10.1021/ic0515249.s001
Steve Comby
Steve
Comby
Daniel Imbert
Daniel
Imbert
Anne-Sophie Chauvin
Anne-Sophie
Chauvin
Jean-Claude G. Bünzli
Jean-Claude G.
Bünzli
Stable 8-Hydroxyquinolinate-Based Podates as Efficient Sensitizers of
Lanthanide Near-Infrared Luminescence
American Chemical Society
2006
ligand
NIR
IIII
Nd III
H 2 O
Yb III compounds
D 2 O
Yb III ions
Ln III ions
Eu III ion
2006-01-23 00:00:00
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Stable_8_Hydroxyquinolinate_Based_Podates_as_Efficient_Sensitizers_of_Lanthanide_Near_Infrared_Luminescence/3242401
New polydentate ligands (e.g., <b>Tsox</b> and <b>TsoxMe)</b> have been synthesized to take advantage of the chelating
effect of bidentate 8-hydroxyquinolinate subunits connected to a <i>N,N,N</i>‘,<i>N</i>‘-tetraaminopropyl-1,2-ethylenediamine
framework and with the aim of sensitizing the NIR luminescence of Nd<sup>III</sup> and Yb<sup>III</sup> ions. Ten p<i>K</i><sub>a</sub>'s have been
determined and the interaction between the ligands and Ln<sup>III</sup> ions in dilute aqueous solution has been probed both
by potentiometric and spectrophotometric titrations. These studies have been mostly performed with the Eu<sup>III</sup> ion,
which is in the middle of the lanthanide series, and extended to other ions (La<sup>III</sup>, Er<sup>III</sup>, Lu<sup>IIII</sup>). Stable complexes with
Ln<sup>III</sup> ions are formed (pLn in the range of 14−16), the four chromophoric units being coordinated to the metal
center, exploiting the entropic effect generated by the anchor. The monometallic complexes [Ln(H<sub>2</sub>L)]<sup>3-</sup> exist as
the major species at physiological pH regardless of the lanthanide used. Lifetime determinations of the Nd(<sup>4</sup>F<sub>3/2</sub>)
and Yb(<sup>2</sup>F<sub>5/2</sub>) excited levels in both H<sub>2</sub>O and D<sub>2</sub>O at buffered pH point to the absence of water molecules bound
in the inner coordination sphere of the Ln<sup>III</sup>. Photophysical properties of the free ligands and of their lanthanide
complexes have been investigated in buffered aqueous solutions both at room temperature and 77 K. The low-energy triplet state makes energy transfers from the ligand to the metal ions possible; this leads to a sizable
sensitization of the Nd<sup>III</sup>- or Yb<sup>III</sup>-centered luminescence (
= 0.02% and
= 0.18%) for <b>Tsox</b> chelates.
Methylation of the amide functions removes the quenching mechanism induced by the proximate N−H vibrations
and increases both the lifetimes and quantum yields of the <b>TsoxMe</b> chelates (
= 0.04% and
= 0.37%).
In fact, <b>TsoxMe</b> yields one of the most luminescent Yb<sup>III</sup> compounds known in water, and this ligand appears to
be suitable for the development of NIR probes for bioanalyses.