A symmetric oxyselenenylation of simple olefins using optically active selenobinaphthyls

Asymmetric trans-addition reactions of simple olefins have been performed by using optically active 2-selenobinaphthyls 1 , 2a–g. Introduction of an amide group at the 2′-position in the binaphthyl skeleton enhances considerably the diastereomeric excess (de) of the asymmetric methoxyselenenylation. In the case of trans-olefins, introduction of another chiral center in the amide group further enhances the de due to double stereodifferentiation between the (R)-binaphthyl skeleton and the chiral amide group introduced at the 2′-position in the binaphthyl skeleton. The use of chiral nucleophiles is also effective to enhance the de for symmetrical cis-olefins.     

Stimulated emission cross sections and temperature-dependent spectral shifts of neutral nitrogen-vacancy centers in diamonds

The neutral nitrogen-vacancy (NV⁰) defects in diamond are photostable color centers, suitable for a wide range of applications in science and engineering. However, the photophysical properties of the centers have not yet been fully characterized. This work measured the stimulated emission cross sections of NV⁰ in a single-crystal diamond by two-photon excitation of its matrix at 344 nm. From the measured photoluminescence spectrum and the fluorescence lifetime of 20 ± 1 ns, we determined a peak stimulated emission cross section of 1.43 ± 0.07 × 10⁻¹⁷ cm² at 650 nm for the NV⁰ centers. In addition, we have also examined the thermal shifts of the zero-phonon line of NV⁰ centers in nanoscale diamonds (~100 nm in diameter) over the temperature range of 30–120°C. A temperature measurement sensitivity of 0.2 K·Hz^−1/2 was achieved, which is about two-fold better than that of NV⁻, despite that the fluorescence intensity of NV⁰ is about six-fold lower than that of NV⁻ in the same nanoparticles. The result is attributed to the smaller electron–phonon coupling strength of the neutral center, compared with its negatively charged counterpart.