Cooperative effect of acid sites in the photocyclization of azobenzene within the zeolite microenvironment

Article abstract of DOI:10.1021/ja00059a011

Photolysis of azobenzene in the presence of a series of acidic zeolites with different crystal size (0.8 and 0.3 μm), crystalline structure (Y, β, ZSM-5), and framework Si-to-Al ratio (Al/cage ranging from 4.6 to 0.25) gives rise to benzo[c]cinnoline and benzidine. The latter remains protonated within the zeolite cavities, as has been established by FT-IR spectroscopy of the hosts. The lack of influence of the crystallite size on the activity of the zeolite reveals that the reaction is mainly taking place on the internal surface of these microporous solids. Finally, the relationship between the activity of the zeolite and the number of Bro?nsted sites per α-cage indicates that only two H⁺ per supercavity can participate in the photocyclization of azobenzene. This result agrees with the relative size of the zeolite cavities and the reactant molecules.