Manipulating photochemical reactivity of coumarins within cucurbituril nanocavities

Coumarin derivatives that are either cationic (7-ammonium) or neutral (7-hydroxy, 7-methoxy, 6-methyl) form a 1:2 host-guest complex with cucurbit[8]uril (CB[8]). Direct irradiation of these coumarin@CB[8] complexes in water gives head-to-tail (HT) adduct as the major product. The nature of the functional group (polar or nonpolar) at the 6 or 7 position on the coumarin dictates the type of HT adduct ( syn- or anti-). It is postulated that the available free volume and the hydrophobic confined environment are responsible for the observed selectivity.