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

A (N boolean AND O)(N boolean AND O) bridging ligand, 5-bromopyrimidine-2-carboxylic acid (bpmc), was used for connecting Ir and Ln(III) centers to construct the series of d-f bimetallic complexes Ir(pdt)(2)(mu-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 angstrom), 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 x 10(9), 2.8 x 10(8), and 4.0 x 10(8) s(-1), respectively.