title: Self-structuring of lamellar bridged silsesquioxanes with long side spacers.
abstract: Diurea cross-linked bridged silsesquioxanes (BSs) C(10)C(n)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) 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.
authors.affiliation: Chemistry Departement, University of Trás-os-Montes e Alto Douro 5001-801 Vila Real, Portugal.
authors.forename: Mariana
authors.initials: M
authors.lastname: Fernandes
authors.forename: Sónia S
authors.initials: SS
authors.lastname: Nobre
authors.forename: Qinghong
authors.initials: Q
authors.lastname: Xu
authors.forename: Carole
authors.initials: C
authors.lastname: Carcel
authors.forename: Jean Nicolas
authors.initials: JN
authors.lastname: Cachia
authors.forename: Xavier
authors.initials: X
authors.lastname: Cattoën
authors.forename: José M
authors.initials: JM
authors.lastname: Sousa
authors.forename: Rute A S
authors.initials: RA
authors.lastname: Ferreira
authors.forename: Luís D
authors.initials: LD
authors.lastname: Carlos
authors.forename: Celso V
authors.initials: CV
authors.lastname: Santilli
authors.forename: Michel
authors.initials: M
authors.lastname: Wong Chi Man
authors.forename: Verónica de Zea
authors.initials: Vde Z
authors.lastname: Bermudez