Variant coordination sphere, for efficient photo- and electroluminescence of 0.4–1.8 μm, of lanthanide(III) complexes containing a β-diketone ligand with low vibrational frequency C–F bonds and a flexible 2,2′-bipyridine ligand

Abstract

Lanthanide tris(β-diketonate) complexes of variant coordination numbers with the compositions [La(hfaa)3(bpy)2] (1), [Nd(hfaa)3(bpy)(H2O)]·½bpy (2), [Sm(hfaa)3(bpy)(H2O)]·bpy (3) and [Ln(hfaa)3(bpy)] (Ln=Nd (4), Sm (5), Eu (6), Ho (7), Er (8) and Yb (9); hfaa=anion of hexafluoroacetylacetone and bpy=2,2′-bipyridine) have been synthesized and fully characterized. The single crystal analysis of (2) and (3) reveals that Nd and Sm are mononuclear and nine-coordinate (LnO7N2) with a monocapped square antiprismatic geometry. The photophysical parameters obtained are lower than their anhydrous eight-coordinated analogues. The complexes show high quantum efficiencies in the both visible and NIR regions, which could be related to the formation of highly protected coordination environments (LnO6N4 or LnO6N2) by the hfaa− and bpy ligands around the Ln(III) ions. Finally, these volatile and luminescent complexes were used to fabricate OLEDs. The best Vis–NIR devices with the structures: ITO/CuPc (15nm)/[Sm(hfaa)3(bpy)] or [Nd(hfaa)3bpy]:CBP or [Er(hfaa)3bpy]:CBP or [Yb(hfaa)3bpy]:CBP (50nm)/BCP (20nm)/AlQ (30nm)/LiF (1nm)/Al (100nm), show a maximum brightness of 45cd/m2 with a current efficiency of 0.19cd/A for visible devices, while the NIR devices exhibit a maximum NIR irradiance and a maximum external quantum efficiency (EQE) of 28μWcm−2 and 0.022% for Nd(III), 0.50μWcm−2 and 0.011% for Er(III) and 93μWcm−2 and 0.18% for Yb(III), respectively, which indicate highly improved EL performance over devices reported in the literature.