Probing Interactions between Hydrocarbons and Auxiliary Guests inside Cucurbit[8]uril.

The affinities of 20 hydrocarbons for the cavity formed by the inner wall of cucurbit[8]uril and a tolyl unit linked to an auxiliary guest were measured in aqueous solution. Cucurbit[8]uril and the auxiliary guest, a substituted ruthenium tris(2,2'-bipyridyl) complex bearing a trifluoromethyl 19F NMR probe, displayed perfect selectivity toward cyclic hydrocarbons, and cis- and trans-decalin, in particular. Unlike π-π interactions, CH-π interactions, as well as differences in hydrocarbon solvation, contribute significantly to the recognition process.