Visible, Near-Infrared, and Dual-Range Luminescence Spanning the 4f Series Sensitized by a Gallium(III)/Lanthanide(III) Metallacrown Structure.

Lanthanide(III) ions (Ln) in coordination compounds exhibit unique luminescence properties with narrow and characteristic f-f transitions throughout the visible and near-infrared (NIR) ranges. In addition, some Ln such as Pr, Sm, Dy, Ho, Er, and Tm possess an exceptional ability, although less explored, to exhibit dual-range emissions. Such remarkable features allow highly specific use in materials science and biology, for example, for the creation of sophisticated barcode modules or for the next generation of optical imaging applications. Herein, a series of Ga/Ln metallacrowns (MCs) with the general composition [LnGa(shi)(OH)]Na·CHOH·HO (, Ln = Pr, Nd, Sm-Yb and analogue Y; Hshi = salicylhydroxamic acid) is presented. were obtained by reacting Ga and Ln nitrate salts with the Hshi ligand. X-ray single crystal unit cell analysis confirmed that all MCs are isostructural. The crystal structure was solved for the Nd analogue and revealed that Nd is centered between two [12-MC-4] MC rings and bound to eight hydroximate oxygen ions (four from each ring) in a pseudosquare antiprismatic fashion adopting a pseudo- symmetry. Pulsed gradient spin echo diffusion ordered H NMR spectroscopy and electrospray ionization mass spectrometry confirmed that the structure of remains intact in methanol solutions while mass spectrometry suggests that four OH bridges are exchanged with CHO/CDO. An exceptional ability of this series of MCs to sensitize the characteristic emission of Ln was confirmed with the observation of bright red and green emission signals of and , NIR emissions of and , and dual-range emissions of , , , , , and in the solid state upon excitation into ligand-centered bands at 340 nm. The luminescence properties of (Ln = Nd, Sm, Eu, Tb, Dy, and Yb) were also investigated in CHOH and CDOD solutions. For and MCs, more extensive analyses of the photophysical properties were performed, which included the determination of radiative lifetimes, intrinsic quantum yields, and sensitization efficiencies. The absolute quantum yields () of in the visible and NIR ranges have been determined. In the case of , the values of in CHOH and CDOD solutions are exceptionally high, that is, 10.1(5) and 83(1) %. Values obtained for , that is, 0.78(4) % in CHOH and 8.4(1)% in CDOD, are among the highest ones reported today for Yb complexes formed with nondeuterated and nonhalogenated ligands.