Hypersensitivity in the Luminescence and 4f–4f Absorption Properties of Mono- and Dinuclear EuIII and ErIII Complexes Based on Fluorinated β-Diketone and Diimine/ Bis-Diimine Ligands

Abstract

The results of our investigation on the sensitized luminescence properties of three Eu(III) β-diketonate complexes of the form [Eu(2)(fod)(6)(μ-bpm)], [Eu(fod)(3)(phen)] and [Eu(fod)(3)(bpy)] and 4f-4f absorption properties of their Er(III) analogues ( fod = anion of 6,6,7,7,8,8,8- heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2'-bipyrimidine, phen = 1,10-phenanthroline and bpy = 2,2'-bipyridyl) in a series of non-aqueous solvents are presented. The Eu(III) complexes are highly luminescent and their luminescence properties (intensity and band shape) are sensitive to the changes in the inner coordination sphere of the Eu(III) ion. The luminescence intensity of the mononuclear complexes in pyridine is drastically decreased. The coordination structure of the complexes in pyridine is transformed into a more symmetrical one which results into a slow radiative rate of the emission from the complexes. The ancillary ligands, phen and bpy are found better co-sensitizers as compared to the bpm to sensitize Eu(III)-luminescence. The 4f-4f absorption properties (oscillator strength and band shape) of the Er(III) complexes demonstrate that (4)G(11/2) ← (4)I(11/2) and (2)H(11/2) ← (4)I(15/2) hypersensitive transitions of Er(III) are very sensitive in some coordinating solvents which reflects complex-solvent interaction in solution. The hypersensitive transitions of [Er(fod)(3)(phen)] remain unaffected in any of the solvents and this complex retains its bulk composition in solution. The erbium complexes as well as the Er(fod)(3) chelate are invaded by DMSO. This solvent enters the inner coordination sphere by replacing heterocyclic ligand and the complexes acquire similar structure [Er(fod)(3)(DMSO)(2)] in this solvent. The results reveal that the luminescence and absorption properties of lanthanide complexes in solution can be controlled by tuning the coordination structure through ancillary ligands and donor solvents. This work shall prove useful in designing new biological applications with such probes.