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

Abstract

The luminescent transition metal complexes [Re(CO)₃Cl(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 ³MLCT excited state of the Pt(II) or Re(I) centre, quenching the ³MLCT 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)₃Cl(bppz)] or [Pt(CC–C₆H₄CF₃)₂(bppz)], and (ii) the degree of quenching of the ³MLCT 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 ³MLCT 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.