Luminescent PtII(bipyridyl)(diacetylide) chromophores with pendant binding sites as energy donors for sensitised near-infrared emission from lanthanides: Structures and photophysics of PtII/Ln III assemblies

The complexes [Pt(bipy)(CC-(4-pyridyl)}2] (1) and [Pt(tBu 2bipy){CC-(4-pyridyl)}2] (2) and [Pt(rBu 2-bipy)-(CC-phen)2] (3) all contain a Pt-(bipy) (diacetylide) core with pendant 4-pyridyl (1 and 2) or phenanthroline (3) units which can be coordinated to (Ln(diketonate)3} fragments (Ln = a lanthanide) to make covalently-linked PtII/LnIII polynuclear assemblies in which the PtII chromophore, absorbing in the visible region, can be used to sensitise near-infrared luminescence from the LnIII centres. For 1 and 2 one-dimensional coordination polymers [1·Ln(tta)3]∞ and [2·Ln(hfac) 3]∞ are formed, whereas 3 forms trinuclear adducts [3·(Ln(hfac)3}2] (tta = anion of thenoyl-trifluoroacetone; hfac = anion of hexafluoroacetylacetone). Com plexes 1-3 show typical PtII-based 3MLCT luminescence in solution at ≈ 510 nm, but in the coordination polymers [1Middot;Ln(tta) 3]∞ and [2·Ln(hfac)3] ∞ the presence of stacked pairs of PtII units with short Pt⋯Pt distances means that the chromophores have 3MMLCT character and emit at lower energy (≈630 nm). Photophysical studies in solution and in the solid state show that the 3MMLCT luminescence in [1·Ln(tta)3]∞ and [2∞Ln(hfac) 3]∞ in the solid state, and the 3MLCT emission of [3·(Ln(hfac)3)2] in solution and the solid state, is quenched by Pt → Ln energy transfer when the lanthanide has low-energy f-f excited states which can act as energy acceptors (Ln = Yb, Nd, Er, Pr). This results in sensitised near-infrared luminescence from the Ln III units. The extent of quenching of the PtII-based emission, and the Pt → Ln energy-transfer rates, can vary over a wide range according to how effective each LnIII ion is at acting as an energy acceptor, with YbIII usually providing the least quenching (slowest Pt → Ln energy transfer) and either NdIII or ErIII providing the most (fastest Pt → Ln energy transfer) according to which one has the best overlap of its f-f absorption manifold with the Pt IIbased luminescence. © 2006 Wiley-VCH Verlag GmbH & Co. KGaA.