Luminescent Lanthanide Complexes of a Bis-bipyridine-phosphine-oxide Ligand as Tools for Anion Detection

Abstract

The Gd(3+), Tb(3+), and Eu(3+) complexes of a bis-bipyridine-phenylphosphine oxide ligand PhP(O)(bipy)(2) 1 (bipy for 6-methylene-6'-methyl-2,2'-bipyridine) have been synthesized. In acetonitrile solutions at room temperature, the Tb(3+) and Eu(3+) complexes show a metal-centered luminescence, indicative of an efficient energy transfer from the two bipy subunits to the Ln center. The photophysical properties drastically depend on the nature of the anions present in solution. In particular, addition of 2 equiv of nitrate anions to a solution containing the [Ln.1](OTf-)(3) leads to an 11-fold increase of the luminescence intensity for the Eu(3+) and a 7-fold increase for the Tb(3+) complexes. Similar effects are provided with Cl-, F-, and CH(3)COO- anions. UV-vis titration experiments were used to determine association constants for binding of, respectively, one, two, and three anions. Stepwise anion addition has also been investigated on the molecular level using quantum mechanical (QM) calculations for the Eu complexes. These calculations reproduce the experimental findings, especially if solvent molecule addition is taken into account. The X-ray crystal structure of the nitrate salt of the Tb complex, as well as QM calculation of a similar Eu complex, demonstrates the coordination of three nitrate anions in a bidentate mode and the step-by-step relegation of the bipy subunits in the second coordination sphere. These features give valuable insights into the mechanism of the overall light amplification process.

Advances in Rare Earth Spectroscopy and Applications

“…Charbonniere et al 148 observed the increase of the Eu complex luminescence lifetime (combining a hard donor with two soft pyridine donors) upon the addition of ATP, whereas ADP and AMP did not induce significant changes. Ln ions in liquid chromatography 149 can also serve the purpose of detection of single stranded nucleic acids, 150 hormones, 151 amino compounds 152 and labeled thiols.…”

Synthesis, photophysical characterisation and metal ion binding properties of new ligands containing anthracene chromophores

“…Spectrophotometric and fluorimetric titrations and data analysis were carried out as elsewhere described [13].…”

An Efficient Design for the Rigid Assembly of Four Bidentate Chromophores in Water‐Stable Highly Luminescent Lanthanide Complexes

“…[1,2] Lanthanide complexes are increasingly used for sensor development [3] and as luminescent probes in time-resolved high-throughput assays and fluorescence imaging because of their ability to discriminate between background fluorescence and the target signal. [4][5][6][7][8] Numerous studies have been directed to design efficient luminescence probes containing the long-lived visible emitters Eu iii and Tb iii [9][10][11][12][13][14] and more recently near-infrared (NIR) emitters (Pr iii , Er iii , Yb iii , Nd iii ). [15][16][17][18] As the Laporte-forbidden 4f-4f transition prevents direct excitation of lanthanide luminescence, lanthanide ions require sensitization by suitable organic chromophores.…”