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Issue 44, 2014
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Two-photon sensitized visible and near-IR luminescence of lanthanide complexes using a fluorene-based donor–π-acceptor diketonate

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Abstract

A fluorene-based donor–acceptor ligand was successfully employed to sensitize visible and near-IR emitting lanthanide centers. The ligand construct is based on a donor–π-acceptor architecture with diphenylamino acting as the donor and a fluorenyl π bridge derivatized with a trifluoroacetonate moiety acting as both a strong acceptor and the classic bidentate scaffold for complexing metals. 1H NMR analysis in the polar solvents THF and CDCl3 revealed the enolic form of the diketone dominant in solution equilibria at room temperature. This preferred cis-enol form binds strongly to the lanthanide(III) ions (Ln = Eu, Sm, Dy, Tb, Yb, Nd, Er, and Gd) in the presence of phenanthroline affording the resulting ternary tris(diketonates) complexes with 1,10-phenanthroline. Detailed characterization of these complexes was conducted, with particular emphasis on linear and nonlinear photophysical properties. Steady-state and time-resolved emission spectroscopy and overall photoluminescence quantum yield (PLQY) measurements were performed on all the complexes. Sizeable visible and near-IR efficiency for europium (room temperature, visible), samarium (low temperature, visible) and ytterbium, neodymium and erbium (room temperature, near-IR) was displayed, with long luminescent lifetimes for the europium and samarium complexes of 85 and 70 μs, respectively Measurement of the luminescence decay for the Yb complex at 976 nm, Nd complex at 874 nm, and Er complex at 1335 nm yielded mono-exponential decay curves, with lifetimes of ∼13 μs, ∼1.6 μs, and ∼2.5 μs, respectively, inferring that the emission was generated by a single species. In addition, fluorescence anisotropy and two-photon absorption (2PA) spectra (via Z-scan) were obtained for the ligand and europium complex, revealing a maximum 2PA cross section of 340 GM for the latter upon excitation at 760 nm. A quadratic relationship was found by varying laser excitation power vs. luminescence intensity of the europium complex, confirming sensitization via two-photon excitation.

Graphical abstract: Two-photon sensitized visible and near-IR luminescence of lanthanide complexes using a fluorene-based donor–π-acceptor diketonate

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Supplementary files

Article information


Submitted
22 May 2014
Accepted
24 Jul 2014
First published
08 Aug 2014

Dalton Trans., 2014,43, 16626-16639
Article type
Paper

Two-photon sensitized visible and near-IR luminescence of lanthanide complexes using a fluorene-based donor–π-acceptor diketonate

A. W. Woodward, A. Frazer, A. R. Morales, J. Yu, A. F. Moore, A. D. Campiglia, E. V. Jucov, T. V. Timofeeva and K. D. Belfield, Dalton Trans., 2014, 43, 16626
DOI: 10.1039/C4DT01507J

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