Luminescence and energy transfer processes in europium and terbium complexes with 2-substituted cycloalkanones and 1,10-phenanthroline derivatives

A series of solid lanthanide complexes with 2-substituted cycloalkanones (CA) of the composition Ln (CA)(3)center dot Phn and Ln(CA)(3)center dot Bpy (Ln = Eu, Tb, Gd) have been synthesized and investigated using luminescence spectroscopy. CA = 2-acetylcyrclohexanone (AcCHex), 2-isobutyrylcyclohexanone, 2-acetylcyclopentanone, 2-acetylbutyrolactone, 2-benzoylcyclohexanone, 2-acetyltetralone; Phn = 1,10-phenanthroline (Phen), 4,7-dimethyl-phenanthroline, 3,4,7,8-tetramethyl-phenanthroline, 5-phenyl-phenanthroline, 4,7-diphenyl-phenanthroline; Bpy = 2,2'-bipyridine. Tris and tetrakis compounds Ln(CA)(3)center dot 2H(2)O and LnNa(CA)(4) were also synthesized. The composition, structure and photophysical properties of the lanthanide cycloalkanonates having oligomethylene chain in the ligand are close to peculiarities of beta-diketonates without tethered chain. But the presence of this chain can cause a decrease in the energy of the lowest triplet state of the ligand. The Stark structure of the Eu3+ electronic states in the europium CA adducts with heterocyclic diimines corresponds to the distorted tetragonal anti-prismatic coordination geometry of the luminescence center. The lifetimes of D-5(4) (Tb3+) and D-5(0) (Eu3+) states at 77 K are 0.55-0.85 ms. The luminescence efficiencies of the lanthanide CA adducts at 77 K are comparable with them for known beta-diketonates. The back energy transfer from the D-5(4) (Tb3+) state to the lowest triplets of the ligands is the main cause for the decrease in the 51% lifetime and the Tb3+ luminescence efficiency at 295 K. In the Ln(AcCHex)(3).Phn complexes the energy absorbed by the two ligands is transferred to the lowest triplet state of Phn and then to Ln(3+) ion. In other Ln(CA)(3)center dot Phen compounds, the energy transfer to Ln(3+) ion is carried out through the lowest triplet state of CA, which is located below the Phen triplet. The preliminary data on photochemical stability of the compounds were obtained. (C) 2015 Elsevier B.V. All rights reserved.