Effects of Ligand Geometry on the Photophysical Properties of Photoluminescent Eu(III) and Sm(III) 1‑Hydroxypyridin-2-one Complexes in Aqueous Solution
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Abstract
A series of 10 tetradentate 1-hydroxy-pyridin-2-one
(1,2-HOPO)
ligands and corresponding eight-coordinated photoluminescent Eu(III)
and Sm(III) complexes were prepared. Generally, the ligands differ
by the linear (nLI) aliphatic linker length, from 2 to 8 methylene
units between the bidentate 1,2-HOPO chelator units. The photoluminescent
quantum yields (Φ<sub>tot</sub>) were found to vary with the
linker length, and the same trend was observed for the Eu(III) and
Sm(III) complexes. The 2LI and 5LI bridged complexes are the brightest (Φ<sub>tot</sub>xε).
The change in ligand wrapping pattern between 2LI and 5LI complexes
observed by X-ray diffraction (XRD) is further supported by density
functional theory (DFT) calculations. The bimodal Φ<sub>tot</sub> trends of the Eu(III) and Sm(III) complexes are rationalized by
the change in ligand wrapping pattern as the bridge (<i>n</i>LI) is increased in length