Mechanistic analysis of the photocycloaddition of silyl-tethered alkenes.

The photochemistry of substituted cinnamyloxy silanes has been examined in both cyclohexane and acetonitrile solvents. Alkene isomerization occurs in addition to cycloaddition. Fluorescence quantum yields and excited singlet state lifetimes have been determined for each compound.

Methoxy-substituted stilbenes, styrenes, and 1-arylpropenes: photophysical properties and photoadditions of alcohols.

The photochemistry of trans-stilbene and four methoxy-substituted stilbene derivatives has been investigated in a variety of solvents. The fluorescence of all five trans isomers was quenched by 2,2,2-trifluoroethanol (TFE). Upon irradiation of the five substrates in TFE, the products derived from photoaddition of the solvent were detected.

Activation energies for the singlet excited state processes of substituted benzenes: para, meta, and ortho isomers of methylbenzonitrile and methylanisole in acetonitrile.

The rate constants of decay of the excited singlet states of the methylbenzonitriles (1-3) and the methylanisoles (4-6) have been determined by the measurement of fluorescence lifetimes over a broad range of temperatures (-45 to +65 degrees C) in acetonitrile. By fitting this data to a nonlinear expression that includes the Arrhenius equation, rate constants for the activated process (reaction) and the unactivated ones (fluorescence and intersystem crossing) can be reliably obtained. Available literature data for benzene, toluene, and ortho-xylene were also analyzed.

The photochemical addition of 2,2,2-trifluoroethanol to methoxy-substituted stilbenes.

The excited-state lifetime of the trans-stilbene chromophore in acetonitrile is prolonged by methoxy substituents in the meta positions. The long-lived singlet excited state of trans-3,5-dimethoxystilbene (trans-2d) is quenched upon the addition of 2,2,2-trifluoroethanol (TFE), and the Markovnikov ether is observed as the major product from steady-state irradiations. The results indicate that the reaction pathway proceeds through a carbocation intermediate.

Zeolite-confined Nano-RuO(2): A green, selective, and efficient catalyst for aerobic alcohol oxidation.

The development of green, selective, and efficient catalysts, which can aerobically oxidize a variety of alcohols to their corresponding aldehydes and ketones, is of both economic and environmental significance. We report here the synthesis of a novel aerobic oxidation catalyst, a zeolite-confined nanometer-sized RuO(2) (RuO(2)-FAU), by a one-step hydrothermal method. Using the spatial constraints of the rigid zeolitic framework, we sucessfully incorporated RuO(2) nanoparticles (1.

Substituent effects on the rate constants for the photo-Claisen rearrangement of allyl aryl ethers.

The photochemistry of 11 substituted allyl 4-X- and 3-X-aryl ethers 3 (ArOCH2-CH=CH2) has been examined in both methanol and cyclohexane as solvents. The ethers react by the photo-Claisen rearrangement to give allyl substituted phenols as the major primary photoproducts, as expected from the well-established radical pair mechanism. The excited singlet state properties (absorption spectra, fluorescence spectra, fluorescence quantum yields, and singlet lifetimes) were compared with a parallel set of unreactive 4-X- and 3-X-anisoles 4.