resumo
Novel amide cross-linked alkylene-siloxane hybrid materials (di-amidosils) synthesized by the sol-gel process have been investigated. Two samples identified by the notation d-A(x) with x 5 4 and 8 (where x is the number of methylene groups of the alkylene chain) have been produced as transparent, amorphous, rigid monoliths. The d-A( 8) material is thermally stable up to approximately 245 degrees C. In this hybrid the siliceous framework is mainly composed of [-(CH2) Si(OSi)(3))] and [-(CH2) Si(OSi)(2)(OH)] substructures. Structural unit distances of 4.1 and 4.2 angstrom and average interparticle distances of 12 and 17 angstrom have been determined for d-A(4) and d-A(8), respectively. In these compounds the alkylene chains are disordered and adopt gauche conformations. While a negligible proportion of the amide linkages remain non-bonded, the great majority of these groups belong to highly disordered strong hydrogen-bonded amide - amide associations. The hybrids introduced are room temperature white light emitters, presenting an intense, broad emission band in the blue/purplish-blue spectral region. The origin of such a band has been ascribed to the convolution of donor - acceptor pair (D - A) recombinations that occur in the NH groups of the amide linkages and in the siliceous nanodomains. The maximum quantum yield value of the d-A(8) di-amidosil is 5.4%.
palavras-chave
ORGANIC-INORGANIC NANOCOMPOSITES; METAL ACTIVATOR IONS; INFRARED TEMPERATURE; LIGHT EMISSION; POLYMERS; LUMINESCENCE; PHOSPHORS; ACID; RECOMBINATION; CONFORMATION
categoria
Chemistry; Materials Science
autores
Nunes, SC; Bermudez, VDZ; Cybinska, J; Ferreira, RAS; Legendziewicz, J; Carlos, LD; Silva, MM; Smith, MJ; Ostrovskii, D; Rocha, J
nossos autores
João Rocha
Prof. Catedrático
Luís Carlos
Professor Catedrático