New tris(heterocyclic beta-diketonato)europium(III) complexes of the general formula Eu(PBI)3.L [where HPBI = 3-phenyl-4-benzoyl-5-isoxazolone and L = H2O, 2,2'-bipyridine (bpy), 4,4'-dimethoxy-2,2'-bipyridine (dmbpy), 1,10-phenanthroline (phen), or 4,7-diphenyl-1,10-phenanthroline (bath)] were synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), 1H NMR, high-resolution mass spectrometry, thermogravimetric analysis, and photoluminescence (PL) spectroscopy. Single-crystal X-ray structures have been determined for the complexes Eu(PBI)3.H2O.EtOH and Eu(PBI)3.phen. The complex Eu(PBI)3.H2O.EtOH is mononuclear, and the central Eu3+ ion is coordinated by eight oxygen atoms to form a bicapped trigonal prism coordination polyhedron. Six oxygens are from the three bidentate HPBI ligands, one is from a water molecule, and another is from an ethanol molecule. On the other hand, the crystal structure of Eu(PBI)3.phen reveals a distorted square antiprismatic geometry around the europium atom. The room-temperature PL spectra of the europium(III) complexes are composed of the typical Eu3+ red emission, assigned to transitions between the first excited state (5D0) and the multiplet (7F0-4). The results demonstrate that the substitution of solvent molecules by bidentate nitrogen ligands in Eu(PBI)3.H2O.EtOH richly enhances the quantum yield and lifetime values. To elucidate the energy transfer process of the europium complexes, the energy levels of the relevant electronic states have been estimated. Judd-Ofelt intensity parameters (Omega2 and Omega4) were determined from the emission spectra for Eu3+ ion based on the 5D0 --> 7F2 and 5D0 --> 7F4 electronic transitions, respectively, and the 5D0 --> 7F1 magnetic dipole allowed transition was taken as the reference. The high values obtained for the 4f-4f intensity parameter Omega2 for europium complexes suggest that the dynamic coupling mechanism is quite operative in these compounds.
A novel class of efficient antenna complexes of Tb 3+ based on the use of 3-phenyl-4-acyl-5-isoxazolone ligands has been designed, synthesized, characterized and their photophysical properties evaluated . The new heterocyclic b-diketonate complexes of Tb 3+ exhibit high green luminescence efficiency in the solid state with quantum yields between 59-72%. Furthermore in this work, the synthesis, characterization and luminescent properties of poly-b-hydroxybutyrate (PHB) polymer films doped with Tb 3+ -3-phenyl-4-acyl-5-isoxazolonate complexes at 5, 10, 15 and 20% (mass) are reported. The fact that the luminescent efficiency of doped films is enhanced (quantum yields between 74-86%) compared with precursor samples revealed that the polymer matrix acts as a co-sensitizer for Tb 3+ centers. The luminescence intensity decreases, however, with increasing precursor concentration in the doped PHB to greater than 15% where a saturation effect is observed, indicating that changes in the polymer matrix improve the absorption properties of the film, consequently quenching the luminescent effect. Synthesized luminescent polymers containing Tb 3+ -hetrocyclic b-diketonate complexes showed promising photoluminescence efficiency for applications to polymer light-emitting diodes and active polymer optical fibers.
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