Sensitized Near-Infrared Emission from Complexes of YbIII, NdIII and ErIII by Energy-Transfer from Covalently Attached PtII-Based Antenna Units

A series of dinuclear platinum(II)–lanthanide(iii) complexes has been prepared in which a square-planar PtII unit, either [(PPh3)2Pt(pdo)] (H2pdo=5,6-dihydroxyphenanthroline) or [Cl2Pt(dppz)] [dppz=2,3-bis(2-pyridyl)pyrazine], is connected to a {Ln(dik)3} unit (“dik”=a 1,3-diketonate ligand). The mononuclear complexes [(PPh3)2Pt(pdo)] and [Cl2Pt(dppz)] both have external, vacant N,N-donor diimine-type binding sites that react with various [Ln(dik)3(H2O)2] units to give complexes [(PPh3)2Pt(μ-pdo)Ln(tta)3] (series A; Htta=thenoyltrifluoroacetone), [Cl2Pt(μ-dppz)Ln(tta)3] (series B); and [Cl2Pt(μ-dppz)Ln(btfa)3] (series C; Hbtfa=benzoyltrifluoroacetone); in all of these the lanthanide centres are eight-coordinate. The lanthanides used exhibit near-infrared luminescence (Nd, Yb, Er). Crystal structures of members of each series are described. In all complexes, excitation into the Pt-centred absorption band (at 520 nm for series A complexes; 440 nm for series B and C complexes) results in characteristic near-IR luminescence from the Nd, Yb or Er centres in both the solid state and in CH2Cl2, following energy-transfer from the Pt antenna chromophore. This work demonstrates how d-block-derived chromophores, with their intense and tunable electronic transitions, can be used as sensitisers to achieve near-infrared luminescence from lanthanides in suitably designed heterodinuclear complexes based on simple bridging ligands