Comparison of the Structural Information on Sol-Gel Systems Provided by Pyrene Labeled Fluorescent Probes |
| |
Authors: | LM Ilharco AM Santos MJ Silva JMG Martinho |
| |
Institution: | (1) Centro de Química-Física Molecular, Instituto Superior Técnico, Av. Rovisco Pais, 1096 Lisboa Codex, Portugal |
| |
Abstract: | The influence of the acid catalyst concentration on the structural evolution of a sol-gel system was studied by doping TEOS
based starting solutions with two fluorescent probes: a polystyrene chain (M
n
=1700) and a much shorter alkane chain (M=172), both of them labeled at both ends with 1-pyrenyl. For this purpose, each probe was incorporated in two TEOS∶H2O∶C2H5OH mixtures (molar ratios 1∶4∶1), one at pH 1.2 and the other at pH 2.5 (respectively below and above the isoelectric point
of silica). Very low concentrations of the probes were used (≤10−6
M), so the pyrene dimmers and excimers were formed only intramolecularly. The ratios of excimer to monomer fluorescence intensities
at excitation wavelength of 360 nm (where mainly the ground state pyrene dimmers are excited) were studied as a function of
time. Different evolutions of these ratios were observed, which allowed us to predict that the silica structure developsvia the formation of primary particles, even at pH values below the isoelectric point of silica, where it is not possible to
directly detect their formation. |
| |
Keywords: | sol-gel structure doping probe pyrene intramolecular excimer |
本文献已被 SpringerLink 等数据库收录! |
|