resumo
Two structurally different but chemically similar families of alkyl/siloxane mono-amidosil hosts, represented by m-A(x) [where x = 14 or 8 represents the number of CH, groups of the pendant alkyl chains directly bonded to the carbonyl group of the amide cross-link] have been doped with a wide range of concentrations of Eu(CF3SO3)(3). Mono-amidosils m-A(x)(n)Eu(CF3SO3)(3) with n >= 10 (where n is the molar ratio of carbonyl groups per Eu3+ ion) have been analyzed. The m-A(8)(n)Eu(CF3SO3)(3) mono-amidosils are transparent and amorphous films, in which the alkyl chains adopt gauche conformations. In contrast, the m-A(14)(n)Eu(CF3SO3)(3) monoamidosils are solid powders; here the lamellar bilayer hierarchical structure of m-A(14) coexists with a new lamellar phase in which the Eu3+ ions are bonded to carbonyl oxygen atoms of the amide groups. At n = 10 the hydrogen-bonded associations formed are highly ordered and considerably stronger than those found in the less concentrated hybrids and in the nondoped matrices. "Free" and weakly coordinated triflate ions occur in all the mono-amidosil samples. The hybrids are white light emitters (maximum quantum yield: 0.08 +/- 0.01), presenting a broad emission band in the blue/purplish-blue spectral region (ascribed to the hybrid host) superimposed on the D-5(0)-> F-7(0-4) Eu3+ intra-4f(6) transitions. Two Eu3+ local coordination sites (named A and B) have been discerned in both systems. Site A is attributed to weakly coordinated Eu3+/CF3SO3- ion pairs, whereas site B involves Eu3+ coordination to the oxygen atoms of the C=0 groups, of the CF3SO3- ions and of the water molecules. For site B, the long-range order of the hybrid host induces distinct features in the energy of the D-5(0)-> F-7(0-4) transitions, the D-5(0) lifetime and the degree of covalency of the Eu3+-first-ligand bonds.
palavras-chave
ORGANIC-INORGANIC HYBRIDS; SOLID-STATE NMR; ENERGY-TRANSFER MECHANISMS; EMISSION QUANTUM YIELDS; WHITE-LIGHT EMISSION; FULL-COLOR PHOSPHORS; BRIDGED SILSESQUIOXANES; INFRARED TEMPERATURE; LANTHANIDE COMPOUNDS; ALKYL CHAINS
categoria
Chemistry
autores
Nunes, SC; Planelles-Arago, J; Ferreira, RAS; Carlos, LD; Bermudez, VD
nossos autores
Luís Carlos
Professor Catedrático
Maria Rute de Amorim e Sá Ferreira André
Professor Catedráticoagradecimentos
This work was supported by the Fundacao para a Ciencia e Tecnologia and FEDER (PTDC/CTM/72093/2006). S. C. N. acknowledges the Fundacao para a Ciencia e Tecnologia (SFRH/BPD/63152/2009), and J. P. thanks the Spanish Ministerio de Ciencia e Innovacion (FPU fellowship). The authors are grateful to Denis Ostrovskii of the Department of Applied Physics, Chalmers University of Technology, Goteborg, Sweden, for recording the FT-IR and FT-Raman spectra.