These photons are substantially lower in energy than the blue or ultraviolet light most often used in photochemistry. This gave us product specificity because we were below the dissociation energies of the reaction partners. Excitation above dissociation energies often leads to unwanted byproducts. Now, working with Fritz Blatter and Hai Sun, Frei has developed a new technique for selective hydrocarbon oxidation that not only permits the use of red and near-infrared photons, but also enables photochemical reactions to take place at room temperature. What makes this possible is the immobilization of reactants not in a cryogenic matrix, but in molecular-sized cages of inert solid materials called zeolites.
Zeolites are alumino silicates used widely in the petrochemical industry as catalysts.
They feature unique pore structures inside which smaller molecules can be imprisoned. Using a synthetic version of a natural zeolite called faujasite, Frei and his colleagues successfully held and photo-oxidized small alkene molecules into industrially important chemical building blocks and intermediaries such as hydroperoxides, carbonyls, and epoxides. This was accomplished without the customary release of carbon dioxide, the chief contributor to global warming and the greenhouse effect. To photo-oxidize their alkene molecules, Frei and Blatter loaded them as a gas into zeolite pellets and added oxygen. Reactant molecules paired with one another and were held together by the zeolite cages in close contact so that irradiation with red light triggered oxidation.