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 Ir^III and Ln^III 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 Ir^III chromophore for sensitization of near-infrared (NIR) lanthanide ions, both of which are two important factors for efficient Ir^III → Ln^III energy transfer. The energy transfer rates for Ir^III-Nd^III, Ir^III-Yb^III, and Ir^III-Er^III are calculated to be 3.6 × 10⁹, 2.8 × 10⁸, and 4.0 × 10⁸ s^–1, respectively.