The Influence of Different Ammonium Cations on the Optical Properties of Tetrakis GdIII and EuIII Complexes

A series of tetrakis-β-diketonate Q+[Ln(β-dik)4]–, where Ln = GdIII or EuIII, Q = ammonium cations and β-dik = tta (2-thenoyltrifluoracetone) or bmdm (1-(4-tert-butylphenyl)-3-(4-methoxyphenyl)-1,3-propanedione) have been synthesized and characterized. The environment surrounding the EuIII ion depends on the lateral groups of the ligand and on the alkyl chains of the counter ion Q. The shortest lifetime (τ) = 0.29 ms, and lowest quantum efficiencies (η) = 24%, were obtained for (N(C12H25)2(CH3)2)+[Eu(bmdm)4]–, while (N(C4H9)4)+[Eu(bmdm)4]– has the longest τ = 1.04 ms and η = 90%. The Judd-Ofelt intensity parameters (Ω2 and Ω4) strongly changes for tta series pointing to stronger ion-dipole interactions between the –CF3 group with the ammonium cations. The agreement between the experimental results of photoluminescence and theoretical data suggests that the geometries optimized by the Sparkle model are correct. These results point to potential candidates for building up Langmuir-Blodgett (LB) luminescent films, since it is possible to maximize the intermolecular interactions and the photoluminescent properties of tetrakis LnIII complexes.