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Near-infrared (NIR) fluorescent dyes with favorable photophysical properties are highly useful for bioimaging, but such dyes are still rare. The development of a unique class of NIR dyes via modifying the rhodol scaffold with fused tetrahydroquinoxaline rings is described. These new dyes showed large Stokes shifts (>110 nm). Among them, WR3, WR4, WR5, and WR6 displayed high fluorescence quantum yields and excellent photostability in aqueous solutions. Moreover, their fluorescence properties were tunable by easy modifications on the phenolic hydroxy group. Based on WR6, two NIR fluorescent turn-on probes, WSP-NIR and SeSP-NIR, were devised for the detection of H S. The probe SeSP-NIR was applied in visualizing intracellular H S. These dyes are expected to be useful fluorophore scaffolds in the development of new NIR probes for bioimaging.

We have investigated the electronic structure of Sr 2 FeMoO 6 by photoemission spectroscopy and bandstructure calculations within the local-density approximationϩU (LDAϩU) scheme. In valence-band photoemission spectra, a distinct double-peak feature has been observed near the Fermi level (E F ). A photon-energy dependence of the spectra and the LDAϩU band-structure calculation have revealed that the first peak crossing E F consists of the ͑FeϩMo͒ t 2g↓ states and the second peak well below E F is dominated by the Fe e g↑ states. This clearly shows that only the down-spin states contribute to the E F intensity, thus the half-metallic density of states ͑DOS͒ is realized. We point out that the observed half-metallic DOS can be attributed to the strong Hund's rule energy stabilization due to the high-spin 3d 5 configuration at the Fe site.

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