Silica sols and gels doped with pyrene (Py) and pyrene-3-carboxaldehyde (PyCHO) were prepared by the acidic hydrolysis of tetraethyl orthosilicate in ethanol. We studied the fluorescence of these molecules during the sol–gel–xerogel stages. The fluorescence intensity ratio of the vibronic bands of Py changed remarkably, while the fluorescence maximum of PyCHO showed a significant red shift as the gel dried. Such a spectral change was ascribed to an increase in the environmental polarity of the probe molecules upon the evaporation of the ethanol. The estimated dielectric constant of the gel after drying in a vacuum is about 72, just slightly less polar than water (80). The silica cage produced by the sol–gel process is probably rich in silanols, resulting in a relatively polar environment.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.