Self-structuring of lamellar bridged silsesquioxanes with long side spacers

Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(11)C(10) derived from organosilane precursors, including decylene chains as side spacers and alkylene chains with variable length as central spacers (EtO)(3)Si- (CH(2))(10)-Y(CH(2))(n)-Y-(CH(2))(10)-Si(OEt)(3) (n = 7, 9-12; Y = urea group and Et = ethyl), have been synthesized through the combination of self-directed assembly and an acid-catalyzed sol gel route involving the addition of dimethylsulfoxide (DMSO) and a large excess of water. This new family of hybrids has enabled us to conclude that the length of the side spacers plays a unique role in the structuring of alkylene-based BSs, although their morphology remains unaffected. All the samples adopt a lamellar structure. While the alkylene chains are totally disordered in the case of the C(10)C(7)C(10) sample, a variable proportion of all-trans and gauche conformers exists in the materials with longer central spacers. The highest degree of structuring occurs for n = 9. The inclusion of decylene instead of propylene chains as side spacers leads to the formation of a stronger hydrogen-bonded urea-urea array as evidenced by two dimensional correlation Fourier transform infrared spectroscopic analysis. The emission spectra and emission quantum yields of the C(10)C(n)C(10) Cm materials are similar to those reported for diurea cross-linked alkylene-based BSs incorporating propylene chains as side spacers and prepared under different experimental conditions. The emission of the C(10)C(n)C(10) hybrids is ascribed to the overlap of two distinct components that occur within the urea cross-linkages and within the siliceous nanodomains. Time-resolved photoluminescence spectroscopy has provided evidence that the average distance between the siliceous domains and the urea cross-links is similar in the C(10)C(n)C(10) BSs and in oxyethylene-based hybrid analogues incorporating propylene chains as side spacers (diureasils), an indication that the longer side chains in the former materials adopt gauche conformations. It has also allowed us to demonstrate for the first time that the emission features of the urea-related component of the emission of alkylene-based BSs depend critically on the length of the side spacers

Incorporation Of Water-Soluble Porphyrins In Sol-Gel Matrices And Application To pH Sensing

The incorporation of H₂TPPS⁴- into sol-gel materials has been used to determine the pH inside a sol-gel matrix

Self-Organized Bridged Silsesquioxanes

An innovative and general method for the synthesis of shape-controlled bridged silsesquioxanes by the hydrolysis of urea-derived organo-bis(trialkoxy)silanes has been developed. This method relies on the ability of the hydrogen bonds of the urea groups to self-assemble the molecules in a supramolecular architecture. The controlled hydrolysis of the latter efficiently leads to new hybrid silsesquioxanes wirh sought-after morphologies. Following the reaction conditions (acid- or base-catalyzed hydrolysis) and also depending on the solvent used (purely aqueous or a mixture of water and ethanol), different forms of hybrid materials were obtained from the hydrolysis of chiral diureido derivatives of trans-diaminocyclohexane. Right- and left-handed helices were formed under acid-catalyzed hydrolysis of the enantiopure (R,R) and (S,S) compound respectively

Electrochemical preparation of anthraquinone and zinc porphyrin coated electrodes: redox activity and film stability

This study concerns some aspects of the electrochemical design and characterization of zinc porphyries and anthraquinone-based polymers. The electro-formation of the films on the electrode surface has been achieved by cyclic voltammetry in organic solvents such as dichloromethane and acetonitrile. It is based on the electrochemical oxidative polymerization of the pyrrole or hydroxy-substituted phenyl groups attached to the porphyrin or anthraquinone molecules. The redox characteristics of the polymer films as well as their stability were studied by cyclic voltammetry and spectrophotometry and are compared to those of the starting monomers. The conditions of the electropolymerization of stable and reproducible multicomponent films are also discussed

Synthesis and Properties of Polymeric Schiff-Bases and Their CO(II), CU(II) and NI(II) Complexes

Soluble and insoluble polymeric Schiff bases PolySalPn and PolySal-DPT* have been synthesised. The polymers and their copper(II), nickel(II) and cobalt(II) complexes have been fully characterised by their elemental analyses and by spectroscopic methods. The Co—PolySalDPT proved to be as efficient as the corresponding monomeric complex in catalysing the oxidation of 2,6-di-t-butylphenol

Silices hybrides pour la catalyse hétérogène

International audienceDifférents matériaux hybrides préparés par voie sol-gel à partir de ligands triéthoxysilylés ont conduit, après complexation à un métal (rhodium, ruthénium ou palladium) à des catalyseurs hétérogènes efficaces et recyclables, en particulier pour trois types de réactions catalytiques : 1. Réduction asymétrique de cétones prochirales par transfert d'hydrures. 2. Couplage de type Suzuki. 3. Cyclisations par métathèse de diènes et d'enynes