Highly efficient blue photoexcitation of europium in a bimetallic Pt-Eu complex

We report the preparation and characterization of dinuclear Pt-Ln complexes constructed from a square-planar P-II core bearing an ethynyl-terpyridine residue connected to platinum by the ethynyl bond. Complexation of the neutral Eu(hfaC)(3) (hfac=hexafluoroacetylacetonate) fragment to free terpyridine (terpy) gives a stable bimetallic complex (log beta=6.7). In the crystal structure, the flat Pt terpy core coordinates to Eu-III, which is nonacoordinated with the three nitrogen atoms of the terpy subunit and six oxygen atoms of the three hfac ligands. These atoms form a distorted monocapped square antiprism with a pseudo-C-2 symmetry axis passing through the nitrogen atom of the central pyridine ring and the Eu atom. Spectroscopic measurements showed that irradiation with visible light of wavelength up to 460 nm in the (MLCT)-M-1 state of the Pt subunit resulted in a quantitative energy transfer to the Eu center, which strongly luminesces in the red with an overall luminescence quantum yield of 38%. The energy-transfer process is quantitative and not sensitive to oxygen, and the complexation of Eu to the Pt metallosynthon allows the recovery of the energy lost due to triplet-oxygen quenching of the (MLCT)-M-3 state observed in the uncomplexed Pt precursor.