Excimer Fluorescence of Pyrene in Sol–Gel Silica

Abstract The fluorescence and excitation spectra of pyrene at high concentrations were studied along the sol to xerogel stages of the sol–gel silica formed by the acidic hydrolysis of tetraethyl orthosilicate. The monomer and excimer fluorescence of pyrene were observed in the reaction system. Their relative intensities revealed that complex changes occurred that depended on the reaction time and the excitation wavelengths. The environmental polarity of the probe molecules also changed as shown by the fluorescence vibronic structure. The excitation spectrum of the excimer fluorescence in some stages was red shifted in comparison with that of the monomer fluorescence, indicating the existence of bimolecular ground-state pyrene associations. The mechanism by which pyrene molecules are trapped in the silica network is discussed on the basis of the results.