Photochemical Reactions in a Water Soluble Supramolecular System: Influence of Confinement on Guest Reactivity and Product Selectivity

In this study, a synthetic, water soluble cavitand octa acid (OA) is used as medium for conducting photochemical reactions. The cavitand octa acid is soluble in water in slightly basic conditions. OA forms different types of complexes with variety of organic guest molecules. Remarkably, in presence of a hydrophobic guest, two of these OA molecules self assemble to form a capsular complex (guest@(OA)2). The confined inner phase of the cavitand can be utilized to control both photochemistry and photophysics of organic guest molecules. Stilbene derivatives undergo cis/trans (Z/E) photoisomerization in organic solvents. The results of our studies with stilbenes@(OA)2 suggest that the available free volume for encapsulated guest stilbenes could be manipulated by changing the number and position of the substituent methyl groups which has a significant influence on the photoisomerization process. Further, energy transfer from caged donor ((fluorenone)2@(OA)2) to caged acceptor ((stilbene)@(OA)2) was explored. It is also demonstrated that photoinduced electron transfer (PET) between acceptor (cationic) present outside the OA capsule to donor (a stilbene) present within the capsule is feasible and occurs at a higher than diffusion controlled rate. The PET in the above supramolecular system could be controlled by employing another cavitand, cucurbit[7]uril (CB7) to complex with cationic acceptor. Also, studies with carefully chosen guest molecules suggest that selective photocyclodimerization can be carried out within the inner phase of OA