Structure and photophysics of near-infrared emissive ytterbium(III) monoporphyrinate acetate complexes having neutral bidentate ligands

Substitution reactions between [Yb(TPP)(OOCCH₃)(CH₃OH)₂] (1) and neutral bidentate ligands NN led to the formation of monoporphyrinate ytterbium(III) complexes [Yb(TPP)(OOCCH₃)(NN)] (TPP = 5,10,15,20-tetraphenylporphyrinate anion; NN = 4-methyl-1,10-phenanthroline (2), 1,10-phenanthroline (3), 4,7-dimethyl-1,10-phenanthroline (4), 5,6-epoxy-5,6-dihydroxy-1,10-phenanthroline (5) and 2,2′-dipyridylamine (6)). Single-crystal X-ray diffraction analysis revealed that ytterbium(III) ions in 1 and 6 were seven-coordinate with OOCCH₃⁻ in monodentate coordination, whereas those in 2, 3, 4 and 5 were eight-coordinate with OOCCH₃⁻ in bidentate coordination. The visible emission (650 and 720 nm) from the porphyrin and near-infrared (NIR) emission (980 and 1003 nm) from ytterbium(III) ion were observed for all complexes. The eight-coordinate complexes exhibited stronger NIR emission and longer lifetimes in toluene solution than the seven-coordinate complexes. The NIR emission of complexes with decreased lifetimes was also observed when they were blended into organic polymer PMMA.