Sensitization of lanthanide luminescence by two different Pt-->Ln energy transfer pathways in PtLn3 heterotetranuclear complexes with 5-ethynyl-2,2'-bipyridine.

Reactions of 5-[2-(trimethylsilyl)-1-ethynyl]-2,2'-bipyridine (Me3SiC-Cbpy) with Pt(bpy)C12 (bpy = 2,2'-bipyridine) and Pt(bpyC[triple bond]C-C[triple bond]Cbpy)Cl2 (bpyC[triple bond]C-C[triple bond]Cbpy=bis(2,2'-bipyridin-5-yl)butadiyne) induced isolation of Pt(bpy)(C[triple bond]Cbpy)2 (1) and Pt(bpyC[triple bond]C-C[triple bond]Cbpy)(C[triple bond]Cbpy)2 (5), respectively. Incorporating Ln(hfac)3(H2O)2 (hfac = hexafluoroacetylacetone) with 1 or 5 gave the corresponding PtLn2 (Ln = Nd (2), Eu (3), Yb (4)) or PtLn3 arrays (Ln=Nd (6), Eu (7), Gd (8), Yb (9)). With excitation at 360 < or = lamda(ex)0 < or =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 Pt(II) antenna chromophores. In contrast with quite efficient Pt-->Ln energy transfer in the Pt-C[triple bond]Cbpy-Ln(Pt...Ln = 8.6 A) array, energy transfer transmitted across the Pt-bpyC[triple bond]C-C[triple bond]Cbpy-Ln(Pt...Ln = 13.3 A) array is less efficient owing to the much longer Pt...Ln separation in the latter.