Unusual Reactivities of <i>ortho</i>-Hydroxy-β-nitrostyrene

Nitrostyrene derivatives are widely used in organic syntheses as a substrate for Michael addition, photoisomerization and cycloaddition. In contrast, ortho-hydroxy derivatives exhibit unusual behaviors in these reactions. Conjugate addition proceeded upon treatment of the ortho-hydroxy-β-nitrostyrene with an amine; however, subsequent C–C bond cleavage readily occurred to afford the corresponding imine. Moreover, conversion of the trans-isomer to a cis-isomer did not occur efficiently, even when UV light was irradiated. We studied these unusual behaviors of β-nitrostyrene, focusing on the role of the ortho-hydroxy group

Spectroscopic Features of Silica Glasses Doped with Tin

Abstract -The absorption, photoluminescence, and photoluminescence excitation spectra are investigated for tin-doped silica glasses synthesized by different methods. In all the glasses studied, two new centers belonging to the tin dopant in the SiO 2 network are revealed in addition to the well-known oxygen-deficient center with the absorption band at 4.9 eV. One new center is associated with the absorption band at 5.9 eV and the photoluminescence bands at 2.7 and 3.6 eV, whereas the other center is characterized by the absorption band in the range of 4.56 eV and the photoluminescence band at 2.95 eV. Both new centers are identified as oxygen-deficient centers. The latter center is an analog of the centers observed in pure silica glasses synthesized in a nitrogen atmosphere and in germanosilicate glasses prepared by the MCVD and SPCVD methods. It is revealed that the formation of the oxygen-deficient center is one of the main channels of incorporating tin into the SiO 2 network in all tin-containing silica glasses. Consideration is given to the reasons for the lower efficiency of the photodecay of oxygen-deficient centers in the SiO 2 network in tin-containing glasses as compared to that in germanosilicate glasses and for the relatively high efficiency in the formation of the photoinduced refractive index in optical fibers with a core consisting of tin-containing silica glass