The UV–VIS absorption spectrum of thymol blue (TB), which was used for an in situ probe for the proton donor–acceptor property of the surrounding matrix, has been observed as a function of time during the sol–gel–xerogel reactions of tetraethyl orthosilicate under HCl catalyzed and uncatalyzed conditions. The value of relative abundance, RA Z , of zwitter ion species was calculated. In the ethanol-containing system, RA Z increased for 7 h, then decreased until 114 h had passed, and finally increased gradually. These dynamic changes of the RA Z were commonly observed for all the systems. The final RA Z values were expected larger than 0.7 irrespective of the initial chemical composition. The characteristic increase and decrease in RA Z are ascribed to the increase and decrease in proton-donating ability from the surrounding matrix to encapsulated TB molecules. A general acidity function, H −, of the matrix was estimated.
Research on Chemical Intermediates – Springer Journals
Published: Jan 28, 2009
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