Modification of Photochemical Reactivity by Cyclodextrin Complexation: Consequences of Restricted Rotation of Norrish Type II 1,4-Diradicals from Aryl Alkyl Ketones

Photochemical behavior of aryl alkyl ketones complexed to β-cyclodextrin both in aqueous solution and in the solid state have been investigated. Comparison of the above behavior with that in isotropic solvents reveals that cyclodextrin inclusion provides an environment wherein photoreactions may be carried out with consequences different from those observed in homogeneous solution. Products of elimination and cyclization resulting from the Norrish type II hydrogen abstraction were monitored. The ratio of these products was dependent on the length but not on the bulkiness of the alkyl substituent. These observations are rationalized on the basis of the steric constraints by the cyclodextrin cavity on the rotational motions of the 1,4-diradical.