Relationship Between the Ligand Structure and the Luminescent Properties of Water‐Soluble Lanthanide Complexes Containing Bis(bipyridine) Anionic Arms

Abstract

A series of six new ligands (L1–L6) suitable for the formation of luminescent lanthanide complexes in water is described. Ligands L1–L4 are constructed from two 6′‐carboxy‐6‐methylene‐2,2′‐bipyridine chromophoric arms bonded to the amino function of a 2‐aminomethylene‐6‐carboxy‐pyridine (L1), an N,N‐diacetate‐ethylene diamine (L2), a serine (L3), or an aminomalonic acid (L4). For ligands L5 and L6, the linking amino function is provided by a glutamic acid, and the anionic functions at the 6′‐position of the bipyridyl arms are made of the sodium salts of monoethylphosphonic ester (L5) and phosphonic acid (L6). The synthesis and characterisation of the ligands are described, together with the study of the formation of lanthanide complexes with europium and terbium. In the case of L3, the europium complex obtained in acidic conditions was crystallised and the X‐ray crystal structure is depicted. Photophysical properties of the complexes were studied by means of UV‐visible absorption, and steady‐state and time‐resolved luminescence spectroscopy. Excited‐state luminescence lifetimes of the complexes were determined in water and deuterated water to gain insight into the number of water molecules directly coordinated in the first coordination sphere of the complexes. The coordination behaviour of the series of ligands is questioned in the light of the spectroscopic data and discussed in terms of protection of the cation towards water molecules and their impact on the luminescence efficiency.

The effect of ring size variation on the structure and stability of lanthanide(iii) complexes with crown ethers containing picolinate pendants

“…2, see also Table 2). 33 The emission spectra of both complexes recorded under excitation through the ligand bands show the typical narrow transitions characteristic of the corresponding metal ion as a consequence of ligand-to-metal energy transfer. 34 In the case of the Eu III complex the 5 D 0 → 7 F J transitions are observed around 580 (J = 0), 593 (J = 1), 612 (J = 2), 652 (J = 3) and 678 nm (J = 4).…”

Luminescence behaviour in acetonitrile and in the solid state of a series of lanthanide complexes with a single helical ligand

“…For instance, such structural modifications lead to the tuning of luminescence efficiency and the band appearances of the ff emission. [22][23][24][25][26] Moreover, the enhanced ff emission may be induced, if the ligands act as a shield from the outer-sphere with a stable structure in solution 23,[27][28][29][30] or in the solid state. 24,[31][32][33][34][35] A chelate effect provides a fundamental but most useful technique to design stable metal complexes, and the coordination number of the chelate ring contributes to the stability constant of the coordination in solution.…”

Molecular-Size Fluorescence Emitters

“…The latter interacting with inner coordinating sphere dissipate energy via O-H vibrations. Thus a special effort has been made for achieving the high emissive properties of these complexes in water (Charbonniere et al 2007) by constructing the saturated co-ordination sphere around the ion. Finally, this allowed realizing different simple and sensitive bioassays (Yuan and Wang 2006).…”