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

Reaction of [Pt(View the MathML sourceBu3ttpy)Cl]+ (View the MathML sourceBu3ttpy = 4,4′,4′′-tri-tert -butyl-2,2′:6′,2′′-terpyridine) with 5-ethynyl-2,2′-bipyridine (HCtriple bond; length of mdashCbpy) or 5,5′-bis(trimethylsilylethynyl)-2,2′-bipyridine (Me3SiCtriple bond; length of mdashCbpyCtriple bond; length of mdashCSiMe3) in the presence of cuprous iodide gives [Pt(t Bu3tpy)(Ctriple bond; length of mdashCbpy)]+ (1) or [{Pt(View the MathML sourceBu3ttpy)}2(Ctriple bond; length of mdashCbpyCtriple bond; length of mdashC)]2+ (2) through Pt-acetylide σ -coordination, respectively. Incorporating 1 or 2 with Ln(hfac)3(H2O)2 through 2,2′-bipyridyl chelating the LnIII (Ln = Nd, Eu, and Yb) centers induces formation of a series of [Pt(View the MathML sourceBu3ttpy)(Ctriple bond; length of mdashCbpy){Ln(hfac)3}]+ (PtLn) or [{Pt(View the MathML sourceBu3ttpy)}2(Ctriple bond; length of mdashCbpyCtriple bond; length of mdashC){Ln(hfac)3}]2+ (Pt2Ln) 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 dπ(Pt) → π∗(View the MathML sourceBu3ttpy) MLCT and π(Ctriple bond; length of mdashCbpy/Ctriple bond; length of mdashCbpyCtriple bond; length of mdashC) → π∗(View the MathML sourceBu3ttpy) LLCT transitions. Upon formation of the PtLn or PtLn2 complexes, the low-energy absorption bands are obviously blue-shifted (15–20 nm) compared with those in the PtII precursor 1 or 2. With excitation at 350 nm < λ < 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 Pt2Ln 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 Pt → Ln energy transfer is operating from the Pt(View the MathML sourceBu3ttpy)(acetylide) chromophore to the lanthanide(III) centers.