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Ligand-field asymmetry-controlled luminescent europium (III) and samarium(III) tris(β-diketonate) complexes of diphenyl-(2-pyridyl-N-oxide)- phosphine oxide
Eight new complexes of the type Ln(OO)3.2 L1, Ln(OO)3.L2 (where Ln=Eu, Sm; OO=thenoyl trifluroacetonate(TTA) and dibenzoylmethanate(DBM); L1=diphenyl, (2-pyridyl) phosphine oxide (PON) and diphenyl-(2-pyridyl-N-oxide)phosphine oxide (PONO)) were synthesized for the first time. Complexes were characterized by FTIR, CHN analyses and Single crystal X-ray diffraction techniques. Structures of samarium complexes show that the L1 behaves as a monodentate ligand and bonds through P=O group to metal centre, whereas L2 behaves as a bidentate ligand and bonds through P=O as well as N−O groups to metal centre. Photophysical properties of all the complexes were measured in solid as well as solution states. Due to increase in ligand field asymmetry around the metal centre (by changing ligand from L1 to L2), the asymmetry ratio REu in Europium(III) tris( diketonate)-L2 complexes were increased. This leads to increase in intrinsic quantum yield complexes with ligand L2 as compared to that of complexes of ligand L1
Green, Water-Dispersible Photoluminescent On–Off–On Probe for Selective Detection of Fluoride Ions
Considering the high
toxicity and widespread availability of fluoride ions in different
environmental matrices, it is imperative to design a probe for its
detection. In view of this, a selective fluorescent on–off–on
probe based on carbon quantum dots (CQDs) and Eu<sup>3+</sup> has
been designed. We have synthesized water-soluble carboxylic acid-functionalized
CQDs and monitored their interaction with Eu<sup>3+</sup>. Luminescence
quenching in the CQD emission was observed (switch-off) on adding
Eu<sup>3+</sup> ions. We investigate the reason for this luminescence
quenching using time-resolved emission and high-resolution transmission
electron microscopy (HRTEM) studies and observed that both electron
transfer from CQDs to Eu<sup>3+</sup> and aggregation of CQDs are
responsible for the luminescence quenching. ζ-Potential and
X-ray photoelectron spectroscopy studies confirm Eu<sup>3+</sup> binding
with the COOH groups on CQD surface. Interestingly, luminescence
regains after the addition of fluoride ions to the CQDs/Eu<sup>3+</sup> system (switch-on). This has been assigned to the removal of Eu<sup>3+</sup> from the CQD surface due to the formation of EuF<sub>3</sub> and is confirmed by X-ray diffraction and HRTEM measurements. The
sensitivity of the probe was tested by carrying out experiments with
other competing ions and was found to be selective for fluoride ions.
Experiments with variable concentrations of fluoride ions suggest
that the working range of the probe is 1–25 ppm. The probe
has been successfully tested for the detection of fluoride ions in
a toothpaste sample and the results were compared to those of ion
chromatography. To the best of our knowledge, this is the first report
based on CQDs and Eu<sup>3+</sup> for the detection of fluoride ions,
wherein a clear mechanism of the detection has been demonstrated,
which, in turn, will help to develop better detection methods. The
suggested probe is green, economical, rapid, efficient, and, most
importantly, selective and can be used for the detection of fluoride
ions in real environmental samples