Guest-size determining the selective binding modes of cucurbit[8]uril, electron-rich guests and N-alkyl-N′-methyl-4,4′-bipyridinium

The supramolecular self-assembly in aqueous solution of N-alkyl-N′-methyl-4,4′-bipyridinium ([CmMV]2+) (m = 4, 5, 7, 12), 1,4-dihydroxybenzene (HB), and 2,6-dihydroxynaphthalene (HN) with cucurbit[8]uril (CB[8]) was investigated with 1H NMR, NOESY, ESI-MS, and UV–vis spectroscopy. It has been reported that these three compounds ([CmMV]2+ (m = 12), HN and CB[8]) can form 1:1:1 inclusion complex with the C12 alkyl chain of [C12MV]2+ being present outside the cavity. Here we report that [CmMV]2+ (m ⩾5), HB, and CB[8] can form a new supramolecular self-assembly binding mode with the alkyl chain being present inside the cavity.