Photoluminescence of Bridged Silsesquioxanes Containing Urea or Urethane Groups with Nanostructures Generated by the Competition between the Rates of Self-Assembly of Organic Domains and the Inorganic Polycondensation

The aim of this study was to investigate the changes produced in the nanostructures and the photoluminescence spectra of bridged silsesquioxanes containing urea or urethane groups, by varying the relative rates between the self-assembly of organic domains and the inorganic polycondensation. Precursors of the bridged silsesquioxanes were 4,4‘-[1,3-phenylenebis(1-methylethylidene)]bis(aniline) and 4,4‘-isopropylidenediphenol, end-capped with 3-isocyanatopropyltriethoxysilane. The inorganic polycondensation was produced using either high or low formic acid concentrations, leading to transparent films with different nanostructures as revealed by FTIR, SAXS, and ²⁹Si NMR spectra. For the bridged silsesquioxanes containing urea groups the self-assembly of organic domains was much faster than the inorganic polycondensation for both formic acid concentrations. However, the arrangement was more regular and the short-range order higher when the rate of inorganic polycondensation was lower. The photoluminescence spectra of the most ordered structures revealed the presence of two main processes:  radiative recombinations in inorganic clusters and photoinduced proton-transfer generating NH₂⁺ and N⁻ defects and their subsequent radiative recombination. In the less-ordered urea-bridged silsesquioxanes a third process was present assigned to a photoinduced proton transfer in H-bonds exhibiting a broad range of strengths. For urethane-bridged silsesquioxanes the driving force for the self-assembly of organic bridges was lower than for urea-bridged silsesquioxanes. When the synthesis was performed with a high formic acid concentration, self-assembled structures were not produced. Instead, large inorganic domains composed of small inorganic clusters were generated. Self-assembly of organic domains took place only when employing low polycondensation rates. For both materials the photoluminescence was mainly due to radiative processes within inorganic clusters and varied significantly with their state of aggregation.The financial support of the National Research Council (CONICET, Argentina), the National Agency for the Promotion of Science and Technology (ANPCyT, Argentina, PICT 14738-03), the University of Mar del Plata, the Grant Agency of the Czech Republic (Project 203/05/2252), and Project Nanoter (Project MAT2004/01347, MEC-DGI, Spain) is gratefully acknowledged. INTEMA and the Institute of Macromolecular Chemistry acknowledge the support of the European Network of Excellence Nanofun-Poly for the diffusion of their research results

Nanoestructured bridged silsesquioxanes via sol-gel synthesis

Two types of hybrid materials with different degree of nanoestructuring (a bridged silsesquioxane (BS) and hybrid microspheres (MS)) were obtained from a bridged precursor (P) synthesized by the reaction of glycidoxypropyl(trimethoxysilane) with cyclohexylamine. The polycondensation of P in presence of formic acid produced a hybrid material (BS) exhibiting a short-range order based on elongated organic channels, accommodating the cyclohexyl fragments pending from the organic bridge, bounded by inorganic domains. Also, nanostructured hybrid microspheres (MS) were synthesized from P by employing ultrasound-assisted sol-gel processing. The mild reaction conditions produced the nanostructuring of the silsesquioxane characterized by a fine structure in SAXS spectrum. Inorganic domains were arranged in a twodimensional hexagonal system leading to the formation of cavities in the microspheres which could be employed as host-guest systems in advanced technologies.Dos tipos de materiales híbridos con diferente grado de nano-estructuración (un silsesquioxano puenteado (BS) y microesferas híbridas (MS)) fueron obtenidos a partir de un precursor puenteado (P) sintetizado mediante la reacción de glicidoxipropil (trimetoxisilano) con ciclohexilamina. La policondensación del precursor (P) en presencia de ácido fórmico produjo un material híbrido (BS) que presenta un ordenamiento de corto alcance basado en canales orgánicos alargados, que acomodan grupos ciclohexilo pendientes del puente orgánico, enlazados por dominios inorgánicos. También, a partir del precursor P fueron sintetizadas microesferas híbridas nanoestructuradas (MS) empleando una vía de síntesis sol-gel asistida por irradiación ultrasónica. Las suaves condiciones de reacción produjeron la nanoestructuración del silsesquioxano caracterizado por una estructura fina en el espectro SAXS. Los dominios inorgánicos presentaron un arreglo bidimensional hexagonal que dio lugar a la formación de cavidades en las microesferas, las que podrían ser empleadas para contener pequeñas moléculas útiles en tecnologías avanzadas.Fil: Romeo, Hernan Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Williams, Roberto Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Matejka, Libor. Academy of Sciences of the Czech Republic; República ChecaFil: Plestil, Josef. Academy of Sciences of the Czech Republic; República ChecaFil: Brus, Jirí. Academy of Sciences of the Czech Republic; República ChecaFil: Fanovich, Maria Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Fast synthesis of nanostructured microspheres of a bridged silsesquioxane via ultrasound-assisted sol-gel processing

Microspheres of a nanostructured bridged silsesquioxane were synthesized by employing ultrasound-assisted self-assembly of a bridged monomer via sol-gel processing. The bridged precursor was synthesized from glycidoxypropyl(trimethoxysilane) (GPMS) (2 mol) and cyclohexylamine (1 mol). The main factor controlling the generation of a stable dispersion of microspheres was the time at which the phase separation of the silsesquioxane was produced during the hydrolytic condensation. An appropriate blend of THF/n-hexane as a solvent enabled to rapidly generate a stable dispersion exhibiting a low polydispersity. The mild reaction conditions produced the nanostructuring of the silsesquioxane characterized by a fine structure in SAXS spectrum. Inorganic domains were arranged in a two-dimensional hexagonal system leading to the formation of cavities in the microspheres which could be employed as host-guest systems in advanced technologies. © 2009 WILEY-VCH Verlag GmbH & Co. KCaA.Fil: Romeo, Hernan Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Fanovich, Maria Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Williams, Roberto Juan Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Matejka, Libor. Academy of Sciences of the Czech Republic; República ChecaFil: Plestil, Josef. Academy of Sciences of the Czech Republic; República ChecaFil: Brus, Jirí. Academy of Sciences of the Czech Republic; República Chec