Luminescent properties of Ln(III) complexes with 2-[(phenylamino)methylene]-5,5-dimethyl-cyclohexane-1,3-dione as an antenna

Abstract Seven lanthanide-based coordination compounds with 2-[(phenylamino)methylene]-5,5-dimethyl-cyclohexane-1,3-dione were synthesized: [Eu(HL)2(NO3)3] (1), [Sm(HL)2(NO3)3] (2), [Ce(HL)2(NO3)3] (3), [Tm(HL)2Cl3]·H2O (4), [Tb(HL)2Cl3]·H2O (5), [Dy(HL)2(H2O)(NO3)3] (6) and [Gd(HL)2Cl3]·H2O (7). The obtained Eu(III), Sm(III) and Ce(III) nitrate complexes was established to be isostructural just like Tm(III), Tb(III) and Gd(III) chloride ones. Using X-ray diffraction analysis, the structures of cerium and samarium were determined, which occurred to be polymer chains. On the contrary, the dysprosium compound was mononuclear. Ligand was shown to emit in blue region with quantum yield near 12%. For lanthanide complexes of Eu(III), Sm(III), and Tb(III), during the energy transfer from the ligand triplet state to the central atom, characteristic bands of the metal ion are observed in the emission spectra. The lifetimes and quantum yields of luminescence for these complexes were also determined. For other compounds, no energy transfer is observed due to lower energy of ligand triplet state than corresponding emitting state of the lanthanide ions.