Consequences of controlling free space within a reaction cavity with a remote alkyl group: photochemistry of para-alkyl dibenzyl ketones within an organic capsule in water

With the aim of controlling free space available for the reactants, photochemical reactivity of several 4-alkyl dibenzyl ketones included within a water-soluble self-assembled organic capsule ( octa acid) has been investigated. One and two-dimensional NMR spectroscopic techniques were employed to characterize the structure of the guest@host complexes. Free space controlled by the remote alkyl group influences the distribution of photoproducts. Correlation between the structures of the guest@host complexes and products selectivity suggested that the free space that could be controlled by a remote tether has a determining role during a photoreaction within the restricted space of the capsule. The fact that the same alkyl tether has no effect on the photobehavior of 4-alkyl dibenzyl ketones in hexane solution suggests that the role of substituents in free ( solution) and restricted space (supramolecular assemblies) is different. The current observation suggests that rules of physical organic chemistry and photochemistry developed based on solution chemistry cannot be simply extended to supramolecular assemblies.