The flexible solution chemistry of the sol-gel process has been used to encapsulate a wide variety of organic, organometallic, and biomolecules in inorganic solids. This paper reviews different types of photochemical reactions which we have used to produce specific products or to generate oxygen within sol-gel matrices. By controlling synthesis conditions, the molecules can be made to exhibit desired reactivities when trapped in the sol-gel matrix.
Three different examples of photochemical reactions are presented in this paper. An organometallic gold precursor compound, dimethyl (hexafluoroacetylacetonato)gold, dissolved in a silicate sol is used to produce gold nanoparticles of desired sizes. The second example is based on sol-gel encapsulated photochromic (and thermochromic) spiropyran, that converts to a colored form using thermal energy or UV radiation. The synthesis strategies for selectively isolating the colored or the colorless form in sol-gel materials are presented. Materials of these types may be useful in writeonce- read-many (WORM) optical data storage applications. The third example involves sol-gel matrices doped with a biosystem, the green plant photosystem H (PS II). The resulting aged gels and xerogels are photoactive and are capable of photooxidizing water. Oxygen illumination was measured under white light and there is an indication that PS II particles are stabilized by the encapsulation process.