Banca de DEFESA: VIVIANE PEREIRA DE SOUZA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : VIVIANE PEREIRA DE SOUZA
DATE: 18/10/2024
TIME: 14:00
LOCAL: Programa de Pós-Graduação em Ciência de Materiais
TITLE:

Novel Lanthanide Benzoates: Green Syntheses, Structural Studies, and Luminescent Properties.

KEY WORDS:

lanthanides; benzoates; luminescence; green synthesis.

PAGES: 173
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

The application of mild synthesis protocols, using water as a solvent and few steps, for the formation of lanthanide complexes with pentafluorobenzoic acid (H1) produced networks Na[Ln(1)3(H2O)4](1)(H2O)2 (Ln: Eu, Gd, Tb, EuxGd1-x, EuxTb1-x, and TbxGd1-x; x: 0,05, 0,25, 0,50, and 0,75), dimers [Ln2(1)6(H2O)8](H2O)2 (Ln: Eu, Eu0,50Gd0,50, and Eu0,50Tb0,50) and two other structures still unknown. The network structure is unpublished and quite unusual, with Ln sites connected by a single symmetric bridge and a long Ln···Ln distance (6.865 Å). The network synthesis in solution involves a crystallization step by slow evaporation of the solvent, but it was obtained by the mechanochemical method in a single step, quickly, efficiently and solvent-free. The quantum efficiency of the europium ion in homo- and heterometallic networks is less than 10%. The barycenter of the H1 triplet level was estimated at 20400 cm−1 . The networks EuxTb1-x show energy transfer Tb → Eu and a strong dependence of the emission lifetime of the 5D0 level of Eu3+ on the excitation wavelength. The network Eu0,05Tb0,95, for example, exhibits lifetimes of 0.61, 0.80, and 0.22 ms when excited at 295, 370, and 395 nm, respectively. Lanthanide complexes with o-(methylthio)-, o-(o-cyanophenylthio)-, and o-(benzylthio)-benzoic acids (H2, H3 and H4, respectively) were also synthesized: (i) three networks based on o-(methylthio)- benzoates [Eu2(2)6(H2O)4], [Ln(2)3] (Ln: La, Ce, Eu, Gd, Tb, Tm, Yb) and [La(2)3(H2O)2]·H2O; (ii) three europium complexes with unknown structure, namely, one o-(o-cyano-phenylthio)-benzoate, and two o- (benzylthio)-benzoates, and three analogous complexes with Gd3+ . The triplet levels were estimated at 23150 cm−1 for H3, and 19160 cm−1 and 22.170 cm−1 for H4. Changes were observed in the emission spectra with spectral scanning for the Gd3+ complexes with o-(o-cyanophenylthio)- and o-(benzylthio)- benzoates, i.e., with exposure to UV radiation, evidencing a photoinduced process. These changes present an isosbestic point, suggesting an equilibrium of different species. The quantum efficiencies of the europium complexes are similar for the systems with H2, H3 and H4 (14%–17%), indicating the little influence of the substituents on the intrinsic rates of the Eu3+ ion, except for one of the europium o- (benzylthio)-benzoates which exhibits a much higher quantum efficiency of 40%.

COMMITTEE MEMBERS:
Interna - 1857515 - GIOVANNIA ARAUJO DE LIMA PEREIRA
Externa à Instituição - INGRID TAVORA WEBER - UnB
Externo à Instituição - LEONIS LOURENÇO DA LUZ
Externa à Instituição - MARYENE ALVES CAMARGO - UnB
Presidente - 1134371 - RICARDO LUIZ LONGO