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

Ronson, Tanya K., Lazarides, Theodore, Adams, Harry, Pope, Simon J.A., Sykes, Daniel, Faulkner, Stephen, Coles, Simon J., Hursthouse, Michael B., Clegg, William, Harrington, Ross W. and Ward, Michael D. (2006) Luminescent Pt-II(bipyridyl)(diacetylide) chromophores with pendant binding sites as energy donors for sensitised near-infrared emission from lanthanides: structures and photophysics of Pt-II/Ln(III) assemblies. Chemistry - A European Journal, 12 (36), 9299-9313. (doi:10.1002/chem.200600698).

Abstract

The complexes [Pt(bipy){CC(4-pyridyl)}(2)] (1) and [Pt(tBu(2)bipy){CC-(4-pyridyl)}(2)] (2) and [Pt(tBu(2)-bipy)(CC-phen)(2)] (3) all contain a Pt(bipy)(diacetylide) core with pendant 4-pyridyl (I and 2) or phenanthroline (3) units which can be coordinated to [Ln(diketonate)(3)} fragments (Ln = a lanthanide) to make covalently-linked Pt-II/Ln(II) polynuclear assemblies in which the Pt-II, chromophore, absorbing in the visible region, can be used to sensitise near-infrared luminescence from the Ln(III) centres. For 1 and 2 one-dimensional coordination polymers [1.Ln(tta)(3)](infinity) and [2(.)Ln(hfaC)(3)](infinity) are formed, whereas 3 forms trinuclear adducts [3(.){Ln(hfac)(3)}2] (tta anion of thenoyi-trifluoroacetone; hfac = anion of hexafluoroacetylacetone). Com-plexes 1-3 show typical Pt-II-based (MLCT)-M-3 luminescence in solution at approximate to 510 nm, but in the coordination polymers [1(.)Ln(tta)(3)](infinity) and [2(.)Ln(hfaC)(3)]infinity the presence of stacked pairs of Pt-II units with short (PtPt)-Pt-... distances means that the chromophores have (MMLCT)-M-3 character and emit at lower energy (approximate to 630 nm). Photophysical studies in solution and in the solid state show that the (MMLCT)-M-3 luminescence in [1.Ln(tta)(3)](infinity) and [2(.)Ln(htaC)(3)](infinity) in the solid state, and the (MLCT)-M-3 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 Pt-II-based emission, and the Pt -> Ln energy-transfer rates, can vary over a wide range according to how effective each Ln(III) ion is at acting as an energy acceptor, with Yb-III usually providing the least quenching (slowest Pt -> Ln energy transfer) and either Nd-III or Er-III 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-II-based luminescence.

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Contributors

Author: Simon J. Coles

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