Abstract
Two hybrid materials based on dodecatungstophosphoric acid (HPW) dispersed in ormosils modified with 3-aminopropiltrietoxysilane (APTS) or with N-(3-(trimethoxysilyl)-propyl)-ethylenediamine (TSPEN) show reversible photochromic response induced by irradiation in the 200−390 nm UV range. A set of solid-state nuclear magnetic resonance (NMR) techniques was used to analyze the structural properties of the main components of these hybrids (the HPW polyanion, the inorganic matrix, and the organic functionalities). For the ormosils, the use of 29Si NMR, {1H}-29Si cross-polarization, and {1H}-29Si HETCOR revealed a homogeneous distribution of silicon species Qn, T2, and T3 for the APTS hybrid, contrasting with the separation of T3 species in the TSPEN hybrid. The combination of 31P NMR, {1H}-31P cross-polarization and 31P-{1H} spin−echo double resonance (SEDOR) revealed the dispersion of the HPW ions in the ormosil, occupying sites with a high number of close protons (>50). Differences in the molecular dynamics ...
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