Sensitized Near-Infrared Emission from Ir^III-Ln^III (Ln = Nd, Yb, Er) Bimetallic Complexes with a (N^∧O)(N^∧O) Bridging Ligand

A (N∧O)­(N∧O) bridging ligand, 5-bromopyrimidine-2-carboxylic acid (bpmc), was used for connecting IrIII and LnIII centers to construct the series of d–f bimetallic complexes Ir­(pdt)2(μ-bpmc)­Ln­(TTA)3, where pdt = 1,3-dimethyl-5-phenyl-1H-[1,2,4]­triazole, TTA = 4,4,4-trifluoro-1-(thiophen-2-yl)-butane-1,3-dionate, and Ln = Nd, Yb, Er, Gd. Crystallographic analyses reveal that there are very short spatial distances between the d–f centers (about 6 Å), and photophysical studies demonstrate the appropriate energy level of the IrIII chromophore for sensitization of near-infrared (NIR) lanthanide ions, both of which are two important factors for efficient IrIII → LnIII energy transfer. The energy transfer rates for IrIII-NdIII, IrIII-YbIII, and IrIII-ErIII are calculated to be 3.6 × 109, 2.8 × 108, and 4.0 × 108 s–1, respectively.