SÃntese e estudo espectroscÃpico de complexos de Ãons lantanÃdeos incorporados em materiais hÃbridos orgÃnicos-inorgÃnicos

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

In this work two new europium and gadolinium b-diketonate complexes, [Ln(btfa)3(4,4 -bpy)(EtOH)] (Ln = Eu, Gd; 4,4 -bpy = 4,4 -bipyridine; btfa = 4,4,4- trifluoro-l-phenyl- 1,3-butanedione), were prepared and incorporated into a organicinorganic hybrid material. The general formulae of these complexes were confirmed by X-rays single crystal data and elemental analysis. The host framework of these materials, named as di-ureasil, consists of a siliceous skeleton grafted, through urea cross-linkages, to both ends of poly(ethylene oxide) chains. The host is characterized by a white-light photoluminescence which results from a convolution of donor-acceptor pairs recombinations that occur in the NH/C=O groups of the urea linkages and in âO−O−SiÂ(CO2) oxygen-related defects of the siliceous nanodomains. The [Eu(TPI)3Â3H2O] and [Eu(TPI)3Â2TOPO] (TPI = 3-phenyl-4-(4-toluoyl)-5- isoxazolone; TOPO = tri-n-octylphosphine oxide), and [Tb(acac)3.3H2O] (acac = acethylacetonate) complexes also were incorporated into di-ureasil. The incorporation of these complexes into the hybrid matrix was made through conventional hydrolytic sol-gel method, acetic acid solvolysis and via sol-gel acid-catalyzed reaction (using HCl at 1.0, 1.5 and 2.0 mol/L). The last method was also used to prepare the non-doped matrix. The resulting Eu3+, Tb3+ and Gd3+-based di-ureasils were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, 13C, 29Si and 31P nuclear magnetic resonance and photoluminescence spectroscopy. The emission quantum yields of non-doped hybrids prepared via acid catalyzed sol-gel reaction are 30-35% higher than those calculated for the di-ureasil synthesized via the conventional sol-gel technique. An increase in the emission quantum yield and luminescence lifetime also was observed to Tb3+-based di-ureasil prepared via acid catalyzed sol gel reaction in comparison that those synthesized via the conventional solgel technique suggesting that this method is a promise is a prominent method to improve the luminescent properties of these compounds. The negligible intensity of the di-ureasil emission observed in the emission spectra of the hybrid incorporating [Eu(btfa)3(4,4 -bpy)(EtOH)] complex and the increase in lifetime, emission quantum yield and quantum efficiency in comparison with Eu3+ complex indicates an effective channel for energy transfer of the hybrid emitting levels and Eu3+ ion. This also suggest that the coordination ability of the hybrid host, through the oxygen atom of the carbonyl group, is strong enough to substitute the ethanol molecule in the coordination sphere of the Eu3+ ion. The ground state geometry of the non-doped di-ureasil and incorporating the [Eu(btfa)3(4,4 -bpy)(EtOH)] complex were optimized by the AM1 method and Sparkle model, respectively. With these geometries calculated, for the first time, the energy transfer rates were estimated to non-doped organic-inorganic hybrid and incorporating the [Eu(btfa)3(4,4 -bpy)(EtOH)] complex. The photostability study was realized on the [Eu(btfa)3(4,4 -bpy)(EtOH)] complex isolated and incorporated into the hybrid. For an exposure time of 10 hours the hybrid incorporating the [Eu(btfa)3(4,4 -bpy)(EtOH)] complex are photostable under UV-A (360 nm) excitation, whereas under UV-B (320 nm) and UV-C (290 nm) excitation photodegradation occurs, demonstrating the potential of these hybrid materials to be used as UV-B and UV-C dosimeters. Photodegradation occurs in the isolated complex, under UV-A, UV-B and UV-C irradiations. The consequences of the photodegradation process observed for these compounds have been investigated, but until the present moment no explanation for such phenomenon was found

ASSUNTO(S)

quimica luminescence complexo de lantanÃdeos materiais luminescentes lanthanide complex organic hybrid hÃbridos orgÃnicos

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