Sensitised near-infrared luminescence from lanthanide(III) centres using Re(I) and Pt(II) diimine complexes as energy donors in d-f dinuclear complexes based on 2,3-bis(2-pyridyl)pyrazine

The luminescent transition metal complexes [Re(CO)(3)Cl(bppz)] and [Pt(CC - C6H4CF3)(2)(bppz)] [bppz = 2,3-bis(2-pyridyl) pyrazine], in which one of the diimine binding sites of the potentially bridging ligand bppz is vacant, have been used as 'complex ligands' to make heterodinuclear d - f complexes by attachment of a {Ln(dik)(3)} fragment (dik = a 1,3-diketonate) at the vacant site. When Ln = Pr, Nd, Er or Yb the lanthanide centre has low-energy f - f excited states capable of accepting energy from the (MLCT)-M-3 excited state of the Pt(II) or Re( I) centre, quenching the (MLCT)-M-3 luminescence and affording sensitised lanthanide(III)-based luminescence in the near-IR region. UV/Vis and luminescence spectroscopic titrations allowed measurement of (i) the association constants for binding of the {Ln( dik)(3)} fragment at the vacant diimine site of [Re(CO)(3)Cl(bppz)] or [Pt(CC - C6H4CF3)(2)(bppz)], and (ii) the degree of quenching of the (MLCT)-M-3 luminescence according to the nature of the Ln( III) centre. In all cases Nd( III) was found to be the most effective of the series at quenching the (MLCT)-M-3 luminescence of the d-block component because the high density of f - f excited states of the appropriate energy make it a particularly effective energy-acceptor.