Structure of hybrid silica gels incorporated with hydrophobic dye molecules

Hybrid gels incorporated with functional organic molecules are interesting for their physical properties and microstructures as well as their potential applications. Organic-inorganic hybrid silica gels incorporated with hydrophobic organic dye were prepared by hydrolysis of phenyltriethoxysilane (PhTES) and tetraethoxysilane (TEOS) in ethanol solution containing organic dye, pyrene or rhodamine-B (RB). The structure of the gels were investigated by mean of IR absorption spectra and UV-visible absorption/fluorescence spectra. The xerogel prepared from the solution of [PhTES]/[PhTES + TEOS] < 0.3 was stable, and the incorporated dyes hardly dissolved into ethanol. Si-Ph bond increased with increasing PhTES content in the precursor solutions. The UV-visible absorption spectra of the gels incorporated with RB show increase in the amount of dimer with increasing Ph-content. The fluorescence spectra for the gels incorporated with pyrene show that the hydrophobic dye is preferentially incorporated as monomers when the amount of Ph-group in the gels increases in contrast with hydrophilic RB. It is also suggested that the hydrophobic dye is preferentially incorporated into gels as monomers when the gelation rate is low.