Sensitised near-infrared emission from lanthanides using a covalently-attached Pt(II) fragment as an antenna group

In a series of heterodinuclear complexes in which a Pt(PPh3)2(catecholate) chromophore is covalently linked to a lanthanide tris(diketonate) unit, sensitised near-IR emission from Yb(III), Nd(III) and Er(III) occurs on excitation of the Pt(II) chromophore at 520 nm.     

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 Pt(II) unit, either [(PPh(3))(2)Pt(pdo)] (H(2)pdo=5,6-dihydroxyphenanthroline) or [Cl(2)Pt(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 [(PPh(3))(2)Pt(pdo)] and [Cl(2)Pt(dppz)] both have external, vacant N,N-donor diimine-type binding sites that react with various [Ln(dik)(3)(H(2)O)(2)] units to give complexes [(PPh(3))(2)Pt(micro-pdo)Ln(tta)(3)] (series A; Htta=thenoyltrifluoroacetone), [Cl(2)Pt(micro-dppz)Ln(tta)(3)] (series B); and [Cl(2)Pt(micro-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 CH(2)Cl(2), 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.     

Synthesis and properties of [Pt(4-CO2CH3-py)2(dmit)] and [Pt(4-NO2-py)2(mnt)]: Exploring tunable Pt dyes

Two [Pt(II)(substituted-pyridyl)₂(dithiolate)] dyes with the formulas [Pt(4-CO₂CH₃-py)₂(dmit)] and [Pt(4-NO₂-py)₂(mnt)] (where py = pyridyl, dmit = 1,3-dithiol-2-thione-4,5-dithiolate and mnt = maleonitriledithiolate) and their dichloride precursors [PtCl₂(4-R-py)₂] have been synthesized and compared to a previously-reported dye [Pt(4-CO₂CH₃-py)₂(mnt)]. Variation of either the pyridyl ligands or the ditholate ligand showed tuning of the electrochemical and spectroscopic characteristics of the dyes as evidenced by cyclic and differential pulse voltammetry, hybrid DFT calculations, UV/Vis spectroelectrochemistry and in situ EPR spectroelectrochemistry. The HOMO was shown to be mostly dithiolate based and the LUMO pyridyl based allowing absorption characteristics to be predictably tuned to longer wavelengths, which is important for optimization of such dyes in applications such as solar energy conversion.