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

Reaction of [Pt(Bu3ttpy)Cl]+ (Bu3ttpy = 4,4′,4′′-tri-tert-butyl-2,2′:6′,2′′-terpyridine) with 5-ethynyl-2,2′-bipyridine (HCCbpy) or 5,5′-bis(trimethylsilylethynyl)-2,2′-bipyridine (Me3SiCCbpyCCSiMe3) in the presence of cuprous iodide gives [Pt(tBu3tpy)(CCbpy)]+ (1) or [{Pt(Bu3ttpy)}2(CCbpyCC)]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(Bu3ttpy)(CCbpy){Ln(hfac)3}]+ (PtLn) or [{Pt(Bu3ttpy)}2(CCbpyCC){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∗(Bu3ttpy) MLCT and π(CCbpy/CCbpyCC) → π∗(Bu3ttpy) 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(Bu3ttpy)(acetylide) chromophore to the lanthanide(III) centers.

Graphical abstractWith excitation at absorption region of MLCT/LLCT transitions in the platinum(II) terpyridyl acetylide chromophore, Pt–Ln heteronuclear complexes exhibit luminescence characteristic of the corresponding lanthanide(III) ions whereas the Pt-based emission is mostly quenched, revealing unambiguously occurrence of effective Pt → Ln energy transfer.Figure optionsDownload full-size imageDownload as PowerPoint slide