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(Hi) complexes has been prepared in which a square-planar Pt-II unit. either [(PPh3)(2)pt(pdo)] (H(2)pdo = 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)(2)Pt(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)(2)Pt(mu-pdo)Ln(tta)(3)] (series A; Htta = thenoyltrifluoroacetone), [Cl2Pt(mu-dppz)Ln(tta)(3)] (series B); and [Cl2Pt(mu-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.