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

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Abstract
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.