Intrazeolite photochemistry. 8. Influence of the zeolite physicochemical parameters on the laser flash photolysis of 1,1-diphenyl-2-propanone included in acid faujasites

Article abstract of DOI:10.1021/ja00077a010

Time-resolved diffuse reflectance laser flash photolysis studies of 1,1-diphenyl-2-propanone (DPA) included in a consistent series of Y faujasites at four levels of Na⁺-to-H⁺ exchange have shown that the interaction of this guest molecule with the zeolite acid sites leads to transient spectra much different than that due to the diphenylmethyl radical (DPM) characteristic of nonacidic hosts. Similar modification of the photochemical pattern was also observed when DPA was adsorbed onto the all-Lewis acid site Zn Y zeolite, albeit much slower decay traces were recorded in this case. We have found that by using a highly dealuminated acid zeolite (HYD, Si/Al 27.5) a much better resolved transient spectrum characteristic of the diphenylmethyl cation (DPM⁺) was obtained. Methanol quenching experiments have provided firm evidence for the generation of DPM⁺ within acid zeolites. A progressive increase of the DPM/DPM⁺ ratio, as measured from the relative intensities of their corresponding signals, with the time elapsed from the preparation of the complexes has been observed. Finally, the effects of coadsorbed water and the presence of oxygen on the spectra and the kinetics of the transients generated from DPA are reported.