SURFACE COMPLEXES AS PRECURSORS OF PHOTOINDUCED RADICAL CATIONS OF BIPHENYL AND SUBSEQUENT HYDROXYLATION ON LAPONITE

The photochemical reactions of the model compound biphenyl on laponite surfaces have been investigated. Diffuse reflectance and fluorescence spectroscopic studies indicate that adsorbed biphenyl molecules inter act with solid surfaces in two ways, a physical interaction which lead s to a bathochromic shift and broadening of absorption bands and a che mical interaction which leads to surface complexes with charge-transfe r (CT) character. Photoirradiation of the surface complexes results in the formation of radical cations, Ph2.+, which are observed by diffus e reflectance and EPR spectroscopy. Product analysis confirms that bip henyl is photochemically degraded on laponite on irradiation into the CT band and that the mechanism is free radical in nature. The importan t reaction of radical cations on surfaces is hydrolysis resulting in h ydroxy compounds. The present results indicate that layered silicates are more active than silica-alumina gels, in the above processes.