Syntheses, characterization and sensitized lanthanide luminescence of heteronuclear Pt-Ln (Ln = Eu, Nd, Yb) complexes with 2,2′-bipyridyl ethynyl ligands

Reaction of [Pt(Bu-3(t) tpy)Cl](+) (Bu-3(t) tpy = 4,4',4 ''-tri-tert-butyl-2,2':6',2 ''-terpyridine) with 5-ethynyl-2,2'-bipyridine (HC=Cbpy) or 5,5'-bis(trimethylsilylethynyl)-2,2'-bipyridine (Me3SiC=CbpyC=CSiMe3) in the presence of cuprous iodide gives [Pt((t)Bu(3)tpy)(C Cbpy)](+) (1) or [{Pt(Bu-3(t) tpy)}(2)(C CbpyC C)](2+) (2) through Pt-acetylide sigma-coordination, respectively. Incorporating 1 or 2 with Ln(hfac)(3)(H2O)(2) through 2,2'-bipyridyl chelating the Ln(III) (Ln = Nd, Eu, and Yb) centers induces formation of a series of [Pt(Bu-3(t) tpy)(C Cbpy){Ln(hfac)(3)}](+) (PtLn) or [{Pt(Bu-3(t) tpy)}(2)(C CbpyC C){Ln(hfac)(3)}](2+) (Pt(2)Ln) complexes, respectively. The structures of binuclear platinum(II) complex 2(PF6)(2) and heterobinuclear PtNd complex 3(CF3COO) were determined by single crystal X-ray diffraction. Both 1 and 2 exhibit typical low-energy absorption bands in near UV-Vis region, ascribed to d pi(Pt)->pi*(Bu-3(t) tpy) MLCT and pi(C Cbpy/C CbpyC C)-> pi*(Bu-3(t) tpy) LLCT transitions. Upon formation of the PtLn or PtLn(2) complexes, the low-energy absorption bands are obviously blue-shifted (15-20 nm) compared with those in the Pt-II precursor 1 or 2. With excitation at 350 nm < lambda < 550 nm which is the absorption region of MLCT and LLCT transitions, sensitized luminescence that is characteristic of the corresponding lanthanide(III) ions occurs in both PtLn and Pt(2)Ln complexes. In contrast, Pt-based luminescence from the MLCT and LLCT states are mostly quenched in these Pt-Ln heteronuclear complexes, revealing that quite effective PL -> Ln energy transfer is operating from the Pt(Bu-3(t) tpy)(acetylide) chromophore to the lanthanide(III) centers. (C) 2008 Elsevier B. V. All rights reserved.