The Influence of Different Ammonium Cations on the Optical Properties of Tetrakis Gd-III and Eu-III Complexes

A series of tetrakis-beta-diketonate Q(+)[Ln(beta-dik)(4)](-), where Ln = Gd-III or Eu-III, Q = ammonium cations and beta-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 Eu-III ion depends on the lateral groups of the ligand and on the alkyl chains of the counter ion Q. The shortest lifetime (tau) = 0.29 ms, and lowest quantum efficiencies (eta) = 24%, were obtained for (N(C12H25)(2)(CH3)(2))(+)[Eu(bmdm)(4)](-). while (N(C4H9)(4))(+)[Eu(bmdm)(4)](-) has the longest tau = 1.04 ms and eta = 90%. The Judd-Ofelt intensity parameters (Omega(2) and Omega(4)) 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 Ln(III) complexes.