Modification of Photochemical Reactivity by Cyclodextrin Complexation: A Remarkable Effect on the Photobehavior of α-Alkyldibenzyl Ketones

The Norrish type I and type II reactions of cyclodextrin-included α-alkyldibenzyl ketones have been investigated in the aqueous solution and in the solid state. The photolysis of solid cyclodextrin complexes led to a single product, diphenylethane (AB), and that of complexes in the aqueous solution resulted in a product arising from the rearrangement of α-alkyldibenzyl ketones. Conformational and super-cage effects are proposed to be responsible for the dramatic alteration observed in the above photobehavior. The difference in the product distribution between solid and solution complexes is attributed to the differences in the restriction imposed by the host on the translational motions of the geminate radical pairs.