Sensitized Near‐Infrared Emission from Complexes of Yb^III, Nd^III and Er^III by Energy‐Transfer from Covalently Attached Pt^II‐Based Antenna Units

A series of dinuclear platinum(II)–lanthanide(iii) complexes has been prepared in which a square‐planar Pt^II 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.