Transient products in the photoreduction of benzophenone derivatives in poly(ethylene-vinyl alcohol) film

The formation, stability, and reactivity with oxygen of the so-called light-absorbing transient (LAT) photoproducts formed on photoreduction of benzophenone and several benzophenone derivatives in poly(ethylene-vinyl alcohol) (EVOH) films were investigated. The maximum total yield of LAT photoproducts on photoreduction of benzophenone was estimated to be approximately 50%, which was found to comprise around 75% of the para-LAT isomer with the remainder being attributed to the ortho-LAT isomer. The concentrations of these LAT isomers were found to decay over a period of weeks at room temperature in the absence of oxygen, with the decay of the para-LAT isomer being substantially slower than the ortho-LAT isomer. Furthermore, the decay rate of the para-LAT isomer was found to increase markedly in the presence of oxygen. Mechanisms for the decay of the LAT isomers that are consistent with available data are postulated. The presence of alkyl, alkoxy, or aryloxy moieties on the phenyl rings of benzophenone appears to have little effect on the efficiency of formation, stability, and reactivity with oxygen of the LAT photoproducts in EVOH films, for the benzophenone derivatives studied in this work.