Hybrid photochromic mesoporous materials based on MCM-41 and SBA-15 were synthesized by covalent attachment of 3'-butoxy-7-hydroxyflavylium (Fl-OH) and 3'-butoxy-7-metoxyflavylium (Fl-OCH3) hydrogensulfates. The pristine materials were initially grafted with 3-chloropropyl groups, reacted with 3'-hydroxyacetophenone and finally condensed with appropriate salicylaldehydes to yield the new hybrids MCM-41-Fl-OH and SBA-15-Fl-OCH3. The materials were characterized by powder X-ray diffraction, N-2 adsorption, solid-state C-13 CPMAS NMR spectroscopy, and thermogravimetric and elemental analyses, which confirm the successful covalent bonding of the flavylium moieties with loadings of 16.90 +/- 0.05% and 11.78 +/- 0.04% (w/w) for MCM-41-Fl-OH and SBA-15-OCH3, respectively. Flavylium compounds originate in solution a multiequilibria reaction network than can be actuated by pH and light, defining pH-coupled photochromic systems. The new hybrids show pH-dependent reflectance spectra resembling those observed in solution, but shifted to higher pH ranges, indicating a higher stability of the grafted flavylium cations. Irradiation of these materials equilibrated at adequate pH values where the photoisomerizable trans-chalcones predominate shows formation of the respective flavylium cations that recover back to the initial compositions upon standing in the dark, leading these new organic-inorganic hybrids as pH-dependent photochromic materials. (C) 2013 Elsevier Inc. All rights reserved.
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Gago, Sandra Fonseca, Isabel M. Parola, A. Jorge
Fundacao para a Ciencia a Tecnologia through the National Portuguese NMR Network [PEst-c/EQB/LA0006/2011]; [NMP4-SL-2012-310651]; [FP7-NMP-2012-SMALL-6]; [PTDC/QUI-QUI/104129/2008]; [PTDC/QUI-QUI/119932/2010]
This work was supported by European project NMP4-SL-2012-310651 under FP7-NMP-2012-SMALL-6 and by Fundacao para a Ciencia a Tecnologia through the National Portuguese NMR Network, grant PEst-c/EQB/LA0006/2011 and projects PTDC/QUI-QUI/104129/2008 and PTDC/QUI-QUI/119932/2010. Dr. A. Coelho and Prof. F. Lemos (IST-UTL) are acknowledged for TGA and powder X-Ray diffraction data.
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