Preparation, Characterization, and Photophysical Properties of cis- or trans-PtLn2 (Ln = Nd, Eu, Yb) Arrays with 5-Ethynyl-2,2′-bipyridine

Reaction of cis- or trans-Pt(PPh3)(2)Cl-2 (PPh3 = triphenylphosphine) with 5-[2-(trimethylsilyl)-1-ethynyl]-2,2'-bipyridine (bpyC CSiMe3) gave cis-Pt(PPh3)(2)(C Cbpy)(2) (1) or trans-Pt(PPh3)(2)(C bpy)(2) (5). Incorporating 1 or 5 with Ln(hfac)(3)(H2O)(2) (hfac = hexafluoroacetylacetonate) induced formation of the corresponding cis- or traps-PtLn(2) heterotrinuclear complexes cis-Pt(PPh3)(2){(C Cbpy)Ln(hfac)(3)}(2) (Ln = Nd 2, Eu 3, Yb 4) or geometrical isomers traps-Pt(PPh3)(2){(C Cbpy)Ln(hfac)(3)}(2) (Ln = Nd 6, Eu 7, Yb 8). As verified through P-31 NMR characterization as well as determination of the structures of 1, 4, and 8 by X-ray crystallography, the cis- or traps-arranged forms around Pt-II centers remain unchanged in both solutions and solid states without thermal or light-induced isomerization during the reactions. With excitation at 360 < lambda(ex) < 450 nm, which is the absorption region of metal-perturbed pi-->pi*(C C) transitions and d pi(Pt)-->pi*(C Cbpy) MLCT transition, sensitized lanthanide luminescence occurs with a microsecond range of lifetimes in both cis- and traps-arranged PtLn(2) complexes, revealing that efficient Pt-->Ln energy transfer is indeed operating from the platinum(II) acetylide chromophore to lanthanide centers.