Highly Efficient Blue Photoexcitation of Europium in a Bimetallic Pt–Eu Complex

Abstract

We report the preparation and characterization of dinuclear Pt-Ln complexes constructed from a square-planar Pt(II) core bearing an ethynyl-terpyridine residue connected to platinum by the ethynyl bond. Complexation of the neutral Eu(hfac)3 (hfac = hexafluoroacetylacetonate) fragment to free terpyridine (terpy) gives a stable bimetallic complex (log beta = 6.7). In the crystal structure, the flat Pt[triple bond]terpy core coordinates to Eu(III), which is nonacoordinated with the three nitrogen atoms of the terpy subunit and six oxygen atoms of the three hfac ligands. These atoms form a distorted monocapped square antiprism with a pseudo-C2 symmetry axis passing through the nitrogen atom of the central pyridine ring and the Eu atom. Spectroscopic measurements showed that irradiation with visible light of wavelength up to 460 nm in the 1MLCT state of the Pt subunit resulted in a quantitative energy transfer to the Eu center, which strongly luminesces in the red with an overall luminescence quantum yield of 38%. The energy-transfer process is quantitative and not sensitive to oxygen, and the complexation of Eu to the Pt metallosynthon allows the recovery of the energy lost due to triplet-oxygen quenching of the 3MLCT state observed in the uncomplexed Pt precursor.

Spectroscopic Properties of Orthometalated Platinum(II) Bipyridine Complexes Containing Various Ethynylaryl Groups

“…The interest in the photophysical properties arises because platinum(II) complexes are effective as DNA intercalators13 as molecular probes for biological macromolecules,14 in medicinal chemistry,15 and in electroluminescent devices 16. More recently, uses in singlet‐oxygen production,17 photocatalytic hydrogen generation,18, 19 vapochromism,20 luminescence‐based probes for cation sensing,21 and sensitization of lanthanide emission have provided additional motivation for study 22…”

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].…”

“…By judicious modification of substituents in the terpyridyl and/or alkynyl ligands, the light emitting colors are changeable [17][18][19][20][21][22][23]. The intense light absorption character in UV-Vis region makes them act as excellent light-harvesting antennae to photosensitize d-block metal emitting or lanthanide luminescence [16,[24][25][26]. Particularly, as a consequence of Pt ?…”

“…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].…”