and/or aldehydes finally into CO2 and H2O. A reaction scheme involving hydroxyl radicals as real reactive species has been proposed. Although H2O2 was formed via O2\ewdot produced by electron trapping of adsorbed oxygen, its concentration remained constant at a low value during the reaction. About 0.7 mole of O2 was consumed for the consumption of one mole of phenol at the initial stage of the reaction. These results indicated that hydroxyl radicals were formed not only via holes but also via H2O2 from O2\ewdot. It was interesting from the viewpoint of wastewater treatment that phenol was completely mineralized to CO2 in the presence of TiO2 powder under solar irradiation without both aeration and mixing of the solution.

The photocatalytic decomposition of phenol over anatase TiO2 powder followed the first-order kinetics, upto high conversions, of which the apparent rate constant kap depended on initial concentration of phenol [phenol]0, [TiO2], O2 pressure pO2, and incident light intensity I. The dependence of the initial reaction rate Ω0 on [phenol]0 showed characteristic curvature convex to the concentration axis. The pO2 dependence of both Ω0 and kap was very similar each other and showed characteristic curvature to the pO2 axis. The dependence of both Ω0 and kap on [phenol]0 was affected by the [TiO2] and I. Both Ω0 and kap were proportional to I below ca. 1×10−5 mol m−2 s−1 and to I1⁄2 above 2×10−5 mol m−2 s−1. The activation energy was 10 kJ/mol. The results were satisfactorily explained by the equation; Ω=φ·OHIan\fracKO2pO21+KO2pO2·\frac[phenol][phenol]0+β, where Ω is the reaction rate; φ·OHIan, a parameter related to the formation rate of ·OH radicals or real reactive species; KO2, the equilibrium constant of Langmuir adsorption of O2; β, the ratio of the combined first-order rate constant of the reaction of ·OH with species other than organic compounds to the second-order rate constant of the reaction of ·OH with phenol.

The emission properties of poly(N-vinylcarbazole) (PVCz) prepared by radical and cationic polymerization (PVCz(r) and PVCz(c) respectively), the oligomers of N-vinylcarbazole, and poly[2-(N-carbazolyl)ethyl vinyl ether] (PCzEVE) were investigated in solutions. The fluorescence spectrum of PVCz(r) was different from that of PVCz(c). This seems to be attributable to the difference in the tacticity between them. On the basis of this result, the structure of the second excimer site is discussed. PCzEVE, in which the carbazolyl chromophores are widely spaced on the skeletal chains by –O–CH2–CH2– bonds, showed an interesting, new, structureless emission band with a peak at 27000 cm−1. This was different from both the monomeric structured fluorescence and the sandwich-like excimer one which were observed for the model compounds and the polymers. The emission properties of PCzEVE were unique among the vinyl polymers with aromatic chromophores widely spaced on the skeletal chain.

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The solvent viscosity effect on photochromic reaction processes such as cyclization and cycloreversion of a diarylethene derivative, 2-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride (TMTMA), was investigated by means of steady-state spectroscopy, picosecond transient absorption, and fluorescence measurements. The cyclization reaction yields from the excited open-ring isomer decreased with an increase in solvent viscosity. Picosecond transient absorption spectroscopy revealed that the cyclization reaction took place via two pathways; very rapid reaction immediately after the excitation in competition with the relaxation to the fluorescent state and the rather slow reaction from the relaxed fluorescent state with the time constant of several hundred picoseconds. The latter slow process was strongly dependent on the solvent viscosity, whereas the former rapid process was almost independent of the viscosity. This viscosity dependence of the reaction from the fluorescent state was attributed to the solvent molecular friction to the rotation of the thienyl moieties leading to the favorable geometry for the cyclization. For the cycloreversion reaction, much smaller solvent viscosity dependence was observed and reaction time constants less than 1−2 ps were estimated by transient absorption spectroscopy. By integrating these experimental results with the potential energy surfaces predicted from theoretical investigation, the mechanism of the photochromic reaction of TMTMA was discussed.