Due to their remarkable binding affinities and selectivity towards various organic, inorganic or biological guests, cucurbit[n]urils (CB[n], n = 5-8, 10, 13-15) with a hydrophobic non-polarizable cavity and two oxygen-crowned portals have become molecular beads for the synthesis of supramolecular compounds such as rotaxanes, polyrotaxanes, dendrimers and rotaxane-based molecular switches . CB[n] usually form host-guest complexes with a cationic guest inside their hydrophobic cavities with high binding constants in aqueous solution.