Síntese e caracterização de compostos de coordenação de európio contendo diferentes sensibilizadores para o estudo de dispositivos ópticos

Abstract

The particularity of the lanthanides’ (Ln) electron configuration, in which the electrons of the 4f orbitals are protected from the extern chemical environment by the filled and radially outermost orbitals 5s2 and 5p6, results in singular spectroscopic properties, since their spectra retain atomic characteristics. Although the forbidden transitions 4f- 4f leads to low molar absorptivity, in order of 10 dm3 mol-1 cm-1, and consequently low quantum yield, the emission intensification is made via indirect excitation. The known antenna effect occurs when the environment around the lanthanide ion (chromophore ligands) absorbs the energy supplied to the system and transfers it to the metallic center, intensifying the emission. The synthesis of coordination compounds using chromophores, containing mainly chelating groups such as β-diketones and carboxylates, is commonly reported in the literature. In this work we studied the properties of coordination compounds containing lanthanides and commercial chromophores sensitizers: bmdm (avobenzone, 1-(4-Methoxyphenyl)-3-(4-tertbutylphenyl)propane-1,3-dione), bipy (2-2’-bipyridine) and phen (1-10’- phenanthroline). Theoretical calculations using semiempirical models showed Eu-O and Eu-N bond distances close to those described in the literature for similar compounds and excited triplet level (> 19100 cm-1) close to that of ligands usually used in the synthesis of luminescent coordination compounds. The compounds were synthesized with 1:3 molar proportion of Eu:bmdm for obteining the compound [Eu(bmdm)3(H2O)2] and 1:3:1 of Eu:bmdm:bipy and Eu:bmdm:phen for the synthesis of the compounds [Eu(bmdm)3(bipy)] and [Eu(bmdm)3(phen)]. The stoichiometries of the obtained compounds were confirmed by europium complexometric titration and elemental analysis for the CHN content determination. The UV-Vis and infrared spectra confirmed the ligands coordination through the absorption bands in the utraviolet region and changes mainly in stretch bands of C=O and C-N bonds. The water molecules substitution in the compound [Eu(bmdm)3(H2O)2] with chromophore chelating ligands resulted in photoluminescence intensification. In the emission spectra it was possible to observe the europium ion characteristic transitions 5D0→7FJ (J = 0, 1, 2, 3 e 4), with the most intense emission in the 5D0→7F2 hypersensitive transition in 612 nm, indicating that the obtained compounds do not have inversion center. The photoluminescence results demonstrate that the coordination compounds have potential for application in studies of light emitting devices in the red region. The monochromatic emission exhibited by the coordination studied compounds studied is a potential feature for these to act as emitter layer in optical devices.