Sensitization of lanthanide luminescence by two different Pt -> Ln energy transfer pathways in PtLn(3) heterotetranuclear complexes with 5-ethynyl-2,2 '-bipyridine

Reactions of 5-[2-(trimethylsilyl)-1-ethynyl]-2,2'-bipyridine (Me3SiC Cbpy) with Pt(bpy)Cl-2 (bpy = 2,2'-bipyridine) and Pt(bpyC C-C Cbpy)Cl-2 (bpyC C-C Cbpy = bis(2,2'-bipyridin-5-yl)butadiyne) induced isolation of Pt(bpy)(C Cbpy)(2) (1) and Pt(bpyC C C Cbpy)(C Cbpy)(2) (5), respectively. Incorporating Ln(hfac)(3)(H2O)(2) (hfac = hexafluoroacetylacetone) with 1 or 5 gave the corresponding PtLn(2) (Ln = Nd (2), Eu (3), Yb (4)) or PtLn(3) arrays (Ln = Nd (6), Eu (7), Gd (8), Yb (9)). With excitation at 360 <= lambda(ex) <= 480 nm, which is the MLCT absorption region of the Pt(2,2'-bipyridyl)(acetylide)(2) chromophore, sensitized lanthanide luminescence is successfully attained by efficient Pt. Ln energy transfer from the PtII antenna chromophores. In contrast with quite efficient Pt. Ln energy transfer in the Pt-C Cbpy-Ln (Pt center dot center dot center dot Ln = 8.6 angstrom) array, energy transfer transmitted across the Pt-bpyC C-C Cbpy-Ln (Pt center dot center dot center dot Ln = 13.3 angstrom) array is less efficient owing to the much longer Pt center dot center dot center dot Ln separation in the latter.