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Hexagonal Sodium Yttrium Fluoride Based Green and Blue Emitting Upconversion Phosphors. -Pure hexagonal Na 3x Ln 2-x F 6 (Ln: Y, Nd, Er, Tm, Yb; x = 0.45) phosphor powder samples are synthesized from Ln2O3, Na2CO3, HBr, and HF in H2O (550-540°C, 40 h). As revealed by powder XRD the samples crystallize in the space group P63/m with Z = 1. The samples doped with 18% Yb + 2% Er and 25% Yb + 0.3% Tm show the highest upconversion efficiencies for green and blue emission, respectively. The obtained phosphor materials show no degradation under high-power IR laser excitation. -(KRAEMER*, K. W.; BINER, D.; FREI, G.; GUEDEL, H. U.; HEHLEN, M. P.; LUETHI, S. R.; Chem. Mater. 16 (2004) 7, 1244-1251; Inst. Chem. Biochem., Univ. Bern, CH-3012 Bern, Switz.; Eng.) -W. Pewestorf 26-017

An efficient synthetic approach to construct a fully substituted benzo[1,2-b:4,5-b']difuran (BDF) 2a via base-catalyzed double annulations is presented. Compound 2a can readily undergo Suzuki, Heck, and Sonogashira coupling reactions to afford in good yields a manifold of extended pi-conjugated BDF derivatives, e.g., with pyridine termini (4-6) and with different spacers. These are highly luminescent materials that undergo two reversible one-electron oxidations. Remarkably, their photophysical and electrochemical properties can be largely tuned by methylation or protonation. Consequently, they can function as pH-dependent fluorescence switches. Finally, the observed electronic properties are explained on the basis of density functional theory.

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Benzodifuran-functionalised pyrene and anthracene fluorophores 1 and 2 were obtained in reasonable yields. Their single crystal structures, electrochemical, optical absorption, and fluorescence characteristics have been described. They show strong luminescence with high quantum yields of 0.53 for 1 and 0.48 for 2.

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The crystal structure of [Rh(phpy)2(bpy)]PF6 (phpyH = 2-phenylpyridine, bpy = 2,2,-bipyridine) is determined and described. Crystallographic data at 100 K: chemical formula C32H24F6N4PRh, orthorhombic crystal system, space group Pbca (No. 61), Z = 8, a = 10.821 (1) A, b = 15.798 (1) A, c = 33.328 (3) A, V= 5697.4 (9) A3. There is one complex cation, i.e. two crystallographically inequivalent phpy ligands, per asymmetric unit. Polarized single-crystal absorption spectra of [Rh(phpy)2(bpy)]PF6 and excitation and site-selective luminescence spectra of [Rh(thpy)2(bpy)]+ and [Rh(thpy)(phpy)(bpy)]+ (thpyH = 2-thienylpyridine) doped into [Rh(phpy)2(bpy)]PF6 are reported and interpreted on the basis of the crystal structure of [Rh(phpy)2(bpy)]PF6. The two lowest-energy excitations of [Rh(phpy)2(bpy)]PF6, and also of [Rh(phpy)2(bpy)]BPh4, [Rh(phpy)2(en)]PF6, and [Rh(phpy)2-(en)]BPh4 (BPh4" = tetraphenylborate anion, en = ethylenediamine), are found in the region between 21 400 and 22 200 cm-1 with an energy splitting ranging from 22 to 242 cm-1. They are assigned to electronic transitions involving the phpy ligands. The third excited state of [Rh(phpy)2(bpy)]PFe lies 967 cm-1 above the first excited state and is ascribed to an analogous transition involving the bpy ligand. The polarization properties of these three lowest-energy transitions and the crystal structure of [Rh(phpy)2(bpy)]PF6 show that the transition moments are parallel to the ligand planes: The bpy transition is short-axis polarized, and the two phpy transitions are oriented approximately parallel to the respective Rh-N(phpy) bonds. It is concluded that the three lowest-energy excited states are essentially 3 * states, localized on the three ligands of the complex. They have a small admixture of the lowest-energy 'drr* excitations through spin-orbit coupling.