Contribution of Energy Transfer from the Singlet State to the Sensitization of Eu3+ and Tb3+ Luminescence by Sulfonylamidophosphates.

ABSTRACT

A series of stable lanthanide complexes Na[Ln(L)4 ] (Ln=La3+ , Eu3+ , Gd3+ , Tb3+ , with L=dimethyl(4-methylphenylsulfonyl)amidophosphate and dimethyl-2-naphthylsulfonylamidophosphate) were synthesized. The compounds were characterized by single-crystal X-ray diffraction, IR, absorption, and emission spectroscopy at 293 and 77 K. In contrast to the usual and well-known dominant role of the ligand triplet state in intramolecular energy transfer processes in Ln complexes, in this particular new class of Ln compounds with sulphonylamidophosphate ligands, strong experimental and detailed theoretical evidence suggest a dominant role is played by the ligand first excited singlet state. The importance of the role played by the 7 F5 level in the case of the Tb3+ compound in this process is shown. The theoretical approach for the energy transfer rates was successfully applied to the rationalization of the experimental data. The higher-lying excited levels of Eu (5 DJ , 5 LJ , 5 GJ ) and Tb (5 DJ , 5 GJ , 5 LJ , 5 HJ , 5 FJ , 5 IJ ) were included in the calculations for the first time. Both the multipolar and exchange mechanisms were taken into account. The experimental intensity parameters (Ωλ ), emission lifetimes (τ), radiative (Arad ) and non-radiative (Anrad ) decay rates, and quantum yields (theoretical and experimental) were determined and are discussed in detail.