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

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 (1 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(III) 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 [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) are formed, whereas 3 forms trinuclear adducts [3{Ln(hfac)(3)}(2)] (tta=anion of thenoyl-trifluoroacetone; hfac=anion of hexafluoroacetylacetone). Complexes 1-3 show typical Pt(II)-based (3)MLCT luminescence in solution at approximately 510 nm, but in the coordination polymers [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) the presence of stacked pairs of Pt(II) units with short PtPt distances means that the chromophores have (3)MMLCT character and emit at lower energy ( approximately 630 nm). Photophysical studies in solution and in the solid state show that the (3)MMLCT luminescence in [1Ln(tta)(3)](infinity) and [2Ln(hfac)(3)](infinity) in the solid state, and the (3)MLCT 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.

Facile Synthesis of Luminescent Ir–Pt–Ir Trimetallic Complexes

“…[51] Complex 3 was prepared according to the literature procedure. [62] CD 3 CN was used for NMR experiments, owing to the good solubility of the trimetallic complexes 4a-c in this solvent. CH 2 Cl 2 was used for photophysical studies to allow better comparison to other photoluminescence experiments we have reported on cationic isocyanide-bound cyclometalated iridium complexes [52,53] and closely-related analogues of platinum complex 3, [59] all of which were conducted in CH 2 Cl 2 solvent.…”

Quantification of energy transfer in bimetallic Pt(ii)–Ln(iii) complexes featuring an N^C^N-cyclometallating ligand

“…Nonetheless, a variety of Pt(II) polypyridyl luminophores have been used successfully in a range of d--f systems, including heterometallic complexes, 6--8 coordination polymers, 9 and supramolecular systems. 10--12 Interestingly then, despite the myriad of Pt(II) polypyridyl--based antennae which have been reported, to the best of our knowledge only two examples of cyclometalated arylpolypyridyl Pt(II) d--f complexes 13,14 have been demonstrated to show sensitised Ln(III) emission.…”

Syntheses, characterization and sensitized lanthanide luminescence of heteronuclear Pt–Ln (Ln=Eu, Nd, Yb) complexes with 2,2′-bipyridyl ethynyl ligands

“…As the model complex Eu(hfac) 3 (bpyC"C) lacks of intensity at k > 350 nm in the excitation spectrum (Fig. S11, Supplementary material), the sensitized lanthanide emission of Pt-Ln heteronuclear complexes should originate from energy transfer from the platinum(II) terpyridyl alkynyl antenna chromophore [10][11][12][13][14][15][16].…”

“…The entire quenching of Pt-based luminescence in these Pt-Ln complexes except for 7 in solid state together with the observation of sensitized lanthanide luminescence with excitation at the absorption region of Pt-based chromophore reveals unambiguously that quite effective Pt ? Ln energy transfer is operating in these Pt-Ln heteronuclear complexes [9][10][11][12][13][14][15][16].…”

“…This opens a feasible strategy to access d-f heterometallic arrays containing both dblock metal alkynyl chromphores and lanthanide emitters, allowing effective d ? f energy transfer to occur from the former to the latter and thus achieving sensitized luminescence from the corresponding lanthanide ions [11][12][13][14][15][16].…”