abstract
Mono-amide cross-linked alkyl-siloxane hybrids synthesized through the sol-gel process and the self-directed assembly have been doped with variable concentrations of monomethinecyanines SSCH2(C6H5)I, SSCH3Cl and SSC2H5ClO4. The host matrix m-A(14) is a lamellar structured hybrid composed of short methyl-capped alkyl chains grafted to the siliceous framework through amide groups. The doped mono-amidosil hybrid materials were obtained as solid powders. The bulky SSCH2(C6H5)I dye inhibited the condensation of the silica network. In the SSCH3Cl- and SSC2H5ClO4-doped m-A(14)-based materials the original lamellar structure coexists with a new lamellar ordered phase with a lower interlamellar distance in which the alkyl chains adopt essentially all-trans conformations. The efficient encapsulation of these two dyes by m-A(14), which ensures their complete dissolution, is due to the coordination of the S atoms of SSCH3Cl and SSC2H5ClO4 to the carbonyl oxygen atoms of the amide cross-links. This process leads to a major breakdown of the disordered and ordered hydrogen-bonded aggregates of m-A(14), but does not affect globally the strength of the hydrogen-bonded array. The most dilute SSC2H5ClO4-doped mono-amidosil studied displays room temperature emission in the visible spectral region (380-680 nm) due to the convolution of the intrinsic emission (blue spectral region) of m-A(14) with that of the SSC2H5ClO4 dye (green and red spectral regions) due to the formation of fluorescent J-dimers. The excitation spectra (monitored along the emission spectra) reveal the occurrence of host-to-monomethinecyanine energy transfer.
keywords
ORGANIC-INORGANIC HYBRIDS; NORMAL-ALKYL CHAINS; H STRETCHING MODES; SOLID-STATE LASERS; OPTICAL-PROPERTIES; INFRARED TEMPERATURE; SILICA NANOPARTICLES; MESOPOROUS SILICA; CLAY-MINERALS; GEL MATRICES
subject category
Materials Science; Physics
authors
Nunes, SC; Ferreira, CB; Hummer, J; Ferreira, RAS; Carlos, LD; Almeida, P; Bermudez, VD
our authors
Luís Carlos
Full professor
Maria Rute de Amorim e Sá Ferreira André
Full professoracknowledgements
This work was supported by Fundacao para a Ciencia e a Tecnologia (FCT) and FEDER (contracts PTDC/CTM/101324/2008, PTDC/QUI-QUI/100896/2008, Pest-14C/CTM/LA0011/2011 and Pest-C/SAU/UI0709/2011). S. C. Nunes and C. B. Ferreira acknowledge FCT for grants (SFRH/BPD/63152/2009 and BIC/PEst-C/QUI/UI0616/2011, respectively). J. Hummer, a student of Technology of Functional Materials at the Julius-Maximilian-University in Wurzburg (Germany), was involved in this work in the framework of an internship at the Department of Chemistry of UTAD, Vila Real, from September to October 2010. The authors thank Dr. Raquel Rosa, of the Communication and Image Office of the University of Beira Interior (Portugal) for the Cover artwork.