Highly NIR-emissive lanthanide polyselenides

Ln(SePh)(3) (Ln = Ce, Pr, Nd), prepared by reduction of PhSeSePh with elemental Ln and Hg catalyst, reacts with excess elemental Se to give (py)(11)Ln(7)Se(21)HgSePh, an ellipsoidal polyselenide cluster. The molecular structure contains two square arrays of eight- or nine-coordinate Ln fused at one edge to form a V shape that is also capped on the concave side by a centrally located nine-coordinate (Se(3))pyLn(Se(3)) and on the convex side by a 2-fold disordered SeHgSePh. The central Ln coordinates to selenido, triselenido, and pyridine ligands, while all other Ln coordinate to selenido, diselenido, triselenido, and pyridine ligands. Thermal treatment of the Pr compound at 650 °C gave Pr(2)Se(3) and Pr(3)Se(4). NIR emission studies of the Nd compound show four transitions from the excited-state (4)F(3/2) ion to (4)I(9/2), (4)I(11/2), (4)I(13/2), and (4)I(15/2) states. The (4)F(3/2) ion to (4)I(11/2) transition (1075 nm emission) exhibited 43% quantum efficiency. This is the highest quantum efficiency reported for a 'molecular' Nd compound and leads a group of selenide-based clusters that has shown extraordinary quantum efficiency. In terms of efficiency and concentration, these compounds compare favorably with solid-state materials.